| Title of Invention | "AN ISOLATED ANTIBODY THAT SPECIFICALLY BINDS TO AN AMINO ACID SEQUENCE" |
|---|---|
| Abstract | The present invention provides isolated polypeptides having an amino acid sequence having at least 70% identity to SEQ ID NO:20, wherein the polypeptide has ER-α36 activity. The invention further provides methods for identifying agents that bind to such polypeptides, methods for detecting such polypeptides, and methods for altering the activity of such polypeptides. Also provided are antibodies that specifically bind to an amino acid sequence depicted at SEQ ID NO: 1, or an immunogenic fragment thereof, and methods for making and using such antibodies. |
| Full Text | ESTROGEN RECEPTORS AND METHODS OF USE CONTINUING APPLICATION DATA This application claims the benefit of U.S. Provisional Application Serial No. 60/552,067, filed 10 March 2004, and 60/643,469, filed 13 January 2005, each of which is incorporated by reference herein. Government Funding The invention described herein was developed with support from the Department of Health and Human Services under Grant Number CA84328. The U.S. Government has certain rights in the invention. BACKGROUND OF THE INVENTION Estrogen is a generic term for steroid compounds that are formed in the ovary, the testis, and possibly the adrenal cortex. Examples of estrogens and compounds having estrogen activity include diethylstilbestrol, fosfestrol, hexestrol, polyestradiol phosphate, broparoestrol, chlorotrianisene, dienestrol, diethylstilbestrol, methestrol, colpormon, equilenin, equilin, estradiol, estriol, estrone, ethinyl estradiol, mestranol, mexestrol, quinestradiol and quinestrol. Estrogens regulate diverse physiological processes in reproductive tissues and in mammary, cardiovascular, bone, liver, and brain tissues. Estrogens are also used in oral contraceptives. Other uses for estrogens include the relief of the discomforts of menopause, inhibition of lactation, and treatment of osteoporosis, threatened abortion, and various functional ovarian disorders. Anti-estrogens are used to treat metastatic breast carcinoma and advanced prostate cancer. The effects of estrogens are mediated via estrogen receptors. The first estrogen receptor (ER) was cloned in 1986 (Green et. al., Nature, 320:134 (1986) and Greene et. al., Science, 231:1150 (1986)). Until 1995, it was assumed that there was only one estrogen receptor responsible for all of the physiological and pharmacological effects of natural and synthetic estrogens and antiestrogens. However, in 1995, a second estrogen receptor was cloned (Kuiper et. al., PNAS, 93:5925 (1996)). The first estrogen receptor discovered is now called estrogen receptor-alpha (ER-ot) and the second estrogen receptor is called estrogen receptor-beta (ER-P). ER-ot and ER-P share a common structural architecture (Zhang et. al., FEES Letters, 546:17 (2003) and Kong et. al., Biochem. Soc. Trans., 31:56 (2003)). Both are composed of three independent but interacting functional domains: the N-terminal A/B domain, the C or DNA-binding domain, and the D/E/F or ligand-binding domain (Figure 1). The N-terminal domain of ER-a encodes a ligand-independent activation function (AF-1), a region involved in interaction with co-activators, and transcriptional activation of target genes. The DNA-binding domain or C domain contains a two zinc-finger structure, which plays an important role in receptor dimerization and binding to specific DNA sequences. The C-terrm'nal D/E/F domain is a ligand-binding domain that mediates ligand binding, receptor dimerization, nuclear translocation, and a ligand-dependent transactivation function (AF-2). The relative contributions that both AF-1 and AF-2 exert on transcriptional control vary in a cell-specific and DNA promoter-specific manner (Berry et. al., EMBO J., 9:2811 (1990) and Tzukerman et. al., Mol. Endocrin., 8:21 (1994)). A 46-kDa ER-a isoform lacking the first 173 amino acids of the full-length gene product of the ER-a gene (A/B or AF-1 domain) was shown to be derived from alternative splicing of the ER-a gene by skipping exon I (Flouriot et. al., EMBO J., 19:4688 (2000)). This alternative splicing event generates an mRNA that has an AUG in a favorable Kozak sequence for translation initiation in frame with the remainder of the original open reading frame. Therefore, this new isoform of ER-cc was named as ER-a46 and the original one was named ER-a66 (Flouriot et. al., EMBO J., 19:4688 (2000)). ER-a46 forms homodimers and binds to an estrogen response element (ERE), and it can also form heterodimers with ER-ct66 (Flouriot et. al., EMBO J., 19:4688 (2000)). ER-a46 homodimers show a higher affinity for an ERE than ER-a66 homodimers. Furthermore, the ER-a46/66 heterodimers form preferentially over the ER-a66 homodimers and ER-a46 acts competitively to inhibit transact!vation mediated by the AF-1 domain of Hganded-ER-a66, but does not effect AF-2-dependent transactivation (Floutiot et. al., EMBO J., 19:4688 (2000)). Therefore, it is thought that ER-ot46 is a naturally occurring isoform of ER-a that regulates estrogen signaling mediated by the AF-1 domain of ER-a66. ER-a is expressed in approximately 15-30% of luminal epithelial cells and not at all in any of the other cell types in the normal human breast. Dual label immunofluorescent techniques revealed that ER-a-expressing cells are separate from those labeled with proliferation markers in both normal human and rodent mammary glands (Clarke et. al., Cancer Res., 57:4987 (1997)). ER-a expression is increased at the very earliest stages of ductal hyperplasia and increases even more with increasing atypia, such that most cells in atypical ductal hyperplasias and in ductal cancer in situ of low and intermediate nuclear grade contain the ER-a (Khan et. al., Cancer Res., 54:993 (1994) andLawsonet. al., Lancet, 351:1787 (1994)). As ER-a expression increases, the inverse relationship between receptor expression and cell proliferation become dysregulated (Shoker et. al., Amer. Jour. Path., 155:1811 (1999)). Approximately 70% of invasive breast carcinomas express the ER-a and most of these tumors contain ER-a-positive proliferating cells (Clarke et. al., Cancer Res., 57:4987 (1997)). Estrogen receptors are members of the nuclear receptor superfamily of ligand-activated transcription factors that control numerous physiological processes. This control often occurs through the regulation of gene transcription (Katzenellenbogen and Katzenellenbogen, Breast Cancer Res., 2:335 (2000); Hull et al., J. Biol. Chem., 276:36869 (2001); McDonnell andNorris, Science, 296:1642 (2002)). The estrogen receptor utilizes multiple mechanisms to either activate or repress transcription of its target genes. These mechanisms include: (a) direct interaction of the ligand-occupied receptor with DNA at estrogen response elements followed by recruitment of transcriptional coregulator or mediator complexes, (b) interaction of the ligand-occupied ER with other transcription factors such as AP-1 (Kushner at al., J. Steroid Biochem. Mol. Biol., 74:311 (2000)), Spl (Safe, Vitam. Horm., 62:231 (2001)) or NF-icB (McKay and Cidlowski, Endocr. Rev., 20:435 (1999)), or (c) indirect modulation of gene transcription via sequestration of general/common transcriptional components (Harnish et al., Endocrinology, 141:3403 (2000) and Speir et al., Circ. Res., 87:1006 (2000)). In addition, the ability of an estrogen receptor to regulate transcription through these various mechanisms appears to be cell-type specific, perhaps due to differences in the complement of transcriptional coregulatory factors available in each cell type (Cerillo et al., J. Steroid Biochem. Mol. Biol., 67:79 (1998); Evans et al., Circ. Res., 89:823 (2001); Maret et al., Endocrinology, 140:2876 (1999)). Also, transcriptional regulation is dependent upon the nature of the ligand, with various natural and synthetic selective estrogen receptor modulators acting as either estrogen receptor agonists or antagonists through each of these various mechanisms (Shang and Brown, Science, 295:2465 (2002); Katzenellenbogen and Katzenellenbogen, Science, 295:2380 (2002); Margeat et al., J. Mol. Biol., 326:77 (2003); Dang et al., J. Biol. Chem., 278:962 (2003)). Another signaling pathway mediated by estrogens, also known as a 'non-classic', 'non-genomic' or 'membrane signaling' pathway, exists that involves cytoplasmic proteins, growth factors and other membrane-initiated signaling pathways (Segars et. al., Trends Endocrin. Met., 13:349 (2002)). Several intracellular signaling pathways have been shown to cross-talk with rapid estrogen-initiated effects: the adenylate cyclase pathway (Aronica et. al., PNAS, 91:8517 (1994)), the phospholipase C pathway (Le Mellay et. al., J. Cell. Biochem., 75:138 (1999)), the G-protein-coupled receptor-activated pathways ..(Razandi et. al., Mol. Endocrin., 13:307 (1999)) and the mitogen activated protein kinaase (MAPK) pathway (Watters et. al., Endocrinology, 138:4030 (1997)). However, all membrane forms described to date are related to ER-a but not ER-p (Segars et. al., Trends Endocrin. Met., 13:349 (2002)). Estrogen signaling has been associated pathologically with an increased risk for breast and endometrial cancer (Summer and Fuqua, Semin. Cancer Biol., 11:339 (2001); Turner et al., Endocr. Rev., 15:275 (1994); Farhat et al., FASEB J., 10:615 (1996); Beato et al., Cell, 83:851 (1995); Dobrzyckaet al., Endo. Rel. Cancer, 10:517 (2003)). Consequently, estrogen receptors have been found to be essential in the initiation and development of most of these cancers. Current endocrine therapies for estrogen receptor-positive breast cancers are primarily designed to target estrogen levels, estrogen receptor levels, or the activity of estrogen and estrogen receptors. Use of a partial antiestrogen, tamoxifen, in the management of early-stage breast cancer has clearly demonstrated an increase in both disease-free and overall survival. In addition, recent studies demonstrate that tamoxifen can be used as a chemopreventive agent for hormone-dependent breast cancer. The major concerns of long-term therapy with tamoxifen are its uterotropic effects, which result in an increase risk for endometrial cancer, and the acquired clinical resistance to tamoxifen. This has led to the active pursuit of better selective estrogen receptor modulators (SERM) that display the optimal agonistic or antagonistic activities in various estrogen responsive target tissues. Accordingly, what are needed are additional methods and materials that can be used to screen for agents that modulate estrogen signaling, as well as methods and materials that can be used to modulate estrogen signaling. SUMMARY OF THE INVENTION The present invention provides an isolated antibody that specifically binds to an amino acid sequence depicted at SEQ ID NO:1, or an immunogenic fragment thereof, preferably, an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO: 1. The antibody may be a monoclonal antibody or a polyclonal antibody. Optionally, the antibody is a humanized antibody. The antibody may be covalently attached to a compound such as, for instance, a chemotherapeutic agent or a detectable marker such as a fluorescent marker. The antibody may be present in a composition, and the composition may include a pharmaceutically acceptable carrier. Also provided are kits that include an antibody of the present invention. The present invention also provides a method for making an antibody. The antibody may be polyclonal or monoclonal. The method includes administering to an animal a polypeptide having an amino acid sequence depicted at SEQ ID NO:1, or an immunogenic fragment thereof, preferably, an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO:1. The method further includes isolating antibody from the animal, wherein the isolated antibody specifically binds to the amino acid sequence. The polypeptide or immunogenic subunit thereof may be covalently attached to a carrier polypeptide. The isolating may include obtaining from the animal a cell that produces the antibody, and making a monoclonal-antibody producing hybridoma using the cell. The invention further includes a polyclonal antibody produced by the method and a monoclonal antibody produced by the method. The invention is also directed to a cell including an exogenous coding region, wherein the coding region encodes a polypeptide including SEQ ID NO:20. The coding region may encode a polypeptide having an amino acid sequence with at least 90% identity to SEQ ID NO:20, wherein the polypeptide has ER-a36 activity. The coding region may be operably linked to a constitutive promoter. The cell may be a eukaryotic cell or a prokaryotic cell. Also provided by the invention is a cell that expresses such polypeptides. The present invention further provides a method for identifying an agent that binds a polypeptide. The method includes combining a polypeptide that includes an amino acid sequence depicted at SEQ ID NO:1, and an agent, and detecting the formation of a complex between the agent and the polypeptide, detecting an alteration in the activity of the polypeptide, or the combination thereof. The binding of the agent to the polypeptide may be detected by directly detecting the binding of the agent to the polypeptide, detecting the binding of the agent to the polypeptide using a competition binding assay, or the combination thereof. Optionally, the method also includes determining whether the agent binds a polypeptide including SEQ ID NO: 18. Also provided by the present invention are methods for detecting polypeptides. In one aspect, the method includes providing a cell, analyzing the cell for a polypeptide having ER-a36 activity and a molecular weight of 36 kDa as measured following electrophoresis on a sodium dodecyl sulfate (SDS)-polyacrylamide gel, and determining whether the cell expresses the polypeptide. The cell may be ex vivo or in vivo. The cell may be, for instance, a tumor cell, such as a breast tumor cell. The analyzing may include contacting the cell with an antibody that specifically binds to an amino acid sequence depicted at SEQ ID NO: 1, or an immunogenic fragment thereof. The analyzing may include amplifying an mRNA polynucleotide to form amplified polynucleotides. The amplification includes contacting polynucleotides obtained from the cell with a primer pair that will amplify an mRNA polynucleotide that includes SEQ ID NO:22 or SEQ ID NO:25, or the combination thereof, wherein the presence of amplified polynucletides indicates the cell expresses the polypeptide. One primer of the primer pair may be chosen from nucleotides of SEQ ID NO:22, nucleotides complementary to nucleotides of SEQ ID NO:25, or the combination thereof. The invention also provides a method for inhibiting ER-a36 activity of a cell. The method includes contacting a cell expressing a polypeptide having an amino acid sequence depicted at SEQ ID NO:1 with a compound that inhibits ER-a36 activity. Such a compound may be an antibody that specifically binds to a polypeptide having an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO: 1. The cell may be in vivo or ex vivo, and optionally may be ER-a66 negative, ER-a46 negative, or the combination thereof. In some aspects the compound is not an anti-estrogen. Further provided by the present invention is an isolated polypeptide that includes an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO:1, preferably an amino acid sequence depicted SEQ ID NO: 1, more preferably, an amino acid sequence depicted at SEQ ID NO:20. In another aspect, the isolated polynucleotide has at least 70% identity to SEQ ID NO:20, wherein the polypeptide has ER-a36 activity. The present invention also includes an immunogenic fragment of SEQ ID NO:1. The terms "comprises" and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Unless otherwise specified, "a," "an," "the," and "at least one" are used interchangeably and mean one or more than one. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the domain structure representation of Human estrogen receptor-alpha (ER-a) isoforms. Domains (labeled A-F), amino acid sequence numbering, AF-1 and AF-2, the DNA binding domain, the ligand-binding domain, and the dimerization domain are shown. The phosphorylation sites and function of each domain are also indicated. Figure 2 is a schematic demonstrating the possible crosstalk between the membrane and genomic signaling pathways of ER-a. Cav-1 represents caveolin-1, ER-a, estrogen receptor-alpha; RTK, a receptor tyrosine kinase; Ras, Ras oncogene; Mek, MAP/ERK kinase; MAPK, a mitogen activated protein kinase; PI3K, phosphoinositol-triphosphate kinase; AKT, protein kinase 13; PDK1, phosphoinositol-dependent protein kinase; RSK, p90 ribosome S6 kinase. Figure 3 is a picture showing that pRET-infected MCF1OA cells grow a big colony in soft-agar in the presence of estradiol (E2). The ST1 clone shows an accelerated growth in E2-containging soft-agar. MCF7 and MCF10A cells are included as a positive and negative control, receptively. Figure 4 is a Western blot showing downregulation of Caveolin-1 (Cav-1) expression in pRET-infected MCF 1 OA cells. Equal amounts of total cellular extracts from various cell lines were analyzed by Western blot using a rabbit anti-Cav-1 antibody (N20). The position of Cav-1 is indicated by an arrow and the cell extract analyzed in each lane is indicted above each lane. Figure 5 is a western blot showing upregulation of ER-a expression in pRET-infected MCF 1 OA cells. Equal amounts of total cellular extracts from various cell lines were analyzed by Western blot using antibodies against ER-a (H222) and ER-p. The positions of ER-a and ER-P are indicated by arrows and the cell extract analyzed in each lane is indicted above each lane. Figure 6 is a Western blot showing activation of ERK1/2 phosphorylation in pRET-infected MCF10A cells. Equal amounts of total cellular extracts from the cell lines were analyzed by Western blot using antibodies against ERK1/2 and phosphorylated ERK1/2. Figure 7 is a Western blot showing the existence of three ER-α proteins in Cav-1 haploinsufficient cells, ST land ST3, and MCF7 breast cancer cells. Equal amounts of total cellular extracts from the cell lines were analyzed by Western blot using the H222 antibody against ER-α The positions of ER-α66, ER-α46 and ER-α36 are indicated by arrows and the cell extract analyzed in each lane is indicted above each lane. Figure 8 illustrates the genomic organization of the human ER-α gene. The location of multiple promoters are shown as arrows. The translation start and stop sites are indicated as AUG and UGA, The exons are shown as numbered boxes. Intron 1 is also shown with the exon 1' in a box. The lower panel shows the mRNA structure of ER-α isoforms. Poly A sites are indicated by AAA. Figure 9 is a picture of an agarose gel showing the isolation of cDNA encoding the open-reading frame of ER-α36 by PCR. The position of the cDNA in the gel is indicated by an arrow. Figure 10 shows the predicted amino acid sequence of the ER-α36 open-reading frame. The amino acid positions are indicated by numbers on the left side of the amino acid sequence (SEQ ID NO:20). The last 27 amino acids that are unique to ER-α36 are underlined (SEQ ID NO:l ) Figure 11 shows a Western blot analysis of ER-α66, ER-α46 and ER-cx36. The lanes marked ER-α66, ER-α46 and ER-α36 represent separated cultures of HEK 293 cells that were transfected with expression plasmids encoding the indicated estrogen receptor isoform, and lysed two days after being transfected. The lysate of each transfectant was immunodetected with an anti-ER-α antibody (H222). The cell extracts from MCF7 cells used as a positive control. The positions of ER-α66, ER-α46 and ER-α36 are indicated by arrows. and the cell extract analyzed in each lane is indicted above each lane. Figure 8 illustrates the genomic organization of the human ER-a gene. The location of multiple promoters are shown as arrows. The translation start and stop sites are indicated as AUG and UGA. The exons are shown as numbered boxes. Intron 1 is also shown with the exon 1' in a box. The lower panel shows the mRNA structure of ER-a isoforms. Poly A sites are indicated by AAA. Figure 9 is a picture of an agarose gel showing the isolation of cDNA encoding the open-reading frame of ER-a36 by PCR. The position of the cDNA in the gel is indicated by an arrow. Figure 10 shows the predicted amino acid sequence of the ER-a36 open-reading frame. The amino acid positions are indicated by numbers on the left side of the amino acid sequence (SEQ ID NO:20). The last 27 amino acids that are unique to ER-a36 are underlined. Figure 11 shows a Western blot analysis of ER-a66, ER-a46 and ER-a36. The lanes marked ER-a66, ER-a46 and ER-a36 represent separated cultures of HEK 293 cells that were transfected with expression plasmids encoding the indicated estrogen receptor isoform, and lysed two days after being transfected. The lysate of each transfectant was immunodetected with an anti-ER-a antibody (H222). The cell extracts from MCF7 cells used as a positive control. The positions of ER-a66, ER-a46 and ER-a36 are indicated by arrows. Figure 12 shows (a) the DNA sequence of the 5' flanking sequence (SEQ ID NO:22) of the gene that encodes ER-a36 and which includes the ER-a36 promoter, and (b) the DNA sequence of the 3' flanking sequence (SEQ ID NO:25) of the gene that encodes ER-a36 and which includes the nucleotides encoded by exon 9. In the 5' flanking sequence the putative transcription binding sites are underlined and the proteins that bind to the nucleic acid sequence are also indicated. The initiation site of the cDNA is also indicated by an arrow. Figure 13 shows Northern blot analysis of ER-a36 in different breast cancer cells MCF10A, ~ T47D, MCF7, and MDA-MB-231. The positions of ER-a36 and actin are indicated by arrows. Figure 14 shows inhibition by ER-a36 of the transcriptional transact! vation activities mediated by the AF-1 and AF-2 domains of ER-a66 and ER-|3. (+E2), cells treated with E2; (-E2), cells net treated with E2. Figure 15 shows ER-ct36 mediates membrane-initiated MAPK kinase pathway stimulated by E2. (a) Western blot shows treatment of ER36-293 cells with estradiol-17(3 (E2(3) induces rapid phosphorylation of Mekl/2 and ERK1/2. P-Mekl/2 and P-ERK1/2, phosphorylated forms of Mekl/2 and ERK1/2, respectively, (b) Serum but not E2p induces phosphorylation of ERK1/2 in control vector-293 cells. P-ERK172, phosphorylated form of ERK1/2. (c) Different estrogens and antiestrogens induce rapid phosphorylation of ERK1/2 in ER36-293 cells. P-ERK1/2, phosphorylated form of ERK 1/2. (d) Tamoxifen treatment constitutively stimulates ERK1/2 phosphorylation in ER36-293 cells. P-ERK112, phosphorylated form of ERK1/2. Figure 16 shows ER-o.36 mediates E2P induced MAPK kinase nuclear signaling and stimulates cell growth, (a) Effects of E2p on MAPK kinase nuclear signaling. ER36-293 and control vector-293 cells were transiently transfected with 5 X Gal4-LUC, a luciferase reporter plasmid containing five Gal4 DN A binding sites, and Gal-ELK expression vector containing an ELK transcriptional activation domain fused with the Gal4 DNA binding domain (Upper panel). After transfection, the cell culture was maintained in estrogen free medium for 36 hours before E2p (1 nM or lOnM) was added for 12 hours. Luciferase activities with standard deviation are representative of more than three experiments performed in duplicates, (b) E2|3 and anti-estrogens stimulate growth of ER36-293 cells. Absorbance data at 490nm are shown. Results of more than five independent experiments have were averaged; the mean and SEM are shown. The statistical significance of these results was also evaluated by paired /-test. P-values were Figure 17 shows ER- a36 is mainly a membrane-based estrogen receptor, (a) Western blot analysis of expression of ER-a36 in different established breast cancer cell lines. The same blot was stripped and probed with an anti-actin antibody to ensure equal loading, (b) Subcellular localization of ER-a36 in ER-a36 transfected 293 cells. Immunoblot of ER-a36 in different subcellular fractions with the ER-a36 specific antibody. W, whole cell lysate; PM, plasma membrane; C, cytosol; N, nucleus. Subcellular fraction purity was examined by immunoblotting various protein markers for the plasma membrane, cytosol, nucleus and Golgi. 5'NT, 5'nucleotidase; D4-GDI, GDP dissociation inhibitor; mSin3A, a component of histone remodeling complex; COPB, p coat protein. Figure 18 shows that E2p promotes growth of ER-a66 negative breast cancer cells, MDA-MB-231, in soft agar. MDA-MB-231 cells were grown on soft agar for three weeks in the absence of E2p (0), and in the presence of lOnM E2p (E2) 10 nM E2p and 10 nM Tamoxifen (E2+TAM) and 10 nM Tamoxifen alone (TAM). Figure 19 shows that E2P induces membrane initiated estrogen signaling in ER-a66 negative breast cancer cells MDA-MB-231. Treatment of MDA-MB-231 cells with estradiol-17p (E2P) induced rapid phosphorylation of ERK1/2. Cells were treated with E2p (lOnM) for different time points, lysed and analyzed with Western blot using phosphorylation dependent and independent antibodies. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION It has been discovered that downregulation of the Caveolin-1 (Cav-1) system constitutively . activates the mitogen activated protein kinase (MAPK) pathway, activates expression of estrogen receptor-alpha (ER-a), and triggers positive estrogen signaling. This discovery has, for the first time, provided a clear link between activated MAPK signaling and mammary tumorigenesis, especially breast cancer progression that is stimulated by estrogens. This discovery strongly suggests that Cav-1 plays an important role in maintaining normal growth of mammary epithelial cells by coordinating the cross-talk between the MAPK and estrogen signaling pathways, and its downregulation may contribute to dysregulation of these two important pathways which eventually lead to mammary tumorigenesis. A schematic of the estrogen signaling pathway and the MAPK signaling pathway is presented in Figure 2. An estrogen receptor-alpha isoform has also been identified and cloned. This 36-kDa isoform (ER-a36) of estrogen receptor-alpha is generated from a promoter located in the first intron of the original 66-kDa ER-a (ER-a66) gene. ER-a.36 differs from ER-a66 because it lacks both transcriptional activation domains (AF-1 and AF-2) but retains the DNA-binding, dimerization and most of the ligand-binding domains. The structure of ER-a36 indicates that ER-a36 is a regulator of estrogen signaling. ER-a36 may also mediate the membrane effects of estrogen signaling as it is primarily expressed on the plasma membrane, and also in cytosol and nucleus. ER-p1 has been proposed as a constitutive regulator of ER-a66 mediated estrogen signaling. The finding that ER-a46 lacking the AF-1 domain can dimerize to ER-o.66 and inhibit the transactsvation activity mediated by the AF-1 domain of ER-a66 indicates that ER-a46 plays a regulatory role in the functional activity mediated by the AF-1 domain of ER-o.66. ER-a36 lacks both AF-1 and AF-2 domains. Thus, it is thought that ER-a36 inhibits biological functions mediated by both AF-1 and AF-2 of ER-o.66, and AF-2 mediated functions of ER-a46 as well. With regulation mediated by ER-a36 and ER-a46, both of which might be expressed at different levels in different tissues, ER-a66 may function differently in different target tissues. Such a mechanism is thought to provide an explanation for the pleiotrophic roles of estrogen signaling in different biological processes. Polypeptides and peptidomimetics of the Invention The invention provides polypeptides. As used herein, the term "polypeptide" refers broadly to a polymer of two or more amino acids joined together by peptide bonds. The terms peptide, oligopeptide, and protein are all included within the definition of polypeptide and these terms are used interchangeably. It should be understood that these terms do not connote a specific length of a polymer of amino acids, nor are they intended to imply or distinguish whether the polypeptide is produced using recombinant techniques, chemical or enzymatic synthesis, or is naturally occurring. Numerous examples of polypeptides that are within the scope of the invention are disclosed and described herein. In the case of a polypeptide or polynucleotide that is naturally occurring, it is preferred that such polypeptide or polynucleotide be isolated and, optionally, purified. An "isolated" polypeptide or polynucleotide is one that is separate and discrete from its natural environment. A "purified" polypeptide or polynucleotide is one that is at least 60% free, preferably 75% free, and most preferably 90% free from other components with which they are naturally associated. Polypeptides and nucleotides that arc produced outside the organism in which they naturally occur, e.g., through chemical or recombinant means, are considered to be isolated and purified by definition, since they were never present in a natural environment. An "exogenous polypeptide" refers to a foreign polypeptide, i.e., a polypeptide that is not normally present in a cell, or a polypeptide that is normally present in a cell but has been introduced into the cell by experimental procedure, e.g., by introduction of a polynucleotide encoding the polypeptide. The polypeptides of the present invention may be biologically active. Such biological activity is referred to herein as "ER-a36 activity." A example of a bioassay that can be used to determine if a polypeptide of the invention is biologically active involves contacting a cell that expresses this polypeptide with an estrogen or anti-estrogen and determining if activities of the MAPK pathway are increased or decreased in the presence of the estrogen or anti-estrogen, when compared to the MAPK .activities in a control cell that was not expressing the polypeptide of the invention. Preferably, the MAPK activities are phosphorylation of ERK 1/2 and Mek 1/2, and preferably the phosphorylation of ERK 1/2 induced by a polypeptide of the present invention is not decreased in the presence of an anti-estrogen. Preferably, ER-o36 activity is membrane initiated. ER-a36 activity may be measured by exposing a cell expressing a polypeptide that may have ER-a36 activity to a different ligands. Examples of ligands that can be used include, but are not limited to, estrone (El), 17a-estradiol (E2.g), 17P -estradiol (E2p), estriol (E3), estetrol (E4), or an estrogen attached to a membrane impermeable molecule, for instance, bovine serum albumin (BSA). Generally, when the ER-a36 activity to be measured is to be limited to membrane initiated ER-a36 activity, an estrogen attached to a membrane impermeable molecule is used. The amount of estrogen used can vary, and is preferably in the range of between 1 nM and 10 nM. The cell exposed to the estrogen is preferably a quiescent cell. The exposure is allowed to occur for between 5 and 90 minutes, the cell is then lysed, and the polypeptides present in the cell are resolved by SDS-polyacrylamide gel electrophoresis. After transfer of the resolved polypeptides to a membrane, antibodies against the non-phosphorylated and phosphorylated forms of ERK 112 and Mek 112 are used to evaluate activation of the MAPK pathway. Optionally, an anti-estrogen, such as Tamoxifen, 4OH-Tamoxifen, or ICI-182,780, may be included to determine if the phosphorylation of ERK 1/2 is insensitive to anti-estrogens. The invention provides a polypeptide having the amino acid sequence depicted in SEQ ID NO: 20. This polypeptide, and related polypeptides as described herein, are also referred to herein as ER-a36, ER-a36 isoform, and ER receptor a36-subunit. As shown in Figure 1, the ER-a36 isoform lacks amino-terminal amino acid residues 1-183, carboxyl-terminal amino acid residues 430-595, and has an addition of 27 amino acid residues to its C-terminus when compared to the ER-a66 isoform (see Table 1). Estrogen receptor alpha isomers include ER-a36, ER-a46, ER-a66. Estrogen receptor beta isomers include ER-p. The present invention also provides estrogen receptors that include an ER-a36'isofonn. Without intending to be limiting, the ER-a36 isoform is believed to modulate the response of a cell to estrogen through regulation of estrogen receptor function by forming a dimer with ER-a66, ER-a46 or ER-p. Further, ER-a36 is thought to lack activation factor 1 (AF-1) and activation factor 2 (AF-2) activity, and thus lacks intrinsic transcription activity. However, ER-a36 is thought to retain an intact dimerization domain that allows ER-ot36 to dimerize with an ER-a46, ER-a66 or ER-p. This interaction is thought to allow ER-o.36 to modulate the activity of ER-o.46, ER-a66 and ER-p containing estrogen receptors. Table 1 Amino acid and nucleotide sequences (Table Removed) Polypeptides of the present invention include polypeptides having an amino acid sequence that is at least 70% identical to SEQ ID NO:20. Such polypeptides include those having an amino acid sequence that is at least single unit percentages greater than 70% identical to SEQ ID NO:2(), for example 71%, 72%, 73% identity, and so on to 100% identity to SEQ ID NO:20. Preferably, the polypeptide includes those having an amino acid sequence that is, in increasing order of preference, at least about 80% identity, at least about 90% identity, or at least about 95% identity to SEQ ID NO:20. Preferably the polypeptide is biologically active. Preferably the polypeptide has a molecular weight of 36 kDa as measured following electrophoresis on a sodium dodecyl sulfate (SDS)-polyacrylamide gel. Typically, residues involved in phosphorylation of ER-a66, e.g., S236, K302, and K303 are conserved, as are those residues involved in the function of the DNA binding domain, ligand binding domain, and dimerization domains of ER-o.66. Residues that function in DNA binding, ligand binding, and/or dimerization are known in the art. Percent identity between two polypeptide sequences is generally determined by aligning the residues of the two amino acid sequences to optimize the number of identical amino acids along the lengths of their sequences; gaps in either or both sequences are permitted in making the alignment in order to optimize the number of identical amino acids, although the amino acids in each sequence must nonetheless remain in their proper order. Preferably, two amino acid sequences are compared using the Blastp program, version 2.0.9, of the BLAST 2 search algorithm, as described by Tatusova et al. (FEMS Microbiol. Lett., 174, 247-250 (1999)), and available on the world wide web at http://www.ncbi.nlm.nih.gov/blast/bl2seq/bl2.html. Preferably, the default values for all BLAST 2 search parameters are used, including matrix = BLOSUM62; open gap penalty =11, extension gap penalty = 1, gap x_dropoff - 50, expect = 10, wordsize = 3, and optionally, filter on. In the comparison of two amino acid sequences using the BLAST search algorithm, structural similarity is referred to as "identity." Polypeptides that are fragments of the ER-o.36 estrogen receptor isoform are also provided by the invention. Preferably, a fragment is immunogenic. In some aspects, a fragment has ER-a36 activity. An example of an immunogenic fragment is the amino acid sequence depicted at amino acids 13-27 of SEQ ID NO: 1, more preferably, 1 -27 of SEQ ID NO: 1. Such fragments are useful for preparing antibodies that specifically bind to the ER-a36 estrogen receptor isoform. Examples of fragments include an estrogen receptor isoform that has been truncated at either the N-terminus, or the C-terminus, or both, by one or more amino acids, as long as the fragment contains at least 5 contiguous amino acids, more preferably at least 7 contiguous amino acids, even more preferably at least contiguous 10 amino acids, and most preferably at least contiguous 12 amino acids. The invention provides fusion polypeptides having a carrier polypeptide coupled to a polypeptide of the invention. A carrier polypeptide may be used to increase or decrease the solubility of a fusion polypeptide. The carrier polypeptide may also be used to increase the immunogenicity of the fusion polypeptide to increase production of antibodies that bind to a polypeptide of the invention. For example, a carrier polypeptide may be fused to a fragment of a polypeptide of the present invention to facilitate production of antibodies that specifically bind ER-o36. An example of such a fragment is a polypeptide having amino acids 13-27 SEQ ID NO: 1. The invention is not limited by the types of carrier polypeptides used to create fusion polypeptides of the invention. Examples of carrier polypeptides include keyhole limpet hemacyanin, bovine serum albumin, ovalbumin, mouse serum albumin, rabbit serum albumin, and the like. The carrier polypeptides may also be used to provide for the separation or detection of a fusion polypeptide. Examples of such carrier proteins include glutathione-S-transferase, maltose-binding protein, chitin-binding protein, and polypeptides having the following amino acid sequences: QFFGLM (SEQ ID NO:2), EQKLISEEDL (SEQ ID NO:3), KAEDESS (SEQ ID NO:4), YPYDVPDYA (SEQ ID NO:5), DYKDDDDK(SEQ ID NO:6), YTDIEMNRLGK(SEQ IDNO:7), MASMTGGQQMG (SEQ ID N0:8), DTYRYI (SEQ ID NO:9), TDFYLK(SEQ ID NO: 10), HHHHHH (SEQ ID NO:11), HPOL (SEQ ID NO: 12), QYPALT (SEQ ID NO: 13), QRQYGDVFKGD (SEQ ID NO: 14), EYMPME (SEQ ID NO: 15), EFMPME (SEQ ID NO: 16), and RYIRS (SEQ ID NO: 17). Accordingly, a fusion polypeptide can be detected or isolated by interaction with other components that bind to the carrier . polypeptide portion of the fusion polypeptide. For example, a fusion polypeptide having avidin as a carrier polypeptide can be detected or separated with biotin through use of known methods. A carrier polypeptide may also be used to cause the fusion polypeptide to form an inclusion body upon expression within a cell. A carrier polypeptide can also be an export signal that causes export of a fusion polypeptide out of a cell, or directs a fusion polypeptide to a compartment within a cell, such as the periplasm. The invention also provides two or more polypeptides of the invention that are continuously linked into a single amino acid chain. Such a polypeptide is referred to herein as a polypeptide. The polypeptides can be connected by linkers (see Stahl et al., U.S. Patent No. 6,558,924). Such a polyprotein can be isolated and then cleaved to produce polypeptides or coupled polypeptides of the invention. The polyprotein can be cleaved through use of numerous methods, such as chemical or protease cleavage. Accordingly, linkers can be designed to be cleaved by specific proteases or chemicals. Examples of compounds that can be used to cleave polyproteins of the invention include chemicals and enzymes. Examples of chemicals include cyanogen bromide, formic acid and heat, hydroxylamine and heat, iodosobenzoic acid-2-(2-nitrophenyl)-3-methyl-3-bromoindole-nine in acetic acid, and the like. Examples of enzymes include Ala-64 subtilisin, clostripain, collagenase, enterokinase, factor Xa, renin, a-thrombin, trypsin, chymotrypsin, tobacco etch virus protease, and the like. Polyproteins may be used to increase the production efficiency of the polypeptides of the invention. Methods to produce polyproteins are known in the art (see Coolidge et al., U.S. Patent No. 6,127,150). The polypeptides of the invention include analogs that have been modified by the addition, substitution, or deletion of one or more contiguous or noncontiguous amino acids, or that have been chemically or enzymatically modified, e.g., by attachment of a reporter group, by an N-terminal, C-terminal or other functional group modification or derivatization, or by cyclization, as long as the analog retains biological activity or is able to stimulate the production of antibodies that bind to ER-a36. An analog can thus include additional amino acids at one or both of the termini of a polypeptide. Preferably, an analog is immunogenic, more preferably, an analog is immunogenic and has ER-a36 activity. In some aspects, the invention provides polypeptides that are not analogs. Substitutes for an amino acid in the polypeptides of the invention are preferably conservative substitutions, which are selected from other members of the class to which the amino acid belongs. For example, it is well-known in the art of protein biochemistry that an amino acid belonging to a grouping of amino acids having a particular size or characteristic (such as charge, hydrophobicity and hydrophilicity) can generally be substituted for another amino acid without substantially altering the structure of a polypeptide. For example, nonpolar (hydrophobic) amino acids include alanine, leucine, ispleucine, valine, proline, phenylalanine, tryptophan, and tyrosine. Polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids include arginine, lysine and histidine. The negatively charged (acidic) amino acids include aspartic acid and glutamic acid. Examples of preferred conservative substitutions include Lys for Arg and vice versa to maintain a positive charge; Glu for Asp and vice versa to maintain a negative charge; Ser for Thr so that a free -OH is maintained; and Gin for Asn to maintain a free NHi. Related amino acids (such as 3-hydroxyproline, 4-hydroxyproline, homocysteine, 2-aminoadipic acid, 2-aminopimelic acid, y-carboxyglutamic acid, J3-carboxyaspartic acid), amino acid amides (ornithine, homoarginine, N-methyl lysine, dimethyl lysine, trimethyl lysine, 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, homoarginine, sarcosine and hydroxylysine) and substituted phenylalanines, norleucine, norvaline, 2-aminooctanoic acid, 2-aminoheptanoic acid, statine, (3-valine, naphthylalanines, tetrahydroisoquinoline-3-carboxylic acid, and halogenated tyrosines may be exchanged for a like amino acid. The invention provides peptidomimetics of the polypeptides of the invention. A peptidomimetic describes a polypeptide in which at least one of the peptide bonds has been replaced with a non-peptide bond, such as those commonly used in the pharmaceutical industry as non-peptidc drugs, with properties analogous to those of the template polypeptide. (Fauchere, J., Adv. Drug Res., 15: 29 (1986), Evans et al., J. Med. Chem., 30:1229 (1987), and Janda et al., U.S. Patent No. 6,664,372). Peptidomimetics are structurally similar to polypeptides having peptide bonds, but have one or more peptide linkages optionally replaced by a linkage such as, --CH2NH-, --Cl^S--, --CIIi-CHi-, --CH=CH- (cis and trans), ~COCH2--, --CH(OH)CH2--, and --CH2SO-, by methods known in the art. Advantages of peptidomimetics over natural polypeptide embodiments may include more economical production, greater chemical stability, altered specificity and enhanced pharmacological properties such as half-life, absorption, potency and efficacy. Substitution of one or more amino acids within a polypeptide or a peptidomimetic with a D-amino acid of the same type (e.g., D-lysine in place of L-lysine) may be used to generate polypeptides and peptidomimetics that are, for instance, more stable and more resistant to endogenous proteases. Polypeptides and peptidomimetics of the invention can be modified for in vivo use by the addition, at the amino-terminus and/or the carboxyl-terminus, of a blocking agent to decrease degradation in vivo. This can be useful in those situations in which the polypeptide termini tend to be degraded by proteases in vivo. Such blocking agents can include, without limitation, additional related or unrelated peptide sequences that can be attached to the amino and/or carboxyl terminal residues of the polypeptide or peptidomimetic of the invention. This can be done during chemical synthesis, or by recombinant DN A technology by methods familiar to artisans of average skill. Alternatively, blocking agents such as pyroglutamic acid, or other molecules known in the art, can be attached to the amino and/or carboxyl terminal residues, or the amino group at the amino terminus or carboxyl group at the carboxyl terminus can be replaced with a different moiety. Accordingly, the invention provides polypeptides and peptidomimetics that are blocked and the amino terminus, the carboxyl terminus, or the combination thereof. Polypeptides of the invention can be produced on a small or large scale through use of numerous expression systems that include, but are not limited to, cells or microorganisms that are transformed with a recombinant vector into which a polynucleotide of the invention has been inserted. Such recombinant vectors and methods for their use are described below. These vectors can be used to transform a variety of organisms. Examples of such organisms include bacteria (for example, E. coli or B. subtilis); yeast (for example, Saccharomyces and Pichid); insects (for example, baculovirus); plants; or mammalian cells (for example, COS, CHO, BHK, 293, VERO, HeLa, MDCK, W138, and NIH 3T3 cells). Also useful as host cells are primary or secondary cells obtained directly from a mammal that are transfected with a vector. Synthetic methods may also be used to produce polypeptides and peptidomimetics of the invention. Such methods are known in the art and are routine. For instance, the solid phase peptide synthetic method is an established and widely used method. Polypeptides can be readily purified by fractionation on immunoaffmity or ion-exchange columns; ethanol precipitation; reverse phase HPLC; chromatography on silica or on an anion-exchange resin such as DEAE; chromatofocusing; SDS-PAGE; ammonium sulfate precipitation; gel filtration using, for example, Sephadex G-75; ligand affinity chromatography, and the like. Polypeptides can also be readily purified through binding of a fusion polypeptide to separation media, followed by cleavage of the fusion polypeptide to release a purified polypeptide. For example, a fusion polypeptide that includes a factor Xa cleavage site between the polypeptide and the carrier polypeptide can be created. The fusion polypeptide can be bound to an affinity column to which the carrier polypeptide portion of the fusion polypeptide binds. The fusion polypeptide can then be cleaved with factor Xa to release the polypeptide. Such a system has been used in conjunction with a factor Xa removal kit for purification of the polypeptides of the invention. Polynucleotides The invention provides polynucleotides that encode the polypeptides of the invention. The term "polynucleotide" refers broadly to a polymer of two or more nucleotides covalently linked in a 5' to 3' orientation. A polynucleotide may include nucleotide sequences having different functions, including for instance coding sequences, and non-coding sequences such as regulatory sequences. Coding sequence, non-coding sequence, and regulatory sequence are defined below. The terms nucleic acid, nucleic acid molecule, and oligonucleotide and protein included within the definition of polynucleotide and these terms are used interchangeably. It should be understood that these terms do not connote a specific length of a polymer of nucleotides, nor are they intended to imply or distinguish whether the polynucleotide is produced using recombinant techniques, chemical or enzymatic synthesis, or is naturally occurring. Polynucleotides can be single-stranded or double-stranded, and the sequence of the second, complementary strand is dictated by the sequence of the first strand. The term "polynucleotide" is therefore to be broadly interpreted as encompassing a single stranded nucleic acid polymer, its complement, and the duplex formed thereby. "Complementarity" of polynucleotides refers to the ability of two single-stranded polynucleotides to base pair with each other, in which an adenine on one polynucleotide will base pair with a thymidine (or uracil, in the case of RNA) on the other, and a cytidine on one polynucleotide will base pair with a guanine on the other. Two polynucleotides are complementary to each other when a nucleotide sequence in one polynucleotide can base pair with a nucleotide sequence in a second polynucleotide. For instance, 5'-ATGC and 5'-GCAT are fully complementary, as are S'-GCTA and 5'-TAGC. An example of a polynucleotide of the present invention is SEQ ID NO:21 (sec Table 1, also nucleotides 234-1166 of the nucleotide sequence present at GenBank accession number BX640939). Preferred polynucleotides of the invention also include polynucleotides having a nucleotide sequence that is "substantially complementary" to a nucleotide sequence that encodes a polypeptide according to the invention, or the complement of such nucleotide sequence. "Substantially complementary" polynucleotides can include at least one base pair mismatch, however the two polynucleotides will still have the capacity to hybridize. For instance, the middle nucleotide of each of the two DNA molecules 5'-AGCAAATAT and 5'-ATATATGCT will not base pair, but these two polynucleotides are nonetheless substantially complementary as defined herein. Two polynucleotides are substantially complementary if they hybridize under hybridization conditions exemplified by 2X SSC (SSC: 150mM NaCl, 15 mM trisodium citrate, pH 7.6) at 55°C. Substantially complementary polynucleotides for purposes of the present invention preferably share at least one region of at least 20 nucleotides in length which shared region has at least 60% nucleotide identity, preferably at least 80% nucleotide identity, more preferably at least 90% nucleotide identity, and most preferably at least 95% nucleotide identity. Particularly preferred substantially complementary polynucleotides share a plurality of such regions. Preferably the polynucleotides have a nucleotide sequence that is at least 70% identical to SEQ ID NO:24. More preferably the polynucleotides have a nucleotide sequence that is at least single unit percentages greater than 70% identical to SEQ ID NO:21, for example 71 %, 72%, 73% identity, and so on to 100% identity to SEQ ID NO:21. Even more preferably, the polynucleotides have a nucleotide sequence that is at least 80% identical, at least 90% identical, or at least 95% identity to SEQ ID NO:21. Most preferably, the polynucleotides have a nucleotide sequence that is 100% identical to SEQ ID NO:21. A polynucleotide having at least 70% identity to SEQ ID NO:21 has ER-a36 activity. Percent identity between two polynucleotide sequences is generally determined by aligning the bases of the two polynucleotide sequences to optimize the number of identical bases along the lengths of their sequences; gaps in either or both sequences are permitted in making the alignment in order to optimize the number of identical bases, although the bases in each sequence must nonetheless remain in their proper order. The two polynucleotide sequences are preferably compared using the Blastn program, version 2.0.11, of the BLAST 2 search algorithm, also as described by Tatusova et al. (FEMS Microbiol. Lett, 174, 247-250 (1999)), and available on the world wide web at http://www.ncbi.nlm.nih.govMast/bl2seq/bl2.html. Preferably, the default values for all BLAST 2 search parameters are used, including reward for match = 1, penalty for mismatch = -2, open gap penalty = 5, extension gap penalty = 2, gap x_dropoff = 50, expect = 10, wordsize =11, and optionally, filter on. Locations and levels of nucleotide sequence identity between two polynucleotide sequences can also be readily determined using CLUSTALW multiple sequence alignment software (J. Thompson et al,, Nucl. Acids Res., 22:4673-4680 (1994)), available at from the world wide web at www. ebi. ac .uk/clustal w/. It should be understood that a polynucleotide that encodes a polypeptide of the invention is not limited to a polynucleotide that contains all or a portion of naturally occurring genomic or cDNA nucleotide sequence, but also includes the class of polynucleotides that encode such polypeptides as a result of the degeneracy of the genetic code. For example, the naturally occurring polynucleotide sequence SEQ ID NO:21 is but one member of the class of nucleotide sequences that encodes a polypeptide having amino acid SEQ ID NO:20. The class of nucleotide sequences that encode a selected polypeptide sequence is large but finite, and the nucleotide sequence of each member of the class can be readily determined by one skilled in the art by reference to the standard genetic code, wherein different nucleotide triplets (codons) are known to encode the same amino acid. A polynucleotide that "encodes" a polypeptide of the invention optionally includes both coding and noncoding regions, and it should therefore be understood that, unless expressly stated to the contrary, a polynucleotide that "encodes" a polypeptide is not structurally limited to nucleotide sequences that encode a polypeptide but can include other nucleotide sequences outside (i.e., 5' or 3' to) the coding region. A "coding region" or "coding sequence" is a nucleotide sequence that encodes a polypeptide and, when placed under the control of appropriate regulatory sequences expresses the encoded polypeptide. The boundaries of a coding region are generally determined by a translation start codon at its 5' end and a translation stop codon at its 3' end. An "exogenous coding region" refers to a foreign coding region, i.e., a coding region that is not normally present in a cell, or a coding region that is normally present in a cell but has been introduced into the cell by experimental procedure, is operably linked to a regulatory region to which it is not normally operably linked, or the combination thereof. A polynucleotide of the invention can be linear or circular in topology. A polynucleotide can be, for example, a portion of a vector. A vector can provide for further cloning (amplification of the polynucleotide), i.e., a cloning vector, or for expression of the polypeptide encoded by the coding region, i .e., an expression vector. A vector may include, but is not limited to, plasmid, phagemid, F-factor, virus, cosmid, or phage. The vector may be in a double-stranded or single-stranded linear or circular form. The vector can also transform a prokaryotic or eukaryotic host either by integration into the cellular genome or exist extrachromosomally (e.g., as an autonomous replicating plasmid with an origin of replication). The polynucleotide in the vector can be under the control of, and operably linked to, an appropriate promoter or other regulatory sequence for transcription in vitro or in a host cell, such as a eukaryotic cell, or a microbe, e.g. bacteria. Preferred examples of eukaryotic cells include MDA-MB-231, Hela, CHO, and MCF1OA cell lines. A regulatory sequence, or regulatory region, refers to nucleotide sequences located upstream, within, or downstream of a coding sequence, and operably linked to, a coding sequence. Examples of regulatory sequences include enhancers, promoters, translation leader sequences, introns, and polyadenylation signal sequences. They include natural and synthetic sequences as well as sequences that may be a combination of synthetic and natural sequences. Regulatory sequences are not limited to promoters. However, some suitable regulatory sequences useful in the present invention will include, but are not limited to, constitutive promoters, tissue-specific promoters, development- specific promoters, inducible promoters and viral promoters. The term "operably linked" refers to a juxtaposition of components such that they are in a relationship permitting them to function in their intended manner. A regulatory sequence is "operably linked" to a coding region when it is joined in such a way that expression of the coding region is achieved under conditions compatible with the regulatory sequence. The vector may be a shuttle vector that functions in multiple hosts. The vector may also be a cloning vector which typically contains one or a small number of restriction endonuclease recognition sites at which foreign DNA sequences can be inserted in a determinable fashion. Such insertion can occur without loss of essential biological function of the cloning vector. A cloning vector may also contain a marker gene that is suitable for use in the identification and selection of cells transformed with the cloning vector. Examples of marker genes are tetracycline resistance or ampicillin resistance. Many cloning vectors are commercially available (for instance Stratagene, New England Biolabs, Clonetech). A vector may be an expression vector that contains regulatory sequences which direct the expression of a polynucleotide that is inserted into the expression vector. Numerous vectors are commercially available and are known in the art (Stratagene, La Jolla, CA; New England Biolabs, Beverly, MA). An expression vector may be used in in vitro transcription and translation assays. Methods to introduce a polynucleotide into a vector are well known in the art (Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (2001)). Briefly, a vector into which a polynucleotide is to be inserted is treated with one or more restriction enzymes (restriction endonuclease) to produce a linearized vector having a blunt end, a "sticky" end with a 5' or a 3' overhang, or any combination of the above. The vector may also be treated with a restriction enzyme and subsequently treated with another modifying enzyme, such as a polymerasc, an exonuclease, a phosphatase or a kinase, to create a linearized vector that has characteristics useful for ligation of a polynucleotide into the vector. The polynucleotide that is to be inserted into the vector is treated with one or more restriction enzymes to create a linearized segment having a blunt end, a "sticky" end with a 5' or a 3' overhang, or any combination of the above. The polynucleotide may also be treated with a restriction enzyme and subsequently treated with another DNA modifying enzyme. Such DNA modifying enzymes include, but are not limited to, polymerase, exonuelease, phosphatase or a kinase, to create a polynucleotide that has characteristics useful for ligation of a polynucleotide into the vector. The treated vector and polynucleotide are then ligated together to form a construct containing a polynucleotide according to methods known in the art (Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (2001)). Briefly, the treated nucleic acid fragment and the treated vector are combined in the presence of a suitable buffer and ligase. The mixture is then incubated under appropriate conditions to allow the ligase to ligate the nucleic acid fragment into the vector. The invention further provides methods for making a polypeptide of the invention and methods for making the polynucleotides that encode them. The methods include biological, enzymatic, and chemical methods, as well as combinations thereof, and are well-known in the art. For example, a polynucleotide can be expressed in a host cell using standard recombinant DNA technologies, it can be enzymatically synthesized in vitro using a cell-free RNA based system, or it can be synthesized using chemical technologies such as solid phase peptide synthesis. When recombinant DNA technologies are used, the host cell can be, for example, a bacterial cell, an insect cell, a yeast cell, or a mammalian cell. The present invention also provides polynucleotides having promoter activity. In one aspect, the promoter of the present invention includes a nucleotide sequence depicted at SEQ ID NO:22, or a portion thereof. In another aspect, a promoter of the present invention has a nucleotide sequence that is at least single unit percentages greater than 70% identical SEQ ID NO:22, for example 71 %, 72%, 73% identity, and so on to 100% identity to SEQ ID NO:22. Methods for determining percent identity arc described herein. Even more preferably, the promoter has a nucleotide sequence that is at least 80% identical, at least 90% identical, or at least 95% identity to SEQ ID NO:22. A promoter of the present invention has estrogen receptor (ER) regulated activity. As used herein, ER regulated activity refers to increased expression of an operably linked coding region in the presence of ER-a66, preferably, in the presence of ER-a66 bound to an estrogen. A promoter of the present invention is expressed in an estrogen dependent and independent manner. A promoter of the present invention may be operably linked to a coding region encoding a polypeptide, including a marker polypeptide. Examples of marker polypeptides include detectable markers (for instance, fluorescent proteins, enzymes, antigenic markers, and the like) t and selectable markers (polypeptides causing drug resistance, drug susceptibility, or nutritional deficiency, or correcting a nutritional deficiency, and the like). Antibodies The invention provides antibodies that specifically bind to the polypeptides and peptidomimetics of the invention. As used herein, an antibody that can "specifically bind" a polypeptide is an antibody that interacts only with the epitope of the antigen that induced the synthesis of the antibody, or interacts with a structurally related epitope. An antibody that "specifically binds" to an epitope will, under the appropriate conditions, interact with the epitope even in the presence of a diversity of potential binding targets. In some aspects, an antibody of the present invention specifically binds to ER-a36 or B portion thereof, and does not specifically bind to ER-a66 or ER-a46. Accordingly, the polypeptides and peptidomimetics of the invention and fragments thereof can be used as antigens to produce antibodies, including vertebrate antibodies, hybrid antibodies, chimeric antibodies, humanized antibodies, altered antibodies, univalent antibodies, monoclonal and polyclonal antibodies, Fab proteins, and single domain antibodies. For example, a polypeptide having SEQ ID NO: 1 or a fragment thereof, such as amino acids 13-27 of SEQ ID NO: 1, can be used to generate antibodies that specifically bind to ER-a36. A polypeptide or peptidomimetic of the present invention, or fragments thereof, can be modified by covalently linking them to an immunogenic carrier, such as keyhole limpet hemocyanin (KLH), bovine serum albumin, ovalbumin, mouse serum albumin, rabbit serum albumin, and the like. If polyclonal antibodies are desired, a selected animal (e.g., mouse, rabbit, goat, horse or bird, such as chicken) may immunized with the desired antigen. Serum from the immunized animal is collected and treated according to known and routine methods. If serum containing polyclonal antibodies to a polypeptide of the invention contains antibodies to other antigens, the polyclonal antibodies can be purified by immunoaffinity chromatography. Techniques for producing and processing polyclonal antisera are known in the art (see, for example, Harlow et al., Antibodies: A Laboratory Manual, Cold Spring Harbor Pub. 1988)). Monoclonal antibodies directed against the polypeptides or peptidomimetics of the present invention or fragments thereof can also be readily produced by one skilled in the art. The general methodology for making monoclonal antibodies by hybridomas is well known (see, for example, Harlow et al., Antibodies: A Laboratory Manual, Cold Spring Harbor Pub. 1988). Immortal antibody-producing cell lines (hybridimas) can be created by cell fusion, and also by other techniques such as direct transformation of B lymphocytes with oncogenic DNA, or transfection with Epstein-Barr virus. Panels of monoclonal antibodies produced against the polypeptides and peptidomimetics of the invention can be screened for various properties, for example epitope affinity. Other well known methods for making antibody include the use of phage display techniques (see, for instance, Kay et al., Phage display of peptides and proteins: A laboratory manual. San Diego: Academic Press (1996)) An antibody of the invention may be derived from a "humanized" monoclonal antibody. Humanized monoclonal antibodies may be produced by transferring mouse complementarity determining regions from heavy and light variable chains of a mouse immunoglobulin into a human variable domain, and then substituting human residues in the framework regions of the murinc counterparts. The use of antibody components derived from humanized monoclonal antibodies obviates potential problems associated with the immunogenicity of murine constant regions. General techniques for cloning murine immunoglobulin variable domains are described (Orlandi et al., Proc. Nat'l Acad. Sci. USA,"86:3833 (1989), and techniques for producing humanized monoclonal antibodies are described (Jones et al., Nature, 321:522 (1986); Riechmann et al., Nature, 332:323 (1988)). Antibody fragments of the invention can be prepared by routine known methods including proteolytic hydrolysis of the antibody or by expression in E. coli of a polynucleotide encoding the fragment. Antibody fragments can be obtained by digestion (with, for instance, pepsin or papain) of whole antibodies by conventional methods. For example, antibody fragments can be produced by enzymatic cleavage of antibodies with pepsin to provide a 5S fragment denoted F(ab')2. This fragment can be further cleaved using a thiol reducing agent, and optionally a blocking group for the sulfhydryl groups resulting from cleavage of disulfide linkages, to produce 3.5S Fab' monovalent fragments. Alternatively, an enzymatic cleavage using pepsin produces two monovalent Fab1 fragments and an Fc fragment directly. Other methods of cleaving antibodies, such as separation of heavy chains to form monovalent light-heavy chain fragments, further cleavage of fragments, or other enzymatic, chemical, or genetic techniques may also be used, so long as the fragments bind to the antigen that is recognized by the intact antibody. Antibodies can be screened to determine the identity of the epitope to which they bind. An epitope refers to the site on an antigen, such as a polypeptide of the invention, to which the paratope of an antibody binds. An epitope usually consists of chemically active surface groupings of molecules, such as amino acids or sugar side chains, and can have specific three-dimensional structural characteristics, as well as specific charge characteristics. Methods which can be used to identify an epitope are known in the art (Harlow et al., Antibodies: A Laboratory Manual, page 319 (Cold Spring Harbor Pub. 1988). Antibodies may be screened for their ability to specifically bind to a polypeptide or peptidomimetic of the present invention. For example, antibodies that specifically bind to the ER-a36 isoform or a portion thereof, but not the ER-a46 or a66 isoform, can be selected through use of methods routine in the art (see Kitajima et al., U.S. Patent No. 6,534,281, and Harlow et al., Antibodies: A Laboratory Manual, Cold Spring Harbor Pub. 1988). The antibodies of the invention may be coupled to a large variety of compounds. Examples of compounds include detectable markers. Examples of such detectable markers include fluorescent markers, enzymes, radioisotopes, and the like, such as avidin or biotin, which permit the detection of an antibody. Methods to couple antibodies to detectable markers, and useful detectable markers, are known in the art. Such antibodies are useful within automated systems for detection of ER-a36. An antibody can be covalently attached to a chemotherapeutic agent. Chemotherapeutic agents useful in the treatment of cancers such as breast cancer and prostate cancer are known in the art. Examples of chemotherapeutic agents include centchroman, delmadinone acetate, droloxifene, idoxifene, tamoxifen, raloxifene, toremifene, iulvcstrani anil faslodex, abisphosphonate, calcitonin, tribolone, parathyroid hormone, or strontium ranelate. Other examples include a cytokine, or a toxin, such as diphtheria toxin A chain. Compositions The present invention also provides compositions including a polynucleotide, peptidomimetic, or antibody of the present invention. Such compositions typically include a pharmaceutically acceptable carrier. As used herein "pharmaceutically acceptable carrier" includes saline, solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Additional active compounds can also be incorporated into the compositions. The compositions of the invention may be prepared in many forms that include tablets, hard or soft gelatin capsules, aqueous solutions, suspensions, and liposomes and other slow-release formulations, such as shaped polymeric gels. An oral dosage form may be formulated such that the polypeptide, peptidomimetic, or antibody is released into the intestine after passing through the stomach. Such formulations are described in Hong et al., U.S. Patent No. 6,306,434 and in the references contained therein. Oral liquid compositions may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid compositions may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), or preservatives. A composition can be formulated for parenteral administration (e.g., by injection, for example, bolus injection or continuous infusion) and may be presented in unit dosage form in ampules, prefilled syringes, small volume infusion containers or multi-dose containers with an added preservative. The compositions may take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents," Compositions suitable for rectal administration can be prepared as unit dose suppositories. Suitable carriers that may be included in the composition include those exemplified by saline solutions and other materials commonly used in the art. For administration by inhalation, a composition can be conveniently delivered from an insufflator, nebulizer or a pressurized pack or other convenient means of delivering an aerosol spray. Pressurized packs may include a suitable propellant such as dichlorodifluoromethane, trichlorofiuoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Alternatively, for administration by inhalation or insufflation, a composition may take the form of a dry powder composition, for example, a powder mix of a modulator and a suitable powder base such as lactose or starch. The powder composition may be presented in unit dosage form in, for example, capsules or cartridges or, e.g., gelatin or blister packs from which the powder may be administered with the aid of an inhalator or insufflator. For intra-nasal administration, a composition may be administered via a liquid spray, such as via a plastic bottle atomizer. A composition can be formulated for transdermal administration. A composition can also be formulated as an aqueous solution, suspension or dispersion, an aqueous gel, a water-in-oil emulsion, or an oil-in-water emulsion. A transdermal formulation may also be prepared by encapsulation of a composition within a polymer. The dosage form may be applied directly to the skin as a lotion, cream, salve, or through use of a patch. Compositions of the invention may also contain other ingredients such as flavorings, colorings, anti-microbial agents, and preservatives. In addition, a composition of the invention can include pharmaceutically active ingredients, such as hormones, anti-necrotic agents, vasodilators, pharmaceutical agents and the like. Toxicity and therapeutic efficacy of such compositions can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LDso (the dose lethal to 50% of the population) and the EDso (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LDso/EDso. Compounds which exhibit high therapeutic indices are preferred. The data obtained from cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compounds lies preferably within a range of circulating concentrations that include the EDso with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For a compound used i in the methods of the invention, the therapeutically effective dose can be estimated initially from cell ' culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range that includes the ICSo (i.e., the concentration of the test compound which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography. In one aspect, the range of dosage for use in humans is an amount sufficient to result in serum concentrations that are at least 10 micromolar (uM), preferably, at least 25 uM, more preferably, 50 uM, The compositions can be administered one or more times per day to one or more times per week, including once every other day. The skilled artisan will appreciate that certain factors may influence the dosage and timing required to effectively treat a subject, including but not limited to the severity of the disease or disorder, previous treatments, the general health and/or age of the subject, and other diseases present. Moreover, treatment of a subject with an effective amount of a composition can include a single treatment or, preferably, can include a series of treatments. Methods of detection The present invention provides methods for detecting a polypeptide of the present invention. The method typically includes providing a cell, analyzing the cell for a polypeptide of the present invention, and determining whether the cell expresses the polypeptide. The cell may be ex vivo or in vivo. As used herein, the term "ex vivo" refers to a cell that has been removed, for instance, isolated, from the body of a subject. Ex vivo cells include, for instance, primary cells (e.g., cells that have recently been removed from a subject and are capable of limited growth or maintenance in tissue culture medium), and cultured cells (e.g., cells that are capable of extended growth or maintenance in tissue culture medium). As used herein, the term "in vivo" refers to a cell that is within the body of a subject. An in vivo cell may be a cell present in an organ or a tumor. The cell is preferably a mammalian cell, such as, for instance, mouse, rat, or primate (e.g., monkey, human), preferably, human. Preferred examples of cells include breast cells, such as a breast tumor cell, and prostate cells, such as a prostate tumor cell. A cell maybe obtained from a subject by, for example, biopsy of human breast or prostate tissue. Samples obtained from nearly any type of tissue may be used. Control cells may be cultured in vitro according to methods known in the art. Cells that do not express an ER-a36 kDa estrogen receptor and thus can be used as a negative control include HEK293 cells. Positive control cells include cells grown at low cell density in the presence of serum, and BRCA1 negative cells. Preferably, cells are grown at low density in the presence of serum. Control cells may also be obtained from tissue samples through, for example, biopsy. In one aspect, the method includes analyzing the cell by contacting the cell with an antibody of the present invention. Whether a cell expresses a polypeptide of the present invention can be determined using detection methods that are routine and known in the art. Examples of immunoassays include competitive and non-competitive assays such as radioimmunoassay, immunoenzymometric assay, immunofluorometric assay, or enzymoimmunassays assays. Chemiluminescent methods with horseradish peroxidase, alkaline phosphatase, or other Chemiluminescent detection agents can also be used. Western blotting and chromatographic assays can also be used within the method of the invention. An antibody of the present invention used to detect a polypeptide of the present invention may be coupled to a detectable marker and thereby detected directly, or a second antibody may be used. When detection methods are used that permit detection of the polypeptide in different areas of the cell, a cell expressing an ER-a36 is typically considered ER-a36 positive when the polypeptide is associated predominantly with the plasma membrane and the cytoplasm, and less than 20% of the signal is associated with the nucleus. In another aspect, the method includes analyzing the cell by amplifying a polynucleotide, preferably, an RNA polynucleotide (e.g., an mRNA), to form amplified polynucleotides. Preferably, a polynucleotide is ampli tied by polymerase chain reaction (PCR), preferably, by reverse transcriptase (RT) PCR. Methods for synthesizing a DN A polynucleotide from an RN A polynucleotide are known in the art and routine. Polynucleotides obtained from the cell are contacted with a primer pair that will amplify a polynucleotide that includes SEQ ID NO:22 or SEQ ID NO:25, or the combination thereof. The presence of amplified polynucleotides resulting from such a primer pair indicates the cell expresses the estrogen receptor. As used herein, the term "primer pair" refers two oligonucleotides designed to flank a region of a polynucleotide to be amplified. One primer is complementary to nucleotides present on the sense strand at one end of a polynucleotide to be amplified and another primer is complementary to nucleotides present on the antisense strand at the other end of the polynucleotide to be amplified. The polynucleotide to be amplified can be referred to as the template polynucleotide. The nucleotides of a polynucleotide to which a primer is complementary can be referred to as a target sequence. A primer can have at least about 15 nucleotides, preferably, at least about 20 nucleotides, most preferably, at least about 25 nucleotides. The conditions for amplifying a polynucleotide by PCR vary depending on the nucleotide sequence of primers used, and methods for determining such conditions are routine in the art.- After amplification, the presence of the amplified polynucleotides may be determined, for instance, by gel electrophoresis. The amplified polynucleotides can be visualized by staining (e.g., with ethidium bromide) or labeling with a suitable label known to those skilled in the art, including radioactive and nonradioactive labels. Typical radioactive labels include P. Nonradioactive labels include, for example, ligands such as biotin or digoxigenin as well as enzymes such as phosphatase or peroxidases, or the various chemiluminescers such as luciferin, or fluorescent compounds like fluoresccin and its derivatives. Optionally, the presence in a cell of an ER-a66 polypeptide, ER-a46 polypeptide, ER-P, or the combination thereof, may also be determined. Methods for detecting the presence of ER-a66, ER-a46, ER-p, or the combination thereof, include the use of immunological detection using antibody or polynucleotide based detection methods such as amplification of a polynucleotide. When detection methods are used that permit detection of the polypeptide in different areas of the cell, a cell expressing an ER-a66 or ER-o46 is typically considered ER-a66 or ER-a46 positive when the polypeptide is associated predominantly with the nucleus of the cell, e.g., greater than 90 % of the signal is associated with the nucleus. Approximately 70-80% of all breast cancers expresses ER-a66 and are referred to as ER-positive breast cancer. These tumors usually grow more slowly, are better differentiated, and are associated with a better overall prognosis (Clark, In: Harris JR, editor. Diseases of the breast, volume 2. Lippincott Williams & Wilkins, 38:103-116 (2000)). The methods for detecting the presence of a polypeptide of the present invention are useful as a diagnostic marker to differentiate estrogen-positive and estrogen-negative cancer, preferably, breast cancer. The results disclosed in the Examples herein strongly indicate that estrogen signaling mediated by ER-a36 contributes to mammary tumorigenesis and suggest that ER-a36 may be involved in tumorigenesis of ER-a66 negative breast cancers. The results disclosed in the Examples herein also indicate that a cell highly expressing a polypeptide of the present invention is more resistant to lower dose of an anti-estrogen, for instance, tamoxifen, than a cell that expresses high levels of ER-a66 but lower levels of ER-a36. Thus, methods for detecting the presence of a polypeptide of the present invention permit the identification of a new class of patients, i.e., ER-a66-negative and ER-a36-positive. Methods for detecting the presence of a polypeptide of the present invention are also useful in determining the sensitivity of a cell to an anti-estrogen, and providing information relevant to, for instance, determining an appropriate course of treatment for an individual. For instance, a physician may decide that a subject with ER-a36-positive breast tumor cells may require higher doses of tamoxifen to overcome resistance to lower levels. Detection of the presence of ER-a66, ER-a46, ER-a36, ER-0, or the combination thereof, also i permits comparing the ratio of the estrogen receptors. Determination of the ratio of two or more of the estrogen receptors allows the sensitivity of a cell to an anti-estrogen, for instance, tamoxifen, to be predicted. For instance, in this aspect of the invention the ratio of ER-a36 to ER-a46, the ratio of ER-a36 to ER-a66, the ratio of ER-a36 to ER-p\ or a combination thereof, in a cell is determined and compared to the corresponding ratio in a control cell. Such a ratio is referred to herein as an ER-a36 ratio. In one example, the control cell can be a cell that is refractory to treatment with an anti-estrogen. In another example, the control cell is a cell that is not refractory to the anti-estrogen. If an above described ER-a36 ratio determined in the test cell is the same as the ER-a36 ratio described in the control cell, then the test cell is classified according to the status of the control cell. For example, if the ER-a36 to ER-a66 ratio of the test cell is the same as the ER-ct36 to ER-a66 ratio in a control cell known to be refractory to tamoxifen treatment, then the test cell is classified as being refractory to tamoxifen treatment. However, if the ER-a36 to ER-a66 ratio in the test cell is the same as the ER-a36 to ER-a66 ratio in a control cell that is not refractory to tamoxifen treatment, then the test cell is classified as not being refractory to tamoxifen treatment. In another example, the ER-a36 ratio determined in a test cell is compared to the corresponding ratio in a control cell known to be refractory to tamoxifen treatment, and to the ratio in a control cell that is known not to be refractory to tamoxifen treatment. The test cell is then classified as being refractory to tamoxifen treatment, or not refractory to tamoxifen treatment, as described above. An example of a control cell that is known not to be refractory to tamoxifen treatment is MCF7 (ATTC Collection accession number HTB-22). An example of a control cell that is known to be refractory to low dose tamoxifen treatment is MDA-MB-231. Breast cancer cells that are known to be refractory to tamoxifen treatment can also be used as control cells by comparing an ER-a36 ratio in a test cell. Identification of agents that hind a polypeptide of the present invention The present invention also provides methods for identifying an agent that binds a polypeptide of the present invention. Such methods are also referred to as screening assays. The method includes combining a polypeptide of the present invention with an agent, and determining whether the agent binds the polypeptide. Typically, determining whether an agent binds the polypeptide includes detecting the formation of a complex between the agent and the polypeptide. Methods for determining the complex include, for instance, directly detecting the binding of an agent to the polypeptide, and detecting the binding of the agent to the polypeptide using a competition binding assay. The assay may be a cell-free assay. The assay may be done in the presence or absence of an estrogen or anti-estrogen. Optionally, the method also includes determining whether the agent binds an ER-o.66 polypeptide, such as a polypeptide with an amino acid sequence depicted at SEQ ID NO: 18. Preferably, an agent does not bind an ER-a66 polypeptide. An agent can be obtained using any of the numerous approaches in combinatorial library methods known in the art, including biological libraries, spatially addressable parallel solid phase or solution phase libraries, synthetic library methods requiring deconvolution, the "one-bead one-compound" library method, and synthetic library methods using affinity chromatography selection. The biological library approach includes peptide libraries, while the other four approaches are applicable to peptide, nonpeptide oligomer, or small molecule libraries of compounds (Lam, AnticancerDrug Des. 12:145 (1997)). Examples of methods for the synthesis of molecular libraries can be found in the art (see, for example DeWitt et al. Proc. Natl. Acad. Sci. USA 90:6909 (1993); Erb et al. Proc. Natl. Acad. Sci. USA 91:11422 (1994); Zuckermann et al. J. Med. Chem. 37:2678 (1994); Cho et al. Science 261:1303 (1993); Carrell et al. Angew. Chem. Int. Ed. Engl. 33:2059 (1994); Carell et al. Angew. Chem. Int. Ed. Engl. 33:2061(1994); and Gallop etal. J. Med. Chem. 37:1233 (1994)). The sources for potential agents to be screened include also include, for instance, fermentation media of bacteria and fungi, and cell extracts of plants and other vegetations. Libraries of compounds maybe presented, for instance, in solution (e.g. Houghten Bio/Techniques t 13:412-421(1992)), or on beads (Lam Nature 354:82-84(1991)), chips (Fodor Nature 364:555-556 • (1993)), bacteria (U.S. Pat. No. No. 5,223,409), spores (U.S. Pat. Nos. 5,571,698; 5,403,484; and 5,223,409), plasmids (Cull et al. Proc. Natl. Acad. Sci. USA 89:1865-1869(1992)), orphage (Scott etal. Science 249:386-390(1990); Devlin Science 249:404-406(1990); Cwirla et al. Proc. Natl. Acad. Sci. USA 87:6378-6382(1990); and Felici J. Mol. Biol. 222:301-310(1991)). Determining the ability of an agent to bind to a polypeptide of the present invention can be accomplished, for example, by coupling the agent with a radioisotope or enzymatic label such that binding of the agent to the polypeptide of the present invention can be determined by detecting the labeled compound in a complex. For example, agents can be labeled with I251,35S, I4C, or 3H, either directly or indirectly, and the radioisotope detected by direct counting of radioemmission or by scintillation counting. Alternatively, agents can be enzymatically labeled with, for example, horseradish peroxidase, alkaline phosphatase, or luciferase, and the enzymatic label detected by determination of conversion of an appropriate substrate to product. In a similar manner, one may determine the ability of an agent to alter (e.g., stimulate or inhibit) the binding of a polypeptide of the present invention to a known ligand of the polypeptide, e.g., molecule with which a polypeptide of the present invention binds or interacts in nature. An example of such a ligand is estrogen, as well as an anti-estrogen, such as tamoxifen. In a preferred aspect, the ability of an agent to alter the binding of a polypeptide of the present invention to bind to a ligand can be determined by monitoring the activity of the polypeptide of the invention. In yet another aspect, an assay of the present invention includes contacting a polypeptide of the present invention with an agent and determining the ability of the agent to bind to the polypeptide. Binding of the agent to the polypeptide can be determined either directly or indirectly as described above. In a preferred aspect, the assay includes contacting a polypeptide of the present invention with a ligand known to bind a polypeptide of the present invention to form an assay mixture, contacting the assay mixture with an agent, and determining the ability of the agent to preferentially bind to the polypeptide as compared to the ligand. In another aspect, an assay includes contacting a polypeptide of the present invention with an agent and determining the ability of the agent to alter (e.g., stimulate or inhibit) the activity of the polypeptide of the present invention. In a further aspect, an assay includes screening for agents that alter (e.g., stimulate or inhibit) the ability of a polypeptide of the present invention to regulate transcriptional transactivation of an estrogen response element, including, for instance, activities mediated by the AF-1 and/or AF-2 domains of ER-a66. Preferably, a fusion polypeptide including a polypeptide of the present invention and a polypeptide having a transcriptional activation domain, or a transcriptional represser domain, is used. An example of a polypeptide having a transcriptional activation domain is VP-16, and other useful polypeptides having a transcriptional activation domain or a transcriptional represser domain are known in the art. Typically, such a fusion polypeptide is used in conjunction with a polynucleotide having an estrogen response element upstream of a promoter and an operably linked coding sequence. A variety of promoters can be used, including, for instance, a thymidine kinase promoter. Preferably, the operably linked coding region encodes a detectable marker, such as luciferase, or a fluorescent polypeptide such as green fluorescent protein. In one aspect, the fusion polypeptide with transcriptional activation domain, polynucleotide, and agent are combined under conditions that promote expression of the coding region present on the polynucleotide in the absence of the agent, and the effect of the agent in altering transcription is determined. Optionally, an ER-a66 polypeptide and/or an ERp polypeptide may also be present, and the assay used to identify agents that alter (e.g., stimulate, or inhibit) the ability of a polypeptide of the present invention to modulate ligand-dependent and ligand-independent transcriptional activities of ER-a66polypeptide or ER(3. Preferably, both the fusion polynucleotide and the polynucleotide that includes an i estrogen response element upstream of a promoter and an operably linked coding sequence are present in a cell. Without intending to be limiting, it is expected that agents that alter the ability of a polypeptide of the present invention to regulate transcriptional transactivation may include agents that alter the conformation of a polypeptide of the present invention to increase or decrease the ability of the In the assays, it may be desirable to immobilize either a polypeptide of the present invention, its ligand, or the agent to facilitate separation of complexed from uncomplexed forms of one or both of the molecules, as well as to accommodate automation of the assay. In one embodiment, a fusion protein can be provided that adds a domain that allows the polypeptide of the present invention to be bound to a matrix. For example, fusion polypeptides with glutathione-S-transferase can be adsorbed onto glutathione sepharose beads (Sigma Chemical, St. Louis, Mo.) or glutathione-derivatized microtitre plates, which are then combined with the agent, and the mixture incubated under conditions conducive to complex formation (e.g. at physiological conditions for salt and pH). Following incubation, the beads or microtitre plate wells can be washed to remove any unbound components and complex formation is measured either directly or indirectly, for example, as described above. Alternatively, the complexes can be dissociated from the matrix, and the level of binding determined. Other techniques for immobilizing polypeptides on matrices can also be used in the screening assays of the invention. For example, a polypeptide of the present invention can be immobilized using conjugation of biotin and streptavidin. A polypeptide of the present invention can be biotinylated using biotin-NHS (N-hydroxy-succinimide) with techniques well known in the art (e.g., biotinylation kit, Pierce Chemicals, Rockford, 111.), and, for instance, immobilized in the wells of streptavidin-coated 96-well plates (Pierce Chemicals). Alternatively, antibodies reactive with a polypeptide of the present invention can be derivatized to the wells of the plate, and unbound polypeptide of the present invention trapped in the wells by antibody conjugation. Methods for detecting such complexes, in addition to those described above for the GST-immobilized complexes, include immunodetection of complexes using antibodies reactive with antibody that specifically binds a polypeptide of the present invention. The present invention also includes novel agents identified by the above-described screening assays and uses thereof for treatments as described herein. Methods of treatment The present invention is further directed to methods for treating certain diseases in a subject. The subject is a mammal, preferably a human. As used herein, the term "disease" refers to any deviation from or interruption of the normal structure or function of a part, organ, or system, or combination thereof, of a subject that is manifested by a characteristic symptom or set of symptoms. Diseases include cancers dependent upon signalling via steroid hormone receptors, such as estrogen receptors. Examples of such diseases are referred to as estrogen-related cancers and include breast cancer and prostate cancer. Typically, whether a subject has a disease, and whether a subject is responding to treatment, is determined by evaluation of symptoms associated with the disease. As used herein, the term "symptom" refers to objective evidence of a disease present in a subject. Symptoms associated with diseases referred to herein and the evaluation of such symptoms are routine and known in the art. Examples of symptoms of cancers dependent upon signalling via steroid hormone receptors include, for instance, the presence and size of tumors, and the presence and amount of biomarkers. Biomarkers are compounds, typically polypeptides, present in a subject and indicative of the progression of cancer. Examples of biomarkers include, for instance, Her-2 expression, and cyclin Dl expression. Treatment of a disease can be prophylactic or, alternatively, can be initiated after the development of a disease. Treatment that is prophylactic, for instance, initiated before a subject manifests symptoms of a disease, is referred to herein as treatment of a subject that is "at risk" of h developing a disease. An example of a subject that is at risk of developing a disease is a person having a risk factor, such as a genetic marker, that is associated with the disease. Examples of genetic markers indicating a subject has a predisposition to develop certain cancers such as breast, or prostate cancer include alterations in the BRAC1 and/or BRAC2 genes. Treatment can be performed before, during, or after the occurrence of the diseases described herein. Treatment initiated after the development of a disease may result in decreasing the severity of the symptoms of one of the conditions, or completely removing the symptoms. In some aspects, the methods typically include contacting a cell with a composition including an effective amount of an agent that inhibits the activity of a polypeptide of the present invention, for instance, an agent identified using a method described herein. Preferably, such an agent binds to a polypeptide of the present invention. In some aspects, the agent is preferably not an anti-estrogen. As used herein, an "effective amount" is an amount effective to inhibit in a cell the activity of a polypeptide of the present invention, decrease symptoms associated with a disease, or the combination thereof. In one aspect, a composition may include an effective amount of an antibody of the present invention. Preferably, an antibody is covalently attached to a chemotherapeutic agent, such as, for instance, tamoxifen. The composition may optionally include other chemotherapeutic agents. Whether an agent or antibody, preferably, antibody, is expected to function in this aspect of the invention can be evaluated using ex vivo models and animal models. Such models are known in the art and are generally accepted as representative of disease or methods of treating humans. A preferred example of such an animal model is the nude mouse. For instance, breast cancer cells can be inoculated into the mammary fatpad of ovariectomized female nude mice, and lesion formation followed and evaluated, for example, by palpation, measurement by vernier calipers, and tumor weight. Transgenic animal models are also available. For instance, models for the study of prostate cancer such as the TRAMP model (see, for instance, Greenberg et al., Proc. Natl. Acad. Sci. USA, 92:2429-3443 (1995)) and for breast cancer such as the MMTV-Wnt-1 model (see, for instance, Tsukamoto et al., Cell, 55:619-625 (1988)) are commonly accepted as models for human disease. In another aspect, a cell is contacted with a composition including a polynucleotide, where the polynucleotide causes the post-transcriptional silencing of a coding region encoding a polypeptide of the present invention. Such a polynucleotide is referred to herein as a silencing polynucleotide. The silencing polynucleotide may be introduced into a cell as an RNA polynucleotide, or as a vector including a DN A polynucleotide that encodes and will express the RNA polynucleotide. More than one type of polynucleotide can be administered. For instance, two or more polynucleotides that are designed to silence the same mRN A can be combined and used in the methods herein. Alternatively, two or more polynucleotides can be used together where the polynucleotides are each designed to silence different mRNAs. As used herein, the term "polynucleotide" refers to a polymeric form of nucleotides of any length, either ribonucleotides, deoxynucleotides, or a combination thereof, and includes both single-stranded molecules and double-stranded duplexes. A polynucleotide can be obtained directly from a natural source, or can be prepared with the aid of recombinant, enzymatic, or chemical techniques. Preferably, a polynucleotide of the present invention is isolated. As used herein, a "target coding region" and "target coding sequence" refer to the coding region whose expression is inhibited by a silencing polynucleotide. As used herein, a "target mRNA" is an mRNA encoded by a target coding region. An example of a target coding region is the nucleotide sequence encoding an ER-a36 (SEQ ID NO: 21), the 5' flanking nucleotide sequence (SEQ ID NO:20), or the 3' flanking nucleotide sequence, includingthe nucleotide sequence encoded by exon 9 (SEQ ID NO:25). Silencing polynucleotides include double stranded RNA (dsRNA) polynucleotides. The sequence of a silencing polynucleotide includes one strand, referred to herein as the sense strand, of between 16 to 30 nucleotides, for instance, 16, 17, 18, 19, 20,21, 22,23, 24, 25,26, 27, 28, 29, or 30 nucleotides. The sense strand is substantially identical, preferably, identical, to a target mRN A. As used herein, the term "identical" means the nucleotide sequence of the sense strand has the same nucleotide sequence as a portion of the target mRNA. As used herein, the term "substantially identical" means the sequence of the sense strand differs from the sequence of a target mRNA at 1,2, or 3 nucleotides, preferably 1 nucleotide, and the remaining nucleotides are identical to the sequence of the mRNA. These 1,2, or 3 nucleotides of the sense strand are referred to as non-complementary nucleotides. When a silencing polynucleotide includes a sense strand that is substantially identical to a target mRNA, the 1,2, or 3 non-complementary nucleotides are preferably located in the middle of the sense strand. For instance, if the sense strand is 21 nucleotides in length, the non-complementary nucleotides are typically at nucleotides 9, 10, 11, or 12, preferably nucleotides 10 or 11. The other strand of a dsRNA polynucleotide, referred to herein as the anti-sense strand, is complementary to the sense strand. The term "complementary" refers to the ability of two single stranded polynucleotides to base pair with each other, where an adenine on one polynucleotide will base pair to a thymine or uracil on a second polynucleotide and a cytosine on one polynucleotide will base pair to a guanine on a second polynucleotide. The silencing polynucleotides also include the double stranded DNA polynucleotides that correspond to the dsRNA polynucleotides. Also included are the single stranded RNA polyncleotides and single stranded DNA polynucleotides corresponding to the sense strands and anti-sense strands disclosed herein. It should be understood that the sequences disclosed herein as DNA sequences can be converted from a DNA sequence to an RNA sequence by replacing each thymidine nucleotide with a uracil nucleotide. Without intending to be limiting, the polynucleotides of the present invention cause the post-transcriptional silencing of a target coding region. Modifications to polynucleotides for use in silencing are known in the art and the silencing polynucleotides can be so modified. The sense and anti-sense strands of a dsRNA silencing polynucleotide of the present invention may also be covalently attached, typically by a spacer made up of nucleotides. Such a polynudeotide is often referred to in the art as a short hairpin RNA (shRNA). Upon base pairing of the sense and anti-sense strands, the spacer region forms a loop. The number of nucleotides making up the loop can vary, and loops between 3 and 23 nucleotides have been reported (Sui et al., Proc. Nat'l. Acad. Sci. USA, 99, 5515-5520 (2002), and Jacque et al., Nature, 418, 435-438 (2002)). A silencing polynucleotide causes the post-transcriptional inhibition of expression, also referred to as silencing, of a target coding region. Without intending to be limited by theory, after introduction into a cell a silencing polynucleotide will hybridize with a target mRNA and signal cellular endonucleases to cleave the target mRNA. The result is the inhibition of expression of the polypeptide encoded by the mRNA. Whether the expression of a target coding region is inhibited can be determined by, for instance, measuring a decrease in the amount of the target mRNA in the cell, measuring a decrease in the amount of polypeptide encoded by the mRNA, or by measuring a decrease in the activity of the polypeptide encoded by the mRNA. A silencing polynucleotide can be present in a vector. A silencing polynucleotide can be present in a vector as two separate complementary polynucleotides, each of which can be expressed to yield a sense and an antisense strand of the dsRNA, or as a single polynucleotide containing a sense strand, a loop region, and an anti-sense strand, which can be expressed to yield an RNA polynucleotide having a sense and an antisense strand of the dsRNA. A silencing polynucleotide can be designed using methods that are routine and known in the art. For instance, a silencing polynucleotide may be identified by scanning the coding region AA dinucleotide sequences; each AA and the downstream (3') consecutive 16 to 30 nucleotides of the mRNA can be used as the sense strand of a candidate polynucleotide. A candidate polynucleotide is the polynucleotide that is being tested to determine if it decreases expression of one of a polypeptide of the present invention. The candidate polynucleotide can be identical to nucleotides located in the region encoding the polypeptide, or located in the 5' or 3' untranslated regions of the mRNA. Optionally and preferably, a candidate polynucleotide is modified to include 1, 2, or 3, preferably 1, non-complementary nucleotides. Other methods are known in the art and used routinely for designing and selecting candidate polynucleotides. A silencing polynucleotide may, but need not, begin with the dinucleotide AA at the 5' end of the sense : strand. A candidate polynucleotide may also include overhangs of 1,2, or 3 nucleotides, typically on the 3' end of the sense strand, the anti-sense strand, or both. Candidate polynucleotides are typically screened using publicly available algorithms (e.g., BLAST) to compare the candidate polynucleotide sequences with coding sequences. Those that are likely to form a duplex with an mRNA expressed by a non-target coding region are typically eliminated from further consideration. The remaining candidate polynucleotides may then be tested to determine if they inhibit expression of one of the polypeptides described herein. In general, candidate polynucleotides are individually tested by introducing a candidate polynucleotide into a cell that expresses polypeptide of the present invention. The candidate polynucleotides may be prepared in vitro and then introduced into a cell. Methods for in vitro synthesis include, for instance, chemical synthesis with a conventional DNA/RNA synthesizer. Commercial suppliers of synthetic polynucleotides and reagents for such synthesis are well known. Methods for in vitro synthesis also include, for instance, in vitro transcription using a circular or linear vector in a cell free system. The candidate polynucleotides may also be prepared by introducing into a cell a construct that encodes the candidate polynucleotide. Such constructs are known in the art and include, for example, a vector encoding and expressing a sense strand and an anti-sense strand of a candidate polynucleotide, and RN A expression cassettes that include the sequence encoding the sense strand and an anti-sense strand of a candidate polynucleotide flanked by operably linked regulatory sequences, such as an RNA polymerase III promoter and an RNA polymerase III terminator, that result in the production of an RNA polynucleotide. The cell can be ex vivo or in vivo. Candidate polynucleotides may also be tested in animal models. When evaluating whether a candidate polynucleotide functions to inhibit expression of one of the polypeptides described herein, the amount of target mRNA in a cell containing a candidate polynucleotide can be measured and compared to the same type of cell that does not contain the candidate polynucleotide. Methods for measuring mRNA levels in a cell are known in the art and routine. Such methods include quantitative RT-PCR. Primers and specific conditions for amplification of an mRNA vary depending upon the mRNA, and can be readily determined by the skilled person. Other methods include, for instance, Northern blotting, and array analysis. Other methods for evaluating whether a candidate polynucleotide functions to inhibit expression of one of the polypeptides described herein include monitoring the polypeptide. For instance, assays can be used to measure a decrease in the amount of polypeptide encoded by the mRNA, or to measure a decrease in the activity of the polypeptide encoded by the mRNA. Methods for measuring a decrease in the amount of a polypeptide include assaying for the polypeptide present in cells containing a candidate polynucleotide and comparing to the same type of cell that does not contain the candidate polynucleotide. For instance, an antibody of the present invention may be used in, for example, Western immunoblot, immunoprecipitation, or immunohistochemistry. Antibodies to each of the polypeptides described herein are commercially available. Methods for measuring a decrease in the activity of one of a polypeptide of the present invention may also be used. Kits The invention provides kits that contain reagents that can be used in the methods of the present invention, including, for instance, determining if a cell expresses a polypeptide of the present invention. Such kits can contain packaging material and an antibody of the present invention. Such kits may also be used by medical personal for the formulation of compositions, such as pharmaceutical compositions, that contain an antibody of the invention. The packaging material provides a protected environment for the antibody. For example, the f packaging material may keep the antibody from being contaminated. In addition, the packaging material may keep an antibody in solution from becoming dry. Examples of suitable materials that can be used for packaging materials include glass, plastic, metal, and the like. Such materials may be silanized to avoid adhesion of an antibody to the packaging material. In one example, the invention provides a kit that includes packaging material, a first antibody that specifically binds to a polypeptide of the invention, and a second antibody that specifically binds to an ER-a66 polypeptide. The kit may optionally include additional components such as buffers,- reaction vessels, secondary antibodies, and syringes. EXAMPLES Example 1 Caveolin-1 haploinsufficiency produces activation of ER-a expression and estrogen stimulated transformation of normal breast epithelial cells A gene-trapped library of cell clones from normal human mammary epithelial MCF 1 OA cells was prepared through use of a poly-A trap retrovirus vector (RET) obtained from Dr. Philip Leder's laboratory at Harvard Medical School (Ishida et. al., Nucl. Acid Res., 27:580 (1999)). Briefly, this vector used an improved poly-A trap strategy for the efficient identification of functional genes regardless of their expression status in target cells. A combination of a strong splice acceptor and an effective polyadenylation signal assures the complete disruption of the function of "trapped" genes. Inclusion of a promoterless GFP cDN A in the RET vector allows the expression pattern of the trapped gene to be easily monitored in living cells. A retrovirus containing the RET vector was used to infect MCF 1 OA cells. The cells were then screened for G418-resistant to establish a gene-trapped library of MCF 1 OA cells. After selection by G418 for three weeks, GFP expression, under the control of the endogenous promoter of the "trapped" gene, was monitored and G418 resistant and GFP expressing clones were then selected. This library represented 3xl05 independent infected clones in which one allele of a functional gene was disrupted by the RET vector. It was thought that loss of expression of genes with tumor suppression activity could confer the transformed phenotype to normal MCF10A cells. A soft-agar cloning assay was performed and cells from the gene-trapped cell library that acquired anchorage-independent growth, a characteristic of the transformed phenotype, were identified. More than 100 positive colonies ( 30 cells) from the library of G418-resistant cells grew in soft-agar while the parental MCF10A cells did not. Twenty cell clones were isolated, expanded, and then selected again in soft-agar containing regular serum plus 10-8 M 17b-estradiol (E2) and dextrin coated charcoal-stripped serum that lacks steroid hormones for three weeks. Four cell clones (ST1, ST3, ST4 and ST6) that exhibited accelerated growth in soft-agar containing extra E2 were isolated and expanded (Figure 3). 3' -RACE, which permits the capture of unknown 3 'mRNA sequences that lie between the exon of a candidate gene and the poly-A tail, was used to clone potential genes whose disruption leads to MCF10A cell transformation. Transformation of the MCF10A cells was thought to be due to positive estrogen signaling. The purified PCR fragments resulting from the RACE procedure were cloned and sequenced. Using a BLASTN search, the DNA sequences from two clones (ST1 and ST3) were matched identically to the sequence of caveolin-1 (Cav-1) exon-3 located on chromosome 7 (GenBank accession number XM048940). This result indicated that an allele of the Cav-1 gene was disrupted in at least 2 clones. In addition to Cav-1, two other genes were identified using the same technique. The gene disrupted in clone ST4 was SPRR1B (GenBank accession number NT-004441.5), a member of the cornifin/small proline-rich protein family involved in structural organization of cornified cell envelopes. Another gene from clone ST6 is a putative novel gene (GenBank accession number 6599139) with no known function. Cav-1 protein levels were analyzed in parental MCF10A cells to test whether expression levels of Cav-1 were decreased in the cav-1 gene trapped cells. Four cell clones (ST 1,3,4 and 6) described above, and MCF1 OA-Ha-ras, (MCF 1 OA cells transformed by a Ha-ras mutant) were analyzed. Compared to the levels in parental MCF 1 OA cells, Cav-1 protein levels were about 2-fold lower in all transformed cells as demonstrated by Western blot analysis (Figure 4). This data is consistent with Cav-1 expression being decreased when only one functional allele of the cav-1 gene is functional in ST1 and ST3 cells. This indicates that Cav-1 haploinsufficiency created by "gene trapping" leads to transformation stimulated by E2. This data also indicates that downregulation of Cav-1 is also involved in transformation resulted from the disruption of other genes in ST4 and ST6 cells. To determine the mechanism by which Cav-1 haploinsufficiency leads to estrogen-stimulated cell growth and transformation, the expression levels of ER-a and ER-P in the transformed cells described above was examined. It was found that all of the four transformed cell clones expressed ER-a at a level comparable to that in the Ha-ras transformed cells, whereas parental MCF 1 OA cells and HBL-100 cells, another normal mammary epithelial cell line, expressed undetectable levels of ER-a (Figure 5). ER-p expression was without any change in all of the cells tested (Figure 5). This data indicated that ER-a expression was activated and that estrogen signaling in these transformed cells is responsible for the estrogen-stimulated cell growth on soft-agar. It has been shown before that both ER-a expression and estrogen signaling are activated in Ha-ras transformed cells (Shekhar et. al., Int. J. Oncol., 13:907 (1998) and Shekhar et. al., Am. J. of Pathl., 152:1129 (1998)). The present results indicate that the Ras/MAPK pathway is involved in the regulation of ER-a expression and positive estrogen signaling. Activation of the MAPK pathway in these transformed cells was analyzed by examining the phosphorylation levels of ERK1/2 using phospho-specific antibodies. It was found that ERK1/2 are highly and constitutively phosphorylated in all transformed cells but not in MCF10A cells (Figure 6). Taken together, these data indicate that the Cav-1/Ras/MAPK pathway is involved in the activation of ER-a expression during human breast cancer development and cooperates with estrogen signaling pathway to stimulate transformed cell proliferation. Example 2 IDENTIFICATION, CLONING, EXPRESSION AND CHARACTERIZATION OF AN ISOFORM OF ESTROGEN RECEPTOR ALPHA (ER-a36) During the course of the work described above, three protein bands (66-kDa, 46-kDa and 36-kDa) were consistently observed in western blot analysis using the Rat anti-ER-a antibody (clone 11222) from Research Diagnostic, INC. The H222 antibody recognizes the ligand-binding domain of ER-a. To exclude the possibility that 46-kDa and 36-kDa protein bands were the degradation products of ER-a66, as suggested by a previous report (Abbondanza et. al., Steroids, 58:4 (1993)), cells were lysed in culture plates using a buffer containing 8 M urea and tested by western blot analysis. Three distinct bands were readily observed in Cav-1 haploinsufficient cells, ST1 and ST3, and MCF7 breast cancer cells (Figure 7). These results indicated the existence of ER-a isoforms that share a similar epitope that is recognized by the antibody H222. Through a literature search, it was found that a 46-kDa isoform of ER-a had been cloned that functions as a dominant-negative inhibitor of transactivation mediated by the AF-1 domain of ER-a66 (Flouriot et. al., EMBO J., 19:4688 (2000)). A continued search identified a clone from a normal human edometrium cDNA library (RZPD clone number: DKFZp686N23123) that contains a 5.4 kb cDNA. This i cDN A clone harbors a 310 amino acid open reading frame that theoretically can produce a protein with a predicted molecular weight of 35.7 kDa. The cDN A sequence of the open-reading frame matched 100% to DNA sequence of the exons 2 to 6 of the ER-a66 gene. The 5'untraslated region (5'UTR) of the cDNA showed 100% homology to the DNA sequence of the first intron of the ER-a66 gene from 734 to 907 (the first base pair of the 34,233 bp first intron of ER-a66 gene was designated as 1). Thus, it was determined that the transcript of ER-a36 is initiated from a previously unidentified promoter in the first intron of the ER-a66 gene. A small, non-coding novel exon from 734 to 907 of the first intron of the ER-a66 gene was designated as "exon 1'". The exon 1' is then spliced directly into the exon 2 of the ER-a66gene and continues from exon 2 to exon 6 of the ER-a66 gene. Exon 6 is then spliced to an exon located 64,141 bp downstream of the ER-a66 gene (GeneBank accession number AY425004, see Table 1). The cDNA sequence encoding the last 27 amino acids and the 4,293 bp 3 'untranslated region was matched 100% to a continuous sequence from the genomic sequence of clone RP1-1304 on chromosome 6q24.2-25.3 (GeneBank accession number AL078582), indicating the remaining cDN A sequence of this novel ER-a isoform is transcribed from one exon of 4,374 bp located downstream of the previously reported ER-a66 gene. This exon is thus designated as exon 9 to reflect the extra exon beyond the previous reported eight exons (Figure 8). All of these splicing events are supported by the identification of perfect splice donors and acceptors at the splice juncture. The protein ER-o.36 can be produced from a perfect Kozak sequence located in the second exon, the same initiation codon used to produce ER-ot46 (Flouriot et. al., EMBO J., 19:4688 (2000)). ER-a36 differs from ER-a66 by lacking both transcriptional activation domains, AF-1 and AF-2, but retaining the dimerization, DNA-binding and partial ligand-binding domains. It also possesses an extra, unique 27 amino acid domain to replace the last 138 amino acids encoded by exon 7 and 8 of the ER-a66 (Figure 1). Here, this novel isoform of ER-a is herein named ER-a36. The open reading frame encoding ER-a36 was obtained by using the PCR from the Marathon Ready cDNA prepared from human placenta RNA (Clonetech) according to the procedure described by the manufacture. The PCR primer pairs are designed according to the cDNA sequence of DKFZp686N23123. The 5' primer is 5'-CGGAATTCCGAAGGGAAGTATGGCTATGGAATCC-3' (SEQ ID NO:23) with an EcoRI site at the end, and the 3' primer is 5'-CGGGATCCAGAGGCTTTAGACACGAGGAAAC-3' (SEQ ID NO:24) with a Baml II site at the end. The PCR product was subjected to electrophoresis on a 1% agarose gel, and an expected 1.1 kb DNA fragment was observed (Figure 9). The DNA fragment was purified, digested with EcoRI and BamHI, cloned into a pBluescript vector (pBS- ER-a36) and fully sequenced. The sequence showed 100% identity to the cDNA clone DKFZp686N23123, indicated that ER-a36 is a naturally occurring isoform of ER-a that can be cloned from another source. The predicted amino acid sequence encoded by the open-reading frame is shown in Figure 10. Transient transfection assays were performed in human embryonic kidney 293 cells using expression vectors containing ER-a66, ER-a46 and ER-a36 to test whether the cloned cDNA will produce the ER-a36 protein. Whole cell extracts from these transfected cells and MCF7 cells were subjected to western blot analysis with the monoclonal antibody H222 raised against the ligand-binding domain of ER-a (Abbondanza et. al., Steroids, 58:4 (1993)). A 36 kDa protein that was recognized by the H222 antibody was produced in ER-a36 vector transfected cells (Figure 11). The size of this protein and its failure to react with the antibody H226 directed to the B-domain of the ER-a66, and with the antibody HC 20 which recognizes the C-terminal of ER-a66, indicates that the ER-a isoform lacked both the N-terminus and C-terminus of ER-a66, resulting in an ER-a lacking both AF-1 and AF 2 domains. A series of computer searches were performed on the ER-a36 protein. FindMod and SCANPROSITE algorithms predicted three myristoylation sites in ER-a36, suggesting that it may localize in the peripheral membrane. This is in agreement with the k-nearest neighbors (PSPORT II) algorithm that predicts 21.7%, 34.8%, 17.4%, and 26% of ER-a36 is localized to the nucleus, cytoplasm, mitochondria, and membrane fractions, respectively. This is similar to the prediction for ER-a46 (26.1 %, 30.4%, 17.4%, and 26.1%, respectively). By contrast, 73.9% 8.7%, 0.1% and 17.3% of ER-a66 carries comparative predictions. Thus, the differential compartmentalization of ER-o.66, ER-a46, and ER-cx36 indicates that the functional site and primary role of each receptor may be different. A computer search was also performed on the putative 5' flanking region of the gene encoding ER-o.36 that is located in the first intron of ER-a66 gene. A TATA binding protein (TBP) recognition sequence was found upstream of the cDNA start site and several Spl, NF-KB and Apl binding sites in the 5' flanking region (Figure 12). A perfect half estrogen response element (ERE) site was identified at the 5' upstream region of ER-a36, indicating that ER-a36 is subjected to E2-mediated transcriptional regulation. Example 3 ER-cx36 mediates membrane-initiated estrogen signaling and is expressed in ER-negative breast cancer Methods Cell culture, establishment of stable cell lines and membrane-labeling with E2-BSA-FITC. MCF10A cells were obtained from Karmanos Cancer Institute at Detroit, MI, and human embryonic kidney 293 cells, and all breast cancer cells were obtained from ATCC. All cells were maintained at 37°C in a 5% CC>2 atmosphere in appropriate tissue culture medium. To establish stable cells that express recombinant ER-a36, HEK293 cells were plated at a density of IxlO5 cells per 60-mm dish and transfected 24 hours later with ER-a36 expression vector driven by the cytomagalovirus (CMV) promoter using the FuGene6 transfection reagent (Roche Molecular Biochemicals). The ER-a36 expression vector was constructed by cloning a 1.1 -kb EcoRI-BamHIcDNA fragment of ER-a36 from pBS-ER-a36 into the EcoRI and BamHI sites of mammalian expression vector pCB6+. Empty vector was also transfected into cells to serve as controls. Forty-eight hours after transfection, the cells were replated and selected with 500 Hg/ml of G418 (Invitrogen) for two weeks. The resulting uncloned population of G418-resistant cells was expanded to generate cells used for further analysis. To label the cell surface of stable cells that express recombinant ER-a36, cells were labeled at 4°C for 15 minutes with 1 uM fluorescein isothiocyanate (FITC)-labeled BSA covalently attached to E2p-hemisuccinate (Sigma), fixed in freshly prepared 4% paraformaldehyde and mounted with mounting solution containing DAPI for microscopic evaluation. Cellular stimulation with estrogens and anti-estrogens, and MTT assay. Before treatment, cells were cultured in phenol-red free medium with 2.5% dextrin-coated charcoal-stripped Fetal Calf Serum for 48-72 hours, and then washed with PBS and placed in fresh phenol red-free, serum-free medium containing 0.1 ug/ml of BSA and 5 ug/ml of insulin for 12 hours. Stimulation of quiescent cells was carried out at 37°C in serum free medium for different period of time. Different estrogens and antiestrogens were purchased from Steraloids Inc. BSA-E2P was obtained from Sigma. For 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, cells in suspension were added to each well of a 96-well culture plate for a final concentration of 1 X 103 cells/well, and incubated for 24 hours at 37°C in a COa incubator. Media containing 10 nM E2(3, 10 nM of Tamoxifen or 4OH-Tamoxifen or 7.2 nM UO126 (Calbiochem) were added to each well for 48 hours. MTT assay was performed with the CellTiter96 Aqueous One Solution Cell Proliferation Assay Kit (Bio Rad) as the manufacture recommended. A microplate reader (Promega) was used to measure absorbance at 49()nm. Cell fractionation assay. Cell fractionation was done as described by Marquez et al. (Oncogene, 20, 5420-5430(2001)). Western blot analysis, indirect immunofluorescence and antibodies. For Western blot analysis, cells were disrupted with RIP A buffer, boiled in gel loading buffer and separated on a 10% SDS-PAGE gel. After electrophoresis, the proteins were transferred to a PVDF membrane (Millipore). The filter was probed with various antibodies and visualized with appropriate HRP-conjugated secondary antibodies (Santa Cruz Biotechnology) and ECL reagents (Perkin Elmer Life Sciences). Antibody against ERK112 (K-23) was purchased from Santa Cruz Biotechnology. Antibodies used to analyze activation of the MAP kinase pathway included the phosphorylated forms of Mekl and ERK1/2, and were purchased from Cell Signaling Technology. Rat anti-ER-a antibody (H222) was purchased from Research Diagnostic Inc. Antibodies of COPB (Y-20), mSin3A (AK-11), and 5'nucleotidase (H-300) were purchased from Santa Cruz biotechnology Inc. D4-GDI (clone 97A1015) was obtained from Upstate Biotechnology. The polyclonal anti-ER-a36 antibody was raised in rabbit against the synthesized peptide antigen according to the last 15 amino acids at the C-terminal region of ER-a36 that are unique to ER-a36 (Alpha Diagnostic Inc.). An affinity column of synthesized peptide used to raise the antibody was used to purify the antibody. The specificity of the antibody has also been tested in ER-a36 expression vector transfected HEK293 cells that do not express endogenous ER-a36. Immunofluorescence assay showed that immunoreactive signals of the anti-ER-a36 antibody were detected only in transient transfectants with ER-ot36-expressing vectors but not in transfectants expressing a mutant ER-a36 lacking the C-terminus, suggesting that the ER-a36 antibody is highly specific. DNA transfection and luciferase assay. For transient transfection assays, HEK293 cells subseeded in 6 well dishes were grown to 60-70% confluence in phenol-red free medium plus 2.5% steroid-free fetal calf serum. Cells were washed and transiently transfected with total 5 ug of plasmids (2 \.\.g of the reporter plasmid 2 X ERE-tk-Luc together with 1.5 ug of the expression vector pSG5, 1.5 (ag of pSG hERa66 or 1.5 ug of pSG hERp alone or with 1.5 (J.g of ER-a36 expression vector) with FuGene6 reagent (Roche Molecular Biochemicals). A reporter plasmid containing two EREs (sequence from -331 to -289 of the chicken Vitellogenin A2 gene) placed upstream of the thymidine kinase promoter (2 X ERE-tk-Luc, obtained from Dr. Katarine Pettersson, Karolinska Institute, Sweden) was used. The expression vectors containing ER-a66 and p were also obtained from Dr. Katarine Pettersson. The expression vector of ER-a46 was obtained from Dr. Zafar Nawaz (Creighton University Medical Center, Omaha, Nebraska). Cells were treated with or without E2 (10 nM) for 12 hours before being assayed for luciferase activity. Luciferase assays were performed using the Luciferase Assay kit from Promega. Values correspond to the average ± standard deviation of more than three separate transfection experiments. RNA extraction and Northern blot analysis. Total cellular RNA was isolated using Trizol (Invitrogen), according to the manufacturer's instruction. Ten jig of total RNA was separated by electrophoresis on a 1.2 % formamide/formaldehyde gel and blotted onto a nylon membrane (Hybond-N, Amersham Pharmacia Biotech). The blots were prehybridized for 1 hour and hybridized for 2 hours in Quick-Hybridization solution (Amersham Pharmacia Biotech) at 65°C. The probes included a 410 bp cDNA fragment from the 3' untranslated region of ER-a36 that is unique to ER-cx36, and a p-actin DNA probe from BD Clonetech. The DNA probes were labeled with 32P dCTP and a Rediprime II DNA labeling kit (Amersham Biotech). Blots were autoradiographed using intensifying screens at -70°C overnight. The same membranes were stripped and reprobed with a labeled p-actin DNA probe to confirm equal loading. Breast cancer specimens and immunmohistochemistry assay. Paraffin-embedded human breast cancer specimens were obtained from the Department of Pathology, the Sir Run Run Shaw Hospital, Hangzhou P. R. China. Immunohistochemical staining was done using Ultrasensitive'M S-P kit (Maixin-4 Bio, China) according to the manufacturer's instruction, with an ER-a66 specific antibody (LabVision Corporation, USA) and the ER-a36 specific antibody as primary antibody, respectively. Results To further confirm that ER-a36 is a naturally occurring isoform of ER-a 66, Northern blot analysis of total RNA from a normal mammary epithelial cell line, MCF10A, and ER-positive and-negative (i.e., ER-a66-positive and -negative) breast cancer cells was performed. A DNA probe was synthesized using the RT-PCR method with the primer pairs designed according to the 3' untranslated region of the ER-o36 that is unique to ER-a36 (5' GCAAAGAAGAGAATCCTGAACTTGCATCCT (SEQ ID NO:26) and 5' TTAGTCAGGTATTTAATAACTAGGAATTG (SEQ ID NO:27)). The Northern blot analysis showed that^a single mRNA with estimated size of 5.6 kb was identified in ER-positive (i.e., ER-a66-positive) breast cancer cells MCF7 but not in MCF10A cells (Fig. 13). Surprisingly, ER-o.36 was also expressed in MDA-MB-231 cells, a well known ER-negative (i.e., ER-a66-negative) breast cancer cell line (Fig. 13). This data indicates that transcripts with the predicted size of the ER-a36 mRNA are expressed in breast cancer cells, and even in breast cancer cells that lack the ER-a66. ER-a36 inhibits transactivation activities of liganded-and unliganded-ER-a66 and -p\ We first tested whether ER-a36 that lacks both AF-1 and AF-2 domains retains any transcriptional activity. Transient transfection assays were performed in HEK293 cells using a luciferase-expressing reporter construct that contains two estrogen response elements (ERE) placed upstream of the thymidine kinase promoter (2 X ERE-tk-Luc). The HEK293 cell line was selected since it was reported previously that the AF-1 and -2 of ER-a66 function equally well in HEK293 cells (Denger et al., Mol. Endocrinol., 15, 2064-2077 (2001)). As shown in Fig. 14, we found that ER-a36 exhibits no intrinsic transcriptional activity in the presence and absence of E2p, consistent with the finding that ER-a36 lacks both transcription activation domains. We then assessed the regulatory function of ER-a36 in transcriptional transactivation activities mediated by the AF-1 and -2 domains of the ER-a66. Co-expression of ER-a36 strongly inhibited the transactivation activity of ER-a66 in the presence and absence of E2 p (Fig. 14), suggesting that ER-a36 inhibits the transactivation activities mediated by the AF-1 and AF-2 domains of ER-o.66. Furthermore, ER-o.36 also inhibited ligand-dependent and -independent transactivation activities of ER-p (Fig. 14). ER-a36 mediates membrane-initiated estrogen signaling pathway. Previous reports have indicated that E2p stimulates a rapid activation of the MAPK/ERK pathway (Razandi et al., Mol. Endocrinol., 13, 307-319 (1999), Watters et al., Endocrinol., 138, 4030-4033 (1997), and Migliaccio et al., EMBO J., 15, 1292-1300 (1996)). To determine whether ER-a36 is involved in this signaling pathway, we established stable cells that express exogenous ER-a36 in HEK293 cells that do not express endogenous ER-a. Whole ER-a36 transfected HEK293 cells were incubated with fluorescein isothiocyanate (FITC)-conjugated E2P-BSA (E2P-BSA-FITC) that is membrane impermeable. The cell surface of the ER-a36 transfected cells was strongly labeled by the E2P-BSA-FTIC whereas the control cells transfected with empty vector were not labeled by E2P-BSA-FITC. Cell lysates were prepared from quiescent cells that were either untreated or treated with E2P (10 nM) for various lengths of time. ERK activation was measured by immunoblotting using phosphorylation state-dependent and independent antibodies. A 10-fold increase in the phosphorylation of ERK1/2 that lasted about 45 minutes was observed within 5 minutes in the cells transfected with ER-a36 expression vector but not in the control cells transfected with empty vector (Fig. 15a and 15b). However, serum (20% for 10 minutes) was able to activate ERK 1/2 in these control cells (Fig. 15b), indicating that there is no global defect of the MAPK signaling pathway in these cells. Furthermore, Mekl, the kinase that phosphorylates and activates ERK1/2, is also activated in response to E2p in ER-a36 transfected cells (Fig. 15a). To provide further evidence for activation of the ERK1/2 by a membrane-initiated estrogen signaling, ER-a36 transfected cells were also treated with E2P-BSA, a membrane impermeable form of E2p. A strong activation of ERK1/2 phosphorylation was also observed in E2|3-BSA treated cells (Fig. 15a). ER-a36 mediates activation of the MAPK signaling pathway stimulated by different estrogens and anti-estrogens. We also treated ER-a36 transfected cells for 10 minutes with estrone (El), 170-estradiol (E2P), 17a-estradiol (E2a), estriol (E3), or estetrol (E4), and found that all of these estrogens except El activated ERK1/2 phosphorylation at a very similar level, suggesting ER-a36 may recognize these estrogens at a similar level (Fig. 15c). We then included the anti-estrogens including Tamoxifen, 4OH-Tamoxifen, ICI-182, 780 in the experiment to test whether ER-a36 mediated estrogen signaling is sensitive to anti-estrogens. Tamoxifen, 4OH-Tamoxifen and the pure anti-estrogen ICI-182,780 did not block ERK1/2 activation mediated by ER-a36. On the contrary, the effects are even stronger compared to the effects mediated by E2p alone (Fig. 15c). When ER-a36 transfected cells were treated with 1 fjM Tamoxifen alone, a concentration that can blunt both ER-a66 and p, a strong and persistent ERK1/2 activation that lasted longer than eight hours was observed (Fig. 15d). Tamoxifen at the same concentration, however, had no effect in control 293 cells transfected with empty expression vector. ER-a36 mediates E2-stimulated cell proliferation. To further determine whether the estrogen activated MAPK pathway mediated by ER-a36 can lead to the transcriptional signaling in cell nucleus, we examined the ability of membrane-initiated estrogen signaling to activate the transcription factor Elk, a downstream effector of the MAPK/ERK signaling pathway. We transiently transfected ER-a36 expressing 293 cells with the ERK-responsive GAL-Elk chimeric transcription factor, consisting of the DNA-binding domain of yeast transcription factor GAL4 fused to the ERK-responsive /ra«s-activation domain of human Elkl, and measured its activity in vivo on the expression of a GAL4-binding reporter gene in the presence of E2p. The reporter gene was 5 X Gal4-LUC, a luciferase reporter plasmid containing five Gal4 DNA binding sites. A bacteria p-glactosidase expression vector was used to control transfection efficiency. After transfection, the cell culture was maintained in estrogen free medium for 36 hours before E2p (lOnM) was added for 12 hours. Luciferase activities with standard deviation are representative of more than three experiments performed in duplicates. Estrogen treatment of ER-a36 transfected cells induced about two-fold increase of Elk/Gal4 fusion protein-mediated /raw-activation of the reporter whereas E2p had no effect on the transcription activity of the Elk/Gal4 fusion protein in the control cells transfected with empty vector (Fig. 16a). We next addressed whether the ER-a36 can mediate estrogen-stimulated cell proliferation. Proliferation of the ER-a36 transfected cells and control cells in the presence and absence of E2P was evaluated by the MTT assay. Proliferation of ER-a36 transfected cells was stimulated by E2p treatment while E2P had no effect on the growth of the control cells transfected with empty expression vector (Fig. 16b). The inclusion of the anti-estrogens including Tamoxifen and 4OH-Tamoxifen did not block E2P-stimulated cell growth (Fig. 16b). Tamoxifen or 4OH-Tamoxifen alone strongly stimulated growth of the ER-a36 transfected cells. However, the specific inhibitor of MAPK pathway, UO126, strongly inhibited E2p-stimulated cell growth. These data suggest that ER-a36-mediated membrane estrogen signaling stimulates cell growth through activation of the MAPK/ERK signaling pathway. The data also suggest anti-estrogens also stimulate cell growth through ER-a36. ER-a36 is predominantly a membrane-based estrogen receptor. To further characterize ER-a36, we have successfully developed a polyclonal anti-ER-a36 antibody raised against the 15 amino acids at the C-terminal region of ER-a36 that are unique to ER-ot36. An affinity column of synthesized peptide used to raise the antibody was used to purify the antibody. Western blot analysis of proteins prepared from normal mammary epithelial cells and established breast cancer cell lines using this antibody demonstrated a single protein band with 37-kDa molecular weight in some breast cancer cells but not in normal mammary epithelial cells (Fig. 17a). ER-a36 is expressed in MDA-MB-231, MDA-MB436 and HB3396 cells, three well-known ER-a66 negative breast cancer cell lines, and also is expressed in ER-a66 positive breast cancer cells MCF7 but not in T47D (Fig. 17a), consistent with our Northern blot data that ER-cx36 is expressed in ER-a66 negative breast cancer cells. To evaluate further the possibility that ER-a36 is expressed in ER-a66 negative breast cancer cells, indirect immunofluorescent assay and confocal microscopy in permeabilized MDA-MB-231 cells using the anti-ER-ct36 specific antibody showed that ER-a36 is expressed on the plasma membrane, cytoplasm and nucleus of the ER-a66 negative breast cancer cells, MDA-MB-231. To further assess the ER-a36 compartmentalization in cells, the subcellular fractionation assay was performed to isolate nuclei, plasma membranes, and cytosol from ER-a36 transfected HEiK293 cells. ER-a36 was identified by immunodetection from the different fractions. A high percentage of ER-a36 (-50%) was localized on the plasma membrane and a low percentage of it in cytosol (-40%) and nucleus (-10%). To exclude cross-contamination of different fractions, the fraction purity was examined by Western blot analysis with different marker proteins including mSin3A (nucleus), GDP dissociation inhibitor (cytosol), 5'nucleotidase (plasma membrane), and P-COP (Golgi). These results confirmed that there was no contamination among different fractions. This experiment established that ER-a36 is predominantly a membrane-based estrogen receptor (Fig. 17b). ER-a36 is expressed in ER-a66 negative breast cancer specimens. To further determine the relevance of ER-a36 to human breast cancer, we examined the ER-a36 expression patterns in human * breast cancer specimens with an immunohistochemistry assay using the specific anti-ER-a36 antibody. In situ analysis of human breast tissue showed the up-regulation of ER-a36 in breast cancer. Cells that were positive for ER protein stained brown, and nuclei were stained blue with hematoxylin. Among 35 cases of breast cancer specimens examined, 21 of them (60%) stained positive for ER-a36, and 21 of them (60%) positive for ER-o.66 (Table 2). Consistent with our Northern and Western blot analyses, 11 out of 14 (78%) breast cancer specimens that stained negative for ER-a66 were stained positive for ER-a36, indicating most ER-negative (i.e., ER-a66-negative) breast cancers still express ER-a36. In situ staining of ER-o.36 in a normal section of tissue found in a human ductal carcinoma showed ER-a36 expression only in lumenal epithelial cells and mainly localized in cytoplasm and plasma membrane. Tumor sections were from human infiltrating ductal carcinoma and from invasive ductal carcinoma. All 21 cases ER-a36 positive specimens exhibited ER-a36 immunostaining patterns predominantly outside of the cell nucleus, contrary to the mainly nuclear staining of ER-a66. Like ER-a66, some luminal epithelial cells in neighboring normal tissue were also stained positive for ER-a36. These results demonstrate that like ER-a66, ER-a36 is expressed in two-thirds of the human breast cancer examined, and suggest that ER-a36 may be involved in development of ER-a66-negative breast cancer. Table 2.ER-a3 6 and 66 expression: Survey of immunostaining in human breast cancer. (Table Removed) In this study, a novel variant of ER-a, ER-a36, has been identified, cloned and characterized. This ER-a isoform is the product of a transcript initiated from a previous unidentified promoter in the first intron of ER-a66 gene. The putative promoter region of the ER-a36 contains a TATA binding protein (TBP) recognition sequence upstream of the ER-a36 cDNA start site, and several Spl, NF-kB and Apl binding sites (Fig. 12). We have cloned the 5' flanking region of ER-a36 and confirmed that it possess strong promoter activity. Furthermore, a perfect half ERE site was identified at the 5' flanking region of ER-a36, suggesting that ER-a36 is subjected to ER-mediated transcriptional regulation. ER-a36 protein is identical to the ER-a66 protein encoded by exons 2-6 of the ER-a66 gene. This isoform is devoid of the domains previously identified to have transactivation activities, AF-1 and -2. Indeed, analysis of ER-a36 transactivation activity demonstrated that ER-a36 lacks intrinsic transcriptional activity. However, ER-a36 efficiently suppresses the transactivation activities mediated by the AF-1 and -2 domains of liganded-and unliganded-ER-a66 and-(3, indicating that ER-a36 is a potent inhibitor of the genomic estrogen signaling. This finding parallels the previous report that ER-a46 that lacks the AF-1 domain functions as a powerful competitor to suppress the AF-1 activity of the ER-06.6. The presence of a plasma membrane-based ER that triggers rapid estrogen signaling was controversial for a long time, since the molecular identity of this receptor has not been established. Previously, Razandi using transfection assay reported that both ER-a66 and -p can initiate membrane estrogen signaling, although only a very small percentage of them was expressed on the cell surface (Razandi et al, Mol. Endocrinol., 13, 307-319 (1999)), suggesting that these ERs may be involved in membrane-initiated estrogen signaling in addition to their traditional roles in genomic estrogen signaling. Recently, the 46-kDa isoform of ER-a was localized on cell surface and found to mediate estrogen-stimulated eNOS phosphorylation (Li et al., Pro. Natl. Acad. Sci. USA, 100,4807-4812 (2003)). Here, we demonstrated that another ER-a variant, ER-a36, is predominantly localized on the plasma membrane and mediates activation of the MAPK/ERK pathway induced by membrane-initiated estrogen signaling. Moreover, since ER-a36 totally lacks intrinsic transactivation activity and only functions as a regulator of genomic estrogen signaling, ER-a36 may act primarily as a membrane-based estrogen receptor to mediate membrane-initiated estrogen signaling. Previously, it has been reported that some E2p-mediated rapid actions occur in neurons of ER-a gene knockout (aERKO) mice and these actions are not blocked by 1CI 182,780 (Gu et al., Endocrinology, 140, 660-666 (1999)), suggesting that the existence of more i than one membrane-initiated estrogen signaling pathway. We demonstrated here that anti-estrogens did not block ER-a36-mediated MAPK/ERK activation, suggesting that ER-a36 is involved in the anti-estrogen insensitive signaling pathway previously described. As aERKO mice were created by an insertional disruption of the first coding exon of the mouse ER-a gene (the exon that is skipped in the generation of transcripts of ER-a36), it is likely that the production of the mouse counterpart of ER-a36 remains normal in these knockout mice. Thus, ER-a36 may contribute to the remaining estrogen effects observed in these mice. Recently, Toran-Allerand et al. (J. Neuroscience 22, 8391-8401 (2002)) reported the existence of a novel plasma membrane-associated estrogen receptor (ER-X) with an estimated molecular weight of 63-65 kDa. ER-X shows some similarities with ER-a36, such as reacting with antibodies to the ligand-binding domain of ER-a66 and responding equally well to E2a and p. However, the molecular identity of these two receptors awaits for the cloning and sequencing of ER-X. We have also shown that ER-a36 promotes membrane-initiated activation of the MAPK/ERK pathway that leads to estrogen-stimulated cell proliferation. Thus, ER-a36, that is devoid of intrinsic transcription activity, is sufficient to promote estrogen-stimulated cell growth, offering support to the previous report that a transcriptionally inactive mutant of ER—a66 induces DNA synthesis. These data together suggest that transcriptional activities of ER may not be required to promote estrogen-stimulated cell growth. Surprisingly, we also observed that anti-estrogens such as Tamoxifen strongly activated the MAPK/ERK signaling and stimulated cell growth during the experiment period (48 hours). This finding is in good agreement with the idea that Tamoxifen functions as both agonist and antagonist of estrogen signaling, and suggests that ER-a36 maybe also involved in membrane-initiated anti-estrogen signaling. It is well known that breast cancer cells with an ER-a66 positive phenotype (ER-positive breast cancer) are more differentiated and have lower metastatic potential than ER-a-negative tumors (McGuire, W.L. Prognostic factors in primary breast cancer. Cancer Surv. 5, 527-536 (1986)). It is interesting that ER-a36 is expressed not only in the subset of ER-a66-positive breast cancers but also in most ER~a66 negative breast cancers examined. Corroborating these results, it has been reported that estrogen signaling induced a rapid activation of the PI3K/Akt pathway in MDA-MB-231 cells that could not be blocked by estrogen antagonists (Tsai et al., Cancer Res.. 61, 8390-8392 (2001)), which was explained as estrogen signaling through an ER-independent pathway. High concentration of Tamoxifen also has been shown to induce apoptosis in MDA-MB-231 cells (Mandleker et al., Apoptosis 6,469-477 (2001)). These data strongly suggest that ER-a66-negative breast cancer may still retain estrogen or anti-estrogen effects mediated by membrane-initiated signaling. ER-a36 also possess a unique ligand-binding domain by replacing the last 5 helixes (helix 8-12) of the 12 helixes in the ER-a66 with a unique 27 amino acid domain, which may change the ligand-binding specificity and affinity of ER-a36. Indeed, we found that ER-a36 elicited membrane-initiated signaling equally well in response to E2a and p, E3 and E4. Thus, ER-a36 appears to possess a much broader ligand-binding spectrum than ER-a66, which makes ER-a36 potentially a more potent mediator of mitogenic signaling. Further analysis of the ligand-binding specificity and affinity of ER- E2p promotes growth of ER-a66 negative MDA-MB-231 cells in soft agar. To determine anchorage-independent growth in soft-agar in the presence and absence of E2p and tamoxifen together or separately, five hundred MDA-MB-231 cells were suspended in 3 ml of 3.5% (wt/vol) agar containing phenol red-free DMEM/F12 medium plus 10% E2-free fetal calf serum. The cells were then overlaid onto a 0.7% (wt/vol) agar containing phenol-red free DMEM/F12 medium plus 10% E2-free fetal calf serum in five replica 60mm dishes. Cells on soft agar were covered with medium plus 10% E2 free fetal calf serum with or without 1 nM E20, or combined with InM tamoxifen. After three weeks, colonies were scored using an inverted microscope. As seen in Figure 18, we found that E2 treatment strongly promoted anchorage-independent growth of ER-a66 negative MDA-MB-231 cells in soft agar, whereas anti-estrogen Tamoxifen inhibits the effect of E2|3, indicating that ER-o.66 negative MDA-MB-231 cells retain responsiveness to estrogen signaling presumably through Er-o.36. Example 5 E2p induces membrane-initiated estrogen signaling in ER-a66 negative MDA-MB-231 cells. To determine whether E2p induces membrane initiated estrogen signaling in ER-a66 negative MDA-MB-231, serum starved MDA-MB-231 cells were treated with 1 nM E2P for different time periods. For Western blot analysis, cells were disrupted with RIPA buffer, boiled in gel loading buffer and separated on a 10% SDS-PAGE gel. After electrophoresis, the proteins were transferred to a PVDF membrane (Millipore). The filter was probed with antibody against ERK1/2 (K-23) (Santa Cruz Biotechnology), or antibody used against the phosphorylated form of ERK1/2 (Cell -Signaling Technology). As seen in Fig. 19, treatment of MDA-MB-231 cells with estradiol-17p (E2P) induced rapid phosphorylation of ERK1/2. These data strongly suggested that E2P stimulates activation of the MAPK pathway in ER-o.66 negative MDA-MB-231 cells. All publications, patents and patent applications are incorporated herein by reference. While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein may be varied considerably without departing from the basic principles of the invention. We claim: 1. An isolated antibody that specifically binds to an amino acid sequence depicted at SEQ ID NO: 1, or an immunogenic fragment thereof. 2. The antibody of claim 1 wherein the antibody is a monoclonal antibody. 3. The antibody of claim 1 wherein the antibody is a polyclonal antibody. 4. The antibody of claim 1 wherein the antibody is a humanized antibody. 5. The antibody of claim 1 wherein the antibody is covalently attached to a compound. 6. The antibody of claim 5 wherein the compound is a chemotherapeutic agent. 7. The antibody of claim 5 wherein the compound is a detectable marker. 8. The antibody of claim 7 wherein the detectable marker is a fluorescent marker. 9. The antibody of claim 1 wherein the antibody specifically binds to an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO:1. 10. A composition comprising an antibody of claim 1. 11. The composition of claim 10 further comprising a pharmaceutically acceptable carrier. 12. A method for making an antibody comprising administering to an animal a polypeptide comprising an amino acid sequence depicted at SEQ ID NO: 1, or an immunogenic fragment thereof, and isolating antibody from the animal, wherein the isolated antibody specifically binds to the amino acid sequence. 13. The method of claim 12 wherein the polypeptide or immunogenic subunit thereof is covalently attached to a carrier polypeptide. 14. The method of claim 12 wherein the isolating comprises obtaining from the animal a cell that produces the antibody, the method further comprising making a monoclonal-antibody producing hybridoma using the cell. 15. A polyclonal antibody produced by a method of claim 12. 16. A monoclonal antibody produced by a method of claim 14. 17. A cell comprising an exogenous coding region, wherein the coding region encodes a first polypeptide comprising SEQ ID NO:20 or a second polypeptide comprising an amino acid sequence having at least 90% identity to SEQ ID NO:20, wherein the second polypeptide has ER-a36 activity. 18. The cell of claim 17 wherein the coding region is operably linked to a constitutive promoter. 19. The cell of claim 17 wherein the cell is a eukaryotic cell. 20. The cell of claim 17 wherein the cell is a prokaryotic cell. ,21. A cell expressing an exogenous polypeptide, wherein the polypeptide comprises SEQ ID NO:20, or comprises an amino acid sequence having at least 90% identity to SEQ ID NO.20 and has- ER-a36 activity. 22. The cell of claim 21 wherein the coding region is operably linked to a constitutive promoter. 23. The cell of claim 21 wherein the cell is a eukaryotic cell. 24. The cell of claim 21 wherein the cell is a prokaryotic cell. 25. A method for identifying an agent that binds a polypeptide, the method comprising: combining a polypeptide comprising an amino acid sequence depicted at SEQ ID NO:1 and an agent; and detecting the formation of a complex between the agent and the polypeptide. 26. The method of claim 25 wherein the binding of the agent to the polypeptide is detected by a method selected from the group consisting of directly detecting the binding of the agent to the polypeptide and detecting the binding of the agent to the polypeptide using a competition binding assay. 27. The method of claim 25 further comprising determining whether the agent binds a polypeptide comprising SEQ ID NO: 18. 28. The method of claim 25 further comprising determining whether the agent inhibits ER-a36 activity of the polypeptide. 29. A method for detecting a polypeptide comprising: providing a cell; analyzing the cell for a polypeptide having ER-a36 activity and a molecular weight of 36 kDa as measured following electrophoresis on a sodium dodecyl sulfate (SDS)-polyacrylamide gel; and determining whether the cell expresses the polypeptide. 30. The method of claim 29 wherein the cell is ex vivo. 31. The method of claim 30 wherein the cell is a tumor cell. 32. The method of claim 31 wherein the tumor is a breast tumor. 33. The method of claim 29 wherein the cell is in vivo. 34. The method of claim 30 wherein the cell is a tumor cell. 35. The method of claim 31 wherein the tumor is a breast tumor. 36. The method of claim 29 wherein the analyzing comprises contacting the cell with an antibody that specifically binds to an amino acid sequence depicted at SEQ ID NO:1, or an immunogenic fragment thereof. 37. The method of claim 36 wherein the antibody is covalently attached to a detectable marker. 38. The antibody of claim 37 wherein the detectable marker is a fluorescent marker. 39. The method of claim 29 wherein the analyzing comprises amplifying an mRNA polynucleotide to form amplified polynucleotides, wherein the amplification comprises contacting polynucleotides obtained from the cell with a primer pair that will amplify an mRNA polynucleotide that comprises SEQ ID NO:22 or SEQ ID NO:25, or the combination thereof, wherein the presence of amplified polynucletides indicates the cell expresses the polypeptide. 40. The method of claim 39 wherein one primer of the primer pair is chosen from nucleotides of SEQ ID NO:22, nucleotides complementary to nucleotides of SEQ ID NO:25, or the combination thereof, and wherein each primer has at least 15 nucleotides. 41. A method for inhibiting ER-a36 activity of a cell comprising contacting a cell expressing a polypeptide comprising an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO:1 with a compound that inhibits ER-o.36 activity. 42. The method of claim 41 wherein the compound comprises an antibody that specifically binds to a polypeptide comprising an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO:1. 43. The method of claim 41 wherein the cell is in vivo. 44. The method of claim 41 wherein the cell is ER-a66 negative. 45. The method of claim 41 wherein the cell is ER-ct46 negative. 46. The method of claim 41 wherein the compound is not an anti-estrogen. 47. An isolated polypeptide comprising an amino acid sequence depicted at amino acids 13-27 of SEQ ID NO: 1. 48. The isolated polypeptide of claim 47 further comprising amino acids 1 -12 of SEQ ID NO: 1. 49. The isolated polypeptide of claim 48 further comprising an amino acid sequence depicted at SEQ ID NO:20. 50. An isolated polynucleotide having at least 70% identity to SEQ ID NO:20, wherein the polypeptide has ER-a36 activity. 51. An immunogenic fragment of SEQ ID NO: 1. 52. A kit comprising an isolated antibody that specifically binds to an amino acid sequence depicted at SEQ ID NO: 1 and a packaging material. 53. An isolated antibody substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 54. A composition substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 55. A method substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 56. A polyclonal antibody substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 57. A monoclonal antibody substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 58. A cell substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 59. An isolated polypeptide substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 60. An isolated polynucleotide substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 61. An immunogenic fragment substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. 62. A kit substantially as herein described with reference to the foregoing description, examples, tables and the accompanying drawings. |
|---|
| Patent Number | 259131 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Indian Patent Application Number | 5102/DELNP/2006 | ||||||||||||
| PG Journal Number | 09/2014 | ||||||||||||
| Publication Date | 28-Feb-2014 | ||||||||||||
| Grant Date | 26-Feb-2014 | ||||||||||||
| Date of Filing | 04-Sep-2006 | ||||||||||||
| Name of Patentee | CREIGHTON UNIVERSITY | ||||||||||||
| Applicant Address | 2500 CALIFORNIA PLAZA, OMAHA, NEBRASKA 68178, U.S.A. | ||||||||||||
Inventors:
|
|||||||||||||
| PCT International Classification Number | C07K 16/28 | ||||||||||||
| PCT International Application Number | PCT/US2005/007857 | ||||||||||||
| PCT International Filing date | 2005-03-10 | ||||||||||||
PCT Conventions:
|
|||||||||||||