Analysis of the Molecular Mechanisms of Human Estrogen Receptors α and β Reveals Differential Specificity in Target Promoter Regulation by Xenoestrogens

Most of the currently available information on the transcriptional activities of endocrine-disrupting chemicals (xenoestrogens) through estrogen receptors α (ERα) and β (ERβ) has been derived from transactivation studies on synthetic estrogen-responsive reporters. Thus, the ability of the xenoestrogen-liganded ERs to regulate endogenous estrogen-responsive gene expression has not been well characterized. Here, we have evaluated the activities of xenoestrogens through ERα and ERβ on the vitellogenin A2 estrogen-response element (ERE) and the human pS2, lactoferrin, and complement 3 physiological target gene promoters. Using mammalian cell transient transfection assays, we found that the activities of xenoestrogens were mediated in a promoter-specific manner. For example, when bound to all ligands examined, ERα displayed high levels of transcription on the vitellogenin ERE and the lactoferrin promoter, but substantially lower activity on the complement 3 and pS2 promoters. However, one of the most important observations was that there were significant differences in the relative transcriptional activities of xenoestrogen-bound ERα and ERβ on different promoters, suggesting that ERα and ERβ make unique contributions to xenoestrogen action in target cells. When probing the molecular mechanism of the promoter-specific activities observed, we found that the transcriptional activity of the ERs correlated with the ability of each receptor to assume an active conformation on specific promoters. Taken together, the results indicate that the transcriptional activities of xenoestrogens are mediated in a promoter-specific manner and that estrogen-responsive promoters communicate differently with ERα and ERβ by influencing their structures in a distinct manner that leads to diversity in their transcriptional responses. Most of the currently available information on the transcriptional activities of endocrine-disrupting chemicals (xenoestrogens) through estrogen receptors α (ERα) and β (ERβ) has been derived from transactivation studies on synthetic estrogen-responsive reporters. Thus, the ability of the xenoestrogen-liganded ERs to regulate endogenous estrogen-responsive gene expression has not been well characterized. Here, we have evaluated the activities of xenoestrogens through ERα and ERβ on the vitellogenin A2 estrogen-response element (ERE) and the human pS2, lactoferrin, and complement 3 physiological target gene promoters. Using mammalian cell transient transfection assays, we found that the activities of xenoestrogens were mediated in a promoter-specific manner. For example, when bound to all ligands examined, ERα displayed high levels of transcription on the vitellogenin ERE and the lactoferrin promoter, but substantially lower activity on the complement 3 and pS2 promoters. However, one of the most important observations was that there were significant differences in the relative transcriptional activities of xenoestrogen-bound ERα and ERβ on different promoters, suggesting that ERα and ERβ make unique contributions to xenoestrogen action in target cells. When probing the molecular mechanism of the promoter-specific activities observed, we found that the transcriptional activity of the ERs correlated with the ability of each receptor to assume an active conformation on specific promoters. Taken together, the results indicate that the transcriptional activities of xenoestrogens are mediated in a promoter-specific manner and that estrogen-responsive promoters communicate differently with ERα and ERβ by influencing their structures in a distinct manner that leads to diversity in their transcriptional responses. The steroid hormone estrogen is a key regulator of the cellular processes involved in the growth and differentiation of a wide variety of target tissues of diverse functions. The predominant biological effects of estrogen are mediated through two intracellular receptors (ERα and ERβ) 1The abbreviations used are: ER, estrogen receptor; ERE, estrogen-response element; E2, 17β-estradiol; 3-TCB, 4-hydroxy-2′,4′,6′-trichlorobiphenyl; 4-CB, 4-hydroxy-2′,3′,4′,5′-tetrachlorobiphenyl that belong to the steroid/nuclear receptor superfamily of ligand-inducible transcription factors (1Mangelsdorf D.J. Thummel T. Beato M. Herrlich P. Schutz G. Umesono K. Blumberg B. Kastner P. Mark M. Chambon P. Evans R.M. Cell. 1995; 83: 835-839Abstract Full Text PDF PubMed Scopus (6107) Google Scholar, 2Giguere V. Tremblay A. Tremblay G.B. Steroids. 1998; 63: 335-339Crossref PubMed Scopus (102) Google Scholar). The classical mechanism of ER action is similar to that of other nuclear receptors (3Hall J.M. Couse J.F. Korach K.S. J. Biol. Chem. 2001; 276: 36869-36872Abstract Full Text Full Text PDF PubMed Scopus (1004) Google Scholar). In the absence of hormone, the receptor is sequestered within the nuclei of target cells in an inactive state. The binding of ligand induces an activating conformational change within the ER and promotes homodimerization and high affinity binding to specific DNA response elements (EREs), which are cis-acting enhancers located within the regulatory regions of target genes. The DNA-bound receptors contact the general transcription apparatus either directly or indirectly via cofactor proteins (reviewed in Ref. 4McKenna N.J. Lanz R.B. O'Malley B.W. Endocr. Rev. 1999; 20: 321-344Crossref PubMed Scopus (1657) Google Scholar). ER-coactivator interactions stabilize the formation of a transcription preinitiation complex and facilitate the necessary disruption of chromatin at the ERE. Depending on the cell and promoter context, the DNA-bound receptor exerts either a positive or negative effect on expression of the downstream target gene. In addition to the endogenous hormone estradiol, ER activity can be modulated by chemicals in the environment termed xenoestrogens, which include natural plant compounds (phytoestrogens) and industrial byproducts (industrial estrogens). In the past several decades, there has been increasing awareness and concern about the endocrine-disrupting effects of these chemicals and their impact on humans and wildlife (5Carson R. Silent Spring. Houghton Mifflin, Boston, MA1994Google Scholar, 6Colburn T. Dumanoski A. Meyers J.P. Our Stolen Future. Penguin Books Inc., New York, NY1996Google Scholar). Although the molecular mechanisms of xenoestrogens are not well understood, it is clear that many of these chemicals function by binding ERs and blocking estrogen access (7McLachlan J.A. Environ. Health Perspect. 1993; 101: 386-387Crossref PubMed Scopus (197) Google Scholar). In addition to their potential antagonist activities, however, xenoestrogens can also induce activating conformational changes in ERs that enable the receptors to interact with coactivators and to activate target gene transcription (8Routledge E.J. White R. Parker M.G. Sumpter J.P. J. Biol. Chem. 2000; 275: 35986-35993Abstract Full Text Full Text PDF PubMed Scopus (298) Google Scholar, 9An J. Tzagarakis-Foster C. Scharschmidt T.C. Lomri N. Leitman D.C. J. Biol. Chem. 2001; 276: 17808-17814Abstract Full Text Full Text PDF PubMed Scopus (300) Google Scholar, 10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). An additional level of complexity in ER action was revealed by studies demonstrating that the transcriptional activity of estradiol-liganded ERα is significantly influenced by the nature of the target promoter (11Berry M. Metzger D. Chambon P. EMBO J. 1990; 9: 2811-2818Crossref PubMed Scopus (664) Google Scholar, 12Tzukerman M.T. Esty A. Santiso-Mere D. Danielian P. Parker M.G. Stein R.B. Pike J.W. McDonnell D.P. Mol. Endocrinol. 1994; 8: 21-30Crossref PubMed Scopus (612) Google Scholar). The majority of known estrogen-responsive genes contain permutations of the consensus vitellogenin ERE (GGTCAcagTGACC) within their regulatory regions (reviewed in Ref. 13Klinge C.M. Nucleic Acids Res. 2001; 29: 2905-2919Crossref PubMed Scopus (812) Google Scholar). We have recently demonstrated that the nature of the ERE sequence can influence the ability of xenoestrogen-bound ERs to recruit coactivators and to activate target gene transcription (10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). However, native estrogen-responsive promoters also contain binding sites for other transcription factors, which can impact on the activity of ERs (14Nunez A.M. Berry M. Imler J.L. Chambon P. EMBO J. 1989; 8: 823-829Crossref PubMed Scopus (252) Google Scholar,15Liu Y. Yang N. Teng C.T. Mol. Cell. Biol. 1993; 13: 1836-1846Crossref PubMed Scopus (97) Google Scholar). Thus, although ERE reporter assays for xenoestrogen activity are informative with regard to the potential of environmental chemicals to activate ERs, they do not predict the activity of xenoestrogens on physiological target gene promoters. In this study, we hypothesized that the nature of the estrogen-responsive promoter would influence the activity of endocrine-disrupting chemicals through ERs, akin to the way in which selective estrogen receptor modulators manifest their gene-specific activities. Thus, we have used a panel of xenoestrogens and native estrogen-responsive promoters to investigate whether xenoestrogen ligands display promoter-specific activities through ERα and ERβ. This study provides the first systematic assessment of xenoestrogen activity through the two ER subtypes on physiological target promoters and furthermore reveals a regulatory role for different promoters in ER structure and function. DNA restriction and modification enzymes were obtained from New England Biolabs Inc. (Beverly, MA) or Promega (Madison, WI). PCR reagents were obtained from PerkinElmer Life Sciences or Promega. 17β-Estradiol (E2), genistein, and zearalenone were purchased from Sigma. Coumestrol was obtained from Acros Organics (Morris Plains, NJ). Bisphenol A was purchased from Aldrich. Nonylphenol was purchased from Schenectady International (Schenectady, NY). 4-Hydroxy-2′,4′,6′-trichlorobiphenyl (4-TCB) and 4-hydroxy-2′,3′,4′,5′-tetrachlorobiphenyl (4-CB) were purchased from Ultra Scientific (North Kingstown, RI). The mammalian expression plasmids for ERα (pcDNA-hERα) and ERβ (pcDNA-hERβ) contain the cDNAs of human ERα and ERβ subcloned into pcDNA3 (Invitrogen, San Diego, CA). The reporter pS2-Luc (a gift from Dr. V. Giguere, McGill University) contains the estrogen-responsive pS2 gene promoter fused upstream of the luciferase reporter gene. The 3x-Vit-ERE-TATA-Luc reporter contains three copies of the vitellogenin ERE in the pGL2-TATA-Inr plasmid (a gift from Dr. D. P. McDonnell, Duke University Medical Center). C3-Luc contains the human complement 3 gene promoter (16Norris J.D. Fan D. McDonnell D.P. Mol. Endocrinol. 1996; 10: 1605-1616Crossref PubMed Scopus (123) Google Scholar). Lf-Luc was constructed as follows. The estrogen-responsive human lactoferrin gene promoter was PCR-amplified from the 2.6mL14-CAT plasmid (a gift from Dr. C. T. Teng) (17Liu Y. Teng C.T. J. Biol. Chem. 1991; 266: 21880-21885Abstract Full Text PDF PubMed Google Scholar) and cloned into the XhoI and HindIII sites of the pGL2-basic vector (Promega). The sequences of the oligonucleotides for PCR were 5′-gtggacctcgaggctttcacatcattagaattc and 3′-gtggacaagcttgtctgtggtcttgggagacc. pVP16-RIP140 contains the RIP140 coding sequence fused in-frame downstream of the VP16 activation domain in the pVP16 mammalian expression plasmid (Invitrogen). HepG2 cells were maintained in with and (Invitrogen). were in with to DNA was into the cells In of reporter or of receptor or and of the vector were used for each and all were in For of pVP16 or pVP16-RIP140 were used for each well in addition to the to cells were with and of were to each were with the for and receptor ligands in of were to the cells and for assays were the reporter to the was to luciferase and each is the of were a of three and results were obtained in transfection assays were to the transcriptional activities of xenoestrogen-bound ERα and ERβ on different estrogen-responsive promoters. We to HepG2 cells for studies they ERα or ERβ to activate an assessment of the transcriptional of each receptor in J.M. McDonnell D.P. 1999; PubMed Google Scholar). HepG2 cells were with an ERα or ERβ expression plasmid with a luciferase reporter vector and the luciferase The reporter three copies of the vitellogenin ERE or the estrogen-responsive promoters from the pS2, lactoferrin, and complement 3 genes and The 3x-Vit-ERE-TATA-Luc reporter was used as a positive studies that ERα and ERβ display high levels of activity on this promoter J.M. McDonnell D.P. 1999; PubMed Google Scholar, J.M. McDonnell D.P. Mol. Endocrinol. 2000; PubMed Scopus Google Scholar). the vitellogenin ERE is currently a for xenoestrogen activity in cell P. Y. J. Mol. Endocrinol. PubMed Scopus Google Scholar, B. 1998; PubMed Google Scholar). The pS2, lactoferrin, and gene regulatory sequences were a of ER transactivation on physiological ER target gene promoters. of the as activation to the transcriptional response in on the complex promoters. Using this the transcriptional of ERα and ERβ were a of of different ER the endogenous ligand and a of known active xenoestrogens that affinity not influence the response for each each study was at a ligand that levels of reporter activity as by to displayed the on the reporter transcriptional response was on the vector ERE sequences not activity was also on the lactoferrin promoter substantially lower were on the and pS2 promoters and the was on the and lactoferrin promoters for all of the xenoestrogens in the however, the relative activity of ERα on the promoters was for most of the ligands In the were also influenced by the promoter and for example, ERα displayed of and on the pS2, and lactoferrin promoters, differences ligands were observed, as the industrial 3-TCB, and were in ERα activation in most or the to their lower for the receptor B. 1998; PubMed Google Scholar, B. K. J. PubMed Scopus Google Scholar). these studies that the activities of and xenoestrogens through ERα are mediated in a promoter-specific the of and xenoestrogen ligands in transactivation of ER were to study the effect of promoter on the of and xenoestrogen ligands for HepG2 cells were with an ERα expression vector with the plasmid and the or C3-Luc reporter were by cells with or increasing from to of E2, zearalenone A 3-TCB, or cells were and luciferase assays were was to the luciferase and from a were to each The of for each is ERα activity on each promoter was by each as a of the activity obtained at were in for each of xenoestrogens in transcriptional activation of ER α and ER β is influenced by the promoter The transcriptional activities of or ERα and ERβ were in HepG2 cells on the estrogen-responsive pS2, lactoferrin, and complement 3 promoters or on three copies of the vitellogenin A2 gene ERE. Full were by with or increasing from to of E2, zearalenone A 3-TCB, or are as the each of the examined, and ligand is to the of the of were the is the response of is the of the response of is the is the is the is the and is the the for ERα on the lactoferrin promoter and ERα on the pS2 promoter are not as not be from the the for ERβ on the pS2 promoter and ERβ on the lactoferrin promoter are and by or xenoestrogen-bound ERβ was to ER activities displayed the on However, the relative activity of ERβ on the promoters was distinct from that for for lactoferrin pS2 and and for vitellogenin ERE lactoferrin pS2 and and although ERα displayed lower activation on with the lactoferrin promoter for all ligands the was for ERβ with the majority of the compounds the pS2 and promoters were to ERβ ERα and this promoter-specific differences in the transcriptional activities of the two The relative activities of ERβ on the vitellogenin ERE and promoter were similar for and most of the xenoestrogens and for several of the the of was vitellogenin ERE pS2 of ERβ transcriptional activity also revealed and ER effects on ligand the of E2, genistein, and through ERβ were significantly influenced by the nature of the promoter Most were from the lactoferrin promoter, on which displayed high and displayed with the other promoters the of each of the ligands were distinct when on ERα and ERβ displayed through ERβ in all promoter a of ER in ligand promoter-specific differences the two ER subtypes were by the of through ERβ on the lactoferrin promoter, displayed and was a of ERα on the pS2 promoter 3 and studies were in and in which and ER effects were also on the and of and the xenoestrogens not Taken together, these results indicate that transcriptional activation by xenoestrogens is on the ligand and promoter and that there are promoter-specific differences in the transcriptional activities of ERα and ERβ. The transcriptional activity of the ERs is mediated by conformational changes in the that enable the receptors to interact with cellular coactivators N.J. Lanz R.B. O'Malley B.W. Endocr. Rev. 1999; 20: 321-344Crossref PubMed Scopus (1657) Google Scholar). mechanism by which different estrogen-responsive promoters regulate transcriptional activation by the ER is through distinct conformational changes in the receptor at the The cofactor RIP140 the ERs and as a of transcription by for binding N.J. Lanz R.B. O'Malley B.W. Endocr. Rev. 1999; 20: 321-344Crossref PubMed Scopus (1657) Google Scholar). This for the of RIP140 as a to the active conformation of ERα in the absence of receptor and K. Korach at the of the In this study, to the that the specific promoter formation of an active the ability of the xenoestrogen-bound ERs to interact with the cofactor RIP140 was in different promoter a mammalian demonstrated that RIP140 the activity of ERα and of the nature of the promoter not Thus, when RIP140 is fused to the VP16 activation RIP140 ER activity VP16 activity to be manifest when to DNA by the of the when on an promoter, transcriptional activity is to the transcriptional from the ER were used to the of that with the ERs in all promoter which was in the of transcription in each the effect of the promoter on HepG2 cells were with an ERα or ERβ expression plasmid with the and the or C3-Luc in revealed effect of the pVP16 vector on ER transcriptional activity of the not When or ERα was in the the of RIP140 binding on the promoters was vitellogenin ERE lactoferrin pS2, for or the was vitellogenin ERE pS2 lactoferrin these results with the relative transcriptional activities of ERα and ERβ on the and A similar the and relative of RIP140 on the different promoters was when other receptor were in the not these results that different estrogen-responsive promoters influence the ability of the ER to a active a mechanism for the promoter-specific activities differences in the relative transcriptional activities of ERα and ERβ on distinct promoters be to effects of each promoter on the formation of an active receptor of the most significant of this study was that xenoestrogens do not activate transcription from all estrogen-responsive promoters in an manner. when the activities of a of receptor and industrial for ERα and ERβ were examined, significant diversity in ligand was on the native pS2, lactoferrin, and complement 3 promoters. this is of a different of ER selective estrogen receptor which are also known to display promoter-specific biological activities. For example, the selective estrogen receptor as an ERα on the complement 3 gene promoter (16Norris J.D. Fan D. McDonnell D.P. Mol. Endocrinol. 1996; 10: 1605-1616Crossref PubMed Scopus (123) Google but as an antagonist of pS2 gene M. D. P. McDonnell, and K. as for it is that the promoter-specific activities of xenoestrogens in estrogen-responsive gene This provides a potential mechanism by which endocrine-disrupting chemicals the biological effects of estrogen in and hormone action in as a of their diverse biological studies demonstrated that on target promoters, ERs can with other steroid receptors and a of and R. M. C. R. PubMed Scopus Google Scholar, D. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, it is that in the promoter-specific ER activities interactions ERs and other transcription This would not be that the pS2, lactoferrin, and promoters contain binding sites for diverse cellular regulatory proteins (14Nunez A.M. Berry M. Imler J.L. Chambon P. EMBO J. 1989; 8: 823-829Crossref PubMed Scopus (252) Google Scholar, Y. Yang N. Teng C.T. Mol. Cell. Biol. 1993; 13: 1836-1846Crossref PubMed Scopus (97) Google Scholar, J.D. Fan D. McDonnell D.P. Mol. Endocrinol. 1996; 10: 1605-1616Crossref PubMed Scopus (123) Google Scholar). An additional is the of the ERE sequence to the promoter-specific ER activity of the native promoters contains an ERE, which from the consensus vitellogenin element by at Although it was that the ERE as a to the ER to a of have a role for ERE sequences C.M. Nucleic Acids Res. 2001; 29: 2905-2919Crossref PubMed Scopus (812) Google Scholar, McDonnell D.P. Mol. Endocrinol. 1994; 8: PubMed Scopus Google Scholar, C.M. Mol. Cell. Endocrinol. 2001; PubMed Scopus Google Scholar, A.M. Mol. Endocrinol. 2001; PubMed Scopus Google Scholar). In this it was that receptor for many of the are ER transcriptional activity on the nature of the response The that affinity not with transcriptional activity that information in the specific sequences is by the receptor in a manner that on transcriptional We recently demonstrated that the nature of the ERE sequence the transcriptional activities of or xenoestrogen-bound ERα and ERβ. these studies also revealed that different DNA response elements induce distinct in the ER to cofactor and gene response (10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). The that transcriptional activity on native estrogen-responsive promoters with cofactor on the ERE that the response element sequence is an important of ER promoter-specific transcriptional activity by xenoestrogen to these the of RIP140 as a for the active receptor conformation in this study demonstrated that estrogen-responsive promoters regulate ER transcriptional activity by influencing receptor The of chromatin assays to on physiological target promoters additional into the mechanisms by which the ERs display their gene-specific activities. Our also that the transcriptional activities of ERα and ERβ are on the nature of the bound we found that different xenoestrogens from to receptor on the promoters The in transactivation of ERα and ERβ were significantly lower for the industrial affinity for the receptors B. 1998; PubMed Google Scholar). However, this not for their differences in gene although also display significantly lower for ERα and ERβ B. 1998; PubMed Google we found that the and of the were similar to or of This was by which displayed through ERβ in all promoter Thus, the transcriptional activities The that ligands an active role in ER function was by McDonnell and D.P. T. Pike J.W. Mol. Endocrinol. 1995; 9: PubMed Google Scholar, D.J. J.D. McDonnell D.P. A. 1999; PubMed Scopus Google Scholar, D.J. J.D. McDonnell D.P. 1999; PubMed Google demonstrating that different ligands induce distinct conformational changes in the ER, with diversity in transcriptional responses. Our studies have also revealed that different xenoestrogen ligands for ERα and ERβ induce distinct in the receptor to cofactor and biological activity (10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). on these we that different endocrine-disrupting chemicals their distinct activities through ERα and ERβ by of their to induce active of the receptors and to recruit of has been the of ERα and ERβ in estrogen and xenoestrogen We have that ERα and ERβ are not and that each receptor a different role in ER action in and in J.M. McDonnell D.P. 1999; PubMed Google Scholar, J.M. McDonnell D.P. Mol. Endocrinol. 2000; PubMed Scopus Google Scholar, J.F. M. Korach K.S. 1999; PubMed Scopus Google Scholar, J.F. Korach K.S. Endocr. Rev. 1999; 20: PubMed Scopus Google Scholar). In this study, although the of xenoestrogen ligands for ERα and ERβ were similar B. 1998; PubMed Google Scholar, B. K. J. PubMed Scopus Google the relative transcriptional of the two receptors were distinct in most bound receptors with similar but was through ERβ on the vitellogenin ERE, as J.M. McDonnell D.P. 1999; PubMed Google Scholar). potential is that or xenoestrogen-bound ERα and ERβ in their to recruit as was recently by (8Routledge E.J. White R. Parker M.G. Sumpter J.P. J. Biol. Chem. 2000; 275: 35986-35993Abstract Full Text Full Text PDF PubMed Scopus (298) Google Scholar, 9An J. Tzagarakis-Foster C. Scharschmidt T.C. Lomri N. Leitman D.C. J. Biol. Chem. 2001; 276: 17808-17814Abstract Full Text Full Text PDF PubMed Scopus (300) Google Scholar, 10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). However, these observations do not for the promoter-specific activities of the two ER the of the two receptors are V. Tremblay A. Tremblay G.B. Steroids. 1998; 63: 335-339Crossref PubMed Scopus (102) Google it is that ERα and ERβ the information by the specific promoter in a different manner. This is by that different estrogen-responsive promoters influence the ability of ERα and ERβ to assume active one to the activities of ERα and ERβ be the influence of the response as we have that different can induce distinct conformational changes in the two ER to (10Hall J.M. McDonnell D.P. Korach K.S. Mol. Endocrinol. 2002; 16: 469-486Crossref PubMed Scopus (227) Google Scholar). these observations indicate that estrogen-responsive promoters communicate differently with the two receptors by their structures in a distinct manner. An additional for the promoter-specific activities of ERα and ERβ is differences in the manner by which the receptors influence the activity of other proteins on native estrogen-responsive promoters. In of this ERα has been to transcriptional ERβ is to activate transcription of genes when bound to ER R.M. P. J. Mol. Biol. 2000; PubMed Scopus Google Scholar). these observations indicate the of distinct physiological for the two ERs in xenoestrogen via the of unique of genes. In this of studies has revealed that the biological activities of xenoestrogens through ERα and ERβ are mediated in a promoter-specific manner and that estrogen-responsive promoters communicate differently with ERα and ERβ by their structures in a distinct manner that leads to diversity in their relative transcriptional responses. also a to the assays for endocrine-disrupting chemicals through the ERs to include of xenoestrogen transcriptional activity on different physiological estrogen-responsive gene promoters, which be We V. Giguere, D. P. McDonnell, and C. T. Teng for the of We are to Dr. J. for of the We and B. and D. for of the

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