A Transcriptional Coactivator, Steroid Receptor Coactivator-3, Selectively Augments Steroid Receptor Transcriptional Activity

Abstract

Estrogen receptors ERα and ERβ are members of the family of nuclear hormone receptors and act as ligand-inducible transcriptional factors, which regulate the expression of target genes on binding to cognate response elements. We report here the characterization of steroid receptor coactivator-3 (SRC-3), a coactivator of nuclear receptor transcription that is a member of a family of steroid receptor coactivators that includes SRC-1 and transcription intermediate factor-2. SRC-3 enhanced ERα and progesterone receptor-stimulated gene transcription in a ligand-dependent manner, but stimulation of ERβ-mediated transcription was not observed. Protein-protein interaction assays, including real-time interaction analyses with BIAcore, demonstrated that the affinity of the ERα interaction with SRC-3 was much higher than that observed for the ERβ interaction with SRC-3. Mutational analysis suggests a potential interplay between the transactivation function-1 and -2 domains of ERα and SRC-3. Furthermore, an intrinsic transactivation function was observed in the C-terminal half of SRC-3. Finally, SRC-3 was differentially expressed in various tissues and, among several tumor cells examined, was most abundant in the nuclear fraction of MCF-7 breast cancer cells. Therefore, SRC-3, a third member of a family of steroid receptor coactivators, has a distinct tissue distribution and intriguing selectivity between ERα and ERβ. Estrogen receptors ERα and ERβ are members of the family of nuclear hormone receptors and act as ligand-inducible transcriptional factors, which regulate the expression of target genes on binding to cognate response elements. We report here the characterization of steroid receptor coactivator-3 (SRC-3), a coactivator of nuclear receptor transcription that is a member of a family of steroid receptor coactivators that includes SRC-1 and transcription intermediate factor-2. SRC-3 enhanced ERα and progesterone receptor-stimulated gene transcription in a ligand-dependent manner, but stimulation of ERβ-mediated transcription was not observed. Protein-protein interaction assays, including real-time interaction analyses with BIAcore, demonstrated that the affinity of the ERα interaction with SRC-3 was much higher than that observed for the ERβ interaction with SRC-3. Mutational analysis suggests a potential interplay between the transactivation function-1 and -2 domains of ERα and SRC-3. Furthermore, an intrinsic transactivation function was observed in the C-terminal half of SRC-3. Finally, SRC-3 was differentially expressed in various tissues and, among several tumor cells examined, was most abundant in the nuclear fraction of MCF-7 breast cancer cells. Therefore, SRC-3, a third member of a family of steroid receptor coactivators, has a distinct tissue distribution and intriguing selectivity between ERα and ERβ. estradiol estrogen receptor human ER transactivation function ligand binding domain nuclear hormone receptor steroid receptor coactivator transcription intermediate factor fetal bovine serum chloramphenicol acetyltransferase Chinese hamster ovary progesterone receptor. Estradiol (E2)1 exerts numerous biological effects in different tissues through an interaction with the estrogen receptor (ER), a member of the steroid/nuclear hormone receptor superfamily (1Evans R.M. Science. 1988; 240: 889-895Crossref PubMed Scopus (6341) Google Scholar, 2Tsai M.-J. O'Malley B.W. Annu. Rev. Biochem. 1994; 63: 451-486Crossref PubMed Scopus (2702) Google Scholar). Amino acid sequence analyses, transient transfection studies, and mutational dissections of ER indicate that ER can be subdivided into several functional domains (3Katzenellenbogen J.A. O'Malley B.W. Katzenellenbogen B.S. Mol. Endocrinol. 1996; 10: 119-131Crossref PubMed Scopus (526) Google Scholar). The N-terminal A/B domain contains a transactivation function, referred to as TAF-1. The DNA binding domain, the C region, contains two zinc fingers and is responsible for DNA recognition. The ligand binding domain (LBD) and a second transactivation function, referred to as TAF-2, is located at the C-terminal of ER. On binding to hormone, the receptor undergoes an activation and transformation step. The activated ER interacts with specific estrogen response elements that are located in the promoter region of estrogen-regulated genes and influences the rate of gene transcription. Over the past decade, numerous studies have provided a basic understanding of both the effects of ligand (agonist and antagonist) on the ER and the relationship between the structure and function of the ER (4Glass C.K. Endocr. Rev. 1994; 15: 391-407PubMed Google Scholar). Nevertheless, little is known regarding the mechanisms involved in the gene-specific and tissue-selective effects mediated by either estrogens or antiestrogens. Furthermore, the molecular mechanisms by which ligand-activated ER influences the basal transcriptional machinery and regulates target gene transcription are mostly unknown. Recently, a new estrogen receptor, named ERβ, has been isolated from rat prostate and human testis (5Kuiper G.G.J.M. Enmark E. Pelto-Huikko M. Nilsson S. Gustafsson J.A. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5925-5930Crossref PubMed Scopus (4239) Google Scholar, 6Mosselman S. Polman J. Dijkema R. FEBS Lett. 1996; 392: 49-53Crossref PubMed Scopus (2060) Google Scholar). The DNA binding domain of ERβ is 90% identical to that of ERα. However, the overall homology between the LBD of ERα and ERβ is <60%. Like ERα, ERβ can stimulate transcription from an estrogen response element in a ligand-dependent manner. Currently, the biological significance of the existence of two ER subtypes is not clear. However, the potential functional differences and differential localization between ERα and ERβ (7Kuiper G.G.J.M. Carlsson B. Grandien K. Enmark E. Haggblad J. Nilsson S. Gustafsson J.A. Endocrinology. 1997; 138: 863-870Crossref PubMed Scopus (3678) Google Scholar) may contribute to the selective actions of E2 in different target tissues. The mechanisms by which nuclear hormone receptors (NRs) regulate target gene transcription is currently under intensive investigation. The ligand-activated NRs may promote formation of the preinitiation complex of the basal transcriptional apparatus and facilitate transcription by RNA polymerase II. These effects may be transmitted in part by direct interactions between NRs and basal transcriptional factors (8Schulman I.G. Chakravarti D. Juguilon H. Romo A. Evans R.M. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8288-8292Crossref PubMed Scopus (91) Google Scholar, 9Ing N.H. Beekman J.M. Tsai S.Y. Tsai M.-J. O'Malley B.W. J. Biol. Chem. 1992; 267: 17617-17623Abstract Full Text PDF PubMed Google Scholar, 10Baniahmad A. Ha I. Reinberg D. Tsai S.Y. Tsai M.-J. O'Malley B.W. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 8832-8836Crossref PubMed Scopus (301) Google Scholar, 11Hadzic E. Desai-Yajnik V. Helmer E. Guo S. Wu S. Koudinova N. Casanova J. Raaka B.M. Samuel H. Mol. Cell. Biol. 1995; 15: 4507-4517Crossref PubMed Google Scholar, 12Blanco J.G. Wang I.-M. Tsai S.Y. Tsai M.-J. O'Malley B.W. Jurutka P.W. Haussler M.R. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 1535-1539Crossref PubMed Scopus (190) Google Scholar). In addition, NR-induced transcription of different target genes may be transmitted through indirect interactions, mediated by intermediary transcriptional coactivators. Recently, a number of NR-associated proteins that interact with steroid and thyroid receptors have been reported (for review, see Refs. 13Torchia J. Glass C. Rosenfeld M.G. Curr. Opin. Cell Biol. 1998; 10: 373-383Crossref PubMed Scopus (515) Google Scholar, 14Moras D. Gronemeyer H. Curr. Opin. Cell Biol. 1998; 10: 384-391Crossref PubMed Scopus (710) Google Scholar). Among these NR-associated proteins, several corepressors have been described that inhibit basal level transcription by interacting with unliganded thyroid hormone receptor and retinoic acid receptor (15Horlein A.J. Naar A.M. Heinzel T. Yorchia J. Gloss B. Kurokawa R. Ryan A. Kamei Y. Soderstorm M. Glass C.K. Rosenfeld M.G. Nature. 1995; 377: 397-403Crossref PubMed Scopus (1714) Google Scholar, 16Chen J.D. Evan R.M. Nature. 1995; 377: 454-457Crossref PubMed Scopus (1715) Google Scholar, 17Lee J.W. Choi H.-S. Moore D.D. Mol. Endocrinol. 1995; 9: 243-254Crossref PubMed Google Scholar), and ligand causes the dissociation of these corepressors from the thyroid hormone receptor and retinoic acid receptor. Furthermore, proteins that interact with NRs in a ligand-dependent manner and augment transcription have also been identified (12Blanco J.G. Wang I.-M. Tsai S.Y. Tsai M.-J. O'Malley B.W. Jurutka P.W. Haussler M.R. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 1535-1539Crossref PubMed Scopus (190) Google Scholar). To date, steroid receptor coactivator-1 (SRC-1) (18Onate S.A. Tsai S.Y. Tsai M.-J. O'Malley B.W. Science. 1995; 270: 1354-1357Crossref PubMed Scopus (2063) Google Scholar), transcription intermediate factor-2 (TIF-2) (19Voegel J.J. Heine M.J.S. Zechel C. Chambon P. Gronemeyer H. EMBO J. 1996; 15: 3667-3675Crossref PubMed Scopus (953) Google Scholar), androgen receptor-associated protein 70 (ARA70) (20Yeh S. Chang C. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5517-5521Crossref PubMed Scopus (532) Google Scholar), cAMP response element-binding protein (CBP) (21Kamei Y. Xu L. Heinzel T. Torchia J. Kurokawa R. Gloss B. Glass C.K. Rosenfeld M.G. Cell. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar) and M. L. Chambon P. I. 1997; PubMed Scopus Google Scholar) have been to function as transcriptional coactivators, and gene transcription was enhanced by of these coactivators with and a described coactivator H. Chakravarti D. A. L. Y. Evans R.M. Cell. 1997; 90: Full Text Full Text PDF PubMed Scopus Google Scholar), H. J.D. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar), J. J. Science. 1997; PubMed Scopus Google Scholar), A. N. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google and a family of coactivators. of family have been to augment gene transcription and, to date, SRC-1 has been to ERβ-mediated gene transcription A. D. V. Mol. Endocrinol. 1997; PubMed Scopus Google Scholar). To the molecular mechanisms of gene transcription mediated by ERα, a human was the to potential coactivators. potential coactivator was which referred to as SRC-3, that was to SRC-1 and and that is identical to SRC-3 enhanced and progesterone receptor-stimulated gene but stimulation of ERβ-mediated transcription was not observed. Protein-protein interaction assays, including real-time interaction analyses with BIAcore, demonstrated that the affinity of the ERα interaction with SRC-3 was much higher than that observed for the ERβ interaction with SRC-3. The distinct tissue distribution and intriguing selectivity between ERα and ERβ SRC-3 a member of a family of steroid receptor coactivators. DNA and to and DNA of by DNA J. T. Scholar). and progesterone from was from the Cell fetal bovine serum and from and was from The the and from The for was affinity and from ERα was from The was to the the LBD of the human estrogen receptor in the DNA binding domain expression was in the of into cells with a human in the activation domain and and and for of these isolated from was by a human of various human tissues in a and to a was for in and DNA at was under the with of The was in at for and to at with cancer cells in including MCF-7 human breast cancer human cancer human and in with and cells nuclear and proteins as described Mol. Cell. Biol. 1993; PubMed Scopus Google Scholar). of nuclear and proteins on to was to of SRC-3 protein was a specific to an acid sequence that sequence to both SRC-1 and The was with second The SRC-3 was the the by the The was into a expression and was into The to at with cells for and by The was in of and for on a on was to The was at for and was by at was on a affinity with was with two of a of in the and on a with ERβ and a and proteins with of the receptor, between and and a with The by and and binding of and the of the receptor and and to interaction assays, both the N-terminal and the ligand binding domain of into the and the identified in that contains of SRC-3, was into the of into on assays, the of and into the and and was into the The the chloramphenicol acetyltransferase gene was under of the response element cells in into and by the in the or of as an and as a DNA In of ERα provided the of the in the that the of not the expression of the cells and for To the interactions of with either ERα or ERβ in analysis a was as described S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). was expressed in the expression To SRC-3, the of a was with to from the with of was by of at of at a in Finally, the with coactivator was by of of E. of SRC-3 of the with coactivator was with of in of was to binding was with a of of ER the a the the the with the for an at at and on a the from of a analysis for the of rate binding for The for was with a interactions with cells in tissue with and To the coactivator of SRC-3, cells in in with and the cells with of receptor expression of and of SRC-3 expression as an and was as a cells with and in the or of E2 in for to the and was a The the LBD of human ERα was to a that in the of was and the sequence a of a protein of with a molecular of referred to as SRC-3, homology to SRC-1 and (18Onate S.A. Tsai S.Y. Tsai M.-J. O'Malley B.W. Science. 1995; 270: 1354-1357Crossref PubMed Scopus (2063) Google Scholar, J.J. Heine M.J.S. Zechel C. Chambon P. Gronemeyer H. EMBO J. 1996; 15: 3667-3675Crossref PubMed Scopus (953) Google Scholar) and has been described by under various Refs. H. Chakravarti D. A. L. Y. Evans R.M. Cell. 1997; 90: Full Text Full Text PDF PubMed Scopus Google Scholar, H. J.D. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar, J. J. Science. 1997; PubMed Scopus Google Scholar, A. N. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). analysis of from various human tissues was to the of the and the tissue distribution of SRC-3. with an of was The was abundant in and was in and was in and not that SRC-3 is differentially expressed among tissues. a was in testis and a potential of SRC-3. Finally, the of SRC-3 was expressed in cells and MCF-7 breast cancer cells not and to the expression of SRC-3 with a molecular of was in the nuclear fraction of MCF-7 breast cancer SRC-3 is in the Furthermore, analysis of nuclear from several human cancer that SRC-3 was expressed and most abundant in human breast cancer MCF-7 cells In the of SRC-3, with the LBD but not the of Furthermore, interaction was on the of ligand To interaction between the and in a interaction was In the of E2 cells with the LBD of ERα with the of a known transcription activation function in region However, in the of was by an Furthermore, the interaction between and was on the of and Recently, a second estrogen receptor, ERβ, has been and the homology between the LBD of the ERα and ERβ is Therefore, was of to can also interact with the LBD of ERβ. Like ERα, was by E2 cells with the LBD of ERβ the of a transcription activation function the LBD of ERβ. Nevertheless, in the of was enhanced These indicate that the affinity of the interaction of with ERα was higher than that with ERβ. To the interaction between and analyses, which interactions between in of the interacting was on the of a the either ERα or ERβ, was by with of the was with of ERα or ERβ and interactions for both proteins not of of receptor in the of E2 are and as as the dissociation of the interactions The affinity of interaction with ERα is higher than the affinity of interaction with ERβ. The for the interaction between SRC-3 and ERα and for the interaction with ERβ. Furthermore, the of ligand on the interaction of with ERα was also ERα was with E2 or was the with of ERα with either E2 or and unliganded ERα are that E2 and interaction with ERα. The transcriptional of ERα in the or of SRC-3 was to SRC-3 is a transcriptional coactivator that gene transcription. In the of SRC-3, E2 gene transcription that of the and However, the transcriptional was enhanced to in the of of SRC-3, and transcriptional Furthermore, in the of SRC-3 not basal level transcription of ERα under the not The interaction described demonstrated a interaction of with the LBD of ERα ERβ Therefore, gene transcription also be by SRC-3. in the of E2 ERβ-mediated gene transcription However, transcriptional was not with of SRC-3 In a was but binding that of ERα and ERβ expressed in the a with the of transcriptional observed in the of SRC-3 not stimulation of ERα by SRC-3 is with that a C-terminal of SRC-3, with the LBD of the ERα. To potential receptor selectivity of SRC-3, the of progesterone receptor gene transcription was gene transcription the basal level transcription in the of ERα, the transcriptional of was enhanced by of SRC-3. However, transcriptional of was of SRC-3 and was not observed with ERα of SRC-3 and To domains of ERα are involved in the of transcription by SRC-3, expression of ERα, and into cells with SRC-3 in the and of with the ERα, the gene transcriptional of these receptors The of a and acid the LBD of ERα, was by SRC-3 and that SRC-3 to augment transcription in the of either or in However, SRC-3 was not to augment transcription of the that domain of ERα was for SRC-3 coactivator To SRC-3 contains an transcriptional activation function, both SRC-3 and to the DNA binding domain of and into the cells with a The was by both SRC-3 and a stimulation was observed with the of suggests that a potential transcriptional activation function is SRC-3 and the of is the C-terminal half of the have been to the potential by which nuclear receptors stimulate gene transcription. a direct binding of NRs to proteins in the preinitiation complex as and (8Schulman I.G. Chakravarti D. Juguilon H. Romo A. Evans R.M. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8288-8292Crossref PubMed Scopus (91) Google Scholar, 9Ing N.H. Beekman J.M. Tsai S.Y. Tsai M.-J. O'Malley B.W. J. Biol. Chem. 1992; 267: 17617-17623Abstract Full Text PDF PubMed Google Scholar, 10Baniahmad A. Ha I. Reinberg D. Tsai S.Y. Tsai M.-J. O'Malley B.W. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 8832-8836Crossref PubMed Scopus (301) Google Scholar, 11Hadzic E. Desai-Yajnik V. Helmer E. Guo S. Wu S. Koudinova N. Casanova J. Raaka B.M. Samuel H. Mol. Cell. Biol. 1995; 15: 4507-4517Crossref PubMed Google Scholar, 12Blanco J.G. Wang I.-M. Tsai S.Y. Tsai M.-J. O'Malley B.W. Jurutka P.W. Haussler M.R. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 1535-1539Crossref PubMed Scopus (190) Google Scholar, C. Y. I. Chambon P. L. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar, C. M. M. V. L. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). However, in which NRs interact with the basal transcriptional apparatus not the known involved in either ligand or promoter and tissue and Gronemeyer H. B. D. Chambon P. Cell. 1988; Full Text PDF Scopus Google Scholar, Cell. Full Text PDF PubMed Scopus Google Scholar, Y. P. J.D. E. V. M.G. Mol. Cell. Biol. 1995; 15: PubMed Google Scholar) proteins, referred to as and function as between the NRs and the basal transcription apparatus and regulate the expression of different target with several proteins that interact with NRs have been identified (for review, see 12Blanco J.G. Wang I.-M. Tsai S.Y. Tsai M.-J. O'Malley B.W. Jurutka P.W. Haussler M.R. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 1535-1539Crossref PubMed Scopus (190) Google Scholar). Among these proteins, SRC-1 (18Onate S.A. Tsai S.Y. Tsai M.-J. O'Malley B.W. Science. 1995; 270: 1354-1357Crossref PubMed Scopus (2063) Google Scholar), (19Voegel J.J. Heine M.J.S. Zechel C. Chambon P. Gronemeyer H. EMBO J. 1996; 15: 3667-3675Crossref PubMed Scopus (953) Google Scholar), androgen receptor-associated protein 70 (ARA70) (20Yeh S. Chang C. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5517-5521Crossref PubMed Scopus (532) Google Scholar), and cAMP response element-binding protein (21Kamei Y. Xu L. Heinzel T. Torchia J. Kurokawa R. Gloss B. Glass C.K. Rosenfeld M.G. Cell. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar) have been to gene transcription by a number of that these proteins function as coactivators. We report here a steroid receptor SRC-3, that ERβ-mediated gene transcription. In addition, transcriptional of is also enhanced with of SRC-3. The overall and among SRC-3, and a family of nuclear receptor coactivators that have an N-terminal region a domain, an transcription activation function, and the region of the coactivators for nuclear receptor These also referred to as identified J. J. Kamei Y. S. Glass C.K. Rosenfeld M.G. Nature. 1997; PubMed Scopus Google Scholar, E. S. M.G. Nature. 1997; PubMed Scopus Google Scholar) as involved in the ligand-dependent interaction between the nuclear hormone receptors and several transcriptional coactivators. of are in SRC-3, and are located between and the of the in the region of SRC-3 are in and and are in the region of these coactivators that interacts with nuclear hormone receptors J. J. Kamei Y. S. Glass C.K. Rosenfeld M.G. Nature. 1997; PubMed Scopus Google E. S. M.G. Nature. 1997; PubMed Scopus Google Scholar). from the interaction and that the at the domain, a region not in the is for a interaction between SRC-3 and ERα. the at and of nuclear receptor binding J. J. Kamei Y. S. Glass C.K. Rosenfeld M.G. Nature. 1997; PubMed Scopus Google Scholar). with SRC-1 (18Onate S.A. Tsai S.Y. Tsai M.-J. O'Malley B.W. Science. 1995; 270: 1354-1357Crossref PubMed Scopus (2063) Google Scholar) and (19Voegel J.J. Heine M.J.S. Zechel C. Chambon P. Gronemeyer H. EMBO J. 1996; 15: 3667-3675Crossref PubMed Scopus (953) Google Scholar), the expression of SRC-3 is and that differential expression of these coactivators among tissues may be involved in the of tissue-selective gene SRC-3 is expressed in a breast cancer with tumor of Furthermore, SRC-3 was observed in the nuclear fraction of MCF-7 cells Recently, the gene SRC-3, referred as was identified as a of that is in breast and the expression of was in than half of these J. J. Science. 1997; PubMed Scopus Google Scholar). by J. J. Science. 1997; PubMed Scopus Google Scholar), may contribute to the of in tissues in which is J. J. Science. 1997; PubMed Scopus Google Scholar). Recently, a second referred to as ERβ, has been identified and to transcription of an estrogen response gene in the of E2 (5Kuiper G.G.J.M. Enmark E. Pelto-Huikko M. Nilsson S. Gustafsson J.A. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5925-5930Crossref PubMed Scopus (4239) Google Scholar, 6Mosselman S. Polman J. Dijkema R. FEBS Lett. 1996; 392: 49-53Crossref PubMed Scopus (2060) Google Scholar). However, the acid the and of ERα and ERβ that the of ERα and ERβ genes may different molecular including the of distinct coactivators. with was to interact with ERα ERβ C and and the transcriptional of ERα but not ERβ was by SRC-3 and Nevertheless, transcriptional is not to ERα, SRC-3 also enhanced transcriptional of SRC-3 to the transcriptional of than ERα and suggests that of SRC-3 and a are to regulate the expression of different target of of nuclear hormone gene transcription has also been observed with (19Voegel J.J. Heine M.J.S. Zechel C. Chambon P. Gronemeyer H. EMBO J. 1996; 15: 3667-3675Crossref PubMed Scopus (953) Google Scholar), androgen receptor-associated protein 70 (ARA70) (20Yeh S. Chang C. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5517-5521Crossref PubMed Scopus (532) Google Scholar), and M. L. Chambon P. I. 1997; PubMed Scopus Google Scholar). Therefore, as the number of coactivators corepressors and as functional are identified acetyltransferase the interplay among the coactivators and the basal transcriptional apparatus at in an understanding of and gene expression mediated by ligand-activated of the for coactivators is that transcriptional be the of an has been that the of in the domain but not receptor or ligand binding affinity R. J.A. M.G. EMBO J. 1992; PubMed Scopus Google Scholar). However, was also that the complex promoter can be by in the of that is mediated by A. D. P. M.G. R. J.W. Mol. Endocrinol. 1994; PubMed Scopus Google Scholar). Recently, O'Malley B.W. Mol. Endocrinol. 1997; PubMed Scopus Google Scholar) reported that SRC-1 promoter transcriptional of ER that an domain is not for SRC-1 coactivator in and promoter The of the SRC-1 on the was not in We have demonstrated that SRC-3 transcriptional of both the ERα and the ERα to The a on the of SRC-3 to as be SRC-3 not interact with the region Furthermore, SRC-3 was to augment the transcription of the that SRC-3 augment transcription through a of direct of SRC-3 may an protein that the interaction of SRC-3 and the an interaction with the domain the of the These are with reported for two coactivators. J.D. D. M.R. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar) also reported that can the transcriptional of the ERα and that is not to be the in the interaction of with ERα J.D. D. M.R. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). Furthermore, SRC-1 has been to the transcriptional that between and of ERα Tsai M.-J. O'Malley B.W. Katzenellenbogen B.S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: PubMed Scopus Google Scholar). Therefore, different coactivators have been demonstrated to an intriguing in transcription. Finally, a transcriptional coactivator is to gene transcription by transcription factors with the of the basal transcriptional Therefore, a transcriptional coactivator be to have a transcriptional activation function that target gene expression through either the of the structure or by the preinitiation complex D. Cell. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, Curr. Opin. 1996; PubMed Scopus Google Scholar), in an rate of transcription. Like and cAMP response element-binding protein both and SRC-3 activated gene transcription to the DNA binding domain of the of a transcriptional activation function These also that the domain at the of SRC-3 is not for either receptor interaction or transcriptional In the and characterization of SRC-3, a transcriptional coactivator involved in and gene transcription. SRC-3 the transcriptional of ERα ERβ. the tissue distribution and the to augment transcriptional that SRC-3 may an in steroid gene The of SRC-3 in steroid hormone and gene can be by the expression of SRC-3 as or gene Furthermore, of SRC-3 in also an to the potential of SRC-3 in the of We the members of for DNA and members of for including M. for analyses, for and and for ERβ, and R. R. J. R. J. P. and B. L. identified in the thyroid hormone receptor that are involved in and SRC-1 The in ERα are identical between ERα and ERβ and differences at these for the differences in affinity of SRC-3 for ERα and ERβ.