title: Analysis of estrogen receptor transcriptional enhancement by a nuclear hormone receptor coactivator.
abstract: The estrogen receptor (ER), a member of a large superfamily of nuclear hormone receptors, is a ligand-inducible transcription factor that regulates the expression of estrogen-responsive genes. The ER, in common with other members of this superfamily, contains two transcription activation functions (AFs)--one located in the amino-terminal region (AF-1) and the second located in the carboxyl-terminal region (AF-2). In most cell contexts, the synergistic activity of AF-1 and AF-2 is required for full estradiol (E2)-stimulated activity. We have previously shown that a ligand-dependent interaction between the two AF-containing regions of ER was promoted by E2 and the antiestrogen trans-hydroxytamoxifen (TOT). This interaction, however, was transcriptionally productive only in the presence of E2. To explore a possible role of steroid receptor coactivators in transcriptional synergism between AF-1 and AF-2, we expressed the amino terminal (AF-1-containing) and carboxyl-terminal (AF-2-containing) regions of ER as separate polypeptides in mammalian cells, along with the steroid receptor coactivator-1 protein (SRC-1). We demonstrate that SRC-1, which has been shown to significantly increase ER transcriptional activity, enhanced the interaction, mediated by either E2 or TOT, between the AF-1-containing and AF-2-containing regions of the ER. However, this enhanced interaction resulted in increased transcriptional effectiveness only with E2 and not with TOT, consistent with the effects of SRC-1 on the full-length receptor. Our results suggest that after ligand binding, SRC-1 may act, in part, as an adapter protein that promotes the integration of amino- and carboxyl-terminal receptor functions, allowing for full receptor activation. Potentially, SRC-1 may be capable of enhancing the transcriptional activity of related nuclear receptor superfamily members by facilitating the productive association of the two AF-containing regions in these receptors.
authors.affiliation: Department of Molecular and Integrative Physiology, University of Illinois, Urbana 61801, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: McInerney
authors.forename: M J
authors.initials: MJ
authors.lastname: Tsai
authors.forename: B W
authors.initials: BW
authors.lastname: O'Malley
authors.forename: B S
authors.initials: BS
authors.lastname: Katzenellenbogen
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008322:Mammals; D016133:Polymerase Chain Reaction; D011960:Receptors, Estrogen / Q000378:metabolism*; D017471:Receptors, Interferon; D011994:Recombinant Proteins / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D004965:Estrogen Antagonists; C086185:IFNGR2 protein, human; D011960:Receptors, Estrogen; D017471:Receptors, Interferon; D011994:Recombinant Proteins; D015534:Trans-Activators; D013629:Tamoxifen; D004958:Estradiol