title: Signaling within a coactivator complex: methylation of SRC-3/AIB1 is a molecular switch for complex disassembly.
abstract: Recent studies indicate that steroid receptor-mediated transcriptional initiation is a cyclical process involving multiple rounds of coactivator assembly and disassembly. Steroid receptor coactivator 3 (SRC-3) coactivator phosphorylation has been shown to regulate coactivator complex assembly, but the mechanisms by which coactivator disassembly is triggered are not well understood. In this study, we provide in vitro and in vivo evidence that members of the SRC coactivator family serve as substrates for the enzymatic coactivator coactivator-associated arginine methyltransferase 1 (CARM1). Methylation of SRC-3 was localized to an arginine in its CARM1 binding region and correlated with decreased estrogen receptor alpha-mediated transcription, as seen with both cell-based and in vitro transcription assays. Consistent with this finding, we demonstrated that methylation promotes dissociation of the SRC-3/CARM1 coactivator complex. Methylation of SRC-3 is regulated by estrogen signaling in MCF7 cells and serves as a molecular switch for disassembly of the SRC-3 transcriptional coactivator complex. We propose that CARM1 is a dual-function coactivator, as it not only activates transcription by modifying core histone tails but also terminates hormone signaling by disassembly of the coactivator complex.
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Feng
authors.forename: Ping
authors.initials: P
authors.lastname: Yi
authors.forename: Jiemin
authors.initials: J
authors.lastname: Wong
authors.forename: Bert W
authors.initials: BW
authors.lastname: O'Malley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005786:Gene Expression Regulation; D051548:Histone Acetyltransferases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008745:Methylation; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D056921:Nuclear Receptor Coactivator 3; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011484:Protein-Arginine N-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D047628:Estrogen Receptor alpha; D004967:Estrogens; D046912:Multiprotein Complexes; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D011484:Protein-Arginine N-Methyltransferases; C119966:coactivator-associated arginine methyltransferase 1; D051548:Histone Acetyltransferases; C538866:NCOA3 protein, human; C538867:Ncoa3 protein, mouse; D056921:Nuclear Receptor Coactivator 3