title: Ternary complexes and cooperative interplay between NCoA-62/Ski-interacting protein and steroid receptor coactivators in vitamin D receptor-mediated transcription.
abstract: The vitamin D receptor (VDR) is a ligand-dependent transcriptional factor that binds to vitamin D-responsive elements as a heterodimer with retinoid X receptor (RXR) to regulate target gene transcription. The steroid receptor coactivator (SRC) proteins are coactivators that interact with the AF-2 domain of VDR to augment 1,25-dihydroxyvitamin D3-dependent transcription. In contrast, NCoA-62/Ski-interacting protein (SKIP) is a distinct, activation function-2-independent coactivator for VDR. The current study examined whether these two distinct classes of coactivators impact functionally on VDR-mediated transcription. Using a ternary complex binding assay, we observed a marked preference for the direct interaction of NCoA-62/SKIP with the VDR-RXR heterodimer as compared with the VDR-VDR homodimer or VDR monomer. The liganded VDR also formed a ternary complex with NCoA-62/SKIP and SRC proteins in vitro. Competition experiments using LXXLL peptides showed that NCoA-62/SKIP and SRC coactivators contact different domains of the VDR-RXR heterodimer. Synergistic interplays were observed between NCoA-62/SKIP and SRC coactivators in VDR-mediated transcriptional assays, and protein interference assays indicated a requirement for both NCoA-62/SKIP and SRCs in VDR- mediated transcription. These studies suggest that the ligand-dependent and simultaneous interaction of NCoA-62/SKIP and SRC coactivators with distinct interaction domains within the VDR-RXR heterodimer results in cooperative interplays between coactivators in VDR-mediated transcription.
authors.affiliation: Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: C
authors.initials: C
authors.lastname: Zhang
authors.forename: T A
authors.initials: TA
authors.lastname: Baudino
authors.forename: D R
authors.initials: DR
authors.lastname: Dowd
authors.forename: H
authors.initials: H
authors.lastname: Tokumaru
authors.forename: W
authors.initials: W
authors.lastname: Wang
authors.forename: P N
authors.initials: PN
authors.lastname: MacDonald
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D019281:Dimerization; D051548:Histone Acetyltransferases; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D056920:Nuclear Receptor Coactivator 1; D056918:Nuclear Receptor Coactivators; D011485:Protein Binding; D011487:Protein Conformation; D018167:Receptors, Calcitriol / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D009687:Nuclear Proteins; D056918:Nuclear Receptor Coactivators; D018167:Receptors, Calcitriol; C111791:SNW1 protein, human; D014157:Transcription Factors; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; D056920:Nuclear Receptor Coactivator 1