Interactions of SKIP/NCoA-62, TFIIB, and retinoid X receptor with vitamin D receptor helix H10 residues.
The vitamin D receptor (VDR) is a ligand-dependent transcription factor that heterodimerizes with retinoid X receptor (RXR) and interacts with the basal transcription machinery and transcriptional cofactors to regulate target gene activity. The p160 coactivator GRIP1 and the distinct coregulator Ski-interacting protein (SKIP)/NCoA-62 synergistically enhance ligand-dependent VDR transcriptional activity. Both coregulators bind directly to and form a ternary complex with VDR, with GRIP1 contacting the activation function-2 (AF-2) domain and SKIP/NCoA-62 interacting through an AF-2 independent interface. It was previously reported that SKIP/NCoA-62 interaction with VDR was independent of the heterodimerization interface (specifically, helices H10/H11). In contrast, the present study defines specific residues within a conserved and surface-exposed region of VDR helix H10 that are required for interaction with SKIP/NCoA-62 and for full ligand-dependent transactivation activity. SKIP/NCoA-62, the basal transcription factor TFIIB, and RXR all interacted with VDR helix H10 mutants at reduced levels compared with wild type in the absence of ligand and exhibited different degrees of increased interaction upon ligand addition. Thus, SKIP/NCoA-62 interacts with VDR at a highly conserved region not previously associated with coregulator binding to regulate transactivation by a molecular mechanism distinct from that of p160 coactivators.
Barry
Janelle B
JB
Bone and Mineral Research Program and Molecular Modeling Facility, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney NSW 2010, Australia.
Leong
Gary M
GM
Church
W Bret
WB
Issa
Laura L
LL
Eisman
John A
JA
Gardiner
Edith M
EM
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D051379:Mice; D008958:Models, Molecular; D016296:Mutagenesis; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D018167:Receptors, Calcitriol / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D047488:Retinoid X Receptors; D035581:Transcription Factor TFIIB / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D009687:Nuclear Proteins; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; C491762:Skiip protein, mouse; D035581:Transcription Factor TFIIB; D014157:Transcription Factors