The autonomous transactivation domain in helix H3 of the vitamin D receptor is required for transactivation and coactivator interaction.
A ligand-inducible transactivation function (AF-2) exists in the extreme carboxyl terminus of the vitamin D receptor (VDR) that is essential for 1alpha,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-activated transcription and p160 coactivator interaction. Crystallographic data of related nuclear receptors suggest that binding of 1, 25-(OH)2D3 by VDR induces conformational changes in the ligand-binding domain (LBD), the most striking of which is a packing of the AF-2 helix onto the LBD adjacent to helices H3 and H4. In this study, a panel of VDR helix H3 mutants was generated, and residues in helix H3 that are important for ligand-activated transcription by the full-length VDR were identified. In particular, one mutant (VDR (Y236A)) exhibited normal ligand binding and heterodimerization with the retinoid X receptor (RXR) but was transcriptionally inactive. Yeast two-hybrid studies and in vitro protein interaction assays demonstrated that VDR (Y236A) was selectively impaired in interaction with AF-2-interacting coactivator proteins such as SRC-1 and GRIP-1. These data indicate an importance of helix H3 in the mechanism of VDR-mediated transcription, and they support the concept that helix H3 functions in concert with the AF-2 domain to form a transactivation surface for binding the p160 class of nuclear receptor coactivators.
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002117:Calcitriol / Q000378:metabolism; D018360:Crystallography, X-Ray; D005668:Furylfuramide / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D051958:Nuclear Receptor Coactivator 2; D017354:Point Mutation; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D047488:Retinoid X Receptors; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation