title: Biochemical evidence for a 170-kilodalton, AF-2-dependent vitamin D receptor/retinoid X receptor coactivator that is highly expressed in osteoblasts.
abstract: Human vitamin D receptor (hVDR) fused to glutathione S-transferase was utilized to detect a VDR-interacting protein (VIP) of approximately 170 kDa. VIP(170) is expressed in osteoblast-like ROS 17/2.8 cells and, to a lesser extent, in COS-7 and HeLa cells. VIP(170) may be a coactivator because it interacts only with 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) ligand-bound hVDR and because a mutation (E420A) in the activation function-2 (AF-2) of hVDR abolishes both receptor-mediated transactivation and VIP(170) binding. Unlike L254G hVDR, a heterodimerization mutant with an intact AF-2, the E420A mutant is only partially attenuated in its association with the retinoid X receptor (RXR) DNA-binding partner. Finally, the ability of overexpressed hVDR to squelch glucocorticoid receptor-mediated transactivation is lost in both the L254G and E420A mutants. These results suggest that several protein-protein interactions, including VDR association with RXR and VIP(170), are required for stabilization of a multimeric complex that transduces the signal for 1,25(OH)(2)D(3)-elicited transactivation.
authors.affiliation: Department of Biochemistry, College of Medicine, University of Arizona, Tucson, Arizona, 85724, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Jurutka
authors.forename: L S
authors.initials: LS
authors.lastname: Remus
authors.forename: G K
authors.initials: GK
authors.lastname: Whitfield
authors.forename: M A
authors.initials: MA
authors.lastname: Galligan
authors.forename: C A
authors.initials: CA
authors.lastname: Haussler
authors.forename: M R
authors.initials: MR
authors.lastname: Haussler
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002117:Calcitriol / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D056892:Mediator Complex; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D012516:Osteosarcoma; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D047488:Retinoid X Receptors; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: C113182:DRIP, VDR interacting protein complex; C491863:MED4 protein, human; D056892:Mediator Complex; D009687:Nuclear Proteins; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D015534:Trans-Activators; D014157:Transcription Factors; D003907:Dexamethasone; D002117:Calcitriol