title: 1alpha,25-dihydroxy vitamin D3-enhanced expression of the osteocalcin gene involves increased promoter occupancy of basal transcription regulators and gradual recruitment of the 1alpha,25-dihydroxy vitamin D3 receptor-SRC-1 coactivator complex.
abstract: Binding of 1alpha,25-dihydroxy vitamin D(3) to the C-terminal ligand-binding domain (LBD) of its receptor (VDR) induces a conformational change that enables interaction of VDR with transcriptional coactivators such as members of the p160/SRC family or the DRIP (vitamin D receptor-interacting complex)/Mediator complex. These interactions are critical for VDR-mediated transcriptional enhancement of target genes. The p160/SRC members contain intrinsic histone acetyl transferase (HAT) activities that remodel chromatin at promoter regulatory regions, and the DRIP/Mediator complex may establish a molecular bridge between the VDR complex and the basal transcription machinery. Here, we have analyzed the rate of recruitment of these coactivators to the bone-specific osteocalcin (OC) gene in response to short and long exposures to 1alpha,25-dihydroxy vitamin D3. We report that in intact osteoblastic cells VDR, in association with SRC-1, rapidly binds to the OC promoter in response to the ligand. The recruitment of SRC-1 correlates with maximal transcriptional enhancement of the OC gene at 4 h and with increased histone acetylation at the OC promoter. In contrast to other 1alpha,25-dihydroxy vitamin D3-enhanced genes, binding of the DRIP205 subunit, which anchors the DRIP/Mediator complex to the VDR, is detected at the OC promoter only after several hours of incubation with 1alpha,25-dihydroxy vitamin D(3), concomitant with the release of SRC-1. Together, our results support a model where VDR preferentially recruits SRC-1 to enhance bone-specific OC gene transcription.
authors.affiliation: Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias Biologicas, Universidad de Concepcion, Concepcion, Chile.
authors.forename: Loreto
authors.initials: L
authors.lastname: Carvallo
authors.forename: Berta
authors.initials: B
authors.lastname: Henríquez
authors.forename: Roberto
authors.initials: R
authors.lastname: Paredes
authors.forename: Juan
authors.initials: J
authors.lastname: Olate
authors.forename: Sergio
authors.initials: S
authors.lastname: Onate
authors.forename: Andre J
authors.initials: AJ
authors.lastname: van Wijnen
authors.forename: Jane B
authors.initials: JB
authors.lastname: Lian
authors.forename: Gary S
authors.initials: GS
authors.lastname: Stein
authors.forename: Janet L
authors.initials: JL
authors.lastname: Stein
authors.forename: Martin
authors.initials: M
authors.lastname: Montecino
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation / Q000187:drug effects*; D051548:Histone Acetyltransferases / Q000378:metabolism*; D056913:Mediator Complex Subunit 1; D008957:Models, Genetic; D056920:Nuclear Receptor Coactivator 1; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D015675:Osteocalcin / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding / Q000187:drug effects; D012319:RNA Polymerase II / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000494:pharmacology