Enhancers located in the vitamin D receptor gene mediate transcriptional autoregulation by 1,25-dihydroxyvitamin D3

Abstract

The regulatory actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on target genes are mediated by the vitamin D receptor (VDR). Interestingly, one of the genomic targets of 1,25(OH)2D3 action is the VDR gene itself; however, the mechanism underlying this regulation is unknown. We investigated VDR autoregulation by screening the mouse VDR locus from 20kb upstream of the transcriptional start site (TSS) to 10kb downstream of the last exon using chromatin immunoprecipitation (ChIP)-DNA microarray analysis (ChIP/chip). Three potential VDR binding sites were located within introns lying downstream of the TSS and their activities confirmed through direct ChIP analysis. Further exploration revealed that one of these intronic regions was capable of conferring 1,25(OH)2D3 response to both a downstream heterologous promoter and the minimal VDR promoter. Importantly, this regulatory region contained a classic vitamin D response element and was highly conserved within the human gene. We also demonstrated using ChIP analysis that the binding of VDR is associated with co-localization of RXR and the enhanced entry of RNA polymerase II. Thus, each of these sites appears likely to contribute to VDR autoregulation. Our studies using ChIP/chip analysis coupled to more traditional approaches define a direct mechanism whereby the VDR gene is upregulated by 1,25(OH)2D3.