Enhancers located within two introns of the vitamin D receptor gene mediate transcriptional autoregulation by 1,25-dihydroxyvitamin D3

The biological actions of 1,25-(OH)(2)D-3 are mediated by the vitamin D receptor (VDR), a protein that binds to target genes and alters their expression. 1,25-(OH)(2)D-3 is also capable of inducing transcription of the VDR gene itself. In the present study, we explored both the capacity of 1,25-(OH)(2)D-3 to induce VDR gene expression in bone cells and the mechanism instrumental to this up-regulation. After establishing the ability of 1,25-(OH)(2)D-3 to stimulate VDR mRNA up-regulation both in bone in vivo and in osteoblastic cells, we screened the mouse VDR gene locus from 20 kb upstream of the gene's transcriptional start site (TSS) to 10 kb downstream of the final exon to identify VDR binding sites using chromatin immunoprecipitation-DNA microarray (ChIP- chip) analysis. Three conserved regions were identified 20, 27, and 29 kb downstream of the TSS. VDR binding to these sites in response to 1,25-(OH)(2)D-3 was confirmed by ChIP analysis and was accompanied by differential localization of retinoid X receptor, histone acetylation, and RNA polymerase II recruitment. One of these regions was able to confer 1,25-( OH)(2)D-3 regulation to downstream promoters, thereby permitting identification and characterization of the regulatory element located within. Importantly, a highly conserved region within the human VDR gene analogous to that discovered in the mouse was also capable of mediating 1,25-(OH)(2)D-3 response. Our results demonstrate that 1,25-(OH)(2)D-3 and its receptor autoregulate the expression of the VDR gene. The location of these regulatory regions and their apparent distances from the TSS are consistent with new findings suggesting the emerging relevance of distant enhancers.