Spatio-temporal Activation of Chromatin on the Human CYP24 Gene Promoter in the Presence of 1α,25-Dihydroxyvitamin D3

The vitamin D3 24-hydroxylase gene (CYP24) is one of the most strongly induced genes known. Despite this, its induction by the hormone 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) has been characterized only partially. Therefore, we monitored the spatio-temporal, 1α,25(OH)2D3-dependent chromatin acetylation status of the human CYP24 promoter by performing chromatin immunoprecipitation (ChIP) assays with antibodies against acetylated histone 4. This was achieved by performing PCR on 25 contiguous genomic regions spanning the first 7.7 kb of the promoter. ChIP assays using antibodies against the 1α,25(OH)2D3 receptor (VDR) revealed that, in addition to the proximal promoter, three novel regions further upstream associated with VDR. Combined in silico/in vitro screening identified in three of the four promoter regions sequences resembling known VDREs and reporter gene assays confirmed the inducibility of these regions by 1α,25(OH)2D3. In contrast, the fourth VDR-associated promoter region did not contain any recognizable classical VDRE that could account for the presence of the protein on this region. However, re-ChIP assays monitored on all four promoter regions simultaneous association of VDR with retinoid X receptor, coactivator, mediator and RNA polymerase II proteins. These proteins showed a promoter region-specific association pattern demonstrating the complex choreography of the CYP24 gene promoter activation over 300 minutes. Thus, this study reveals new information concerning the regulation of the CYP24 gene by 1α,25(OH)2D3, and is a demonstration of the simultaneous participation of multiple, structurally diverse response elements in promoter activation in a living cell.