Regulation of mouse Cyp24a1 expression via promoter-proximal and downstream-distal enhancers highlights new concepts of 1,25-dihydroxyvitamin D3 action

CYP24A1 functions in vitamin D target tissues to degrade 1,25-dihydroxyvitamin D-3 (1,25(OF)(2)D-3). Thus, the concentration of this enzyme and the regulation of its expression is a primary determinant of the overall biological activity of 1,25(OH)(2)D-3 within cells. The principle regulator of CYP24A1 expression is 1,25(OH)(2)D-3 itself, which functions through the vitamin D receptor to upregulate the transcriptional activity of the Cyp24a1 gene. In this report, we explore the mechanism of this regulation using recently developed ChIP-chip and ChIP-seq techniques that permit an unbiased search for enhancer elements that participate in this transcriptional control. Our studies both confirm a regulatory region defined earlier and located proximal to the transcriptional start site (TSS) of mouse Cyp24a1 (-160 and -265 nt) and identify a novel intergenic region located downstream of the transcription unit that contains two enhancers (+35 and +37 kb) that facilitate 1,25(OH)(2)D-3-dependent upregulation of Cyp24a1 expression. Interestingly, while C/EBP beta also binds under basal conditions to a site located immediately upstream of the Cyp24a1 promoter (-345 nt), occupancy by this factor is strikingly increased following 1,25(OH)(2)D-3 treatment. The locations and activities of these regulatory regions that mediate 1,25(OH)(2)D-3 actions were confirmed in mice in vivo. We conclude that the mechanism through which 1,25(OH)(2)D-3 induces the CYP24A1 enzyme, thereby autoregulating its own destruction, involves both promoter-proximal as well as downstream-distal enhancers. These findings highlight new concepts regarding the molecular mechanism of action of 1,25(OH)(2)D-3 and other hormonal regulators. (C) 2011 Elsevier Inc. All rights reserved.