The Human Peroxisome Proliferator-activated Receptor δ Gene is a Primary Target of 1α,25-Dihydroxyvitamin D3 and its Nuclear Receptor

Peroxisome proliferator-activated receptor (PPAR) δ is the most widely expressed member of the PPAR family of nuclear receptor fatty acid sensors. Real-time PCR analysis of breast and prostate cancer cell lines demonstrated that PPARδ expression was increased 1.5 to 3.2-fold after three hours stimulation with the natural vitamin D receptor (VDR) agonist, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3). In silico analysis of the 20 kb of the human PPARδ promoter revealed a DR3-type 1α,25(OH)2D3 response element approximately 350 bp upstream of the transcription start site, which was able to bind VDR-retinoid X receptor (RXR) heterodimers and mediate a 1α,25(OH)2D3-dependent upregulation of reporter gene activity. Chromatin immuno-precipitation assays demonstrated that a number of proteins representative for 1α,25(OH)2D3-mediated gene activation, such as VDR, RXR and RNA polymerase II, displayed a 1α,25(OH)2D3-dependent association with a region of the proximal PPARδ promoter that contained the putative DR3-type VDRE. This was also true for other proteins that are involved in or are the subject of chromatin modification, such as the histone acetyltransferase CBP and histone 4, which displayed ligand-dependent association and acetylation, respectively. Finally, real-time PCR analysis demonstrated that 1α,25(OH)2D3 and the synthetic PPARδ ligand L783483 show a cell and time-dependent interference in each otherʹs effects on VDR mRNA expression, so that their combined application shows complex effects on the induction of VDR target genes, such as CYP24. Taken together, we conclude that PPARδ is a primary 1α,25(OH)2D3-responding gene and that VDR and PPARδ signaling pathways are interconnected at the level of cross-regulation of their respective transcription factor mRNA levels.