Figure 5.

PXR transactivates the proximal human CYP24 promoter. (A) VDREs present in the human CYP24 (hCYP24) gene. Schematic representation of the human CYP24 constructs used in this work. (B) Ligand-activated PXR transactivates the –326 to –143 promoter region of human CYP24. Hek293 cells were transiently transfected with human PXR (pSG5-Ø^ATG-hPXR), mouse PXR (pSG5-mPXR), or control expression vector (pSG5) in the presence of reporter vectors driven by the indicated human CYP24 promoter sequences, together with pRSV-β-gal transfection control plasmid. Cells were treated with vehicle (0.1% DMSO; UT), 50 nM 1α,25(OH)₂D₃ (VD₃), 10 μM rifampicin (RIF), or 10 μM pregnenolone 16α-carbonitrile (PCN) for 24 hours. Cells were then harvested and analyzed for both luciferase and β-gal activities. Values represent β-gal–corrected luciferase activities normalized to the corresponding level in untreated Hek293 cells and are the average of duplicates ± SE. These were replicated in independent experiments.