Possible involvement of pregnane X receptor–enhanced CYP24 expression in drug-induced osteomalacia
Jean Marc Pascussi, … , Patrick Maurel, Marie Josè Vilarem
Jean Marc Pascussi, … , Patrick Maurel, Marie Josè Vilarem
Published January 3, 2005
Citation Information: J Clin Invest. 2005;115(1):177-186. https://doi.org/10.1172/JCI21867.
View: Text | PDF
Article Endocrinology

Possible involvement of pregnane X receptor–enhanced CYP24 expression in drug-induced osteomalacia

Abstract

Vitamin D controls calcium homeostasis and the development and maintenance of bones through vitamin D receptor activation. Prolonged therapy with rifampicin or phenobarbital has been shown to cause vitamin D deficiency or osteomalacia, particularly in patients with marginal vitamin D stores. However, the molecular mechanism of this process is unknown. Here we show that these drugs lead to the upregulation of 25-hydroxyvitamin D3-24-hydroxylase (CYP24) gene expression through the activation of the nuclear receptor pregnane X receptor (PXR; NR1I2). CYP24 is a mitochondrial enzyme responsible for inactivating vitamin D metabolites. CYP24 mRNA is upregulated in vivo in mice by pregnenolone 16α-carbonitrile and dexamethasone, 2 murine PXR agonists, and in vitro in human hepatocytes by rifampicin and hyperforin, 2 human PXR agonists. Moreover, rifampicin increased 24-hydroxylase activity in these cells, while, in vivo in mice, pregnenolone 16α-carbonitrile increased the plasma concentration of 24,25-dihydroxyvitamin D3. Transfection of PXR in human embryonic kidney cells resulted in rifampicin-mediated induction of CYP24 mRNA. Analysis of the human CYP24 promoter showed that PXR transactivates the sequence between –326 and –142. We demonstrated that PXR binds to and transactivates the 2 proximal vitamin D–responsive elements of the human CYP24 promoter. These data suggest that xenobiotics and drugs can modulate CYP24 gene expression and alter vitamin D3 hormonal activity and calcium homeostasis through the activation of PXR.

Authors

Jean Marc Pascussi, Agnes Robert, Minh Nguyen, Odile Walrant-Debray, Michèle Garabedian, Pascal Martin, Thierry Pineau, Jean Saric, Fréderic Navarro, Patrick Maurel, Marie Josè Vilarem

×

Figure 8

Options: View larger image (or click on image) Download as PowerPoint
Functional and mutational analysis of human CYP24 VDREs. (A) Thymidine k...
Functional and mutational analysis of human CYP24 VDREs. (A) Thymidine kinase promoter luciferase reporter vectors (pGL3tkLUC) driven by 3 repeats of oligonucleotides from the human CYP24 promoter (site 3, VDRE-I, and VDRE-II) were cotransfected with control expression plasmid (pSG5), human VDR (pSG5-hVDR), or human PXR (pSG5-ØATG-hPXR) into Hek293 cells, together with pRSV-β-gal transfection control plasmid. Cells were treated with vehicle (0.1% DMSO; UT), 50 nM 1α,25(OH)2D3 (VD3), or 10 μM rifampicin (RIF) 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. They were replicated in independent experiments. (B) Hek293 cells were transiently cotransfected with pSG5-ØATG-hPXR expression vector along with various human CYP24 promoter sequence–containing reporter constructs, together with pRSV-β-gal transfection control plasmid. Cells were treated with vehicle, 50 nM 1α,25(OH)2D3, or 10 μM rifampicin for 24 hours. Reporter constructs were as follows: –316 to –22 wild-type sequence in pGL3b (WT) or point mutants of VDRE-I (–168CCC mutated to GTT; ØVDRE-I), VDRE-II (–289CACC to AAAA; ØVDRE-II), or both VDREs (ØVDREs). Values represent β-gal–corrected luciferase activities normalized to the corresponding level in untreated Hek293 cells and are the average of duplicates ± SE. They were replicated in independent experiments.