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.
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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

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CYP2A4 VDREs compete with the CYP3A4 ER6 probe for binding to the PXR:RX...
CYP2A4 VDREs compete with the CYP3A4 ER6 probe for binding to the PXR:RXRα heterodimer in electrophoretic mobility shift assay. (A) PXR-responsive region of CYP24 promoter sequence. VDRE sequences (VDRE-II, –294 to –274, and VDRE-I, –174 to –151) are overlined, and half-sites are indicated in boldface letters. The region between –316 and –291 (site 3), which contains sequences that are homologous to various direct repeats, is underlined. Circles under nucleotides denote those nucleotides that were changed in mutation constructs. The TATA box is indicated. (B) CYP24 VDRE-II and VDRE-I motifs compete with the CYP3A4 ER6 probe for binding to the PXR:RXRα heterodimer. Radiolabeled CYP3A4 ER6 oligonucleotide (50,000 cpm) was incubated in the presence of PXR and RXRα proteins prepared by in vitro translation using a transcription-translation coupled system (lane 1). In parallel experiments, incubation was performed in the presence of a 50-fold molar excess of the CYP24 site 3 region (lane 2), or a 10- to 50-fold molar excess of unlabeled CYP3A4 ER6 (lanes 3 and 4), CYP24 VDRE-I (lanes 5 and 6), and VDRE-II (lanes 7 and 8).