Hypoxia-inducible factor-1 and activator protein-1 modulate the upregulation of CYP3A6 induced by hypoxia

1 Moderate hypoxia in vivo and serum from rabbits subjected to moderate hypoxia (S-HYPO) ill vitro reduce CYP1A1 and IA2 P450 isoforms and upregulate CYP3A6. The aim of this project was to investigate the signal transduction pathways implicated in the upregulation of CYP3A6 expression by hypoxia. 2 Hypoxia in vivo and S-HYPO in vitro increased the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and c-jun, as well as CYP3A6. By electrophoresis mobility shift assay, it was shown that HIF-1 and activator protem-1 (AP-1) bind to CYP3A6 oligonucleotide probe after exposure to hypoxia ill vivo and S-HYPO in vitro. The effects of hypoxia in vivo or S-HYPO ill vitro were reproduced by CoCl2 and lead acetate, activators of HIF-1 and AP-1, respectively. 3 PD98059, a p42/44 MAPK inhibitor, prevented the increase of CYP3A6 and c-jun, but did not impede the increase of HIF-1alpha and binding to CYP3A6 oligonucleotide probe. Genistein, an inhibitor of protein tyrosine kinases (PTKs), prevented the increase in HIF-1alpha, c-jun and CYP3A6, as well as HIF-1 and AP-1 binding to CYP3A6 oligonucleotide probe. Moreover, hypoxia ill vivo induced constitutive androstane receptor (CAR) as well as CAR binding to the CYP3A6 oligonucleotide probe, but not the pregnane X receptor. 4 In conclusion, hypoxia ill vivo and S-HYPO induce the expression of CYP3A6. The ill vitro induction of CYP3A6 by S-HYPO is PTK- and p42/44 MAPK-dependent. The present data support the hypothesis that HIF-1 and AP-1 are part of the signalling pathway leading to CYP3A6 induction by hypoxia.