Possible involvement of the competition for the transcriptional coactivator glucocorticoid receptor-interacting protein 1 in the inflammatory signal-dependent suppression of PXR-mediated CYP3A induction in vitro

Abstract

Pregnane X receptor (PXR) is a xenobiotic-responsive transcription factor that plays a pivotal role in drug metabolism and disposition in livers and intestines through regulating the expression of drug metabolizing enzymes and transporters. It is well known that PXR-mediated induction of CYP3A enzymes is downregulated under inflammatory conditions. Although some reports suggest that the downregulation is caused by an inhibition of transcriptional activity of PXR by nuclear factor-κB (NF-κB), a key inflammation-associated transcription factor, the detailed mechanism remains unclear. In reporter assays using the CYP3A4 promoter, the PXR-mediated transcription was suppressed by inflammatory stimuli and co-expression of NF-κB or activator protein-1 (AP-1), suggesting that not only NF-κB but also AP-1 play a key role in the suppression of CYP3A induction. We also revealed that PXR, NF-κB and AP-1 commonly use the coactivator glucocorticoid receptor-interacting protein 1 (GRIP1) for their transcriptional activation and that inflammatory stimuli inhibited the GRIP1-mediated enhancement of the transcription by PXR. These results suggest that under inflammatory conditions activated NF-κB and/or AP-1 compete with PXR for GRIP1 usage to reduce the PXR/GRIP1-mediated transcription of CYP3A genes.

Keywords: AP-1; CYP3A; Coactivator; GRIP1; Inflammation; NF-κB; PXR.