title: Identification of pregnane-X receptor target genes and coactivator and corepressor binding to promoter elements in human hepatocytes.
abstract: Chromatin immunoprecipitation (ChIP) studies were conducted in human hepatocytes treated with rifampicin in order to identify new pregnane-X receptor (PXR) target genes. Genes, both previously known to be involved and not known to be involved in drug disposition, with PXR response elements (PXREs) located upstream, within or downstream from their potentially associated genes, were identified. Validation experiments identified several new drug disposition genes with PXR binding sites. Of these, only CYP4F12 demonstrated increased binding in the presence of rifampicin. The role of PXR in the basal and inductive response of CYP4F12 was confirmed in hepatocytes in which PXR was silenced. We also assessed the association of PXR-coactivators and -corepressors with known and newly identified PXREs. Both PXR and the steroid receptor coactivator (SRC-1) were found to bind to PXREs in the absence of rifampicin, although binding was stronger after rifampicin treatment. We observed promoter-dependent patterns with respect to the binding of various coactivators and corepressors involved in the regulation of CYP4F12, CYP3A4, CYP2B6, UGT1A1 and P-glycoprotein. In conclusion, our findings indicate that PXR is involved in the regulation of CYP4F12 and that PXR along with SRC1 binds to a broad range of promoters but that many of these are not inducible by rifampicin.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics, Merck & Co, Rahway, NJ 07065, USA. niresh_hariparsad@merck.com
authors.forename: Niresh
authors.initials: N
authors.lastname: Hariparsad
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Chu
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Yabut
authors.forename: Paul
authors.initials: P
authors.lastname: Labhart
authors.forename: Dylan P
authors.initials: DP
authors.lastname: Hartley
authors.forename: Xudong
authors.initials: X
authors.lastname: Dai
authors.forename: Raymond
authors.initials: R
authors.lastname: Evers
mesh_terms: D000328:Adult; D001665:Binding Sites; D047369:Chromatin Immunoprecipitation; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D011987:Receptors, Steroid / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D020218:Response Elements; D012293:Rifampin / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D012097:Repressor Proteins; D015534:Trans-Activators; D012293:Rifampin