title: Glucocorticoid receptor enhancement of pregnane X receptor-mediated CYP2B6 regulation in primary human hepatocytes.
abstract: Although the glucocorticoid receptor (GR) facilitates the xenobiotic-induced expression of CYP2B in rodents, its role in the regulation of human CYP2B6 is unclear. In this report, the role of human GR in the regulation of CYP2B6 was evaluated using primary human hepatocytes and transfection assays with Huh7 cells. CYP2B6 expression was not induced in primary hepatocytes treated with dexamethasone (DEX) concentrations (0.01-1 microM) known to activate GR. In contrast, treatment with 0.1 microM DEX enhanced CYP2B6 induction by different pregnane X receptor (PXR) activators, including rifampin, phenytoin, clotrimazole, and phenobarbital. In Huh7 cells, cotransfection of human (h)GR and hPXR with CYP2B6-phenobarbital-responsive enhancer module (PBREM) reporter constructs revealed that all hPXR ligands induce CYP2B6 reporter gene activity, and this ligand-dependent activation is greatly enhanced by activated hGR. CYP2B6 reporter gene expression was not induced in the presence of hPXR ligands when hGR alone was cotransfected with CYP2B6 reporter construct. In hGR and human constitutive androstane receptor (hCAR) cotransfection assays, activated hGR increased the constitutive activation of PBREM reporter constructs by hCAR in the absence of inducers. In the presence of activated hGR and known inducers of CYP2B6, only PB treatment caused a further 2-fold activation of hCAR compared with control. These studies show that hGR is involved synergistically in the xenobiotic-responsive regulation of human CYP2B6 by hPXR and hCAR. Moreover, the results suggest that the GR-enhanced expression of CYP2B6 is mediated through an indirect mechanism that does not require increased expression of nuclear receptor.
authors.affiliation: Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Hongbing
authors.initials: H
authors.lastname: Wang
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Faucette
authors.forename: Darryl
authors.initials: D
authors.lastname: Gilbert
authors.forename: Summer L
authors.initials: SL
authors.lastname: Jolley
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sueyoshi
authors.forename: Masahiko
authors.initials: M
authors.lastname: Negishi
authors.forename: Edward L
authors.initials: EL
authors.lastname: LeCluyse
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D003022:Clotrimazole / Q000494:pharmacology; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D015151:Immunoblotting; D008024:Ligands; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis* / Q000235:genetics; D010672:Phenytoin / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000096:biosynthesis; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D011987:Receptors, Steroid / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D012293:Rifampin / Q000494:pharmacology; D014157:Transcription Factors / Q000819:agonists
chemical_list: D000090702:Constitutive Androstane Receptor; D008024:Ligands; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; D014157:Transcription Factors; D010672:Phenytoin; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C104464:CYP3A protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D003022:Clotrimazole; D012293:Rifampin