title: CYP3A induction by liver x receptor ligands in primary cultured rat and mouse hepatocytes is mediated by the pregnane X receptor.
abstract: The effects of oxysterol and drug ligands of the liver X receptor (LXR) on cytochrome P450 expression were evaluated in primary cultured rodent hepatocytes. Treatment of rat hepatocyte cultures with either 25-hydroxycholesterol or 24(S),25-epoxycholesterol (10(-5) to 5 x 10(-5) M) produced concentration-dependent elevations in CYP3A mRNA and immunoreactive protein levels but did not increase the amounts of CYP1A1, CYP2B, or CYP4A gene products. The effects of 24(S),25-epoxycholesterol on CYP3A content were much greater than were those of 25-hydroxycholesterol, consistent with the relative abilities of these sterols to bind and activate LXR. To understand the mechanistic basis of these observations, experiments were performed using primary cultured hepatocytes prepared from LXRalpha/beta- or pregnane X receptor (PXR)-null mice. CYP3A mRNA levels were increased after treatment with 24(S),25-epoxycholesterol in both wild-type and LXR-null mouse hepatocytes. In contrast, neither 24(S),25-epoxycholesterol nor either of two additional potent LXR ligands, 22(R)-hydroxycholesterol and N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1(trifluoromethyl)ethyl-]phenyl]-benzenesulfonamide (T0901317), altered CYP3A mRNA levels in hepatocytes prepared from PXR-null mice, although these agents induced CYP3A mRNA content in wild-type cultures. As evidence that the LXR ligands also activated PXR in rat hepatocytes, cotransfection of primary cultures with a dominant negative PXR abolished reporter gene induction after treatment with any of the test agents. These results indicate that selected LXR ligands are capable of activating PXR, probably as a defensive measure to prevent the accumulation of these potentially toxic endogenous molecules.
authors.affiliation: Institute of Environmental Health Sciences, 2727 Second Avenue, Room 4000, Detroit, MI 48201, USA.
authors.forename: Sarita D
authors.initials: SD
authors.lastname: Shenoy
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Spencer
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Mercer-Haines
authors.forename: Masumeh
authors.initials: M
authors.lastname: Alipour
authors.forename: Mary D
authors.initials: MD
authors.lastname: Gargano
authors.forename: Melissa
authors.initials: M
authors.lastname: Runge-Morris
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kocarek
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis*; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A; D004268:DNA-Binding Proteins; D004790:Enzyme Induction / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter / Q000235:genetics; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D006888:Hydroxycholesterols / Q000378:metabolism; D008024:Ligands; D000071518:Liver X Receptors; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D057093:Orphan Nuclear Receptors; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis*; D000077297:Pregnane X Receptor; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000378:metabolism; D011987:Receptors, Steroid / Q000187:drug effects*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D000924:Anticholesteremic Agents; D004268:DNA-Binding Proteins; D006888:Hydroxycholesterols; D008024:Ligands; D000071518:Liver X Receptors; C000605214:Nr1h3 protein, mouse; C000605215:Nr1h3 protein, rat; D057093:Orphan Nuclear Receptors; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; C007997:25-hydroxycholesterol; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating