title: Dual roles of nuclear receptor liver X receptor α (LXRα) in the CYP3A4 expression in human hepatocytes as a positive and negative regulator.
abstract: CYP3A4 is a major drug-metabolizing enzyme in humans, whose expression levels show large inter-individual variations and are associated with several factors such as genetic polymorphism, physiological and disease status, diet and xenobiotic exposure. Nuclear receptor pregnane X receptor (PXR) is a key transcription factor for the xenobiotic-mediated transcription of CYP3A4. In this study, we have investigated a possible involvement of liver X receptor α (LXRα), a critical regulator of cholesterol homeostasis, in the hepatic CYP3A4 expression since several recent reports suggest the involvement of CYP3A enzymes in the cholesterol metabolism in humans and mice. Reporter assays using wild-type and mutated CYP3A4 luciferase reporter plasmids and electrophoretic mobility shift assays revealed that LXRα up-regulated CYP3A4 through the known DNA elements critical for the PXR-dependent CYP3A4 transcription, suggesting LXRα as a positive regulator for the CYP3A4 expression and a crosstalk between PXR and LXRα in the expression. In fact, reporter assays showed that LXRα activation attenuated the PXR-dependent CYP3A4 transcription. Moreover, a PXR agonist treatment-dependent increase in CYP3A4 mRNA levels was suppressed by co-treatment with an LXRα agonist in human primary hepatocytes and HepaRG cells. The suppression was not observed when LXRα expression was knocked-down in HepaRG cells. In conclusion, the present results suggest that sterol-sensitive LXRα positively regulates the basal expression of CYP3A4 but suppresses the xenobiotic/PXR-dependent CYP3A4 expression in human hepatocytes. Therefore, nutritional, physiological and disease conditions affecting LXRα might be one of the determinants for the basal and xenobiotic-responsive expression of CYP3A4 in human livers.
authors.affiliation: Division of Drug Metabolism and Molecular Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Watanabe
authors.forename: Kaori
authors.initials: K
authors.lastname: Sakurai
authors.forename: Yuri
authors.initials: Y
authors.lastname: Tsuchiya
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamazoe
authors.forename: Kouichi
authors.initials: K
authors.lastname: Yoshinari
mesh_terms: D000368:Aged; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D000071518:Liver X Receptors; D008875:Middle Aged; D057093:Orphan Nuclear Receptors / Q000502:physiology*
chemical_list: D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human
keywords: 24(S)-hydroxycholesterol; 24S-HC; 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime; CAR; CITCO; Cholesterol homeostasis; DMSO; DR-4; EMSA; ER-6; Enzyme induction; Human hepatocyte; LXRα; Nuclear receptor; PXR; RXR; SREBP-2; Transcriptional crosstalk; constitutive active/androstane receptor; dimethyl sulfoxide; direct repeat separated by 4 nucleotides; electrophoretic mobility shift assays; everted repeat separated by 6 nucleotides; liver X receptor α; pregnane X receptor; qRT-PCR; quantitative reverse transcription-PCR; retinoid X receptor; sterol regulatory element-binding protein-2