title: Cytokine regulation of human sterol 12alpha-hydroxylase (CYP8B1) gene.
abstract: Sterol 12alpha-hydroxylase (CYP8B1) catalyzes cholic acid synthesis in the liver and is feedback inhibited by bile acids. In addition to activating farnesoid X receptor (nuclear receptor subfamily 1H4), bile acids also induce inflammatory cytokines in hepatocytes. The objective of this study was to investigate the mechanism by which inflammatory cytokines inhibit human CYP8B1 gene transcription. Real-time PCR assays revealed that both chenodeoxycholic acid (CDCA) and interleukin-1beta (IL-1beta) markedly reduced CYP8B1, cholesterol 7alpha-hydroxylase CYP7A1 and hepatic nuclear factor 4alpha (HNF4alpha) mRNA expression levels in human primary hepatocytes. However, CDCA induced, but IL-1beta reduced, small heterodimer partner (SHP) mRNA expression. IL-1beta inhibited human CYP8B1 reporter activity only in liver cells, and a c-Jun NH(2)-terminal kinase (JNK)-specific inhibitor-blocked IL-1beta inhibition. Activated JNK1 or c-Jun inhibited, whereas their dominant negative forms blocked, IL-1beta inhibition of CYP8B1 transcription. Mutagenesis analyses mapped an IL-1beta response element to a previously identified bile acid response element, which contains an HNF4alpha binding site. A dominant negative HNF4alpha inhibited CYP8B1 gene transcription and ectopically expressed HNF4alpha blocked IL-1beta inhibition. Furthermore, IL-1beta inhibited HNF4alpha gene transcription, protein expression, and binding to the CYP8B1 gene. JNK1 phosphorylated HNF4alpha and a JNK-specific inhibitor blocked the IL-1beta inhibition of HNF4alpha expression. These results suggest that IL-1beta inhibits CYP8B1 gene transcription via a mitogen-activated protein kinase/JNK pathway that inhibits HNF4alpha gene expression and its DNA-binding ability. This mechanism may play an important role in the adaptive response to inflammatory cytokines and in the protection of the liver during cholestasis.
authors.affiliation: Dept. of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P. O Box 95, Rootstown, OH 44272, USA.
authors.forename: Asmeen
authors.initials: A
authors.lastname: Jahan
authors.forename: John Y L
authors.initials: JY
authors.lastname: Chiang
mesh_terms: D002460:Cell Line; D002635:Chenodeoxycholic Acid / Q000494:pharmacology; D002874:Chromosome Mapping; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D051557:Hepatocyte Nuclear Factor 4; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D020218:Response Elements / Q000235:genetics; D013253:Steroid 12-alpha-Hydroxylase / Q000037:antagonists & inhibitors / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D007375:Interleukin-1; D010750:Phosphoproteins; D012333:RNA, Messenger; D014157:Transcription Factors; D002635:Chenodeoxycholic Acid; D013253:Steroid 12-alpha-Hydroxylase; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases