Down-regulation of cholesterol 7alpha-hydroxylase (CYP7A1) gene expression by bile acids in primary rat hepatocytes is mediated by the c-Jun N-terminal kinase pathway.
Cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis, is feedback-inhibited at the transcriptional level by hydrophobic bile acids. Recent studies show that bile acids are physiological ligands for farnesoid X receptor (FXR). Activated FXR indirectly represses CYP7A1 transcription through induction of small heterodimer protein (SHP-1). In this study, we provide evidence that bile acids rapidly down-regulate CYP7A1 transcription via activation of the JNK/c-Jun pathway. Furthermore, we demonstrate that SHP-1 is also a direct target of activated c-Jun. In primary rat hepatocyte cultures, taurocholate (TCA) strongly activated JNK in a time- and concentration-dependent manner. Tumor necrosis factor-alpha, a potent activator of JNK, also rapidly activated JNK and down-regulated CYP7A1 mRNA levels. Overexpression of dominant-negative JNK1 or a transactivating domain mutant of c-Jun significantly blocked the ability of TCA to down-regulate CYP7A1 mRNA. In contrast, overexpression of wild-type c-Jun (c-Jun(wt)) enhanced the repression of CYP7A1 by TCA. Moreover, overexpression of c-Jun(wt) resulted in increased SHP-1 promoter activity. Mutation of a putative AP-1 (c-Jun) element suppressed c-Jun-mediated activation of the SHP-1 promoter construct. These results indicate that the bile acid-activated JNK pathway plays a pivotal role in regulating CYP7A1 levels in primary rat hepatocytes.
Gupta
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S
Department of Medicine-Gastroenterology, Virginia Commonwealth University, Medical College of Virginia Campus, Richmond, Virginia 23298, USA.
Stravitz
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RT
Dent
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P
Hylemon
P B
PB
D000818:Animals; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000494:pharmacology*; D002478:Cells, Cultured; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D017930:Genes, Reporter; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology; D008156:Luciferases / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013654:Taurine / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D001647:Bile Acids and Salts; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D013654:Taurine; D008156:Luciferases; D002790:Cholesterol 7-alpha-Hydroxylase; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases