Bile acids and cytokines inhibit the human cholesterol 7 alpha-hydroxylase gene via the JNK/c-jun pathway in human liver cells.
Cholesterol 7 alpha-hydroxylase (CYP7A1) of the bile acid biosynthesis pathway is suppressed by bile acids and inflammatory cytokines. Bile acids are known to induce inflammatory cytokines to activate the mitogen-activated protein kinase/c-Jun N-terminal kinase (JNK) signaling pathway that inhibits CYP7A1 gene transcription. c-Jun has been postulated to mediate bile acid inhibition of CYP7A1. However, the c-Jun target involved in the regulation of CYP7A1 is unknown. Human primary hepatocytes and HepG2 cells were used as models to study chenodeoxycholic acid (CDCA) and interleukin-1 beta (IL-1 beta) regulation of human CYP7A1 gene expression via real-time polymerase chain reaction, reporter assays, co-immunoprecipitation and chromatin immunocipitation (ChIP) assays. IL-1 beta and CDCA reduced CYP7A1 but induced c-Jun messenger RNA expression in human primary hepatocytes. IL-1beta inhibited human CYP7A1 reporter activity via the HNF4 alpha binding site. A JNK-specific inhibitor blocked the inhibitory effect of IL-1 beta on HNF4 alpha expression and CYP7A1 reporter activity. c-Jun inhibited HNF4 alpha and PPARgamma coactivator-1 alpha (PGC-1 alpha) coactivation of CYP7A1 reporter activity, whereas a dominant negative c-Jun did not. Co-immunoprecipitation and ChIP assays revealed that IL-1 beta and CDCA reduced HNF4 alpha bound to the CYP7A1 chromatin, and that c-Jun interacted with HNF4 alpha and blocked HNF4 alpha recruitment of PGC-1 alpha to the CYP7A1 chromatin. In conclusion, IL-1 beta and CDCA inhibit HNF4 alpha but induce c-Jun, which in turn blocks HNF 4 alpha recruitment of PGC-1 alpha to the CYP7A1 chromatin and results in inhibition of CYP7A1 gene transcription. The JNK/c-Jun signaling pathway inhibits bile acid synthesis and protects hepatocytes against the toxic effect of inflammatory agents.
Li
Tiangang
T
Department of Microbiology, Immunology, and Biochemistry, Northeastern Ohio Universities College of Medicine, Rootstown, OH 44272, USA.
Jahan
Asmeen
A
Chiang
John Y L
JY
D001647:Bile Acids and Salts / Q000378:metabolism*; D002478:Cells, Cultured; D002635:Chenodeoxycholic Acid / Q000494:pharmacology; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D007375:Interleukin-1 / Q000494:pharmacology; D011336:Probability; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000235:genetics; D014158:Transcription, Genetic
D001647:Bile Acids and Salts; D016207:Cytokines; D007375:Interleukin-1; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D002635:Chenodeoxycholic Acid; D002790:Cholesterol 7-alpha-Hydroxylase