Bile acids and cytokines inhibit the human cholesterol 7α-hydroxylase gene via the JNK/c-jun pathway in human liver cells

Abstract

Cholesterol 7α‐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‐1β (IL‐1β) regulation of human CYP7A1 gene expression via real‐time polymerase chain reaction, reporter assays, co‐immunoprecipitation and chromatin immunocipitation (ChIP) assays. IL‐1β and CDCA reduced CYP7A1 but induced c‐Jun messenger RNA expression in human primary hepatocytes. IL‐1β inhibited human CYP7A1 reporter activity via the HNF4α binding site. A JNK‐specific inhibitor blocked the inhibitory effect of IL‐1β on HNF4α expression and CYP7A1 reporter activity. c‐Jun inhibited HNF4α and PPARγ coactivator‐1α (PGC‐1α) coactivation of CYP7A1 reporter activity, whereas a dominant negative c‐Jun did not. Co‐immunoprecipitation and ChIP assays revealed that IL‐1β and CDCA reduced HNF4α bound to the CYP7A1 chromatin, and that c‐Jun interacted with HNF4α and blocked HNF4α recruitment of PGC‐1α to the CYP7A1 chromatin. In conclusion, IL‐1β and CDCA inhibit HNF4α but induce c‐Jun, which in turn blocks HNF4α recruitment of PGC‐1α 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. (HEPATOLOGY 2006;43:1202–1210.)