9 However, in the current study, exogenous Fgf15 protein treatment strongly inhibited Cyp7a1 gene

expression in Shp anti-CTLA-4 antibody KO mice as well, indicating that Fgf15 suppresses Cyp7a1 gene expression independent of Shp. This conclusion is also supported by a study that showed, in primary human hepatocytes, that the knockdown of SHP did not affect the FGF19-mediated suppression of CYP7A1 gene expression.11 MAPK activation is associated with the suppression of Cyp7a1/CYP7A1 gene expression by Fgf15/FGF19. p38 activation indirectly increases Cyp7a1 expression by increasing the hepatocyte nuclear factor 4 alpha (HNF4α)-mediated inducton of the Cyp7a1 gene,30 but our results showed that Fgf15 did not activate p38. It was also reported that overexpression of FGFR4 in mice reduces Cyp7a1 expression, which is associated with the activation of JNK in the

liver,14 and in primary human hepatocytes, treatment with FGF19 selectively activates ERK1/2 to suppress CYP7A1 expression.11 The downstream target of JNK and ERK is cJun and Egr1, respectively. This study showed that in mice, treatment with Fgf15 rapidly mainly increased ERK activation and, to a smaller degree, JNK activation. However, the knockdown/KO of cJun or Egr1 markedly reduced the basal expression of Cyp7a1 and Cyp8b1, but did not prevent the Metformin ic50 suppression of Cyp7a1 and Cyp8b1 by the Fgf15 protein. These data also indicate that the ERK and JNK pathways tend to compensate each other in suppressing Cyp7a1 and Cyp8b1 gene expression. Egr1 deficiency led to a strong induction of cJun, and it was reported that ERK activation leads to the

induction of c-fos, which is a partner of cJun, to form AP1.31 Therefore, increased ERK activation with a Egr1 deletion may increase AP1, which may result in the suppression of Cyp7a1 expression. These data may suggest a species difference in the MAPK-pathway–mediated suppression of Cyp7a1/CYP7A1 and Cyp8b1/CYP8B1 gene expression between mice and humans. In addition, despite that cJun and Egr1 support the basal expression of Cyp7a1 and Cyp8b1, Fgf15-activated 上海皓元医药股份有限公司 JNK and ERK activation results in the suppression of Cyp7a1 and Cyp8b1 expression, indicating that Fgf15 may switch the effects of MAPK on regulating Cyp7a1 and Cyp8b1 expression. Another novel finding from this study is that in addition to regulating Cyp7a1 expression, the Fgf15/Fgfr4 pathway affects liver Shp expression. Basal and Fxr-induced Shp mRNA levels were decreased in Fgfr4 KO mice. It will be interesting to determine the mechanisms of the Fgf15/Fgfr4 regulation of Shp expression. This mechanism may involve a post-translational modification of Fxr after MAPK activation. In fact, a post-translational modification of Fxr by acetylation or phosphorylation has been reported to affect Fxr function.