ATPase Class I Type 8B Member 1 and Protein Kinase C ζ Induce the Expression of the Canalicular Bile Salt Export Pump in Human Hepatocytes

The exact molecular mechanism(s) of the disease that results from defects in the ATPase Class I Type 8B Member 1 gene remains controversial. Prior investigations of human ileum and in intestinal and ovarian cell lines have Suggested that familial intrahepatic cholestasis 1 (FIC1) activates the farnesoid X-receptor (FXR) via a pathway involving protein kinase C zeta (PKC zeta). Translational investigations of human liver from individuals with FIC1 disease have been confounded by secondary affects of progressive cholestatic liver disease and limited numbers of samples for analysis. These studies, performed in primarily derived human hepatocytes, circumvent this issue. The canalicular bile salt export pump (BSEP) served as a downstream target of FXR. The siRNA-mediated silencing of FIC1 in human hepatocytes led to a reduction in both human BSEP promoter activity and BSEP protein expression, which correlated with a reduction in FXR expression and redistribution of its localization from the nucleus to the cytoplasm. These changes in BSEP expression could be reproduced by altering the expression of PKC zeta, with a positive correlation of PKC zeta activity and BSEP expression. Overall, these findings Support the hypothesis that FIC1 enhances FXR signaling via a PKC zeta-dependent signaling pathway. (Pediatr Res 67: 183-187, 2010)