Inhibitory effect of the small heterodimer partner on hepatocyte nuclear factor-4 mediates bile acid-induced repression of the human angiotensinogen gene.

Bile acids function as transcriptional regulators for the genes important in bile acid synthesis and cholesterol homeostasis. In this study, we identified angiotensinogen (ANG), the precursor of vasoactive octapeptide angiotensin II, as a novel target gene of bile acids. In human ANG transgenic mice, administration of cholic acid resulted in the down-regulation of human ANG gene expression in the liver. ANG gene expression in HepG2 cells was also repressed by chenodeoxycholic acid. Because the expression of small heterodimer partner (SHP) mRNA was induced by chenodeoxycholic acid in HepG2 cells, we analyzed the effects of SHP on the human ANG promoter. Promoter mutation analysis demonstrated that SHP repressed human ANG promoter activity through the element, which has been previously determined as a binding site for hepatocyte nuclear factor-4 (HNF-4). SHP repressed human ANG promoter activity only when the HNF-4 expression vector was cotransfected in HeLa cells. Furthermore, we found that SHP bound to the HNF-4 N-terminal region including the DNA-binding domain and activation function-1 and that SHP prevented HNF-4 from binding to the human ANG promoter. These results suggest that bile acids negatively regulate the human ANG gene through the inhibitory effect of SHP on HNF-4.