Hepatocyte nuclear factor-4α is a central transactivator of the mouse Ntcp gene

Sodium taurocholate cotransporting polypeptide (Ntcp) is the major uptake system for conjugated bile acids. Deletions of hepatocyte nuclear factor (HNF)-1α and retinoid X receptor-α:retinoic acid receptor-α binding sites in the mouse 5′-flanking region corresponding to putatively central regulatory elements of rat Ntcp do not significantly reduce promoter activity. We hypothesized that HNF-4α, which is increasingly recognized as a central regulator of hepatocyte function, may directly transactivate mouse ( mNtcp). A 1.1-kb 5′-upstream region including the mouse Ntcp promoter was cloned and compared with the rat promoter. In contrast to a moderate 3.5-fold activation of mNtcp by HNF-1α, HNF-4α cotransfection led to a robust 20-fold activation. Deletion analysis of mouse and rat Ntcp promoters mapped a conserved HNF-4α consensus site at −345/−326 and −335/−316 bp, respectively. p-475bp mNtcpLUC is not transactivated by HNF-1α but shows a 50-fold enhanced activity upon cotransfection with HNF-4α. Gel mobility shift assays demonstrated a complex of the HNF-4α-element formed with liver nuclear extracts that was blocked by an HNF-4α specific antibody. HNF-4α binding was confirmed by chromatin immunoprecipitation. Using Hepa 1–6 cells, HNF-4α-knockdown resulted in a significant 95% reduction in NTCP mRNA. In conclusion, mouse Ntcp is regulated by HNF-4α via a conserved distal cis-element independently of HNF-1α.