Induction of hepatic metabolic functions by a novel variant of hepatocyte nuclear factor 4γ.

Hepatocyte nuclear factor 4α (HNF4α) is a critical factor for hepatocyte differentiation. HNF4α expression is decreased in hepatocellular carcinoma (HCC), which suggests a role in repression of hepatocyte dedifferentiation. In the present study, hepatic expression of HNF4γ was increased in liver-specific Hnf4a -null mice. The increased HNF4γ contained two variants, a known short variant, designated HNF4γ1, and a novel long variant, designated HNF4γ2. HNF4G2 mRNA was highly expressed in small intestine, and the transactivation potential of HNF4γ2 was the strongest among these variants, but the potential of HNF4γ1 was the lowest. Co-transfection experiments revealed that HNF4γ1 repressed HNF4α- and HNF4γ2-dependent transactivation while HNF4γ2 promoted the HNF4α-dependent transactivation. HNF4γ1 and HNF4γ2 were able to bind to the HNF4α binding sites with similar affinity as HNF4α. Furthermore, HNF4γ2, but not HNF4γ1, robustly induced expression of typical HNF4α target genes to a greater degree than did HNF4α. Additionally, HNF4γ2 suppressed proliferation of hepatoma cells as well as HNF4α and HNF4γ1, and HNF4γ2 induced critical hepatic functions such as glucose and urea production, and CYP1A2 activity stronger than did HNF4α and HNF4γ1. These results indicate that HNF4γ2 has potential for redifferentiation of HCC and thus may be explored as a target for HCC therapy.