Gankyrin-Mediated Dedifferentiation Facilitates the Tumorigenicity of Rat Hepatocytes and Hepatoma Cells

Gankyrin is a critical oncoprotein overexpressed in human hepatocellular carcinoma (HCC). However, the mechanism underlying gankyrin-mediated hepatocarcinogenesis remains elusive. Herein, we provide evidence that gankyrin expression was progressively elevated in liver fibrosis, cirrhosis, and HCC. Levels of gankyrin expression were closely associated with the dedifferentiation status of hepatoma in patients. Decrease of hepatocyte characteristic markers and increase of cholangiocyte-specific markers were observed in rat primary hepatocytes with enforced gankyrin expression and diethylnitrosamine (DEN)-triggered rat hepatocarcinogenesis. Overexpression of gankyrin also attenuated the hepatic function of primary hepatocytes, which further suggests that gankyrin promotes the dedifferentiation of hepatocytes. Moreover, elevated expression of gankyrin closely correlated with the expression of HCC stem/progenitor cell markers in DEN-triggered hepatocarcinogenesis and human HCCs. Hepatoma cells derived from suspension-cultured spheroids exhibited a higher gankyrin level, and enforced gankyrin expression in hepatoma cells remarkably enhanced cluster of differentiation (CD) 133, CD90, and epithelial cellular adhesion molecule expression, indicating a role of gankyrin in hepatoma cell dedifferentiation and the generation of hepatoma stem/progenitor cells. In contrast, down-regulation of gankyrin in hepatoma cells by lentivirus-mediated microRNA delivery significantly improved their differentiation status and attenuated malignancy. Interference of gankyrin expression in hepatoma cells also diminished the proportion of cancer stem/progenitor cells and their self-renewal capacity. Furthermore, gankyrin was found to bind hepatocyte nuclear factor 4 alpha (HNF4 alpha), which determines hepatocyte differentiation status and enhances proteasome-dependent HNF4 alpha degradation in hepatoma cells. The inverse correlation of gankyrin and HNF4 alpha was further confirmed in primary hepatocytes, DEN-induced hepatocarcinogenesis, and human HCCs. Conclusion: Gankyrin-mediated dedifferentiation of hepatocytes and hepatoma cells via, at least partially, down-regulation of HNF4 alpha facilitates HCC development, and interference of gankyrin expression could be a novel strategy for HCC prevention and differentiation therapy. (HEPATOLOGY 2011;54:1259-1272)