Beta-catenin: A friend or foe in liver pathobiology?

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality worldwide due to poor prognosis and limited therapeutic options. Point mutations affecting phosphorylation sites such as serine-45 in Beta-catenin gene are evident in around 30% of HCC. We developed a transgenic mouse that expresses Ser45 mutated Beta-catenin (TG) in hepatocytes. While this mutation did not induce spontaneous tumorigenesis, it promoted diethylnitrosamine (DEN)-induced HCC through cyclin-D1 overexpression and other factors.The Wnt/Beta-catenin signaling is important in stem cell self-renewal. The adult progenitor cell of the liver, or oval cells that emanate from atypical ductular proliferation (ADP), maybe involved in liver regeneration and/or hepatocarcinogenesis and can be observed after exposure to DDC diet, which induces hepatic and biliary injury. When challenged with chronic-DDC diet, Beta-catenin transgene led to a cellular disparity in the form of increased appearance of atypical hepatocytes (positive for ductular marker A6), which was associated with better resolution of intrahepatic cholestasis. We also utilized DDC diet in conditional Beta-catenin knockout mice (KO) that lacked Beta-catenin in hepatocytes and cholangiocytes. ADP was blunted after short-term DDC feeding in KO mice; however, long-term feeding resulted in gradual increase in ADP, hepatic fibrosis and HCC. Interestingly, the KO livers begin to exhibit periportal Beta-catenin-positive hepatocytes, which eventually populate the entire livers over the course of this process. Finally, we explored targeting of the Wnt pathway with pegylated interferon-alpha2A (Peg-IFN). We found that Peg-IFN decreased Beta-catenin activity in mouse liver and several human hepatoma cell lines. The mechanism seemed to be at least partly due to upregulation of a nuclear export factor, RanBP3.Thus, this study characterizes an animal model utilizing Beta-catenin mutation, which is evident in HCC patients. DEN-exposure in these animals led to HCC development, thus providing a valuable tool to study mechanisms of hepatocarcinogenesis and providing a model to test therapeutic inhibition of Beta-catenin by agents such as peg-IFN and others. Our studies also provide evidence that Wnt activation may resolve intrahepatic cholestasis. Finally, we show that chronic damage to the liver in KO led to appearance of Beta-catenin-positive hepatocytes, which continued to proliferate and in the face of continued injury and fibrosis, led to development of HCC, which is also relevant clinically