β-Catenin regulation during matrigel-induced rat hepatocyte differentiation

Hepatocytes in primary cultures de-differentiate and re-differentiate following addition of Engelbreth-Holm-Swarm mouse sarcoma (matrigel) to the cultures. The Wnt/β-catenin pathway has been shown to be important in liver growth and development. Here, we investigate changes in β-catenin and its mechanism, during matrigel-induced hepatocyte differentiation. Primary rat hepatocytes were cultured for 8 days, and matrigel was added to half of the cultures. Total and nuclear protein and total RNA were extracted at different days of culture and examined for β-catenin and other Wnt pathway components. A significant increase in total β-catenin protein was observed upon matrigel addition, during hepatocyte differentiation, despite a decrease in β-catenin and frizzled-1 (Wnt receptor) expression. A concurrent decrease in the glycogen synthase kinase-3β (GSK3β), axin, and ser45/thr41-phosphorylated β-catenin proteins was observed in matrigel-treated cultures, implying decreased degradation of β-catenin. Interestingly, a decrease in nuclear β-catenin and total active β-catenin was observed in the presence of matrigel. Matrigel also induced an increased association of β-catenin with Met (hepatocyte growth factor receptor), whereas association with E-cadherin remained unchanged. This coexisted with decreased β-catenin tyrosine phosphorylation. Thus, β-catenin undergoes multifactorial regulation during matrigel-induced hepatocyte differentiation and maturation; this induces its stabilization and membrane translocation, possibly contributing to hepatocyte differentiation.