Increased Activation of the Wnt/β-Catenin Pathway in Spontaneous Hepatocellular Carcinoma Observed in Farnesoid X Receptor Knockout Mice

Farnesoid X receptor (FXR), the primary bile acid-sensing nuclear receptor, also is known for its anticancer properties. It is known that FXR deficiency in mice results in spontaneous hepatocellular carcinoma (HCC), but the mechanisms are not completely understood. We report that sustained activation of the Wnt/beta-catenin pathway is associated with spontaneous HCC in FXR-knockout (KO) mice. HCC development was studied in FXR-KO mice at 3, 8, and 14 months of age. No tumors were observed at either 3 or 8 months, but the presence of HCC was observed in 100% of the FXR-KO mice at the age of 14 months. Further analysis revealed no change in beta-catenin activation in the livers of 3-month-old FXR-KO mice, but a moderate increase was observed in 8-month-old FXR-KO mice. beta-Catenin activation further increased significantly in 14-month-old tumor-bearing mice. Further analysis revealed that two independent mechanisms might be involved in beta-catenin activation in the livers of FXR-KO mice. Activation of canonical Wnt signaling was evident as indicated by increased Wnt4 and dishevelled expression along with glycogen synthase kinase-3 beta inactivation. We also observed decreased expression of E-cadherin, a known regulator of beta-catenin, in FXR-KO mice. The decrease in E-cadherin expression was accompanied by increased expression of its transcriptional repressor, Snail. Consistent with the increased HCC in FXR-KO mice, we observed a significant decrease in FXR expression and activity in human HCC samples. Taken together, these data indicate that a temporal increase in the activation of Wnt/beta-catenin is observed during spontaneous HCC development in FXR-KO mice and is potentially critical for tumor development.