A double-negative feedback loop between Wnt-β-catenin signaling and HNF4α regulates epithelial-mesenchymal transition in hepatocellular carcinoma

Wnt-beta-catenin signaling participates in the epithelial-mesenchymal transition (EMT) in a variety of cancers; however, its involvement in hepatocellular carcinoma (HCC) and downstream molecular events is largely undefined. HNF4 alpha is the most prominent and specific factor maintaining the differentiation of hepatic lineage cells and a potential EMT regulator in HCC cells. However, the molecular mechanisms by which HNF4 alpha maintains the differentiated liver epithelium and inhibits EMT have not been completely defined. In this study, we systematically explored the relationship between Wnt-beta-catenin signaling and HNF4 alpha in the EMT process of HCC cells. Our results indicated that HNF4 alpha expression was negatively regulated during Wnt-b-catenin signaling-induced EMT through Snail and Slug in HCC cells. In contrast, HNF4 alpha was found to directly associate with TCF4 to compete with beta-catenin but facilitate transcription corepressor activities, thus inhibiting expression of EMT-related Wnt-beta-catenin targets. Moreover, HNF4 alpha may control the switch between the transcriptional and adhesion functions of beta-catenin. Overexpression of HNF4 alpha was found to completely compromise the Wnt-beta-catenin-signaling-induced EMT phenotype. Finally, we determined the regulation pattern between Wnt-beta-catenin signaling and HNF4 alpha in rat tumor models. Our studies have identified a double-negative feedback mechanism controlling Wnt-beta-catenin signaling and HNF4 alpha expression in vitro and in vivo, which sheds new light on the regulation of EMT in HCC. The modulation of these molecular processes may be a method of inhibiting HCC invasion by blocking Wnt-beta-catenin signaling or restoring HNF4 alpha expression to prevent EMT.