Functional interaction between Wnt3 and Frizzled-7 leads to activation of the Wnt/β-catenin signaling pathway in hepatocellular carcinoma cells

Background/Aims The canonical Wnt signaling is frequently activated in human hepatocellular carcinoma (HCC). We previously demonstrated that upregulation of Frizzled-7 receptor (FZD7) in HCC was associated with nuclear accumulation of wild-type β-catenin. Here, we investigated Wnt ligand(s) that may activate the Wnt/β-catenin pathway through FZD7 in HCC cells. Methods To identify Wnt ligand expression, RT-PCR was performed in HCC cells. To evaluate the function of Wnt3 and FZD7 in HCC, we utilized Wnt3 overexpressing FOCUS HCC cells (FOCUS-Wnt3) and human tumors. Results In hepatitis B virus (HBV)-induced HCC, Wnt3 was upregulated in tumor and peritumoral tissues compared to normal liver and downstream β-catenin target genes were also increased in these samples. Activation of the Wnt/β-catenin pathway in FOCUS-Wnt3 cells was demonstrated by β-catenin accumulation, enhanced TCF transcriptional activity and proliferation rate. The activation of Wnt/β-catenin signaling in FOCUS-Wnt3 was abolished by a knockdown of FZD7 expression by siRNA. More important, a specific Wnt3-FZD7 interaction was observed by co-immunoprecipitation experiments, which suggest that the action of Wnt3 was mediated via FZD7. Conclusions These findings demonstrate a functional interaction between Wnt3 and FZD7 leading to activation of the Wnt/β-catenin signaling pathway in HCC cells and may play a role during hepatocarcinogenesis.