Molecular pathogenesis of hepatocellular carcinoma: altering transforming growth factor-β signaling in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) occurs subsequent to liver injury, where regenerative hepatocytes develop into a dysplastic nodule and then early HCC, supporting the multistep hepatocarcinogenesis theory. Molecular alterations such as the p53 mutation, p16 gene silencing, and AKT signaling activation are found in the late stage of HCC progression. The overexpression of some marker molecules is observed at the early stage. Transforming growth factor-β (TGF-β), a potent inhibitor of cell proliferation, is frequently overexpressed in HCC, although the role of TGF-β signaling during HCC development remains controversial. We previously reported that HCC cells show TGF-β receptor-dependent growth inhibition in response to TGF-β. Also, reduced TGF-β receptor II in HCC correlates with intrahepatic metastasis and shorter time-to-recurrence, suggesting a role of TGF-β signaling in tumor suppression. In contrast, TGF-β overexpression in HCC is known to correlate with malignant potential, suggesting a role in tumor promotion. Enhanced formation of stroma is a feature of advanced HCC, and TGF-β also promotes the proliferation of stromal fibroblasts. The microenvironment produced via tumor-stromal interactions may be the key to the modulation of the dual roles of TGF-β signaling in HCC progression.