Transforming growth factor betas and their signaling receptors in human hepatocellular carcinoma

BACKGROUND: Transforming growth factor betas (TGF-βs) are multifunctional polypeptides that have been suggested to influence tumor growth. They mediate their functions via specific cell surface receptors (type I ALK5 and type II TGF-β receptors). The aim of this study was to analyze the roles of the three TGF-βs and their signaling receptors in human hepatocellular carcinoma (HCC). METHODS: HCC tissue samples were obtained from 18 patients undergoing partial liver resection. Normal liver tissues from 7 females and 3 males served as controls. The tissues for histological analysis were fixed in Bouin's solution and paraffin embedded. For RNA analysis, freshly obtained tissue samples were snap frozen in liquid nitrogen and stored at -80°C until used. Northern blot analysis was used in normal liver and HCC to examine the expression of TGF-β1, -β2, -β3 and their receptors: type I ALK5 (TβR-I ALK5), type II (TβR-II), and type III (TβR- III). Immunohistochemistry was performed to localize the corresponding proteins. RESULTS: All three TGF-βs demonstrated a marked mRNA overexpression in HCC in comparison with normal controls, whereas the levels of all three TGF-β receptors showed no significant changes. Intense TGF- β1, TGF-β2, and TGF-β3 immunostaining was found in hepatocellular carcinoma cells and in the perineoplastic stroma with immunohistochemistry, whereas no or mild immunostaining was present in the normal liver. For TβR- I ALK5 and TβR-II, the immunostaining in both HCC and normal liver was mild to moderate, with a slightly higher intensity in the normal tissues. CONCLUSION: The upregulation of TGF-βs in HCC suggests an important role for these isoforms in hepatic carcinogenesis and tumor progression. Moreover, the localization of the immunoreactivity in both malignant hepatocytes and stromal cells suggests that TGF-βs act via autocrine and paracrine pathways in this neoplasm.