Genetic and epigenetic inactivation of T-cadherin in human hepatocellular carcinoma cells

Abstract

T-cadherin is an atypical cadherin and growing evidence has indicated that T-cadherin exerts tumor-suppressive effects on cancers of epithelial cell type and also causes positive effects on tumor angiogenesis. Human hepatocellular carcinoma (HCC) is a hypervascular tumor and T-cadherin has been shown to be overexpressed in intratumoral endothelial cells of HCCs. However, the expression status and functions of T-cadherin in hepatocytes or HCC cells remain unclear. Here, we demonstrated that T-cadherin was underexpressed in HCC cells (26.5%, 13/49 cases), but was frequently (77.6%, 38/49) overexpressed in intratumoral endothelial cells immunohistochemically. Semiquantitative RT-PCR analysis also showed that the T-cadherin gene was underexpressed in 7 of 11 HCC cell lines. Loss of heterozygosity analysis revealed that 32-38% of the 42 human HCC samples had allelic losses at this locus. Upon pharmacological treatment with demethylating agent 5-aza-2'-deoxycytidine or histone deacetylase inhibitor trichostatin A, T-cadherin promoter hypermethylation and/or histone deacetylation was frequently observed in HCC samples and cell lines. Functionally, enforced expression of T-cadherin induced G(2)/M cell cycle arrest, reduced cell proliferation in low serum medium, suppressed anchorage-independent growth in soft agar and increased sensitivity to TNFalpha-mediated apoptosis in HCC cells. Intriguingly, we found that T-cadherin significantly suppressed the activity of c-Jun, a crucial oncoprotein constitutively activated in HCC cells. To conclude, T-cadherin was differentially expressed in human HCCs. The underexpression of T-cadherin in HCC cells suggests it may be another critical event in addition to T-cadherin-mediated angiogenesis during HCC development.