C-terminus-truncated hepatitis B virus X protein enhances cell invasiveness in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the fifth of major malignancies worldwide and chronic hepatitis B virus (HBV) infection is one of its well known risk factors. Random integration of the HBV DNA into host genome is frequent in human HCCs and this leads to truncation of the HBV DNA, particularly at the C-terminal end of the HBV X protein (HBx). In this study, we investigated the frequency of this C-terminal truncation of HBx in human HCCs and its functional significance in HCC cells. In the 51 HBV-positive patients with HCC, full-length HBx was detected in all of the non-tumorous livers. Interestingly, natural COOH-truncated HBx was found in 47% tumours. Upon clinicopathological analysis, presence of natural COOH-truncated HBx significantly correlated with the presence of venous invasion, a hallmark of metastasis (p < 0.01). Doxycycline- inducible stable expression of the full-length HBx and C-terminal truncated forms of HBx in HepG2 cells was employed for in vitro cell invasion assay and cell signalling analysis involved in cell invasiveness. Inducible expression of COOH-truncated HBx protein (with 24 amino acids truncated at C-terminal end) in HepG2 cells enhanced cell invasiveness, and C-Jun transcriptional activity, and increased MMP10 transcription production, as compared with the full-length HBx. The activation of the MMP10 promoter by the COOH-truncated HBx was abolished when the AP-1 binding sites were mutated. Our data suggest that COOH-truncation of HBx may play a significant role in enhancing cell invasiveness and metastasis in HCC, possibly via activation of the MMP10 through C-Jun signaling pathway.