Abstract 814: Truncated HBx-dependent silencing of growth arrest-specific 2 promotes hepatocarcinogenesis through inhibition of p53-mediated apoptosis

Abstract

Abstract Hepatocellular carcinoma (HCC) is a worldwide threat to public health, especially in China where chronic hepatitis B virus (HBV) infection is found in 80-90% of all HCCs. The HBV encoded X antigen (HBx) is a trans-regulatory protein involved in the virus-induced hepatocarcinogenesis. Although the carboxyl-terminus truncated HBx, rather than the full-length counterpart, is frequently overexpressed in human HCCs, its functional mechanisms have yet been fully defined. In this study, we investigated the molecular pathogenesis of a naturally-occurring HBx variant which has 35 amino acids deleted at C-terminus (HBxΔ35). By performing genome-wide scanning analysis and PCR validation, we identified growth arrest-specific 2 (GAS2) as a direct target of HBxΔ35 at transcriptional level in human immortalized liver cells. HBxΔ35 was found to bind the promoter region of GAS2 and suppress its expression to promote hepatocellular proliferation and tumorigenicity. Further functional assays showed that overexpression of GAS2 inhibited tumor growth both in vitro and in vivo by inducing p53-dependent apoptosis. Conversely, siRNA-mediated knockdown of GAS2 in hepatocytes attenuated apoptotic response and reduced cell susceptibility to etoposide-induced apoptosis. Notably, GAS2 expression was significantly down-regulated in truncated HBx-expressing HCCs compared with the corresponding normal tissues. In conclusion, our integrated study uncovered a novel viral mechanism in hepatocarcinogenesis, wherein HBxΔ35 ablates p53-driven apoptosis via direct silencing of GAS2, and thereby provides survival advantage for pre-neoplastic hepatocytes to facilitate cancer development. Citation Format: Alfred S. L. Cheng, Ranxu Zhu, Myth T.S. Mok, Wai Kang, Ka-Fai To, Joseph J.Y. Sung, Henry L.Y. Chan. Truncated HBx-dependent silencing of growth arrest-specific 2 promotes hepatocarcinogenesis through inhibition of p53-mediated apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 814. doi:10.1158/1538-7445.AM2015-814