Downregulation of A20 increases the cytotoxicity of IFN-γ in hepatocellular carcinoma cells

Lei Yin,* Zheng Fang,* Ning-jia Shen, Ying-he Qiu, Ai-jun Li, Yong-jie Zhang The Second Department of Biliary Surgery, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China *These authors contributed equally to this work Abstract: Hepatocellular carcinoma (HCC) is a highly fatal disease mandating development of novel, effective therapeutic strategy. Interferon-gamma (IFN-γ) is a pleiotropic cytokine with immunomodulatory, antiviral, and antitumor effects. Although IFN-γ is a promising antitumor agent, its application is limited by resistance in tumor cells. A20 is a zinc-finger protein that was initially identified as a gene product induced by tumor necrosis factor α in human umbilical vein endothelial cells. In this study, we found that silencing of A20 combined with IFN-γ significantly represses cell viability, and induces apoptosis and cell-cycle arrest in HCC cells. By investigating mechanisms implicated in A20 and IFN-γ-mediated signaling pathways, we revealed that the phosphoinositide 3-kinase/Akt signaling pathway and antiapoptotic B-cell lymphoma 2 proteins were repressed. Moreover, we also found that phosphorylation of STAT1 and STAT3 was significantly enhanced after the downregulation of A20 in combination with treatment of IFN-γ. Inhibitor of STAT1 but not STAT3 could block the antitumor effect of IFN-γ. Therefore, targeting A20 enhances the cytotoxicity of IFN-γ against HCC cells and may present a promising therapeutic strategy for HCC. Keywords: IFN-γ, A20, hepatocellular carcinoma, PI3K/Akt, STAT1, STAT3