Identification of Type I and Type II Interferon-Induced Effectors Controlling Hepatitis C Virus Replication

Persistent infection with hepatitis C virus (HCV) can lead to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. All current therapies of hepatitis C include interferon-alpha (IFN-alpha). Moreover, IFN-gamma (IFN-gamma), the only type II IFN, strongly inhibits HCV replication in vitro and is the primary mediator of HCV-specific antiviral T-cell responses. However, for both cytokines the precise set of effector protein(s) responsible for replication inhibition is not known. The aim of this study was the identification of IFN-alpha and IFN-gamma stimulated genes (ISGs) responsible for controlling HCV replication. We devised an RNA interference (RNAi)-based "gain of function" screen and identified, in addition to known ISGs earlier reported to suppress HCV replication, several new ones with proven antiviral activity. These include IFIT3 (IFN-induced protein with tetratricopeptide repeats 3), TRIM14 (tripartite motif containing 14), PLSCR1 (phospholipid scramblase 1), and NOS2 (nitric oxide synthase 2, inducible). All ISGs identified in this study were up-regulated both by IFN-alpha and IFN-gamma, demonstrating a substantial overlap of HCV-specific effectors induced by either cytolcine. Nevertheless, some ISGs were more specific for IFN-alpha or IFN-gamma, which was most pronounced in case of PLSCR1 and NOS2 that were identified as main effectors of IFN-gamma-mediated anti-HCV activity. Combinatorial knockdowns of ISGs suggest additive or synergistic effects demonstrating that with either IFN, inhibition of HCV replication is caused by the combined action of multiple ISGs. Conclusion: Our study identifies a number of novel ISGs contributing to the suppression of HCV replication by type I and type II IFN. We demonstrate a substantial overlap of antiviral programs triggered by either cytokine and show that suppression of HCV replication is mediated by the concerted action of multiple effectors. (HEPATOLOGY 2012;56:2082-2093)