Identification of effectors of the Interferon-induced Antiviral response against Hepatitis C Virus

Persistent infection with the hepatitis C virus (HCV) may lead to chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Current therapy relies on the antiviral activity of interferon-alpha (IFN-alpha) that is given alone or in combination with ribavirin. However, treatment outcomes for the most prevalent genotypes are still not optimal, and side effects limit therapy success. Moreover, antiviral T cell responses targeting HCV appear to be mediated primarily by IFN-gamma, but the effectors responsible for replication inhibition are not known. IFNs induce the expression of a multitude of IFN-stimulated genes (ISGs), but for the majority, little is known about their anti-HCV potential and mode-of-action. Here we report a novel RNAi-based screening assay designed to identify ISGs contributing to the inhibition of HCV replication. The assay is based on the restoration of viral replication in the presence of IFNs by knockdown of ISGs. In this way we identified 6 ISGs with previously unreported antiviral activity. One of them was specific for IFN-alpha, one for IFN-gamma and 4 were induced by either cytokine, demonstrating a substantial overlap of the respective signalling and effector pathways. Combinatorial knockdowns of these ISGs after IFN treatment suggest additive effects. In conclusion, our study identifies several ISGs contributing to the block of HCV replication by type 1 and type 2 IFN and they suggest that inhibition is conferred by the combined action of several ISGs.