Elucidating Novel Hepatitis C Virus–Host Interactions Using Combined Mass Spectrometry and Functional Genomics Approaches*

More than 170 million people worldwide are infected with the hepatitis C virus (HCV), for which future therapies are expected to rely upon a combination of oral antivirals. For a rapidly evolving virus like HCV, host-targeting antivirals are an attractive option. To decipher the role of novel HCV–host interactions, we used a proteomics approach combining immunoprecipitation of viral–host protein complexes coupled to mass spectrometry identification and functional genomics RNA interference screening of HCV partners. Here, we report the proteomics analyses of protein complexes associated with Core, NS2, NS3/4A, NS4B, NS5A, and NS5B proteins. We identified a stringent set of 98 human proteins interacting specifically with one of the viral proteins. The overlap with previous virus–host interaction studies demonstrates 24.5% shared HCV interactors overall (24/98), illustrating the reliability of the approach. The identified human proteins show enriched Gene Ontology terms associated with the endoplasmic reticulum, transport proteins with a major contribution of NS3/4A interactors, and transmembrane proteins for Core interactors. The interaction network emphasizes a high degree distribution, a high betweenness distribution, and high interconnectivity of targeted human proteins, in agreement with previous virus–host interactome studies. The set of HCV interactors also shows extensive enrichment for known targets of other viruses. The combined proteomic and gene silencing study revealed strong enrichment in modulators of HCV RNA replication, with the identification of 11 novel cofactors among our set of specific HCV partners. Finally, we report a novel immune evasion mechanism of NS3/4A protein based on its ability to affect nucleocytoplasmic transport of type I interferon-mediated signal transducer and activator of transcription 1 nuclear translocation. The study revealed highly stringent association between HCV interactors and their functional contribution to the viral replication cycle and pathogenesis.