SUMMARY Hepatitis C virus (HCV) chronically infects 3% of the world’s population, and complications from HCV are the leading indication for liver transplantation. Given the need for better anti-HCV therapies, one strategy is to identify and target cellular cofactors of the virus lifecycle. Using a genome-wide siRNA library, we identified 96 human genes that support HCV replication, with a significant number of them being involved in vesicle organization and biogenesis. Phosphatidylinositol 4-kinase PI4KA and multiple subunits of the COPI vesicle coat complex were among the genes identified. Consistent with this, pharmacologic inhibitors of COPI and PI4KA blocked HCV replication. Targeting hepcidin, a peptide critical for iron homeostasis, also affected HCV replication, which may explain the known dysregulation of iron homeostasis in HCV infection. The host cofactors for HCV replication identified in this study should serve as a useful resource in delineating new targets for anti-HCV therapies.

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Emerging data have indicated that hepatitis C virus (HCV) subverts the host antiviral response to ensure its persistence. We previously demonstrated that HCV protein expression suppresses type I interferon (IFN) signaling by leading to the reduction of phosphorylated STAT1 (P-STAT1). We also demonstrated that HCV core protein directly bound to STAT1. However, the detailed mechanisms by which HCV core protein impacts IFN signaling components have not been fully clarified. In this report, we show that the STAT1 interaction domain resides in the N-terminal portion of HCV core (amino acids [aa] 1 to 23). This domain is also required to produce P-STAT1 reduction and inhibit IFN signaling transduction. Conversely, the C-terminal region of STAT1, specifically the SH2 domain (aa 577 to 684), is required for the interaction of HCV core with STAT1. The STAT1 SH2 domain is critical for STAT1 hetero-or homodimerization. We propose a model by which the binding of HCV core to STAT1 results in decreased P-STAT, blocked STAT1 heterodimerization to STAT2, and, therefore, reduced IFN-stimulated gene factor-3 binding to DNA and disrupted IFN-stimulated gene transcription. Hepatitis C virus (HCV)is an enveloped, single-stranded RNA virus member of the family Flaviviridae. Its 9.6-kb genome includes a 5Ј untranslated region that acts as an internal ribosome entry site (IRES). The IRES directs the translation of a single open reading frame encoding the 3,010-amino-acid polyprotein, which is posttranslationally cleaved by host and virus-encoded protease into mature structural and nonstructural proteins (1, 14). The structural proteins include core, which forms the HCV viral nucleocapsid, and two envelope glycoproteins, E1 and E2 (31). The HCV structural proteins are cleaved and further processed to generate the mature and stable form of p21 HCV core (amino acids 1 to 191) (43). The nonstructural proteins NS2 through NS5 support viral RNA replication. For example, the NS3/4A protease catalyzes the posttranslational processing of nonstructural proteins from the viral polyprotein. NS5B encodes the HCV-encoded RNA-dependent RNA polymerase that is critical for HCV RNA replication. The HCV core protein has been found to be primarily located within the membranes of cytoplasmic organelles. The C terminus of HCV core is hydrophobic, while the N-terminal domain of HCV core is basic (33).HCV infection causes the development of chronic hepatitis and progression to liver cirrhosis and hepatocellular carcinoma. More than 170 million people are infected with HCV worldwide. Alpha interferon (IFN-␣) alone or in combination with ribavirin is the only currently approved treatment for HCV infection (9). Unfortunately, in many genotype 1 HCVinfected patients, HCV is refractory to the action of interferon (15). The precise mechanisms for HCV persistence are still not fully understood (21); thus, a more detailed understanding of virus-host interactions is critical.Viral infection stimulates the host type I IFN pathway. Following binding of secreted IFN to t...