Importin [beta]1 targeting by hepatitis C virus NS3/4A protein restricts IRF3 and NF-[kappa]B signaling of IFNB1 antiviral response

In this study, newly identified host interactors of hepatitis C virus (HCV) proteins were assessed for a role in modulating the innate immune response. The analysis revealed enrichment for components of the nuclear transport machinery and the crucial interaction with NS3/4A protein in suppression of interferon-[beta] (IFNB1) induction. Using a comprehensive microscopy-based high-content screening approach combined to the gene silencing of nuclear transport factors, we showed that NS3/4A-interacting proteins control the nucleocytoplasmic trafficking of IFN regulatory factor 3 (IRF3) and NF-[kappa]B p65 upon Sendai virus (SeV) infection. Notably, importin [beta]1 (IMP[beta]1) knockdown--a hub protein highly targeted by several viruses--decreases the nuclear translocation of both transcription factors and prevents IFNB1 and IFIT1 induction, correlating with a rapid increased of viral proteins and virus-mediated apoptosis. Here we show that NS3/4A triggers the cleavage of IMP[beta]1 and inhibits nuclear transport to disrupt IFNB1 production. Importantly, mutated IMP[beta]1 resistant to cleavage completely restores signaling, similar to the treatment with BILN 2061 protease inhibitor, correlating with the disappearance of cleavage products. Overall, the data indicate that HCV NS3/4A targeting of IMP[beta]1 and related modulators of IRF3 and NF-[kappa]B nuclear transport constitute an important innate immune subversion strategy and inspire new avenues for broad-spectrum antiviral therapies.