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Inhibition of RIG-I-Dependent Signaling to the Interferon Pathway during Hepatitis C Virus Expression and Restoration of Signaling by IKKɛ

American Society for Microbiology
Publication Date
  • Virus-Cell Interactions
  • Biology
  • Medicine


Interferon (IFN) is one important effector of the innate immune response, induced by different viral or bacterial components through Toll-like receptor (TLR)-dependent and -independent mechanisms. As part of its pathogenic strategy, hepatitis C virus (HCV) interferes with the innate immune response and induction of IFN-β via the HCV NS3/4A protease activity which inhibits phosphorylation of IRF-3, a key transcriptional regulator of the IFN response. In the present study, we demonstrate that inhibition by the protease occurs upstream of the noncanonical IKK-related kinases IKKɛ and TBK-1, which phosphorylate IRF-3, through partial inhibition of the TLR adapter protein TRIF/TICAM1-dependent pathway. Use of TRIF−/− mouse embryo fibroblasts however revealed the presence of a TRIF-independent pathway involved in IFN induction that was also inhibited by NS3/4A. Importantly, we show that NS3/4A can strongly inhibit the ability of the recently described RIG-I protein to activate IFN, suggesting that RIG-I is a key factor in the TRIF-independent, NS3/4A-sensitive pathway. Expression of IFN signaling components including IKKɛ, TBK-1, TRIF, and wild type or constitutively active forms of RIG-I in the HCV replicon cells resulted in IFN-β promoter transactivation, with IKKɛ displaying the highest efficiency. Subsequently, overexpression of IKKɛ resulted in 80% inhibition of both the positive and negative replicative strands of the HCV replicon. The partial restoration of the capacity of the host cell to transcribe IFN-β indicates that IKKɛ expression is able to bypass the HCV-mediated inhibition and restore the innate antiviral response.

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