Research ArticleControl of temporal activation of hepatitis C virus-induced interferon response by domain 2 of nonstructural protein 5A

Background & AimsHepatitis C virus (HCV) nonstructural protein 5A (NS5A) is a multifunctional protein playing a crucial role in diverse steps of the viral replication cycle and perturbing multiple host cell pathways. We showed previously that removal of a region in domain 2 (D2) of NS5A (mutant NS5AD2Δ) is dispensable for viral replication in hepatoma cell lines. By using a mouse model and immune-competent cell systems, we studied the role of D2 in controlling the innate immune response.MethodsIn vivo replication competence of NS5AD2Δ was studied in transgenic mice with human liver xenografts. Results were validated using primary human hepatocytes (PHHs) and mechanistic analyses were conducted in engineered Huh7 hepatoma cells with reconstituted innate signaling pathways.ResultsAlthough the deletion in NS5A removed most of the interferon (IFN) sensitivity determining-region, mutant NS5AD2Δ was as sensitive as the wild type to IFN-α and IFN-λ in vitro, but severely attenuated in vivo. This attenuation could be recapitulated in PHHs and was linked to higher activation of the IFN response, concomitant with reduced viral replication and virus production. Importantly, immune-reconstituted Huh7-derived cell lines revealed a sequential activation of the IFN-response via RIG-I (retinoic acid-inducible gene I) and MDA5 (Myeloma differentiation associated factor 5), respectively, that was significantly higher in the case of the mutant lacking most of NS5A D2.ConclusionsOur study reveals an important role of NS5A D2 for suppression of the IFN response that is activated by HCV via RIG-I and MDA5 in a sequential manner.