Evasion of interferon signalling by hepatitis C virus non-structural protein 5A and the role of cyclophilin A

Abstract

Hepatitis C virus (HCV) is a positive-sense single stranded RNA (+ssRNA) virus that has immense impacts globally. Immune evasion results in chronic infection, which is a leading cause of liver cirrhosis, hepatocellular carcinoma (HCC), end-stage liver disease, and liver transplants. Currently, direct acting antivirals (DAAs) can cure HCV infection, although these do not undo the pathological damage caused by HCV and there is no vaccine to prevent infection. Cyclophilin A (CypA), a cellular peptidyl-prolyl cis-trans isomerase (PPIase), is a well-established host factor the supports HCV infection, although its specific roles are not fully understood. CypA is known to regulate innate immune pathways, like the interferon (IFN) response, which typically induce an antiviral state that restricts HCV replication. However, this has not yet been studied in cell lines relevant to HCV infection. Furthermore, HCV non-structural 5A (NS5A) protein has been shown to have inhibitory effects on the IFN response. Interestingly, NS5A interacts with CypA, which is proposed to aid in HCV replication. Here, we investigated the role of the CypA-NS5A interaction in evasion of IFN responses, which is not well understood and requires further evaluation. In this study, we show that CypA positively enhances the IFN signaling pathway in hepatoma cell lines, particularly at the stages of STAT1 phosphorylation and nuclear translocation. Furthermore, expression of NS5A was shown to inhibit IFN signaling in a CypA-dependent manner, indicating IFN response evasion. Specifically, our data suggest that NS5A antagonizes IFN signaling by disrupting STAT1 nuclear translocation. In terms of authentic HCV infection, NS5A genotype does not greatly impact HCV RNA replication, or expression of IFN stimulated genes (ISGs) such as myxovirus resistance protein 1 (MX1) or guanylate binding protein 1 (GBP1). Interestingly, CypA influences IFN signaling and sensitivity of HCV to IFN. Overall, these findings provide insight into the mechanism of HCV NS5A-mediated evasion of IFN signaling and the role of CypA in this process. Since CypA has been implicated as a host factor for other viruses, our findings may broadly inform understanding of viral immune evasion strategies.