HCV Activates Protein Kinase R and Attenuates Interferon-Induced MHC Class I Expression to Circumvent CD8+ T-Cell Responses

Abstract

Background and AimsMajor histocompatibility complex (MHC) class I-restricted CD8+ T cells are required for clearance of hepatitis C virus (HCV) infection. MHC class I expression is up-regulated by type I and II interferons (IFNs). This study aimed to investigate the effect of HCV infection on IFN-induced expression of MHC class I and its regulatory mechanisms.MethodsHCV cell culture system (HCVcc)-infected Huh-7.5 cells with the genotype 2a Japanese fulminant hepatitis-1 strain were analyzed by flow cytometry, metabolic labeling, immunoprecipitation, and immunoblotting analyses. Protein kinase R (PKR) was knocked down with lentiviruses expressing small hairpin RNAs. Functional effects of MHC class I regulation by HCV were demonstrated in co-culture studies, using HCV-specific CD8+ T cells.ResultsBaseline level of MHC class I was not affected by HCV infection. However, IFN-induced expression of MHC class I was notably attenuated in HCV-infected cells. This was associated with replicating HCV RNA, not viral protein. HCV infection reduced IFN-induced synthesis of MHC class I protein and induced phosphorylation of PKR and eIF2α. IFN-induced MHC class I expression was restored by small hairpin RNA-mediated knockdown of PKR in HCV-infected cells. Co-culture of HCV-specific CD8+ T cells and HCV-infected cells expressing HLA-A2 demonstrated that HCV infection reduced the effector functions of HCV-specific CD8+ T cells; these were restored by small hairpin RNA-mediated knockdown of PKR.ConclusionsIFN-induced expression of MHC class I is attenuated in HCV-infected cells by activation of PKR, which reduces the effector functions of HCV-specific CD8+ T cells. This appears to be an important mechanism by which HCV circumvents antiviral adaptive immune responses. Background and AimsMajor histocompatibility complex (MHC) class I-restricted CD8+ T cells are required for clearance of hepatitis C virus (HCV) infection. MHC class I expression is up-regulated by type I and II interferons (IFNs). This study aimed to investigate the effect of HCV infection on IFN-induced expression of MHC class I and its regulatory mechanisms. Major histocompatibility complex (MHC) class I-restricted CD8+ T cells are required for clearance of hepatitis C virus (HCV) infection. MHC class I expression is up-regulated by type I and II interferons (IFNs). This study aimed to investigate the effect of HCV infection on IFN-induced expression of MHC class I and its regulatory mechanisms. MethodsHCV cell culture system (HCVcc)-infected Huh-7.5 cells with the genotype 2a Japanese fulminant hepatitis-1 strain were analyzed by flow cytometry, metabolic labeling, immunoprecipitation, and immunoblotting analyses. Protein kinase R (PKR) was knocked down with lentiviruses expressing small hairpin RNAs. Functional effects of MHC class I regulation by HCV were demonstrated in co-culture studies, using HCV-specific CD8+ T cells. HCV cell culture system (HCVcc)-infected Huh-7.5 cells with the genotype 2a Japanese fulminant hepatitis-1 strain were analyzed by flow cytometry, metabolic labeling, immunoprecipitation, and immunoblotting analyses. Protein kinase R (PKR) was knocked down with lentiviruses expressing small hairpin RNAs. Functional effects of MHC class I regulation by HCV were demonstrated in co-culture studies, using HCV-specific CD8+ T cells. ResultsBaseline level of MHC class I was not affected by HCV infection. However, IFN-induced expression of MHC class I was notably attenuated in HCV-infected cells. This was associated with replicating HCV RNA, not viral protein. HCV infection reduced IFN-induced synthesis of MHC class I protein and induced phosphorylation of PKR and eIF2α. IFN-induced MHC class I expression was restored by small hairpin RNA-mediated knockdown of PKR in HCV-infected cells. Co-culture of HCV-specific CD8+ T cells and HCV-infected cells expressing HLA-A2 demonstrated that HCV infection reduced the effector functions of HCV-specific CD8+ T cells; these were restored by small hairpin RNA-mediated knockdown of PKR. Baseline level of MHC class I was not affected by HCV infection. However, IFN-induced expression of MHC class I was notably attenuated in HCV-infected cells. This was associated with replicating HCV RNA, not viral protein. HCV infection reduced IFN-induced synthesis of MHC class I protein and induced phosphorylation of PKR and eIF2α. IFN-induced MHC class I expression was restored by small hairpin RNA-mediated knockdown of PKR in HCV-infected cells. Co-culture of HCV-specific CD8+ T cells and HCV-infected cells expressing HLA-A2 demonstrated that HCV infection reduced the effector functions of HCV-specific CD8+ T cells; these were restored by small hairpin RNA-mediated knockdown of PKR. ConclusionsIFN-induced expression of MHC class I is attenuated in HCV-infected cells by activation of PKR, which reduces the effector functions of HCV-specific CD8+ T cells. This appears to be an important mechanism by which HCV circumvents antiviral adaptive immune responses. IFN-induced expression of MHC class I is attenuated in HCV-infected cells by activation of PKR, which reduces the effector functions of HCV-specific CD8+ T cells. This appears to be an important mechanism by which HCV circumvents antiviral adaptive immune responses.