Double-stranded RNA-activated protein kinase inhibits hepatitis C virus replication but may be not essential in interferon treatment

Fowl adenovirus serotype 4 52/55k protein triggers PKR degradation by ubiquitin-proteasome system to evade effective innate immunity

The pro- and inflammatory cytokines fail to effectively inhibit FAdV-4, which has always puzzled us. In the current study, the data determined that the mRNA levels of interferons were significantly enhanced in the livers and LMH cells from 24 h to 72 h post FAdV-4 infection. But the viral load of FAdV-4 was still significantly increased, which meant that FAdV-4 evaded innate immune response. We additionally revealed that the protein levels not mRNA levels of PKR were degraded in host cell at 48 h post FAdV-4 infection. Moreover, the results of over expression and silent expression of PKR revealed that PKR could inhibit FAdV-4 proliferation. These results indicated that FAdV-4 degraded the protein levels of PKR to evade innate immune response. We also found that the protein degradation levels of PKR induced by FAdV-4 were recovery in LHM cells after treatment with proteasome inhibitor MG132, and ubiquitin-specific proteases inhibitor DUB-IN-1. Furthermore, our current data presented that FAdV-4 52/55 K protein directly interacted with PKR and degraded it determined by Co-immunoprecipitation and immunofluorescence. We also determined that 52/55 K protein triggered PKR degradation, and the degradation of PKR could be recovery in LHM cells after treatment with MG132, or DUB-IN-1, respectively. Finally, our data demonstrated that 52/55 K protein was a ubiquitylase that could directly degrade PKR protein in host cells via the ubiquitin-proteasome pathway. Therefore, the current study firstly revealed that FAdV-4 52/55 K protein played the key role in triggering PKR degradation by ubiquitin-proteasome system pathway to escape from innate immunity response.

Interferon-stimulated genes and their role in controlling hepatitis C virus

Infections with the hepatitis C virus (HCV) are a major cause of chronic liver disease. While the acute phase of infection is mostly asymptomatic, this virus has the high propensity to establish persistence and in the course of one to several decades liver disease can develop. HCV is a paradigm for the complex interplay between the interferon (IFN) system and viral countermeasures. The virus induces an IFN response within the infected cell and is rather sensitive against the antiviral state triggered by IFNs, yet in most cases HCV persists. Numerous IFN-stimulated genes (ISGs) have been reported to suppress HCV replication, but in only a few cases we begin to understand the molecular mechanisms underlying antiviral activity. It is becoming increasingly clear that blockage of viral replication is mediated by the concerted action of multiple ISGs that target different steps of the HCV replication cycle. This review briefly summarizes the activation of the IFN system by HCV and then focuses on ISGs targeting the HCV replication cycle and their possible mode of action.

Innate immune responses in hepatitis C virus infection

Hepatitis C virus (HCV) is a major causative agent of chronic hepatitis and hepatocellular carcinoma worldwide and thus poses a significant public health threat. A hallmark of HCV infection is the extraordinary ability of the virus to persist in a majority of infected people. Innate immune responses represent the front line of defense of the human body against HCV immediately after infection. They also play a crucial role in orchestrating subsequent HCV-specific adaptive immunity that is pivotal for viral clearance. Accumulating evidence suggests that the host has evolved multifaceted innate immune mechanisms to sense HCV infection and elicit defense responses, while HCV has developed elaborate strategies to circumvent many of these. Defining the interplay of HCV with host innate immunity reveals mechanistic insights into hepatitis C pathogenesis and informs approaches to therapy. In this review, we summarize recent advances in understanding innate immune responses to HCV infection, focusing on induction and effector mechanisms of the interferon antiviral response as well as the evasion strategies of HCV.

Preactivation of the interferon signalling in liver is correlated with nonresponse to interferon alpha therapy in patients chronically infected with hepatitis B virus

Interferon alpha (IFN-α) therapy is widely used to treat patients with chronic hepatitis B (CHB) but the sustained response rate is low, and the molecular mechanisms for the ineffectiveness of IFN-α treatments are not known. We screened differentially expressed genes between responders (Rs) and nonresponders (NRs) in patients with CHB treated with IFN-α to explore the molecular basis for treatment failure. Expression profiling was performed on percutaneous needle liver biopsy specimens taken before therapy. Gene expression levels were compared between seven patients who did not respond to therapy (NR) and six who did respond (R). Gene ontology category and KEGG pathway were analysed for differentially expressed genes, and the selected differentially expressed genes were confirmed using real-time polymerase chain reaction. We identified 3592 genes whose expression levels differed significantly between all Rs and NRs (P < 0.05); many of these genes are IFN-stimulated genes (ISGs) and immune-related genes. The ISGs were more highly expressed, while immune-related genes were inhibited in NRs before IFN-α treatment. Two ISGs (CEB1 and USP18) that are linked in an IFN inhibitory pathway are highly expressed in NRs, and a potential antiviral gene ISG20 was inhibited in NRs, suggesting a possible rationale for treatment nonresponse. Patients who do or do not respond to IFN have different liver gene expression profiles before IFN-α treatment. Preactivation of the IFN signalling pathway leading to the increased expression of inhibitory ISGs and inhibition of immune response in the pretreatment livers was associated with treatment failure.

Induction and evasion of innate antiviral responses by hepatitis C virus

Persistent hepatitis C virus infection is associated with progressive hepatic fibrosis and liver cancer. Acute infection evokes several distinct innate immune responses, but these are partially or completely countered by the virus. Hepatitis C virus proteins serve dual functions in replication and immune evasion, acting to disrupt cellular signaling pathways leading to interferon synthesis, subvert Jak-STAT signaling to limit expression of interferon-stimulated genes, and block antiviral activities of interferon-stimulated genes. The net effect is a multilayered evasion of innate immunity, which negatively influences the subsequent development of antigen-specific adaptive immunity, thereby contributing to virus persistence and resistance to therapy.