Control of PKR protein kinase by hepatitis C virus nonstructural 5A protein: molecular mechanisms of kinase regulation

Unraveling the dynamics of hepatitis C virus adaptive mutations and their impact on antiviral responses in primary human hepatocytes

Hepatitis C virus (HCV) infection progresses to chronicity in the majority of infected individuals. Its high intra-host genetic variability enables HCV to evade the continuous selection pressure exerted by the host, contributing to persistent infection. Utilizing a cell culture-adapted HCV population (p100pop) which exhibits increased replicative capacity in various liver cell lines, this study investigated virus and host determinants that underlie enhanced viral fitness. Characterization of a panel of molecular p100 clones revealed that cell culture adaptive mutations optimize a range of virus-host interactions, resulting in expanded cell tropism, altered dependence on the cellular co-factor micro-RNA 122 and increased rates of virus spread. On the host side, comparative transcriptional profiling of hepatoma cells infected either with p100pop or its progenitor virus revealed that enhanced replicative fitness correlated with activation of endoplasmic reticulum stress signaling and the unfolded protein response. In contrast, infection of primary human hepatocytes with p100pop led to a mild attenuation of virion production which correlated with a greater induction of cell-intrinsic antiviral defense responses. In summary, long-term passage experiments in cells where selective pressure from innate immunity is lacking improves multiple virus-host interactions, enhancing HCV replicative fitness. However, this study further indicates that HCV has evolved to replicate at low levels in primary human hepatocytes to minimize innate immune activation, highlighting that an optimal balance between replicative fitness and innate immune induction is key to establish persistence.

IMPORTANCE

Hepatitis C virus (HCV) infection remains a global health burden with 58 million people currently chronically infected. However, the detailed molecular mechanisms that underly persistence are incompletely defined. We utilized a long-term cell culture-adapted HCV, exhibiting enhanced replicative fitness in different human liver cell lines, in order to identify molecular principles by which HCV optimizes its replication fitness. Our experimental data revealed that cell culture adaptive mutations confer changes in the host response and usage of various host factors. The latter allows functional flexibility at different stages of the viral replication cycle. However, increased replicative fitness resulted in an increased activation of the innate immune system, which likely poses boundary for functional variation in authentic hepatocytes, explaining the observed attenuation of the adapted virus population in primary hepatocytes.

Hepatitis C virus cell culture adaptive mutations enhance cell culture propagation by multiple mechanisms but boost antiviral responses in primary human hepatocytes

Hepatitis C virus (HCV) infection progresses to chronicity in the majority of infected individuals. Its high intra-host genetic variability enables HCV to evade the continuous selection pressure exerted by the host, contributing to persistent infection. Utilizing a cell culture adapted HCV population (p100pop) which exhibits increased replicative capacity in various liver cell lines, this study investigated virus and host determinants which underlie enhanced viral fitness. Characterization of a panel of molecular p100 clones revealed that cell culture adaptive mutations optimize a range of virus-host interactions, resulting in expanded cell tropism, altered dependence on the cellular co-factor micro-RNA 122 and increased rates of virus spread. On the host side, comparative transcriptional profiling of hepatoma cells infected either with p100pop or its progenitor virus revealed that enhanced replicative fitness correlated with activation of endoplasmic reticulum stress signaling and the unfolded protein response. In contrast, infection of primary human hepatocytes with p100pop led to a mild attenuation of virion production which correlated with a greater induction of cell-intrinsic antiviral defense responses. In summary, long-term passage experiments in cells where selective pressure from innate immunity is lacking improves multiple virus-host interactions, enhancing HCV replicative fitness. However, this study further indicates that HCV has evolved to replicate at low levels in primary human hepatocytes to minimize innate immune activation, highlighting that an optimal balance between replicative fitness and innate immune induction is key to establishing persistence.

Author Summary

HCV infection remains a global health burden with 58 million people currently chronically infected. However, the detailed molecular mechanisms which underly persistence are incompletely defined. We utilized a long-term cell culture adapted HCV, exhibiting enhanced replicative fitness in different human liver cell lines, in order to identify molecular principles by which HCV optimizes its replication fitness. Our experimental data revealed that cell culture adaptive mutations confer changes in the host response and usage of various host factors. The latter allows functional flexibility at different stages of the viral replication cycle. However, increased replicative fitness resulted in an increased activation of the innate immune system, which likely poses boundary for functional variation in authentic hepatocytes, explaining the observed attenuation of the adapted virus population in primary hepatocytes.

Suppression of Innate Immunity by the Hepatitis C Virus (HCV): Revisiting the Specificity of Host-Virus Interactive Pathways

The hepatitis C virus (HCV) is a major causative agent of hepatitis that may also lead to liver cancer and lymphomas. Chronic hepatitis C affects an estimated 2.4 million people in the USA alone. As the sole member of the genus Hepacivirus within the Flaviviridae family, HCV encodes a single-stranded positive-sense RNA genome that is translated into a single large polypeptide, which is then proteolytically processed to yield the individual viral proteins, all of which are necessary for optimal viral infection. However, cellular innate immunity, such as type-I interferon (IFN), promptly thwarts the replication of viruses and other pathogens, which forms the basis of the use of conjugated IFN-alpha in chronic hepatitis C management. As a countermeasure, HCV suppresses this form of immunity by enlisting diverse gene products, such as HCV protease(s), whose primary role is to process the large viral polyprotein into individual proteins of specific function. The exact number of HCV immune suppressors and the specificity and molecular mechanism of their action have remained unclear. Nonetheless, the evasion of host immunity promotes HCV pathogenesis, chronic infection, and carcinogenesis. Here, the known and putative HCV-encoded suppressors of innate immunity have been reviewed and analyzed, with a predominant emphasis on the molecular mechanisms. Clinically, the knowledge should aid in rational interventions and the management of HCV infection, particularly in chronic hepatitis.

Directed natural evolution generates a next-generation oncolytic virus with a high potency and safety profile

Oncolytic viruses (OVs) represent a type of encouraging multi-mechanistic drug for the treatment of cancer. However, attenuation of virulence, which is generally required for the development of OVs based on pathogenic viral backbones, is frequently accompanied by a compromised killing effect on tumor cells. By exploiting the property of viruses to evolve and adapt in cancer cells, we perform directed natural evolution on refractory colorectal cancer cell HCT-116 and generate a next-generation oncolytic virus M1 (NGOVM) with an increase in the oncolytic effect of up to 9690-fold. The NGOVM has a broader antitumor spectrum and a more robust oncolytic effect in a range of solid tumors. Mechanistically, two critical mutations are identified in the E2 and nsP3 genes, which accelerate the entry of M1 virus by increasing its binding to the Mxra8 receptor and antagonize antiviral responses by inhibiting the activation of PKR and STAT1 in tumor cells, respectively. Importantly, the NGOVM is well tolerated in both rodents and nonhuman primates. This study implies that directed natural evolution is a generalizable approach for developing next-generation OVs with an expanded scope of application and high safety.

NS5A domain I antagonises PKR to facilitate the assembly of infectious hepatitis C virus particles

Hepatitis C virus NS5A is a multifunctional phosphoprotein comprised of three domains (DI, DII and DIII). DI and DII have been shown to function in genome replication, whereas DIII has a role in virus assembly. We previously demonstrated that DI in genotype 2a (JFH1) also plays a role in virus assembly, exemplified by the P145A mutant which blocked infectious virus production. Here we extend this analysis to identify two other conserved and surface exposed residues proximal to P145 (C142 and E191) that exhibited no defect in genome replication but impaired virus production. Further analysis revealed changes in the abundance of dsRNA, the size and distribution of lipid droplets (LD) and the co-localisation between NS5A and LDs in cells infected with these mutants, compared to wildtype. In parallel, to investigate the mechanism(s) underpinning this role of DI, we assessed the involvement of the interferon-induced double-stranded RNA-dependent protein kinase (PKR). In PKR-silenced cells, C142A and E191A exhibited levels of infectious virus production, LD size and co-localisation between NS5A and LD that were indistinguishable from wildtype. Co-immunoprecipitation and in vitro pulldown experiments confirmed that wildtype NS5A domain I (but not C142A or E191A) interacted with PKR. We further showed that the assembly phenotype of C142A and E191A was restored by ablation of interferon regulatory factor-1 (IRF1), a downstream effector of PKR. These data suggest a novel interaction between NS5A DI and PKR that functions to evade an antiviral pathway that blocks virus assembly through IRF1.

A short hepatitis C virus NS5A peptide expression by AAV vector modulates human T cell activation and reduces vector immunogenicity

Viral vector-mediated gene therapies have the potential to treat many human diseases; however, host immune responses against the vector and/or the transgene pose a safety risk to the patients and can negatively impact product efficacy. Thus, novel strategies to reduce vector immunogenicity are critical for the advancement of these therapies. T cell activation (TCA) is required for the development of immune responses during gene therapy. We hypothesized that modulation of TCA by incorporating a novel viral immunomodulatory factor into a viral vector may reduce unwanted TCA and immune responses during gene therapy. To test this hypothesis, we identified an immunomodulatory domain of the hepatitis C virus (HCV) NS protein 5A (NS5A) protein and studied the effect of viral vectors expressing NS5A peptide on TCA. Lentiviral vector-mediated expression of a short 20-mer peptide derived from the NS5A protein in human T cells was sufficient to inhibit TCA. Synthetic 20-mer NS5A peptide also inhibited TCA in primary human T cells. Mechanistically, the NS5A protein interacted with Lck and inhibited proximal TCR signaling. Importantly, NS5A peptide expression did not cause global T cell signaling dysfunction as distal T cell signaling was not inhibited. Finally, recombinant adeno-associated virus (AAV) vector expressing the 20-mer NS5A peptide reduced both the recall antigen and the TCR-mediated activation of human T cells and did not cause global T cell signaling dysfunction. Together, these data suggest that expression of a 20-mer NS5A peptide by an AAV vector may reduce unwanted TCA and may contribute to lower vector immunogenicity during gene therapy.

Hepatitis C Virus Nonstructural Protein 5A Interacts with Immunomodulatory Kinase IKKε to Negatively Regulate Innate Antiviral Immunity

Hepatitis C virus (HCV) infection can lead to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. HCV employs diverse strategies to evade host antiviral innate immune responses to mediate a persistent infection. In the present study, we show that nonstructural protein 5A (NS5A) interacts with an NF-κB inhibitor immunomodulatory kinase, IKKε, and subsequently downregulats beta interferon (IFN-β) promoter activity. We further demonstrate that NS5A inhibits DDX3-mediated IKKε and interferon regulatory factor 3 (IRF3) phosphorylation. We also note that hyperphosphorylation of NS5A mediats protein interplay between NS5A and IKKε, thereby contributing to NS5A-mediated modulation of IFN-β signaling. Lastly, NS5A inhibits IKKε-dependent p65 phosphorylation and NF-κB activation. Based on these findings, we propose NS5A as a novel regulator of IFN signaling events, specifically by inhibiting IKKε downstream signaling cascades through its interaction with IKKε. Taken together, these data suggest an additional mechanistic means by which HCV modulates host antiviral innate immune responses to promote persistent viral infection.

dsRNA-induced condensation of antiviral proteins modulates PKR activity

Mammalian cells respond to dsRNA in multiple manners. One key response to dsRNA is the activation of PKR, an eIF2α kinase, which triggers translational arrest and the formation of stress granules. However, the process of PKR activation in cells is not fully understood. In response to increased endogenous or exogenous dsRNA, we observed that PKR forms novel cytosolic condensates, referred to as dsRNA-induced foci (dRIFs). dRIFs contain dsRNA, form in proportion to dsRNA, and are enhanced by longer dsRNAs. dRIFs enrich several other dsRNA-binding proteins, including ADAR1, Stau1, NLRP1, and PACT. Strikingly, dRIFs correlate with and form before translation repression by PKR and localize to regions of cells where PKR activation is initiated. We hypothesize that dRIF formation is a mechanism that cells use to enhance the sensitivity of PKR activation in response to low levels of dsRNA or to overcome viral inhibitors of PKR activation.

The Human Liver-Expressed Lectin CD302 Restricts Hepatitis C Virus Infection

C-type lectin domain-containing proteins (CTLDcps) shape host responses to pathogens and infectious disease outcomes. Previously, we identified the murine CTLDcp Cd302 as restriction factor, limiting hepatitis C virus (HCV) infection of murine hepatocytes. In this study, we investigated in detail the human orthologue's ability to restrict HCV infection in human liver cells. CD302 overexpression in Huh-7.5 cells potently inhibited infection of diverse HCV chimeras representing seven genotypes. Transcriptional profiling revealed abundant CD302 mRNA expression in human hepatocytes, the natural cellular target of HCV. Knockdown of endogenously expressed CD302 modestly enhanced HCV infection of Huh-7.5 cells and primary human hepatocytes. Functional analysis of naturally occurring CD302 transcript variants and engineered CD302 mutants showed that the C-type lectin-like domain (CTLD) is essential for HCV restriction, whereas the cytoplasmic domain (CPD) is dispensable. Coding single nucleotide polymorphisms occurring in human populations and mapping to different domains of CD302 did not influence the capacity of CD302 to restrict HCV. Assessment of the anti-HCV phenotype at different life cycle stages indicated that CD302 preferentially targets the viral entry step. In contrast to the murine orthologue, overexpression of human CD302 did not modulate downstream expression of nuclear receptor-controlled genes. Ectopic CD302 expression restricted infection of liver tropic hepatitis E virus (HEV), while it did not affect infection rates of two respiratory viruses, including respiratory syncytial virus (RSV) and the alpha coronavirus HVCoV-229E. Together, these findings suggest that CD302 contributes to liver cell-intrinsic defense against HCV and might mediate broader antiviral defenses against additional hepatotropic viruses. IMPORTANCE The liver represents an immunoprivileged organ characterized by enhanced resistance to immune responses. However, the importance of liver cell-endogenous, noncytolytic innate immune responses in pathogen control is not well defined. Although the role of myeloid cell-expressed CTLDcps in host responses to viruses has been characterized in detail, we have little information about their potential functions in the liver and their relevance for immune responses in this organ. Human hepatocytes endogenously express the CTLDcp CD302. Here, we provide evidence that CD302 limits HCV infection of human liver cells, likely by inhibiting a viral cell entry step. We confirm that the dominant liver-expressed transcript variant, as well as naturally occurring coding variants of CD302, maintain the capacity to restrict HCV. We further show that the CTLD of the protein is critical for the anti-HCV activity and that overexpressed CD302 limits HEV infection. Thus, CD302 likely contributes to human liver-intrinsic antiviral defenses.

Emerging Roles of Cyclophilin A in Regulating Viral Cloaking

Cellular cyclophilins (Cyps) such as cyclophilin A (CypA) have emerged as key players at the virus-host interface. As host factors required for the replication of many unrelated viruses, including human immunodeficiency virus (HIV), hepatitis C virus (HCV) and coronaviruses (CoVs), Cyps are attractive targets for antiviral therapy. However, a clear understanding of how these viruses exploit Cyps to promote their replication has yet to be elucidated. Recent findings suggest that CypA contributes to cloaking of viral replication intermediates, an evasion strategy that prevents detection of viral nucleic acid by innate immune sensors. Furthermore, Cyps are emerging to have roles in regulation of cellular antiviral signaling pathways. Recruitment of Cyps by viral proteins may interfere with their ability to regulate these signaling factors. Consistent with disruption of viral cloaking and innate immune evasion, treatment with Cyp inhibitors such as cyclosporine A (CsA) restores antiviral innate immunity and induces expression of a subset of antiviral genes that restrict viral infection, which may help to explain the broad antiviral spectrum of CsA. In this review, we provide an overview of the roles of CypA in viral cloaking and evasion of innate immunity, focusing on the underlying mechanisms and new perspectives for antiviral therapies.

Inhibition of PKR by Viruses

Cells respond to viral infections through sensors that detect non-self-molecules, and through effectors, which can have direct antiviral activities or adapt cell physiology to limit viral infection and propagation. Eukaryotic translation initiation factor 2 alpha kinase 2, better known as PKR, acts as both a sensor and an effector in the response to viral infections. After sensing double-stranded RNA molecules in infected cells, PKR self-activates and majorly exerts its antiviral function by blocking the translation machinery and inducing apoptosis. The antiviral potency of PKR is emphasized by the number of strategies developed by viruses to antagonize the PKR pathway. In this review, we present an update on the diversity of such strategies, which range from preventing double-stranded RNA recognition upstream from PKR activation, to activating eIF2B downstream from PKR targets.

Cyclophilins and Their Roles in Hepatitis C Virus and Flavivirus Infections: Perspectives for Novel Antiviral Approaches

Cyclophilins are cellular peptidyl-prolyl isomerases that play an important role in viral infections, with demonstrated roles in the replication of hepatitis C virus (HCV) and other viruses in the Flaviviridae family, such as dengue virus (DENV) and yellow fever virus (YFV). Here, we discuss the roles of cyclophilins in HCV infection and provide a comprehensive overview of the mechanisms underlying the requirement for cyclophilins during HCV replication. Notably, cyclophilin inhibitor therapy has been demonstrated to be effective in reducing HCV replication in chronically infected patients. While the roles of cyclophilins are relatively well-understood for HCV infection, cyclophilins are more recently emerging as host factors for flavivirus infection as well, providing potential new therapeutic avenues for these viral infections which currently lack antiviral therapies. However, further studies are required to elucidate the roles of cyclophilins in flavivirus replication. Here, we review the current knowledge of the role of cyclophilins in HCV infection to provide a conceptual framework to understand how cyclophilins may contribute to other viral infections, such as DENV and YFV. Improved understanding of the roles of cyclophilins in viral infection may open perspectives for the development of cyclophilin inhibitors as effective antiviral therapeutics for HCV and related viruses.

Host Cell Restriction Factors of Bunyaviruses and Viral Countermeasures

The Bunyavirales order comprises more than 500 viruses (generally defined as bunyaviruses) classified into 12 families. Some of these are highly pathogenic viruses infecting different hosts, including humans, mammals, reptiles, arthropods, birds, and/or plants. Host cell sensing of infection activates the innate immune system that aims at inhibiting viral replication and propagation. Upon recognition of pathogen-associated molecular patterns (PAMPs) by cellular pattern recognition receptors (PRRs), numerous signaling cascades are activated, leading to the production of interferons (IFNs). IFNs act in an autocrine and paracrine manner to establish an antiviral state by inducing the expression of hundreds of IFN-stimulated genes (ISGs). Some of these ISGs are known to restrict bunyavirus infection. Along with other constitutively expressed host cellular factors with antiviral activity, these proteins (hereafter referred to as “restriction factors”) target different steps of the viral cycle, including viral entry, genome transcription and replication, and virion egress. In reaction to this, bunyaviruses have developed strategies to circumvent this antiviral response, by avoiding cellular recognition of PAMPs, inhibiting IFN production or interfering with the IFN-mediated response. Herein, we review the current knowledge on host cellular factors that were shown to restrict infections by bunyaviruses. Moreover, we focus on the strategies developed by bunyaviruses in order to escape the antiviral state developed by the infected cells.

The Impact of Hepatitis C Virus Genotypes on Oxidative Stress Markers and Catalase Activity

Hepatitis C virus (HCV) is a major cause of liver disease worldwide. Chronic HCV infections are usually associated with increased oxidative stress in the liver tissue. The intensity of oxidative stress may be a detrimental factor in liver injury and may determine the severity of the disease. The aim of the present case-control study was to determine the level of lipid peroxidation (TBARS), protein oxidative modification (AOPP), and catalase activity in sera of patients infected with HCV, in relation to different HCV genotypes and viral load. Considering the HCV patients with chronic hepatitis C (52) and control subject (50) recruitment, the study was designed as a case-control-type. The HCV RNA isolation, viral load, and HCV genotyping were performed according to the standard protocols. A significant difference compared to control healthy subjects was reported for TBAR (p < 0.001), AOPP (p = 0.001), and catalase activity (p = 0.007). In a gender-based comparison, a significantly higher level of AOPP for females was reported (p < 0.001). As stratified by HCV genotype, the most common was HCV-1 (HCV-1a and HCV 1b), with the overall participation of more than 60%, followed by genotype 3, while the least represented was genotype 2. No significant difference was documented among genotypes in regard to oxidative stress markers, although somewhat higher TBARS level, but not significant, was registered in patients infected with genotype 1b. A statistically significant positive correlation was found between the concentration of HCV genome copies and AOPP (r = 0.344; p = 0.012). A high level of HCV viral load was more likely to have a higher TBARS, but still without statistical significance (p = 0.072). In conclusion, the results obtained confirmed an imbalance between the ROS production and antioxidative defense system in HCV-infected patients. Since oxidative stress may have a profound influence on disease progression, fibrosis, and carcinogenesis, our results may meet the aspirations of mandatory introduction of antioxidants as early HCV therapy to counteract ROS consequences.

Oncolytic Virotherapy: The Cancer Cell Side

Simple Summary

Oncolytic viruses (OVs) are a promising immunotherapy that specifically target and kill cancer cells and stimulate anti-tumor immunity. While different OVs are endowed with distinct features, which enhance their specificity towards tumor cells; attributes of the cancer cell also critically contribute to this specificity. Such features comprise defects in innate immunity, including antiviral responses, and the metabolic reprogramming of the malignant cell. The tumorigenic features which support OV replication can be intrinsic to the transformation process (e.g., a direct consequence of the activity of a given oncogene), or acquired in the course of tumor immunoediting—the selection process applied by antitumor immunity. Oncogene-induced epigenetic silencing plays an important role in negative regulation of immunostimulatory antiviral responses in the cancer cells. Reversal of such silencing may also provide a strong immunostimulant in the form of viral mimicry by activation of endogenous retroelements. Here we review features of the cancer cell that support viral replication, tumor immunoediting and the connection between oncogenic signaling, DNA methylation and viral oncolysis. As such, this review concentrates on the malignant cell, while detailed description of different OVs can be found in the accompanied reviews of this issue.

Abstract

Cell autonomous immunity genes mediate the multiple stages of anti-viral defenses, including recognition of invading pathogens, inhibition of viral replication, reprogramming of cellular metabolism, programmed-cell-death, paracrine induction of antiviral state, and activation of immunostimulatory inflammation. In tumor development and/or immunotherapy settings, selective pressure applied by the immune system results in tumor immunoediting, a reduction in the immunostimulatory potential of the cancer cell. This editing process comprises the reduced expression and/or function of cell autonomous immunity genes, allowing for immune-evasion of the tumor while concomitantly attenuating anti-viral defenses. Combined with the oncogene-enhanced anabolic nature of cancer-cell metabolism, this attenuation of antiviral defenses contributes to viral replication and to the selectivity of oncolytic viruses (OVs) towards malignant cells. Here, we review the manners by which oncogene-mediated transformation and tumor immunoediting combine to alter the intracellular milieu of tumor cells, for the benefit of OV replication. We also explore the functional connection between oncogenic signaling and epigenetic silencing, and the way by which restriction of such silencing results in immune activation. Together, the picture that emerges is one in which OVs and epigenetic modifiers are part of a growing therapeutic toolbox that employs activation of anti-tumor immunity for cancer therapy.

Association of Mutations in the NS5A-PKRBD Region and IFNL4 Genotypes with Hepatitis C Interferon Responsiveness and its Functional and Structural Analysis

Background:

The cellular antiviral responses induced by interferons require some cellular protein kinase for its activation. Evidence indicated that a number of Hepatitis C Virus (HCV) proteins can repress double-stranded (ds) RNA-dependent Protein Kinase (PKR) function and help HCV to escape. However, the reports are controversial, some researchers have suggested that a region in Nonstructural 5A (NS5A) gene called Protein Kinase R-Binding Domain (PKR-BD) is associated with HCV sensitivity to the antiviral effects of Interferon (IFN). In addition, the other factor that might be associated with response to PEGylated-IFNα (Peg-IFNα) and Ribavirin (RBV) combination therapy, is IFNL4 genotypes.

Objective:

The aim of this study was to investigate the association between amino acid (aa) substitutions in the NS5A region and the IFNL4 genotypes in two Single Nucleotide Polymorphism (SNP) (rs8099917. rs12979860) in patients with HCV genotypes 1a and 3a. We also examined their response to combination therapy and the effect of these mutations on the function and structure of PKR-BD.

Methods:

Eighty-six patients with hepatitis C were recruited and follow-up for 6 months. Several tests, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), viral load, IFNL4 genotyping, and PKR-BD sequencing were performed. Using several well-known and trustworthy bioinformatics tools, sequences were analyzed to define physio-chemical properties, structural features, immune epitopes and protein-protein interaction.

Results:

Of the 86 patients, 65.1% had high viral load at baseline, 64% had CT genotype for rs12979860 and 57% had GT genotype for rs8099917. Several aa residues changes were found in the PKR-BD region. We could not find any link between mutations in the PKR-BD region and different genotypes of IFNL4 in response to antiviral therapy. Regardless of pI, PKR-BD 1a and 3a showed similar physio-chemical properties, and 2 phosphorylation sites and one glycosylation site were estimated for both PKR-BD 1a and 3a. Trustworthy software were employed in order to predict B-cell epitopes, 3 regions (6-17, 26-32, 34-41) were found for both proteins, indicating a huge potential of PKR-BD protein to induce humoral immune system. Docking analysis determined non-responder sequences in both 1a and 3a genotypes to have higher energy value and are more compatible with PKR.

Conclusion:

To sum up, our results could not determine any significant relationship between mutations of PKR-BD and genotypes of IFNL4 with other factors; ALT, AST, viral load. However, docking results showed strengthened interaction between PKR-BD and PKR in non-responders that could have a momentous impact on the illness severity.

Virus systems biology: Proteomics profiling of dynamic protein networks during infection

The host cell proteome undergoes a variety of dynamic changes during viral infection, elicited by the virus itself or host cell defense mechanisms. Studying these changes on a global scale by integrating functional and physical interactions within protein networks during infection is an important tool to understand pathology. Indeed, proteomics studies dissecting protein signaling cascades and interaction networks upon infection showed how global information can significantly improve understanding of disease mechanisms of diverse viral infections. Here, we summarize and give examples of different experimental designs, proteomics approaches and bioinformatics analyses that allow profiling proteome changes and host-pathogen interactions to gain a molecular systems view of viral infection.

The A150V Polymorphism of Genotype 3 Hepatitis C Virus Polymerase Inhibits Interferon Alfa by Suppressing Protein Kinase R Activation

BACKGROUND & AIMS

Despite recent advances in antiviral therapy for hepatitis C virus (HCV), a proportion of patients with genotype 3 (G3) HCV infection do not respond to current all oral treatment regimens. Genomic analyses have identified key polymorphisms correlating with increased resistance to direct-acting antivirals. We previously reported that amino the acid polymorphism, A150V, in the polymerase (NS5B) of G3 HCV reduces response to sofosbuvir. We now demonstrate that this polymorphism alters the response to interferon alpha.

METHODS

Quantitative polymerase chain reaction, immunofluorescence, luciferase activity assay, immunoblotting, and flow cytometry were used to study the antiviral effect of interferon (IFN) on DBN G3 HCV-infected cells and G3 HCV replicons.

RESULTS

We show the presence of the A150V polymorphism markedly reduces the response to IFN alpha (IC₅₀ of S52_WT = 1.162 IU/mL and IC₅₀ of S52_A150V = 14.45 IU/mL, 12.4-fold difference). The induction of IFN-stimulated genes in A150V replicon cells is unaffected, but nuclear localization of active protein kinase R (PKR) is reduced. Blockade of PKR activity reduced the antiviral effect of IFN on wild-type replicons, whereas augmented PKR activation promoted the antiviral effect of IFN on A150V replicons. Furthermore, we show that impaired activation of PKR in A150V replicon cells diminishes cellular apoptosis.

CONCLUSIONS

These results demonstrate that polymorphisms reducing response rates to direct-acting antivirals may function beyond conferring drug resistance by modulating the intrinsic cellular antiviral response.

A Novel Cis-Acting RNA Structural Element Embedded in the Core Coding Region of the Hepatitis C Virus Genome Directs Internal Translation Initiation of the Overlapping Core+1 ORF

Hepatitis C virus (HCV) genome translation is initiated via an internal ribosome entry site (IRES) embedded in the 5'-untranslated region (5'UTR). We have earlier shown that the conserved RNA stem-loops (SL) SL47 and SL87 of the HCV core-encoding region are important for viral genome translation in cell culture and in vivo. Moreover, we have reported that an open reading frame overlapping the core gene in the +1 frame (core+1 ORF) encodes alternative translation products, including a protein initiated at the internal AUG codons 85/87 of this frame (nt 597-599 and 603-605), downstream of SL87, which is designated core+1/Short (core+1/S). Here, we provide evidence for SL47 and SL87 possessing a novel cis-acting element that directs the internal translation initiation of core+1/S. Firstly, using a bicistronic dual luciferase reporter system and RNA-transfection experiments, we found that nucleotides 344-596 of the HCV genotype-1a and -2a genomes support translation initiation at the core+1 frame AUG codons 85/87, when present in the sense but not the opposite orientation. Secondly, site-directed mutagenesis combined with an analysis of ribosome-HCV RNA association elucidated that SL47 and SL87 are essential for this alternative translation mechanism. Finally, experiments using cells transfected with JFH1 replicons or infected with virus-like particles showed that core+1/S expression is independent from the 5'UTR IRES and does not utilize the polyprotein initiation codon, but it requires intact SL47 and SL87 structures. Thus, SL47 and SL87, apart from their role in viral polyprotein translation, are necessary elements for mediating the internal translation initiation of the alternative core+1/S ORF.

Cell fate determined by the activation balance between PKR and SPHK1

Double-stranded RNA (dsRNA)-dependent protein kinase R (PKR) activation via autophosphorylation is the central cellular response to stress that promotes cell death or apoptosis. However, the key factors and mechanisms behind the simultaneous activation of pro-survival signaling pathways remain unknown. We have discovered a novel regulatory mechanism for the maintenance of cellular homeostasis that relies on the phosphorylation interplay between sphingosine kinase 1 (SPHK1) and PKR during exogenous stress. We identified SPHK1 as a previously unrecognized PKR substrate. Phosphorylated SPHK1, a central kinase, mediates the activation of PKR-induced pro-survival pathways by the S1P/S1PR1/MAPKs/IKKα signal axis, and antagonizes PKR-mediated endoplasmic reticulum (ER) stress signal transduction under stress conditions. Otherwise, phosphorylated SPHK1 also acts as the negative feedback factor, preferentially binding to the latent form of PKR at the C-terminal kinase motif, inhibiting the homodimerization of PKR, suppressing PKR autophosphorylation, and reducing the signaling strength for cell death and apoptosis. Our results suggest that the balance of the activation levels between PKR and SPHK1, a probable hallmark of homeostasis maintenance, determines cell fate during cellular stress response.

Genotypic Regulation of Type I Interferon Induction Pathways by Frameshift (F) Proteins of Hepatitis C Virus

Hepatitis C virus (HCV) has evolved mechanisms to evade innate immunity that are leading to chronic infections. The immunological function of the HCV frameshift (F) protein, which is a frameshift product of core coding sequences, has not been well characterized. The HCV F protein is produced during natural HCV infections and is found most commonly in genotype 1 HCV. In this study, we investigated whether the F protein plays a role in type I interferon (IFN) induction pathways. We engineered F expression constructs from core coding sequences of 4 genotypes (1a, 2a, 3a, and 4a) of HCV as well as the sequences which would only be able to produce core proteins. The peptide lengths and amino acids sequences of F proteins are highly variable. We hypothesized that F proteins from different genotypes might control the type I IFN production and response differently. We found that both IFN-beta (IFN-β) promoter activities are significantly higher in genotype 1a F protein (F1a)-expressing cells. Conversely, the IFN-β promoter activities are lower in genotype 2a F (F2a) protein-expressing cells. We also used real-time PCR to confirm IFN-β mRNA expression levels. By generating chimera F proteins, we discovered that the effects of F proteins were determined by the amino acid sequence 40 to 57 of genotype 1a. The regulation of type I IFN induction pathway is related but not limited to the activity of F1a to interact with proteasome subunits and to disturb the proteasome activity. Further molecular mechanisms of how F proteins from different genotypes of HCV control these pathways differently remain to be investigated.IMPORTANCE Although naturally present in HCV infection patient serum, the virological or immunological functions of the HCV F protein, which is a frameshift product of core coding sequences, remain unclear. Here, we report the effects of the HCV F protein between genotypes and discuss a potential explanation for the differential responses to type I IFN-based therapy among patients infected with different genotypes of HCV. Our study provides one step forward to understanding the host response during HCV infection and new insights for the prediction of the outcome of IFN-based therapy in HCV patients.

Hepatitis C virus exploits cyclophilin A to evade PKR

Counteracting innate immunity is essential for successful viral replication. Host cyclophilins (Cyps) have been implicated in viral evasion of host antiviral responses, although the mechanisms are still unclear. Here, we show that hepatitis C virus (HCV) co-opts the host protein CypA to aid evasion of antiviral responses dependent on the effector protein kinase R (PKR). Pharmacological inhibition of CypA rescues PKR from antagonism by HCV NS5A, leading to activation of an interferon regulatory factor-1 (IRF1)-driven cell intrinsic antiviral program that inhibits viral replication. These findings further the understanding of the complexity of Cyp-virus interactions, provide mechanistic insight into the remarkably broad antiviral spectrum of Cyp inhibitors, and uncover novel aspects of PKR activity and regulation. Collectively, our study identifies a novel antiviral mechanism that harnesses cellular antiviral immunity to suppress viral replication.

Baseline Amino Acid Substitutions in the NS5A ISDR and PKR Binding Domain of Hepatitis C and Different Fibrosis Levels and Levels of Development of Hepatocellular Carcinoma in Patients Treated with DAAs

Variations in the interferon sensitivity-determining region (ISDR) within the NS5A region were related to the development of hepatocellular carcinoma (HCC) in patients infected with hepatitis C virus (HCV). The aim of the study was to investigate a relationship between ISDR/PKR substitutions and their association with liver fibrosis or HCC development. A total of 316 patients infected with HCV and treated with DAAs were evaluated. HCV RNA was quantified and sequenced before treatment. The liver fibrosis stage was assessed by transient elastography and equalized to METAVIR scores. Multivariate analysis showed that ≥3 substitutions in ISDR and ≥6 in PKR-bd were significantly associated with advanced fibrosis. Advanced fibrosis was observed in patients with higher substitutions in ISDR and PKR-bd. A higher correlation between advanced fibrosis and a high frequency of ≥3 substitutions in ISDR and ≥6 in PKR-bd was observed in patients infected with genotype 2c. In addition, in a higher proportion of HCC patients, advanced fibrosis (40.4% vs. 88.2%; p < 0.001) and ≥6 substitutions in PKR-bd (15.4% vs. 41.2%; p = 0.01) was observed. In conclusion, a higher number of substitutions in ISDR and PKR-bd were associated with advanced liver fibrosis, suggesting a use of like predictors for progression in the liver damage. A significantly higher number of PKR-bd substitutions was observed in HCC patients; in particular, in patients infected with HCV genotype 2c.

Interactions between Viperin, Vesicle-Associated Membrane Protein A, and Hepatitis C Virus Protein NS5A Modulate Viperin Activity and NS5A Degradation

The radical SAM enzyme, viperin, exerts a wide range of antiviral effects through both the synthesis of the antiviral nucleotide 3'-deoxy-3',4'-didehydro-CTP (ddhCTP) and through its interactions with various cellular and viral proteins. Here we investigate the interaction of viperin with hepatitis C virus nonstructural protein 5A (NS5A) and the host sterol regulatory protein, vesicle-associated membrane protein A (VAP-33). NS5A and VAP-33 form part of the viral replication complex that is essential for replicating the RNA genome of the hepatitis C virus. Using transfected enzymes in HEK293T cells, we show that viperin binds independently to both NS5A and the C-terminal domain of VAP-33 (VAP-33C) and that this interaction is dependent on the proteins being colocalized to the ER membrane. Coexpression of VAP-33C and NS5A resulted in changes to the catalytic activity of viperin that depended upon viperin being colocalized to the ER membrane. The viperin-NS5A-VAP-33C complex exhibited the lowest specific activity, indicating that NS5A may inhibit viperin's ability to synthesize ddhCTP. Coexpression of viperin with NS5A was also found to significantly reduce cellular NS5A levels, most likely by increasing the rate of proteasomal degradation. An inactive mutant of viperin, unable to bind the iron-sulfur cluster, was similarly effective at reducing cellular NS5A levels.

Liraglutide Inhibits Hepatitis C Virus Replication Through an AMP Activated Protein Kinase Dependent Mechanism

Insulin resistance and diabetes are both associated with chronic hepatitis C virus (HCV) infection, and the glucagon-like peptide-1(GLP-1) receptor agonist, liraglutide, is a common therapy for diabetes. Our aim was to investigate whether liraglutide treatment can inhibit HCV replication. A cell culture-produced HCV infectious system was generated by transfection of in vitro-transcribed genomic JFH-1 ribonucleic acid (RNA) into Huh-7.5 cells. Total RNA samples were extracted to determine the efficiency of HCV replication. The Ava5 cells were treated with liraglutide and cell viability was calculated. A Western blot analysis of the protein expression was performed. The immunoreactive blot signals were also detected. Liraglutide activated GLP-1 receptors in the HCV infectious system, and inhibited subgenomic HCV RNA replication in the HuH-7.5 cells. The Western blot analysis revealed both HCV protein and replicon RNA were reduced after treatment with liraglutide in a dose-dependent manner. Liraglutide decreased the cell viability of HCV RNA at an optimum concentration of 120 μg/mL, activated the 5′ adenosine monophosphate-activated protein kinase (AMPK) and the phosphorylated- transducer of regulated cyclic adenosine monophosphate (CAMP) response element-binding protein 2 (TORC2), thereby decreasing the cell viability of phosphoenolpyruvate carboxykinase (PEPCK) and G6pase RNA Therefore, we conclude that liraglutide can inhibit HCV replication via an AMPK/TORC2-dependent pathway.

Global virus outbreaks: Interferons as 1st responders

Outbreaks of severe virus infections with the potential to cause global pandemics are increasing. In many instances these outbreaks have been newly emerging (SARS coronavirus), re-emerging (Ebola virus, Zika virus) or zoonotic (avian influenza H5N1) virus infections. In the absence of a targeted vaccine or a pathogen-specific antiviral, broad-spectrum antivirals would function to limit virus spread. Given the direct antiviral effects of type I interferons (IFNs) in inhibiting the replication of both DNA and RNA viruses at different stages of their replicative cycles, and the effects of type I IFNs on activating immune cell populations to clear virus infections, IFNs-α/β present as ideal candidate broad-spectrum antivirals.

The search for a PKR code-differential regulation of protein kinase R activity by diverse RNA and protein regulators

The interferon-inducible protein kinase R (PKR) is a key component of host innate immunity that restricts viral replication and propagation. As one of the four eIF2α kinases that sense diverse stresses and direct the integrated stress response (ISR) crucial for cell survival and proliferation, PKR's versatile roles extend well beyond antiviral defense. Targeted by numerous host and viral regulators made of RNA and proteins, PKR is subject to multiple layers of endogenous control and external manipulation, driving its rapid evolution. These versatile regulators include not only the canonical double-stranded RNA (dsRNA) that activates the kinase activity of PKR, but also highly structured viral, host, and artificial RNAs that exert a full spectrum of effects. In this review, we discuss our deepening understanding of the allosteric mechanism that connects the regulatory and effector domains of PKR, with an emphasis on diverse structured RNA regulators in comparison to their protein counterparts. Through this analysis, we conclude that much of the mechanistic details that underlie this RNA-regulated kinase await structural and functional elucidation, upon which we can then describe a "PKR code," a set of structural and chemical features of RNA that are both descriptive and predictive for their effects on PKR.

Manipulation of Type I Interferon Signaling by HIV and AIDS-Associated Viruses

Type I Interferons were first described for their profound antiviral abilities in cell culture and animal models, and later, they were translated into potent antiviral therapeutics. However, as additional studies into the function of Type I Interferons progressed, it was also seen that pathogenic viruses have coevolved to encode potent mechanisms allowing them to evade or suppress the impact of Type I Interferons on their replication. For chronic viral infections, such as HIV and many of the AIDS-associated viruses, including HTLV, HCV, KSHV, and EBV, the clinical efficacy of Type I Interferons is limited by these mechanisms. Here, we review some of the ways that HIV and AIDS-associated viruses thrive in Type I Interferon-rich environments via mechanisms that block the function of this important antiviral cytokine. Overall, a better understanding of these mechanisms creates avenues to better understand the innate immune response to these viruses as well as plan the development of antivirals that would allow the natural antiviral effect of Type I Interferons to manifest during these infections.

Substitutions in interferon sensitivity-determining region and hepatocarcinogenesis after hepatitis C virus eradication

BACKGROUND AND AIM

Amino-acid substitutions in the interferon sensitivity-determining region (ISDR) within the NS5A region are known to be associated with responsiveness to interferon (IFN)-based therapy. Additionally, previous studies reported that the ISDR was related to the development of hepatocellular carcinoma (HCC) in patients infected with hepatitis C virus (HCV). However, the association between substitutions in the ISDR and the development of HCC in patients who achieved sustained virological response (SVR) is unclear. The aim of this study was to clarify the association between amino-acid substitutions in the ISDR and development of HCC after SVR.

METHODS

One thousand five hundred eighty-eight patients infected with HCV who were treated with IFN-based therapy were enrolled, and 475 patients who achieved SVR and underwent complete virological analysis at pretreatment were investigated. HCV genotypes consisted of 1a (n = 10), 1b (n = 307), 2a (n = 110), 2b (n = 41), and 3a (n = 7), and the ISDR in each genotype was examined by direct sequencing.

RESULTS

Nineteen patients developed HCC after SVR. The cumulative incidence of HCC was 2.1% and 15.9% at 5 and 10 years after SVR, respectively. Multivariate analysis indicated older age (≥ 60 years: hazard ratio [HR], 3.23; P = 0.014), higher γ-glutamyl transpeptidase level (≥ 50 IU/L: HR, 8.42; P < 0.001) and ≥ 3 substitutions in the ISDR (HR, 3.24; P = 0.016) as independent factors that were significantly associated with HCC development.

CONCLUSION

Amino-acid substitutions in the ISDR are useful to predict not only IFN responsiveness but also HCC development in patients who achieved SVR by IFN-based therapy.

Two novel SNPs in the promoter region of PKR gene in hepatitis C patients and their impact on disease outcome and response to treatment

BACKGROUND AND STUDY AIMS

The double-stranded RNA dependent protein kinase (PKR) plays a vital role in the immune system. During HCV infection, PKR has antiviral effect by inhibition of protein synthesis of the HCV. The functional single nucleotide polymorphisms (SNPs) in PKR promoter region might have a relation to HCV disease outcome and response to treatment. The objective of the present work was threefold. First, it proposed an optimized protocol for PCR amplification of PKR promoter. Second, it screened the promoter region of PKR gene in HCV Egyptian patients to detect the possible SNPs' function. Third, to study the association between the detected SNPs and the response to treatment.

PATIENTS AND METHODS

The functional SNPs in PKR promoter region were detected using DNA sequencing in 40 HCV infected patients; 20 sustained virologic response (SVR) patients and 20 nonresponse (NR) patients after combined interferon/ribavirin therapy. Twenty healthy subjects were included as a control.

RESULTS

Two functional SNPs were detected: rs62133148T>G and rs12992188C>T within our target PKR promoter region. In rs62133148 polymorphism, there is a significant difference between patients and control subjects for TT and TG genotypes (p < 0.0001). In addition, the G allele is more predominant in HCV patients. In rs12992188 polymorphism, the CC genotype is significantly different between patients and healthy control subjects (OR/95% CI: 0.033/0.006-0.172, p < 0.0001). The presence of C allele was significantly associated with the NR patients (OR/95%CI: 0.25/0.097-0.643, p = 0.006). The TT genotype is significantly different between SVR and NR (OR/95%CI: 8.5/1.54-46.871, p = 0.014).

CONCLUSION

This study is a pioneer clinical study on these two functional SNPs (rs62133148T>G and rs12992188 C>T). The rs62133148 polymorphism does not show any association with response to treatment. The TT genotype in rs12992188 polymorphism shows association with response to treatment. Therefore, patients with TT genotypes were more likely to achieve SVR.

Strategies for immune evasion by human tumor viruses

Immune evasion is a hallmark of viral persistence. For the seven human tumor viruses to establish lifelong infection in their hosts, they must successfully control the host response to them. Viral inhibition of immune responses occurs at many levels. While some viruses directly target the pattern recognition receptors (PRR) of the innate immune system, they may also antagonize downstream effectors of PRR signaling cascades or activation of transcription, which would otherwise induce a type I interferon (IFN) and/or pro-inflammatory cytokine response. Secretion of IFN activates the type I interferon receptor (IFNAR) signaling pathway, which is also prone to viral inhibition. To evade the adaptive host response, viruses also target various mechanisms including antigen processing and presentation.

Flaviviridae virus nonstructural proteins 5 and 5A mediate viral immune evasion and are promising targets in drug development

Infections with viruses in the Flaviviridae family have a vast global and economic impact because of the high morbidity and mortality. The pathogenesis of Flaviviridae infections is very complex and not fully understood because these viruses can inhibit multiple immune pathways including the complement system, NK cells, and IFN induction and signalling pathways. The non-structural (NS) 5 and 5A proteins of Flaviviridae viruses are highly conserved and play an important role in resisting host immunity through various evasion mechanisms. This review summarizes the strategies used by the NS5 and 5A proteins of Flaviviridae viruses for evading the innate immune response by inhibiting pattern recognition receptor (PRR) signalling pathways (TLR/MyD88, IRF7), suppressing interferon (IFN) signalling pathways (IFN-γRs, STAT1, STAT2), and impairing the function of IFN-stimulated genes (ISGs) (e.g. protein kinase R [PKR], oligoadenylate synthase [OAS]). All of these immune evasion mechanisms depend on the interaction of NS5 or NS5A with cellular proteins, such as MyD88 and IRF7, IFN-αRs, IFN-γRs, STAT1, STAT2, PKR and OAS. NS5 is the most attractive target for the discovery of broad spectrum compounds against Flaviviridae virus infection. The methyltransferase (MTase) and RNA-dependent RNA polymerase (RdRp) activities of NS5 are the main therapeutic targets for antiviral drugs against Flaviviridae virus infection. Based on our site mapping, the sites involved in immune evasion provide some potential and promising targets for further novel antiviral therapeutics.

Viral proteins targeting host protein kinase R to evade an innate immune response: a mini review

The innate immune system offers a first line of defense by neutralizing foreign pathogens such as bacteria, fungi, and viruses. These pathogens express molecules (RNA and proteins) that have discrete structures, known as the pathogen-associated molecular patterns that are recognized by a highly specialized class of host proteins called pattern recognition receptors to facilitate the host's immune response against infection. The RNA-dependent Protein Kinase R (PKR) is one of the host's pattern recognition receptors that is a key component of an innate immune system. PKR recognizes imperfectly double-stranded non-coding viral RNA molecules via its N-terminal double-stranded RNA binding motifs, undergoes phosphorylation of the C-terminal kinase domain, ultimately resulting in inhibition of viral protein translation by inhibiting the guanine nucleotide exchange activity of eukaryotic initiation factor 2α. Not surprisingly, viruses have evolved mechanisms by which viral non-coding RNA or protein molecules inhibit PKR's activation and/or its downstream activity to allow viral replication. In this review, we will highlight the role of viral proteins in inhibiting PKR's activity and summarize currently known mechanisms by which viral proteins execute such inhibitory activity.

Evolutionary Analysis Provides Insight Into the Origin and Adaptation of HCV

Hepatitis C virus (HCV) belongs to the Hepacivirus genus and is genetically heterogeneous, with seven major genotypes further divided into several recognized subtypes. HCV origin was previously dated in a range between ∼200 and 1000 years ago. Hepaciviruses have been identified in several domestic and wild mammals, the largest viral diversity being observed in bats and rodents. The closest relatives of HCV were found in horses/donkeys (equine hepaciviruses, EHV). However, the origin of HCV as a human pathogen is still an unsolved puzzle. Using a selection-informed evolutionary model, we show that the common ancestor of extant HCV genotypes existed at least 3000 years ago (CI: 3192–5221 years ago), with the oldest genotypes being endemic to Asia. EHV originated around 1100 CE (CI: 291–1640 CE). These time estimates exclude that EHV transmission was mainly sustained by widespread veterinary practices and suggest that HCV originated from a single zoonotic event with subsequent diversification in human populations. We also describe a number of biologically important sites in the major HCV genotypes that have been positively selected and indicate that drug resistance-associated variants are significantly enriched at positively selected sites. HCV exploits several cell-surface molecules for cell entry, but only two of these (CD81 and OCLN) determine the species-specificity of infection. Herein evolutionary analyses do not support a long-standing association between primates and hepaciviruses, and signals of positive selection at CD81 were only observed in Chiroptera. No evidence of selection was detected for OCLN in any mammalian order. These results shed light on the origin of HCV and provide a catalog of candidate genetic modulators of HCV phenotypic diversity.

Polyoma small T upregulates the expression of cytoskeletal proteins in mammalian cells during mitosis

Mammalian cells expressing murine polyoma small T antigen are known to undergo prolonged mitotic arrest followed by extensive cell death. However, the detailed mechanism of this process is not fully understood. While studying the mechanism related to small T induced mitotic arrest in mammalian cells, we observed that the expression of various cytoskeletal proteins was unusually altered in polyoma small T expressing cell line. Since most of the cytoskeletal proteins are reoriented during mitosis and are involved in spindle formation, so it was pertinent to investigate the expression of these genes in PyST expressing cell line. In this study, we evaluated the expression of tubulin, vinculin and actin. We report that polyoma small T antigen leads to upregulation of tubulin and vinculin in a time dependent manner with tubulin expression being most significantly affected. Intriguingly, we demonstrate that dividing cells normally change the expression of these proteins during mitotic progression. The alteration in cytoskeletal elements specifically occurs during mitosis as cells arrested in replicative phase did not show any change. Together these results reveal that the protein levels of tubulin and vinculin do not remain constant throughout cell cycle but change during mitosis and in polyoma small T expressing cells.

HCV viraemia associates with NK cell activation and dysfunction in antiretroviral therapy-treated HIV/HCV-co-infected subjects

The impact of hepatitis C virus (HCV) RNA levels on immune status in chronically HCV mono-infected when compared to HIV/HCV co-infected on antiretroviral therapy (ART) remains poorly understood. A total of 78 African American subjects HCV viraemic/naïve to HCV treatment (33 HCV genotype 1 mono-infected, 45 ART-treated HIV/HCV genotype 1 co-infected) were studied. Clinical and liver enzyme measurements were performed. Whole blood was analysed for immune subset changes by flow cytometry. Peripheral blood mononuclear cells (PBMC) were used for same-day constitutive and in vitro Interferon (IFN)-α-induced signal transducer and activator of transcription (STAT) phosphorylation, K562 target cell lysis and K562 target cell recognition-mediated IFN-γ production. Statistical analysis was performed using R (2.5.1) or JMP Pro 11. While both groups did not differ in the level of liver enzymes, HIV/HCV had higher T-cell activation/exhaustion, and constitutive STAT-1 phosphorylation compared to HCV. In contrast, CD4⁺ FoxP3⁺ CD25⁺ frequency, IFN-αR expression on NK cells, as well as constitutive and IFN-α-induced direct cytotoxicity were lower in HIV/HCV. Linear regression models further supported these results. Finally, increase in HCV viral load and CD4⁺ T-cell count had an opposite effect between the two groups on NK cell activity and T-cell activation, respectively. HCV viral load in ART-treated HIV/HCV co-infection was associated with greater immune activation/exhaustion and NK dysfunction than HCV viral load alone in HCV mono-infection. The more pronounced immune modulation noted in ART-treated HIV-co-infected/untreated HCV viraemic subjects may impact HCV disease progression and/or response to immunotherapy.

A New Mixed All-Atom/Coarse-Grained Model: Application to Melittin Aggregation in Aqueous Solution

We introduce a new mixed resolution, all-atom/coarse-grained approach (AACG), for modeling peptides in aqueous solution and apply it to characterizing the aggregation of melittin. All of the atoms in peptidic components are represented, while a single site is used for each water molecule. With the full flexibility of the peptide retained, our AACG method achieves speedups by a factor of 3-4 for CPU time reduction and another factor of roughly 7 for diffusion. An Ewald treatment permits the inclusion of long-range electrostatic interactions. These characteristics fit well with the requirements for studying peptide association and aggregation, where the system sizes and time scales require considerable computational resources with all-atom models. In particular, AACG is well suited for biologics since changes in peptide shape and long-range electrostatics may play an important role. The application of AACG to melittin, a 26-residue peptide with a well-known propensity to aggregate in solution, serves as an initial demonstration of this technology for studying peptide aggregation. We observed the formation of melittin aggregates during our simulations and characterized the time-evolution of aggregate size distribution, buried surface areas, and residue contacts. Key interactions including π-cation and π-stacking involving TRP19 were also examined. Our AACG simulations demonstrated a clear salt effect and a moderate temperature effect on aggregation and support the molten globule model of melittin aggregates. As a showcase, this work illustrates the useful role for AACG in investigations of peptide aggregation and its potential to guide formulation and design of biologics.

Novel nucleoside analogues targeting HCV replication through an NS5A-dependent inhibition mechanism

A series of new tricyclic nucleosides were synthesized and evaluated as hepatitis C virus (HCV) replication inhibitors. Initial screening in a HCV replicon system, derived from a genotype 1b isolate, identified 9-benzylamino-3-(β-D-ribofuranosyl)-3H-imidazo[4',5':5,6]pyrido[2,3-b]pyrazine (15d) as the most potent analogue. Comparative assessment of 15d activity against HCV full-length viruses or subgenomic replicons derived from genotypes 1 to 4 revealed a specificity of the compound for genotypes 1 and 3. Surprisingly, resistance mutations selected against 15d were mapped to domains II and III of the non-structural protein 5A (NS5A), but not to the RNA-dependent RNA polymerase residing in NS5B. These results argue that compound 15d might represent a lead for the development of a novel class of NS5A inhibitors.

Systematic identification of anti-interferon function on hepatitis C virus genome reveals p7 as an immune evasion protein

Hepatitis C virus (HCV) encodes mechanisms to evade the multilayered antiviral actions of the host immune system. Great progress has been made in elucidating the strategies HCV employs to down-regulate interferon (IFN) production, impede IFN signaling transduction, and impair IFN-stimulated gene (ISG) expression. However, there is a limited understanding of the mechanisms governing how viral proteins counteract the antiviral functions of downstream IFN effectors due to the lack of an efficient approach to identify such interactions systematically. To study the mechanisms by which HCV antagonizes the IFN responses, we have developed a high-throughput profiling platform that enables mapping of HCV sequences critical for anti-IFN function at high resolution. Genome-wide profiling performed with a 15-nt insertion mutant library of HCV showed that mutations in the p7 region conferred high levels of IFN sensitivity, which could be alleviated by the expression of WT p7 protein. This finding suggests that p7 protein of HCV has an immune evasion function. By screening a liver-specific ISG library, we identified that IFI6-16 significantly inhibits the replication of p7 mutant viruses without affecting WT virus replication. In contrast, knockout of IFI6-16 reversed the IFN hypersensitivity of p7 mutant virus. In addition, p7 was found to be coimmunoprecipitated with IFI6-16 and to counteract the function of IFI6-16 by depolarizing the mitochondria potential. Our data suggest that p7 is a critical immune evasion protein that suppresses the antiviral IFN function by counteracting the function of IFI6-16.

Nonstructural 5A Protein of Hepatitis C Virus Interferes with Toll-Like Receptor Signaling and Suppresses the Interferon Response in Mouse Liver

The hepatitis C virus nonstructural protein NS5A is involved in resistance to the host immune response, as well as the viral lifecycle such as replication and maturation. Here, we established transgenic mice expressing NS5A protein in the liver and examined innate immune responses against lipopolysaccharide (LPS) in vivo. Intrahepatic gene expression levels of cytokines such as interleukin-6, tumor necrosis factor-α, and interferon-γ were significantly suppressed after LPS injection in the transgenic mouse liver. Induction of the C-C motif chemokine ligand 2, 4, and 5 was also suppressed. Phosphorylation of the signal transducer and activator of transcription 3, which is activated by cytokines, was also reduced, and expression levels of interferon-stimulated genes, 2’-5’ oligoadenylate synthase, interferon-inducible double-stranded RNA-activated protein kinase, and myxovirus resistance 1 were similarly suppressed. Since LPS binds to toll-like receptor 4 and stimulates the downstream pathway leading to induction of these genes, we examined the extracellular signal-regulated kinase and IκB-α. The phosphorylation levels of these molecules were reduced in transgenic mouse liver, indicating that the pathway upstream of the molecules was disrupted by NS5A. Further analyses revealed that the interaction between interleukin-1 receptor-associated kinase-1 and tumor necrosis factor receptor associated factor-6 was dispersed in transgenic mice, suggesting that NS5A may interfere with this interaction via myeloid differentiation primary response gene 88, which was shown to interact with NS5A. Since the gut microbiota, a source of LPS, is known to be associated with pathological conditions in liver diseases, our results suggest the involvement of NS5A in the pathogenesis of HCV infected-liver via the suppression of innate immunity.

Modulation of HCV replication and translation by ErbB3 binding protein1 isoforms

We recently identified a cell-factor, ErbB3 binding protein 1 (Ebp-1), which specifically interacts with the viral RNA genome and modulates HCV replication and translation. Ebp1 has two isoforms, p48, and p42, that result from differential splicing. We found that both isoforms interact with HCV proteins NS5A and NS5B, as well as cell-factor PKR. The p48 isoform, which localizes in the cytoplasm and nuclei, promoted HCV replication, whereas the shorter p42 isoform, which resides exclusively in the cytoplasm, strongly inhibited HCV replication. Transient expression of individual isoforms in Ebp1-knockdown MH14 cells confirmed that the p48 isoform promotes HCV replication, while the p42 isoform inhibits it. We found that Ebp1-p42 significantly enhanced autophosphorylation of PKR, while Ebp1-p48 isoform strongly inhibited it. We propose that modulation of autophosphorylation of PKR by p48 isoform is an important mechanism whereby the HCV virus escapes innate antiviral immune responses by circumventing p42-mediated inhibition of its replication.

Oncogenes: The Passport for Viral Oncolysis Through PKR Inhibition

The transforming properties of oncogenes are derived from gain-of-function mutations, shifting cell signaling from highly regulated homeostatic to an uncontrolled oncogenic state, with the contribution of the inactivating mutations in tumor suppressor genes P53 and RB, leading to tumor resistance to conventional and target-directed therapy. On the other hand, this scenario fulfills two requirements for oncolytic virus infection in tumor cells: inactivation of tumor suppressors and presence of oncoproteins, also the requirements to engage malignancy. Several of these oncogenes have a negative impact on the main interferon antiviral defense, the double-stranded RNA-activated protein kinase (PKR), which helps viruses to spontaneously target tumor cells instead of normal cells. This review is focused on the negative impact of overexpression of oncogenes on conventional and targeted therapy and their positive impact on viral oncolysis due to their ability to inhibit PKR-induced translation blockage, allowing virion release and cell death.

Staufen1 promotes HCV replication by inhibiting protein kinase R and transporting viral RNA to the site of translation and replication in the cells

Persistent hepatitis C virus (HCV) infection leads to chronic hepatitis C (CHC), which often progresses to liver cirrhosis (LC) and hepatocellular carcinoma (HCC). The molecular mechanisms that establish CHC and cause its subsequent development into LC and HCC are poorly understood. We have identified a cytoplasmic double-stranded RNA binding protein, Stau1, which is crucial for HCV replication. In this study, Stau1 specifically interacted with the variable-stem-loop region in the 3′ NTR and domain IIId of the HCV-IRES in the 5′ NTR, and promoted HCV replication and translation. Stau1 coimmunoprecipitates HCV NS5B and a cell factor, protein kinase R (PKR), which is critical for interferon-induced cellular antiviral and antiproliferative responses. Like Stau1, PKR displayed binding specificity to domain IIId of HCV-IRES. Stau1 binds to PKR and strongly inhibits PKR-autophosphorylation. We demonstrated that the transport of HCV RNA on the polysomes is Stau1-dependent, being mainly localized in the monosome fractions when Stau1 is downregulated and exclusively localized in the polysomes when Stau1 is overexpressed. Our findings suggest that HCV may appropriate Stau1 to its advantage to prevent PKR-mediated inhibition of eIF2α, which is required for the synthesis of HCV proteins for translocation of viral RNA genome to the polysomes for efficient translation and replication.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Robust expression of vault RNAs induced by influenza A virus plays a critical role in suppression of PKR-mediated innate immunity

Protein kinase R (PKR) is a vital component of host innate immunity against viral infection. However, the mechanism underlying inactivation of PKR by influenza A virus (IAV) remains elusive. Here, we found that vault RNAs (vtRNAs) were greatly induced in A549 cells and mouse lungs after infection with IAV. The viral NS1 protein was shown to be the inducer triggering the upregulation of vtRNAs. Importantly, silencing vtRNA in A549 cells significantly inhibited IAV replication, whereas overexpression of vtRNAs markedly promoted the viral replication. Furthermore, in vivo studies showed that disrupting vtRNA expression in mice significantly decreased IAV replication in infected lungs. The vtRNA knockdown animals exhibited significantly enhanced resistance to IAV infection, as evidenced by attenuated acute lung injury and spleen atrophy and consequently increased survival rates. Interestingly, vtRNAs promoted viral replication through repressing the activation of PKR and the subsequent antiviral interferon response. In addition, increased expression of vtRNAs was required for efficient suppression of PKR by NS1 during IAV infection. Moreover, vtRNAs were also significantly upregulated by infections of several other viruses and involved in the inactivation of PKR signaling by these viruses. These results reveal a novel mechanism by which some viruses circumvent PKR-mediated innate immunity.

Effect of Hepatitis C Virus Genotype 1b Core and NS5A Mutations on Response to Peginterferon Plus Ribavirin Combination Therapy

We examined whether hepatitis C virus (HCV) genotype 1b core- and NS5A-region mutations are associated with response to peginterferon α-2b plus ribavirin combination therapy. A total of 103 patients with high HCV genotype 1b viral loads (≥100 KIU/mL) were treated with the combination therapy. Pretreatment mutations in the core region and interferon sensitivity determining region (ISDR) in the NS5A region were analyzed. In univariate analysis, arginine and leucine at positions 70 and 91 in the core region, defined as double wild (DW)-type, were associated with early virologic response (p = 0.002), sustained virologic response (SVR) (p = 0.004), and non-response (p = 0.005). Non-threonine at position 110 was associated with SVR (p = 0.004). Multivariate analysis showed the following pretreatment predictors of SVR: hemoglobin level ≥ 14 g/dL (odds ratio (OR) 6.2, p = 0.04); platelet count ≥ 14 × 10⁴/mm³ (OR 5.2, p = 0.04); aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio < 0.9 (OR 6.17, p = 0.009); DW-type (OR 6.8, p = 0.02); non-threonine at position 110 (OR 14.5, p = 0.03); and ≥2 mutations in the ISDR (OR 12.3, p = 0.02). Patients with non-DW-type, non-threonine at position 110, and <2 ISDR mutations showed significantly lower SVR rates than others (11/45 (24.4%) vs. 27/37 (73.0%), respectively; p < 0.001). SVR can be predicted through core and NS5A region mutations and host factors like hemoglobin, platelet count, and AST/ALT ratio in HCV genotype 1b-infected patients treated with peginterferon and ribavirin combination therapy.

Interference of HCV replication by cell penetrable human monoclonal scFv specific to NS5B polymerase

A new class of hepatitis C virus (HCV)-targeted therapeutics that is safe, broadly effective and can cope with virus mutations is needed. The HCV's NS5B is highly conserved and different from human protein, and thus it is an attractive target for anti-HCV therapeutics development. In this study, NS5B bound-phage clones selected from a human single chain variable antibody fragment (scFv) phage display library were used to transform appropriate E. coli bacteria. Two scFv inhibiting HCV polymerase activity were selected. The scFvs were linked to a cell penetrating peptide to make cell penetrable scFvs. The transbodies reduced the HCV RNA and infectious virus particles released into the culture medium and inside hepatic cells transfected with a heterologous HCV replicon. They also rescued the innate immune response of the transfected cells. Phage mimotope search and homology modeling/molecular docking revealed the NS5B subdomains and residues bound by the scFvs. The scFv mimotopes matched residues of the NS5B, which are important for nucleolin binding during HCV replication, as well as residues that interconnect the fingers and thumb domains for forming a polymerase active groove. Both scFvs docked on several residues at the thumb armadillo-like fold that could be the polymerase interactive sites of other viral/host proteins for the formation of the replication complex and replication initiation. In conclusion, human transbodies that inhibited HCV RdRp activity and HCV replication and restored the host innate immune response were produced. They are potentially future interferon-free anti-HCV candidates, particularly in combination with other cognates that are specific to NS5B epitopes and other HCV enzymes.

Hepatitis C Virus Nonstructural Protein 5A Inhibits MG132-Induced Apoptosis of Hepatocytes in Line with NF-κB-Nuclear Translocation

Background

Hepatitis C virus (HCV) infection is one of the major causes of cirrhosis and hepatocellular carcinoma. HCV nonstructural protein 5A (NS5A) is an attractive antiviral target and plays an important role in HCV replication as well as hepatocarcinogenesis. The aim of this study was to assess the effect of HCV NS5A protein in the abrogation of apoptotic cell death induced by the proteasome inhibitor MG132.

Methods

Apoptotic responses to MG132 and the expression of molecules involved in NF-κB signaling pathways in human hepatocytes were investigated with or without the expression of HCV NS5A.

Results

HCV NS5A protected HepG2 cells against MG132-induced apoptosis, in line with NF-κB-nuclear translocation. A similar NF-κB-nuclear translocation was observed in Huh7 cells infected with HCV JFH1. In agreement with this, after treatment with MG132, HCV NS5A could elevate the transcription of several NF-κB target genes such as BCL2 and BCLXL to inhibit MG132-induced apoptosis in hepatocytes. HCV HCV NS5A also enhanced phosphorylation of IκBα. Consistent with a conferred prosurvival advantage, HCV NS5A reduced MG132-induced poly(adenosine diphosphate-ribose) polymerase cleavage.

Conclusions

HCV NS5A expression enhances phosphorylation of IκBα, liberates NF-κB for nuclear translocation and downregulates MG132-induced apoptotic pathways in human hepatocytes. It is possible that the disruption of proteasome-associated apoptosis plays a role in the pathogenesis of HCV infection.

PKR activation enhances replication of classical swine fever virus in PK-15 cells

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CSFV infection triggers PKR and eIF2α protein phosphorylation.

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PKR overexpression stimulates viral replication.

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PKR depletion blocks eIF2α phosphorylation and suppresses viral replication.

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PKR depletion increases IFN-β, and enhances the antiviral effect of IFN.

Classical swine fever (CSF) is a highly contagious swine disease that is responsible for economic losses worldwide. Protein kinase R (PK)R is an important protein in the host viral response; however, the role of PKR in CSFV infection remains unknown. This issue was addressed in the present study using the PK-15 swine kidney cell line. We found that CSFV infection increased the phosphorylation of eukaryotic translation initiation factor (eIF)2α and its kinase PKR. However, the expression of viral proteins continued to increase. Furthermore, PKR overexpression enhanced CSFV replication, while PKR inhibition resulted in reduced CSFV replication and an increase in interferon (IFN) induction. In addition, PKR was responsible for eIF2α phosphorylation in CSFV-infected cells. These results suggest that the activation of PKR during CSFV infection is beneficial to the virus. The virus is able to commandeer the host cell's translation machinery for viral protein synthesis while evading innate immune defenses.