Hepatitis C virus (HCV) employs multiple strategies to subvert the host innate antiviral response

Hepatitis C Virus Infection: Host⁻Virus Interaction and Mechanisms of Viral Persistence

Hepatitis C (HCV) is a major cause of liver disease, in which a third of individuals with chronic HCV infections may develop liver cirrhosis. In a chronic HCV infection, host immune factors along with the actions of HCV proteins that promote viral persistence and dysregulation of the immune system have an impact on immunopathogenesis of HCV-induced hepatitis. The genome of HCV encodes a single polyprotein, which is translated and processed into structural and nonstructural proteins. These HCV proteins are the target of the innate and adaptive immune system of the host. Retinoic acid-inducible gene-I (RIG-I)-like receptors and Toll-like receptors are the main pattern recognition receptors that recognize HCV pathogen-associated molecular patterns. This interaction results in a downstream cascade that generates antiviral cytokines including interferons. The cytolysis of HCV-infected hepatocytes is mediated by perforin and granzyme B secreted by cytotoxic T lymphocyte (CTL) and natural killer (NK) cells, whereas noncytolytic HCV clearance is mediated by interferon gamma (IFN-γ) secreted by CTL and NK cells. A host-HCV interaction determines whether the acute phase of an HCV infection will undergo complete resolution or progress to the development of viral persistence with a consequential progression to chronic HCV infection. Furthermore, these host-HCV interactions could pose a challenge to developing an HCV vaccine. This review will focus on the role of the innate and adaptive immunity in HCV infection, the failure of the immune response to clear an HCV infection, and the factors that promote viral persistence.

Newcastle disease virus strain AF2240 as an oncolytic virus: A review

The discovery of tumour selective virus-mediated apoptosis marked the birth of an alternative cancer treatment in the form of oncolytic viruses. Even though, its oncolytic efficiency was demonstrated more than 50 years ago, safety concerns which resulted from mild to lethal side effects hampered the progress of oncolytic virus research. Since the classical oncolytic virus studies rely heavily on its natural oncolytic ability, virus manipulation was limited, thereby, restricted efforts to improve its safety. In order to circumvent such restriction, experiments involving non-human viruses such as the avian Newcastle disease virus (NDV) was conducted using cultured cells, animal models and human subjects. The corresponding reports on its significant tumour cytotoxicity along with impressive safety profile initiated immense research interest in the field of oncolytic NDV. The varying degree of oncolytic efficiency and virulency among NDV strains encouraged researchers from all around the world to experiment with their respective local NDV isolates in order to develop an oncolytic virus with desirable characteristics. Such desirable features include high tumour-killing ability, selectivity and low systemic cytotoxicity. The Malaysian field outbreak isolate, NDV strain AF2240, also currently, receives significant research attention. Apart from its high cytotoxicity against tumour cells, this strain also provided fundamental insight into NDV-mediated apoptosis mechanism which involves Bax protein recruitment as well as death receptor engagement. Studies on its ability to selectively induce apoptosis in tumour cells also resulted in a proposed p38 MAPK/NF-κB/IκBα pathway. The immunogenicity of AF2240 was also investigated through PBMC stimulation and macrophage infection. In addition, the enhanced oncolytic ability of this strain under hypoxic condition signifies its dynamic tumour tropism. This review is aimed to introduce and discuss the aforementioned details of the oncolytic AF2240 strain along with its current challenges which outlines the future research direction of this virus.

Hepatitis C Virus Activates a Neuregulin-Driven Circuit to Modify Surface Expression of Growth Factor Receptors of the ErbB Family

Recently, the epidermal growth factor (EGF) receptor (EGFR), a member of the ErbB receptor family, and its down-stream signalling have been identified as co-factors for HCV entry and replication. Since EGFR also functions as a heterodimer with other ErbB receptor family members, the subject of the present study was to investigate a possible viral interference with these cellular components. By using genotype 1b replicon cells as well as an infection-based system we found that while transcript and protein levels of EGFR and ErbB2 were up-regulated or unaffected, respectively, HCV induced a substantial reduction of ErbB3 and ErbB4 expression. Down-regulation of ErbB3 expression by HCV involves specificity protein (Sp)1-mediated induction of Neuregulin (NRG)1 expression as well as activation of Akt. Consistently, at transcript level disruption of ErbB3 expression by HCV can be prevented by knockdown of NRG1 or Sp1 expression, whereas reconstitution of ErbB3 protein levels requires inhibition of HCV-induced NRG1 expression and of Akt activity. Interestingly, the NRG1-mediated suppression of ErbB3 expression by HCV results in an enhanced expression of EGFR and ErbB2 on the cell surface, which can be mimicked by siRNA-mediated knockdown of ErbB3 expression. These data delineate a novel mechanism enabling HCV to sway the composition of the ErbB family members on the surface of its host cell by an NRG1-driven circuit and unravels a yet unknown cross-regulation between ErbB3 and the two other family members ErbB2 and EGFR. The shift of the receptor surface expression of the ErbB family towards enhanced expression of ErbB2 and EGFR triggered by HCV was found to promote viral RNA replication and infectivity. This suggests that HCV rearranges expression of ErbB family members to adapt the cellular environment to its requirements.

Comparative Immunogenicity in Rabbits of the Polypeptides Encoded by the 5' Terminus of Hepatitis C Virus RNA

Recent studies on the primate protection from HCV infection stressed the importance of immune response against structural viral proteins. Strong immune response against nucleocapsid (core) protein was difficult to achieve, requesting further experimentation in large animals. Here, we analyzed the immunogenicity of core aa 1–173, 1–152, and 147–191 and of its main alternative reading frame product F-protein in rabbits. Core aa 147–191 was synthesized; other polypeptides were obtained by expression in E. coli. Rabbits were immunized by polypeptide primes followed by multiple boosts and screened for specific anti-protein and anti-peptide antibodies. Antibody titers to core aa 147–191 reached 10⁵; core aa 1–152, 5 × 10⁵; core aa 1–173 and F-protein, 10⁶. Strong immunogenicity of the last two proteins indicated that they may compete for the induction of immune response. The C-terminally truncated core was also weakly immunogenic on the T-cell level. To enhance core-specific cellular response, we immunized rabbits with the core aa 1–152 gene forbidding F-protein formation. Repeated DNA immunization induced a weak antibody and sustained proliferative response of broad specificity confirming a gain of cellular immunogenicity. Epitopes recognized in rabbits overlapped those in HCV infection. Our data promotes the use of rabbits for the immunogenicity tests of prototype HCV vaccines.

Long-term follow-up of successful hepatitis C virus therapy: waning immune responses and disappearance of liver disease are consistent with cure

BACKGROUND

A sustained viral response (SVR) after interferon-based therapy of chronic hepatitis C virus (HCV) infection is regarded to represent a cure. Previous studies have used different markers to clarify whether an SVR truly represents a cure, but no study has combined a clinical work-up with highly sensitive HCV RNA detection, and the determination of immune responses.

AIM

To determine clinical, histological, virological and immunological markers 5-20 years after SVR.

METHODS

In 54 patients, liver biochemistry, histology and elastography were evaluated. Liver biopsies, plasma and peripheral blood mononuclear cells (PBMCs) were tested for minute amounts of HCV RNA. HCV-specific T-cell responses were monitored by ELISpot and pentamer staining, and humoral responses by measuring HCV nonstructural (NS)3-specific antibodies and virus neutralisation.

RESULTS

Liver disease regressed significantly in all patients, and 51 were HCV RNA-negative in all tissues tested. There was an inverse association between liver disease, HCV-specific T-cell responses and HCV antibody levels with time from SVR, supporting that the virus had been cleared. The three patients, who all lacked signs of liver disease, had HCV RNA in PBMCs 5-9 years after SVR. All three had HCV-specific T cells and NS3 antibodies, but no cross-neutralising antibodies.

CONCLUSIONS

Our combined data confirm that a SVR corresponds to a long-term clinical cure. The waning immune responses support the disappearance of the antigenic stimulus. Transient HCV RNA traces may be detected in some patients up to 9 years after SVR, but no marker associates this with an increased risk for liver disease.

Virus-related liver cirrhosis: molecular basis and therapeutic options

Chronic infections with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) are the major causes of cirrhosis globally. It takes 10-20 years to progress from viral hepatitis to cirrhosis. Intermediately active hepatic inflammation caused by the infections contributes to the inflammation-necrosis-regeneration process, ultimately cirrhosis. CD8(+) T cells and NK cells cause liver damage via targeting the infected hepatocytes directly and releasing pro-inflammatory cytokine/chemokines. Hepatic stellate cells play an active role in fibrogenesis via secreting fibrosis-related factors. Under the inflammatory microenvironment, the viruses experience mutation-selection-adaptation to evade immune clearance. However, immune selection of some HBV mutations in the evolution towards cirrhosis seems different from that towards hepatocellular carcinoma. As viral replication is an important driving force of cirrhosis pathogenesis, antiviral treatment with nucleos(t)ide analogs is generally effective in halting the progression of cirrhosis, improving liver function and reducing the morbidity of decompensated cirrhosis caused by chronic HBV infection. Interferon-α plus ribavirin and/or the direct acting antivirals such as Vaniprevir are effective for compensated cirrhosis caused by chronic HCV infection. The standard of care for the treatment of HCV-related cirrhosis with interferon-α plus ribavirin should consider the genotypes of IL-28B. Understanding the mechanism of fibrogenesis and hepatocyte regeneration will facilitate the development of novel therapies for decompensated cirrhosis.

The role of chemokines in hepatitis C virus-mediated liver disease

The hepatitis C virus (HCV) is a global health problem affecting more than 170 million people. A chronic HCV infection is associated with liver fibrosis, liver cirrhosis and hepatocellular carcinoma. To enable viral persistence, HCV has developed mechanisms to modulate both innate and adaptive immunity. The recruitment of antiviral immune cells in the liver is mainly dependent on the release of specific chemokines. Thus, the modulation of their expression could represent an efficient viral escape mechanism to hamper specific immune cell migration to the liver during the acute phase of the infection. HCV-mediated changes in hepatic immune cell chemotaxis during the chronic phase of the infection are significantly affecting antiviral immunity and tissue damage and thus influence survival of both the host and the virus. This review summarizes our current understanding of the HCV-mediated modulation of chemokine expression and of its impact on the development of liver disease. A profound knowledge of the strategies used by HCV to interfere with the host's immune response and the pro-fibrotic and pro-carcinogenic activities of HCV is essential to be able to design effective immunotherapies against HCV and HCV-mediated liver diseases.

Cleavage of the T cell protein tyrosine phosphatase by the hepatitis C virus nonstructural 3/4A protease induces a Th1 to Th2 shift reversible by ribavirin therapy

Ribavirin has proven to be a key component of hepatitis C therapies both involving IFNs and new direct-acting antivirals. The hepatitis C virus-mediated interference with intrahepatic immunity by cleavage of mitochondrial antiviral signaling protein (MAVS) and T cell protein tyrosine phosphatase (TCPTP) suggests an avenue for compounds that may counteract these effects. We therefore studied the effects of ribavirin, with or without inhibition of the nonstructural (NS)3/4A protease, on intrahepatic immunity. The intrahepatic immunity of wild-type and NS3/4A-transgenic mice was determined by Western blot, ELISA, flow cytometry, and survival analysis. Various MAVS or TCPTP constructs were injected hydrodynamically to study their relevance. Ribavirin pretreatment was performed in mice expressing a functional or inhibited NS3/4A protease to analyze its effect on NS3/4A-mediated changes. Intrahepatic NS3/4A expression made mice resistant to TNF-α-induced liver damage and caused an alteration of the intrahepatic cytokine (IFN-γ and IL-10) and chemokine (CCL3, CCL17, CCL22, CXCL9, and CXCL11) profiles toward an anti-inflammatory state. Consistent with this, the number of intrahepatic Th1 cells and IFN-γ(+) T cells in NS3/4A-transgenic mice decreased, whereas the amount of Th2 cells increased. These effects could be reversed by injection of uncleavable TCPTP but not uncleavable MAVS and were absent in a mouse expressing a nonfunctional NS3/4A protease. Importantly, the NS3/4A-mediated effects were reversed by ribavirin treatment. Thus, cleavage of TCPTP by NS3/4A induces a shift of the intrahepatic immune response toward a nonantiviral Th2-dominated immunity. These effects are reversed by ribavirin, supporting that ribavirin complements the effects of direct-acting antivirals as an immunomodulatory compound.

Association of killer cell immunoglobulin-like receptor polymorphisms with chronic hepatitis C and responses to therapy in Brazil

Soroprevalence for Hepatitis C virus is reported as 2.12% in Northern Brazil, with about 50% of the patients exhibiting a sustained virological response (SVR). Aiming to associate polymorphisms in Killer Cell Immunoglobulin-like Receptors (KIR) with chronic hepatitis C and therapy responses we investigated 125 chronic patients and 345 controls. Additionally, 48 ancestry markers were genotyped to control for population stratification. The frequency of the KIR2DL2 and KIR2DL2+HLA-C^Asp80 gene and ligand was higher in chronic infected patients than in controls (p < 0.0009, OR = 3.4; p = 0.001, OR = 3.45). In fact, KIR2DL3 is a weaker inhibitor of NK activity than KIR2DL2, which could explain the association of KIR2DL2 with chronic infection. Moreover, KIR2DS2 and KIR2DS2+HLA-C^Asp80 (p < 0.0001, OR = 2.51; p = 0.0084, OR = 2.62) and KIR2DS3 (p < 0.0001; OR = 2.57) were associated with chronic infection, independently from KIR2DL2. No differences in ancestry composition were observed between control and patients, even with respect to therapy response groups. The allelic profile KIR2DL2/KIR2DS2/KIR2DS3 was associated with the chronic hepatitis C (p < 0.0001; OR = 3). Furthermore, the patients also showed a higher mean number of activating genes and a lower frequency of the homozygous AA profile, which is likely secondary to the association with non-AA and/or activating genes. In addition, the KIR2DS5 allele was associated with SVR (p = 0.0261; OR = 0.184).The ancestry analysis of samples ruled out any effects of population substructuring and did not evidence interethnic differences in therapy response, as suggested in previous studies.

Non-structural 3 protein expression is associated with T cell protein tyrosine phosphatase and viral RNA levels in chronic hepatitis C patients

The hepatitis C virus (HCV) non-structural 3 (NS3) protein plays key roles in both the viral life cycle and in the modulation of intrahepatic signaling and immunity. We recently showed that NS3 cleaves the T cell protein tyrosine phosphatase (TCPTP). To better understand the inactivation of TCPTP in HCV-infected humans, we investigated whether there is an association between TCPTP cleavage, NS3 protein levels and clinical parameters in hepatitis C patients. Liver biopsies were obtained from 69 HCV RNA positive patients with confirmed chronic HCV infection and 16 control patients. Hepatic NS3 and TCPTP protein levels were determined and correlated to viral load or clinical parameters for the severity of liver disease. We found a positive correlation between the viral load and the intrahepatic NS3 protein levels in patients infected with HCV. HCV-infected patients had significantly lower intrahepatic TCPTP levels than non-infected control patients. In HCV-infected patients both intrahepatic NS3 expression and the viral load were inversely correlated with the intrahepatic TCPTP protein levels. Detection of NS3 did not associate with any other clinical parameters such as liver damage, the grade of liver inflammation or fibrosis stage. This is the first study reporting a detailed analysis of HCV NS3 and TCPTP protein levels in the liver. It demonstrates a clear link between HCV viral load, NS3 expression in the liver and intrahepatic TCPTP levels. Thus, the association between TCPTP cleavage and viral replication may have important consequences for the HCV life cycle and HCV-induced liver diseases.

Granulocyte-macrophage colony-stimulating factor genetic adjuvant enhances the immune stimulatory effects of plasmid DNA encoding the hepatitis C virus core protein

AIM: To study the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) genetic adjuvant on immune response induced by plasmid DNA encoding the hepatitis C virus (HCV) core (C) protein.

METHODS: The gene encoding the HCV C protein was amplified by PCR from HCV 1b genotype and inserted into the pUC119 vector. The HCV C gene was then subcloned into the pCMH6K eukaryotic vector, and the resulting plasmid was named pCMH6K/HCV-C. The recombinant vector was confirmed by restriction enzyme analysis and DNA sequencing, and transfected into China hamster ovary (CHO) cells with Lipofectamine 2000. Distribution of the HCV C protein in transfected CHO cells was detected by immunofluorescence. Balb/c mice were vaccinated with the recombinant plasmid with or without the GM-CSF gene. HCV C-specific antibody in serum was measured by ELISA. The changes in T lymphocyte subsets and levels of Th cell intracellular cytokines interferon-γ (IFN-γ) and interleukin-4 (IL-4) in splenic cell suspension from immunized mice were evaluated by flow cytometric analysis. CTL activity was assessed by LDH assay.

RESULTS: Restrict enzyme digestion and DNA sequencing indicated that the recombinant pCMH6K/HCV-C was successfully constructed. The expression of plasmid-encoded protein was mainly distributed in membrane and scarcely in cytoplasm of transfected CHO cells. The percentage of CD4⁺ T cells in spleen cells in the pCMH6K/HCV-C+pGM-CSF co-vaccination group was significantly higher than those in other groups (all P < 0.05). The percentage of CD8⁺ T cells showed no significant differences among each group (P > 0.05). CTL activity induced by GM-CSF DNA co-vaccination was significantly higher than that immunized with the same amount of other naked DNA (P < 0.05). The ratio of IFN-γ to IL-4 in spleen cells from GM-CSF DNA co-vaccination group was significantly higher than those in other groups (all P < 0.05).

CONCLUSION: GM-CSF DNA could enhance the immune stimulatory effects of HCV DNA vaccine and induce Th1-type immune response.

Down-regulation of Toll-like receptor 7 expression in hepatitis-virus-related human hepatocellular carcinoma

Toll-like receptors (TLRs) play a pivotal role in innate immunity, controlling inflammatory responses, and further development of adaptive immunity. Hepatitis virus can establish chronic infection, and the associated inflammatory responses are important determinants of virus-associated liver damage. However, the contributions of the host immune system to chronic presence of virus are not clear in patients with hepatitis virus infection. Chronic inflammatory conditions caused by persistent hepatitis virus infections and interferon (IFN)-γ-related immunopathology are known to be related to carcinogenesis. To gain insight into the role of immune modulation in the pathogenesis of hepatocellular carcinoma (HCC), we studied the expression of TLR7 in cancerous and non-cancerous liver tissue from 87 patients with HCC. Our results showed that TLR7 is significantly down-regulated in neoplastic hepatocytes (P < .001), especially in the patients with hepatitis B (n = 52) or C (n = 24) virus infection. We confirmed this decreased TLR7 expression by quantitative analysis of mRNA using real-time reverse transcription-polymerase chain reaction in 26 liver specimens of HCC patients. Using serial deletion analysis of the TLR7 promoter, a hepatocyte-specific regulatory region was found at nucleotides -156 to -98 in the TLR7 promoter. Furthermore, the effects of IFN-γ on TLR7 expression in a hepatoma cell line (HepG2) were investigated in vitro. We demonstrated that IFN-γ significantly decreased TLR7 promoter activity and expression in a dose-dependent manner. We thus propose that hepatitis virus induces down-regulation of TLR7 gene expression through IFN-γ, thereby modulating inflammatory signaling in hepatoma cells.

Specific acquisition of functional CD59 but not CD46 or CD55 by hepatitis C virus

Viruses of different families encode for regulators of the complement system (RCAs) or acquire such RCAs from the host to get protection against complement-mediated lysis (CML). As hepatitis C virus (HCV) shares no genetic similarity to any known RCA and is detectable at high titers in sera of infected individuals, we investigated whether HCV has adapted host-derived RCAs to resist CML. Here we report that HCV selectively incorporates CD59 while neither CD55, nor CD46 are associated with the virus. The presence of CD59 was shown by capture assays using patient- and cell culture-derived HCV isolates. Association of CD59 with HCV was further confirmed by Western blot analysis using purified viral supernatants from infected Huh 7.5 cells. HCV captured by antibodies specific for CD59 remained infectious for Huh 7.5 cells. In addition, blocking of CD59 in the presence of active complement reduced the titer of HCV most likely due to CML. HCV produced in CD59 knock-down cells were more significantly susceptible to CML compared to wild type virus, but neither replication, assembly nor infectivity of the virus seemed to be impaired in the absence of CD59. In summary our data indicate that HCV incorporates selectively CD59 in its envelope to gain resistance to CML in serum of infected individuals.

Hepatitis C virus-mediated modulation of cellular immunity

The hepatitis C virus (HCV) is a major cause of chronic liver disease globally. A chronic infection can result in liver fibrosis, liver cirrhosis, hepatocellular carcinoma and liver failure in a significant ratio of the patients. About 170 million people are currently infected with HCV. Since 80 % of the infected patients develop a chronic infection, HCV has evolved sophisticated escape strategies to evade both the innate and the adaptive immune system. Thus, chronic hepatitis C is characterized by perturbations in the number, subset composition and/or functionality of natural killer cells, natural killer T cells, dendritic cells, macrophages and T cells. The balance between HCV-induced immune evasion and the antiviral immune response results in chronic liver inflammation and consequent immune-mediated liver injury. This review summarizes our current understanding of the HCV-mediated interference with cellular immunity and of the factors resulting in HCV persistence. A profound knowledge about the intrinsic properties of HCV and its effects on intrahepatic immunity is essential to be able to design effective immunotherapies against HCV such as therapeutic HCV vaccines.

Peripheral blood monocyte subsets predict antiviral response in chronic hepatitis C

BACKGROUND

Hepatitis C virus infection evolves into chronic progressive liver disease in a significant percentage of patients. Monocytes constitute a diverse group of myeloid cells that mediate innate and adaptive immune response. In addition to proinflammatory CD16+ monocytes, a Tie-2+ subgroup - Tie-2 expressing monocytes (TEMs) - that has robust proangiogenic potential has been recently defined.

AIM

To study the heterogeneity of peripheral blood monocytes in chronic hepatitis C (CHC) patients and to examine their proposed pathophysiological roles on disease progression and response to antiviral therapy.

METHODS

We studied CD16+ and Tie-2+ peripheral monocyte subpopulations in 21 healthy subjects and 39 CHC patients in various stages of disease and responses to antiviral treatment using flow cytometry. Expression profiles of proangiogenic and tissue remodelling factors in monocyte supernatants were measured using ELISA and protein arrays. Intrahepatic expression of CD14, CD31 and Tie-2 was analysed using immunofluorescence.

RESULTS

Increases of certain peripheral monocyte subsets were observed in the blood of CHC patients, wherein those cells with proinflammatory (CD16+) or proangiogenic (TEMs) potential expanded (P < 0.005, both). Notably, TEMs were significantly increased in nonresponders, particularly those with lower CD16 expression. In addition, many angiogenic factors were differentially expressed by peripheral monocytes from control or CHC patients, such as angiopoietin-1 and angiogenin (P < 0.05). Interestingly, intrahepatic TEMs were distinguished within portal infiltrates of CHC patients.

CONCLUSIONS

These findings suggest for the first time the relevance of peripheral monocytes phenotypes for the achievement of response to treatment. Hence, the study of monocyte subset regulation might effect improved CHC prognoses and adjuvant therapies.

Hepatitis C virus core protein promotes the migration and invasion of hepatocyte via activating transcription of extracellular matrix metalloproteinase inducer

The chronic infection of hepatitis C virus (HCV) becomes a main factor evoking hepatocellular carcinoma, where the HCV core protein plays a central role in hepatocarcinogenesis. Whether the core protein directly contributes to metastasis of hepatocytes still remains to be reported in literature. Transwell chamber migration assay, Boyden chamber invasion assays and scanning electron microscopy observations were performed to determine the prometastatic ability of HCV core protein when expressed in human hepatocyte L02 cells. In addition, western blots, dual-luciferase assays, and chromatin immunoprecipitation assays were used to elucidate HCV core protein dependent pathways that promote metastasis in hepatocytes. Our investigation suggests that HCV core protein markedly enhances the capability of migration and invasion in L02 clones expressing HCV core proteins. The metastasis-promoting effect of the core protein is, in part, highly dependent on its effect on promoting the binding of transcription factor Sp1 to the extracellular matrix metalloproteinase inducer promoter. The effect of Sp1 binding resulted in an increase in extracellular matrix metalloproteinase inducer expression and progression of metastasis. Thus, we report that the expression of HCV core protein contributes to the metastasis of hepatocyte cells through activating transcription of extracellular metalloproteinase inducer.

Anti-tumor necrosis factor α treatment promotes apoptosis and prevents liver regeneration in a transgenic mouse model of chronic hepatitis C

Tumor necrosis factor α (TNFα) has been implicated in a variety of inflammatory diseases, and anti-TNFα has been shown to improve therapy when added to standard of care in chronic hepatitis C virus (HCV) infection. In addition, patients with chronic HCV have increased serum levels of TNFα and the macrophage-attracting chemokine (C-C motif) ligand 2 (CCL2). A mouse model of chronic HCV with hepatic nonstructural (NS) 3/4A protein expression mimics the human infection through a reduced response to double-stranded RNA and cleavage of the T cell protein tyrosine phosphatase. The mice also display a resistance to TNFα in vivo. We therefore analyzed the relationship between NS3/4A and TNFα. Wild-type and NS3/4A-transgenic (Tg) mice were treated with TNFα/D-galactosamine (D-galN), acting through the TNF receptor 1 on hepatocytes and macrophages, or lipopolysaccharide (LPS)/D-galN, acting through Toll-like receptor 4 on sinusoidal endothelial cells, macrophages, and dendritic cells. Mice were analyzed for hepatic signaling, liver damage, TNFα, and CCL2. Similar to HCV-infected humans, NS3/4A-Tg mice displayed elevated basal levels of TNFα and CCL2. Treatment of NS3/4A-Tg mice with TNFα/D-galN or LPS/D-galN led to increased hepatic nuclear factor kappa B (NFκB) activation, increased TNFα and CCL2 levels, decreased apoptosis, and increased hepatocyte regeneration. Importantly, blocking NFκB activation (bortezomib) or administering anti-TNFα (infliximab) 4 hours after LPS/D-galN injection reversed the resistance of NS3/4A-Tg mice to TNFα-induced liver injury.

CONCLUSION

Resistance to TNFα seen in NS3/4A-Tg mice is explained by a hepatoprotective effect of NFκB and TNFα. Hence, anti-TNFα agents block these effects and are antiviral by promoting hepatocyte apoptosis and preventing hepatocyte regeneration.

Hepatitis C virus core protein induces neuroimmune activation and potentiates Human Immunodeficiency Virus-1 neurotoxicity

Background

Hepatitis C virus (HCV) genomes and proteins are present in human brain tissues although the impact of HIV/HCV co-infection on neuropathogenesis remains unclear. Herein, we investigate HCV infectivity and effects on neuronal survival and neuroinflammation in conjunction with HIV infection.

Methodology

Human microglia, astrocyte and neuron cultures were infected with cell culture-derived HCV or exposed to HCV core protein with or without HIV-1 infection or HIV-1 Viral Protein R (Vpr) exposure. Host immune gene expression and cell viability were measured. Patch-clamp studies of human neurons were performed in the presence or absence of HCV core protein. Neurobehavioral performance and neuropathology were examined in HIV-1 Vpr-transgenic mice in which stereotaxic intrastriatal implants of HCV core protein were performed.

Principal Findings

HCV-encoded RNA as well as HCV core and non-structural 3 (NS3) proteins were detectable in human microglia and astrocytes infected with HCV. HCV core protein exposure induced expression of pro-inflammatory cytokines including interleukin-1β, interleukin-6 and tumor necrosis factor-α in microglia (p<0.05) but not in astrocytes while increased chemokine (e.g. CXCL10 and interleukin-8) expression was observed in both microglia and astrocytes (p<0.05). HCV core protein modulated neuronal membrane currents and reduced both β-III-tubulin and lipidated LC3-II expression (p<0.05). Neurons exposed to supernatants from HCV core-activated microglia exhibited reduced β-III-tubulin expression (p<0.05). HCV core protein neurotoxicity and interleukin-6 induction were potentiated by HIV-1 Vpr protein (p<0.05). HIV-1 Vpr transgenic mice implanted with HCV core protein showed gliosis, reduced neuronal counts together with diminished LC3 immunoreactivity. HCV core-implanted animals displayed neurobehavioral deficits at days 7 and 14 post-implantation (p<0.05).

Conclusions

HCV core protein exposure caused neuronal injury through suppression of neuronal autophagy in addition to neuroimmune activation. The additive neurotoxic effects of HCV- and HIV-encoded proteins highlight extrahepatic mechanisms by which HCV infection worsens the disease course of HIV infection.

Common threads in persistent viral infections

Most viral infections are self-limiting, resulting in either clearance of the pathogen or death of the host. However, a subset of viruses can establish permanent infection and persist indefinitely within the host. Even though persisting viruses are derived from various viral families with distinct replication strategies, they all utilize common mechanisms for establishment of long-lasting infections. Here, we discuss the commonalities between persistent infections with herpes-, retro-, flavi-, arena-, and polyomaviruses that distinguish them from acutely infecting viral pathogens. These shared strategies include selection of cell subsets ideal for long-term maintenance of the viral genome, modulation of viral gene expression, viral subversion of apoptotic pathways, and avoidance of clearance by the immune system.

HCV innate immune responses

Hepatitis C virus (HCV) establishes a persistent infection in more than 70% of infected individuals. This striking ability to evade the powerful innate immune system results from viral interference occurring at several levels of the interferon (IFN) system. There is strong evidence from cell culture experiments that HCV can inhibit the induction of IFNβ by cleaving important proteins in the virus sensory pathways of cells such as MAVS and TRIF. There is also evidence that HCV interferes with IFNα signaling through the Jak-STAT pathway, and that HCV proteins target IFN effector systems such as protein kinase R (PKR). These in vitro findings will have to be confirmed in clinical trials investigating the molecular mechanisms of HCV interference with the innate immune system in liver samples.

Nonstructural 3/4A protease of hepatitis C virus activates epithelial growth factor-induced signal transduction by cleavage of the T-cell protein tyrosine phosphatase

The hepatitis C virus (HCV) is a worldwide major cause of chronic liver disease with a high tendency to establish a persistent infection. To permit persistent replication of viral genomes through the cellular translation machinery without affecting host cell viability, viruses must have developed mechanisms to control cellular cascades required for sufficient viral replication, on the one hand, and to adapt viral replication to the cellular requirements on the other hand. The present study aimed to further elucidate mechanisms by which HCV targets growth factor signaling of the host cell and their implications for viral replication. The study describes a novel mechanism by which HCV influences the activation of the epithelial growth factor receptor/Akt pathway through a nonstructural (NS)3/4A-dependent down-regulation of the ubiquitously expressed tyrosine phosphatase T cell protein tyrosine phosphatase (TC-PTP). NS3/4A is demonstrated to cleave TC-PTP protease-dependently in vitro at two cleavage sites. The in vivo relevance of this finding is supported by the fact that down-regulation of TC-PTP protein expression could also be demonstrated in HCV-infected individuals and in transgenic mice with intrahepatic expression of NS3/4A.

CONCLUSION

This down-regulation of TC-PTP results in an enhancement of epithelial growth factor (EGF)-induced signal transduction and increases basal activity of Akt, which is demonstrated to be essential for the maintenance of sufficient viral replication. Hence, therapeutic targeting of NS3/4A may not only disturb viral replication by blocking the processing of the viral polyprotein but also exerts unforeseen indirect antiviral effects, further diminishing viral replication.

Pursuing different 'TRADDes': TRADD signaling induced by TNF-receptor 1 and the Epstein-Barr virus oncoprotein LMP1

The pro-apoptotic tumor necrosis factor (TNF)-receptor 1-associated death domain protein (TRADD) was initially identified as the central signaling adapter molecule of TNF-receptor 1 (TNFR1). Upon stimulation with the pro-inflammatory cytokine TNFalpha, TRADD is recruited to the activated TNFR1 by direct interaction between the death domains of both molecules. TRADD mediates TNFR1 activation of NF-kappaB and c-Jun N-terminal kinase (JNK), as well as caspase-dependent apoptosis. Surprisingly, TRADD is also recruited by latent membrane protein 1 (LMP1), the major oncoprotein of the human Epstein-Barr tumor virus. By mimicking a constitutively active receptor, LMP1 is essential for B-cell transformation by the virus, activating NF-kappaB, phosphatidylinositol 3-kinase, JAK/STAT and mitogen-activated protein kinase signaling. In contrast to TNFR1, LMP1's interaction with TRADD is independent of a functional death domain. The unique structure of the LMP1-TRADD complex dictates an unusual type of TRADD-dependent NF-kappaB signaling and subverts TRADD's potential to induce apoptosis. This article provides an overview of TNFR1 and LMP1 signal transduction with a focus on TRADD's functions in apoptotic and transforming signaling, incorporating recent results from TRADD RNAi and knockout studies.

Influenza viruses and the NF-κB signaling pathway – towards a novel concept of antiviral therapy

Influenza A virus remains a major public health concern, both in its annual toll in death and debilitation and its potential to cause devastating pandemics. Like any other virus, influenza A viruses are strongly dependent on cellular factors for replication. One of the hallmark signaling factors activated by viral pathogens is the transcription factor NF-κB. Activation of NF-κB leads to the up-regulation of a variety of antiviral genes. Thus, the factor is commonly regarded as a major regulator of the innate immune defense to infection. However, several recent studies indicate that influenza viruses have acquired the capability to reprogram this antiviral activity and to exploit the factor for efficient replication. These data provide novel insights into the pathophysiological function of NF-κB in the special environment of a virus-infected cell. Furthermore, the unexpected viral dependency on a cellular signaling factor may pave the path for novel antiviral approaches targeting essential cellular components rather than viral factors.

RNA viruses and the mitogenic Raf/MEK/ERK signal transduction cascade

The Raf/MEK/ERK signal transduction cascade belongs to the mitogen-activated protein kinase (MAPK) cascades. Raf/MEK/ERK signaling leads to stimulus-specific changes in gene expression, alterations in cell metabolism or induction of programmed cell death (apoptosis), and thus controls cell differentiation and proliferation. It is induced by extracellular agents, including pathogens such as RNA viruses. Many DNA viruses are known to induce cellular signaling via this pathway. As these pathogens partly use the DNA synthesis machinery for their replication, they aim to drive cells into a proliferative state. In contrast, the consequences of RNA virus-induced Raf/MEK/ERK signaling were less clear for a long time, but since the turn of the century the number of publications on this topic has rapidly increased. Research on this virus/host-interaction will broaden our understanding of its relevance in viral replication. This important control center of cellular responses is differently employed to support the replication of several important human pathogenic RNA viruses including influenza, Ebola, hepatitis C and SARS corona viruses.