The nonstructural NS5A protein of hepatitis C virus: an expanding, multifunctional role in enhancing hepatitis C virus pathogenesis

Oncoviruses: How do they hijack their host and current treatment regimes

Viruses have the ability to modulate the cellular machinery of their host to ensure their survival. While humans encounter numerous viruses daily, only a select few can lead to disease progression. Some of these viruses can amplify cancer-related traits, particularly when coupled with factors like immunosuppression and co-carcinogens. The global burden of cancer development resulting from viral infections is approximately 12%, and it arises as an unfortunate consequence of persistent infections that cause chronic inflammation, genomic instability from viral genome integration, and dysregulation of tumor suppressor genes and host oncogenes involved in normal cell growth. This review provides an in-depth discussion of oncoviruses and their strategies for hijacking the host's cellular machinery to induce cancer. It delves into how viral oncogenes drive tumorigenesis by targeting key cell signaling pathways. Additionally, the review discusses current therapeutic approaches that have been approved or are undergoing clinical trials to combat malignancies induced by oncoviruses. Understanding the intricate interactions between viruses and host cells can lead to the development of more effective treatments for virus-induced cancers.

Role of p53 suppression in the pathogenesis of hepatocellular carcinoma

In the world, hepatocellular carcinoma (HCC) is among the top 10 most prevalent malignancies. HCC formation has indeed been linked to numerous etiological factors, including alcohol usage, hepatitis viruses and liver cirrhosis. Among the most prevalent defects in a wide range of tumours, notably HCC, is the silencing of the p53 tumour suppressor gene. The control of the cell cycle and the preservation of gene function are both critically important functions of p53. In order to pinpoint the core mechanisms of HCC and find more efficient treatments, molecular research employing HCC tissues has been the main focus. Stimulated p53 triggers necessary reactions that achieve cell cycle arrest, genetic stability, DNA repair and the elimination of DNA-damaged cells’ responses to biological stressors (like oncogenes or DNA damage). To the contrary hand, the oncogene protein of the murine double minute 2 (MDM2) is a significant biological inhibitor of p53. MDM2 causes p53 protein degradation, which in turn adversely controls p53 function. Despite carrying wt-p53, the majority of HCCs show abnormalities in the p53-expressed apoptotic pathway. High p53 in-vivo expression might have two clinical impacts on HCC: (1) Increased levels of exogenous p53 protein cause tumour cells to undergo apoptosis by preventing cell growth through a number of biological pathways; and (2) Exogenous p53 makes HCC susceptible to various anticancer drugs. This review describes the functions and primary mechanisms of p53 in pathological mechanism, chemoresistance and therapeutic mechanisms of HCC.

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.

The Genetic Profile and Serum Level of IL-8 Are Associated with Chronic Hepatitis B and C Virus Infection

The present study evaluated the IL8-251 A/T polymorphism in samples from 74 patients with chronic hepatitis B (HBV), 100 patients with chronic hepatitis C (HCV), and 300 healthy donors (CG). The correlations of this polymorphism with plasma IL-8 and disease stage were calculated. Polymorphisms were identified by real-time PCR. IL-8 was measured by enzyme-linked immunosorbent assay. The IL8-251 A/T genotype was not associated with susceptibility to infection by HBV or HCV. The wild-type allele (A) was associated with higher levels of inflammation (p = 0.0464) and fibrosis scores (p = 0.0016) in the HBV group, representing an increased risk for increased inflammatory activity (OR = 1.84; p = 0.0464) and for high fibrosis scores (OR = 2.63; p = 0.0016). Viral load was higher in HBV patients with polymorphic genotypes (TA and TT) at the IL8-251 A/T polymorphism than in those with the wild-type genotype (p = 0.0272 and p = 0.0464, respectively). Plasma IL-8 was higher among patients infected with HBV or HCV than in the control group (p = 0.0445 and p = 0.0001, respectively). The polymorphic genotype was associated with lower IL-8 than the wild-type genotype in the HBV group (p = 0.0239) and the HCV group (p = 0.0372). The wild-type genotype for IL8-251 A/T and high IL-8 were associated with a worse prognosis for infections; therefore, they may contribute to viral persistence and the development of more severe forms of chronic viral liver diseases.

The Persistence of Hepatitis C Virus Infection in Hepatocytes Promotes Hepatocellular Carcinoma Progression by Pro-Inflammatory Interluekin-8 Expression

Background: A large amount of epidemiological evidence indicates that persistent HCV infection is the main risk factor for HCC. We aimed to study the effects of persistent HCV infection on the interaction of the virus and host cell to identify cancer gene profiles. Methods: Next-generation sequencing (NGS) was used to identify differentially expressed genes between uninfected Huh7.5.1 control cells, short-term HCV (S-HCV), early long-term HCV (eL-HCV), and long-term HCV (L-HCV) infections, which were analyzed using different dynamic bioinformatics and analytic tools. mRNA expression was validated and quantified using q-PCR. One hundred ninety-six serum samples of HCV patients with IFN/RBV treatment were used to study chemokine levels. Results: S-HCV activates an inflammatory response and drives cell death and apoptosis through cell cycle arrest via MAPK signaling. L-HCV promotes cell growth and alters cell adhesion and chemokine signaling via CXCL8-mediated-SRC regulation. A total of 196 serum samples from the HCV and HCV-HCC cohorts demonstrated significantly upregulated pro-inflammatory CXCL8 in non-SVR (persistent HCV infection) patients in the HCV-HCC group. Conclusions: Persistent infection with HCV induced pro-inflammatory CXCL8 and the oncogene SRC, thereby triggering and promoting hepatocarcinogenesis. CXCL8 may be a potential biomarker for monitoring HCV-related HCC progression.

Prognostic value and underlying mechanism of KIAA0101 in hepatocellular carcinoma: database mining and co-expression analysis

Although KIAA0101 is involved in many diseases, its expression and prognostic value in HCC remain undefined. According to CCLE, KIAA0101 is highly expressed in HCC, with a weak positive correlation between copy number and gene expression. Four studies involving 760 samples in ONCOMINE report elevated KIAA0101 expression in HCC (p=3.11E-22). The KM plotter revealed high KIAA0101 expression to be associated with worse overall survival in HCC (HR=2.09, p=4.1e-05); this prognostic power was stronger for male than female, early-stage than advanced-stage, and Asian than Caucasian patients. RNA sequencing data for 8 pairs of HCC and adjacent tissue samples validated the significantly high KIAA0101 level (p=0.00497). Moreover, functional annotations of 31 KIAA0101-coexpressed genes show enrichment of terms associated with mitosis, cytoskeleton construction, and chromosome segregation. Among 9 genes having STRING-validated protein-protein interactions with KIAA0101, two are involved in virus-related pathways. Alternative splicing analysis indicated higher expression of variant 1 and variant 2 in HCC and no significant differences in exon usage of KIAA0101 between cancer and normal tissues. These findings support that KIAA0101 is a potential prognostic biomarker for HCC and highlight the association between virus infection and the mechanism underlying the process by which KIAA0101 contributes to poor prognosis of patients.

Induction of Profibrotic Microenvironment via TLR4 MyD88-Dependent and -Independent Inflammatory Signaling in Chronic Hepatitis C Virus Infection

Hepatitis C virus (HCV) is a well-known pathogen to establish chronic infection leading to end-stage liver disease. The destruction of liver tissues takes its roots under chronic inflammation and proinflammatory signaling in liver microenvironment. The viral proteins interact with certain pattern recognition receptors, including Toll-like receptors, activating the innate immune system to clear the virus. HCV achieves immune evasion through other mechanisms and induce a continuous inflammatory microenvironment via Kupffer cells and Hepatic Stellate cells. This promotes disease progression. The current study aims to elucidate that the role of Toll-like receptor 4 (TLR4) induced innate immune response in chronic inflammation in patients chronically infected with HCV. For this purpose, changes in downstream signaling cascade of TLR4 during chronic HCV infection using peripheral blood mononuclear cells of chronic HCV patients were studied. We found significant increase in expression levels of proinflammatory and profibrotic genes induced by TLR4 Myeloid differentiation factor 88 (MyD88)-dependent pathway between treatment naive and healthy controls, while no significant difference between the expressions of genes involved in TLR4 signaling was found between treatment responders and healthy controls. Interestingly, both TLR4 MyD88-dependent and -independent pathways were found to be operational in nonresponders to interferon treatment. This further strengthens the involvement of innate immune signaling as a leading factor in HCV-mediated liver disease progression and the role of TLR4 MyD88-dependent and -independent pathway in ensuring the conditions for chronic inflammation.

Blood-based gene expression profile of oxidative stress and antioxidant genes for identifying surrogate markers of liver tissue injury in chronic hepatitis C patients

Oxidative stress is the process by which reactive molecules and free radicals are formed in cells. In this study, we report the blood-based gene expression profile of oxidative stress and antioxidant genes for identifying surrogate markers of liver tissue in chronic hepatitis C (CHC) patients by using real-time PCR. A total of 144 untreated patients diagnosed with CHC having genotype 3a and 20 healthy controls were selected for the present study. Liver biopsy staging and grading of CHC patients were performed using the METAVIR score. Total RNA was extracted from liver tissue and blood samples, followed by cDNA synthesis and real-time PCR. The relative expression of genes was calculated using the ΔΔCt method. The expression profile of 84 genes associated with oxidative stress and antioxidants was determined in liver tissue and blood samples. In liver tissue, 46 differentially expressed genes (upregulated, 27; downregulated, 19) were identified in CHC patients compared to normal samples. In blood, 61 genes (upregulated, 51; downregulated; 10) were significantly expressed in CHC patients. A comparison of gene expression in liver and whole blood showed that 20 genes were expressed in a similar manner in the liver and blood. The expression levels of commonly expressed liver and blood-based genes were also correlated with clinical factors in CHC patients. A receiver operating curve (ROC) analysis of oxidative stress genes (ALB, CAT, DHCR24, GPX7, PRDX5, and MBL2) showed that infections in patients with CHC can be distinguished from healthy controls. In conclusion, blood-based gene expression can reflect the behavior of oxidative stress genes in liver tissue, and this blood-based gene expression study in CHC patients explores new blood-based non-invasive biomarkers that represent liver damage.

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.

The Microbiota and Pancreatic Cancer

Pancreatic cancer is one of the most lethal diseases. In pancreatic cancer development and progression, genetic (gene mutations and activation of oncogenes) and environmental factors (smoking, alcohol consumption, type 2 diabetes mellitus, obesity) play an essential role. Recently, molecular studies revealed that dysbiosis of microbiota also has influence on cancer development. Research indicates that bacteria and viruses can lead to chronic inflammation, antiapoptotic changes, cell survival, and cell invasion. This review presents bacteria and viruses oncogenic for the pancreas. Possible mechanisms of carcinogenic action are also described.

Hepatitis C virus: Morphogenesis, infection and therapy

Hepatitis C virus (HCV) is a major cause of liver diseases including liver cirrhosis and hepatocellular carcinoma. Approximately 3% of the world population is infected with HCV. Thus, HCV infection is considered a public healthy challenge. It is worth mentioning, that the HCV prevalence is dependent on the countries with infection rates around 20% in high endemic countries. The review summarizes recent data on HCV molecular biology, the physiopathology of infection (immune-mediated liver damage, liver fibrosis and lipid metabolism), virus diagnostic and treatment. In addition, currently available in vitro, ex vivo and animal models to study the virus life cycle, virus pathogenesis and therapy are described. Understanding of both host and viral factors may in the future lead to creation of new approaches in generation of an efficient therapeutic vaccine.

Molecular alterations in hepatocellular carcinoma associated with hepatitis B and hepatitis C infections

Chronic infections with hepatitis B (HBV) and hepatitis C viruses (HCV) are the leading cause of cirrhosis and hepatocellular carcinoma (HCC) worldwide. Both viruses encode multifunctional regulatory proteins activating several oncogenic pathways, which induce accumulation of multiple genetic alterations in the infected hepatocytes. Gene mutations in HBV- and HCV-induced HCCs frequently impair the TP53, Wnt/b-catenin, RAS/RAF/MAPK kinase and AKT/mTOR pathways, which represent important anti-cancer targets. In this review, we highlight the molecular mechanisms underlying the pathogenesis of primary liver cancer, with particular emphasis on the host genetic variations identified by high-throughput technologies. In addition, we discuss the importance of genetic alterations, such as mutations in the telomerase reverse transcriptase (TERT) promoter, for the diagnosis, prognosis, and tumor stratification for development of more effective treatment approaches.

Interactions of the Disordered Domain II of Hepatitis C Virus NS5A with Cyclophilin A, NS5B, and Viral RNA Show Extensive Overlap

Domain II of the nonstructural protein 5 (NS5A) of the hepatitis C virus (HCV) is involved in intermolecular interactions with the viral RNA genome, the RNA-dependent RNA polymerase NS5B, and the host factor cyclophilin A (CypA). However, domain II of NS5A (NS5A^DII) is largely disordered, which makes it difficult to characterize the protein-protein or protein-nucleic acid interfaces. Here we utilized a mass spectrometry-based protein footprinting approach in attempts to characterize regions forming contacts between NS5A^DII and its binding partners. In particular, we compared surface topologies of lysine and arginine residues in the context of free and bound NS5A^DII. These experiments have led to the identification of an RNA binding motif (³⁰⁵RSRKFPR³¹¹) in an arginine-rich region of NS5A^DII. Furthermore, we show that K308 is indispensable for both RNA and NS5B binding, whereas W316, further downstream, is essential for protein-protein interactions with CypA and NS5B. Most importantly, NS5A^DII binding to NS5B involves a region associated with RNA binding within NS5B. This interaction down-regulated RNA synthesis by NS5B, suggesting that NS5A^DII modulates the activity of NS5B and potentially regulates HCV replication.

Ankyrin Repeat Domain 1 is Up-regulated During Hepatitis C Virus Infection and Regulates Hepatitis C Virus Entry

Hepatitis C virus (HCV) is highly dependent on host proteins for its own propagation. By transcriptome sequencing (RNA-Seq) analysis, we identified 30 host genes that were significantly differentially expressed in cell culture-grown HCV (HCVcc)-infected cells. Of these candidate genes, we selected and characterized ankyrin repeat domain 1 (ANKRD1). Here, we showed that protein expression of ANKRD1 was up-regulated in HCVcc-infected cells. We further showed that protein expression level of ANKRD1 was increased by nonstructural 5A (NS5A) protein. ANKRD1 specifically interacted with NS5A both in vitro and coimmunoprecipitation assays. Protein interaction was mediated through the domain II of NS5A and the C-terminal region of ANKRD1. Promoter activity of ANKRD1 was also increased by NS5A protein. Moreover, up-regulation of ANKRD1 expression was mediated through alteration in intracellular calcium homeostasis and ER stress in HCVcc-infected cells. We showed that silencing of ANKRD1 impaired HCV propagation without affecting HCV replication. By using HCV-like infectious particle (HCV-LP), we demonstrated that HCV single-cycle infection was drastically impaired in ANKRD1 knockdown cells. Finally, we verified that ANKRD1 was required for HCV entry. These data suggest that HCV coopts ANKRD1 for its own propagation and up-regulation of ANKRD1 may contribute to HCV-mediated liver pathogenesis.

Hepatitis C virus-associated cancer

Hepatitis C virus (HCV) is one of the major etiologic agents of liver cancer. HCV is an RNA virus that, unlike hepatitis B virus, is unable to integrate into the host genome. Through complex interactions between viral and host proteins that induce host responses and promote inflammation, fibrosis, and ultimately cirrhosis, HCV infection can result in the development of hepatocellular carcinoma (HCC). The HCV oncogenic process involves genetic and epigenetic alterations and oncogenic effects mediated by viral proteins in the activation of cellular oncogenes, inactivation of tumor-suppressor genes, and dysregulation of multiple signal-transduction pathways. Advances in genetics and gene expression profiling have enhanced our current understanding of the pathways involved in HCV-associated liver cancer development. In this review, we summarize the current understanding of mechanisms of hepatocarcinogenesis induced by HCV infection.

An insight into the diagnosis and pathogenesis of hepatitis C virus infection

This review focuses on research findings in the area of diagnosis and pathogenesis of hepatitis C virus (HCV) infection over the last few decades. The information based on published literature provides an update on these two aspects of HCV. HCV infection, previously called blood transmitted non-A, non-B infection, is prevalent globally and poses a serious public health problem worldwide. The diagnosis of HCV infection has evolved from serodetection of non-specific and low avidity anti-HCV antibodies to detection of viral nucleic acid in serum using the polymerase chain reaction (PCR) technique. Current PCR assays detect viral nucleic acid with high accuracy and the exact copy number of viral particles. Moreover, multiplex assays using real-time PCR are available for identification of HCV-genotypes and their isotypes. In contrast to previous methods, the newly developed assays are not only fast and economic, but also resolve the problem of the window period as well as differentiate present from past infection. HCV is a non-cytopathic virus, thus, its pathogenesis is regulated by host immunity and metabolic changes including oxidative stress, insulin resistance and hepatic steatosis. Both innate and adaptive immunity play an important role in HCV pathogenesis. Cytotoxic lymphocytes demonstrate crucial activity during viral eradication or viral persistence and are influenced by viral proteins, HCV-quasispecies and several metabolic factors regulating liver metabolism. HCV pathogenesis is a very complex phenomenon and requires further study to determine the other factors involved.

Cyclophilin A as a New Therapeutic Target for Hepatitis C Virus-induced Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) related to hepatitis B virus (HBV) and hepatitis C virus (HCV) infections is thought to account for more than 80% of primary liver cancers. Both HBV and HCV can establish chronic liver inflammatory infections, altering hepatocyte and liver physiology with potential liver disease progression and HCC development. Cyclophilin A (CypA) has been identified as an essential host factor for the HCV replication by physically interacting with the HCV non structural protein NS5A that in turn interacts with RNA-dependent RNA polymerase NS5B. CypA, a cytosolic binding protein of the immunosuppressive drug cyclosporine A, is overexpressed in many cancer types and often associated with malignant transformation. Therefore, CypA can be a good target for molecular cancer therapy. Because of antiviral activity, the CypA inhibitors have been tested for the treatment of chronic hepatitis C. Nonimmunosuppressive Cyp inhibitors such as NIM811, SCY-635, and Alisporivir have attracted more interests for appropriating CypA for antiviral chemotherapeutic target on HCV infection. This review describes CypA inhibitors as a potential HCC treatment tool that is contrived by their obstructing chronic HCV infection and summarizes roles of CypA in cancer development.

Hepatocellular carcinoma in patients with chronic hepatitis C virus infection in the Asia-Pacific region

Hepatocellular carcinoma (HCC) is the third-leading cause of cancer-related mortality worldwide. Although hepatitis B still remains the most common risk factor worldwide, chronic hepatitis C virus (HCV) infection is the driving force for the increased incidence of HCC especially in Western countries and Japan. In hepatitis B virus (HBV)-endemic areas, after successful vaccination programs against HBV, chronic HCV infection is now emerging as an important cause of chronic liver diseases. Unlike patients with chronic hepatitis B, those with chronic hepatitis C (CHC) develop HCC in the presence of established cirrhosis in most cases. However, a significant minority of CHC develops HCC in the absence of cirrhosis. Although HCV is a RNA virus with little potential for integrating its genetic material into host genome, various HCV proteins, including core, envelope, and nonstructural proteins, have oncogenic properties by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses. Overall, a combination of virus-specific, host genetic, environmental, and immune-related factors are likely to determine progression to HCC. Strategies aimed at eliminating the virus may provide opportunities for effective prevention of the development of HCC. Pegylated interferon plus ribavirin therapy appears to be effective at reducing the risk of HCC in patients who achieve sustained virologic responses. In summary, with the emerging importance of CHC, mechanisms of HCV-associated hepatocellular carcinogenesis should be clarified to provide insight into advanced therapeutic and preventive approaches, which eventually decrease the incidence and mortality of HCC.

Hepatitis C virus: the role of molecular mimicry in response to interferon treatment

Chronic hepatitis C virus (HCV) infection is one of the major causes of chronic liver disease worldwide. In order for HCV to persist, the virus must escape immune recognition or inhibit the host immune response. The NS5A protein contains the interferon sensitivity-determining region (ISDR) and is able to repress dsRNA-dependent protein kinase (PKR) thus influencing the response to interferon (IFN) therapy. Patients who respond to IFN therapy have stronger antibody reactivity against the NS5A compared to IFN non-responders. Therefore, given the possible role for the ISDR in IFN resistance and differential antibody reactivity, it is possible that variation in ISDR may be involved in viral immune escape and development of persistent HCV infection employing aspects of host mimicry. In this study, pre-treatment samples obtained from HCV infected patients were used to investigate the effect of different NS5A ISDR variants on the IFN antiviral response and their involvement in immune evasion. The NS5A was identified as a homologue of the variable region of immunoglobulins (Ig). The IFN resistant genotypes had higher levels of similarity to Ig compared to IFN sensitive genotypes. Expression of NS5A-6003 (HCV genotype 1b) and NS5A-6074 (HCV genotype 2a) was able to rescue vesicular stomatitis virus (VSV) from IFN inhibition and restore luciferase activity. A correlation between Ig-like NS5A structure and also antibody response with the outcome of IFN treatment was observed.

The Rubella virus capsid is an anti-apoptotic protein that attenuates the pore-forming ability of Bax

Apoptosis is an important mechanism by which virus-infected cells are eliminated from the host. Accordingly, many viruses have evolved strategies to prevent or delay apoptosis in order to provide a window of opportunity in which virus replication, assembly and egress can take place. Interfering with apoptosis may also be important for establishment and/or maintenance of persistent infections. Whereas large DNA viruses have the luxury of encoding accessory proteins whose primary function is to undermine programmed cell death pathways, it is generally thought that most RNA viruses do not encode these types of proteins. Here we report that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis. Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur. Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation. Importantly, data from reverse genetic studies are consistent with a scenario in which the anti-apoptotic activity of capsid protein is important for virus replication. If so, this would be among the first demonstrations showing that blocking apoptosis is important for replication of an RNA virus. Finally, it is tempting to speculate that other slowly replicating RNA viruses employ similar mechanisms to avoid killing infected cells.

Among the variety of defense systems employed by mammalian cells to combat virus infection, apoptosis or programmed cell death is the most drastic response. Some large DNA viruses encode proteins whose sole function is to block apoptosis. Conversely, very little is known about whether RNA viruses encode analogous proteins. In many cases, RNA viruses are able to replicate before cell death occurs, which may be one reason why so little thought has been given to this topic. However, a number of RNA viruses, some of which are important human pathogens, have slow replication cycles and it stands to reason that they must block apoptosis during this time period. Here we show that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. Data from reverse genetic experiments suggest that the anti-apoptotic function of a virus-encoded protein is important for replication of an RNA virus. We anticipate that other slowly replicating RNA viruses may employ similar mechanisms and, as such, these studies have implications for development of novel anti-virals and vaccines.

Prediction of prognostic biomarkers for interferon-based therapy to hepatitis C virus patients: a meta-analysis of the NS5A protein in subtypes 1a, 1b, and 3a

Background

Hepatitis C virus (HCV) is a worldwide health problem with no vaccine and the only approved therapy is Interferon-based plus Ribavarin. Response prediction to treatment has health and economic impacts, and is a multi-factorial problem including both host and viral factors (e.g: age, sex, ethnicity, pre-treatment viral load, and dynamics of the HCV non-structural protein NS5A quasispecies). We implement a novel approach for extracting features including informative markers from mutations in the non-structural 5A protein (NS5A), specifically its Interferon sensitivity determining region (ISDR) and V3 regions, and use a novel bioinformatics approach for pattern recognition on the NS5A protein and its motifs to find biomarkers for response prediction using class association rules and comparing the predictability of the different features.

Results

A total of 58 sequences from sustained responders and 94 from non-responders were downloaded from the HCV LANL database. Site-specific signatures for response prediction from the NS5A protein were extracted from the alignments. Class association rules were generated (e.g.: sustained response is associated with position A2368T in subtype 1a (support 100% and confidence 52.19%); in subtype 1b, response is associated with E2356G/D/K (support 76.3% and confidence 67.3%).

Conclusion

The V3 region was a more accurate biomarker than the ISDR region. Subtype-specific class association rules gave better support and confidence than profile hidden Markov models HMMs scores, genetic distances or number of variable sites, and would thus aid in the prediction of prognostic biomarkers and improve the accuracy of prognosis. Sites-specific class association rules in the V3 region of the NS5A protein have given the best support and confidence.

The successful immune response against hepatitis C nonstructural protein 5A (NS5A) requires heterologous DNA/protein immunization

The aim of this study was to evaluate the immunogenicity of NS5A protein of human hepatitis C virus (HCV) when delivered as naked DNA (NS5A DNA), or recombinant protein (rNS5A). DBA/2J mice received NS5A DNA, rNS5A, or NS5A DNA/rNS5A in different prime-boost combinations with a peptidoglycan Immunomax((R)). The weakest response was induced after rNS5A prime and NS5A DNA boost; rNS5A alone induced an immune response with a strong Th2-component; and NS5A DNA alone, a relatively weak secretion of IL-2 and IFN-gamma. The most efficient was co-injection of NS5A DNA and rNS5A, which induced a significant increase in CD4(+) and CD8(+) T-cell counts, anti-NS5A antibodies, specific T-cell proliferation, and proinflammatory cytokine production in vitro against a broad spectrum of NS5A epitopes. Administration of the mixture of adjuvanted DNA and protein immunogens can be selected as the best regimen for further preclinical HCV-vaccine trials.

Computational identification of post-translational modification sites and functional families reveal possible moonlighting role of rotaviral proteins

Rotavirus (RV) diarrhoea causes huge number deaths in children less than 5 years of age. In spite of available vaccines, it has been difficult to combat RV due to large number of antigenically distinct genotypes, high mutation rates, generation of reassortant viruses due to segmented genome. RV is an eukaryotic virus which utilizes host cell machinery for its propagation. Since RV only encodes 12 proteins, post­translational modification (PTM) is important mechanism for modification, which consequently alters their function. A single protein exhibiting different functions in different locations or in different subcellular sites, are known to be ’moonlighting‘. So there is a possibility that viral proteins moonlight in separate location and in different time to exhibit diverse cellular effects. Based on the primary sequence, the putative behaviour of proteins in cellular environment can be predicted, which helps to classify them into different functional families with high reliability score. In this study, sites for phosphorylation, glycosylation and SUMOylation of the six RV structural proteins (VP1, VP2, VP3, VP4, VP6 & VP7) & five non­structural proteins (NSP1, NSP2,NSP3,NSP4 & NSP5) and the functional families were predicted. As NSP6 is a very small protein and not required for virus growth & replication, it was not included in the study. Classification of RV proteins revealed multiple putative functions of each structural protein and varied number of PTM sites, indicating that RV proteins may also moonlight depending on requirements during viral life cycle. Targeting the crucial PTM sites on RV structural proteins may have implications in developing future anti­rotaviral strategies.

Hepatitis B and C virus-related carcinogenesis

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection are the most important causes of hepatocellular carcinoma (HCC), accounting for the majority of the cases worldwide. The geographical distribution of HCC therefore coincides with the distribution of HBV and HCV infections in those areas. Similar to nonviral liver diseases, HBV and HCV infection can cause chronic injury to the liver, with subsequent progression to severe fibrosis and cirrhosis. The presence of cirrhosis is a major risk factor for the development of HCC. However, HCC can occur in the absence of cirrhosis, suggesting that both HBV and HCV may be directly involved in hepatocarcinogenesis. Several HBV factors have been implicated in hepatocarcinogenesis, including the HBx gene, the pre-S2/S gene and the HBV spliced protein. Furthermore, HBV can be integrated into the host genome, leading to changes in genomic function or chromosomal instability. By contrast to HBV, HCV cannot integrate into the host genome. Various HCV proteins, including the core, envelope and nonstructural proteins, have been shown to have oncogenic properties. For HBV infection, antiviral therapy and vaccination have been shown to decrease the risk of HCC. Antiviral therapy for HCV can also reduce the risk of HCC.

The heat shock protein inhibitor Quercetin attenuates hepatitis C virus production

The hepatitis C viral (HCV) genome is translated through an internal ribosome entry site (IRES) as a single polyprotein precursor that is subsequently cleaved into individual mature viral proteins. Nonstructural protein 5A (NS5A) is one of these proteins that has been implicated in regulation of viral genome replication, translation from the viral IRES and viral packaging. We sought to identify cellular proteins that interact with NS5A and determine whether these interactions may play a role in viral production. Mass spectrometric analysis of coimmunoprecipitated NS5A complexes from cell extracts identified heat shock proteins (HSPs) 40 and 70. We confirmed an NS5A/HSP interaction by confocal microscopy demonstrating colocalization of NS5A with HSP40 and with HSP70. Western analysis of coimmunoprecipitated NS5A complexes further confirmed interaction of HSP40 and HSP70 with NS5A. A transient transfection, luciferase-based, tissue culture IRES assay demonstrated NS5A augmentation of HCV IRES-mediated translation, and small interfering RNA (siRNA)-mediated knockdown of HSP70 reduced this augmentation. Treatment with an inhibitor of HSP synthesis, Quercetin, markedly reduced baseline IRES activity and its augmentation by NS5A. HSP70 knockdown also modestly reduced viral protein accumulation, whereas HSP40 and HSP70 knockdown both reduced infectious viral particle production in an HCV cell culture system using the J6/JFH virus fused to the Renilla luciferase reporter. Treatment with Quercetin reduced infectious particle production at nontoxic concentrations. The marked inhibition of virus production by Quercetin may partially be related to reduction of HSP40 and HSP70 and their potential involvement in IRES translation, as well as viral morphogenesis or secretion.

CONCLUSION

Quercetin may allow for dissection of the viral life cycle and has potential therapeutic use to reduce virus production with low associated toxicity.

Hepatitis C virus-induced hepatocarcinogenesis

Although there is strong evidence that hepatitis C virus (HCV) is one of the leading causes of hepatocellular carcinoma (HCC), there is still much to understand regarding the mechanism of HCV-induced transformation. While liver fibrosis resulting from long-lasting chronic inflammation and liver regeneration resulting from immune-mediated cell death are likely factors that contribute to the development of HCC, the direct role of HCV proteins remains to be determined. In vitro studies have shown that HCV expression may interfere with cellular functions that are important for cell differentiation and cell growth. However, most studies were performed in artificial models which can only give clues for potential mechanisms that need to be confirmed in more relevant models. Furthermore, the difficulty to identify HCV proteins and infected liver cells in patients, contributes to the complexity of our current understanding. For these reasons, there is currently very little experimental evidence for a direct oncogenic role of HCV. Further studies are warranted to clarify these issues.

Hepatitis C virus NS5A and core proteins induce oxidative stress-mediated calcium signalling alterations in hepatocytes

BACKGROUND/AIMS

The hepatitis C virus (HCV) structural core and non-structural NS5A proteins induce in liver cells a series of intracellular events, including elevation of reactive oxygen and nitrogen species (ROS/RNS). Since oxidative stress is associated to altered intracellular Ca(2+) homeostasis, we aimed to investigate the effect of these proteins on Ca(2+) mobilization in human hepatocyte-derived transfected cells, and the protective effect of quercetin treatment.

METHODS

Ca(2+) mobilization and actin reorganization were determined by spectrofluorimetry. Production of ROS/RNS was determined by flow cytometry.

RESULTS

Cells transfected with NS5A and core proteins showed enhanced ROS/RNS production and resting cytosolic Ca(2+) concentration, and reduced Ca(2+) concentration into the stores. Phenylephrine-evoked Ca(2+) release, Ca(2+) entry and extrusion by the plasma membrane Ca(2+)-ATPase were significantly reduced in transfected cells. Similar effects were observed in cytokine-activated cells. Phenylephrine-evoked actin reorganization was reduced in the presence of core and NS5A proteins. These effects were significantly prevented by quercetin. Altered Ca(2+) mobilization and increased calpain activation were observed in replicon-containing cells.

CONCLUSIONS

NS5A and core proteins induce oxidative stress-mediated Ca(2+) homeostasis alterations in human hepatocyte-derived cells, which might underlie the effects of both proteins in the pathogenesis of liver disorders associated to HCV infection.

Retracted: Genetic diversity in hepatitis C virus (HCV): A brief review

The following article from Reviews in Medical Virology, Genetic diversity in hepatitis C virus (HCV) a brief review, by M Irshad, published online on December 16 2008 in Wiley InterScience (www.interscience.wiley.com) has been retracted by agreement between the author, the journal Editor in Chief, P.D. Griffiths, and the publisher Wiley Blackwell. The retraction has been agreed due to overlap with the following article by P Simmonds, Genetic diversity and evolution of hepatitis C virus fifteen years on, published in Journal of General Virology, 2004, 85, 3173-3178.

The non-structural 5A protein of hepatitis C virus exhibits genotypic differences in interferon antagonism

BACKGROUND/AIMS

Patients infected with hepatitis C virus (HCV) genotype 2 or 3 usually respond better to interferon (IFN) treatment than those infected with genotype 1. In this study, we investigated whether the non-structural 5A protein (NS5A) of HCV genotypes 1 and 2 (1b-NS5A and 2a-NS5A, respectively) exerted differential counteractivities against IFN treatment.

METHODS

We compared the inhibitory effects of 1b-NS5As and 2a-NS5As on IFN activity. We also investigated the replication inhibition of HCV subgenomic replicons containing 1b-NS5A or 2a-NS5A in response to IFN treatment.

RESULTS

1b-NS5As exerted more profound inhibitory effects on IFN activity than 2a-NS5As. The replication of the 2a-NS5A-containing replicons was more sensitive to IFN treatment than that of the 1b-NS5A-containing replicons. Deletion of the interferon sensitivity-determining region/protein kinase R-binding domain (PKR-BD), the V3 domain, or the C-terminus region of NS5A significantly abrogated its anti-IFN activity. Domain swapping between 1b-NS5A and 2a-NS5A in the V3 domain and/or the C-terminus region resulted in a transfer of their anti-IFN activity.

CONCLUSIONS

1b-NS5As exert higher magnitudes of IFN antagonism than do 2a-NS5As. The V3 and the C-terminus regions are responsible for the differential anti-IFN effects. This phenomenon may partly explain the genotype-linked differences in the response of HCV to IFN treatment.

Hepatitis C virus infection: molecular pathways to metabolic syndrome

Chronic infection with hepatitis C virus (HCV) can induce insulin resistance (IR) in a genotype-dependent fashion, thus contributing to steatosis, progression of fibrosis and resistance to interferon therapy. The molecular mechanisms in genotype 1 patients that lead to metabolic syndrome are still ambiguous. Based on our current understanding, HCV proteins associate with mitochondria and endoplasmic reticulum and promote oxidative stress. The latter mediates signals involving the p38 mitogen-activated protein kinase and activates nuclear factor kappa B. This transcription factor plays a key role in the expression of cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin 6, interleukin 8, tumor growth factor beta, and Fas ligand. TNF-alpha inhibits the function of insulin receptor substrates and decreases the expression of the glucose transporter and lipoprotein lipase in peripheral tissues, which is responsible for the promotion of insulin resistance. Furthermore, reduced adiponectin levels, loss of adiponectin receptors, and decreased anti-inflammatory peroxisome proliferator-activated receptor alpha in the liver of HCV patients may contribute to reduced fatty acid oxidation, inflammation, and eventually lipotoxicity. This chain of events may be initiated by HCV-associated IR and provides a direction for future research in the areas of therapeutic intervention.

Role for conserved residues of sindbis virus nonstructural protein 2 methyltransferase-like domain in regulation of minus-strand synthesis and development of cytopathic infection

The plus-strand RNA genome of Sindbis virus (SINV) encodes four nonstructural proteins (nsP1 to nsP4) that are involved in the replication of the viral RNA. The approximately 800-amino-acid nsP2 consists of an N-terminal domain with nucleoside triphosphatase and helicase activities and a C-terminal protease domain. Recently, the structure determined for Venezuelan equine encephalitis virus nsP2 indicated the presence of a previously unrecognized methyltransferase (MTase)-like domain within the C-terminal approximately 200 residues and raised a question about its functional importance. To assess the role of this MTase-like region in viral replication, highly conserved arginine and lysine residues were mutated to alanine. The plaque phenotypes of these mutants ranged from large/wild-type to small plaques with selected mutations demonstrating temperature sensitive lethality. The proteolytic polyprotein processing activity of nsP2 was unaffected in most of the mutants. Some of the temperature-sensitive mutants showed reduction in the minus-strand RNA synthesis, a function that has not yet been ascribed to nsP2. Mutation of SINV residue R615 rendered the virus noncytopathic and incapable of inhibiting the host cell translation but with no effects on the transcriptional inhibition. This property differentiated the mutation at R615 from previously described noncytopathic mutations. These results implicate nsP2 in regulation of minus-strand synthesis and suggest that different regions of the nsP2 MTase-like domain differentially modulate host defense mechanisms, independent of its role as the viral protease.

NS5ATP9, a gene up-regulated by HCV NS5A protein

Non-structural protein 5A (NS5A) appears to interact with a variety of cellular proteins and play an important role in mediating cell growth, cellular signaling pathways and pathogenesis of hepatitis C virus (HCV). NS5ATP9 was identified as a NS5A trans-activated protein in suppression subtractive hybridization (SSH), and the regulation was confirmed by luciferase reporter assay and quantitative real time PCR (qRT-PCR). A minimal promoter region contained within the 211bp (nucleotides -161 to +50bp) immediately upstream of the transcription initiation site. NS5ATP9 is a NS5A up-regulation gene which may play a role in the pathogenesis of HCV-associated hepatocellular carcinoma.

Heterogeneity of CK2 phosphorylation sites in the NS5A protein of different hepatitis C virus genotypes

BACKGROUND/AIMS

The hepatitis C virus NS5A protein is phosphorylated by several cellular kinases, including casein kinase 2 (CK2). Little is known about CK2 phosphorylation of NS5A from different HCV genotypes and clinical isolates.

METHODS

NS5A from patients with HCV-1a (24 cases), HCV-1b (9) or HCV-3 (16) was analyzed by direct sequencing and CK2 phosphorylation sites were defined using a well-validated prediction rule. In vitro phosphorylation assays were performed using recombinant CK2 and synthetic peptides or full-length NS5A. In vivo phosphorylation by endogenous CK2 of NS5A expressed in hepatoma cells was also investigated.

RESULTS

The mean number of CK2 sites within full-length NS5A, was significantly higher in HCV-3 compared to HCV-1a (P<0.01) and HCV-1b (P<0.01). The number of CK2 sites was more homogeneous in HCV-3 variants compared to HCV-1a and HCV-1b variants (P<0.05). The number of predicted CK2 sites correlated with the degree of in vitro and in vivo phosphorylation of NS5A by CK2.

CONCLUSIONS

CK2-dependent phosphorylation of NS5A is heterogeneous among different HCV genotypes and clinical isolates. This might have an influence on virus biology and pathogenicity.

NS3 protein of hepatitis C virus regulates cyclooxygenase-2 expression through multiple signaling pathways

Hepatitis C virus (HCV) causes chronic hepatitis, which often results in the development of liver cirrhosis and hepatocellular carcinoma (HCC) worldwide. In this study, we demonstrated that the non-structural protein NS3 of HCV enhances cyclooxygenase-2 (COX-2) gene promoter activity, COX-2 mRNA expression, COX-2 protein production, and prostaglandin E2 (PGE2) release in HepG2 cells in a concentration-dependent fashion. We also showed that transcription factor NF-κB is required for the activation of COX-2 regulated by NS3. In addition, multiple signaling pathways are involved cooperatively in the expression of COX-2 activated by the viral protein in a calcium-independent manner, which requires signaling components including JNK, ERK, and PKD2. A thorough investigation of mechanism involved in the activation of COX-2 regulated by HCV would provide insights into our understanding the processes of liver inflammatory response and hepatocellular carcinoma development caused by the viral infection and also into the development of novel therapeutics against HCV infection.

Evolution of hepatitis C virus non-structural 5A gene in the progression of liver disease to hepatocellular carcinoma

BACKGROUND

The interaction between the hepatitis C virus (HCV) non-structural 5A (NS5A) protein of HCV and the protein kinase R (PKR), which is an effector of the cellular antiviral response and has been defined as a tumour suppressor, may affect the control of protein synthesis and cell growth.

AIM

We investigated the genetic evolution of the NS5A region in the NS5A PKR-binding domain (NS5A-PKRbd) of patients with HCV 1b-related cirrhosis who subsequently developed or not hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

The quasispecies composition of NS5A-PKRbd was inferred by sequencing an average of 15 clones per sample in specimens obtained from 26 patients with cirrhosis who developed or not HCC during a follow-up of 5 years.

RESULTS

At baseline, 13/17 patients with final HCC and six out of nine patients with cirrhosis who subsequently did not develop HCC harboured a wild-type (wt) strain master sequence. Over time, the prevalence of wt strain was higher in patients who developed HCC with respect to those who maintained the cirrhosis status (15/17 vs 4/9, respectively; P=0.0166).

CONCLUSION

The maintenance of or evolution to the wt strain of the NS5A domain in cirrhotic patients with final HCC highlights the central role of NS5A protein in the viral life cycle and in the progression of liver disease.

Dynamics of Apoptotic Activity during Antiviral Treatment of Patients with Chronic Hepatitis C

Introduction

Cell death during antiviral therapy of patients with chronic hepatitis C is not well understood.

Methods

In the present study, apoptotic activity was monitored by quantification of apoptotic cytokeratin-18 neoepitopes in serum from patients with chronic hepatitis C before and 4, 12, 24 and 48 weeks after initiation of antiviral therapy with pegylated interferon-α2a and ribavirin and was compared with viral kinetic parameters.

Results

After 4 weeks of treatment apoptotic activity decreased significantly compared with baseline. Later during treatment, however, apoptotic activity increased again to levels similar to baseline. Alanine aminotransferase (ALT) activity also showed a significant decrease at week 4 compared with baseline but, in contrast to apoptotic activity, ALT remained at a reduced level during the treatment period. Baseline apoptotic activity was inversely correlated with the infected cell loss while an increase of apoptotic activity within the first 4 treatment weeks compared with baseline was positively correlated with the infected cell loss.

Conclusions

Apoptosis appears to be an important form of cell death during interferon-α-based treatment and is associated with infected cell loss and underestimated by ALT activity.

Hepatitis C virus proteins

Hepatitis C virus (HCV) encodes a single polyprotein, which is processed by cellular and viral proteases to generate 10 polypeptides. The HCV genome also contains an overlapping +1 reading frame that may lead to the synthesis of an additional protein. Until recently, studies of HCV have been hampered by the lack of a productive cell culture system. Since the identification of HCV genome approximately 17 years ago, structural, biochemical and biological information on HCV proteins has mainly been obtained with proteins produced by heterologous expression systems. In addition, some functional studies have also been confirmed with replicon systems or with retroviral particles pseudotyped with HCV envelope glycoproteins. The data that have accumulated on HCV proteins begin to provide a framework for understanding the molecular mechanisms involved in the major steps of HCV life cycle. Moreover, the knowledge accumulated on HCV proteins is also leading to the development of antiviral drugs among which some are showing promising results in early-phase clinical trials. This review summarizes the current knowledge on the functions and biochemical features of HCV proteins.

Hepatitis C virus genetic variability in patients undergoing antiviral therapy

Hepatitis C virus (HCV) has been the subject of intense research and clinical investigations due to its worldwide prevalence and major role in chronic liver disease. Like most RNA viruses, HCV circulates in vivo as a complex population of different but closely related viral variants, commonly referred to as a quasispecies. Recent studies suggest that ribavirin might exert an antiviral effect against HCV through both mutagenic effect and an impairment of RNA replication. The introduction of alpha interferon (IFN-alpha) plus ribavirin combination therapy was an important breakthrough in the treatment of chronic HCV infection. However, the rate of sustained virological response is still unsatisfactory, particularly in patients infected with HCV genotype 1. Viral persistence, a hallmark of HCV, may result from a dynamic control of the host response by the virus. In children with chronic HCV infection, the viral population is initially highly homogeneous, but diversifies during prolonged infection which seems to be a common event during chronic hepatitis C in childhood. Coinfection of human immunodeficiency virus 1 (HIV-1) patients by HCV can complicate the treatment of these patients with highly active antiretroviral therapy (HAART). HIV coinfection is associated with a decrease of HCV quasispecies variability, which appears to be reversed by effective HAART.

Induction of a unique gene expression profile in primary human hepatocytes by hepatitis C virus core, NS3 and NS5A proteins

Hepatocellular carcinoma (HCC) is a fatal disease and hepatitis B and C viruses (HBV and HCV) are considered as major causative factors for the development of HCC. We have conducted gene expression profiling studies to search for potential target genes responsible for HCV-mediated HCC. Adenoviruses encoding core (HCV structural protein), NS3 and NS5A [HCV non-structural (NS) proteins] were generated and infected individually or together in freshly isolated primary human hepatocytes. An adenovirus harboring the oncogenic HBV protein, HBx, was included for comparison. A microarray platform of over 22,000 human oligos was analyzed to seek out significant differentially expressed genes among these viral proteins. We also compared these gene expression profiles with those obtained from HCV-infected liver samples from chronic liver disease (CLD) patients and HCV-related HCC. We found that HCV-related proteins largely induce unique genes when compared with HBx. In particular, interferon-inducible gene 27 (IFI27) was highly expressed in HCV or core-infected hepatocytes and HCV-related CLD or HCC, but was not significantly expressed in HBx-infected hepatocytes or HBV-related CLD or HCC, indicating that IFI27 may play a role in HCV-mediated HCC. In conclusion, our results suggest that HBV and HCV promote HCC development mainly through different mechanisms.

The role of cytokines in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a frequent malignancy worldwide with a high rate of metastasis. The hepatitis B and C viruses are considered major etiological factors associated with the development of HCC, particularly as a result of their induction of chronic inflammation. There is increasing evidence that the inflammatory process is inherently associated with many different cancer types, including HCC. Specifically, this review aims to cover evidence for the potential roles of cytokines, an important component of the immune system, in promoting HCC carcinogenesis and progression. A global summary of cytokine levels, functions, polymorphisms, and therapies with regard to HCC is presented. In particular, the role of proinflammatory Th1 and anti-inflammatory Th2 cytokine imbalances in the microenvironment of HCC patients with metastasis and the possible clinical significance of these findings are addressed. Overall, multiple studies, spanning many decades, have begun to elucidate the important role of cytokines in HCC.

The NS5A protein of the hepatitis C virus genotype 1a is cleaved by caspases to produce C-terminal-truncated forms of the protein that reside mainly in the cytosol

The nonstructural 5A (NS5A) protein of the hepatitis C virus (HCV) is a multifunctional protein that is implicated in viral replication and pathogenesis. We report here that NS5A of HCV-1a is cleaved at multiple sites by caspase proteases in transfected cells. Two cleavage sites at positions Asp154 and 248DXXD251 were mapped. Cleavage at Asp154 has been previously recognized as one of the caspase cleavage sites for the NS5A protein of HCV genotype 1b (1, 2) and results in the production of a 17-kDa fragment. The sequence 248DXXD251 is a novel caspase recognition motif for NS5A and is responsible for the production of a 31-kDa fragment. Furthermore, we show that Arg217 is implicated in the production of the previously described 24-kDa product, whose accumulation is affected by both calpain and caspase inhibitors. We also showed that caspase-mediated cleavage occurs in the absence of exogenous proapoptotic stimuli and is not related to the accumulation of the protein in the endoplasmic reticulum. Interestingly, our data indicate that NS5A is targeted by at least two different caspases and suggest that caspase 6 is implicated in the production of the 17-kDa fragment. Most importantly, we report that, all the detectable NS5A fragments following caspase-mediated cleavage are C-terminal-truncated forms of NS5A and are mainly localized in the cytosol. Thus, in sharp contrast to the current view we found no evidence supporting a role for caspase-mediated cleavage in the transport of the NS5A protein to the nucleus, which could lead to transcriptional activation.

The protein phosphatase 2A represents a novel cellular target for hepatitis C virus NS5A protein

It is well established that HCV NS5A protein when expressed in mammalian cells perturbs the extracellular signal regulated kinase (ERK) pathway. The protein serine/threonine phosphatase 2A controls the phosphorylation of numerous proteins involved in cell signaling and one characterized function is the regulation of Ras-Raf mitogen activated protein (MAP) kinase signaling pathways. Our results showed that expression of HCV NS5A protein stimulates phosphatase 2A (PP2A) activity in cells, indicating the relevance of NS5A as a regulator of PP2A in vivo. We found that transient expression of the full length NS5A protein in different cell lines leads to a significant increase of the PP2A activity and this activity is specifically inhibited by the addition of okadaic acid, a PP2A inhibitor, in living cells. Further investigation showed that NS5A protein interacts in vivo and in vitro with the scaffolding A and the catalytic C subunits of PP2A. We propose that HCV NS5A represents a viral PP2A regulatory protein. This is a novel function for the NS5A protein which may have a key role in the ability of the virus to deregulate cell growth and survival.

Differential contribution of hepatitis C virus NS5A and core proteins to the induction of oxidative and nitrosative stress in human hepatocyte-derived cells

BACKGROUND/AIMS

We aimed to explore the effects of hepatitis C virus (HCV) core and NS5A proteins on reactive oxygen (ROS) and nitrogen species (RNS) formation and on gene expression profile of iNOS in human hepatocyte-derived cells.

METHODS

Production of ROS and RNS and nitrotyrosine residues accumulation were determined by flow cytometry and fluorescent microscopy as well as by Western blot, respectively, in NS5A- and core-transfected cells. Northern blot, Western blot, real-time PCR, and luciferase assays were used to assess iNOS gene expression in both transfectants.

RESULTS

Cytokine-activated NS5A- and core-transfected cells induced ROS and RNS production but an earlier and more marked increase was observed in NS5A-expressing cells. Superoxide production was also augmented, showing a similar temporal pattern of appearance in both NS5A- and core-transfected cells. Although both NS5A and core HCV proteins were able to up-regulate iNOS gene expression, accompanied by a nitrotyrosine-containing proteins accumulation, an earlier iNOS overexpression was observed in NS5A-expressing cells, suggesting a different time course of iNOS activation pattern for core and NS5A HCV proteins.

CONCLUSIONS

Our results indicate a differential contribution of both HCV proteins to oxidative and nitrosative stress generation.

Hepatitis C Virus Nonstructural Protein 5A (NS5A) Is an RNA-binding Protein

Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) has been shown to antagonize numerous cellular pathways, including the antiviral interferon-alpha response. However, the capacity of this protein to interact with the viral polymerase suggests a more direct role for NS5A in genome replication. In this study, we employed two bacterially expressed, soluble derivatives of NS5A to probe for novel functions of this protein. We find that NS5A has the capacity to bind to the 3'-ends of HCV plus and minus strand RNAs. The high affinity binding site for NS5A in the 3'-end of plus strand RNA maps to the polypyrimidine tract, an element known to be essential for genome replication and infectivity. NS5A has a preference for single-stranded RNA containing stretches of uridine or guanosine. Values for the equilibrium dissociation constants for high affinity binding sites were in the 10 nM range. Two-dimensional gel electrophoresis followed by Western blotting revealed the presence of unphosphorylated NS5A in Huh-7 cells stably expressing the subgenomic replicon. Moreover, RNA immunoprecipitation and NS5A pull-down experiments showed the capacity of replicon-derived NS5A to bind to synthetic RNA and the HCV genome, respectively. Deletion of all of the casein kinase II phosphorylation sites in NS5A supported stable replication of a subgenomic replicon in Huh-7. However, this derivative could not be labeled with inorganic phosphate, suggesting that extensive phosphorylation of NS5A is not required for the replication functions of NS5A. The discovery that NS5A is an RNA-binding protein defines a new functional target for development of agents to treat HCV infection and a new structural class of RNA-binding proteins.