Hepatitis C virus core protein differently regulates the JAK-STAT signaling pathway under interleukin-6 and interferon-gamma stimuli

Toll-like Receptor Response to Hepatitis C Virus Infection: A Recent Overview

Hepatitis C virus (HCV) infection remains a major global health burden, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that detect pathogen-associated molecular patterns and activate downstream signaling to induce proinflammatory cytokine and chemokine production. An increasing number of studies have suggested the importance of TLR responses in the outcome of HCV infection. However, the exact role of innate immune responses, including TLR response, in controlling chronic HCV infection remains to be established. A proper understanding of the TLR response in HCV infection is essential for devising new therapeutic approaches against HCV infection. In this review, we discuss the progress made in our understanding of the host innate immune response to HCV infection, with a particular focus on the TLR response. In addition, we discuss the mechanisms adopted by HCV to avoid immune surveillance mediated by TLRs.

Epigenetic Mechanisms Involved in HCV-Induced Hepatocellular Carcinoma (HCC)

Hepatocellular carcinoma (HCC), is the third leading cause of cancer-related deaths, which is largely caused by virus infection. About 80% of the virus-infected people develop a chronic infection that eventually leads to liver cirrhosis and hepatocellular carcinoma (HCC). With approximately 71 million HCV chronic infected patients worldwide, they still have a high risk of HCC in the near future. However, the mechanisms of carcinogenesis in chronic HCV infection have not been still fully understood, which involve a complex epigenetic regulation and cellular signaling pathways. Here, we summarize 18 specific gene targets and different signaling pathways involved in recent findings. With these epigenetic alterations requiring histone modifications and DNA hyper or hypo-methylation of these specific genes, the dysregulation of gene expression is also associated with different signaling pathways for the HCV life cycle and HCC. These findings provide a novel insight into a correlation between HCV infection and HCC tumorigenesis, as well as potentially preventable approaches. Hepatitis C virus (HCV) infection largely causes hepatocellular carcinoma (HCC) worldwide with 3 to 4 million newly infected cases diagnosed each year. It is urgent to explore its underlying molecular mechanisms for therapeutic treatment and biomarker discovery. However, the mechanisms of carcinogenesis in chronic HCV infection have not been still fully understood, which involve a complex epigenetic regulation and cellular signaling pathways. Here, we summarize 18 specific gene targets and different signaling pathways involved in recent findings. With these epigenetic alterations requiring histone modifications and DNA hyper or hypo-methylation of these specific genes, the dysregulation of gene expression is also associated with different signaling pathways for the HCV life cycle and HCC. These findings provide a novel insight into a correlation between HCV infection and HCC tumorigenesis, as well as potentially preventable approaches.

Hepatitis C Virus: Evading the Intracellular Innate Immunity

Hepatitis C virus (HCV) infections constitute a major public health problem and are the main cause of chronic hepatitis and liver disease worldwide. The existing drugs, while effective, are expensive and associated with undesirable secondary effects. There is, hence, an urgent need to develop novel therapeutics, as well as an effective vaccine to prevent HCV infection. Understanding the interplay between HCV and the host cells will certainly contribute to better comprehend disease progression and may unravel possible new cellular targets for the development of novel antiviral therapeutics. Here, we review and discuss the interplay between HCV and the host cell innate immunity. We focus on the different cellular pathways that respond to, and counteract, HCV infection and highlight the evasion strategies developed by the virus to escape this intracellular response.

Induction of Chemokines by Hepatitis C Virus Proteins: Synergy of the Core Protein with Interleukin-1β and Interferon-γ in Liver Bystander Cells

Chronic hepatitis C virus (HCV) infection accounts for a large proportion of hepatic fibrosis and carcinoma cases observed worldwide. Mechanisms involved in HCV-induced hepatic injury have yet to be fully elucidated. Of particular interest is the capacity of HCV to regulate inflammatory responses. Here, we reveal modulation of cytokine activity by the HCV proteins non-structural protein 3 (NS3), glycoprotein E2, and core protein for their ability to induce chemokine expression in various liver bystander cells. Chemokines sustain chronic liver inflammation and relay multiple fibrogenic effects. CCL2, CCL3, CCL20, CXCL8, and CXCL10 were differentially expressed after treatment of monocytes, fibroblasts, or liver sinusoidal microvascular endothelial cells (LSECs) with HCV proteins. In comparison to NS3 and glycoprotein E2, core protein was a stronger inducer of chemokines in liver bystander cells. Interferon-γ (IFN-γ) and interleukin-1β (IL-1β) synergized with core protein to induce CCL2, CCL20, CXCL8, or CXCL10 in fibroblasts or LSECs. These findings reveal new mechanisms of hepatic injury caused by HCV.

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

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

Interleukin-6: A promising cytokine to support liver regeneration and adaptive immunity in liver pathologies

Liver pathologies (fibrosis, cirrhosis, alcoholic, non-alcoholic diseases and hepatocellular carcinoma) represent one of the most common causes of death worldwide. A number of genetic and environmental factors contribute to the development of liver diseases. Interleukin-6 (IL-6) is a pleiotropic cytokine, exerting variety of effects on inflammation, liver regeneration, and defence against infections by regulating adaptive immunity. Due to its high abundance in inflammatory settings, IL-6 is often viewed as a detrimental cytokine. However, accumulating evidence supports the view that IL-6 has a beneficial impact in numerous liver pathologies, due to its roles in liver regeneration and in promoting an anti-inflammatory response in certain conditions. IL-6 promotes proliferation, angiogenesis and metabolism, and downregulates apoptosis and oxidative stress; together these functions are critical for mediating hepatoprotection. IL-6 is also an important regulator of adaptive immunity where it induces T cell differentiation and regulates autoimmunity. It can augment antiviral adaptive immune responses and mitigate exhaustion of T cells during chronic infection. This review focuses on studies that present IL-6 as a key factor in regulating liver regeneration and in supporting effector immune functions and suggests that these functions of IL-6 can be exploited in treatment strategies for liver pathologies.

Interactome of the hepatitis C virus: Literature mining with ANDSystem

A study of the molecular genetics mechanisms of host-pathogen interactions is of paramount importance in developing drugs against viral diseases. Currently, the literature contains a huge amount of information that describes interactions between HCV and human proteins. In addition, there are many factual databases that contain experimentally verified data on HCV-host interactions. The sources of such data are the original data along with the data manually extracted from the literature. However, the manual analysis of scientific publications is time consuming and, because of this, databases created with such an approach often do not have complete information. One of the most promising methods to provide actualisation and completeness of information is text mining. Here, with the use of a previously developed method by the authors using ANDSystem, an automated extraction of information on the interactions between HCV and human proteins was conducted. As a data source for the text mining approach, PubMed abstracts and full text articles were used. Additionally, external factual databases were analyzed. On the basis of this analysis, a special version of ANDSystem, extended with the HCV interactome, was created. The HCV interactome contains information about the interactions between 969 human and 11 HCV proteins. Among the 969 proteins, 153 'new' proteins were found not previously referred to in any external databases of protein-protein interactions for HCV-host interactions. Thus, the extended ANDSystem possesses a more comprehensive detailing of HCV-host interactions versus other existing databases. It was interesting that HCV proteins more preferably interact with human proteins that were already involved in a large number of protein-protein interactions as well as those associated with many diseases. Among human proteins of the HCV interactome, there were a large number of proteins regulated by microRNAs. It turned out that the results obtained for protein-protein interactions and microRNA-regulation did not depend on how well the proteins were studied, while protein-disease interactions appeared to be dependent on the level of study. In particular, the mean number of diseases linked to well-studied proteins (proteins were considered well-studied if they were mentioned in 50 or more PubMed publications) from the HCV interactome was 20.8, significantly exceeding the mean number of associations with diseases (10.1) for the total set of well-studied human proteins present in ANDSystem. For proteins not highly poorly-studied investigated, proteins from the HCV interactome (each protein was referred to in less than 50 publications) distribution of the number of diseases associated with them had no statistically significant differences from the distribution of the number of diseases associated with poorly-studied proteins based on the total set of human proteins stored in ANDSystem. With this, the average number of associations with diseases for the HCV interactome and the total set of human proteins were 0.3 and 0.2, respectively. Thus, ANDSystem, extended with the HCV interactome, can be helpful in a wide range of issues related to analyzing HCV-host interactions in the search for anti-HCV drug targets. The demo version of the extended ANDSystem covered here containing only interactions between human proteins, genes, metabolites, diseases, miRNAs and molecular-genetic pathways, as well as interactions between human proteins/genes and HCV proteins, is freely available at the following web address: http://www-bionet.sscc.ru/psd/andhcv/.

Virtual screening and optimization of Type II inhibitors of JAK2 from a natural product library

Amentoflavone has been identified as a JAK2 inhibitor by structure-based virtual screening of a natural product library. In silico optimization using the DOLPHIN model yielded analogues with enhanced potency against JAK2 activity and HCV activity in cellulo. Molecular modeling and kinetic experiments suggested that the analogues may function as Type II inhibitors of JAK2.

Immunocompetent mouse models to evaluate intrahepatic T cell responses to HCV vaccines

Despite considerable progress in the development of immunocompetent mouse models using different high end technologies, most available small animal models for HCV study are unsuitable for challenge experiments, which are vital for vaccine development, as they fail to measure the T cell response in liver. A recently developed intra-hepatic challenge model results in HCV antigen expression in mouse hepatocytes and through the detection of the surrogate marker, SEAP, in serum, the effect of prior vaccination can be monitored longitudinally.

Autophagy in HCV infection: keeping fat and inflammation at bay

Hepatitis C virus (HCV) infection is one of the main causes of chronic liver disease. Viral persistence and pathogenesis rely mainly on the ability of HCV to deregulate specific host processes, including lipid metabolism and innate immunity. Recently, autophagy has emerged as a cellular pathway, playing a role in several aspects of HCV infection. This review summarizes current knowledge on the molecular mechanisms that link the HCV life cycle with autophagy machinery. In particular, we discuss the role of HCV/autophagy interaction in dysregulating inflammation and lipid homeostasis and its potential for translational applications in the treatment of HCV-infected patients.

Interaction of hepatitis C virus core protein with janus kinase is required for efficient production of infectious viruses

Chronic hepatitis C virus (HCV) infection is responsible for the development of liver cirrhosis and hepatocellular carcinoma. HCV core protein plays not only a structural role in the virion morphogenesis by encapsidating a virus RNA genome but also a non-structural role in HCV-induced pathogenesis by blocking innate immunity. Especially, it has been shown to regulate JAK-STAT signaling pathway through its direct interaction with Janus kinase (JAK) via its proline-rich JAK-binding motif (⁷⁹PGYPWP⁸⁴). However, little is known about the physiological significance of this HCV core-JAK association in the context of the virus life cycle. In order to gain an insight, a mutant HCV genome (J6/JFH1-79A82A) was constructed to express the mutant core with a defective JAK-binding motif (⁷⁹AGYAWP⁸⁴) using an HCV genotype 2a infectious clone (J6/JFH1). When this mutant HCV genome was introduced into hepatocarcinoma cells, it was found to be severely impaired in its ability to produce infectious viruses in spite of its robust RNA genome replication. Taken together, all these results suggest an essential requirement of HCV core-JAK protein interaction for efficient production of infectious viruses and the potential of using core-JAK blockers as a new anti-HCV therapy.

The hepatitis C virus core protein can modulate RNA-dependent RNA synthesis by the 2a polymerase

RNA replication enzymes are multi-subunit protein complexes whose activity can be modulated by other viral and cellular factors. For genotype 1b Hepatitis C virus (HCV), the RNA-dependent RNA polymerase (RdRp) subunit of the replicase, NS5B, has been reported to interact with the HCV Core protein to decrease RNA synthesis (Kang et al., 2009). Here we used a cell-based assay for RNA synthesis to examine the Core-NS5B interaction of genotype 2a HCV. Unlike the 1b NS5B, the activity of the 2a NS5B was stimulated by the Core protein. Using the bimolecular fluorescence complementation assay, the 2a Core co-localized with 2a NS5B when they were transiently expressed in cells. The two proteins can form a co-immunoprecipitable complex. Deletion analysis showed that the N-terminal 75 residues of 2a Core were required to contact 2a NS5B to modulate its activity. The C-terminal transmembrane helix of 2a NS5B also contributes to the interaction with the 2a Core. To determine the basis for the differential effects of the Core-RdRp interaction, we found that the 2a RdRp activity was enhanced by both the 1b Core and 2a Core. However, the 1b NS5B activity was slightly inhibited by either Core protein. The replication of the 2a JFH-1 replicon was increased by co-expressed 2a Core while the genotype 1b Con1 replicon was not significantly affected by the corresponding Core. Mutations in 2a NS5B that affected the closed RdRp structure were found to be less responsive to 2a Core. Finally, we determined that RNA synthesis by the RdRps from genotypes 2a, 3a and 4a HCV were increased by the Core proteins from HCV of genotypes 1-4. These results reveal another difference between RNA syntheses by the different genotype RdRps and add additional examples of a viral structural protein regulating viral RNA synthesis.

RNA virus capsid proteins: more than just a shell

Capsid proteins are obligatory components of infectious virions. Their primary structural function is to protect viral genomes during entry and exit from host cells. Evidence suggests that these proteins can also modulate the activity and specificity of viral replication complexes. More recently, it has become apparent that they play critical roles at the virus–host interface. Here, we discuss how capsid proteins of RNA viruses interact with key host cell proteins and pathways to modulate cell physiology in order to benefit virus replication. Capsid–host cell interactions may also have implications for viral disease. Understanding how capsids regulate virus–host interactions may lead to the development of novel antiviral therapies based on targeting the activities of cellular proteins.

Viral infection: an evolving insight into the signal transduction pathways responsible for the innate immune response

The innate immune response is initiated by the interaction of stereotypical pathogen components with genetically conserved receptors for extracytosolic pathogen-associated molecular patterns (PAMPs) or intracytosolic nucleic acids. In multicellular organisms, this interaction typically clusters signal transduction molecules and leads to their activations, thereby initiating signals that activate innate immune effector mechanisms to protect the host. In some cases programmed cell death-a fundamental form of innate immunity-is initiated in response to genotoxic or biochemical stress that is associated with viral infection. In this paper we will summarize innate immune mechanisms that are relevant to viral pathogenesis and outline the continuing evolution of viral mechanisms that suppress the innate immunity in mammalian hosts. These mechanisms of viral innate immune evasion provide significant insight into the pathways of the antiviral innate immune response of many organisms. Examples of relevant mammalian innate immune defenses host defenses include signaling to interferon and cytokine response pathways as well as signaling to the inflammasome. Understanding which viral innate immune evasion mechanisms are linked to pathogenesis may translate into therapies and vaccines that are truly effective in eliminating the morbidity and mortality associated with viral infections in individuals.

Suppression of signal transducers and activators of transcription 1 in hepatocellular carcinoma is associated with tumor progression

Signal transducers and activators of transcription (STAT) 1 plays a pivotal role in cell-cycle and cell-fate determination, and vascular endothelial growth factor (VEGF) also contributes tumor growth. Recently, interferon (IFN) α has been reported to be effective for prevention of hepatocellular carcinomas (HCCs) recurrence, but the detailed mechanisms remain elusive. In vitro, cobalt chloride-treated VEGF induction and hypoxia responsive element (HRE) promoter activity were inhibited by IFNs and this abrogation was cancelled by introduction of small interfering RNA for STAT1. Immunoprecipitation/chromatin immunoprecipitation analyses showed STAT1 bound to hypoxia-inducible factor (HIF)-1α and dissociated HIF-complex from HRE promoter lesion. In a xenograft model using Balb/c nude mice, tumor growth was suppressed by IFNα through inhibition of VEGF expression and it was oppositely enhanced when STAT1-deleted cells were injected. This augmentation was due to upregulation of VEGF and hyaluronan synthase 2. In human samples, 29 HCCs were resected, divided into two groups based on STAT1 activation in tumor and the clinical features were investigated. Patients with suppressed STAT1 activity had a shorter recurrence-free survival. Histological and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses showed portal vein microinvasion and increased VEGF levels in tumors from suppressed STAT1 group. These human samples also showed a reverse correlation between VEGF and STAT1-regulated genes expression. These results in vitro and in vivo suggested that IFNα are potential candidates for prevention of vessel invasion acting through inhibition of VEGF expression and need to be properly used when STAT1 expression is suppressed.

Prolactin promotes hepatocellular carcinoma through Janus kinase 2

BACKGROUND

Hepatocellular carcinoma (HCC) is one human cancer with obvious gender disparity. This study investigated the association of aberrant prolactin levels with HCC risk and the potential impacts on HCC of the prolactin receptor (PRLR)/Janus kinase 2 (JAK2) signaling.

METHODS

Serum prolactin of 63 HCC patients and 162 subjects without HCC was measured by radioimmunoassay. The expressions of PRLR and phosphorylated JAK2 (p-JAK2) in 82 retrospectively collected HCC specimens were evaluated by immunohistochemistry and further incorporated into the survival analysis. The immunoblotting and proliferation assays were used to analyze the effects of PRLR/JAK2 signaling on liver cancer cells with prolactin treatment.

RESULTS

Serum prolactin level was significantly higher in HCC patients than in controls. Hepatocellular carcinoma patients with high p-JAK2 expression had a significantly higher postoperative risk than those with low p-JAK2 expression. Moreover, results from the multivariate analysis indicated the prognostic role of p-JAK2 expression with respect to overall survival in HCC patients. In addition, the Kaplan-Meier survival curve showed that high p-JAK2 expression was associated with poor survival in HCC patients with high PRLR expression. The immunoblotting assay showed that prolactin induced the expression of both p-JAK2 and cyclin D1 in Hep-G2 cells. Importantly, the proliferative effects induced by prolactin could be effectively attenuated by adding AG490, a JAK2 inhibitor.

CONCLUSIONS

Increased circulating prolactin was found in HCC patients and high p-JAK2 expression could predict poor overall survival in those patients expressing high PRLR. In addition, prolactin contributed to the proliferation of liver cancer cells through PRLR/JAK2 signaling.

Hepatitis C virus-host interactions: Etiopathogenesis and therapeutic strategies

Hepatitis C virus (HCV) is a significant health problem facing the world. This virus infects more than 170 million people worldwide and is considered the major cause of both acute and chronic hepatitis. Persons become infected mainly through parenteral exposure to infected material by blood transfusions or injections with nonsterile needles. Although the sexual behavior is considered as a high risk factor for HCV infection, the transmission of HCV infection through sexual means, is less frequently. Currently, the available treatment for patients with chronic HCV infection is interferon based therapies alone or in combination with ribavirin and protease inhibitors. Although a sustained virological response of patients to the applied therapy, a great portion of patients did not show any response. HCV infection is mostly associated with progressive liver diseases including fibrosis, cirrhosis and hepatocellular carcinoma. Although the focus of many patients and clinicians is sometimes limited to that problem, the natural history of HCV infection (HCV) is also associated with the development of several extrahepatic manifestations including dermatologic, rheumatologic, neurologic, and nephrologic complications, diabetes, arterial hypertension, autoantibodies and cryglobulins. Despite the notion that HCV-mediated extrahepatic manifestations are credible, the mechanism of their modulation is not fully described in detail. Therefore, the understanding of the molecular mechanisms of HCV-induced alteration of intracellular signal transduction pathways, during the course of HCV infection, may offer novel therapeutic targets for HCV-associated both hepatic and extrahepatic manifestations. This review will elaborate the etiopathogenesis of HCV-host interactions and summarize the current knowledge of HCV-associated diseases and their possible therapeutic strategies.

Hepatitis C virus E2 protein induce reactive oxygen species (ROS)-related fibrogenesis in the HSC-T6 hepatic stellate cell line

Chronic infection of hepatitis C virus (HCV) leads to hepatic fibrosis and subsequently cirrhosis, although the underlying mechanisms have not been established. Previous studies have indicated that the binding of HCV E2 protein and CD81 on the surface of hepatic stellate cells (HSCs) lead to the increased protein level and activity of matrix metallopeptidase (MMP) 2, indicating that E2 may involve in the HCV-induced fibrosis. This study was designed to investigate the involvement of HCV E2 protein in the hepatic fibrogenesis. Results showed that E2 protein may promote the expression levels of α-smooth muscle actin (α-SMA) and collagen α(I). Furthermore, several pro-fibrosis or pro-inflammatory cytokines, including transforming growth factor (TGF)-β1, connective tissue growth factor (CTGF), interleukin (IL)-6 and IL-1β, were significantly increased in E2 transfected-HSC cell lines, while the expression of MMP-2 are also considerably increased. Moreover, the significant increases of CTGF and TGF-β1 in a stable E2-expressing Huh7 cell line were also observed the same results. Further molecular studies indicated that the impact of E2 protein on collagen production related to higher production of ROS and activated Janus kinase (JAK)1, JAK2 and also enhance the activation of ERK1/2 and p38, while catalase and inhibitors specific for JAK, ERK1/2, and p38 abolish E2-enhanced expression of collagen α(I). Taken together, this study indicated that E2 protein involve in the pathogenesis of HCV-mediated fibrosis via an up-regulation of collagen α(I) and oxidative stress, which is JAK pathway related.

Chronic hepatitis C

The goal of antiviral therapy for patients with chronic hepatitis C virus (HCV) infection is to attain a sustained virologic response (SVR), which is defined as undetectable serum HCV-RNA levels at 6 months after the cessation of treatment. Major improvements in antiviral therapy for chronic hepatitis C have occurred in the past decade. The addition of ribavirin to interferon-alfa therapy and the introduction of pegylated interferon (PEG-IFN) have substantially improved SVR rates in patients with chronic hepatitis C. The optimization of HCV therapy with PEG-IFN and ribavirin continues to evolve. Studies are ongoing that use viral kinetics to tailor therapy to an individual's antiviral response and determine the ideal length of treatment to maximize the chance of SVR. Improved SVR can be achieved with new specific inhibitors that target the HCV NS3/4A protease and the NS5B polymerase. Several long-term follow-up studies have shown that SVR, when achieved, is associated with a very low risk of virologic relapse. Furthermore, antiviral therapy can reduce the morbidity and mortality rates associated with chronic hepatitis C by reducing fibrosis progression, the incidence of cirrhosis, and hepatocellular carcinoma.

Tumor viruses and cancer biology: Modulating signaling pathways for therapeutic intervention

Tumor viruses have provided relatively simple genetic systems, which can be manipulated for understanding the molecular mechanisms of the cellular transformation process. A growing body of information in the tumor virology field provides several prospects for rationally targeted therapies. However, further research is needed to better understand the multiple mechanisms utilized by these viruses in cancer progression in order to develop therapeutic strategies. Initially viruses were believed to be associated with cancers as causative agents only in animals. It was almost half a century before the first human tumor virus, Epstein-Barr virus (EBV), was identified in 1964. Subsequently, several human tumor viruses have been identified including Kaposi sarcoma associated herpesvirus (KSHV), human Papillomaviruses (HPV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human T lymphotropic virus (HTLV-1) and recently identified Merkel cell Polyomavirus (MCPyV). Tumor viruses are sub-categorized as either DNA viruses, which include EBV, KSHV, HPV, HBV, and MCPyV, or RNA viruses such as HCV and HTLV-1. Tumor-viruses induce oncogenesis through manipulating an array of different cellular pathways. These viruses initiate a series of cellular events, which lead to immortalization and proliferation of the infected cells by disrupting the mitotic checkpoint upon infection of the host cell. This is often accomplished by functional inhibition or proteasomal degradation of many tumor suppressor proteins by virally encoded gene products. The virally infected cells can either be eliminated via cell-mediated apoptosis or persist in a state of chronic infection. Importantly, the chronic persistence of infection by tumor viruses can lead to oncogenesis. This review discusses the major human tumor associated viruses and their ability to modulate numerous cell signaling pathways, which can be targeted for potential therapeutic approaches.

Hepatitis C virus core protein interacts with fibrinogen-beta and attenuates cytokine stimulated acute-phase response

Fibrinogen-beta (FBG-beta), an important acute-phase protein (APP), is generated by the liver as a target for inflammatory mediators. Here we identified FBG-beta as a hepatitis C virus (HCV) core interacting protein by screening a human liver complementary DNA (cDNA) library using mammalian two-hybrid analysis. An association between FBG-beta and HCV core protein was verified by confocal microscopy and coimmunoprecipitation from the transfected human hepatocyte (Huh-7) cell line. HCV core or genomic RNA transfected Huh-7 cells modestly increased FBG-beta protein expression when compared to the basal level in control hepatocytes. Transfection of HCV core or full-length (FL) gene into Huh-7 cells up-regulated basal FBG-beta promoter activity. Exogenous addition of IL-6 stimulates FBG-beta promoter activity in hepatocytes. However, ectopic expression of HCV core or FL in hepatocytes inhibited IL-6-stimulated FBG-beta promoter activation. Inhibition of endogenous FBG-beta expression following introduction of small interfering RNA (siRNA) into cells displayed a gain of function of promoter regulation by HCV core protein. Further studies suggested that HCV core gene expression in stable transfectants of Huh-7 cells resulted in a basal up-regulation of FBG-beta and other APPs. However, treatment with cytokines, interleukin-6 (IL-6), or tumor necrosis factor-alpha repressed FBG-beta and other acute-phase response (APR) genes.

CONCLUSION

Our results reveal that the core/FBG-beta interaction may act as a regulatory feedback, allowing repression of IL-6-stimulated APR genes. Together, these data suggested a network of interactions between HCV core and the hepatic APR genes, and may contribute to impaired innate immunity for viral persistence.

Loss of STAT5 causes liver fibrosis and cancer development through increased TGF-{beta} and STAT3 activation

The molecular mechanisms underlying the development of hepatocellular carcinoma are not fully understood. Liver-specific signal transducer and activator of transcription (STAT) 5A/B–null mice (STAT5-LKO) were treated with carbon tetrachloride (CCl₄), and histological analyses revealed liver fibrosis and tumors. Transforming growth factor (TGF)–β levels and STAT3 activity were elevated in liver tissue from STAT5-LKO mice upon CCl₄ treatment. To define the molecular link between STAT5 silencing and TGF-β up-regulation, as well as STAT3 activation, we examined STAT5-null mouse embryonic fibroblasts and primary hepatocytes. These cells displayed elevated TGF-β protein levels, whereas messenger RNA levels remained almost unchanged. Protease inhibitor studies revealed that STAT5 deficiency enhanced the stability of mature TGF-β. Immunoprecipitation and immunohistochemistry analyses demonstrated that STAT5, through its N-terminal sequences, could bind to TGF-β and that retroviral-mediated overexpression of STAT5 decreased TGF-β levels. To confirm the in vivo significance of the N-terminal domain of STAT5, we treated mice that expressed STAT5 lacking the N terminus (STAT5-ΔN) with CCl₄. STAT5-ΔN mice developed CCl₄-induced liver fibrosis but no tumors. In conclusion, loss of STAT5 results in elevated TGF-β levels and enhanced growth hormone–induced STAT3 activity. We propose that a deregulated STAT5–TGF-β–STAT3 network contributes to the development of chronic liver disease.

Hepatitis C virus and ethanol alter antigen presentation in liver cells

Alcoholic patients have a high incidence of hepatitis C virus (HCV) infection. Alcohol consumption enhances the severity of the HCV disease course and worsens the outcome of chronic hepatitis C. The accumulation of virally infected cells in the liver is related to the HCV-induced inability of the immune system to recognize infected cells and to develop the immune responses. This review covers the effects of HCV proteins and ethanol on major histocompatibility complex (MHC) class I- and class II-restricted antigen presentation. Here, we discuss the liver which functions as an immune privilege organ; factors, which affect cleavage and loading of antigenic peptides onto MHC class I and class II in hepatocytes and dendritic cells, and the modulating effects of ethanol and HCV on antigen presentation by liver cells. Altered antigen presentation in the liver limits the ability of the immune system to clear HCV and infected cells and contributes to disease progression. HCV by itself affects dendritic cell function, switching their cytokine profile to the suppressive phenotype of interleukin-10 (IL-10) and transforming growth factor beta (TGFβ) predominance, preventing cell maturation and allostimulation capacity. The synergistic action of ethanol with HCV results in the suppression of MHC class II-restricted antigen presentation. In addition, ethanol metabolism and HCV proteins reduce proteasome function and interferon signaling, thereby suppressing the generation of peptides for MHC class I-restricted antigen presentation. Collectively, ethanol exposure further impairs antigen presentation in HCV-infected liver cells, which may provide a partial explanation for exacerbations and the poor outcome of HCV infection in alcoholics.

Specific targeting of hepatitis C virus core protein by an intracellular single-chain antibody of human origin

The hepatitis C virus (HCV) core protein is essential for viral genome encapsidation and plays an important role in steatosis, immune evasion, and hepatocellular carcinoma. It may thus represent a promising therapeutic target to interfere with the HCV life-cycle and related pathogenesis. In this study, we used phage display to generate single-chain variable domain antibody fragments (scFv) to the core protein from bone marrow plasma cells of patients with chronic hepatitis C. An antibody with high-affinity binding (scFv42C) was thus identified, and the binding site was mapped to the PLXG motif (residues 84-87) of the core protein conserved among different genotypes. Whereas scFv42C displayed diffuse cytoplasmic fluorescence when expressed alone in the Huh7 human hepatoma cell line, cotransfection with the core gene shifted its subcellular distribution into that of core protein. The intracellular association of scFv42C with its target core protein was independently demonstrated by the fluorescence resonance energy transfer technique. Interestingly, expression of the single-chain antibody reduced core protein levels intracellularly, particularly in the context of full HCV replication. Moreover, cell proliferation as induced by the core protein could be reversed by scFv4C coexpression. Therefore, scFv42C may represent a novel anti-HCV agent, which acts by sequestering core protein and attenuating core protein-mediated pathogenesis.

CpG island hypermethylation of SOCS-1 gene is inversely associated with HBV infection in hepatocellular carcinoma

The CpG island hypermethylation of the suppressor of cytokine signaling-1 (SOCS-1) gene is frequently methylated in hepatocellular carcinoma (HCC), but its clinicopathological significance and the potential risk factors for the epigenetic change in HCC remain poorly understood. The methylation status of SOCS-1 CpG island was evaluated in fresh-frozen tissues from 284 HCC patients using the methylation-specific polymerase chain reaction. The expression of SOCS-1 protein was analyzed by immunohistochemical staining. SOCS-1 methylation was found in 163 (57%) of 284 HCCs. SOCS-1 methylation was positively associated with patient age (P=0.002) and HCV infection status (P=0.004), and was inversely associated with HBV infection (P=0.0002). In the multivariate logistic regression analysis, the HB(s)Ag-negative HCCs showed a 2.78 (95% CI=1.31-5.89, P=0.007) times greater risk of SOCS-1 methylation than the HB(s)Ag-positive HCCs. SOCS-1 methylation also occurred at a 4.34 times (95% CI=1.24-14.25, P=0.02) higher prevalence in antiHCV-positive cases than in antiHCV-negative cases. No prognostic effect of SOCS-1 methylation was observed in the HCCs. In conclusion, the present study suggests that SOCS-1 methylation in HCC may be negatively associated with HB(s)Ag status.

Proteasome activation by hepatitis C core protein is reversed by ethanol-induced oxidative stress

BACKGROUND & AIMS

The proteasome is a major cellular proteinase. Its activity is modulated by cellular oxidants. Hepatitis C core protein and ethanol exposure both cause enhanced oxidant generation. The aim was to investigate whether core protein, by its ability to generate oxidants, alters proteasome activity and whether these alterations are further affected by ethanol exposure.

METHODS

These interactions were examined in Huh-7 cell lines that expressed inducible HCV core protein and/or constitutive cytochrome P450 2E1 (CYP2E1) and as purified components in a cell-free system. Chymotrypsin-like proteasome activity was measured fluorometrically.

RESULTS

Proteasome activity in core-positive 191-20 cells was 20% higher than that in core-negative cells and was enhanced 3-fold in CYP2E1-expressing L14 cells. Exposure of core-positive cells to glutathione ethyl ester, catalase, or the CYP2E1 inhibitor diallyl sulfide partially reversed the elevation of proteasome activity in core-positive cells, whereas ethanol exposure suppressed proteasome activity. The results indicate that proteasome activity was up-regulated by low levels of core-induced oxidative stress but down-regulated by high levels of ethanol-elicited stress. These findings were partially mimicked in a cell-free system. Addition of core protein enhanced the peptidase activity of purified 20S proteasome containing the proteasome activator PA28 and was further potentiated by addition of liver mitochondrial and/or microsome fractions. However, proteasome activation was significantly attenuated when fractions were obtained from ethanol-fed animals.

CONCLUSIONS

HCV core protein interacts with PA28, mitochondrial, and endoplasmic reticulum proteins to cause low levels of oxidant stress and proteasome activation, which is dampened during ethanol metabolism when oxidant generation is higher.

Molecular virology of the hepatitis C virus: implication for novel therapies

With the advent of second-generation agents that for the first time specifically target individual HCV proteins, HCV-specific therapy has arrived. The study of HCV molecular virology has helped make this possible and is helping us to identify additional new antiviral targets that will be targeted by third-generation drugs. Key to these efforts is the development of high-efficiency HCV replicons. The future effective pharmacologic control of HCV will likely consist of a cocktail of simultaneously administered virus-specific agents with independent targets. This should minimize the emergence of resistance against any single agent. The way we treat HCV should change dramatically over the next few years.

Modulation of signaling pathways by RNA virus capsid proteins

Capsid proteins are structural components of virus particles. They are nucleic acid-binding proteins whose main recognized function is to package viral genomes into protective structures called nucleocapsids. Research over the last 10 years indicates that in addition to their role as genome guardians, viral capsid proteins modulate host cell signaling networks. Disruption or alteration of intracellular signaling pathways by viral capsids may benefit replication of the virus by affecting innate immunity and in some cases, may underlie disease progression. In this review, we describe how the capsid proteins from medically relevant RNA viruses interact with host cell signaling pathways.

Role of hepatitis C virus proteins (C, NS3, NS5A) in hepatic oncogenesis

In recent years, the effects of hepatitis C virus (HCV) proteins on hepatocarcinogenesis have undergone intense investigations. The potentially oncogenic proteins include at least three HCV proteins: core (C) protein, NS3, and NS5A. Several authors indicated relationships between subcellular localization, concentration, a specific molecular form of the proteins (full length, truncated, phosphorylated), the presence of specific domains (the nuclear localization signal homologous to e.g. Bcl-2) and their effects on the mechanisms linked to oncogenesis. The involvement of all the proteins has been described as being in control of the cell cycle, through interactions with key proteins of the process (p53, p21, cyclins, proliferating cell nuclear antigen), transcription factors, proto-oncogenes, growth factors/cytokines and their receptors, and proteins linked to the apoptotic process. Untilnow, the involvement of the core protein of HCV in liver carcinogenesis is the most recognized. One of the most common proteins affected by HCV proteins is the p53 tumor-suppressor protein. The p21/WAF1 gene is a major target of p53, and the effect of HCV proteins on the gene is frequently considered in parallel. The results of studies on the effects of HCV proteins on the apoptotic process are controversial. This work summarizes the information collected thus far in the field of HCV molecular virology and principal intracellular signaling pathways in which HCV oncogenic proteins are involved.

Mitogen-activated protein kinase signalling pathways triggered by the hepatitis C virus envelope protein E2: implications for the prevention of infection

OBJECTIVE

Hepatitis C virus (HCV) is a major pathogenic factor of liver diseases. During HCV infection, interaction of the envelope protein E2 of the virion, with target cells, is a crucial process for viral penetration into the cell and its propagation. We speculate that such interaction may trigger early signalling events required for HCV infection.

MATERIALS AND METHODS

Human liver cell line L-02 was treated with HCV E2. The kinase phosphorylation levels of mitogen-activated protein kinase (MAPK) signalling pathways in the treated cells were analyzed by Western blotting. The proliferation of the E2-treated cells was evaluated by MTT assay.

RESULTS

HCV E2 was shown to be an efficient activator for MAPK pathways. Levels of phosphorylation of upstream kinases Raf-1 and MEK1/2 were seen to be elevated following E2 treatment and similarly, phosphorylation levels of downstream kinases MAPK/ERK and p38 MAPK also increased in response to E2 treatment, and specificity of kinase activation by E2 was confirmed. E2-induced MAPK/ERK activation was inhibited by the MEK1/2 inhibitor U0126 in a concentration-dependent manner. Blockage of relevant cellular receptors reduced activation of Raf-1, MEK1/2, MAPK/ERK and p38 MAPK by E2, indicating efflux of the E2 signal from extracellular to the intracellular spaces. Thus, kinase cascades of MAPK pathways were continuously affected by E2 presence. Moreover, enhancement of cell proliferation by E2 appeared to be associated with the dynamic phosphorylation of MAPK/ERK and p38 MAPK.

CONCLUSION

These results suggest that MAPK signalling pathways triggered by E2 may be a potential target for prevention of HCV infection.

Role of signal transducer and activator of transcription 3 in liver fibrosis progression in chronic hepatitis C-infected patients

In vitro and animal data suggest that hepatitis C virus (HCV) proteins might interfere with signal transducer and activator of transcription 3 (Stat3) signaling. It remains unknown whether Stat3 influences the apoptotic-proliferation balance and how this may relate to liver fibrosis progression in HCV-infected patients. We assessed Stat3 expression and DNA-binding as well as expression of its regulators protein inhibitor of activated Stat 3 (Pias3) and suppressor of cytokine signaling 3 (Socs3) in 65 HCV-infected livers at various stages of fibrosis progression. We then determined the level of expression of the proliferation markers cyclin D1 and proliferating cell nuclear antigen (PCNA) in conjunction with pro- and antiapoptotic markers Bax and Bcl-2 in the same liver samples. With the onset of fibrosis, Stat3 DNA-binding decreased and became almost undetectable in livers with bridging fibrosis or cirrhosis. Stat3 DNA-binding inversely correlated with Pias3 expression and Stat3-Pias3 interaction increased with the progression of fibrosis. Cyclin D1 and PCNA in hepatocytes decreased dramatically during fibrosis progression and levels highly correlated with Stat3 expression. In addition, an antiapoptotic profile due to upregulation of Bcl-2 principally in infiltrating inflammatory cells was observed with progressing fibrosis. In conclusion, fibrosis progression is characterized by a continuous decline in Stat3 DNA-binding activity related to overexpression and progressive interaction of Pias3-Stat3. The decrease in Stat3 activity correlated with reduced hepatocytes proliferation and a positive antiapoptotic balance in infiltrating inflammatory cells that are known mediators of cell damage in HCV.

[Pathogenesis of the hepatocellular carcinoma associated with hepatitis C virus]

Hepatitis C virus (HCV) is known as one of major causative agents of hepatocellular carcinoma (HCC) in the world. The pathogenesis of HCC associated with HCV, however, has not been fully elucidated yet, although the chronic inflammation induced by HCV infection is considered to contribute greatly to the HCC development. Some HCV gene products have been shown to possess transformation activities in cultured cells. Several oncogenic signal pathways in the cells were modulated by the exogenous expression of the HCV proteins. A few lines of the transgenic mice producing the core protein among those products was also reported to develop liver steatosis and HCC without apparent inflammation after rearing for a relatively long period. So, the functions of the core on the modulation of cellular events have been extensively examined and characterized. Here, I would summarize the progress of the research for the pathogenesis of HCC associated with HCV.

Hepatitis C virus: virology and experimental systems

Over the past several years, significant progress has been made toward the understanding of hepatitis C virus, especially the development of in vitro cell culture models. The scientific community now has the tools to gain a better understanding of the virus, which should translate into better clinical therapeutic modalities. Many new drugs are currently being evaluated, and a few are already undergoing clinica trials. This article focuses on the current advances in hepatitis C virus virology.

Hepatitis C virus core protein blocks interferon signaling by interaction with the STAT1 SH2 domain

Emerging data have indicated that hepatitis C virus (HCV) subverts the host antiviral response to ensure its persistence. We previously demonstrated that HCV protein expression suppresses type I interferon (IFN) signaling by leading to the reduction of phosphorylated STAT1 (P-STAT1). We also demonstrated that HCV core protein directly bound to STAT1. However, the detailed mechanisms by which HCV core protein impacts IFN signaling components have not been fully clarified. In this report, we show that the STAT1 interaction domain resides in the N-terminal portion of HCV core (amino acids [aa] 1 to 23). This domain is also required to produce P-STAT1 reduction and inhibit IFN signaling transduction. Conversely, the C-terminal region of STAT1, specifically the SH2 domain (aa 577 to 684), is required for the interaction of HCV core with STAT1. The STAT1 SH2 domain is critical for STAT1 hetero- or homodimerization. We propose a model by which the binding of HCV core to STAT1 results in decreased P-STAT, blocked STAT1 heterodimerization to STAT2, and, therefore, reduced IFN-stimulated gene factor-3 binding to DNA and disrupted IFN-stimulated gene transcription.

Proteomic profiling of lipid droplet proteins in hepatoma cell lines expressing hepatitis C virus core protein

Hepatitis C virus (HCV) core protein has been suggested to play crucial roles in the pathogeneses of liver steatosis and hepatocellular carcinomas due to HCV infection. Intracellular HCV core protein is localized mainly in lipid droplets, in which the core protein should exert its significant biological/pathological functions. In this study, we performed comparative proteomic analysis of lipid droplet proteins in core-expressing and non-expressing hepatoma cell lines. We identified 38 proteins in the lipid droplet fraction of core-expressing (Hep39) cells and 30 proteins in that of non-expressing (Hepswx) cells by 1-D-SDS-PAGE/MALDI-TOF mass spectrometry (MS) or direct nanoflow liquid chromatography-MS/MS. Interestingly, the lipid droplet fraction of Hep39 cells had an apparently lower content of adipose differentiation-related protein and a much higher content of TIP47 than that of Hepswx cells, suggesting the participation of the core protein in lipid droplet biogenesis in HCV-infected cells. Another distinct feature is that proteins involved in RNA metabolism, particularly DEAD box protein 1 and DEAD box protein 3, were detected in the lipid droplet fraction of Hep39 cells. These results suggest that lipid droplets containing HCV core protein may participate in the RNA metabolism of the host and/or HCV, affecting the pathopoiesis and/or virus replication/production in HCV-infected cells.

Suppressive effect on hepatocyte differentiation of hepatitis C virus core protein

The influence of hepatitis C virus (HCV) protein(s) on cellular differentiation remains to be clarified. Using murine normal liver epithelial cells, we investigated whether HCV core protein affects differentiation into hepatocytes. Mock and HCV core-expressing cells were stimulated with oncostatin M (OSM) and dexamethasone, and the degree of differentiation was evaluated by measuring the expression of albumin and tyrosine aminotransferase (TAT). Lower amounts after stimulation were found in HCV core-expressing cells than in mock cells. Phosphorylation of the signal transducer and activator transcription factor 3 (STAT3) was prevented by the HCV core under OSM stimulation. Reporter gene assay revealed that the HCV core/Janus kinase (JAK) interaction directly suppressed the OSM-dependent JAK-STAT signal transduction. Furthermore, expression of OSM receptor beta (OSMRbeta) after stimulation was prevented by the HCV core. In conclusion, the HCV core may suppress differentiation into hepatocytes via inhibition of the JAK-STAT pathway and OSMRbeta expression.

Diverse effects of cyclosporine on hepatitis C virus strain replication

Recently, a production system for infectious particles of hepatitis C virus (HCV) utilizing the genotype 2a JFH1 strain has been developed. This strain has a high capacity for replication in the cells. Cyclosporine (CsA) has a suppressive effect on HCV replication. In this report, we characterize the anti-HCV effect of CsA. We observe that the presence of viral structural proteins does not influence the anti-HCV activity of CsA. Among HCV strains, the replication of genotype 1b replicons was strongly suppressed by treatment with CsA. In contrast, JFH1 replication was less sensitive to CsA and its analog, NIM811. Replication of JFH1 did not require the cellular replication cofactor, cyclophilin B (CyPB). CyPB stimulated the RNA binding activity of NS5B in the genotype 1b replicon but not the genotype 2a JFH1 strain. These findings provide an insight into the mechanisms of diversity governing virus-cell interactions and in the sensitivity of these strains to antiviral agents.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Cryoglobulinemic vasculitis

PURPOSE OF REVIEW

Cryoglobulinemic vasculitis is an immune-complex-mediated systemic vasculitis involving small-medium-sized vessels. A causative role of hepatitis C virus in over 80% patients has been definitively established, with heterogeneous geographical distribution. This review focuses on recent etiopathogenetic, clinico-diagnostic, and therapeutical studies.

RECENT FINDINGS

Hepatitis C virus cannot be integrated into the host genome; it may exert a chronic stimulus to the immune system. The interaction between hepatitis C virus envelope protein E2 with B-cell CD 81 receptor may increase the frequency of VDJ rearrangement in antigen-reactive B lymphocytes. One consequence is the activation of various protooncogenes, including anti-apoptotic Bcl-2. The extended B-cell survival is responsible for autoantibody and immune-complex production, including mixed cryoglobulins; some malignancies, mainly B-cell lymphomas, may complicate cryoglobulinemic vasculitis. Environmental or viral/host genetic cofactors should be relevant in the pathogenesis of hepatitis C virus-related diseases. Cryoglobulinemic vasculitis may overlap with other diseases (systemic vasculitides, Sjögren's syndrome, autoimmune hepatitis, lymphoma), which should be carefully considered for a correct diagnosis and treatment. Cumulative survival of cryoglobulinemic vasculitis is significantly lower compared with the general population. Therapeutic strategies for cryoglobulinemic vasculitis include etiologic (antiviral), pathogenetic (cyclophosfamide, rituximab), or symptomatic (steroids, plasmapheresis) treatments, which should be tailored to the individual patient according to the severity/activity of clinical symptoms.

SUMMARY

Cryoglobulinemic vasculitis represents a crossroads among autoimmune and lymphoproliferative disorders; as hepatitis C virus infection is the major causative factor, cryoglobulinemic vasculitis is an important model for etiopathogenetic studies of virus-related diseases.

Hepatitis C virus core protein exerts an inhibitory effect on suppressor of cytokine signaling (SOCS)-1 gene expression

BACKGROUND/AIMS

Suppressor of cytokine signaling (SOCS)-1, a negative feedback regulator of cytokine signaling pathway, also has a tumor suppressor activity, the silencing of its gene by hypermethylation is suggested to contribute to hepatocarcinogenesis. We studied the effect of the core protein of hepatitis C virus (HCV) on the expression of SOCS-1 gene.

METHODS

HCV core gene transgenic mice, which develop hepatocellular carcinoma late in life, HepG2 cells expressing the core protein, and human liver tissues were analyzed.

RESULTS

The expression of SOCS-1 gene was significantly suppressed in the liver of core gene transgenic mice and HepG2 cells expressing the core protein, while that of SOCS-3 gene was conserved. SOCS-1 expression levels also decreased in HCV-positive human liver tissues. The core protein differentially down-regulated the expression of signal transducer and activator of transcription (STAT) target genes, but rather enhanced STAT1 and STAT3 activation after interleukin-6 stimulation in mouse liver tissues and cells.

CONCLUSIONS

HCV core protein down-regulates the expression of SOCS-1 gene. This is a mechanism leading to SOCS-1 silencing, an alternative to the hypermethylation of the gene; this effect of the core protein may modulate the intracellular signaling pathway, contributing to the pathogenesis in HCV infection including hepatocarcinogenesis.

Defective Jak-Stat activation in hepatoma cells is associated with hepatitis C viral IFN-alpha resistance

Interferon-alpha (IFN-alpha) has been widely used to treat viral infections and certain types of cancers. Large numbers of patients with chronic hepatitis C viral (HCV) infection do not respond to IFN and ribavirin combination therapy, and the majority of patients do not respond to IFN monotherapy. The underlying mechanisms of HCV nonresponse to IFN are unknown. In this report, using a HCV subgenomic replicon cell culture system, we show that (1) long-term IFN stimulation can select cells defective for Stat3 activation, and the defect appears to be responsible for HCV IFN resistance in cell culture, (2) HCV subgenomic sequence mutations associated with long-term culture do not appear to be responsible for IFN resistance, (3) expression of the activated Stat3 reverses IFN resistance while a dominant negative form of Stat3 renders an IFN-sensitive cell line resistant to IFN, and (4) the IFN-resistant cell line exhibits enhanced suppressor of cytokine signaling 3 (SOCS3) expression in response to IFN stimulation, and blocking SOCS3 in the IFN-resistant cell line partially restores IFN sensitivity. These findings strongly suggest that the IFN-resistant phenotype in vitro is associated with defective Stat3 activation and an enhanced SOCS3 response but is not associated with viral sequence mutations. Our study implies that long-term IFN stimulation in vitro selects cells that exhibit alterations in the host Jak-Stat signaling pathway, thereby representing a potential mechanism by which HCV resists IFN therapy.

Deficient Stat3 DNA-binding is associated with high Pias3 expression and a positive anti-apoptotic balance in human end-stage alcoholic and hepatitis C cirrhosis

BACKGROUND/AIMS

In vitro and animal data suggest that alcohol and hepatitis C virus (HCV) proteins might interfere with Stat3 signaling, a potential regulator of liver cell apoptosis and proliferation.

METHODS

We assessed Stat3 expression, activity and the apoptotic-proliferation balance in end-stage HCV and alcoholic liver disease (ALD) in man. Explanted livers of HCV and ALD patients were compared to normal and primary biliary cirrhosis (PBC) livers.

RESULTS

Although Stat3 expression and phosphorylation was not altered in HCV and ALD cirrhosis, Stat3 DNA-binding was not detected in all ALD and most HCV samples. Deficient Stat3 DNA-binding was associated with high Pias3 expression, but not with increased Socs3 levels. Bcl-2 was up-regulated in HCV and ALD together with decreased Caspase3 activity. Compared to base-line cell proliferation in normal donor livers, HCV cirrhosis showed a marked reduction in cyclin D1 and PCNA, whereas both markers were only slightly reduced in ALD.

CONCLUSIONS

End-stage HCV and ALD cirrhosis is characterized by impaired Stat3 DNA-binding possibly through up-regulation of Pias3. Therefore, impaired activation of Stat3 target genes might contribute to disturbed liver regeneration and repair. The attempt in cirrhotic livers to favor anti-apoptotic over pro-apoptotic pathways is not sufficient to compensate for the low cellular proliferation rates.

Molecular virology of the hepatitis C virus: implication for novel therapies

The study of hepatitis C virus (HCV) molecular virology is helping to shape the future of our anti-HCV strategies by identifying new antiviral targets. With the advent of agents that specifically target individual HCV proteins, HCV-specific therapy has arrived. Key to these efforts is the development of high-efficiency HCV replicons. The future effective pharmacologic control of HCV will likely consist of a cocktail of simultaneously administered virus-specific agents with independent targets. This should minimize the emergence of resistance against any single agent. The way we treat HCV should change dramatically over the next few years.

Activation of Interferon-Stimulated Response Element in Huh-7 Cells Replicating Hepatitis C Virus Subgenomic RNA

Interferon-alpha (IFN(alpha)) binds to receptors on the cell surface, which initiate a cascade of signal transduction pathways that leads to transcription of selected genes. This transduction pathway involves binding of transcription factors to a common cis-acting DNA sequence called IFN-stimulated response element (ISRE). To test whether these signaling pathways are functional in hepatitis C virus (HCV)-replicating cells, we studied the regulation of ISRE-mediated transcription of firefly luciferase gene in stable replicon cell lines. A plasmid construct was prepared (pISRELuc) which contains four tandem repeats of 9-27 ISRE sequences positioned directly upstream of the herpes virus 1 thymidine kinase promoter TATA box that drives the expression of firefly luciferase. Regulation of ISRE-mediated expression of firefly luciferase by IFN(alpha) was studied by transfecting this clone into Huh-7 cells replicating HCV subgenomic HCV RNA. The significance of ISRE-mediated transcriptional activation was studied in a replicon cell line by pretreatment of cells with actinomycin D, which inhibits cellular DNA-dependent RNA transcription. IFN treatment activates ISRE-mediated expression of luciferase, indicating that this pathway is functional in Huh-7 cells. Activation of ISRE-mediated transcription of luciferase is relatively high in two Huh-7 stable cell lines replicating HCV subgenomic RNA. Inhibition of ISRE-mediated transcription of luciferase by actinomycin D also makes HCV replication totally resistant to IFN(alpha). These in vitro studies suggest that activation of IFN-inducible genes is important in mounting a successful antiviral response against HCV.

Hepatitis C virus expression suppresses interferon signaling by degrading STAT1

BACKGROUND & AIMS

The molecular mechanisms by which hepatitis C virus (HCV) antagonizes the antiviral actions of interferon (IFN) have not been fully characterized. Specifically, how HCV proteins impact on IFN signaling components has yet to be elucidated. We used an HCV cell-based expression model to examine the interaction between HCV protein expression and host type I IFN signaling components in the Jak-STAT kinase pathway.

METHODS

Full-length HCV and HCV subgenomic constructs corresponding to structural and each of the nonstructural proteins were transiently transfected into Huh-T7 cells. HCV expression was monitored by an HCV core antigen enzyme-linked immunosorbent assay. STAT1, P-STAT1, and HCV protein expression was investigated with immunoprecipitation and Western blots.

RESULTS

Overexpression and small interfering RNA studies showed that STAT1 was indispensable for control of HCV expression. STAT1 and P-STAT1 expression were markedly reduced in HCV-transfected cells. Full-length HCV, HCV core/E1/E2, and NS3-4A were each associated with decreased STAT1 expression, which was attributable to proteasome-dependent degradation of STAT1. HCV core, but not HCV E1, E2, NS3, NS4, or NS5, bound to STAT1. STAT2 expression was not affected by HCV.

CONCLUSIONS

HCV expression selectively degrades STAT1 and reduces P-STAT1 accumulation in the nucleus in a proteasome-dependent manner. HCV core protein binds STAT1, suggesting that this viral protein is associated with STAT1 degradation. STAT1 plays an indispensable role in innate antiviral immunity against HCV expression. In turn, HCV subverts the Jak-STAT kinase by selectively inducing STAT1 degradation.

Genetic variability of hepatitis C virus in chronically infected patients with viral breakthrough during interferon-ribavirin therapy

Little is known about hepatitis C virus (HCV) breakthrough during antiviral therapy, although it would help in understanding HCV resistance to current antiviral treatments. To analyse the implication of virological factors and the vigour of humoral immune responses in this phenomenon, we studied nine chronic hepatitis C patients with a viral breakthrough during IFN/ribavirin combination therapy, as well as five responders and five non-responders. The IRES and regions coding for the capsid protein, the PePHD domain of envelope glycoprotein E2 and the NS5A and 5B proteins were amplified by RT-PCR before treatment, before and during breakthrough, and after treatment. The major variant sequence was obtained by direct sequencing. The heterogeneity of quasispecies was studied by SSCP in all patients and sequencing after cloning in seven genotype 1b-infected patients. Humoral responses against HCV epitopes were also analysed. The major sequences of IRES, PePHD, and NS5B remained stable during treatment, regardless of the treatment response. However, the capsid protein and the regions flanking PePHD showed sequence variations in breakthrough patients, although no specific mutation was identified. The variable V3 region of NS5A, but not the PKR-binding domain and the ISDR, seemed to be associated with differences in response to treatment. The analysis of HCV quasispecies revealed no characteristic pattern during treatment in breakthrough patients, whose HCV genome profiles looked most similar to that of non-responders. The humoral response was similar between groups. In conclusion, viral breakthrough does not seem to be due to selection of resistant strains with signature mutations.

Effects of the hepatitis C virus core protein on innate cellular defense pathways

The hepatitis C virus (HCV) core protein is thought to contribute to HCV pathogenesis through its interaction with various signal transduction pathways. In this study, we explored the interaction of the core protein with innate defense pathways (interferon [IFN] regulatory factor [IRF], Jak-Stat, and inducible nitric oxide synthase [iNOS]) in HeLa and Huh7 human cell lines. Expression of a patient-derived genotype 1b core protein activated human IRF-1 and guanylate-binding protein-2 (GBP-2) promoters, induced IRF-1 mRNA, but failed to induce IRF-3 phosphorylation. HCV core protein caused dose-dependent induction of the IFN-beta promoter and IFN-beta mRNA but not the IFN-alpha1 and IFN-alpha4 promoters. In the presence of IFN-alpha, core expression was associated with increased IFN-stimulated gene factor 3 (ISGF3) binding to the IFN-stimulated response element (ISRE) and tyrosine phosphorylation of Stat1. Core expression resulted in dose-dependent activation of the ISRE and gamma activated sequence (GAS) promoters, in both the absence and the presence of either IFN-alpha or IFN-gamma. Core stimulated the human iNOS promoter and induced iNOS protein. The data indicate that HCV core can modulate IRF, Jak-Stat, and iNOS pathways and suggest mechanisms by which core could affect HCV persistence and pathogenesis.

STAT3 induces anti-hepatitis C viral activity in liver cells

Hepatitis C virus (HCV) infection is a leading cause a of chronic liver disease worldwide. The main therapeutic regimen is the combination of interferon alpha (IFN) and the nucleoside analog, Ribavirin. IFN initiates an intracellular antiviral state by the JAK-STAT signaling pathway, including a presumed role for STAT1 and STAT2. We have previously shown that the STAT3 activation occurs during IFN treatment of human hepatoma cells, suggesting that the STAT3-mediated pathway is relevant to IFN-induced antiviral activity. In this study, we investigate the role of activated STAT3 in the induction of anti-HCV activity in human hepatoma cells. We demonstrate that the STAT3 activation is involved in efficient IFN-induced anti-HCV activity. Using an inducible, cytokine-independent, STAT3 activation system, in which the entire coding region of STAT3 is fused with the ligand-binding domain of the estrogen receptor, we demonstrate that: activated STAT3 is tightly regulated in a stably transfected cell line by an estrogen analog, 4-HT; activated STAT3 initiates efficient anti-HCV activity in a HCV subgenomic replicon cell line; and activation of STAT3 is associated with the induction of a potential antiviral gene, 1-8U. In addition, we show that the cytokine IL-6, a potent STAT3 activator, inhibits HCV subgenomic RNA replication through STAT3 activation and ERK pathway. These results strongly suggest that STAT3 activation is capable of initiating intracellular antiviral pathways.

Hepatitis C virus core protein associates with detergent-resistant membranes distinct from classical plasma membrane rafts

A subpopulation of hepatitis C virus (HCV) core protein in cells harboring full-length HCV replicons is biochemically associated with detergent-resistant membranes (DRMs) in a manner similar to that of markers of classical lipid rafts. Core protein does not, however, colocalize in immunofluorescence studies with classical plasma membrane raft markers, such as caveolin-1 and the B subunit of cholera toxin, suggesting that core protein is bound to cytoplasmic raft microdomains distinct from caveolin-based rafts. Furthermore, while both the structural core protein and the nonstructural protein NS5A associate with membranes, they do not colocalize in the DRMs. Finally, the ability of core protein to localize to the DRMs did not require other elements of the HCV polyprotein. These results may have broad implications for the HCV life cycle and suggest that the HCV core may be a valuable probe for host cell biology.

The nature of interferon-alpha resistance in hepatitis C virus infection

PURPOSE OF REVIEW

HCV infection becomes chronic in 50-85% of cases. The treatment of chronic hepatitis C is currently based on a combination of pegylated interferon (IFN)-alpha and ribavirin. With this regimen, a failure to eradicate infection occurs in 18-24% of patients infected by genotype 2 or 3, and in 54-58% of patients infected by genotype 1. IFN resistance, i.e. the capacity of HCV strains to attenuate IFN antiviral responses in order to evade them, could play a role in the establishment of chronic infection at the acute stage of infection. IFN resistance could also play a role in the virological response to IFN therapy through similar or different mechanisms. The involved mechanisms however remain unclear.

RECENT FINDINGS

Several viral proteins were recently shown to mediate IFN resistance through inhibition of IFN antiviral effectors in vitro, but the relevance of such mechanisms in vivo is not proven. Whatever the mechanisms, IFN resistance could play a role at the early stages of infection, but a qualitative and quantitative defect of both CD4-positive and CD8-positive immune responses appears as the main determinant of viral persistence. IFN treatment failure to eradicate infection is multifactorial. IFN resistance could play a partial role through unclear mechanisms. However, immune clearance of infected cells appears to be the principal determinant of IFN treatment success.

SUMMARY

In spite of active research, the role and the mechanisms of IFN resistance in HCV persistence and IFN treatment failure remain partly unknown. A better understanding is needed in order to further improve IFN treatment strategies.