The native form and maturation process of hepatitis C virus core protein

Hepatitis C Virus-Core Antigen: Implications in Diagnostic, Treatment Monitoring and Clinical Outcomes

The hepatitis C virus (HCV) infection, a global health concern, can lead to chronic liver disease. The HCV core antigen (HCVcAg), a viral protein essential for replication, offers a cost-effective alternative to HCV RNA testing, particularly in resource-limited settings. This review explores the significance of HCVcAg, a key protein in the hepatitis C virus, examining its structure, function, and role in the viral life cycle. It also evaluates its clinical use in diagnosis and treatment monitoring, comparing its performance to the standard HCV RNA assay using data from PubMed and Google Scholar. HCVcAg assays show high pooled sensitivity (93.5%) and pooled specificity (99.2%) compared to HCV RNA assays, correlating closely (r = 0.87) with HCV RNA levels. Hence, HCVcAg testing offers a cost-effective way to diagnose active HCV infections and monitor treatment, especially in resource-limited settings, but its sensitivity can vary and standardization is needed. HCVcAg also predicts liver disease progression and assesses liver damage risk, aiding patient management. It helps to identify patients at risk for fibrosis or carcinoma, making it vital in hepatitis C care. HCVcAg testing can expand access to HCV care, simplify management, and contribute to global elimination strategies, especially in low- and middle-income countries.

Single-molecule-binding studies of antivirals targeting the hepatitis C virus core protein

IMPORTANCE

The hepatitis C virus is associated with nearly 300,000 deaths annually. At the core of the virus is an RNA-protein complex called the nucleocapsid, which consists of the viral genome and many copies of the core protein. Because the assembly of the nucleocapsid is a critical step in viral replication, a considerable amount of effort has been devoted to identifying antiviral therapeutics that can bind to the core protein and disrupt assembly. Although several candidates have been identified, little is known about how they interact with the core protein or how those interactions alter the structure and thus the function of this viral protein. Our work biochemically characterizes several of these binding interactions, highlighting both similarities and differences as well as strengths and weaknesses. These insights bolster the notion that this viral protein is a viable target for novel therapeutics and will help to guide future developments of these candidate antivirals.

Core amino acid substitutions in HCV-3a isolates from Pakistan and opportunities for multi-epitopic vaccines

Hepatitis C virus (HCV), which infected 71 million worldwide and about 5%-6% are from Pakistan, is an ssRNA virus, responsible for end-stage liver disease. To date, no effective therapy is available to cure this disease. Hence, it is important to study the most prevalent genotypes infecting human population and design novel vaccine or small molecule inhibitors to control the infections associated with HCV. Therefore, in this study clinical samples (n = 35; HCV-3a) from HCV patients were subjected to Sanger sequencing method. The sequencing of the core gene, which is generally considered as conserved, involved in the detection, quantitation and genotyping of HCV was performed. Multiple mutations, that is, R46C, R70Q, L91C, G60E, N/S105A, P108A, N110I, S116V, G90S, A77G and G145R that could be linked with response to antiviral therapies were detected. Phylogenetic analysis suggests emerging viral isolates are circulating in Pakistan. Using ab initio modelling technique, we predicted the 3D structure of core protein and subjected to molecular dynamics simulation to extract the most stable conformation of the structure for further analysis. Immunoinformatic approaches were used to propose a multi-epitopes vaccine against HCV by using core protein. The vaccine constructs consist of nine CTL and three HTL epitopes joined by different linkers were docked against the two reported Toll-like receptors (TLR-3 and TLR-8). Docking of vaccine construct with TLR-3 and TLR-8 shows proper binding and in silico expression of the vaccine resulted in a CAI value of 0.93. These analyses suggest that specific immune responses may be produced by the proposed vaccine.Communicated by Ramaswamy H. Sarma.

Expression of HCV genotype-4 core antigen in prokaryotic E. coli system for diagnosis of HCV infection in Egypt

BACKGROUND

Egypt has a high prevalence of hepatitis C virus (HCV) infection with 92.5% of genotype-4.

AIM

This study aimed to clone and express the core gene of HCV genotype-4 for using it to develop a highly sensitive, specific, and cost-effective diagnostic assay for detecting HCV infection.

METHODS

Using synthetic HCV genotype-4 core gene, pET15b as E. coli expression vector, and 1 mM lactose as inducer, the HCV core protein (MW 17 kDa) was expressed in the form of inclusion bodies (IBs) that was purified and solubilized using 8 M guanidinium HCl. The recombinant core protein was in vitro refolded by a rapid dilution method for further purification using weak cation exchange liquid chromatography. The immunogenicity of the purified protein was tested by ELISA using 129 serum samples.

RESULTS

The recombinant core protein was successfully expressed and purified. The results also showed that the in-house anti-HCV core assay is accurate, specific (_~96.6%), and highly sensitive (_~100%) in accordance with the commercial ELISA kit.

CONCLUSION

The sensitivity, specificity, and reproducibility of the developed assay were high and promising to be used as a screening assay for detecting HCV infection.

Molecular mechanisms underlying hepatitis C virus infection-related diabetes

Diabetes is a noncommunicable widespread disease that poses the risk of severe complications in patients, with certain complications being life-threatening. Hepatitis C is an infectious disease that mainly causes liver damage, which is also a profound threat to human health. Hepatitis C virus (HCV) infection has many extrahepatic manifestations, including diabetes. Multiple mechanisms facilitate the strong association between HCV and diabetes. HCV infection can affect the insulin signaling pathway in liver and pancreatic tissue and change the profiles of circulating microRNAs, which may further influence the occurrence and development of diabetes. This review describes how HCV infection causes diabetes and discusses the current research progress with respect to HCV infection-related diabetes.

HCV Assembly and Egress via Modifications in Host Lipid Metabolic Systems

Hepatitis C virus (HCV) proliferates by hijacking the host lipid machinery. In vitro replication systems revealed many aspects of the virus life cycle; in particular, viral utilization of host lipid metabolism during HCV proliferation. HCV interacts with lipid droplets (LDs) before starting the process of virus capsid formation at the lipid-rich endoplasmic reticulum (ER) membrane compartment. HCV buds into the ER via lipoprotein assembly and secretion. Exchangeable apolipoproteins, represented by apolipoprotein E (apoE), play pivotal roles in enhancing HCV-specific infectivity. HCV virions are likely to interact with other lipoproteins circulating in blood vessels and incorporate apolipoproteins as well as lipids. This review focuses on virus assembly and egress by briefly describing the recent advances in this area.

Lack of expression of hepatitis C virus core protein in human monocyte-erived dendritic cells using recombinant semliki forest virus

Hepatitis C Virus belongs to the Flaviviridae family.  One proposed mechanism of HCV persistence in the ability to infect hematopoietic cells, including Dendritic cells (DCs). HCV infection of DCs could impair their functions that represent one of the mechanisms, thus hampering viral clearance by the host immune system. Among HCV-encoded proteins, the highly conserved Core protein has been suggested to be responsible for the immunomodulatory properties of this Hepacivirus. Recombinant viral vectors expressing the HCV Core protein and allowing its transduction and therefore the expression of the protein into DCs could be useful tools for the analysis of the properties of the Core protein. Vaccinia Virus and retrovirus have been used to transduce human DCs. Likewise, gene transfer into DCs using Semliki Forest Virus has been reported. This study aimed to express the HCV Core protein in human monocyte-derived DCs using an SFV vector, in which the subgenomic RNA encoding the structural proteins was replaced by the HCV Core sequence and then analyze the effects of its expression on DCs functions.

Is the conquest of Hepatitis C imminent?

Hepatitis C virus represents a global pathogen of human health significance. In the space of less than three decades, we have witnessed the discovery of the virus, a growing understanding of the structure and biology of the viral-encoded proteins and their interaction with the host cell and the sequencing of the viral genome. Most importantly, we have moved from early therapeutic strategies aimed at crude boosting of host anti-viral immunity, limited by side effects and with poor response rates, to therapies that directly exploit our understanding of viral biology. In this review, we discuss the significance of the virus, its' discovery and outline the advances in the molecular characterisation of the virus, before setting these within the context of contemporary and emerging therapeutic strategies as well as viral resistance mechanisms.

Immune modulation by the hepatitis C virus core protein

Hepatitis C virus (HCV) infection is currently the most important cause of chronic viral hepatitis in the world and one of the most frequent indications for liver transplantation. HCV uses different strategies to evade the innate and adaptive immune response, and this evasion plays a key role in determining viral persistence. Several HCV viral proteins have been described as immune modulators. In this review, we will focus on the effect of HCV nucleocapsid core protein in the function of immune cells and its correlation with the findings observed in HCV chronically infected patients. Effects on immune cell function related to both extracellular and intracellular HCV core localization will be considered. This review provides an updated perspective on the mechanisms involved in HCV evasion related to one single HCV protein, which could become a key tool in the development of new antiviral strategies able to control and/or eradicate HCV infection.

Role of cleavage at the core-E1 junction of hepatitis C virus polyprotein in viral morphogenesis

In hepatitis C virus (HCV) polyprotein sequence, core protein terminates with E1 envelope signal peptide. Cleavage by signal peptidase (SP) separates E1 from the complete form of core protein, anchored in the endoplasmic reticulum (ER) membrane by the signal peptide. Subsequent cleavage of the signal peptide by signal-peptide peptidase (SPP) releases the mature form of core protein, which preferentially relocates to lipid droplets. Both of these cleavages are required for the HCV infectious cycle, supporting the idea that HCV assembly begins at the surface of lipid droplets, yet SPP-catalyzed cleavage is dispensable for initiation of budding in the ER. Here we have addressed at what step(s) of the HCV infectious cycle SP-catalyzed cleavage at the core-E1 junction is required. Taking advantage of the sole system that has allowed visualization of HCV budding events in the ER lumen of mammalian cells, we showed that, unexpectedly, mutations abolishing this cleavage did not prevent but instead tended to promote the initiation of viral budding. Moreover, even though no viral particles were released from Huh-7 cells transfected with a full-length HCV genome bearing these mutations, intracellular viral particles containing core protein protected by a membrane envelope were formed. These were visualized by electron microscopy as capsid-containing particles with a diameter of about 70 nm and 40 nm before and after delipidation, respectively, comparable to intracellular wild-type particle precursors except that they were non-infectious. Thus, our results show that SP-catalyzed cleavage is dispensable for HCV budding per se, but is required for the viral particles to acquire their infectivity and secretion. These data support the idea that HCV assembly occurs in concert with budding at the ER membrane. Furthermore, capsid-containing particles did not accumulate in the absence of SP-catalyzed cleavage, suggesting the quality of newly formed viral particles is controlled before secretion.

Anti-HCV Activity from Semi-purified Methanolic Root Extracts of Valeriana wallichii

Hepatitis C virus (HCV) is a serious global health problem affecting approximately 130-150 million individuals. Presently available direct-acting anti-HCV drugs have higher barriers to resistance and also improved success rate; however, cost concerns limit their utilization, especially in developing countries like India. Therefore, development of additional agents to combat HCV infection is needed. In the present study, we have evaluated anti-HCV potential of water, chloroform, and methanol extracts from roots of Valeriana wallichii, a traditional Indian medicinal plant. Huh-7.5 cells infected with J6/JFH chimeric HCV strain were treated with water, chloroform, and methanol extracts at different concentrations. Semi-quantitative reverse transcription polymerase chain reaction result demonstrated that methanolic extract showed reduction in HCV replication. The methanolic extract was fractionated by thin layer chromatography, and the purified fractions (F1, F2, F3, and F4) were checked for anti-HCV activity. Significant viral inhibition was noted only in F4 fraction. Further, intrinsic fluorescence assay of purified HCV RNA-dependent RNA polymerase NS5B in the presence of F4 resulted in sharp quenching of intrinsic fluorescence with increasing amount of plant extract. Our results indicated that methanolic extract of V. wallichii and its fraction (F4) inhibited HCV by binding with HCV NS5B protein. The findings would be further investigated to identify the active principle/lead molecule towards development of complementary and alternative therapeutics against HCV. Copyright © 2017 John Wiley & Sons, Ltd.

Charge neutralization as the major factor for the assembly of nucleocapsid-like particles from C-terminal truncated hepatitis C virus core protein

BACKGROUND

Hepatitis C virus (HCV) core protein, in addition to its structural role to form the nucleocapsid assembly, plays a critical role in HCV pathogenesis by interfering in several cellular processes, including microRNA and mRNA homeostasis. The C-terminal truncated HCV core protein (C124) is intrinsically unstructured in solution and is able to interact with unspecific nucleic acids, in the micromolar range, and to assemble into nucleocapsid-like particles (NLPs) in vitro. The specificity and propensity of C124 to the assembly and its implications on HCV pathogenesis are not well understood.

METHODS

Spectroscopic techniques, transmission electron microscopy and calorimetry were used to better understand the propensity of C124 to fold or to multimerize into NLPs when subjected to different conditions or in the presence of unspecific nucleic acids of equivalent size to cellular microRNAs.

RESULTS

The structural analysis indicated that C124 has low propensity to self-folding. On the other hand, for the first time, we show that C124, in the absence of nucleic acids, multimerizes into empty NLPs when subjected to a pH close to its isoelectric point (pH ≈ 12), indicating that assembly is mainly driven by charge neutralization. Isothermal calorimetry data showed that the assembly of NLPs promoted by nucleic acids is enthalpy driven. Additionally, data obtained from fluorescence correlation spectroscopy show that C124, in nanomolar range, was able to interact and to sequester a large number of short unspecific nucleic acids into NLPs.

DISCUSSION

Together, our data showed that the charge neutralization is the major factor for the nucleocapsid-like particles assembly from C-terminal truncated HCV core protein. This finding suggests that HCV core protein may physically interact with unspecific cellular polyanions, which may correspond to microRNAs and mRNAs in a host cell infected by HCV, triggering their confinement into infectious particles.

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

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

The intrinsic disorder status of the human hepatitis C virus proteome

Many viral proteins or their biologically important regions are disordered as a whole, or contain long disordered regions. These intrinsically disordered proteins/regions do not possess unique structures and possess functions that complement the functional repertoire of "normal" ordered proteins and domains, with many protein functional classes being heavily dependent on the intrinsic disorder. Viruses commonly use these highly flexible regions to invade the host organisms and to hijack various host systems. These disordered regions also help viruses in adapting to their hostile habitats and to manage their economic usage of genetic material. In this article, we focus on the structural peculiarities of proteins from human hepatitis C virus (HCV) and use a wide spectrum of bioinformatics techniques to evaluate the abundance of intrinsic disorder in the completed proteomes of several human HCV genotypes, to analyze the peculiarities of disorder distribution within the individual HCV proteins, and to establish potential roles of the structural disorder in functions of ten HCV proteins. We show that the intrinsic disorder or increased flexibility is not only abundant in these proteins, but is also absolutely necessary for their functions, playing a crucial role in the proteolytic processing of the HCV polyprotein, the maturation of the individual HCV proteins, and being related to the posttranslational modifications of these proteins and their interactions with DNA, RNA, and various host proteins.

Virion assembly and release

Hepatitis C Virus (HCV) particles exhibit several unusual properties that are not found in other enveloped RNA viruses, most notably their low buoyant density and interaction with serum lipoproteins. With the advent of systems to grow HCV in cell culture, the molecular basis of HCV particle assembly and release can now be addressed. The process of virus assembly involves protein-protein interactions between viral structural and nonstructural proteins and the coordinated action of host factors. This chapter reviews our current understanding of these interactions and factors.

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.

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.

Morphogenesis of infectious hepatitis C virus particles

More than 170 million individuals are currently infected with hepatitis C virus (HCV) worldwide and are at continuous risk of developing chronic liver disease. Since a cell culture system enabling relatively efficient propagation of HCV has become available, an increasing number of viral and host factors involved in HCV particle formation have been identified. Association of the viral Core, which forms the capsid with lipid droplets appears to be prerequisite for early HCV morphogenesis. Maturation and release of HCV particles is tightly linked to very-low-density lipoprotein biogenesis. Although expression of Core as well as E1 and E2 envelope proteins produces virus-like particles in heterologous expression systems, there is increasing evidence that non-structural viral proteins and p7 are also required for the production of infectious particles, suggesting that HCV genome replication and virion assembly are closely linked. Advances in our understanding of the various molecular mechanisms by which infectious HCV particles are formed are summarized.

Identification of a functional, CRM-1-dependent nuclear export signal in hepatitis C virus core protein

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease worldwide. HCV core protein is involved in nucleocapsid formation, but it also interacts with multiple cytoplasmic and nuclear molecules and plays a crucial role in the development of liver disease and hepatocarcinogenesis. The core protein is found mostly in the cytoplasm during HCV infection, but also in the nucleus in patients with hepatocarcinoma and in core-transgenic mice. HCV core contains nuclear localization signals (NLS), but no nuclear export signal (NES) has yet been identified.We show here that the aa(109-133) region directs the translocation of core from the nucleus to the cytoplasm by the CRM-1-mediated nuclear export pathway. Mutagenesis of the three hydrophobic residues (L119, I123 and L126) in the identified NES or in the sequence encoding the mature core aa(1-173) significantly enhanced the nuclear localisation of the corresponding proteins in transfected Huh7 cells. Both the NES and the adjacent hydrophobic sequence in domain II of core were required to maintain the core protein or its fragments in the cytoplasmic compartment. Electron microscopy studies of the JFH1 replication model demonstrated that core was translocated into the nucleus a few minutes after the virus entered the cell. The blockade of nucleocytoplasmic export by leptomycin B treatment early in infection led to the detection of core protein in the nucleus by confocal microscopy and coincided with a decrease in virus replication.Our data suggest that the functional NLS and NES direct HCV core protein shuttling between the cytoplasmic and nuclear compartments, with at least some core protein transported to the nucleus. These new properties of HCV core may be essential for virus multiplication and interaction with nuclear molecules, influence cell signaling and the pathogenesis of HCV infection.

Assembly of hepatitis C virus particles

Infection with hepatitis C virus (HCV) is a major risk factor for chronic hepatitis, cirrhosis and hepatocellular carcinoma. Once robust cell culture systems for production of recombinant infectious HCV became available, evidence on molecular mechanisms underlying assembly and release of the virus particles began to accumulate. Recent studies have demonstrated that lipid droplets and viral nonstructural proteins play key roles in HCV morphogenesis. This review considers the current knowledge about maturation of HCV structural proteins and production of viral infectious particles.

The human cytomegalovirus protein UL37 exon 1 associates with internal lipid rafts

The human cytomegalovirus (HCMV) protein UL37 exon 1 (pUL37x1), also known as viral mitochondrion-localized inhibitor of apoptosis (vMIA), sequentially traffics from the endoplasmic reticulum (ER) through mitochondrion-associated membranes (MAMs) to the outer mitochondrial membrane (OMM), where it robustly inhibits apoptosis. Here, we report the association of pUL37x1/vMIA with internal lipid rafts (LRs) in the ER/MAM. The MAM, which serves as a site for lipid transfer and calcium signaling to mitochondria, is enriched in detergent-resistant membrane (DRM)-forming lipids, including cholesterol and ceramide, which are found in lower concentrations in the bulk ER. Sigma 1 receptor (Sig-1R), a MAM chaperone affecting calcium signaling to mitochondria, is anchored in the MAM by its LR association. Because of its trafficking through the MAM and partial colocalization with Sig-1R, we tested whether pUL37x1/vMIA associates with MAM LRs. Extraction with methyl-β-cyclodextrin (MβCD) removed pUL37x1/vMIA from lysed but not intact cells, indicating its association with internal LRs. Furthermore, the isolation of DRMs from purified intracellular organelles independently verified the localization of pUL37x1/vMIA within ER/MAM LRs. However, pUL37x1/vMIA was not detected in DRMs from mitochondria. pUL37x1/vMIA associated with LRs during all temporal phases of HCMV infection, indicating the likely importance of this location for HCMV growth. Although detected during its sequential trafficking to the OMM, the pUL37x1/vMIA LR association was independent of its mitochondrial targeting signals. Rather, it was dependent upon cholesterol binding. These studies suggest a conserved ability of UL37 proteins to interact with cholesterol and LRs, which is functionally distinguishable from their sequential trafficking to mitochondria.

Bioluminescence imaging allows monitoring hepatitis C virus core protein inhibitors in mice

Background

The development of small molecule inhibitors of hepatitis C virus (HCV) core protein as antiviral agents has been intensively pursued as a viable strategy to eradicate HCV infection. However, lack of a robust and convenient small animal model has hampered the assessment of in vivo efficacy of any antiviral compound.

Methodology/Principal Findings

The objective of this work was to develop a novel method to screen anti-core protein siRNA in the mouse liver by bioluminescence imaging. The inhibitory effect of two shRNAs targeting the highly conserved core region of the HCV genome, shRNA452 and shRNA523, was examined using this method. In the transient mouse model, the effect of shRNA-523 was detectable at as early as 24 h and became even more pronounced at later time points. The effect of shRNA-452 was not detectable until 48 h post-transduction. In a stable mouse model, shRNA523 reduced luciferase levels by up to 76.4±26.0% and 91.8±8.0% at 6 h and 12 h after injection respectively, and the inhibitory effect persisted for 1 day after a single injection while shRNA-Scramble did not seem to have an effect on the luciferase activity in vivo.

Conclusions/Significance

Thus, we developed a simple and quantitative assay for real-time monitoring of HCV core protein inhibitors in mice.

Role of Hepatitis C virus core protein in viral-induced mitochondrial dysfunction

Hepatitis C virus (HCV) infection results in several changes in mitochondrial function including increased reactive oxygen species (ROS) production and greater sensitivity to oxidant, Ca(2+) and cytokine-induced cell death. Prior studies in protein over-expression systems have shown that this effect can be induced by the core protein, but other viral proteins and replication events may contribute as well. To evaluate the specific role of core protein in the context of viral replication and infection, we compared mitochondrial sensitivity in Huh7-derived HCV replicon bearing cells with or without core protein expression with that of cells infected with the JFH1 virus strain. JFH1 infection increased hydrogen peroxide production and sensitized cells to oxidant-induced loss of mitochondrial membrane potential and cell death. An identical phenomenon occurred in genome-length replicons-bearing cells but not in cells bearing the subgenomic replicons lacking core protein. Both cell death and mitochondrial depolarization were Ca(2+) dependent and could be prevented by Ca(2+) chelation. The difference in the mitochondrial response of the two replicon systems could be demonstrated even in isolated mitochondria derived from the two cell lines with the 'genome-length' mitochondria displaying greater sensitivity to Ca(2+) -induced cytochrome c release. In vitro incubation of 'subgenomic' mitochondria with core protein increased oxidant sensitivity to a level similar to that of mitochondria derived from cells bearing genome-length replicons. These results indicate that increased mitochondrial ROS production and a reduced threshold for Ca(2+) and ROS-induced permeability transition is a characteristic of HCV infection. This phenomenon is a direct consequence of core protein interactions with mitochondria and is present whenever core is expressed, either in infection, full-length replicon-bearing cells, or in over-expression systems.

Viral RNA silencing suppressors (RSS): novel strategy of viruses to ablate the host RNA interference (RNAi) defense system

Pathogenic viruses have developed a molecular defense arsenal for their survival by counteracting the host anti-viral system known as RNA interference (RNAi). Cellular RNAi, in addition to regulating gene expression through microRNAs, also serves as a barrier against invasive foreign nucleic acids. RNAi is conserved across the biological species, including plants, animals and invertebrates. Viruses in turn, have evolved mechanisms that can counteract this anti-viral defense of the host. Recent studies of mammalian viruses exhibiting RNA silencing suppressor (RSS) activity have further advanced our understanding of RNAi in terms of host-virus interactions. Viral proteins and non-coding viral RNAs can inhibit the RNAi (miRNA/siRNA) pathway through different mechanisms. Mammalian viruses having dsRNA-binding regions and GW/WG motifs appear to have a high chance of conferring RSS activity. Although, RSSs of plant and invertebrate viruses have been well characterized, mammalian viral RSSs still need in-depth investigations to present the concrete evidences supporting their RNAi ablation characteristics. The information presented in this review together with any perspective research should help to predict and identify the RSS activity-endowed new viral proteins that could be the potential targets for designing novel anti-viral therapeutics.

Oncogenic potential of hepatitis C virus proteins

Chronic hepatitis C virus (HCV) infection is a major risk factor for liver disease progression, and may lead to cirrhosis and hepatocellular carcinoma (HCC). The HCV genome contains a single-stranded positive sense RNA with a cytoplasmic lifecycle. HCV proteins interact with many host-cell factors and are involved in a wide range of activities, including cell cycle regulation, transcriptional regulation, cell proliferation, apoptosis, lipid metabolism, and cell growth promotion. Increasing experimental evidences suggest that HCV contributes to HCC by modulating pathways that may promote malignant transformation of hepatocytes. At least four of the 10 HCV gene products, namely core, NS3, NS5A and NS5B play roles in several potentially oncogenic pathways. Induction of both endoplasmic reticulum (ER) stress and oxidative stress by HCV proteins may also contribute to hepatocyte growth promotion. The current review identifies important functions of the viral proteins connecting HCV infections and potential for development of HCC. However, most of the putative transforming potentials of the HCV proteins have been defined in artificial cellular systems, and need to be established relevant to infection and disease models. The new insight into the mechanisms for HCV mediated disease progression may offer novel therapeutic targets for one of the most devastating human malignancies in the world today.

Core as a novel viral target for hepatitis C drugs

Hepatitis C virus (HCV) infects over 130 million people worldwide and is a major cause of liver disease. No vaccine is available. Novel specific drugs for HCV are urgently required, since the standard-of-care treatment of pegylated interferon combined with ribavirin is poorly tolerated and cures less than half of the treated patients. Promising, effective direct-acting drugs currently in the clinic have been described for three of the ten potential HCV target proteins: NS3/NS4A protease, NS5B polymerase and NS5A, a regulatory phosphoprotein. We here present core, the viral capsid protein, as another attractive, non-enzymatic target, against which a new class of anti-HCV drugs can be raised. Core plays a major role in the virion's formation, and interacts with several cellular proteins, some of which are involved in host defense mechanisms against the virus. This most conserved of all HCV proteins requires oligomerization to function as the organizer of viral particle assembly. Using core dimerization as the basis of transfer-of-energy screening assays, peptides and small molecules were identified which not only inhibit core-core interaction, but also block viral production in cell culture. Initial chemical optimization resulted in compounds active in single digit micromolar concentrations. Core inhibitors could be used in combination with other HCV drugs in order to provide novel treatments of Hepatitis C.

A hepatitis C virus core polypeptide expressed in chloroplasts detects anti-core antibodies in infected human sera

Hepatitis C virus (HCV) is a major disease agent affecting approximately 3% of the world's population. Expression in plant chloroplasts enables low-cost production of the conserved HCV core protein used in diagnostic tests to combat virus spread in developing countries with high infection rates. The bactericidal activity of the 21 kDa precore protein hinders cloning the core gene in plastid expression cassettes, which are active in bacteria due to the similarities between bacterial and plastid promoters and ribosome binding sites. This was overcome by using a topology-dependent expression cassette containing tandem rrn and psbA plastid promoters, whose activity was shown to be dependent on temperature. The viral core gene and a codon-optimised gene encoding a C-terminal truncated 16 kDa core polypeptide were expressed in tobacco chloroplasts. The codon-optimised gene increased monocistronic core mRNA levels by at least 2-fold and core polypeptides by over 5-fold, relative to the native viral gene. Expression of the 16 kDa core polypeptide was stable in leaves of different ages. Anti-core antibodies in HCV-infected human sera were detected by the 16 kDa core polypeptide in total leaf protein fractionated on Western blots providing a first step towards developing a chloroplast-based HCV diagnostic method.

Hepatitis C virus impairs p53 via persistent overexpression of 3beta-hydroxysterol Delta24-reductase

Persistent infection with hepatitis C virus (HCV) induces tumorigenicity in hepatocytes. To gain insight into the mechanisms underlying this process, we generated monoclonal antibodies on a genome-wide scale against an HCV-expressing human hepatoblastoma-derived cell line, RzM6-LC, showing augmented tumorigenicity. We identified 3beta-hydroxysterol Delta24-reductase (DHCR24) from this screen and showed that its expression reflected tumorigenicity. HCV induced the DHCR24 overexpression in human hepatocytes. Ectopic or HCV-induced DHCR24 overexpression resulted in resistance to oxidative stress-induced apoptosis and suppressed p53 activity. DHCR24 overexpression in these cells paralleled the increased interaction between p53 and MDM2 (also known as HDM2), a p53-specific E3 ubiquitin ligase, in the cytoplasm. Persistent DHCR24 overexpression did not alter the phosphorylation status of p53 but resulted in decreased acetylation of p53 at lysine residues 373 and 382 in the nucleus after treatment with hydrogen peroxide. Taken together, these results suggest that DHCR24 is elevated in response to HCV infection and inhibits the p53 stress response by stimulating the accumulation of the MDM2-p53 complex in the cytoplasm and by inhibiting the acetylation of p53 in the nucleus.

Sequential processing of hepatitis C virus core protein by host cell signal peptidase and signal peptide peptidase: a reassessment

Hepatitis C virus (HCV) core protein is believed to play critical roles in the virus morphogenesis and pathogenesis. In HCV polyprotein, core protein terminates with a signal peptide followed by E1 envelope protein. It has remained unclear whether cleavage by host cell signal peptidase (SP) at the core-E1 junction to generate the complete form of core protein, which is anchored in the endoplasmic reticulum membrane, is absolutely required for cleavage within the signal peptide by host cell signal peptide peptidase (SPP) to liberate the mature form of core protein, which is then free for trafficking to lipid droplets. In this study, the possible sources of disagreement in published reports have been examined, and we conclude that a product generated upon inhibition of SP-catalysed cleavage at the core-E1 junction in heterologous expression systems was incorrectly identified as mature core protein. Moreover, inhibition of this cleavage in the most relevant model of human hepatoma cells replicating a full-length HCV genome was shown to abolish interaction of core protein with lipid droplets and production of infectious progeny virus. These results firmly establish that SPP-catalysed liberation of mature core protein is absolutely dependent on prior cleavage by SP at the correct core-E1 site to generate the complete form of core protein, consistent with this obligatory order of processing playing a role in HCV infectious cycle.

Characterization of hepatitis C virus core protein multimerization and membrane envelopment: revelation of a cascade of core-membrane interactions

The molecular basis underlying hepatitis C virus (HCV) core protein maturation and morphogenesis remains elusive. We characterized the concerted events associated with core protein multimerization and interaction with membranes. Analyses of core proteins expressed from a subgenomic system showed that the signal sequence located between the core and envelope glycoprotein E1 is critical for core association with endoplasmic reticula (ER)/late endosomes and the core's envelopment by membranes, which was judged by the core's acquisition of resistance to proteinase K digestion. Despite exerting an inhibitory effect on the core's association with membranes, (Z-LL)(2)-ketone, a specific inhibitor of signal peptide peptidase (SPP), did not affect core multimeric complex formation, suggesting that oligomeric core complex formation proceeds prior to or upon core attachment to membranes. Protease-resistant core complexes that contained both innate and processed proteins were detected in the presence of (Z-LL)(2)-ketone, implying that core envelopment occurs after intramembrane cleavage. Mutations of the core that prevent signal peptide cleavage or coexpression with an SPP loss-of-function D219A mutant decreased the core's envelopment, demonstrating that SPP-mediated cleavage is required for core envelopment. Analyses of core mutants with a deletion in domain I revealed that this domain contains sequences crucial for core envelopment. The core proteins expressed by infectious JFH1 and Jc1 RNAs in Huh7 cells also assembled into a multimeric complex, associated with ER/late-endosomal membranes, and were enveloped by membranes. Treatment with (Z-LL)(2)-ketone or coexpression with D219A mutant SPP interfered with both core envelopment and infectious HCV production, indicating a critical role of core envelopment in HCV morphogenesis. The results provide mechanistic insights into the sequential and coordinated processes during the association of the HCV core protein with membranes in the early phase of virus maturation and morphogenesis.

The hepatitis C virus core protein contains a BH3 domain that regulates apoptosis through specific interaction with human Mcl-1

The hepatitis C virus (HCV) core protein is known to modulate apoptosis and contribute to viral replication and pathogenesis. In this study, we have identified a Bcl-2 homology 3 (BH3) domain in the core protein that is essential for its proapoptotic property. Coimmunoprecipitation experiments showed that the core protein interacts specifically with the human myeloid cell factor 1 (Mcl-1), a prosurvival member of the Bcl-2 family, but not with other prosurvival members (Bcl-X(L) and Bcl-w). Moreover, the overexpression of Mcl-1 protects against core-induced apoptosis. By using peptide mimetics, core was found to release cytochrome c from isolated mitochondria when complemented with Bad. Thus, core is a bona fide BH3-only protein having properties similar to those of Noxa, a BH3-only member of the Bcl-2 family that binds preferentially to Mcl-1. There are three critical hydrophobic residues in the BH3 domain of the core protein, and they are essential for the proapoptotic property of the core protein. Furthermore, the genotype 1b core protein is more effective than the genotype 2a core protein in inducing apoptosis due to a single-amino-acid difference at one of these hydrophobic residues (residue 119). Replacing this residue in the J6/JFH-1 infectious clone (genotype 2a) with the corresponding amino acid in the genotype 1b core protein produced a mutant virus, J6/JFH-1(V119L), which induced significantly higher levels of apoptosis in the infected cells than the parental J6/JFH-1 virus. Furthermore, the core protein of J6/JFH-1(V119L), but not that of J6/JFH-1, interacted with Mcl-1 in virus-infected cells. Taken together, the core protein is a novel BH3-only viral homologue that contributes to the induction of apoptosis during HCV infection.

Access of viral proteins to mitochondria via mitochondria-associated membranes

By exploiting host cell machineries, viruses provide powerful tools for gaining insight into cellular pathways. Proteins from two unrelated viruses, human CMV (HCMV) and HCV, are documented to traffic sequentially from the ER into mitochondria, probably through the mitochondria-associated membrane (MAM) compartment. The MAM are sites of ER-mitochondrial contact enabling the direct transfer of membrane bound lipids and the generation of high calcium (Ca2+) microdomains for mitochondria signalling and responses to cellular stress. Both HCV core protein and HCMV UL37 proteins are associated with Ca2+ regulation and apoptotic signals. Trafficking of viral proteins to the MAM may allow viruses to manipulate a variety of fundamental cellular processes, which converge at the MAM, including Ca2+ signalling, lipid synthesis and transfer, bioenergetics, metabolic flow, and apoptosis. Because of their distinct topologies and targeted MAM sub-domains, mitochondrial trafficking (albeit it through the MAM) of the HCMV and HCV proteins predictably involves alternative pathways and, hence, distinct targeting signals. Indeed, we found that multiple cellular and viral proteins, which target the MAM, showed no apparent consensus primary targeting sequences. Nonetheless, these viral proteins provide us with valuable tools to access the poorly characterised MAM compartment, to define its cellular constituents and describe how virus infection alters these to its own end. Furthermore, because proper trafficking of viral proteins is necessary for their function, discovering the requirements for MAM to mitochondrial trafficking of essential viral proteins may provide novel targets for the rational design of anti-viral drugs.

The lactate dehydrogenase-elevating virus capsid protein is a nuclear-cytoplasmic protein

Arteriviruses replicate in the cytoplasm and do not require the nucleus function for virus multiplication in vitro. However, nucleocapsid (N) protein of two arteriviruses, porcine reproductive respiratory syndrome virus and equine arteritis virus, has been observed to localize in the nucleus and nucleolus of virus-infected and N-gene-transfected cells in addition to their normal cytoplasmic distribution. In the present study, the N protein of lactate dehydrogenase-elevating virus (LDV) of mice was examined for nuclear localization. The subcellular localization of LDV-N was determined by tagging N with enhanced green fluorescence protein (EGFP) at the N- and C-terminus. Both N-EGFP and EGFP-N fusion proteins localized to the nucleus and nucleolus of gene-transfected cells. Labeled N also accumulated in the perinuclear region, the site of virus replication. The LDV-N sequence contains a putative ‘pat4’-type nuclear localization signal (NLS) consisting of 38-KKKK. To determine its functional significance, a series of deletion constructs of N were generated and individually expressed in cells. The results showed that the ‘pat4’ NLS was essential for nuclear translocation. In addition, the LDV-N interacted with the importin-α and -β proteins, suggesting that the LDV-N nuclear localization may occur via the importin-mediated nuclear transport pathway. These results provide further evidence for the nuclear localization of N as a common feature within the arteriviruses.

Enhancement of the expression of HCV core gene does not enhance core-specific immune response in DNA immunization: advantages of the heterologous DNA prime, protein boost immunization regimen

BACKGROUND

Hepatitis C core protein is an attractive target for HCV vaccine aimed to exterminate HCV infected cells. However, although highly immunogenic in natural infection, core appears to have low immunogenicity in experimental settings. We aimed to design an HCV vaccine prototype based on core, and devise immunization regimens that would lead to potent anti-core immune responses which circumvent the immunogenicity limitations earlier observed.

METHODS

Plasmids encoding core with no translation initiation signal (pCMVcore); with Kozak sequence (pCMVcoreKozak); and with HCV IRES (pCMVcoreIRES) were designed and expressed in a variety of eukaryotic cells. Polyproteins corresponding to HCV 1b amino acids (aa) 1-98 and 1-173 were expressed in E. coli. C57BL/6 mice were immunized with four 25-microg doses of pCMVcoreKozak, or pCMV (I). BALB/c mice were immunized with 100 microg of either pCMVcore, or pCMVcoreKozak, or pCMVcoreIRES, or empty pCMV (II). Lastly, BALB/c mice were immunized with 20 microg of core aa 1-98 in prime and boost, or with 100 microg of pCMVcoreKozak in prime and 20 microg of core aa 1-98 in boost (III). Antibody response, [3H]-T-incorporation, and cytokine secretion by core/core peptide-stimulated splenocytes were assessed after each immunization.

RESULTS

Plasmids differed in core-expression capacity: mouse fibroblasts transfected with pCMVcore, pCMVcoreIRES and pCMVcoreKozak expressed 0.22 +/- 0.18, 0.83 +/- 0.5, and 13 +/- 5 ng core per cell, respectively. Single immunization with highly expressing pCMVcoreKozak induced specific IFN-gamma and IL-2, and weak antibody response. Single immunization with plasmids directing low levels of core expression induced similar levels of cytokines, strong T-cell proliferation (pCMVcoreIRES), and antibodies in titer 103(pCMVcore). Boosting with pCMVcoreKozak induced low antibody response, core-specific T-cell proliferation and IFN-gamma secretion that subsided after the 3rd plasmid injection. The latter also led to a decrease in specific IL-2 secretion. The best was the heterologous pCMVcoreKozak prime/protein boost regiment that generated mixed Th1/Th2-cellular response with core-specific antibodies in titer >or= 3 x 10(3).

CONCLUSION

Thus, administration of highly expressed HCV core gene, as one large dose or repeated injections of smaller doses, may suppress core-specific immune response. Instead, the latter is induced by a heterologous DNA prime/protein boost regiment that circumvents the negative effects of intracellular core expression.

Inhibition of major histocompatibility complex Class I antigen presentation by hepatitis C virus core protein in myeloid dendritic cells

Hepatitis C virus core (HCVcore) protein was expressed in myeloid dendritic cells (DC) from C57/B6 mice (H-2K(b)) by electroporation of HCVcore mRNA to investigate its effect on the ability of DC to prime CD8+ T cells displaying a T cell receptor specific for OVA(257-264) peptide (SIINFEKL)/H-2K(b) complex. Expression of full length HCVcore(191), which is directed to the endoplasmic reticulum (ER) membrane by a C-terminal signal sequence, but not a truncated variant HCVcore(152), which has a wider subcellular localization including the nucleus, significantly reduced surface levels of the H-2K(b)/SIINFEKL complex and impaired the ability of DC to prime naïve CD8+ T cells when they had to process endogenous antigen but not when MHC class I molecules were loaded directly with SIINFEKL peptide. Exploitation of the MHC class I antigen-processing pathway by HCVcore(191) impairs the ability of DC to stimulate CD8+ T cells and may contribute to the persistence of HCV infection.

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.

Acute expression of hepatitis C core protein in adult mouse liver: Mitochondrial stress and apoptosis

OBJECTIVE

In infection with hepatitis C virus (HCV), spontaneous clearance of the virus occurs in 30-40% of cases. By contrast, in chronic infection, this is rare. The basis for viral clearance in acute disease is unknown. Whereas cellular immune responses have been studied in detail, few data exist on the role of viral structural proteins, such as the core protein. The purpose of this study was to investigate the effects of core produced de novo within adult mouse hepatocytes by using a new transgenic mouse line in which expression of HCV core is regulated by tetracycline (tet-off).

MATERIAL AND METHODS

In this work, transgenic mice with conditional HCV core were created, to study the acute expression of HCV core protein in the context of the mature liver. The subcellular distribution of the core, hepatocellular oxidative stress and apoptosis were monitored.

RESULTS

Core protein is readily detectable and strongly associated with cytoplasmic lipid vesicles, endoplasmic reticulum and mitochondria. Mitochondrial oxidative stress was evidenced by a reduction in thioredoxin-2 (trx2). Concurrently, caspase-3 activity and TUNEL increased and, over time, the level of core protein in the liver declined.

CONCLUSIONS

Mice that are conditionally transgenic for HCV core protein, which is readily detected and morphologically associated with steatosis in individual hepatocytes, were developed. Acute expression of core protein causes mitochondrial stress, as demonstrated by a reduction in trx2 and in the apoptosis of core-positive hepatocytes. We speculate that these events could be involved in the clearance of virus during acute hepatitis C, by both reducing the burden of virus in the liver and effectively priming the immune response.

Hepatitis C virus NS5A protein interacts with and negatively regulates the non-receptor protein tyrosine kinase Syk

Hepatitis C virus (HCV) is the major causative agent of hepatocellular carcinoma. However, the precise mechanism underlying the carcinogenesis is yet to be elucidated. It has recently been reported that Syk, a non-receptor protein tyrosine kinase, functions as a potent tumour suppressor in human breast carcinoma. This study first examined the possible effect of HCV infection on expression of Syk in vivo. Immunohistochemical analysis revealed that endogenous Syk, which otherwise was expressed diffusely in the cytoplasm of normal hepatocytes, was localized near the cell membrane with a patchy pattern in HCV-infected hepatocytes. The possible interaction between HCV proteins and Syk in human hepatoma-derived Huh-7 cells was then examined. Immunoprecipitation analysis revealed that NS5A interacted strongly with Syk. Deletion-mutation analysis revealed that an N-terminal portion of NS5A (aa 1-175) was involved in the physical interaction with Syk. An in vitro kinase assay demonstrated that NS5A inhibited the enzymic activity of Syk and that, in addition to the N-terminal 175 residues, a central portion of NS5A (aa 237-302) was required for inhibition of Syk. Moreover, Syk-mediated phosphorylation of phospholipase C-gamma1 was downregulated by NS5A. An interaction of NS5A with Syk was also detected in Huh-7.5 cells harbouring an HCV RNA replicon or infected with HCV. In conclusion, these results demonstrated that NS5A interacts with Syk resulting in negative regulation of its kinase activity. The results indicate that NS5A may be involved in the carcinogenesis of hepatocytes through the suppression of Syk kinase activities.

Hepatitis C virus core protein, lipid droplets and steatosis

Lipid droplets are intracellular organelles involved not only in lipid storage but also in cell signalling and the regulation of intracellular vesicular trafficking. Recent basic studies have suggested that interactions between hepatitis C virus (HCV) core protein and lipid droplets are required for the HCV infection cycle. In infected cells, the HCV core protein is associated with the surface of lipid droplets and the endoplasmic reticulum membranes closely surrounding these droplets, and its self-assembly drives virion budding. This interaction also seems to be directly linked to a virus-induced steatosis, which involves the deposition of triglycerides in the liver and contributes to the progression of fibrosis in patients with chronic hepatitis C. Many clinical studies have reported that virus-induced steatosis is significantly more severe with HCV genotype 3 than with other genotypes, and this phenomenon has been modelled in recent basic studies based on the production of HCV core proteins of various genotypes in vitro. The association of HCV core protein with lipid droplets seems to play a central role in HCV pathogenesis and morphogenesis, suggesting that virus-induced steatosis may be essential for the viral life cycle.

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.

Hepatitis C virus core protein induces spontaneous and persistent activation of peroxisome proliferator-activated receptor alpha in transgenic mice: implications for HCV-associated hepatocarcinogenesis

Persistent infection of hepatitis C virus (HCV) can lead to a high risk for hepatocellular carcinoma (HCC). HCV core protein plays important roles in HCV-related hepatocarcinogenesis, because mice carrying the core protein exhibit multicentric HCCs without hepatic inflammation and fibrosis. However, the precise mechanism of hepatocarcinogenesis in these transgenic mice remains unclear. To evaluate whether the core protein modulates hepatocyte proliferation and apoptosis in vivo, we examined these parameters in 9- and 22-month-old transgenic mice. Although the numbers of apoptotic hepatocytes and hepatic caspase 3 activities were similar between transgenic and nontransgenic mice, the numbers of proliferating hepatocytes and the levels of numerous proteins such as cyclin D1, cyclin-dependent kinase 4 and c-Myc, were markedly increased in an age-dependent manner in the transgenic mice. This increase was correlated with the activation of peroxisome proliferator-activated receptor alpha (PPARalpha). In these transgenic mice, spontaneous and persistent PPARalpha activation occurred heterogeneously, which was different from that observed in mice treated with clofibrate, a potent peroxisome proliferator. We further demonstrated that stabilization of PPARalpha through a possible interaction with HCV core protein and an increase in nonesterified fatty acids, which may serve as endogenous PPARalpha ligands, in hepatocyte nuclei contributed to the core protein-specific PPARalpha activation. In conclusion, these results offer the first suggestion that HCV core protein induces spontaneous, persistent, age-dependent and heterogeneous activation of PPARalpha in transgenic mice, which may contribute to the age-dependent and multicentric hepatocarcinogenesis mediated by the core protein.