Characterization of the genome and structural proteins of hepatitis C virus resolved from infected human liver

Characterization of a multipurpose NS3 surface patch coordinating HCV replicase assembly and virion morphogenesis

The hepatitis C virus (HCV) life cycle is highly regulated and characterized by a step-wise succession of interactions between viral and host cell proteins resulting in the assembly of macromolecular complexes, which catalyse genome replication and/or virus production. Non-structural (NS) protein 3, comprising a protease and a helicase domain, is involved in orchestrating these processes by undergoing protein interactions in a temporal fashion. Recently, we identified a multifunctional NS3 protease surface patch promoting pivotal protein-protein interactions required for early steps of the HCV life cycle, including NS3-mediated NS2 protease activation and interactions required for replicase assembly. In this work, we extend this knowledge by identifying further NS3 surface determinants important for NS5A hyperphosphorylation, replicase assembly or virion morphogenesis, which map to protease and helicase domain and form a contiguous NS3 surface area. Functional interrogation led to the identification of phylogenetically conserved amino acid positions exerting a critical function in virion production without affecting RNA replication. These findings illustrate that NS3 uses a multipurpose protein surface to orchestrate the step-wise assembly of functionally distinct multiprotein complexes. Taken together, our data provide a basis to dissect the temporal formation of viral multiprotein complexes required for the individual steps of the HCV life cycle.

Changes of Gut-Microbiota-Liver Axis in Hepatitis C Virus Infection

Simple Summary

Gut microbiota alteration is linked to many health disorders including hepatitis C virus (HCV) infection. This dysbiosis in turn impacts the coordination between the gut and the liver that is known as the gut–liver-axis. Here, we discuss the latest findings regarding the changes in gut microbiota structure and functionality post HCV infection and its treatment regimens. In addition, we underline the contribution of the microbiota alterations to HCV associated liver complications.

Abstract

The gut–liver-axis is a bidirectional coordination between the gut, including microbial residents, the gut microbiota, from one side and the liver on the other side. Any disturbance in this crosstalk may lead to a disease status that impacts the functionality of both the gut and the liver. A major cause of liver disorders is hepatitis C virus (HCV) infection that has been illustrated to be associated with gut microbiota dysbiosis at different stages of the disease progression. This dysbiosis may start a cycle of inflammation and metabolic disturbance that impacts the gut and liver health and contributes to the disease progression. This review discusses the latest literature addressing this interplay between the gut microbiota and the liver in HCV infection from both directions. Additionally, we highlight the contribution of gut microbiota to the metabolism of antivirals used in HCV treatment regimens and the impact of these medications on the microbiota composition. This review sheds light on the potential of the gut microbiota manipulation as an alternative therapeutic approach to control the liver complications post HCV infection.

Adaptive mutations promote hepatitis C virus assembly by accelerating core translocation to the endoplasmic reticulum

The envelopment of hepatitis C virus (HCV) is believed to occur primarily in the endoplasmic reticulum (ER)-associated membrane, and the translocation of viral Core protein from lipid droplets (LDs) to the ER is essential for the envelopment of viral particles. However, the factors involved are not completely understood. Herein, we identified eight adaptive mutations that enhanced virus spread and infectivity of genotype 1a clone TNcc in hepatoma Huh7 cells through long-term culture adaptation and reverse genetic study. Of eight mutations, I853V in NS2 and C2865F in NS5B were found to be minimal mutation sets that enabled an increase in virus production without apparently affecting RNA replication, thus suggesting its roles in the post-replication stage of the HCV life cycle. Using a protease K protection and confocal microscopy analysis, we demonstrated that C2865F and the combination of I853V/C2865F enhanced virus envelopment by facilitating Core translocation from the LDs to the ER. Buoyant density analysis revealed that I853V/C2865F contributed to the release of virion with a density of ∼1.10 g/ml. Moreover, we demonstrated that NS5B directly interacted with NS2 at the protease domain and that mutations I853V, C2865F, and I853V/C2865F enhanced the interaction. In addition, C2865F also enhanced the interaction between NS5B and Core. In conclusion, this study demonstrated that adaptive mutations in NS2 and NS5B promoted HCV envelopment by accelerating Core translocation from the LDs to the ER and reinforced the interaction between NS2 and NS5B. The findings facilitate our understanding of the assembly of HCV morphogenesis.

Developments in the HCV Screening Technologies Based on the Detection of Antigens and Antibodies

Hepatitis C virus (HCV) accounts for 15%-20% of cases of acute infection, and chronic HCV infection is developed in about 50%-80% of HCV patients. Unfortunately, due to the lack of proper medical care, difficulty in screening for HCV infection, and lack of awareness resulted in chronic HCV infection in 71 million people on a global scale, and about 399,000 deaths in 2016. It is crucial to recognize that the effective use of antiviral medicines can cure more than 95% of HCV infected people. The Global Health Sector Strategy (GHSS) aim is to reduce the new HCV infections and the HCV associated mortality by 90% and 65%, respectively. Therefore, the methods that are simple, yet powerful enough to detect HCV infections with high sensitivity, specificity, and a shorter window period are crucial to restrain the global burden of HCV healthcare. This article focuses on the technologies used for the detection of HCV in clinical specimens.

The acidic domain of the hepatitis C virus NS4A protein is required for viral assembly and envelopment through interactions with the viral E1 glycoprotein

Hepatitis C virus (HCV) assembly and envelopment are coordinated by a complex protein interaction network that includes most of the viral structural and nonstructural proteins. While the nonstructural protein 4A (NS4A) is known to be important for viral particle production, the specific function of NS4A in this process is not well understood. We performed mutagenesis of the C-terminal acidic domain of NS4A and found that mutation of several of these amino acids prevented the formation of the viral envelope, and therefore the production of infectious virions, without affecting viral RNA replication. In an overexpression system, we found that NS4A interacted with several viral proteins known to coordinate envelopment, including the viral E1 glycoprotein. One of the NS4A C-terminal mutations, Y45F, disrupted the interaction of NS4A with E1. Specifically, NS4A interacted with the first hydrophobic region of E1, a region previously described as regulating viral particle production. Indeed, we found that an E1 mutation in this region, D72A, also disrupted the interaction of NS4A with E1. Supernatants from HCV NS4A Y45F transfected cells had significantly reduced levels of HCV RNA, however they contained equivalent levels of Core protein. Interestingly, the Core protein secreted from these cells formed high order oligomers with a density matching the infectious virus secreted from wild-type cells. These results suggest that this Y45F mutation in NS4A causes secretion of low-density Core particles lacking genomic HCV RNA. These results corroborate previous findings showing that the E1 D72A mutation also causes secretion of Core complexes lacking genomic HCV RNA, and therefore suggest that the interaction between NS4A and E1 is involved in the incorporation of viral RNA into infectious HCV particles. Our findings define a new role for NS4A in the HCV lifecycle and help elucidate the protein interactions necessary for production of infectious virus.

Hepatitis C - New drugs and treatment prospects

Hepatitis C virus (HCV) affects approx. 3% of the world's population and accounts for ca 300 000 deaths per year. 80% of individuals with HCV develop chronic symptoms which, when untreated, may cause cirrhosis (27%) or hepatocellular carcinoma (25%). The hepatitis C virus is a (+)ssRNA enveloped virus of the family Flaviviridae. Seven major HCV genotypes and their subtypes (a, b) have been identified. In the 1990s, interferons alpha-2 were used in the treatment of HCV and in the next decade HCV therapy was based on pegylated interferon alpha-2 in combination with ribavirin. Since 2011, interferons alpha, DNA and RNA polymerase inhibitors, NS3/4A RNA protease inhibitors, NS5 RNA serine protease inhibitors, NS5B RNA polymerase inhibitors have been approved for clinical use. Monotherapy is avoided in medication due to rapidly developing viral resistance. A total of 113 papers were included comprising original publications and reviews. The paper reviews the molecular targets and chemical structures of drugs used in HCV treatment. Indications and contraindications for anti-HCV drugs are also discussed together with application regimens.

Genotyping & diagnostic methods for hepatitis C virus: A need of low-resource countries

Hepatitis C virus (HCV) infection is a blood borne and transfusion-transmitted infection (TTI). It has emerged as one of the major health challenges worldwide. In India, around 12-18 million peoples are infected with HCV, but in terms of prevalence percentage, its looks moderate due to large population. The burden of the HCV infection increases due to lack of foolproof screening of blood and blood products before transfusion. The qualified screening and quantification of HCV play an important role in diagnosis and treatment of HCV-related diseases. If identified early, HCV infection can be managed and treated by recently available antiviral therapies with fewer side effects. However, its identification at chronic phase makes its treatment very challenging and sometimes ineffective. The drugs therapy for HCV infection treatment is also dependent on its genotype. Different genotypes of HCV differ from each other at genomic level. The RNA viruses (such as HCV) are evolving perpetually due to interaction and integration among people from different regions and countries which lead to varying therapeutic response in HCV-infected patients in different geographical regions. Therefore, proper diagnosis for infecting virus and then exact determination of genotype become important for targeted treatment. This review summarizes the general information on HCV, and methods used for its diagnosis and genotyping.

Regulation of hepatitis C virus replication via threonine phosphorylation of the NS5A protein

The hepatitis C virus non-structural 5A (NS5A) protein is highly phosphorylated and plays roles in both virus genome replication and assembly of infectious virus particles. NS5A comprises three domains separated by low complexity sequences (LCS). Mass spectrometry analysis of NS5A revealed the existence of a singly phosphorylated tryptic peptide corresponding to the end of LCS I and the beginning of domain II that contained a number of potential phosphorylatable residues (serines and threonines). Here we use a mutagenic approach to investigate the potential role of three of these threonine residues. Phosphomimetic mutations of two of these (T242E and T244E) resulted in significant reductions in virus genome replication and the production of infectious virus, suggesting that the phosphorylation of these residues negatively regulated virus RNA synthesis. Mutation of T245 had no effect, however when T245E was combined with the other two phosphomimetic mutations (TripleE) the inhibitory effect on replication was less pronounced. Effects of the mutations on the ratio of basally/hyperphosphorylated NS5A, together with the apparent molecular weight of the basally phosphorylated species were also observed. Lastly, two of the mutations (T245A and TripleE) resulted in a perinuclear restricted localization of NS5A. These data add further complexity to NS5A phosphorylation and suggest that this analysis be extended outwith the serine-rich cluster within LCS I.

Newly discovered hepatitis C virus minicores circulate in human blood

Hepatitis C virus (HCV) is one of the most prevalent causes of chronic blood‐borne infections worldwide. Despite developments of highly effective treatments, most infected individuals are unaware of their infection. Approximately 75% of infections are in low‐ and middle‐income countries; therefore, continuing research in HCV molecular virology and the development of vaccines and affordable diagnostics is required to reduce the global burden. Various intracellular forms of the HCV nucleocapsid (core) protein are produced in cell culture; these comprise the conventional p21 core and the newly discovered shorter isoforms (minicores). Minicores lack the N‐terminus of p21 core. This study was conducted to determine if minicores are secreted in cell culture and more importantly if they circulate in the blood of individuals infected with HCV. We also developed a new monoclonal antibody that detects minicores targeting a C‐terminal region common to p21 core and minicores. Direct evidence of minicores requires western blot analysis to distinguish the detection of p21 core from minicores. However, the sensitivity for western blot detection of HCV proteins from blood is nil without their prior purification/enrichment from blood. Therefore, we developed a purification method based on a heparin/Mn⁺² precipitation of apolipoprotein B‐containing lipoproteins because HCV is thought to circulate as a hybrid lipoviral particle. Minicores are secreted in culture when cells are grown in the presence of human serum. The heparin/Mn⁺² precipitate from HCV‐infected cell culture supernatants and from the blood of 4 patients with high‐titer genotype‐1 HCV contained minicores. Conclusion: Minicores are major newly discovered HCV proteins that are secreted and circulate in blood during natural infections. Minicore proteins have translational potential as targets in diagnostic assays and in vaccine development. (Hepatology Communications 2018;2:21–28)

Characterization of Nora Virus Structural Proteins via Western Blot Analysis

Nora virus is a single stranded RNA picorna-like virus with four open reading frames (ORFs). The coding potentials of the ORFs are not fully characterized, but ORF3 and ORF4 are believed to encode the capsid proteins (VP3, VP4a, VP4b, and VP4c) comprising the virion. To determine the polypeptide composition of Nora virus virions, polypeptides from purified virus were compared to polypeptides detected in Nora virus infected Drosophila melanogaster. Nora virus was purified from infected flies and used to challenge mice for the production of antisera. ORF3, ORF4a, ORF4b, and ORF4c were individually cloned and expressed in E. coli; resultant recombinant proteins purified and were used to make monospecific antisera. Antisera were evaluated via Western blot against whole virus particles and Nora virus infected fly lysates. Viral purification yielded two particle types with densities of ~1.31 g/mL (empty particles) and ~1.33 g/mL (complete virions). Comparison of purified virus polypeptide composition to Nora virus infected D. melanogaster lysate showed the number of proteins in infected cell lysates is less than purified virus. Our results suggest the virion is composed of 6 polypeptides, VP3, VP4a, two forms of VP4b, and two forms of VP4c. This polypeptide composition is similar to other small RNA insect viruses.

The deletion of residues 268-292 of E1 impairs the ability of HCV envelope proteins to induce pore formation

We have obtained a chimeric protein containing the ectodomains of hepatitis C virus (HCV) envelope proteins but lacking the region 268-292 of E1. All its structural properties are coincident with those of the corresponding full length chimera. The deleted and entire chimeras were compared in terms of their membrane destabilizing properties. No differences were found in their ability to induce vesicle aggregation and lipid mixing but the deleted chimera showed a reduced capacity to promote leakage. The role of the deletion was also studied by obtaining HCV pseudoparticles (HCVpp). Both E1 and E2, and also the E1 deleted mutant, were incorporated into HCVpp to a similar level. However, HCVpp containing the E1 deleted protein are almost unable to infect Huh7 cells. These results point to the involvement of the region 268-292 in the formation of pores in the membrane necessary for the complete fusion of the membranes.

The role of HCV proteins on treatment outcomes

For many years, the standard of treatment for hepatitis C virus (HCV) infection was a combination of pegylated interferon alpha (Peg-IFN-α) and ribavirin for 24–48 weeks. This treatment regimen results in a sustained virologic response (SVR) rate in about 50 % of cases. The failure of IFN-α-based therapy to eliminate HCV is a result of multiple factors including a suboptimal treatment regimen, severity of HCV-related diseases, host factors and viral factors. In recent years, advances in HCV cell culture have contributed to a better understanding of the viral life cycle, which has led to the development of a number of direct-acting antiviral agents (DAAs) that target specific key components of viral replication, such as HCV NS3/4A, HCV NS5A, and HCV NS5B proteins. To date, several new drugs have been approved for the treatment of HCV infection. Application of DAAs with IFN-based or IFN-free regimens has increased the SVR rate up to >90 % and has allowed treatment duration to be shortened to 12–24 weeks. The impact of HCV proteins in response to IFN-based and IFN-free therapies has been described in many reports. This review summarizes and updates knowledge on molecular mechanisms of HCV proteins involved in anti-IFN activity as well as examining amino acid variations and mutations in several regions of HCV proteins associated with the response to IFN-based therapy and pattern of resistance associated amino acid variants (RAV) to antiviral agents.

High-yield production of a chimeric glycoprotein based on permuted E1 and E2 HCV envelope ectodomains

In this report it is described for the first time the expression and purification of large quantities of a soluble and correctly folded chimeric recombinant protein, E2661E1340, containing the permuted Hepatitis C virus (HCV) glycoprotein ectodomains E1 (amino acids 192-340) and E2 (amino acids 384-661). Using the baculovirus/insect cell expression system, 8mg of secreted protein were purified from 1L of culture media, a yield 4 times higher than the described for its counterpart E1341E2661. This permuted chimeric protein is glycosylated and possesses a high tendency to self-associate. The fluorescence emission spectrum indicates that Trp residues occupy a relatively low hydrophobic environment. The secondary structure was determined by deconvolution of the far-UV circular dichroism spectrum yielding 13% α-helix structure, 49% extended structure and 38% non-ordered structure. E2661E1340 binds to antibodies present in human sera from HCV-positive patients, a binding that is blocked at different levels by a rabbit anti-E2661 antibody. All these structural and antigenic features of E2661E1340 are very similar to those described for E1340E2661, Thus, this high-yield isolated chimeric protein may be a valuable tool to study the first steps of the HCV infection.

Production and characterization of the ectodomain of E2 envelope glycoprotein of hepatitis C virus folded in the presence of full-length E1 glycoprotein

Hepatitis C virus (HCV) envelope glycoproteins, E1 and E2, are involved in the first steps of virus infection. The E2 ectodomain can be produced as an isolated form (E2661). However, there is some concern about its proper conformation and the role that E1 can play as a chaperone for the folding of E2. In order to verify this fact we have expressed a chimeric protein (E1tmbE2) based on the full-length E1 sequence followed by the E2 ectodomain using the baculovirus-insect cells system. The E2 ectodomain is folded in the presence of the E1, proteolytically processed by cellular proteases and secreted to cell culture media (E2661p), while the E1 protein is retained into the cell due to its transmembrane sequence. The purification of E2661p from culture media was facilitated by a His tag introduced in its amino terminus. Both E2661 and E2661p glycoproteins shared very similar structural features, monitored by spectroscopic and antigenic studies. Moreover, their functional properties, tested by means of CD81 binding, were almost indistinguishable, indicating that the E2 ectodomain constitutes an independent folding unit.

Generation and epitope mapping of a sub-group cross-reactive anti-respiratory syncytial virus G glycoprotein monoclonal antibody which is protective in vivo

Passively administered antibodies to conserved epitopes on the attachment (G) glycoprotein of human respiratory syncytial virus (hRSV) have potential in the immunoprophylaxis of human infections. This study set out to generate monoclonal antibodies (MAbs) recognizing all prevalent lineages of HRSV and capable of immunoprophylaxis in mice. Two murine MAbs of broad specificity for prevalent virus strains were generated by immunization of mice with hRSV of sub-group A followed by selection of hybridomas on recombinant G glycoprotein from a sub-group B virus. The anti-G hybridomas generated secreted antibody of high affinity but negligible neutralizing capacity one of which was tested in mice and found to be protective against live virus challenge. Western blotting and partial epitope mapping on transiently expressed G-glycoprotein fragments indicate that these antibodies recognize a complex epitope on the protein backbone of the molecule involving residues both C'- and N-terminal to the central conserved motif.

HCV Envelope protein 2 sequence comparison of Pakistani isolate and In-silico prediction of conserved epitopes for vaccine development

BACKGROUND

HCV is causing hundreds of cases yearly in Pakistan and has become a threat for Pakistani population. HCV E2 protein is a transmembrane protein involved in viral attachment and thus can serve as an important target for vaccine development but because of its variability, vaccine development against it has become a challenge. Therefore, this study was designed to isolate the HCV E2 gene from Pakistani HCV infected patients of 3a genotype, to perform In-silico analysis of HCV E2 isolated in Pakistan and to analyze HCV E2 protein sequence in comparison with other E2 proteins belonging to 3a and 1a genotypes to find potential conserved B-cells and T-cell epitopes that can be important in designing novel inhibitory compounds and peptide vaccine against genotype 3a and 1a.

PATIENTS AND METHODS

Patients were selected on the basis of elevated serum ALT and AST levels at least for six months, histological examination, and detection of serum HCV RNA anti-HCV antibodies (3rd generation ELISA). RNA isolation, cDNA synthesis, amplification, cloning and sequencing was performed from 4 patient's serum samples in order to get the HCV E2 sequence. HCV E2 protein of Pakistani origin was analyzed using various bioinformatics tools including sequence and structure tools.

RESULTS

HCV E1 protein modeling was performed with I-TASSER online server and quality of the model was assessed with ramchandran plot and Z-score. A total of 3 B-cell and 3 T-cell epitopes were found to be highly conserved among HCV 3a and 1a genotype.

CONCLUSION

The present study revealed potential conserved B-cell and T-cell epitopes of the HCV E2 protein along with 3D protein modeling. These conserved B-cell and T-cell epitopes can be helpful in developing effective vaccines against HCV and thus limiting threats of HCV infection in Pakistan.

[The molecular biology of hepatitis C virus]

Since the discovery of the hepatitis C virus (HCV), a plethora of experimental models have evolved, allowing the virus's life cycle and the pathogenesis of associated liver diseases to be investigated. These models range from inoculation of cultured cells with serum from patients with hepatitis C to the use of surrogate models for the study of specific stages of the HCV life cycle: retroviral pseudoparticles for the study of HCV entry, replicons for the study of HCV replication, and the HCV cell culture model, which reproduces the entire life cycle (replication and production of infectious particles). The use of these tools has been and remains crucial to identify potential therapeutic targets in the different stages of the virus's life cycle and to screen new antiviral drugs. A clear example is the recent approval of two viral protease inhibitors (boceprevir and telaprevir) in combination with pegylated interferon and ribavirin for the treatment of chronic hepatitis C. This review analyzes the advances made in the molecular biology of HCV and highlights possible candidates as therapeutic targets for the treatment of HCV infection.

Hepatitis C virus: virology and life cycle

Hepatitis C virus (HCV) is a positive sense, single-stranded RNA virus in the Flaviviridae family. It causes acute hepatitis with a high propensity for chronic infection. Chronic HCV infection can progress to severe liver disease including cirrhosis and hepatocellular carcinoma. In the last decade, our basic understanding of HCV virology and life cycle has advanced greatly with the development of HCV cell culture and replication systems. Our ability to treat HCV infection has also been improved with the combined use of interferon, ribavirin and small molecule inhibitors of the virally encoded NS3/4A protease, although better therapeutic options are needed with greater antiviral efficacy and less toxicity. In this article, we review various aspects of HCV life cycle including viral attachment, entry, fusion, viral RNA translation, posttranslational processing, HCV replication, viral assembly and release. Each of these steps provides potential targets for novel antiviral therapeutics to cure HCV infection and prevent the adverse consequences of progressive liver disease.

RNA dependent RNA polymerase of HCV: a potential target for the development of antiviral drugs

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma, cirrhosis and end stage liver disease. More than 200million people are living with HCV worldwide with high morbidity and mortality. There is no vaccine available for this virus; the approved treatment option for the majority of HCV genotypes is the combination of pegylated (Peg) interferon and ribavirin. The therapy has a different response rate on different HCV genotypes and has a number of side effects. Recently, as well as Peg interferon and ribavirin, two protease inhibitors have been introduced to treat patients with HCV genotype 1 infection. The protease inhibitors have rapid onset of resistance and are not approved for use for infections with other HCV genotypes. The HCV NS5B gene encodes RNA dependent RNA polymerase (RdRp), which is the key player in viral replication and is a promising target for the development of antiviral drugs. HCV NS5B has been studied in various biochemical assays, cell based assays and animal model systems. So far, a number of nucleoside and non-nucleoside inhibitors have been screened for effects on viral replication. This review presents a deep insight into the structure and function of HCV polymerase and the effect of various nucleoside and non-nucleoside inhibitors on viral replication.

The insulin-like growth factor (IGF) signaling axis and hepatitis C virus-associated carcinogenesis (review)

Insulin-like growth factor (IGF) signaling plays an important autocrine, paracrine and endocrine role in growth promotion involving various tissues and organs. Synthesis of both IGFs (IGF-1 and IGF-2) in normal conditions takes place mainly in the liver even if the proteins can be produced in every cell of the human body. The alterations in the IGF signaling axis in human hepatocarcinogenesis are described, but mechanisms of the interactions between expression of oncogenic hepatitis C virus (HCV) proteins and components of the IGF system in progression of chronic hepatitis C to primary hepatocellular carcinoma (HCC) have been poorly recognised. In advanced stages of liver diseases, lowered serum levels of IGF-1 and IGF-2 have been documented. This was supposed to reflect significant damage to liver parenchyma, a decreased number of growth hormone receptors and a decreased genomic expression of IGF binding proteins (IGF BPs). In HCC, a decreased tissue expression of IGF-1, and an increased expression of IGF-1 receptor (IGF-1R) were noted, compared to the control. Potential mechanisms of augmented IGF-2 expression in HCC were also described and dysregulation of IGF signaling in HCC was concluded to occur predominantly at the level of IGF-2 bioavailability. The review aimed at presentation of involvement of IGF-1, IGF-1R and IGF BPs (mostly IGF BP-3 and IGF BP-6) in HCV-related hepatocarcinogenesis. Manifestation of various mRNA transcripts and IGF-1 proteins and their potential involvement in carcinogenesis are also discussed.

HCV entry receptors as potential targets for siRNA-based inhibition of HCV

Background

Hepatitis C virus (HCV) is a major health concern with almost 3% of the world's population (350 million individuals) and 10% of the Pakistani population chronically infected with this viral pathogen. The current therapy of interferon-α and ribavirin against HCV has limited efficiency, so alternative options are desperately needed. RNA interference (RNAi), which results in a sequence-specific degradation of HCV RNA has potential as a powerful alternative molecular therapeutic approach. Concerning viral entry, the HCV structural gene E2 is mainly involved in virus attachment to the host cell surface receptors i.e., CD81 tetraspanin, scavenger receptor class B type 1 (SR-B1), low density lipoprotein receptor (LDLR) and claudin1 (CLDN1).

Results

In this report, we studied the relationship of the HCV receptors CD81, LDL, CLDN1 and SR-B1to HCV infection. The potential of siRNAs to inhibit HCV-3a replication in serum-infected Huh-7 cells was demonstrated by treatment with siRNAs against HCV receptors, which resulted in a significant decrease in HCV viral copy number.

Conclusions

Our data clearly demonstrate that the RNAi-mediated silencing of HCV receptors is among the first of its type for the development of an effective siRNA-based therapeutic option against HCV-3a. These findings will shed further light on the possible role of receptors in inhibition of HCV-3a viral titre through siRNA mediated silencing.

Neutralizing activities of caprine antibodies towards conserved regions of the HCV envelope glycoprotein E2

Anti HCV vaccine is not currently available and the present antiviral therapies fail to cure approximately half of the treated HCV patients. This study was designed to assess the immunogenic properties of genetically conserved peptides derived from the C-terminal region of HVR-1 and test their neutralizing activities in a step towards developing therapeutic and/or prophylactic immunogens against HCV infection. Antibodies were generated by vaccination of goats with synthetic peptides derived from HCV E2. Viral neutralizing capacity of the generated anti E2 antibodies was tested using in vitro assays. Goats immunized with E2 synthetic peptides termed p412 [a.a 412-419], p430 [a.a 430-447] and p517 [a.a 517-531] generated high titers of antibody responses 2 to 4.5 fold higher than comparable titers of antibodies to the same epitopes in chronic HCV patients. In post infection experiments of native HCV into cultured Huh7.5 cells anti p412 and anti p 517 were proven to be neutralizing to HCV genotype 4a from patients' sera (87.5% and 75% respectively). On the contrary anti p430 exhibited weak viral neutralization capacity on the same samples (31.25%). Furthermore Ab mixes containing anti p430 exhibited reduced viral neutralization properties. From these experiments one could predict that neutralization by Abs towards different E2-epitopes varies considerably and success in the enrichment of neutralization epitope-specific antibodies may be accompanied by favorable results in combating HCV infection. Also, E2 conserved peptides p517 and p412 represent potential components of a candidate peptide vaccine against HCV infection.

Neutralizing activities of caprine antibodies towards conserved regions of the HCV envelope glycoprotein E2

Anti HCV vaccine is not currently available and the present antiviral therapies fail to cure approximately half of the treated HCV patients. This study was designed to assess the immunogenic properties of genetically conserved peptides derived from the C-terminal region of HVR-1 and test their neutralizing activities in a step towards developing therapeutic and/or prophylactic immunogens against HCV infection. Antibodies were generated by vaccination of goats with synthetic peptides derived from HCV E2. Viral neutralizing capacity of the generated anti E2 antibodies was tested using in vitro assays. Goats immunized with E2 synthetic peptides termed p412 [a.a 412-419], p430 [a.a 430-447] and p517 [a.a 517-531] generated high titers of antibody responses 2 to 4.5 fold higher than comparable titers of antibodies to the same epitopes in chronic HCV patients. In post infection experiments of native HCV into cultured Huh7.5 cells anti p412 and anti p 517 were proven to be neutralizing to HCV genotype 4a from patients' sera (87.5% and 75% respectively). On the contrary anti p430 exhibited weak viral neutralization capacity on the same samples (31.25%). Furthermore Ab mixes containing anti p430 exhibited reduced viral neutralization properties. From these experiments one could predict that neutralization by Abs towards different E2-epitopes varies considerably and success in the enrichment of neutralization epitope-specific antibodies may be accompanied by favorable results in combating HCV infection. Also, E2 conserved peptides p517 and p412 represent potential components of a candidate peptide vaccine against HCV infection.

Boceprevir: a user's guide

Given its essential role in the process of hepatitis C virus (HCV) replication, the viral NS3/4A serine protease is arguably the most thoroughly characterized HCV enzyme and the most intensively pursued anti-HCV target for drug development thus far. Recent data have demonstrated promise for the NS3 protease inhibitor boceprevir, which, when added to the standard of care peginterferon and ribavirin, improves sustained virological response while shortening duration of therapy in genotype-1-infected individuals. This review discusses the mechanism of action of boceprevir, its effects on HCV, and its viral resistance.

Human cell types important for hepatitis C virus replication in vivo and in vitro: old assertions and current evidence

Hepatitis C Virus (HCV) is a single stranded RNA virus which produces negative strand RNA as a replicative intermediate. We analyzed 75 RT-PCR studies that tested for negative strand HCV RNA in liver and other human tissues. 85% of the studies that investigated extrahepatic replication of HCV found one or more samples positive for replicative RNA. Studies using in situ hybridization, immunofluorescence, immunohistochemistry, and quasispecies analysis also demonstrated the presence of replicating HCV in various extrahepatic human tissues, and provide evidence that HCV replicates in macrophages, B cells, T cells, and other extrahepatic tissues. We also analyzed both short term and long term in vitro systems used to culture HCV. These systems vary in their purposes and methods, but long term culturing of HCV in B cells, T cells, and other cell types has been used to analyze replication. It is therefore now possible to study HIV-HCV co-infections and HCV replication in vitro.

Effect of combined siRNA of HCV E2 gene and HCV receptors against HCV

Background/Aim

Hepatitis C virus (HCV) is a major threat as almost 3% of the world's population (350 million individual) and 10% of the Pakistani population is chronically infected with this virus. RNA interference (RNAi), a sequence-specific degradation process of RNA, has potential to be used as a powerful alternative molecular therapeutic approach in spite of the current therapy of interferon-α and ribavirin against HCV which has limited efficiency. HCV structural gene E2 is mainly involved in viral cell entry via attachment with the host cell surface receptors i.e., CD81 tetraspanin, low density lipoprotein receptor (LDLR), scavenger receptor class B type 1 (SR-B1), and Claudin1 (CLDN1). Considering the importance of HCV E2 gene and cellular receptors in virus infection and silencing effects of RNAi, the current study was designed to target the cellular and viral factors as new therapeutic options in limiting HCV infection.

Results

In this study the potential of siRNAs to inhibit HCV-3a replication in serum-infected Huh-7 cells was investigated by combined treatment of siRNAs against the HCV E2 gene and HCV cellular receptors (CD81 and LDLR), which resulted in a significant decrease in HCV viral copy number.

Conclusion

From the current study it is concluded that the combined RNAi-mediated silencing of HCV E2 and HCV receptors is important for the development of effective siRNA-based therapeutic option against HCV-3a.

Hepatitis C virus e2 protein ectodomain is essential for assembly of infectious virions

The Hepatitis C virus E1 and E2 envelope proteins are the major players in all events required for virus entry into target cells. In addition, the recently developed HCV cell culture system has indicated that E1E2 heterodimer formation is a prerequisite for viral particle production. In this paper, we explored a new genetic approach to construct intergenotypic 2a/1b chimeras, maintaining the structural region of the infectious strain JFH1 and substituting the soluble portion of E1 and/or E2 proteins. This strategy provides useful information on the role of the surface-exposed domain of the envelope proteins in virus morphogenesis and allows comparative analysis of different HCV genotypes. We found that substituting the E2 protein ectodomain region abolishes the production of chimeric infectious particles. Our data indicate that the soluble part of the E2 protein is involved in a genotype-specific interplay with remaining viral proteins that affect the HCV assembly process.

Assembly of infectious hepatitis C virus particles

A hallmark of the hepatitis C virus (HCV) replication cycle is its tight link with host cell lipid synthesis. This is best illustrated by the peculiar pathway used for the assembly of infectious HCV particles. Research in the past few years has shown that formation of HC-virions is closely connected to lipid droplets that could serve as an assembly platform. Moreover, HCV particle production appears to be strictly linked to very-low-density lipoproteins. In this review, we focus on new insights into the molecular aspects of the architecture and assembly of this unique type of virus particle.

Emerging therapies for hepatitis C virus

IMPORTANCE OF THE FIELD

Currently, 170 million people worldwide are affected by the HCV. Chronic HCV infection is amongst the leading causes of chronic liver disease and its complications such as cirrhosis and hepatocellular carcinoma, making it the most common reason for liver transplantation. The current standard of treatment for HCV is pegylated IFN-α plus ribavirin. This treatment, when administered for the standard duration, allows sustained virological response (SVR) in ∼ 50% of patients infected with HCV and about 40% for HCV genotype 1, the most prevalent form of HCV in the US. SVR rates for populations with co-morbidities (patients with chronic renal disease) and certain ethnic backgrounds (African Americans and Hispanics) are lower. Given the high prevalence and relatively low cure rates of current antiviral therapy, the burden of HCV is enormous.

AREAS COVERED IN THIS REVIEW

Faced with this urgent and growing medical need, research into novel therapeutic compounds for the treatment of HCV is a rapidly growing industry. Several novel compounds are in advanced stages of clinical development, such as HCV protease inhibitors (particularly those against NS3-4A protease), HCV polymerase inhibitors (including both nucleoside and non-nucleoside analogs) and cyclophilin inhibitors.

WHAT THE READER WILL GAIN

HCV treatment has seen many advances in the last decade and the discovery process has been fraught with both successes and disappointments. Through a process of rigorous research, the current late stage novel HCV therapeutics seem to have overcome some of the obstacles met by their early predecessors and offer the promise of meeting the shortfalls of the current standard of treatment.

TAKE HOME MESSAGE

Data from clinical trials are encouraging and suggest that combination therapies of these novel agents may have the potential to shorten treatment duration and increase viral clearance when used in conjunction with pegylated IFN-α and ribavirin.

Secretion of hepatitis C virus envelope glycoproteins depends on assembly of apolipoprotein B positive lipoproteins

The density of circulating hepatitis C virus (HCV) particles in the blood of chronically infected patients is very heterogeneous. The very low density of some particles has been attributed to an association of the virus with apolipoprotein B (apoB) positive and triglyceride rich lipoproteins (TRL) likely resulting in hybrid lipoproteins known as lipo-viro-particles (LVP) containing the viral envelope glycoproteins E1 and E2, capsid and viral RNA. The specific infectivity of these particles has been shown to be higher than the infectivity of particles of higher density. The nature of the association of HCV particles with lipoproteins remains elusive and the role of apolipoproteins in the synthesis and assembly of the viral particles is unknown. The human intestinal Caco-2 cell line differentiates in vitro into polarized and apoB secreting cells during asymmetric culture on porous filters. By using this cell culture system, cells stably expressing E1 and E2 secreted the glycoproteins into the basal culture medium after one week of differentiation concomitantly with TRL secretion. Secreted glycoproteins were only detected in apoB containing density fractions. The E1-E2 and apoB containing particles were unique complexes bearing the envelope glycoproteins at their surface since apoB could be co-immunoprecipitated with E2-specific antibodies. Envelope protein secretion was reduced by inhibiting the lipidation of apoB with an inhibitor of the microsomal triglyceride transfer protein. HCV glycoproteins were similarly secreted in association with TRL from the human liver cell line HepG2 but not by Huh-7 and Huh-7.5 hepatoma cells that proved deficient for lipoprotein assembly. These data indicate that HCV envelope glycoproteins have the intrinsic capacity to utilize apoB synthesis and lipoprotein assembly machinery even in the absence of the other HCV proteins. A model for LVP assembly is proposed.

Identification of a residue in hepatitis C virus E2 glycoprotein that determines scavenger receptor BI and CD81 receptor dependency and sensitivity to neutralizing antibodies

Hepatitis C virus (HCV) infection is dependent on at least three coreceptors: CD81, scavenger receptor BI (SR-BI), and claudin-1. The mechanism of how these molecules coordinate HCV entry is unknown. In this study we demonstrate that a cell culture-adapted JFH-1 mutant, with an amino acid change in E2 at position 451 (G451R), has a reduced dependency on SR-BI. This altered receptor dependency is accompanied by an increased sensitivity to neutralization by soluble CD81 and enhanced binding of recombinant E2 to cell surface-expressed and soluble CD81. Fractionation of HCV by density gradient centrifugation allows the analysis of particle-lipoprotein associations. The cell culture-adapted mutation alters the relationship between particle density and infectivity, with the peak infectivity occurring at higher density than the parental virus. No association was observed between particle density and SR-BI or CD81 coreceptor dependence. JFH-1 G451R is highly sensitive to neutralization by gp-specific antibodies, suggesting increased epitope exposure at the virion surface. Finally, an association was observed between JFH-1 particle density and sensitivity to neutralizing antibodies (NAbs), suggesting that lipoprotein association reduces the sensitivity of particles to NAbs. In summary, mutation of E2 at position 451 alters the relationship between particle density and infectivity, disrupts coreceptor dependence, and increases virion sensitivity to receptor mimics and NAbs. Our data suggest that a balanced interplay between HCV particles, lipoprotein components, and viral receptors allows the evasion of host immune responses.

Primary hepatocytes as targets for hepatitis C virus replication

Much of our current understanding of hepatitis C virus (HCV) replication has hailed from the use of a small number of cloned viral genomes and transformed hepatoma cell lines. Recent evidence suggests that lipoproteins play a key role in the HCV life cycle and virus particles derived from the sera of infected patients exist in association with host lipoproteins. This report will review the literature on HCV replication in primary hepatocytes and transformed cell lines, focusing largely on host factors defining particle entry.

Characterization of hepatitis C RNA-containing particles from human liver by density and size

Hepatitis C virus (HCV) particles found in vivo are heterogeneous in density and size, but their detailed characterization has been restricted by the low titre of HCV in human serum. Previously, our group has found that HCV circulates in blood in association with very-low-density lipoprotein (VLDL). Our aim in this study was to characterize HCV RNA-containing membranes and particles in human liver by both density and size and to identify the subcellular compartment(s) where the association with VLDL occurs. HCV was purified by density using iodixanol gradients and by size using gel filtration. Both positive-strand HCV RNA (present in virus particles) and negative-strand HCV RNA (an intermediate in virus replication) were found with densities below 1.08 g ml⁻¹. Viral structural and non-structural proteins, host proteins ApoB, ApoE and caveolin-2, as well as cholesterol, triglyceride and phospholipids were also detected in these low density fractions. After fractionation by size with Superose gel filtration, HCV RNA and viral proteins co-fractionated with endoplasmic reticulum proteins and VLDL. Fractionation on Toyopearl, which separates particles with diameters up to 200 nm, showed that 78 % of HCV RNA from liver was >100 nm in size, with a positive-/negative-strand ratio of 6 : 1. Also, 8 % of HCV RNA was found in particles with diameters between 40 nm and 70 nm and a positive-/negative-strand ratio of 45 : 1. This HCV was associated with ApoB, ApoE and viral glycoprotein E2, similar to viral particles circulating in serum. Our results indicate that the association between HCV and VLDL occurs in the liver.

Binding of liver derived, low density hepatitis C virus to human hepatoma cells

HCV recovered from low density fractions of infected blood is associated with lipid and host apo-lipoproteins in lipo-viro-particles (LVP). It has been proposed that these particles are capable of binding and entering hepatocytes by viral glycoprotein independent mechanisms utilizing uptake pathways of normal host lipoproteins after binding to cell surface glycosaminoglycans (GAG), the low density lipoprotein receptor (LDL-r) or scavenger receptor B1 (SR-B1). In this study binding to human hepatoma cells of HCV low density RNA containing particles, semi-purified from macerates of infected human liver, is compared with that of normal host low density lipoprotein (LDL). Binding of both LDL and HCV low density RNA containing particles paralleled LDL-r but not SR-B1 expression on the recipient cells. Binding of both particle types was sensitive to suramin at 0 degrees C but less so at 37 degrees C suggesting that they both bind initially to GAG but, at 37 degrees C, are internalized or transferred to a suramin resistant receptor. Suramin resistant uptake of both particles was blocked in the presence of excess LDL or oxidized LDL. However, whilst LDL uptake was blocked by anti-apoB-100, HCV low density RNA uptake was enhanced by anti-apoB100 and further enhanced by a cocktail of anti-apo-B100 and anti-apoE. Pre-incubation of HCV low density RNA containing particles with antibodies to the E2 glycoprotein had little or no effect on uptake. These data indicate that whilst liver derived HCV RNA containing particles are taken up by HepG2 cells by a virus glycoprotein independent mechanism, the mechanism differs from that of LDL uptake.

Review article: novel therapeutic options for chronic hepatitis C

BACKGROUND

The efficacy of treatment against hepatitis C virus has improved, but it is still far from ideal. Thus, new antihepatitis C virus therapies are required.

AIM

To evaluate the data on antihepatitis C virus approaches beyond the current standard combination of pegylated interferon-alpha and ribavirin.

METHOD

We reviewed the available literature regarding novel antihepatitis C virus options, given alone or in combination with existing agents.

RESULTS

New interferons and ribavirin alternatives have been tried aiming to improve the efficacy and the safety/tolerability profile of standard agents. The hepatitis C virus polymerase and NS3/4A protease have been rather popular targets for new antihepatitis C virus agents. The combination of such inhibitors with pegylated interferon-alpha and ribavirin seems to act synergistically and to prevent viral resistance, compared to monotherapies. Several novel immunomodulators are currently evaluated and may be useful in combination therapies. Alternative strategies (inhibition of hepatitis C virus protein translation, assembly/release or binding) or agents with different modes of action (statins, S-adenosylmethionine and herbs) need further evaluation.

CONCLUSIONS

Many novel promising antihepatitis C virus agents are being developed, offering hope for future therapies that may target multiple points of the viral life cycle and/or host immune response. Newer approaches should ideally provide safe, effective and more tolerable therapy to all chronic hepatitis C virus patients.

Transmission of low-density hepatitis C viral particles during sexually transmitted acute resolving infection

Hepatitis C viruses in the blood of chronically infected patients are heterogeneous in density with the presence of lipoprotein associated viral particles of lower density than conventional virions. If low-density viral particles have been shown to be infectious in animal models it is currently not known whether these particles display the same infectivity for humans. In a case of sexually transmitted acute resolving infection, all isolated NS3 sequences from the acute-phase isolate clustered with a single sequence from the chronic carrier isolate, suggesting bottlenecking during transmission. To determine the density of the transmitted viruses, viral quasispecies from fractions with density below and above 1.055 g/ml were isolated and prepared from the plasma of the chronically infected sexual partner. Interestingly, the three closest sequences to the recipient consensus sequence were isolated from the low-density fraction. These data suggest that low-density viral particles are infectious for humans as they are for chimpanzees and that they can be transmitted during sexual intercourse.

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.

The hepatitis C virus life cycle as a target for new antiviral therapies

The burden of disease consequent to hepatitis C virus (HCV) infection has been well described and is expected to increase dramatically over the next decade. Current approved antiviral therapies are effective in eradicating the virus in approximately 50% of infected patients. However, pegylated interferon and ribavirin-based therapy is costly, prolonged, associated with significant adverse effects, and not deemed suitable for many HCV-infected patients. As such, there is a clear and pressing need for the development of additional agents that act through alternate or different mechanisms, in the hope that such regimens could lead to enhanced response rates more broadly applicable to patients with hepatitis C infection. Recent basic science enhancements in HCV cell culture systems and replication assays have led to a broadening of our understanding of many of the mechanisms of HCV replication and, therefore, potential novel antiviral targets. In this article, we have attempted to highlight important new information as it relates to our understanding of the HCV life cycle. These steps broadly encompass viral attachment, entry, and fusion; viral RNA translation; posttranslational processing; HCV replication; and viral assembly and release. In each of these areas, we present up-to-date knowledge of the relevant aspects of that component of the viral life cycle and then describe the preclinical and clinical development targets and pathways being explored in the translational and clinical settings.

Hepatitis C lipo-Viro-particle from chronically infected patients interferes with TLR4 signaling in dendritic cell

Background

Hepatitis C virus (HCV) can be purified from serum of chronically-infected patients in the form of Lipo-Viro-Particles (LVP), which are triglycerid-rich lipoprotein-like particles containing viral RNA and proteins. Since LVP is a constant feature of chronically infected patients, we asked whether purified LVP could interfere with the immune response by acting directly on dendritic cell (DC) function.

Methods and Findings

We have analyzed the impact of LVP on the maturation monocyte-derived DC induced by TLR3 or TLR4 ligands. Following incubation with LVP, immature DC supported weak transient HCV-RNA replication and type I IFN synthesis. This, however, did not lead to viral particle production nor to maturation of DC. LVP-treatment prior to TLR3 stimulation by polyI:C only enhanced the secretion of IL-12, IL-6 and TNFα yielding typical mature DC. In contrast, LVP-treated DC activated by the TLR4 ligand LPS yielded phenotypically mature DC with reduced capacity to secrete both pro- and anti-inflammatory cytokines. Their ability to stimulate allogeneic T lymphocytes was strongly affected since activated T cells produced IL-5 and IL-13 instead of IFNγ. Addition of IFNα prevented the effect of LVP on DC function. Restoration of IFNγ secretion by T cells was obtained by blocking ERK activation in DC, while induction of IL-5 and IL-13 secretion was inhibited by blocking the p38-MAPK pathway in DC.

Conclusions

LVP can interfere with TLR4-triggered maturation of DC, inducing a shift in DC function that stimulates Th2 cells instead of Th1, by a mechanism that is ERK- and p38-MAPK-dependent. The effect of LVP on DC polarization was reversed by IFNα, providing an additional rationale for the interferon therapy of chronically-infected patients. By acting on TLR4 pathway with LVP, HCV may thus exploit a natural protective mechanism of the liver and the intestine normally used to control inflammation and immunity to commensal microorganisms.

Preferential association of Hepatitis C virus with apolipoprotein B48-containing lipoproteins

Hepatitis C virus (HCV) in cell culture has a density comparable to that of other members of the family Flaviviridae, whereas in vivo infectious particles are found partially in low-density fractions, associated with triacylglycerol (TG)-rich lipoproteins (TRLs). In the blood of infected patients, HCV circulates as heterogeneous particles, among which are lipo-viroparticles (LVPs), globular particles rich in TG and containing viral capsid and RNA. The dual viral and lipoprotein nature of LVPs was addressed further with respect to apolipoprotein composition and post-prandial dynamic lipid changes. The TRLs exchangeable apoE, -CII and -CIII, but not the high-density lipoprotein apoA-II, were present on LVPs, as well as the viral envelope proteins. apoB100 and -B48, the two isoforms of the non-exchangeable apoB, were represented equally on LVPs, despite the fact that apoB48 was barely detectable in the plasma of these fasting patients. This indicates that a significant fraction of plasma HCV was associated with apoB48-containing LVPs. Furthermore, LVPs were enriched dramatically and rapidly in triglycerides after a fat meal. As apoB48 is synthesized exclusively by the intestine, these data highlight the preferential association of HCV with chylomicrons, the intestine-derived TRLs. These data raise the question of the contribution of the intestine to the viral load and suggest that the virus could take advantage of TRL assembly and secretion for its own production and of TRL fate to be delivered to the liver.

Signal Peptide Peptidase-catalyzed Cleavage of Hepatitis C Virus Core Protein Is Dispensable for Virus Budding but Destabilizes the Viral Capsid

The capsid of hepatitis C virus (HCV) particles is considered to be composed of the mature form (p21) of core protein. Maturation to p21 involves cleavage of the transmembrane domain of the precursor form (p23) of core protein by signal peptide peptidase (SPP), a cellular protease embedded in the endoplasmic reticulum membrane. Here we have addressed whether SPP-catalyzed maturation to p21 is a prerequisite for HCV particle morphogenesis in the endoplasmic reticulum. HCV structural proteins were expressed by using recombinant Semliki Forest virus replicon in mammalian cells or recombinant baculovirus in insect cells, because these systems have been shown to allow the visualization of HCV budding events and the isolation of HCV-like particles, respectively. Inhibition of SPP-catalyzed cleavage of core protein by either an SPP inhibitor or HCV core mutations not only did not prevent but instead tended to facilitate the observation of viral buds and the recovery of virus-like particles. Remarkably, although maturation to p21 was only partially inhibited by mutations in insect cells, p23 was the only form of core protein found in HCV-like particles. Finally, newly developed assays demonstrated that p23 capsids are more stable than p21 capsids. These results show that SPP-catalyzed cleavage of core protein is dispensable for HCV budding but decreases the stability of the viral capsid. We propose a model in which p23 is the form of HCV core protein committed to virus assembly, and cleavage by SPP occurs during and/or after virus budding to predispose the capsid to subsequent disassembly in a new cell.

Association between hepatitis C virus and very-low-density lipoprotein (VLDL)/LDL analyzed in iodixanol density gradients

Hepatitis C virus (HCV) RNA circulates in the blood of persistently infected patients in lipoviroparticles (LVPs), which are heterogeneous in density and associated with host lipoproteins and antibodies. The variability and lability of these virus-host complexes on fractionation has hindered our understanding of the structure of LVP and determination of the physicochemical properties of the HCV virion. In this study, HCV from an antibody-negative immunodeficient patient was analyzed using three fractionation techniques, NaBr gradients, isotonic iodixanol, and sucrose gradient centrifugation. Iodixanol gradients were shown to best preserve host lipoprotein-virus complexes, and all HCV RNA was found at densities below 1.13 g/ml, with the majority at low density, < or =1.08 g/ml. Immunoprecipitation with polyclonal antibodies against human ApoB and ApoE precipitated 91.8% and 95.0% of HCV with low density, respectively, suggesting that host lipoprotein is closely associated with HCV in a particle resembling VLDL. Immunoprecipitation with antibodies against glycoprotein E2 precipitated 25% of HCV with low density, providing evidence for the presence of E2 in LVPs. Treatment of serum with 0.5% deoxycholic acid in the absence of salt produced HCV with a density of 1.12 g/ml and a sedimentation coefficient of 215S. The diameters of these particles were calculated as 54 nm. Treatment of serum with 0.18% NP-40 produced HCV with a density of 1.18 g/ml, a sedimentation coefficient of 180S, and a diameter of 42 nm. Immunoprecipitation analysis showed that ApoB remained associated with HCV after treatment of serum with deoxycholic acid or NP-40, whereas ApoE was removed from HCV with these detergents.

Immunohistochemical assessment of hepatitis C virus antigen in cholestatic hepatitis after liver transplantation

BACKGROUND

Patients with common variable immunodeficiency may exhibit rapidly progressive hepatitis when infected with hepatitis C virus (HCV), leading to cirrhosis and liver failure. Liver transplantation in these patients may result in a cholestatic form of HCV reinfection with exceptionally high virus loads.

AIMS

To report an immunohistochemical investigation of the pretransplant and post-transplant liver of one such patient.

METHODS/RESULTS

On immunohistochemical staining of frozen sections with anti-HCV core monoclonal antibody or fluorescein labelled human polyclonal anti-HCV IgG, no HCV antigens were demonstrated in the native cirrhotic liver removed at transplant, despite a viral load of 10(6.4) genomes/g. The transplanted liver, collected six weeks post-transplant, exhibited cholestatic recurrent hepatitis, had an HCV virus load of 10(10) genomes/g of liver, and revealed HCV antigen in the cytoplasm of most hepatocytes, with a pronounced periportal distribution. No virus antigen was demonstrable in other cell types. The core antigen was also detected in paraffin wax embedded, formaldehyde fixed tissue of this liver after high temperature antigen retrieval, but not in the native cirrhotic liver or a selection of HCV positive livers collected pretransplant from immunocompetent patients. Attempts to delineate the distribution of E1, NS3, and NS4 antigens were unsuccessful because monoclonal antibodies to these antigens produced "false positive" staining of foci of hepatocytes in the post-transplant livers of HCV seronegative patients with cholestasis.

CONCLUSION

This case provided an opportunity to study the natural development of HCV during acute infection in the absence of an immune response, and may help to elucidate the pathogenesis of HCV recurrence in liver allografts.

Identification of novel HCV subgenome replicating persistently in chronic active hepatitis C patients

In an effort to clarify the life cycle of HCV, the HCV genome in liver biopsies taken from chronic active hepatitis C patients undergoing interferon treatment was investigated. Molecular cloning by long distance reverse-transcription polymerase chain reaction (RT-PCR) revealed that the HCV genome in two patients with high viral loads in the liver had in-frame deletions of approximately 2 kb between E1 and NS2, which encode the E1-NS2 fusion protein and six other HCV proteins: core, NS3, NS4A, NS4B, NS5A, and NS5B. Among the remaining 21 chronic active hepatitis C patients, these types of deletion were found in another two patients and in two hepatocellular carcinoma patients. Out-of-frame deletions in the structural region were isolated from the other five patients, but the dominant RT-PCR products were non-truncated genomes. Retrospective analysis of a series of serum samples taken from a patient carrying the subgenome with the in-frame deletion revealed that both the subgenome and the full genome persisted through the 2-year period of investigation, with the subgenome being predominant during this period. Sequence analysis of the isolated cDNA suggested that both the subgenome and the full genome evolved independently. Western blotting analysis of HCV proteins from the HCV subgenome indicated that they were processed in the same way as those from the full genome. HCV subgenomes thus appear to be involved in the HCV life cycle.

In vitro assembly into virus-like particles is an intrinsic quality of Pichia pastoris derived HCV core protein

Different variants of hepatitis C virus core protein (HCcAg) have proved to self-assemble in vitro into virus-like particles (VLPs). However, difficulties in obtaining purified mature HCcAg have limited these studies. In this study, a high degree of monomeric HCcAg purification was accomplished using chromatographic procedures under denaturing conditions. Size exclusion chromatography and sucrose density gradient centrifugation of renatured HCcAg (in the absence of structured RNA) under reducing conditions suggested that it assembled into empty capsids. The electron microscopy analysis of renatured HCcAg showed the presence of spherical VLPs with irregular shapes and an average diameter of 35nm. Data indicated that HCcAg monomers assembled in vitro into VLPs in the absence of structured RNA, suggesting that recombinant HCcAg used in this work contains all the information necessary for the assembly process. However, they also suggest that some cellular factors might be required for the proper in vitro assembly of capsids.

Nucleic acid binding properties and intermediates of HCV core protein multimerization in Pichia pastoris

Little is known about the in vivo assembly pathway or structure of the hepatitis C virus nucleocapsid. In this work the intermediates of HCcAg multimerization in Pichia pastoris cells and the nucleic acid binding properties of structured nucleocapsid-like particles (NLPs) were studied. Extensive cross-linking was observed for HCcAg after glutaraldehyde treatment. Data suggest that HCcAg exists in dimeric forms probably representing P21-P21, P21-P23, and P23-P23 dimers. In addition, the presence of HCcAg species that might represent trimers and multimers was observed. After sucrose equilibrium density gradient purification and nuclease digestion, NLPs were shown to contain both RNA and DNA molecules. Finally, the analysis by electron microscopy indicated that native NLPs were resistant to nuclease treatment. These results indicated that HCcAg assembles through dimers, trimers, and multimers' intermediates into capsids in P. pastoris cells. Assembly of NLPs in its natural environment might confer stability to these particles by adopting a compact structure.