Comparative studies of the core gene products of two different hepatitis C virus isolates: two alternative forms determined by a single amino acid substitution

N-terminal HCV core protein fragment decreases 20S proteasome activity in the presence of PA28γ

The Hepatitis C virus (HCV) core protein plays a crucial role in the development of chronic liver diseases such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Its involvement in these diseases is reportedly abolished by a knockout of the proteasome activator PA28γ gene in transgenic mice, suggesting an interaction between the core protein and the PA28γ-proteasome system. This study found a direct interaction between the N-terminal 1-71 fragment of HCV core protein (Core71) and PA28γ in vitro, and that this interaction was found to enhance PA28γ-20S proteasome complex formation. While 20S proteasome activity was increased by PA28γ, it was significantly reduced by Core71 attachment in a dose-dependent manner. These results suggest that the Core-PA28γ interaction has an important role in regulating 20S proteasome activity and furthers our understanding of the pathogenesis of HCV.

Chaperones in hepatitis C virus infection

The hepatitis C virus (HCV) infects approximately 3% of the world population or more than 185 million people worldwide. Each year, an estimated 350000-500000 deaths occur worldwide due to HCV-associated diseases including cirrhosis and hepatocellular carcinoma. HCV is the most common indication for liver transplantation in patients with cirrhosis worldwide. HCV is an enveloped RNA virus classified in the genus Hepacivirus in the Flaviviridae family. The HCV viral life cycle in a cell can be divided into six phases: (1) binding and internalization; (2) cytoplasmic release and uncoating; (3) viral polyprotein translation and processing; (4) RNA genome replication; (5) encapsidation (packaging) and assembly; and (6) virus morphogenesis (maturation) and secretion. Many host factors are involved in the HCV life cycle. Chaperones are an important group of host cytoprotective molecules that coordinate numerous cellular processes including protein folding, multimeric protein assembly, protein trafficking, and protein degradation. All phases of the viral life cycle require chaperone activity and the interaction of viral proteins with chaperones. This review will present our current knowledge and understanding of the role of chaperones in the HCV life cycle. Analysis of chaperones in HCV infection will provide further insights into viral/host interactions and potential therapeutic targets for both HCV and other viruses.

Positive ratio of specific antibodies to F protein in serum samples from chronic HCV-infected patients using an enzyme-linked immunosorbent assay: systematic review and meta-analysis

AIMS AND BACKGROUND

Although some studies have reported a positive ratio of specific antibodies to the alternative reading frame protein in an enzyme-linked immunosorbent assay test, our data from meta-analysis provide evidence supporting the presence of circulating anti-F protein antibodies.

METHODS

We collected studies focused on hepatitis C virus (HCV) and F protein. From an initial identification of 460 articles, we selected 16 studies that were randomized-controlled trials (RCTs).

RESULTS

The results of the Mantel-Haenszel test showed that a statistically significant number of studies reported an effective value in chronic HCV-infected individuals (P<0.00001). We concluded that compared with healthy individuals, the positive ratio of F protein detection was higher in chronic HCV-infected individuals; the odds ratio was 63.61 [95% confidence interval (CI)=28.69, 141.06]. The values for chronic HCV-infected individuals were significantly different from those for non-HCV-infected individuals; the odds ratio was 53.43 (95% CI=23.33, 122.35). The positive ratio of the core protein was higher than that of F protein (rate difference=-38%, 95% CI=-42, -35%).

CONCLUSION

We concluded that F protein elicits specific antibodies in most chronic HCV-infected individuals. Further, we confirmed the results of previous reports. The relationship between anti-F protein antibody and HCV coinfection still needs to be confirmed with further studies. Considering the high polymorphism rate of HCV, further studies are still needed for the selection of synthetic peptides from F protein that can coat the wells on microplates and serve as a commercial reagent.

An alternative -1/+2 open reading frame exists within viral N(pro)(1-19) region of bovine viral diarrhea virus SD-1

We previously reported the engineering of an N(pro)-disrupted bovine viral diarrhea virus (BVDV), BSD1-N(pro)/eGFP2A (Fan and Bird, 2008a). Here, we report that BSD1-N(pro)/eGFP2A survives a single nucleotide missing in its C-terminal eGFP region. By using our established reverse genetics system for BVDV, we confirm that the viral mutant is rescued through a -1/+2 ORF initiated in the N(pro)(1-19)/eGFP region of the mutant viral genome. We furthermore uncover that this event occurs in the N(pro)(1-19) region of BVDV strain SD-1. The rescued viral mutant showed dramatic reductions in levels of both viral RNA and viral protein in host cells. Although the mutant is similar to the native strain in viral kinetics, the peak yield of the mutant is decreased dramatically. These findings reveal the existence of an alternative -1/+2 ORF in the N(pro)(1-19) region during the replication of BVDV and open a new avenue to understand the life cycle and pathogenesis of pestiviruses.

Activity-based protein profiling of host-virus interactions

Virologists have benefited from large-scale profiling methods to discover new host–virus interactions and to learn about the mechanisms of pathogenesis. One such technique, referred to as activity-based protein profiling (ABPP), uses active site-directed probes to monitor the functional state of enzymes, taking into account post-translational interactions and modifications. ABPP gives insight into the catalytic activity of enzyme families that does not necessarily correlate with protein abundance. ABPP has been used to investigate several viruses and their interactions with their hosts. Differential enzymatic activity induced by viruses has been monitored using ABPP. In this review, we present recent advances and trends involving the use of ABPP methods in understanding host–virus interactions and in identifying novel targets for diagnostic and therapeutic applications.

Expression of core antigen of HCV genotype 3a and its evaluation as screening agent for HCV infection in Pakistan

Background

Pakistan is facing a threat from hepatitis C infection which is increasing at an alarming rate throughout the country. More specific and sensitive screening assays are needed to timely and correctly diagnose this infection.

Methods

After RNA extraction from specimen (HCV-3a), cDNA was synthesized that was used to amplify full length core gene of HCV 3a. After verification through PCR, DNA sequencing and BLAST, a properly oriented positive recombinant plasmid for core gene was digested with proper restriction enzymes to release the target gene which was then inserted downstream of GST encoding DNA in the same open reading frame at proper restriction sites in multiple cloning site of pGEX4t2 expression vector. Recombinant expression vector for each gene was transformed in E. coli BL21 (DE3) and induced with IPTG for recombinant fusion protein production that was then purified through affinity chromatography. Western blot and Enzyme Linked Immunosorbant Assay (ELISA) were used to detect immuno-reactivity of the recombinant protein.

Results

The HCV core antigen produced in prokaryotic expression system was reactive and used to develop a screening assay. After validating the positivity (100%) and negativity (100%) of in-house anti-HCV screening assay through a standardized panel of 200 HCV positive and 200 HCV negative sera, a group of 120 serum specimens of suspected HCV infection were subjected to comparative analysis of our method with commercially available assay. The comparison confirmed that our method is more specific than the commercially available assays for HCV strains circulating in this specific geographical region of the world and could thus be used for HCV screening in Pakistan.

Conclusion

In this study, we devised a screening assay after successful PCR amplification, isolation, sequencing, expression and purification of core antigen of HCV genotype 3a. Our developed screening assay is more sensitive, specific and reproducible than the commercially available screening assays in Pakistan.

Role of the hepatitis C virus core+1 open reading frame and core cis-acting RNA elements in viral RNA translation and replication

Four conserved RNA stem-loop structures designated SL47, SL87, SL248, and SL443 have been predicted in the hepatitis C virus (HCV) core encoding region. Moreover, alternative translation products have been detected from a reading frame overlapping the core gene (core+1/ARFP/F). To study the importance of the core+1 frame and core-RNA structures for HCV replication in cell culture and in vivo, a panel of core gene silent mutations predicted to abolish core+1 translation and affecting core-RNA stem-loops were introduced into infectious-HCV genomes of the isolate JFH1. A mutation disrupting translation of all known forms of core+1 and affecting SL248 did not alter virus production in Huh7 cells and in mice xenografted with human liver tissue. However, a combination of mutations affecting core+1 at multiple codons and at the same time, SL47, SL87, and SL248, delayed RNA replication kinetics and substantially reduced virus titers. The in vivo infectivity of this mutant was impaired, and in virus genomes recovered from inoculated mice, SL87 was restored by reversion and pseudoreversion. Mutations disrupting the integrity of this stem-loop, as well as that of SL47, were detrimental for virus viability, whereas mutations disrupting SL248 and SL443 had no effect. This phenotype was not due to impaired RNA stability but to reduced RNA translation. Thus, SL47 and SL87 are important RNA elements contributing to HCV genome translation and robust replication in cell culture and in vivo.

Differential reactivity of putative genotype 2 hepatitis C virus F protein between chronic and recovered infections

To date, all studies regarding hepatitis C virus (HCV) F protein have been based on expression in vitro/in vivo of recombinant protein or monoclonal antibodies derived from genotype 1a or 1b sequences, but not from other genotypes. The objective of this study was to prepare a putative genotype 2 recombinant F protein and evaluate its reactivity in plasma from individuals with chronic HCV infection or who had recovered from infection. One genotype 2 strain was selected for F protein (F-2) and core expression in bacterial culture. An ELISA was developed and applied to samples from patients with chronic infection or recovered infection of various genotypes. The anti-F-2 response in 117 samples showed a significantly higher reactivity in chronic than in recovered HCV-infected blood donors (P<0.001), but no difference was found among genotypes. However, the correlation between anti-F and anti-core was more significant in genotypes 1 and 2 than in genotype 3. Anti-F-2 titres were also significantly higher in chronic than in recovered individuals (P<0.0001). Antibody titres to recombinant genotype 2 core protein or to genotype 1 multiple proteins used in commercial anti-HCV assays paralleled the anti-F-2 end-point antibody titre. This study thus demonstrated the antigenicity of genotype 2 HCV F protein, although the exact location of the natural frameshift position remains unknown. The difference in anti-F-2 response between chronic and recovered infection, the cross-reactivity irrespective of genotype and the correlation of antibody response with structural and non-structural antigens suggest that the immune response to F protein is an integral part of the natural HCV infection.

Hepatitis C virus ARFP/F protein interacts with cellular MM-1 protein and enhances the gene trans-activation activity of c-Myc

The ARFP/F protein is synthesized from the +1 reading frame of the hepatitis C virus (HCV) core protein gene. The function of this protein remains unknown. To study the function of the HCV ARFP/F protein, we have conducted the yeast two-hybrid screening experiment to identify cellular proteins that may interact with the ARFP/F protein. MM-1, a c-Myc interacting protein, was found to interact with HCV ARFP/F protein in this experiment. The physical interaction between ARFP/F and MM-1 proteins was further confirmed by the GST pull-down assay, the co-immunoprecipitation assay and confocal microscopy. As MM-1 can inhibit the gene transactivation activity of c-Myc, we have conducted further analysis to examine the possible effect of the ARFP/F protein on c-Myc. Our results indicate that the HCV ARFP/F protein can enhance the gene trans-activation activity of c-Myc, apparently by antagonizing the inhibitory effect of MM-1. The ability of the ARFP/F protein to enhance the activity of c-Myc raises the possibility that ARFP/F protein might play a role in hepatocellular transformation in HCV patients.

Expression of alternate reading frame protein (F1) of hepatitis C virus in Escherichia coli and detection of antibodies for F1 in Indian patients

Apart from the core (21 kD), a novel hepatitis C virus (HCV) frame shift protein (F1) is synthesized from the initiation codon of the polyprotein sequence followed by ribosomal frame shift into the −2/+1 reading frame. To date, no information is available on F1 protein of Indian isolates, and hence detection of antibodies for F1 protein in Indian patients assumes great relevance. Specific primers have been designed to amplify sequence coding for 120aa of truncated F1 (tF1). The amplified tF1 has been cloned in bacterial expression vector, pET21b for expression in Escherichia coli. Partially purified expressed protein has been subjected to western blot analysis using patients’ sera. Three HCV positive sera employed in western analysis showed positive signals to tF1, while sera from uninfected individuals failed to give any signals. Further, results of western blots, carried out with patients sera titrated with purified core protein, confirmed the presence of antibodies specific to F1. The positive signal observed for F1 in western analysis with HCV infected sera suggests that F1 protein is synthesized in the natural course of HCV infection in Indian patients as well. Presence of antibodies against F1 protein of subtype 1c has been demonstrated, for the first time, in Indian patients.

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.

Characterization of humoral and cell-mediated immune responses directed against hepatitis C virus F protein in subjects co-infected with hepatitis C virus and HIV-1

BACKGROUND

Hepatitis C virus (HCV) F protein is encoded in an alternate reading frame overlapping the core protein region. Its precise sequence, biological function and mode of expression are currently unclear. This study was conducted to examine the prevalence and characteristics of host humoral and cell-mediated immune responses directed against F protein in patients co-infected with HCV and HIV-1.

METHODS

Mutations were introduced to allow the expression of HCV-1a F protein in the absence of core. This recombinant and a truncated form lacking the first 11 amino acid residues shared with core were expressed in Escherichia coli, and their amino acid sequences were verified by mass spectrometry. Vaccinia-F protein recombinants were used to test F protein-specific cytotoxic T lymphocyte (CTL) activity. The binding of F protein-derived peptides to HLA-A*0201 was studied to identify putative CTL epitopes.

RESULTS

Sera from 23 of 39 patients infected with various HCV genotypes recognized the truncated form, including 13 of 25 subjects co-infected with HIV-1, indicative of antigenic crossreactivity and consistent with the conservation of F protein coding sequences between HCV genotypes. Crossreactive F protein-specific CTL precursors were detected in nine of 11 HCV-infected subjects, including seven of nine patients co-infected with HCV and HIV-1. Finally, three novel putative HLA-A*0201-restricted CTL epitopes were identified.

CONCLUSION

These results indicate that patients co-infected with HCV and HIV-1 can mount immunoglobulin and CTL responses directed against HCV F protein that are fully comparable in scope and magnitude with those observed in individuals infected with HCV alone.

Transmission of human hepatitis C virus from patients in secondary cells for long term culture

Infection by human hepatitis C virus (HCV) is the principal cause of post-transfusion hepatitis and chronic liver diseases worldwide. A reliable in vitro culture system for the isolation and analysis of this virus is not currently available, and, as a consequence, HCV pathogenesis is poorly understood. We report here the first robust in vitro system for the isolation and propagation of HCV from infected donor blood. This system involves infecting freshly prepared macrophages with HCV and then transmission of macrophage-adapted virus into freshly immortalized B-cells from human fetal cord blood. Using this system, newly isolated HCV have been replicated in vitro in continuous cultures for over 130 weeks. These isolates were also transmitted by cell-free methods into different cell types, including B-cells, T-cells and neuronal precursor cells. These secondarily infected cells also produced in vitro transmissible infectious virus. Replication of HCV-RNA was validated by RT-PCR analysis and by in situ hybridization. Although nucleic acid sequencing of the HCV isolate reported here indicates that the isolate is probably of type 1a, other HCV types have also been isolated using this system. Western blot analysis shows the synthesis of major HCV structural proteins. We present here, for the first time, a method for productively growing HCV in vitro for prolonged periods of time. This method allows studies related to understanding the replication process, viral pathogenesis, and the development of anti-HCV drugs and vaccines.

Translation of the F protein of hepatitis C virus is initiated at a non-AUG codon in a +1 reading frame relative to the polyprotein

The hepatitis C virus (HCV) genome contains an internal ribosome entry site (IRES) followed by a large open reading frame coding for a polyprotein that is cleaved into 10 proteins. An additional HCV protein, the F protein, was recently suggested to result from a +1 frameshift by a minority of ribosomes that initiated translation at the HCV AUG initiator codon of the polyprotein. In the present study, we reassessed the mechanism accounting for the synthesis of the F protein by measuring the expression in cultured cells of a luciferase reporter gene with an insertion encompassing the IRES plus the beginning of the HCV-coding region preceding the luciferase-coding sequence. The insertion was such that luciferase expression was either in the +1 reading frame relative to the HCV AUG initiator codon, mimicking the expression of the F protein, or in-frame with this AUG, mimicking the expression of the polyprotein. Introduction of a stop codon at various positions in-frame with the AUG initiator codon and substitution of this AUG with UAC inhibited luciferase expression in the 0 reading frame but not in the +1 reading frame, ruling out that the synthesis of the F protein results from a +1 frameshift. Introduction of a stop codon at various positions in the +1 reading frame identified the codon overlapping codon 26 of the polyprotein in the +1 reading frame as the translation start site for the F protein. This codon 26(+1) is either GUG or GCG in the viral variants. Expression of the F protein strongly increased when codon 26(+1) was replaced with AUG, or when its context was mutated into an optimal Kozak context, but was severely decreased in the presence of low concentrations of edeine. These observations are consistent with a Met-tRNA_i-dependent initiation of translation at a non-AUG codon for the synthesis of the F protein.

Molecular determinants for subcellular localization of hepatitis C virus core protein

Hepatitis C virus (HCV) core protein is a putative nucleocapsid protein with a number of regulatory functions. In tissue culture cells, HCV core protein is mainly located at the endoplasmic reticulum as well as mitochondria and lipid droplets within the cytoplasm. However, it is also detected in the nucleus in some cells. To elucidate the mechanisms by which cellular trafficking of the protein is controlled, we performed subcellular fractionation experiments and used confocal microscopy to examine the distribution of heterologously expressed fusion proteins involving various deletions and point mutations of the HCV core combined with green fluorescent proteins. We demonstrated that a region spanning amino acids 112 to 152 can mediate association of the core protein not only with the ER but also with the mitochondrial outer membrane. This region contains an 18-amino-acid motif which is predicted to form an amphipathic alpha-helix structure. With regard to the nuclear targeting of the core protein, we identified a novel bipartite nuclear localization signal, which requires two out of three basic-residue clusters for efficient nuclear translocation, possibly by occupying binding sites on importin-alpha. Differences in the cellular trafficking of HCV core protein, achieved and maintained by multiple targeting functions as mentioned above, may in part regulate the diverse range of biological roles of the core protein.

Novel insights into hepatitis C virus replication and persistence

Hepatitis C virus (HCV) is a small enveloped RNA virus that belongs to the family Flaviviridae. A hallmark of HCV is its high propensity to establish a persistent infection that in many cases leads to chronic liver disease. Molecular studies of the virus became possible with the first successful cloning of its genome in 1989. Since then, the genomic organization has been delineated, and viral proteins have been studied in some detail. In 1999, an efficient cell culture system became available that recapitulates the intracellular part of the HCV life cycle, thereby allowing detailed molecular studies of various aspects of viral RNA replication and persistence. This chapter attempts to summarize the current state of knowledge in these most actively worked on fields of HCV research.

Morphological alteration and biological properties of hepatocytes not related to tumorigenesis following transfection with HCV core protein

The hepatitis C virus (HCV) core protein is supposed to play a critical role in HCV-mediated human liver disease with its capabilities to regulate the growth rate of hepatocytes and to partially contribute to the pathogenesis of hepatocellular carcinoma in association with cellular oncogenes. In this study, to analyse the possible pathological mechanism of the HCV core protein, human primary embryo hepatocytes transfected with HCV core were monitored by immunofluorescence, reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot. The morphological changes and biological properties of the transfected hepatocytes were also studied. The results showed that the HCV core gene integrated in the cellular genome and the protein expressed in the transfected hepatocyte, could be detected following serial passage at both the mRNA and protein level. The proliferation assays indicated that hepatocytes transfected with the HCV core gene alone did not exhibit any tumorigenic tendency. Meanwhile, the morphological alterations of these cells demonstrated obvious changes in size, and large vacuolar degeneration. In conclusion, the hepatocytes transfected with the HCV core gene revealed that the core protein expressed induced pathological changes of degeneration, probably related indirectly to tumorigenicity.

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Unusual multiple recoding events leading to alternative forms of hepatitis C virus core protein from genotype 1b

In addition to its involvement in the formation of the capsid shell of the virus particles, the core protein of hepatitis C virus (HCV) is believed to play an important role in the pathogenesis and/or establishment of persistent infection. We describe here alternative forms of genotype 1b HCV core protein identified after purification of various products of core protein segment 1-169 expressed in Escherichia coli and their analysis by proteolysis, mass spectrometry, and amino acid sequencing. These proteins all result from a +1 frameshift at codon 42 (a different position than that previously reported in genotype 1a) and, for some of them, from a rephasing in the normal open reading frame at the termination codon 144 in the +1 open reading frame. To test the relevance of these recoding events in a eukaryotic translational context, the nucleotide sequences surrounding the two shift sites were cloned in the three reading frames into expression vectors, allowing the production of a C-terminally fused green fluorescent protein, and expressed both in a reticulocyte lysate transcription/translation assay and in culture cells. Both recoding events were confirmed in these expression systems, strengthening the hypothesis that they might occur in HCV-infected cells. Moreover, sera from HCV-positive patients of genotype 1a or 1b were shown to react differently against synthetic peptides encoded in the +1 open reading frame. Together, these results indicate the occurrence of distinct recoding events in genotypes 1a and 1b, pointing out genotype-dependent specific features for F protein.

The roles of hepatitis C virus proteins in modulation of cellular functions: A novel action mechanism of the HCV core protein on gene regulation by nuclear hormone receptors

Hepatitis C virus (HCV) is one of the major causative agents inducing the development of hepatocellular carcinoma. The underlying mechanism of HCV pathogenesis, however, is largely un-known. Recent reports have implicated specific HCV proteins in persistent HCV infection, reduction of interferon sensitivity, and the modulation of cell proliferation, including alterations in apoptotic responses. However, the roles of these viral proteins remain controversial, because of conflicting results. Thus, it remains necessary to elucidate the precise molecular mechanisms through which the viral proteins influence cell growth and pathogenesis. In this review, after briefly describing what is known about the roles of the HCV proteins, in particular HCV core protein (core), in the modulation of cellular functions, we propose a novel molecular mechanism of the core in modulating gene expression via activation of nuclear hormone receptors.

Proteasome activator PA28gamma-dependent nuclear retention and degradation of hepatitis C virus core protein

Hepatitis C virus (HCV) core protein plays an important role in the formation of the viral nucleocapsid and a regulatory protein involved in hepatocarcinogenesis. In this study, we have identified proteasome activator PA28gamma (11S regulator gamma) as an HCV core binding protein by using yeast two-hybrid system. This interaction was demonstrated not only in cell culture but also in the livers of HCV core transgenic mice. These findings are extended to human HCV infection by the observation of this interaction in liver specimens from a patient with chronic HCV infection. Neither the interaction of HCV core protein with other PA28 subtypes nor that of PA28gamma with other Flavivirus core proteins was detected. Deletion of the PA28gamma-binding region from the HCV core protein or knockout of the PA28gamma gene led to the export of the HCV core protein from the nucleus to the cytoplasm. Overexpression of PA28gamma enhanced the proteolysis of the HCV core protein. Thus, the nuclear retention and stability of the HCV core protein is regulated via a PA28gamma-dependent pathway through which HCV pathogenesis may be exerted.

Characterization of the expression of the hepatitis C virus F protein

Hepatitis C virus (HCV) is an important human pathogen that affects 170 million people worldwide. The HCV genome is approximately 9.6 kb in length and encodes a polyprotein that is proteolytically cleaved to generate at least 10 mature viral protein products. Recently, a new protein, named F, has been described to be expressed through a ribosomal frameshift within the capsid-encoding sequence, a mechanism unique among members of the family Flavidiridae: Here, expression of the F protein was investigated in an in vitro transcription/translation assay. Its expression in mammalian cells was confirmed using specific recombinant vaccinia viruses; under these conditions, protein expression is dependent on the HCV IRES. The F protein was tagged with firefly luciferase or the Myc epitope to facilitate its identification. Ribosomal frameshifting was dependent on the presence of mutations in the capsid-encoding sequence. No frameshifting was detected in the absence of any mutation. Furthermore, analysis of the F protein in time-course experiments revealed that the protein is very unstable and that its production can be stabilized by the proteasome inhibitor MG132. Finally, indirect immunofluorescence studies have localized the F protein in the cytoplasm, with notable perinuclear detection.

The hepatitis C virus persistence: how to evade the immune system?

Hepatitis C virus (HCV) is an emerging virus of medical importance. A majority of HCV infections become chronic and lead to chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. HCV usually induces robust immune responses, but it frequently escapes the immune defense to establish persistent infection. The fact that HCV exists as an evolving quasispecies plays an important role in the selection of escape mutants. Furthermore, several viral proteins interfere with cellular functions, in particular, those involved in the immune response of the host. Several HCV proteins also modulate cell signalling through interaction with different effectors involved in cell proliferation and apoptosis, or in the interferon-signalling pathway. In addition, HCV infects immune cells such as B and T cells, and thus affects their normal functions. These various strategies used by HCV to counter the immune response of the host are reviewed here. A better understanding of these mechanisms would help design new therapeutic targets.

Interaction between hepatitis C virus core protein and translin protein- a possible molecular mechanism for hepatocellular carcinoma and lymphoma caused by hepatitis C virus

AIM: To investigate the interaction between hepatitis C virus core protein and translin protein and its role in the pathogenensis of hepatocellular carcinoma and lymphoma.

METHODS: With the components of the yeast two hybrid system 3,“ bait” plasmids of HCV core the gene was constructed. After proving that hepatitis C virus core protein could be firmly expressed in AH109 yeast strains, yeast two- hybrid screening was performed by mating AH109 with Y187 that transformed with liver cDNA library plasmids - pACT2 and then plated on quadrople dropout (QDO) medium and then assayed for α-gal activity. Sequencing analysis of the genes of library plasmids in yeast colonies that could grow on QDO with α-gal activity was performed. The interaction between HCV core protein and the protein we obtained from positive colony was further confirmed by repeating yeast two - hybrid analysis and coimmunoprecipitation in vitro.

RESULTS: A gene from a positive colony was the gene of translin, a recombination hotspot binding protein. The interaction between HCV core protein and translin protein could be proved not only in yeast, but also in vitro.

CONCLUSION: The core protein of HCV can interact with translin protein. This can partly explain the molecular mechanism for hepatocellular carcinoma and lymphoma caused by HCV.

Suppression of hepatitis B virus enhancer 1 and 2 by hepatitis C virus core protein

BACKGROUND/AIMS

Epidemiological studies have shown that coinfection or superinfection with hepatitis B virus (HBV) and C virus (HCV) frequently leads to the suppression of hepatitis B virus replication. The mechanism of this phenomenon is still unclear. Shih et al. [J Virol 1993;67:5823] reported a direct suppression of HBV replication by the core protein of HCV. The target structure of HCV core protein in this system remained unclear.

METHODS

As HCV core protein has been shown to influence expression from transcriptional elements, we studied whether HCV core protein altered the activity of the two HBV enhancers 1 and 2. Luciferase vectors for HBV enhancers 1 or 2 were cotransfected with expression constructs for HCV core protein in murine and human hepatocyte lines.

RESULTS

Full-length HCV core protein suppressed the HBV enhancer 1 up to 11-fold, the enhancer 2 3-4-fold. Suppression of HBV enhancer 1 by HCV core from genotype 1b was stronger than by HCV core of genotypes 3a or 1a. Carboxyterminally truncated core proteins had lower or no suppression activity.

CONCLUSIONS

These data suggest that HCV core protein may directly repress transcription of the HBV RNAs. This trans-repression may contribute to suppression of HBV replication in patients coinfected with both viruses.

Phosphorylation of hepatitis C virus core protein by protein kinase A and protein kinase C

Hepatitis C virus (HCV) core protein can form capsid-like particles and is believed to be the viral capsid protein. Besides its structural functions, this protein is also known to possess multiple regulatory functions. In this article, we have studied the possible phosphorylation of HCV core protein in two different human liver-derived cell lines Huh7 and HepG2. Our results indicated that the HCV core protein could be phosphorylated, albeit inefficiently, independent of its downstream E1 protein in these two cell lines. Two of the basal phosphorylation sites were identified to be serine-53 and serine-116. The phosphorylation of the core protein could be enhanced by the PKC activator phorbol 12-myristic 13-acetate (PMA), and the PKA activator forskolin, and these enhancements could be abolished by the respective inhibitors of PKC and PKA, indicating that the core protein is a substrate of these two kinases. While both serine-53 and serine-116 served as the PKC phosphorylation sites, serine-116 appeared to be the major PKA phosphorylation site. Further analyses using serine-to-alanine mutation to mimic dephosphorylation and serine-to-aspartic acid mutation to mimic phosphorylation revealed that the conversion of serine-116 to aspartic acid led to an enhanced nuclear localization of the core protein. This observation indicates that one function of phosphorylation may be to regulate the nuclear localization of the core protein.

Alternate translation occurs within the core coding region of the hepatitis C viral genome

The majority of hepatitis C virus (HCV) isolates contain an open reading frame (ORF) overlapping with the core coding sequences in the +1 frame, which was assumed to be untranslated. We present evidence supporting the expression of this ORF (designated core+1 ORF) via novel translation mechanisms. First, fusion of the luciferase gene with the HCV-1 core+1 ORF followed by in vitro translation resulted in the synthesis of a chimeric protein (core+1-luciferase) that exhibited approximately 54% luciferase activity relative to the positive control (core-luciferase). Second, antisera raised against two different synthetic core+1 peptides recognized the previously identified p16 (but not p21) core protein band expressed from HCV-1, indicating the presence of epitopes from the core+1 ORF within the p16 protein. Third, HCV-positive sera specifically recognized lysates of Escherichia coli cells expressing recombinant core+1 protein, suggesting the presence of anti-core+1 antibodies in HCV-infected patients. Finally, luciferase tagging experiments designed to assess for -1 frameshifting combined with site-directed mutagenesis experiments supported the presence of +1/-1 ribosomal frameshift translation mechanisms within the core coding region. In conclusion, our data provide evidence for novel translation mechanisms within the core coding region and demonstrate the expression of the core+1 ORF, at least for some HCV isolates.

Hepatitis C virus core protein: intriguing properties and functional relevance

Hepatitis C virus (HCV) often causes a prolonged and persistent infection, and an association between hepatocellular carcinoma (HCC) and HCV infection has been noted. The pathogenesis of liver damage is at least in part related to virus-mediated factors. Understanding the molecular basis of pathogenesis is a major challenge in gaining insight into HCV-associated disease progression. Recent experimental evidence using HCV cloned genomic regions suggests that the core protein has numerous functional activities. These include its likely role in encapsidation of viral RNA, a regulatory effect on cellular and unrelated viral promoters, interactions with a number of cellular proteins, an modulatory role in programmed cell death or apoptosis under certain conditions, involvement in cell growth promotion and immortalization, induction of HCC in transgenic mice, and a possible immunoregulatory role. These intriguing properties suggest that the core protein, in concert with cellular factors, may contribute to pathogenesis during persistent HCV infection.

Synthesis of a novel hepatitis C virus protein by ribosomal frameshift

Hepatitis C virus (HCV) is an important human pathogen that affects approximately 100 million people worldwide. Its RNA genome codes for a polyprotein, which is cleaved by viral and cellular proteases to produce at least 10 mature viral protein products. We report here the discovery of a novel HCV protein synthesized by ribosomal frameshift. This protein, which we named the F protein, is synthesized from the initiation codon of the polyprotein sequence followed by ribosomal frameshift into the -2/+1 reading frame. This ribosomal frameshift requires only codons 8-14 of the core protein-coding sequence, and the shift junction is located at or near codon 11. An F protein analog synthesized in vitro reacted with the sera of HCV patients but not with the sera of hepatitis B patients, indicating the expression of the F protein during natural HCV infection. This unexpected finding may open new avenues for the development of anti-HCV drugs.

Genome of human hepatitis C virus (HCV): gene organization, sequence diversity, and variation

Hepatitis C virus (HCV) is the major etiologic agent of non-A, non-B hepatitis. HCV infection frequently causes chronic hepatitis, which progresses to liver cirrhosis and hepatocellular carcinoma. Since the discovery of HCV in 1989, a large number of genetic analyses of HCV have been reported, and the viral genome structure has been elucidated. An enveloped virus, HCV belongs to the family Flaviviridae, whose genome consists of a positive-stranded RNA molecule of about 9.6 kilobases and encodes a large polyprotein precursor (about 3000 amino acids). This precursor protein is cleaved by the host and viral proteinase to generate at least 10 proteins: the core, envelope 1 (E1), E2, p7, nonstructural (NS) 2, NS3, NS4A, NS4B, NS5A, and NS5B. These HCV proteins not only function in viral replication but also affect a variety of cellular functions. HCV has been found to have remarkable genetic heterogeneity. To date, more than 30 HCV genotypes have been identified worldwide. Furthermore, HCV may show quasispecies distribution in an infected individual. These findings may have important implications in diagnosis, pathogenesis, treatment, and vaccine development. The hypervariable region 1 found within the envelope E2 protein was shown to be a major site for the genetic evolution of HCV after the onset of hepatitis, and might be involved in escape from the host immunesurveillance system.

Hepatitis C virus core protein enhances FADD-mediated apoptosis and suppresses TRADD signaling of tumor necrosis factor receptor

Hepatitis C virus (HCV) core protein has been shown to interact with the death domain (DD) of tumor necrosis factor receptor-1 (TNFR1). In this study, we further examined the interaction of the core protein with the signaling molecules of TNFR1, including FADD, TRADD, and TRAF2, in a human embryonic kidney cell line, HEK-293, that overexpresses the HCV core protein. This core protein-expressing cell line exhibited enhanced sensitivity to TNF-induced apoptosis. By in vitro binding and in vivo coimmunoprecipitation assays, we showed that the HCV core protein interacted with the DD of FADD and enhanced apoptosis induced by FADD overexpression. This enhancement could be blocked by a dominant-negative mutant of FADD. In contrast, the core protein did not directly interact with the DD of TRADD, but could disrupt the binding of TRADD to TNFR1. TRAF2 recruitment to the TNFR1 signaling complex was also disrupted by the core protein. Correspondingly, TRAF2-dependent activation of the protein kinase JNK was suppressed in the core protein-expressing cells. However, NF kappa B activation by TNF was not significantly altered by the HCV core protein, suggesting the existence of TRAF2-independent pathways for NF kappa B activation. These results combined indicate that the HCV core protein sensitizes cells to TNF-induced apoptosis primarily by facilitating FADD recruitment to TNFR1. The inhibition of JNK activation by the HCV core protein may also contribute to the increased propensity of cells for apoptosis. These results, in comparison with other published studies, suggest that the effects of the HCV core protein and their underlying mechanisms vary significantly among cells of different origins.

Ubiquitin-mediated degradation of hepatitis C virus core protein is regulated by processing at its carboxyl terminus

Hepatitis C virus core protein, in addition to being a component of the viral capsid, has a number of regulatory functions. Here we showed two bodies of evidence indicating that a fraction of the core protein species is a substrate of the ubiquitin (Ub)-proteasome pathway of targeted proteolysis. First, the core protein processing the C-terminal hydrophobic region is metabolically unstable, and incubation with a proteasome inhibitor led to a significant accumulation of the protein. Second, an in vivo ubiquitylation assay indicates conjugation of multi-Ub chain to the unstable core protein. In contrast, a stable form of core protein, p21, is also able to be ubiquitylated, but it links to a single or only a few Ub moiety. Therefore, processing event(s) at the C-terminal hydrophobic domain of HCV core protein may affect the ubiquitylation pathway, particularly the efficiency of the multi-Ub chain assembly, resulting in stable, matured core proteins.

Sequence motifs required for lipid droplet association and protein stability are unique to the hepatitis C virus core protein

From analysis of the primary sequence of the hepatitis C virus (HCV) core protein, we have identified three separable regions based on hydrophobicity and clustering of basic amino acids within the protein. Comparison with capsid proteins of related pesti- and flaviviruses suggested that HCV core has a unique central domain (domain 2). Previous findings have revealed that core protein can associate with lipid droplets which are intracellular storage sites for triacylglycerols and cholesterol esters. Confocal analysis of variant forms lacking regions of core indicated that most residues within the unique region are necessary for association of the protein with lipid droplets. A segment within domain 2 (from residues 125 to 144) also was required for stability of the protein and a polypeptide lacking these sequences was degraded apparently by the proteasome. In cells depleted of lipid droplets, core protein remained located in the cytoplasm. Moreover, cleavage of the protein at the maturation site and stability were not affected by inability to bind to lipid droplets.

Amino acid substitutions in codons 9-11 of hepatitis C virus core protein lead to the synthesis of a short core protein product

BACKGROUND

Previous in vitro experiments have indicated that if the ninth codon of the hepatitis C virus (HCV) core gene is mutated from arginine to lysine, a short 16-kDa (P16) instead of a 21-kDa (P21) core protein will be produced. In this study, we aimed to investigate whether similar mutations existed in patients with chronic HCV infection and whether such mutations led to the expression of P16.

METHODS

The core gene was isolated from patients' sera by reverse transcription-polymerase chain reaction and sequenced.

RESULTS

Three of 10 patients with hepatocellular carcinoma were found to have mutant viruses with missense mutations at codons 9-11: arginine-to-glycine mutation at codon 9 (case 1); lysine-to-glutamine mutation at codon 10 (case 5); and lysine-to-asparagine/threonine-to-alanine double mutations at codons 10 and 11 (case 8). Site-directed mutagenesis and in vitro translation experiments revealed that P16 was expressed by all three mutants. Using gel-purified P21 and P16 proteins obtained from transformed Escherichia coli, the serum titres of anti-P21 and anti-P16 were assayed. Unequal titres of anti-P16 and anti-P21 were found in only cases 1, 5 and 8. A rabbit antibody directed against P16 but not P21 was thus generated for immunohistochemical analysis. P16 was detected in the nuclei of hepatocytes in the peri-hepatoma tissue of a single case (case 1).

CONCLUSIONS

These data indicate that missense mutations at codons 9-11 can occur during chronic HCV infection, which results in the expression of P16 core protein.

Properties of the hepatitis C virus core protein: a structural protein that modulates cellular processes

The core protein of hepatitis C virus (HCV) is believed to form the capsid shell of virus particles. Maturation of the protein is achieved through cleavage by host cell proteases to give a product of 21 000 MW, which is found in tissue culture systems and sera from infected individuals. However, efficient propagation of the virus is not possible at present in tissue culture. Hence, studies have focused on the properties of the core protein and its possible role in pathologies associated with HCV infection. This review describes key features of the polypeptide and the status of current knowledge on its ability to influence several cellular processes.

The molecular biology of hepatitis C virus. Genotypes and quasispecies

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. HCV is a positive-strand genotype RNA virus with extensive genetic heterogeneity; HCV isolates define 6 major genotypes, and HCV circulates within an infected individual as a number of closely related but distinct species, termed a quasispecies. This article reviews characteristic aspects of HCV molecular biology and their implications for treatment and vaccine development.

Processing and functions of Hepatitis C virus proteins

Hepatitis C virus (HCV) has a positive-stranded RNA genome of about 9.5 kb and a large open reading frame encoding a precursor polyprotein of ca. 3,000 amino acids (aa). This polyprotein is cleaved by host cellular signalase(s) and viral proteases into 10 viral proteins in the order of NH(2)-Core-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS 5B-COOH. Core and E1/E2 are considered to be a capsid protein and envelope glycoproteins, respectively. NS2-NS5B are putative nonstructural proteins involved in the replication of HCV. NS2/3 is a metalloprotease which cleaves in cis at the NS2/3 junction. NS3 possesses serine protease and RNA helicase activities and is responsible for the cleavage of the remaining nonstructural proteins. NS4A is suggested to be a cofactor for NS3 protease. Although the function of p7, NS4B and NS5A are still unknown, an association of a mutation in NS5A with a susceptibility to interferon (IFN) has been reported. NS5B possesses an RNA-dependent RNA polymerase activity. Most of the current findings in HCV proteins depend on expression studies of HCV cDNA clones because of the lack of an efficient replication system in cell cultures. Therefore, a final assignment of cleavages and functions of HCV proteins has to await the propagation of HCV in cell cultures.

Prevalence of TT virus DNA in eastern Taiwan aborigines

We studied the prevalence of TT virus (TTV) DNA in the general population of the eastern Taiwan aborigine villages, about 11% (34 of 317). There is no association between the presence of HBsAg and TTV DNA or between the presence of HCV RNA and TTV DNA. Therefore, the infection of HBV or HCV and the presence of TTV DNA appear to be independent from each other. The association between the presence of TTV DNA and the elevated alanine aminotransferase (and/or aspartate aminotransferase) activity was also investigated. The presence of TTV DNA was not found to be correlated with abnormal liver function (P = 0.574) when age, gender, and the presence of HBsAg, HCV RNA, and HGV RNA were all considered in the assay. The sequence homology of TTV DNA fragments between different isolates from Taiwan and N22 (the clone obtained from the original prototype strain) from Japan ranged from 84 to 97%. The recombinant protein encoded by the TTV DNA fragment corresponding to the open reading frame of N22 was expressed in E. coli successfully. However, no serum response against the recombinant protein was detected.

Hepatitis C virus core protein binds to apolipoprotein AII and its secretion is modulated by fibrates

Several lines of evidence suggest that hepatitis C virus (HCV) core protein may modulate cellular transduction signals and alter lipid metabolism. We have investigated the binding of HCV core protein to cellular proteins by combining 2 yeast hybrid, confocal, and surface plasmon resonance assays. Our results show the direct binding of the viral protein to apolipoprotein AII (apoAII) and map the interaction domain to the C-terminal of HCV core protein. To investigate the biological relevance of the interaction between HCV core and lipid metabolism, we took advantage of the well-established increase in apoAII expression caused by fibrates in HepG2 cells. After fenofibric acid treatment, we show a parallel increase in apoAII and core protein secretion, this effect being abolished by brefeldin A. Our study identifies apoAII as one of the cellular targets for HCV core protein. We also show that the intervention of fenofibric acid in cellular lipid metabolism directly affects the expression pattern of HCV core protein.

Hepatitis C virus variants circumventing cytotoxic T lymphocyte activity as a mechanism of chronicity

BACKGROUND & AIMS

High rate of chronicity after acute hepatitis C virus (HCV) infection cannot be explained in the presence of a multispecific cytotoxic T lymphocyte (CTL) response. The aim of this study was to investigate the effect of virus variants on CTL activity in patients in whom chronicity developed.

METHODS

CTL clones specific to a decapeptide epitope derived from hypervariable region 1 were generated from 5 HLA-A2-positive patients with acute hepatitis C by in vitro stimulation with synthetic peptides. The sequential change of this CTL epitope and its influence on the CTL recognition were examined.

RESULTS

Virus variants did not appear in 3 patients with recovery, whereas variants with altered peptide ligands capable of antagonizing CTL activity emerged rapidly in the remaining 2 patients in whom chronicity developed. Importantly, these HLA-A2-restricted, hypervariable region 1-specific CTL clones shared the use of T-cell receptor (TCR) genes AV6 and BV17.

CONCLUSIONS

These data suggest that there is only a narrow T-cell repertoire responding to a single viral peptide/HLA ligand. The emergence of HCV variants with altered peptide ligands as TCR antagonists accompanied by a limited TCR repertoire may provide a mechanism for HCV chronicity.

Hepatitis C virus core protein interacts with heterogeneous nuclear ribonucleoprotein K

Hepatitis C virus (HCV) core protein, a component of viral nucleocapsid, has been shown to modulate cellular and viral promoter activities. To identify potential cellular targets for HCV core protein, a human liver cDNA library was screened for core-interacting proteins using the yeast two-hybrid system. Among the proteins identified was heterogeneous nuclear ribonucleoprotein K (hnRNP K), which has been demonstrated to be a transcriptional regulator. The interaction of HCV core protein with hnRNP K was confirmed by glutathione S-transferase fusion protein binding assay, protein-protein blotting assay, and coimmunoprecipitation in vitro and in vivo. Additionally, these two proteins were shown to be partially colocalized in the nucleus. The hnRNP K-binding site in HCV core protein was mapped to the region from amino acid residues 25-91, a hydrophilic area near the N terminus. The HCV core protein-binding domain was located within amino acid residues 250 to 392, which contain the three proline-rich domains, of hnRNP K. Furthermore, HCV core protein relieved the suppression effect of hnRNP K on the activity of the human thymidine kinase gene promoter. The specific binding of HCV core protein to hnRNP K suggests that multiple functions of hnRNP K may be disrupted by the core protein during HCV infection and thus explains, in part, the pathogenesis of HCV.

Hepatitis C virus core protein binds to the cytoplasmic domain of tumor necrosis factor (TNF) receptor 1 and enhances TNF-induced apoptosis

The hepatitis C virus (HCV) core protein is known to be a multifunctional protein, besides being a component of viral nucleocapsids. Previously, we have shown that the core protein binds to the cytoplasmic domain of lymphotoxin beta receptor, which is a member of tumor necrosis factor receptor (TNFR) family. In this study, we demonstrated that the core protein also binds to the cytoplasmic domain of TNFR 1. The interaction was demonstrated both by glutathione S-transferase fusion protein pull-down assay in vitro and membrane flotation method in vivo. Both the in vivo and in vitro binding required amino acid residues 345 to 407 of TNFR 1, which corresponds to the "death domain" of this receptor. We have further shown that stable expression of the core protein in a mouse cell line (BC10ME) or human cell lines (HepG2 and HeLa cells) sensitized them to TNF-induced apoptosis, as determined by the TNF cytotoxicity or annexin V apoptosis assay. The presence of the core protein did not alter the level of TNFR 1 mRNA in the cells or expression of TNFR 1 on the cell surface, suggesting that the sensitization of cells to TNF by the viral core protein was not due to up-regulation of TNFR 1. Furthermore, we observed that the core protein blocked the TNF-induced activation of RelA/NF-kappaB in murine BC10ME cells, thus at least partially accounting for the increased sensitivity of BC10ME cells to TNF. However, NF-kappaB activation was not blocked in core protein-expressing HeLa or HepG2 cells, implying another mechanism of TNF sensitization by core protein. These results together suggest that the core protein can promote cell death during HCV infection via TNF signaling pathways possibly as a result of its interaction with the cytoplasmic tail of TNFR 1. Therefore, TNF may play a role in HCV pathogenesis.

Hepatitis C virus core from two different genotypes has an oncogenic potential but is not sufficient for transforming primary rat embryo fibroblasts in cooperation with the H-ras oncogene

Persistent infection with hepatitis C virus (HCV) is associated with the development of liver cirrhosis and hepatocellular carcinoma. To examine the oncogenic potential of the HCV core gene product, primary rat embryo fibroblasts (REFs) were transfected with the core gene in the presence or absence of the H-ras oncogene. In contrast to a previous report (R. B. Ray, L. M. Lagging, K. Meyer, and R. Ray, J. Virol. 70:4438-4443, 1996), HCV core proteins from two different genotypes (type 1a and type 1b) were not found to transform REFs to tumorigenic phenotype in cooperation with the H-ras oncogene, although the core protein was successfully expressed 20 days after transfection. In addition, REFs transfected with E1A- but not core-expressing plasmid showed the phenotype of immortalized cells when selected with G418. The biological activity was confirmed by observing the transcription activation from two viral promoters, Rous sarcoma virus long terminal repeat and simian virus 40 promoter, which are known to be activated by the core protein from HCV-1 isolate. In contrast to the result with primary cells, the Rat-1 cell line, stably expressing HCV core protein, exhibited focus formation, anchorage-independent growth, and tumor formation in nude mice. HCV core protein was able to induce the transformation of Rat-1 cells with various efficiencies depending on the expression level of the core protein. These results indicate that HCV core protein has an oncogenic potential to transform the Rat-1 cell line but is not sufficient to either immortalize primary REFs by itself or transform primary cells in conjunction with the H-ras oncogene.

[Biology of hepatitis C viruses: clinical implications]

Infection by hepatitis C virus is characterized by a high rate of chronicity and low viremia. The virus has only been recently identified; it is a positively stranded RNA virus which shows homology in its genetic organisation with the pestiviruses and flaviviruses. There is not yet an efficient culture system available. Evidence indicates that the genetic variability of the HCV genome might have important clinical implications.

Virology of hepatitis C virus

Advances in molecular biology techniques have allowed the cloning of HCV and the characterization of this virus. This article provides a short summary of our current knowledge on the genomic organization of HCV, the implications of its genetic heterogeneous nature, and the probable replication strategy of this virus.

Hepatitis C virus core protein shows a cytoplasmic localization and associates to cellular lipid storage droplets

There is now abundant evidence to substantiate an important role of hepatitis C virus (HCV) core protein in cellular gene expression as well as in the viral cycle. Thus the subcellular localization of this protein has important implications. However, several studies have shown controversial results: the HCV core has been, indeed, described as cytoplasmic or nuclear depending on the size of the protein or on the genotype analyzed. We have studied the localization of the HCV core protein in two different cell lines, one nonhepatic (CHO) and the other hepatic (HepG2). Double immunofluorescence staining using a nuclear membrane marker and confocal analysis showed the core protein pattern to be cytoplasmic and globular. This pattern is not cell cycle-regulated. Electron microscopy analysis revealed the nature of the globular staining observed in immunofluorescence. The HCV core protein accumulated at the surface of lipid droplets that were also the unique morphological feature of nonhepatic core transfected cells. The lipid droplets were isolated by sequential ultracentrifugation on the basis of their density; biochemical analysis revealed a prevalence of triglycerides. In addition the core protein colocalized with apolipoprotein AII at the surface of the lipid droplets as revealed by confocal microscopy. Moreover analysis of liver biopsies from chronically HCV-infected chimpanzees revealed that HCV core is cytoplasmic and localized on the endoplasmic reticulum and on lipid droplets. These results clearly define the subcellular localization of the HCV core protein and suggest a relationship between the expression of the HCV core protein and cellular lipid metabolism.

Hepatitis C virus core protein interacts with the cytoplasmic tail of lymphotoxin-beta receptor

Hepatitis C virus (HCV) core protein is a multifunctional protein. We examined whether it can interact with cellular proteins, thus contributing to viral pathogenesis. Using the HCV core protein as a bait to screen a human liver cDNA library in a yeast two-hybrid screening system, we have isolated several positive clones encoding cellular proteins that interact with the HCV core protein. Interestingly, more than half of these clones encode the cytoplasmic domain of lymphotoxin-beta receptor (LT betaR), which is a member of the tumor necrosis factor receptor family. Their binding was confirmed by in vitro glutathione S-transferase fusion protein binding assay and protein-protein blotting assay to be direct and specific. The binding sites were mapped within a 58-amino-acid region of the cytoplasmic tail of LT betaR. The binding site in the HCV core protein was localized within amino acid residues 36 to 91 from the N terminus, corresponding to the hydrophilic region of the protein. In mammalian cells, the core protein was found to be associated with the membrane-bound LT betaR. Since the LT betaR is involved in germinal center formation and developmental regulation of peripheral lymphoid organs, lymph node development, and apoptotic signaling, the binding of HCV core protein to LT betaR suggests the possibility that this viral protein has an immunomodulating function and may explain the mechanism of viral persistence and pathogenesis of HCV.

Induction of cytotoxic T-cell response against hepatitis C virus structural antigens using a defective recombinant adenovirus

A replication-defective recombinant adenovirus (RAd), RAdCMV-CE1, containing core and E1 genes of hepatitis C virus (HCV) was constructed. RAdCMV-CE1 was able to express core and E1 proteins both in mice and human cells. Immunization of BALB/c mice with RAdCMV-CE1 induced a specific cytotoxic T-cell response against the two HCV proteins. This response was characterized using a panel of 60 synthetic 14- or 15-mer overlapping peptides (10 amino-acid overlap) spanning the entire sequence of these proteins. Five main epitopes were found in the core protein, four of which had been previously described either in mice or humans. One single novel epitope was found in E1. Fine mapping of this E1 determinant, showed that octamer GHRMAWDM is the minimal epitope recognized by cytotoxic T lymphocytes (CTL). The cytotoxic T-cell response was H-2d restricted, lasted for at least 100 days, and was mediated by T cells with the classic CD4-CD8+ phenotype. This work demonstrates that replication-defective recombinant adenoviruses can efficiently express HCV proteins and are able to induce an in vivo cytotoxic T-cell response against a diversity of epitopes from HCV antigens. These vectors should be taken into consideration in the design of vaccines and also as a means to stimulate specific T-cell responses in chronic HCV carriers.