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

Increase in the concentration of carbon 18 monounsaturated fatty acids in the liver with hepatitis C: analysis in transgenic mice and humans

Steatosis is one of the histologic characteristics of chronic hepatitis C and is well reproduced in a transgenic mouse model for hepatocellular carcinoma (HCC) in which the core protein of hepatitis C virus (HCV) plays a pivotal role in inducing steatosis and HCC. In the present study, the lipid composition in the liver of the HCV core gene transgenic mice as well as in those of chronic hepatitis C patients was determined. The concentration of carbon 18 monounsaturated (C18:1) fatty acids, such as oleic and vaccenic acids, which are known to increase membrane fluidity leading to higher cell division rates, significantly increased in the livers of transgenic mice compared to nontransgenic control mice. The concentration of C18:1 fatty acids also significantly increased in the livers of chronic hepatitis C patients compared to subjects without HCV infection. These results suggest that HCV may affect a specific pathway in the lipid metabolism and cause steatosis in the liver.

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.

Hepatic steatosis in chronic hepatitis C virus infection: prevalence and clinical correlation

BACKGROUND AND AIMS

Hepatic steatosis is a histological characteristic in patients with chronic hepatitis C virus (HCV) infection. The aim of this study was to evaluate the prevalence of hepatic steatosis in Chinese patients with chronic hepatitis C, and to look for possible correlation with various histopathological changes and to look for possible correlation with various clinical and pathologic variables.

METHODS

One hundred and six patients were enrolled, and patients with alcoholism or diabetes mellitus were excluded. Clinical, biochemical and virologic data, including HCV genotype and serum HCV-RNA titer and histological findings, were compared between patients with and without hepatic steatosis.

RESULTS

Fifty-five (52%) of the 106 patients with chronic hepatitis C had hepatic steatosis. Patients with hepatic steatosis had significantly higher mean serum levels of triglyceride and gamma-glutamyl transpeptidase, higher body mass index, and a higher incidence of obesity compared with patients without hepatic steatosis. No significant differences in serum HCV-RNA titer and HCV genotype or the response to interferon therapy were noted between the two groups. Histological analysis showed patients with hepatic steatosis had a significantly higher mean fibrotic score than patients without hepatic steatosis (1.9 +/- 1.2 vs 1.3 +/- 1.0; P = 0.016). There were no significant differences in the severity of necroinflammation, the presence of lymphoid aggregation/follicle or bile duct damage between the two groups. Multivariate logistic regression analysis showed that independent predictors associated with hepatic steatosis were obesity or a histology fibrotic score of > or = 2.

CONCLUSION

It was found that 52% of Chinese patients with chronic hepatitis C had hepatic steatosis. Patients with hepatic steatosis were more frequently obese and had more severe hepatic fibrosis.

Characterization of cell lines carrying self-replicating hepatitis C virus RNAs

Subgenomic selectable RNAs of the hepatitis C virus (HCV) have recently been shown to self-replicate to high levels in the human hepatoma cell line Huh-7 (V. Lohmann, F. Körner, J. O. Koch, U. Herian, L. Theilmann, and R. Bartenschlager, Science 285:110-113, 1999). Taking advantage of this cell culture system that allows analyses of the interplay between HCV replication and the host cell, in this study we characterized two replicon-harboring cell lines that have been cultivated for more than 1 year. During this time, we observed no signs of cytopathogenicity such as reduction of growth rates or ultrastructural changes. High levels of HCV RNAs were preserved in cells passaged under continuous selection. When selective pressure was omitted replicon levels dropped, but depending on culture conditions the RNAs persisted for more than 10 months. A tight coupling of the amounts of HCV RNA and proteins to host cell growth was observed. Highest levels were found in exponentially growing cells, followed by a sharp decline in resting cells, suggesting that cellular factors required for RNA replication and/or translation vary in abundance and become limiting in resting cells. Studies of polyprotein processing revealed rapid cleavages at the NS3/4A and NS5A/B sites resulting in a rather stable NS4AB5A precursor that was processed slowly into individual products. Half-lives (t(1/2)s) of mature proteins ranged from 10 to 16 h, with the exception of the hyperphosphorylated form of NS5A, which was less stable (t(1/2), approximately 7 h). Results of immunoelectron microscopy revealed an association of the majority of viral proteins with membranes of the endoplasmic reticulum, suggesting that this is the site of RNA replication. In summary, replicon-bearing cells are a good model for viral persistence, and they allow the study of various aspects of the HCV life cycle.

Hepatitis viruses and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is among the most frequent malignancies worldwide. Hepatitis viruses, such as the hepatitis B virus (HBV) and hepatitis C virus (HCV) are undoubtedly listed in the etiology of HCC. Studies show that, in the near future, viral hepatitis will carry increasing weight in the etiology of HCC. This review briefly discusses the known carcinogenic effects of HBV and HCV in the light of experimental and human studies. The data show that viral proteins may directly interfere with gene products responsible for cell proliferation and cell growth. Many other signal transduction cascades may be affected as well. Direct integration of HBV viral sequences into the host genome increases the genomic instability. The genomic imbalance allows the development and survival of malignant clones bearing defected genomic information. HBV and HCV infection induces indirect and direct mechanisms through cellular damage, increased regeneration and cell proliferation, therefore enhancing the development of HCC.

Core protein-coding sequence, but not core protein, modulates the efficiency of cap-independent translation directed by the internal ribosome entry site of hepatitis C virus

Among a myriad of putative functions assigned to the hepatitis C virus (HCV) core protein, several studies suggest that it may modulate internal ribosome entry site (IRES)-mediated initiation of translation. We compared the translational activity of dicistronic reporter transcripts containing the HCV IRES within the intercistronic space fused to downstream sequence encoding either 22 amino acids (aa) or 173 aa of the core protein. The inclusion of the nearly full-length core protein-coding sequence significantly suppressed translation in vitro and in transfected HepG2 cells. However, this suppression was not eliminated by frameshift mutations introduced into the core sequence, suggesting that it occurred at the RNA level and not as a result of core protein expression in cis. Similarly, the expression of core protein (aa 1 to 191) in trans from a recombinant baculovirus did not suppress IRES-directed translation from any of these transcripts in transfected Huh-7 cells. While core protein expression did decrease IRES activity in HepG2 cells (up to 79% suppression), the expression of beta-galactosidase from a control baculovirus also suppressed IRES activity (up to 56%), strongly suggesting that this suppression was nonspecific. Finally, the addition of purified recombinant core protein (aa 1 to 179) to in vitro translation reactions at concentrations up to a 10-fold molar excess over the RNA transcripts resulted in no significant reduction in IRES activity. Consistent with these results, a gel retention assay indicated no difference in the affinities of the recombinant HCV core protein and a recombinant Venezuelan equine encephalitis virus capsid protein for HCV IRES-containing RNA transcripts. We conclude that while the inclusion of core protein-coding sequence downstream of the IRES may reduce the efficiency of cap-independent translation on HCV RNA, the core protein itself has no biologically relevant activity in modulating HCV IRES activity.

Suppression of interferon-induced antiviral activity in cells expressing hepatitis C virus proteins

To elucidate the mechanism of the persistent nature of hepatitis C virus (HCV) infection, we examined whether the expression of HCV proteins affect the antiviral activity of interferon (IFN). Antiviral activity of IFN in HepG2 cells expressing all HCV (type 1b) proteins was much lower than vector control (VC) HepG2 cells when encephalomyocarditis virus (EMCV) was used as a challenge virus. Lesser sensitivity to IFN was also observed in cells expressing NS3, NS4, and NS5 and in cells expressing only NS5A. In contrast, HepG2 cells expressing core, E1, E2, NS2, and NS3 proteins were equally sensitive to IFN as VC cells. We then tested the antiviral activity by IFN in two human amnion-derived FL cell lines expressing NS5A from two different clones, one with an intact sequence of IFN sensitivity-determining region (ISDR) and the other with a mutated ISDR sequence. They were almost equally insensitive to IFN treatment when EMCV was challenged. HCV thus has functional protein(s), possibly NS5A, to suppress IFN-induced antiviral activity and plays an important role in virus-cell interaction and regulation of viral replication.

Leptin has no role in determining severity of steatosis and fibrosis in patients with chronic hepatitis C

OBJECTIVE

The presence of steatosis is a common histological finding in patients with chronic hepatitis C (CHC). The causes of the severity of this condition are not yet clear, although both metabolic and viral factors supposedly are involved. In this study our aim was to examine the possible influence that leptin levels, hepatitis C virus (HCV) RNA levels, and hepatitis G virus (HGV) infection have on the severity of steatosis and on the presence and degree of fibrosis in patients with CHC.

METHODS

One hundred eighty-two CHC patients with histological findings of steatosis were chosen from among a cohort of patients referred to our center for staging of liver disease. Among them 48 CHC patients were accurately selected so as to rule out possible confounding factors for the presence of steatosis (diabetes mellitus, hyperlipemia, obesity, alcohol). Leptin levels, HCV RNA levels, and HCV genotype, and the presence of HGV RNA were assessed in these patients and related to histological findings.

RESULTS

We found that leptin levels in CHC patients were similar to those in healthy subjects. No relationship was found between leptin levels and severity of steatosis. HCV RNA levels, HCV genotype, and the presence of HGV infection were no different among CHC patients with various degrees of steatosis. Leptin was not related to different degrees of fibrosis, whereas higher viral load was the only parameter associated to higher fibrosis scores.

CONCLUSIONS

These findings suggest that the degree of steatosis in patients with CHC does not seem to depend on serum leptin levels or on viral factors, at least as far as HCV viremia and genotype and HGV infection are concerned. The severity of fibrosis does not seem to be influenced by leptin levels, whereas HCV viral load does seem to play some role.

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.

Hepatocyte steatosis is a cytopathic effect of hepatitis C virus genotype 3

BACKGROUND/AIMS

Patients infected with the hepatitis C virus (HCV) often have liver steatosis, suggesting the possibility of a viral cytopathic effect. The aim of this study was to correlate the occurrence and severity of liver steatosis with HCV RNA type, level and sequence of the core-encoding region.

METHODS

We scored the liver steatosis in 101 HCV-infected individuals carefully selected to exclude other risk factors of a fatty liver. Results were compared with HCV RNA genotype and level in serum and liver. In selected patients, we assessed the effect of antiviral therapy on steatosis and the relationship between nucleocapsid sequence heterogeneity and fat infiltration.

RESULTS

Steatosis was found in 41 (40.6%) patients, irrespective of sex, age or route of infection. HCV genotype 3 was associated with higher steatosis scores than other genotypes. A significant correlation between steatosis score and titer of intrahepatic HCV RNA was found in patients infected with genotype 3, but not in those infected with genotype 1. In selected patients, response to alpha-interferon was associated with the disappearance of steatosis. Analysis of the nucleocapsid of 14 HCV isolates failed to identify a sequence specifically associated with the development of steatosis.

CONCLUSIONS

We provide virological and clinical evidence that the steatosis of the liver is the morphological expression of a viral cytopathic effect in patients infected with HCV genotype 3. At variance with published evidence from experimental models, the HCV nucleocapsid protein does not seem to fully explain the lipid accumulation in these patients.

Tumor-derived mutated E-cadherin influences beta-catenin localization and increases susceptibility to actin cytoskeletal changes induced by pervanadate

E-cadherin participates in homophilic cell-to-cell adhesion and is localized to intercellular junctions of the adherens type. In the present study, we investigated the localization of adherens junction components in cells expressing mutant E-cadherin derivatives which had been previously cloned from diffuse-type gastric carcinoma. The mutations are in frame deletions of exons 8 or 9 and a point mutation in exon 8 and affect the extracellular domain of E-cadherin. Our findings indicate that E-cadherin mutated in exon 8 causes beta-catenin staining at lateral cell-to-cell contact sites and, in addition, abnormally located beta-catenin in the perinuclear region. Moreover, the various mutant E-cadherin derivatives increased the steady-state levels of alpha- and beta-catenin and were found in association with these catenins even after induction of tyrosine phosphorylation by pervanadate. Sustained pervanadate treatment led, however, to rounding-up of cells and induction of filopodia, changes which were first detectable in cells expressing E-cadherin mutated in exon 8. The deterioration of the cell contact was not accompanied with disassembly of the E-cadherin-catenin complex. Based on these observations, we propose a model whereby in the presence of mutant E-cadherin tyrosine phoshorylation of components of the cell adhesion complex triggers loss of cell-to-cell contact and actin cytoskeletal changes which are not caused by the disruption of the E-cadherin-catenin complex per se, but instead might be due to phosphorylation of other signaling molecules or activation of proteins involved in the regulation of the actin cytoskeleton.

Hepatitis C virus core protein-induced loss of LZIP function correlates with cellular transformation

Hepatitis C virus (HCV) is the major etiological agent of blood-borne non-A non-B hepatitis and a leading cause of liver cirrhosis and hepatocellular carcinoma worldwide. HCV core protein is a multifunctional protein with regulatory functions in cellular transcription and virus-induced transformation and pathogenesis. Here we report on the identification of a bZIP nuclear transcription protein as an HCV core cofactor for transformation. This bZIP factor, designated LZIP, activates CRE-dependent transcription and regulates cell proliferation. Loss of LZIP function in NIH 3T3 cells triggers morphological transformation and anchorage-independent growth. We show that HCV core protein aberrantly sequesters LZIP in the cytoplasm, inactivates LZIP function and potentiates cellular transformation. Our findings suggest that LZIP might serve a novel cellular tumor suppressor function that is targeted by the HCV core.

Hepatitis C virus core protein interacts with 14-3-3 protein and activates the kinase Raf-1

Persistent hepatitis C virus (HCV) infection is a major cause of chronic liver dysfunction in humans and is epidemiologically closely associated with the development of human hepatocellular carcinoma. Among HCV components, core protein has been reported to be implicated in cell growth regulation both in vitro and in vivo, although mechanisms explaining those effects are still unclear. In the present study, we identified that members of the 14-3-3 protein family associate with HCV core protein. 14-3-3 protein bound to HCV core protein in a phosphoserine-dependent manner. Introduction of HCV core protein caused a substantial increase in Raf-1 kinase activity in HepG2 cells and in a yeast genetic assay. Furthermore, the HCV core-14-3-3 interaction was essential for Raf-1 kinase activation by HCV core protein. These results suggest that HCV core protein may represent a novel type of Raf-1 kinase-activating protein through its interaction with 14-3-3 protein and may contribute to hepatocyte growth regulation.

A transgenic mouse model of steatosis and hepatocellular carcinoma associated with chronic hepatitis C virus infection in humans

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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.

Immunohistochemical detection of hepatitis C virus antigen in paraffin embedded liver biopsies from patients with chronic liver disease

A simple and reproducible immunohistochemical (IHC) staining method that adequately identifies and localizes hepatitis C virus (HCV) in human livers is still not available. We performed IHC staining using both a new monoclonal antibody against HCV and a polyclonal human anti-HCV IgG to 94 liver biopsies from HCV seropositive patients with chronic hepatitis and 15 control liver biopsies. Positive nuclear staining was consistently observed predominantly in hepatocytes and much less in lymphocytes with either antibody in 57% of anti-HCV seropositive cases but in none of the controls. However, the monoclonal antibody yielded a stronger positive reaction and in a greater proportion of hepatocytes. In 78% of the positive cases, more than a quarter of the hepatocytes showed nuclear staining. The degree of hepatic HCV load as revealed by intensity and extent of positive staining did not correlate with histological changes in the liver. The new monoclonal antibody against HCV appeared to be suitable for identifying HCV in tissues by a simple IHC stain and can be used to explore the pathogenesis of liver injury induced by this virus.

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.

Steatosis and intrahepatic hepatitis C virus in chronic hepatitis

Hepatic steatosis has been reported as one of the characteristics which discriminates hepatitis C from other forms of hepatitis, besides lymphoid follicles and bile duct damage. However, it is unclear whether or not the presence of hepatitis C virus (HCV) itself is associated with the development of steatosis. The possibility that the HCV itself is directly related to the development of steatosis was examined. The intrahepatic core protein levels, as a marker of the HCV load, were correlated with the presence of steatosis in 43 patients with chronic hepatitis C. Among 43 patients studied by Western blotting, the core protein was detected in the liver in 27 (62.8%). On the other hand, hepatic steatosis was observed in 21 (48.8%) of the 43 patients. Importantly, the core protein was detectable in 19 (90.4%) of the 21 patients with steatosis, while it was detected in only 8 (36.4%) of the 22 patients without steatosis (P = 0.008). However, serum HCV-RNA levels as determined by the Amplicor monitor were not significantly different between patients with and without steatosis. Multivariate analysis showed that the serum alanine aminotransferase level (P = 0. 013), body mass index (P = 0.038), and intrahepatic HCV core protein positivity (P = 0.038) were the independent parameters best predictive of steatosis. These results indicate a close relationship between intrahepatic HCV and the development of steatosis, and suggest a possible role of the HCV itself or core protein in the pathogenesis of steatosis in human chronic hepatitis C.

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.

Loss of heterozygosity and microsatellite instability in human non-neoplastic hepatic lesions

AIMS/BACKGROUND

Carcinogenesis is thought to be a multistage process that occurs as a result of mutations in oncogenes and tumor suppressor genes. One way to monitor a vast range of these changes is by microsatellite PCR amplification that detects loss of heterozygosity and microsatellite instability between normal and tumor specimens of the same subject. Viral cirrhosis is considered a strong predisposing factor for the development of liver cancer. The aim of the study therefore was to examine precancerous hepatic lesions and compare them with others not considered as high risk for hepatocellular carcinoma.

METHODS

We examined 43 subjects for 19 microsatellite markers spanning chromosomes 1, 9 and 17. Normal specimens were blood samples that were compared to liver needle biopsies. Samples were classified according to histological features as non-cancerous (10 cases) and pre-cancerous (33 cases, chronic hepatitis and cirrhosis).

RESULTS

Our results indicate that there is a tendency of increased chromosomal alteration as lesions become chronic. Samples from patients with antibodies to antibodies for hepatitis C virus show more alterations than hepatitis B positive samples. Steatohepatitis, a disease of unknown etiology, appears to have a high number of microsatellite abnormalities.

CONCLUSIONS

Microsatellite APOA2 located on chromosome 1, shows a statistically significant increase in the rate of loss of heterozygosity as liver lesions become more severe, indicating the presence of tumor suppressor genes which may be involved in the development of these lesions.

Hepatitis C virus core protein interacts with a human DEAD box protein DDX3

Several studies have implicated hepatitis C virus (HCV) core in influencing the expression of host genes. To identify cellular factors with a possible role in HCV replication and pathogenesis, we looked for cellular proteins that interact with the viral core protein. A human liver cDNA library was screened in a yeast two-hybrid assay to identify cellular proteins that bind to core. Several positive clones were isolated, one of which encoded the C-terminal 253 amino acids of a putative RNA helicase, a DEAD box protein designated DDX3. Bacterially expressed glutathione-S-transferase-DDX3 fusion protein specifically pulled down in vitro translated and radiolabeled HCV core, confirming a direct interaction. Immunofluorescent staining of HeLa cells with a polyclonal antiserum showed that DDX3 is located predominantly in nuclear speckles and at low levels throughout the cytoplasm. In cells infected with a recombinant vaccinia virus expressing HCV structural proteins (core, E1, and E2), DDX3 and core colocalized in distinct spots in the perinuclear region of the cytoplasm. The regions of the proteins involved in binding were found by deletion analysis to be the N-terminal 59 amino acid residues of core and a C-terminal RS-like domain of DDX3. The human DDX3 is a putative RNA helicase and a member of a highly conserved DEAD box subclass that includes murine PL10, Xenopus An3, and yeast Ded1 proteins. Their role in RNA metabolism or gene expression is unknown. The significance of core-helicase interaction in HCV replication and pathogenesis is discussed.

Permissiveness of human biliary epithelial cells to infection by hepatitis C virus

The cellular tropism of hepatitis C virus (HCV) is an important but much debated issue. Permissivity to HCV of biliary cells has never been demonstrated. In this context, we used gallbladder epithelial cells (GBEC) as a model of the more proximal biliary epithelium. These cells were isolated from HCV-positive and -negative individuals and cultured for up to 40 days. Biliary cells from HCV-negative subjects were infected in vitro with various inocula. The retention of GBEC functional characteristics was assessed by the expression of cystic fibrosis transmembrane conductance regulator (CFTR). All 12 GBEC tested from HCV-negative patients were successfully infected by HCV. This was assessed by: 1) the detection of HCV-RNA positive and negative strands; 2) the detection of the viral capsid by immunofluorescence; and 3) the combination of single-strand conformation polymorphism (SSCP) and HVR1 sequence analysis demonstrating the distinct majoritary HCV genomes in serum and in GBEC. The level of HCV RNA in cell extracts and supernatants was low, but HCV infection was highly reproducible. Our results expand those showing the cellular tropism of HCV, and demonstrate the sensitivity of biliary cells to HCV infection. This might have an important impact in terms of pathogenesis and pathological features of HCV infection. In addition, given the easy access to these cells and the high reproducibility of in vitro infection, they should constitute an important tool for studies aimed at analyzing the issue of HCV penetration and neutralizing antibodies.

Hepatitis C virus core protein interacts with cellular putative RNA helicase

The nucleocapsid core protein of hepatitis C virus (HCV) has been shown to trans-act on several viral or cellular promoters. To get insight into the trans-action mechanism of HCV core protein, a yeast two-hybrid cloning system was used for identification of core protein-interacting cellular protein. One such cDNA clone encoding the DEAD box family of putative RNA helicase was obtained. This cellular putative RNA helicase, designated CAP-Rf, exhibits more than 95% amino acid sequence identity to other known RNA helicases including human DBX and DBY, mouse mDEAD3, and PL10, a family of proteins generally involved in translation, splicing, development, or cell growth. In vitro binding or in vivo coimmunoprecipitation studies demonstrated the direct interaction of the full-length/matured form and C-terminally truncated variants of HCV core protein with this targeted protein. Additionally, the protein's interaction domains were delineated at the N-terminal 40-amino-acid segment of the HCV core protein and the C-terminal tail of CAP-Rf, which encompassed its RNA-binding and ATP hydrolysis domains. Immunoblotting or indirect immunofluorescence analysis revealed that the endogenous CAP-Rf was mainly localized in the nucleus and to a lesser extent in the cytoplasm, and when fused with FLAG tag, it colocalized with the HCV core protein either in the cytoplasm or in the nucleus. Similar to other RNA helicases, this cellular RNA helicase has nucleoside triphosphatase-deoxynucleoside triphosphatase activity, but this activity is inhibited by various forms of homopolynucleotides and enhanced by the HCV core protein. Moreover, transient expression of HCV core protein in human hepatoma HuH-7 cells significantly potentiated the trans-activation effect of FLAG-tagged CAP-Rf or untagged CAP-Rf on the luciferase reporter plasmid activity. All together, our results indicate that CAP-Rf is involved in regulation of gene expression and that HCV core protein promotes the trans-activation ability of CAP-Rf, likely via the complex formation and the modulation of the ATPase-dATPase activity of CAP-Rf. These findings provide evidence that HCV may have evolved a distinct mechanism in alteration of host cellular gene expression regulation via the interaction of its nucleocapsid core protein and cellular putative RNA helicase known to participate in all aspects of cellular processes involving RNA metabolism. This feature of core protein may impart pleiotropic effects on host cells, which may partially account for its role in HCV pathogenesis.

Hepatitis C virus core protein enhances NF-kappaB signal pathway triggering by lymphotoxin-beta receptor ligand and tumor necrosis factor alpha

Our previous study indicated that the core protein of hepatitis C virus (HCV) can associate with tumor necrosis factor receptor (TNFR)-related lymphotoxin-beta receptor (LT-betaR) and that this protein-protein interaction plays a modulatory effect on the cytolytic activity of recombinant form LT-betaR ligand (LT-alpha1beta2) but not tumor necrosis factor alpha (TNF-alpha) in certain cell types. Since both TNF-alpha/TNFR and LT-alpha1beta2/LT-betaR are also engaged in transcriptional activator NF-kappaB activation or c-Jun N-terminal kinase (JNK) activation, the biological effects of the HCV core protein on these regards were elucidated in this study. As demonstrated by the electrophoretic mobility shift assay, the expression of HCV core protein prolonged or enhanced the TNF-alpha or LT-alpha1beta2-induced NF-kappaB DNA-binding activity in HuH-7 and HeLa cells. The presence of HCV core protein in HeLa or HuH-7 cells with or without cytokine treatment also enhanced the NF-kappaB-dependent reporter plasmid activity, and this effect was more strongly seen with HuH-7 cells than with HeLa cells. Western blot analysis suggested that this modulation of the NF-kappaB activity by the HCV core protein was in part due to elevated or prolonged nuclear retention of p50 or p65 species of NF-kappaB in core protein-producing cells with or without cytokine treatment. Furthermore, the HCV core protein enhanced or prolonged the IkappaB-beta degradation triggering by TNF-alpha or LT-alpha1beta2 both in HeLa and HuH-7 cells. In contrast to that of IkappaB-beta, the increased degradation of IkappaB-alpha occurred only in LT-alpha1beta2-treated core-producing HeLa cells and not in TNF-alpha-treated cells. Therefore, the HCV core protein plays a modulatory effect on NF-kappaB activation triggering by both cytokines, though the mechanism of NF-kappaB activation, in particular the regulation of IkappaB degradation, is rather cell line and cytokine specific. Studies also suggested that the HCV core protein had no effect on TNF-alpha-stimulated JNK activity in both HeLa and HuH-7 cells. These findings, together with our previous study, strongly suggest that among three signaling pathways triggered by the TNF-alpha-related cytokines, the HCV core protein potentiates NF-kappaB activation in most cell types, which in turn may contribute to the chronically activated, persistent state of HCV-infected cells.

Mechanisms of hepatic toxicity. IV. Pathogenetic mechanisms involved in hepatitis C virus-inducedliver diseases

The pathogenetic mechanisms for liver damage in acute hepatitis C are not clear, but a host immune cellular response may be involved. In chronic hepatitis C, there is strong evidence that host cellular immune response is involved in the control of viral replication and contributes to hepatocellular damage. As hepatitis C virus infection persists, continuous liver damage and regeneration, together with enhanced fibrogenesis, may eventually lead to cirrhosis in a proportion of patients. Transplant patients on high-dose immunosuppression may have high-level intrahepatic hepatitis C viral expression, and, in this setting, the virus may induce direct cytopathic liver damage.

Ectopic expression of hepatitis C virus core protein differentially regulates nuclear transcription factors

The putative core protein of hepatitis C virus (HCV) regulates cellular growth and a number of cellular promoters. To further understand its effect, we investigated the role of the core protein in the endogenous regulation of two distinct transcription factors, nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1), and the related mitogen-activated protein kinase kinase (MAPKK) and c-Jun N-terminal kinase (JNK). Stable cell transfectants expressing the HCV core protein suppressed tumor necrosis factor (TNF)-induced NF-kappaB activation. Supershift analysis revealed that NF-kappaB consists of p50 and p65 subunits. This correlated with inhibition of the degradation of IkappaBalpha, the inhibitory subunit of NF-kappaB. The effect was not specific to TNF, as suppression in core protein-expressing cells was also observed in response to a number of other inflammatory agents known to activate NF-kappaB. In contrast to the effect on NF-kappaB, the HCV core protein constitutively activated AP-1, which correlated with the activation of JNK and MAPKK, which are known to regulate AP-1. These observations indicated that the core protein targets transcription factors known to be involved in the regulation of inflammatory responses and the immune system.

Hepatic steatosis: a specific sign of hepatitis C reinfection after liver transplantation

Hepatitis C virus (HCV) infection is one of the major causes leading to orthotopic liver transplantation (OLT) worldwide. Although viral infection persists in almost all patients, the pathology of recurrent HCV infection after OLT is not well characterized. To address this issue, we compared the pathological findings of 28 patients who underwent transplantation for HCV-related cirrhosis (group A, aged 47 +/- 15 years; 23 men, 5 women) with those of 21 patients who underwent transplantation for nonviral indications (group B, aged 45 +/- 21 years; 13 men, 8 women) during the first year after transplantation. Patients from group A were assessed for serum HCV RNA by 5' untranslated region nested polymerase chain reaction before and 1 year after OLT. Patients underwent protocol liver biopsies 3 months and 1 year after transplantation. Group A patients more frequently had histological evidence of hepatic steatosis than group B patients, both at 3 months (P = .003) and 1 year (P = .003) after OLT. Fibrosis and portal inflammation were statistically more frequent in group A 1 year after transplantation. The sensitivity of steatosis in detecting histological disease recurrence was 100% at 3 months and 94% at 1 year; the specificity was 40% and 60%, respectively. Conversely, steatosis was 100% specific in detecting viral recurrence, with a sensitivity of 89%. The 1-year actuarial incidence of abnormal transaminase levels was 52% in group A and 13% in group B (P = .05). No biochemical or histological differences between patients infected with genotype 1b and patients with other HCV genotypes were found. Hepatic steatosis is a specific sign of viral recurrence after liver transplantation and a less specific sign of disease recurrence. HCV-infected liver transplant recipients often develop abnormal transaminase levels and liver fibrosis 1 year after OLT; these features are unrelated to HCV genotypes.

Hepatitis C virus infection, mixed cryoglobulinemia, and non-Hodgkin's lymphoma: an emerging picture

Hepatitis C virus (HCV) is a single-stranded RNA agent which expresses its genetic informations in the form of a single, large polyprotein encoded by an open reading frame (ORF) that extends through most of its genomic RNA. Proteolytic cleavage of the ORF product is essential for the virogenesis and the production of viral progeny. HCV is responsible for chronic liver disease, cirrhosis and possibly hepatocellular carcinoma. Viral persistence is considered the greatest problem in the management of HCV infection. It may result from several mechanisms, two of which are established. In the first, the high rate of genetic variations during viral replication results in the production of mutants capable of escaping the immune attack. In the second, the virus infects cells of the immune system itself, which represent a privileged site that cannot be reached by virus-specific T cell response. Involvement of lymphoid cells in the early stages of HCV infection may provide insight into the pathobiologic patterns of extrahepatic dissemination (lymph nodes, major salivary glands, kidneys, blood vessels). Dissemination of HCV-infected lymphoid cells throughout the organism is likely to maintain a mobile and extensive reservoir of the virus. In this respect, extrahepatic sites may act as a source of continuous reinfection of hepatocytes. Studies of intrahepatic B lymphocytes indicate that they are infected with HCV, clonally expanded and activated to secrete IgM molecules with rheumatoid factor activity. This strongly suggests that HCV directly stimulates B cell expansion, which may result in an indolent stage of lymphoproliferation (i.e., mixed cryoglobulinemia) or in frank B cell non-Hodgkin's lymphoma (NHL). The frequency of NHL, however, is much lower than that of HCV infection, suggesting that HCV alone is not able to induce tumors and that cellular events, in addition to the presence of virus and virus-encoded products, are necessary in order to obtain a malignant B cell phenotype. The demonstration of HCV productive infection in bone marrow-recruited and circulating pluripotent hematopoietic CD34+ stem cells indicates that HCV replication occurs in the early differentiation stages of hematopoietic progenitors. These are stable cell populations and are likely to represent the initial site of infection and a continuous source of virus production.

Detection of widespread hepatocyte infection in chronic hepatitis C

The controversial question of the extent of hepatocyte infection in chronic hepatitis C was re-examined in both chimpanzees and humans using a newly modified in situ hybridization (ISH) method for detecting hepatitis C virus (HCV) RNA. The specificity of the methodology for distinguishing positive- and negative-strand synthetic HCV RNA was at least six magnitudes greater than the reverse-transcription polymerase chain reaction (RT-PCR) assay for HCV. The sensitivity of the methodology as determined by cell culture assay was 14 +/- 2 genomic equivalents (gE) of HCV positive strand per cell, which was three magnitudes less sensitive than RT-PCR quantitation of HCV. In contrast to previous studies in both humans and chimpanzees with chronic hepatitis C, a high percentage of hepatocytes positive for both positive- and negative-strand HCV RNA was found in most specimens studied. In humans, the extent of hepatocyte infection varied with histological activity index (HAI). In the two chimpanzees studied, the liver biopsies showed minimal histological disease activity, but high percentages of hepatocytes were HCV-positive by ISH that correlated with hepatocyte ultrastructural changes associated with HCV infection. Hepatocyte infection was confirmed by RNA extraction and RT-PCR techniques for detecting HCV RNA that minimize the false detection of negative strands. In both human and chimpanzee liver biopsies showing minimal HAI, the hepatocyte concentration of HCV was estimated to be very low. These findings suggested the hypothesis that persistent infection in the liver may be caused in part by low-level HCV replication. The theoretical and clinical implications of these findings are discussed.

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.

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

The maturation and subcellular localization of hepatitis C virus (HCV) core protein were investigated with both a vaccinia virus expression system and CHO cell lines stably transformed with HCV cDNA. Two HCV core proteins, with molecular sizes of 21 kDa (p21) and 23 kDa (p23), were identified. The C-terminal end of p23 is amino acid 191 of the HCV polyprotein, and p21 is produced as a result of processing between amino acids 174 and 191. The subcellular localization of the HCV core protein was examined by confocal laser scanning microscopy. Although HCV core protein resided predominantly in the cytoplasm, it was also found in the nucleus and had the same molecular size as p21 in both locations, as determined by subcellular fractionation. The HCV core proteins had different immunoreactivities to a panel of monoclonal antibodies. Antibody 5E3 stained core protein in both the cytoplasm and the nucleus, C7-50 stained core protein only in the cytoplasm, and 499S stained core protein only in the nucleus. These results clearly indicate that the p23 form of HCV core protein is processed to p21 in the cytoplasm and that the core protein in the nucleus has a higher-order structure different from that of p21 in the cytoplasm. HCV core protein in sera of patients with HCV infection was analyzed in order to determine the molecular size of genuinely processed HCV core protein. HCV core protein in sera was found to have exactly the same molecular weight as the p21 protein. These results suggest that p21 core protein is a component of native viral particles.

Tightly regulated expression of the entire hepatitis C virus structural region in continuous human cell lines

Investigation of the hepatitis C virus (HCV) life cycle is limited by the lack of an efficient cell culture system. Employing a tetracycline-regulated gene expression system we generated a panel of continuous human cell lines allowing the inducible expression and faithful processing of HCV structural proteins as well as of a functional NS2-3 autoprotease. HCV proteins were found in the cytoplasm in a pattern characteristic for the endoplasmic reticulum. High-level expression of HCV proteins was found to be cytotoxic. These cell lines represent a unique in vitro system in which to further investigate the structural proteins of HCV and to evaluate novel antiviral strategies against hepatitis C in a well-defined and reproducible cellular context.

Detection and localization by in situ molecular biology techniques and immunohistochemistry of hepatitis C virus in livers of chronically infected patients

Hepatitis C virus (HCV) detection in the livers of chronically infected patients remains a debatable issue. We used immunohistochemistry, in situ hybridization (ISH) alone or after microwave heating with FITC-labeled probes, RT-PCR with unlabeled primers followed by ISH (RT-PCR-ISH), and in situ RT-PCR with FITC-labeled primers (in situ RT-PCRd) to localize the virus in 38 liver biopsy specimens from 21 chronically infected HCV patients treated with interferon-alpha (IFN-alpha). Biopsies were taken at the beginning and end of IFN-alpha treatment and 1 year later. Results were compared with that of HCV-PCR in serum. RT-PCR-ISH and in situ RT-PCRd showed HCV signal in all liver biopsies even in responders with seronegative HCV PCR. This signal was intranuclear, diffuse, or peripheral, in hepatocytes, bile ductule cells, and lymphocytes. Cytoplasmic signals were occasionally observed. Whereas the percentage of labeled hepatocytes remained constant, the number of labeled lymphoid follicles decreased after INF-alpha therapy. Immunohistochemistry resulted in the same pattern of positivity but it was weaker and inconstant. This study indicates the persistency of HCV latency in IFN-alpha responders 1 year after IFN-alpha treatment cessation, a finding that certainly deserves confirmation.

Efficient conditional transgene expression in hepatitis C virus cDNA transgenic mice mediated by the Cre/loxP system

Conditional gene expression has greatly facilitated the examination of the functions of particular gene products. Using the Cre/loxP system, we developed efficient conditional transgene activation of hepatitis C virus (HCV) cDNA (nucleotides 294-3435) in transgenic mice. Efficient recombination was observed in transgenic mouse liver upon intravenous administration of adenovirus that expresses Cre DNA recombinase. After transgene activation, most hepatocytes were stained with anti-core polyclonal antibody, and 21-, 37-, and 64-kDa proteins were detected by Western blot analysis in liver lysates using anti-core, E1, and E2 monoclonal antibodies, respectively. Serum core protein was detected in transgenic mice 7 days after transgene activation with concurrent increases in serum alanine aminotransferase levels. Subsequently, an anti-core antibody response was detected 14 days after infection. Furthermore, a CD4 and CD8 positive cell depletion assay normalized both the serum alanine aminotransferase increases and pathological changes in the liver. These results suggest that HCV proteins are not directly cytopathic and that the host immune response plays a pivotal role in HCV infection. Thus, this HCV cDNA transgenic mouse provides a powerful tool with which to investigate the immune responses and pathogenesis of HCV infection.

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.

Hepatitis C virus core protein represses p21WAF1/Cip1/Sid1 promoter activity

Hepatitis C virus (HCV) often causes a prolonged and persistent infection, and an association between hepatocellular carcinoma (HCC) and HCV infection has been noted. Recent experimental evidence using a cloned genomic region suggests that the putative core protein of HCV has numerous biological properties and is implicated as a viral factor for HCV mediated pathogenesis. WAF1/Cip1/Sid1 (p21) is the prototype of a family of proteins that inhibit cyclin-dependent kinases (CDK) and regulate cell cycle progression in eukaryotic cells. In this study, we have observed that the HCV core protein represses the transcriptional activity of the p21 promoter when tested separately by an in-vitro transient expression assay using murine fibroblasts (NIH3T3), human hepatocellular carcinoma (HepG2), and human cervical carcinoma (HeLa) cells. A deletion analysis of the p21 promoter suggested that the HCV core responsive region is located downstream of the p53 binding site. A gel mobility shift analysis showed that the HCV core protein does not bind directly to p21 regulatory sequences. Thus, the HCV core protein appears to act as an effector in the promotion of cell growth by repressing p21 transcription through unknown cellular factor(s).

Transgenic mouse expressing a full-length hepatitis C virus cDNA

Hepatitis C virus (HCV), a major causative agent of post transfusion non-A, non-B hepatitis (NANBH), can only infect humans and chimpanzees. We produced nine transgenic mouse lines carrying a full-length HCV cDNA with the human serum amyloid P component (hSAP) promoter that can direct liver-specific expression. In one of these lines HCV mRNA and HCV core protein were detected in the liver of the transgenic mouse, although the levels of expression were very low. In addition, HCV-related antibody was detected in the serum.

Inhibition of tumor necrosis factor (TNF-alpha)-mediated apoptosis by hepatitis C virus core protein

Hepatitis C virus (HCV) putative core protein has displayed many intriguing biological properties. Since tumor necrosis factor (TNF) plays an important role in controlling viral infection, in this study the effect of the core protein was investigated on the TNF-alpha induced apoptosis of human breast carcinoma cells (MCF7). HCV core protein when expressed inhibited TNF-alpha-induced apoptotic cell death unlike the control MCF7 cells, as determined by cell viability and DNA fragmentation analysis. Additionally, HCV core protein blocked the TNF-induced proteolytic cleavage of the death substrate poly(ADP-ribose) polymerase from its native 116-kDa protein to the characteristic 85-kDa polypeptide. Results from this study suggest that the HCV core protein plays a role in the inhibition of TNF-alpha-mediated cell death. Thus, the ability of core protein to inhibit the TNF-mediated apoptotic signaling pathway may provide a selective advantage for HCV replication, allowing for evasion of host antiviral defense mechanisms.

Direct interaction of hepatitis C virus core protein with the cellular lymphotoxin-beta receptor modulates the signal pathway of the lymphotoxin-beta receptor

Previous studies suggest that the core protein of hepatitis C virus (HCV) has a pleiotropic function in the replication cycle of the virus. To understand the role of this protein in HCV pathogenesis, we used a yeast two-hybrid protein interaction cloning system to search for cellular proteins physically interacting with the HCV core protein. One such cellular gene was isolated and characterized as the gene encoding the lymphotoxin-beta receptor (LT-betaR). In vitro binding analysis demonstrated that the HCV core protein binds to the C-terminal 98 amino acids within the intracellular domain of the LT-betaR that is involved in signal transduction, although the binding affinity of the full-length HCV core protein was weaker than that of its C-terminally truncated form. Our results also indicated that the N-terminal 40-amino-acid segment of the HCV core protein was sufficient for interaction with LT-betaR and that the core protein could form complexes with the oligomeric form of the intracellular domain of LT-betaR, which is a prerequisite for downstream signaling of this receptor. Similar to other members of the tumor necrosis factor (TNF) receptor superfamily, LT-betaR is involved in the cytotoxic effect of the signaling pathway, and thus we have elucidated the biological consequence of interaction between the HCV core protein and LT-betaR. Our results indicated that in the presence of the synergizing agent gamma interferon, the HCV core protein enhances the cytotoxic effects of recombinant forms of LT-betaR ligand in HeLa cells but not in hepatoma cells. Furthermore, this enhancement of the cytolytic activity was cytokine specific, since in the presence of cycloheximide, the expression of the HCV core protein did not elicit an increase in the cytolytic activity of TNF in both HeLa and hepatoma cells. In summary, the HCV core protein can associate with LT-betaR, and this protein-protein interaction has a modulatory effect on the signaling pathway of LT-betaR in certain cell types. Given the known roles of LT-betaR/LT-alpha1,beta2 receptor-ligand interactions in the normal development of peripheral lymphoid organs and in triggering cytolytic activity and NF-kappaB activation in certain cell types, our finding implies that the HCV core protein may aggravate these biological functions of LT-betaR, resulting in pathogenesis in HCV-infected cells.

Subcellular localization of hepatitis C virus structural proteins in the liver of transgenic mice

Hepatitis C virus (HCV) core and envelope proteins are suggested to be responsible for the pathogenesis of hepatic and extrahepatic manifestations in chronic hepatitis C. Moreover, the core protein is implicated in the regulation of the transcription of cellular genes including c-myc, RB and p53. Determining the subcellular localization of the core and envelope proteins is therefore necessary to elucidate their behaviors, particularly in vivo ones, regarding the interaction with transcriptional regulatory proteins or gene elements. We defined the subcellular localization of HCV envelope and core proteins which were expressed in substantial levels in the liver of transgenic mice. Subcellular fractionation by ultra-centrifugation revealed that the envelope proteins were present principally in the microsomes of the liver, while a small amount of the protein was detected also in the nuclei. Immunohistochemistry confirmed the localization of envelope proteins in the nuclei. In contrast, the core protein was detected principally in the cytoplasmic fraction, where it was closely associated with lipids. A low level of the core protein was detected also in the nuclei and microsomal fraction. These results suggest possible interaction of the HCV structural proteins with some factors in hepatocytes thereby perturbing intracellular circumstances.