Hepatitis C virus core protein: possible roles in viral pathogenesis

Hepatitis C virus core protein: Not just a nucleocapsid building block, but an immunity and inflammation modulator

Coevolution occurs between viruses and their hosts. The hosts need to evolve means to eliminate pathogenic virus infections, and the viruses, for their own survival and multiplication, have to develop mechanisms to escape clearance by hosts. Hepatitis C virus (HCV) of Flaviviridae is a pathogen which infects human liver and causes hepatitis, a condition of liver inflammation. Unlike most of the other flaviviruses, HCV has an excellent ability to evade host immunity to establish chronic infection. The persistent liver infection leads to chronic hepatitis, liver cirrhosis, hepatocellular carcinoma (HCC), as well as extrahepatic HCV-related diseases. HCV genomic RNA only expresses 10 proteins, many of which bear functions, in addition to those involved in HCV life cycle, for assisting the virus to develop its persistency. HCV core protein is a structural protein which encapsulates HCV genomic RNA and assembles into nucleocapsids. The core protein is also found to exert functions to affect host inflammation and immune responses by altering a variety of host pathways. This paper reviews the studies regarding the HCV core protein-induced alterations of host immunity and inflammatory responses, as well as the involvements of the HCV core protein in pro- and anti-inflammatory cytokine stimulations, host cellular transcription, lipid metabolism, cell apoptosis, cell proliferations, immune cell differentiations, oxidative stress, and hepatocyte steatosis, which leads to liver fibrosis, cirrhosis, and HCC. Implications of roles played by the HCV core protein in therapeutic resistance are also discussed.

Hepatitis C virus infection induces endoplasmic reticulum stress and apoptosis in human fetal liver stem cells

The cellular mechanisms by which hepatitis C virus (HCV) replication might mediate cytopathic effects are controversial and not entirely clear. In this study, we found that blood-borne HCV (bbHCV) infection could lead to endoplasmic reticulum (ER)-stress and mitochondria-related/caspase-dependent apoptosis at the early stages of infection based on use of the highly efficient bbHCV cell culture model established previously. Sections of bbHCV-infected human fetal liver stem cells (hFLSCs) revealed convolution and nonlinear ER, cell vacuolization, swelling of mitochondria, and numerous double membrane vesicles (DMVs). The percentage of apoptotic hFLSCs infected by bbHCV reached 29.8% at 16 h postinfection, and the amount of cytochrome c increased remarkably in the cytosolic protein fraction. However, over time, apoptosis was inhibited due to the activation of NF-κB. The expression of NF-κB-p65, Bcl-xL, XIAP, and c-FLIPL in hFLSCs was increased significantly 24 h after in infection by bbHCV. The accelerated cell death cycles involving apoptosis, regeneration and repair by bbHCV infection might give rise to the development of cirrhosis, and ultimately to hepatocellular carcinogenesis. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Control of the inflammatory response mechanisms mediated by natural and induced regulatory T-cells in HCV-, HTLV-1-, and EBV-associated cancers

Virus infections are involved in chronic inflammation and, in some cases, cancer development. Although a viral infection activates the immune system's response that eradicates the pathogen mainly through inflammatory mechanisms, it is now recognized that this inflammatory condition is also favorable to the development of tumors. Indeed, it is well described that viruses, such as hepatitis C virus (HCV), Epstein Barr virus (EBV), human papillomavirus (HPV) or human T-cell lymphotropic virus type-1 (HTLV-1), are important risk factors for tumor malignancies. The inflammatory response is a fundamental immune mechanism which involves several molecular and cellular components consisting of cytokines and chemokines that are released by various proinflammatory cells. In parallel to this process, some endogenous recruited components release anti-inflammatory mediators to restore homeostasis. The development of tools and strategies using viruses to hijack the immune response is mostly linked to the presence of regulatory T-cells (Treg) that can inhibit inflammation and antiviral responses of other effector cells. In this review, we will focus on current understanding of the role of natural and induced Treg in the control and the resolution of inflammatory response in HCV-, HTLV-1-, and EBV-associated cancers.

HIV-1 Nef interacts with HCV Core, recruits TRAF2, TRAF5 and TRAF6, and stimulates HIV-1 replication in macrophages

Tumor necrosis factor receptor-associated factor (TRAF) signaling plays a central role in many biological activities, such as the regulation of immune and inflammatory responses and control of apoptosis, which are key events in the pathogenesis of the human immunodeficiency virus (HIV)-1 and the hepatitis C virus (HCV) infections. Here we show that TRAF2, TRAF5 and TRAF6 interact with the HIV-1 Nef protein, an immunomodulatory viral protein expressed and released by cells infected by the virus. We also found that TRAF2 and TRAF5 interact with the HCV Core protein. Interestingly, we observed that HIV-1 Nef interacts with HCV Core. The activation of TRAF (2, 5, 6) - mediated by HIV-1 Nef and HCV Core - enhanced the activation of the nuclear factor-kappa B (NF-κB) and increased HIV-1 replication in monocyte- derived macrophages (MDMs). The knockdown of TRAF2, TRAF5 and TRAF6 resulted in decreased NF-κB activation and reduced HIV-1 replication in MDMs. Our results reveal a mechanism by which the activation of the TRAF pathway by HIV-1 Nef and HCV Core favors the replication of HIV-1 in macrophages and could be a critical factor for optimal replication of HIV-1 in macrophages of HIV-HCV-coinfected patients.

Hepatocellular carcinoma in patients with chronic hepatitis C virus infection in the Asia-Pacific region

Hepatocellular carcinoma (HCC) is the third-leading cause of cancer-related mortality worldwide. Although hepatitis B still remains the most common risk factor worldwide, chronic hepatitis C virus (HCV) infection is the driving force for the increased incidence of HCC especially in Western countries and Japan. In hepatitis B virus (HBV)-endemic areas, after successful vaccination programs against HBV, chronic HCV infection is now emerging as an important cause of chronic liver diseases. Unlike patients with chronic hepatitis B, those with chronic hepatitis C (CHC) develop HCC in the presence of established cirrhosis in most cases. However, a significant minority of CHC develops HCC in the absence of cirrhosis. Although HCV is a RNA virus with little potential for integrating its genetic material into host genome, various HCV proteins, including core, envelope, and nonstructural proteins, have oncogenic properties by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses. Overall, a combination of virus-specific, host genetic, environmental, and immune-related factors are likely to determine progression to HCC. Strategies aimed at eliminating the virus may provide opportunities for effective prevention of the development of HCC. Pegylated interferon plus ribavirin therapy appears to be effective at reducing the risk of HCC in patients who achieve sustained virologic responses. In summary, with the emerging importance of CHC, mechanisms of HCV-associated hepatocellular carcinogenesis should be clarified to provide insight into advanced therapeutic and preventive approaches, which eventually decrease the incidence and mortality of HCC.

Hemoglobin subunit beta interacts with the capsid protein and antagonizes the growth of classical swine fever virus

The capsid (C) protein of the Flaviviridae family members is involved in nucleocapsid formation and virion assembly. However, the influence of C protein-interacting partners on the outcome of pestivirus infections is poorly defined. In this study, hemoglobin subunit beta (HB) was identified as a C protein-binding protein by glutathione S-transferase pulldown and subsequent mass spectrometry analysis of PK-15 cells, which are permissive cells for classical swine fever virus (CSFV). Coimmunoprecipitation and confocal microscopy confirmed that HB interacts and colocalizes with the C protein in the cytoplasm. Silencing of HB with small interfering RNAs promoted CSFV growth and replication, whereas overexpression of HB suppressed CSFV replication and growth. Interestingly, HB was found to interact with retinoic acid-inducible gene I and increase its expression, resulting in increased production of type I interferon (IFN). However, HB was unable to suppress CSFV growth when the RIG-I pathway was blocked. Overall, our results suggest that cellular HB antagonizes CSFV growth and replication by triggering IFN signaling, and might represent a novel antiviral restriction factor. This study reports for the first time the novel role of HB in innate immunity.

The identification of three sizes of core proteins during the establishment of persistent hepatitis C virus infection in vitro

Similar to Hepatitis C virus (HCV) infection in humans, HCVcc infection can also result in persistent and chronic infection. The core protein is a variable protein and exists in several sizes. Some sizes of core proteins have been reported to be related to chronic HCV infection. To study the possible role of the core protein in persistent HCV infection, a persistent HCVcc infection was established, and the expression of the core protein was analysed over the course of the infection. The results show that there are three sizes of core proteins (p24, p21 and p19) expressed during the establishment of persistent HCVcc infection. Of these, the p21 core protein is the mature form of the HCV core protein. The p24 core protein is the phosphorylated form of p21. The p19 core protein appears to be a functional by-product generated during the course of infection. These three core proteins are all localized in the cytoplasm and can be encapsidated into the HCV virion. The appearance of the p19 and p24 core proteins might be related to acute HCVcc infection and chronic infection respectively and may play an important role in the pathology of a HCV infection.

Microbes-induced EMT at the crossroad of inflammation and cancer

It is noteworthy that bacterial or viral infections, and the resulting chronic inflammation, have been shown to predispose individuals to certain types of cancer. Remarkably, these microbes upregulated some transcription factors involved in the regulation of the epithelial to mesenchymal transition, referred herein as EMT. EMT is a cellular process that consists in the conversion of epithelial cell phenotype to a mesenchymal phenotype. Under physiological conditions EMT is clearly important for embryogenesis, organ development, wound repair and tissue remodeling. However, EMT may also be activated under pathologic conditions, more particularly in carcinogenesis and metastatic progression. In this review, we make a parallel between microbes- and growth factors- induced transcription factors. A unifying EMT model then emerges that may help in understanding the development of microbial pathogenesis and in defining new potential future therapeutic strategy in treating diseases linked to infections.

Enhancement of canonical Wnt/β-catenin signaling activity by HCV core protein promotes cell growth of hepatocellular carcinoma cells

BACKGROUND

The Hepatitis C virus (HCV) core protein has been implicated as a potential oncogene or a cofactor in HCV-related hepatocellular carcinoma (HCC), but the underlying mechanisms are unknown. Overactivation of the Wnt/β-catenin signaling is a major factor in oncogenesis of HCC. However, the pathogenesis of HCV core-associated Wnt/β-catenin activation remains to be further characterized. Therefore, we attempted to determine whether HCV core protein plays an important role in regulating Wnt/β-catenin signaling in HCC cells.

METHODOLOGY

Wnt/β-catenin signaling activity was investigated in core-expressing hepatoma cells. Protein and gene expression were examined by Western blot, immunofluorescence staining, RT-qPCR, and reporter assay.

PRINCIPAL FINDINGS

HCV core protein significantly enhances Tcf-dependent transcriptional activity induced by Wnt3A in HCC cell lines. Additionally, core protein increases and stabilizes β-catenin levels in hepatoma cell line Huh7 through inactivation of GSK-3β, which contributes to the up-regulation of downstream target genes, such as c-Myc, cyclin D1, WISP2 and CTGF. Also, core protein increases cell proliferation rate and promotes Wnt3A-induced tumor growth in the xenograft tumor model of human HCC.

CONCLUSIONS/SIGNIFICANCE

HCV core protein enhances Wnt/β-catenin signaling activity, hence playing an important role in HCV-associated carcinogenesis.

Hepatocellular carcinoma: management of an increasingly common problem

Hepatocellular carcinoma (HCC) is a common cancer that typically occurs in the setting of cirrhosis and chronic hepatitis virus infections. Hepatitis B and C account for approximately 80% of cases worldwide. HCC is currently the fifth most common malignancy in men and the eighth in women worldwide; its incidence is increasing dramatically in many parts of the world. Recognition of those at risk and early diagnosis by surveillance with imaging, with or without serologic testing, are extremely important. Many highly effective and even curative therapies are now available and include resection, liver transplantation, and local ablation. Appropriate application of these interventions offers hope of prolonged survival to many patients with this otherwise lethal complication of liver disease.

Epidemiology and management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major world health problem because of the high incidence and case fatality rate. In most patients, the diagnosis of HCC is made at an advanced stage, which limits the application of curative treatments. Most HCCs develop in patients with underlying chronic liver disease. Chronic viral hepatitis B and C are the major causes of liver cirrhosis and HCC. Recent improvements in treatment of viral hepatitis and in methods for surveillance and therapy for HCC have contributed to better survival of patients with HCC. This article reviews the epidemiology, cause, prevention, clinical manifestations, surveillance, diagnosis, and treatment approach for HCC.

Oncogenic potential of hepatitis C virus proteins

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

Domain 3 of hepatitis C virus core protein is sufficient for intracellular lipid accumulation

BACKGROUND

Hepatitis C virus (HCV) is a major cause of liver disease worldwide, with steatosis, or "fatty liver," being a frequent histologic finding. In previous work, we identified sequence polymorphisms within domain 3 (d3) of genotype 3 HCV core protein that correlated with steatosis and in vitro lipid accumulation. In this study, we investigated the sufficiency of d3 to promote lipid accumulation, the role of HCV genotype in d3 lipid accumulation, and the subcellular distribution of d3.

METHODS

Stable cell lines expressing green fluorescent protein (GFP) fusions with isolates of HCV genotype 3 core steatosis-associated d3 (d3S), non-steatosis-associated d3 (d3NS), and genotype 1 d3 (d3G1) were analyzed by means of immunofluorescence, oil red O (ORO) staining, and triglyceride quantitation.

RESULTS

Cells that expressed d3S had statistically significantly more ORO than did cells expressing d3NS or d3G1 (P=.02 and <.001, respectively), as well as higher triglyceride levels P =.03 and .003, respectively). Immunofluorescence analysis showed that d3 does not colocalize to lipid droplets but partially colocalizes to the Golgi apparatus.

CONCLUSIONS

Our results suggest that HCV core d3 is sufficient to mediate the accumulation of lipid by means of a mechanism that is independent of domains 1 and 2. Our results also suggest that altered lipid trafficking may be involved.

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

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

Liver cancer-derived hepatitis C virus core proteins shift TGF-beta responses from tumor suppression to epithelial-mesenchymal transition

Background

Chronic hepatitis C virus (HCV) infection and associated liver cirrhosis represent a major risk factor for hepatocellular carcinoma (HCC) development. TGF-β is an important driver of liver fibrogenesis and cancer; however, its actual impact in human cancer progression is still poorly known. The aim of this study was to investigate the role of HCC-derived HCV core natural variants on cancer progression through their impact on TGF-β signaling.

Principal Findings

We provide evidence that HCC-derived core protein expression in primary human or mouse hepatocyte alleviates TGF-β responses in terms or growth inhibition or apoptosis. Instead, in these hepatocytes TGF-β was still able to induce an epithelial to mesenchymal transition (EMT), a process that contributes to the promotion of cell invasion and metastasis. Moreover, we demonstrate that different thresholds of Smad3 activation dictate the TGF-β responses in hepatic cells and that HCV core protein, by decreasing Smad3 activation, may switch TGF-β growth inhibitory effects to tumor promoting responses.

Conclusion/Significance

Our data illustrate the capacity of hepatocytes to develop EMT and plasticity under TGF-β, emphasize the role of HCV core protein in the dynamic of these effects and provide evidence for a paradigm whereby a viral protein implicated in oncogenesis is capable to shift TGF-β responses from cytostatic effects to EMT development.

Proteasomal turnover of hepatitis C virus core protein is regulated by two distinct mechanisms: a ubiquitin-dependent mechanism and a ubiquitin-independent but PA28gamma-dependent mechanism

We have previously reported on the ubiquitylation and degradation of hepatitis C virus core protein. Here we demonstrate that proteasomal degradation of the core protein is mediated by two distinct mechanisms. One leads to polyubiquitylation, in which lysine residues in the N-terminal region are preferential ubiquitylation sites. The other is independent of the presence of ubiquitin. Gain- and loss-of-function analyses using lysineless mutants substantiate the hypothesis that the proteasome activator PA28gamma, a binding partner of the core, is involved in the ubiquitin-independent degradation of the core protein. Our results suggest that turnover of this multifunctional viral protein can be tightly controlled via dual ubiquitin-dependent and -independent proteasomal pathways.

Biological impact of hepatitis B virus X-hepatitis C virus core fusion gene on human hepatocytes

AIM: To investigate the biological impact of hepatitis B virus X- hepatitis C virus core (HBV X-HCV C) fusion gene on hepatoma cells.

METHODS: The recombinant adenoviruses Ad-XC, Ad-X and Ad-C expressing HBV X-HCV C fusion gene, HBV X gene and HCV C gene were constructed, respectively. Hepatoma cells were infected with different recombinant adenoviruses. MTT, colony-forming experiment, FCM, TUNEL assay were performed to observe the biological impact of the HBV X-HCV C fusion gene on liver cells.

RESULTS: MTT showed that the Ad-XC group cells grew faster than the other group cells. Colony-forming experiment showed that the colony-forming rate for the Ad-XC group cells was significantly higher than that for the other group cells. FCM analysis showed that Ad-XC/Ad-X/Ad-C infection enhanced the progression of G1→S phase in the HepG2 cell cycle. The apoptosis index of the Ad-XC, Ad-X, Ad-C group cells was significantly lower than that of the Ad0 and control group cells. Semi-quantitative RT-PCR showed that the expression level of c-myc was the highest in Ad-XC infected cells. Tumor formation was found at the injected site of mice inoculated with Ad-XC-infected LO2 cells, but not in control mice.

CONCLUSION: Ad-XC, Ad-X and Ad-C facilitate the proliferation activity of HepG2 cells and inhibit their apoptosis in vitro. The effect of Ad-XC is significantly stronger than that of Ad-X and Ad-C. Up-regulation of c-myc may be one of the mechanisms underlying the synergism of HBV X and HCV C genes on hepatocarcinogenesis in athymic nude mice.

Cutting the gordian knot-development and biological relevance of hepatitis C virus cell culture systems

Worldwide approximately 180 million people are chronically infected with hepatitis C virus (HCV). HCV isolates exhibit extensive genetic heterogeneity and have been grouped in six genotypes and various subtypes. Additionally, several naturally occurring intergenotypic recombinants have been described. Research on the viral life cycle, efficient therapeutics, and a vaccine has been hampered by the absence of suitable cell culture systems. The first system permitting studies of the full viral life cycle was intrahepatic transfection of RNA transcripts of HCV consensus complementary DNA (cDNA) clones into chimpanzees. However, such full-length clones were not infectious in vitro. The development of the replicon system and HCV pseudo-particles allowed in vitro studies of certain aspects of the viral life cycle, RNA replication, and viral entry, respectively. Identification of the genotype 2 isolate JFH1, which for unknown reasons showed an exceptional replication capability and resulted in formation of infectious viral particles in the human hepatoma cell line Huh7, led in 2005 to the development of the first full viral life cycle in vitro systems. JFH1-based systems now enable in vitro studies of the function of viral proteins, their interaction with each other and host proteins, new antivirals, and neutralizing antibodies in the context of the full viral life cycle. However, several challenges remain, including development of cell culture systems for all major HCV genotypes and identification of other susceptible cell lines.

Hepatitis C virus infection and apoptosis

Apoptosis is central for the control and elimination of viral infections. In chronic hepatitis C virus (HCV) infection, enhanced hepatocyte apoptosis and upregulation of the death inducing ligands CD95/Fas, TRAIL and TNFα occur. Nevertheless, HCV infection persists in the majority of patients. The impact of apoptosis in chronic HCV infection is not well understood. It may be harmful by triggering liver fibrosis, or essential in interferon (IFN) induced HCV elimination. For virtually all HCV proteins, pro- and anti-apoptotic effects have been described, especially for the core and NS5A protein. To date, it is not known which HCV protein affects apoptosis in vivo and whether the infectious virions act pro- or anti-apoptotic. With the availability of an infectious tissue culture system, we now can address pathophysiologically relevant issues. This review focuses on the effect of HCV infection and different HCV proteins on apoptosis and of the corresponding signaling cascades.

Detection of hepatitis C virus core antigen for early diagnosis of hepatitis C virus infection in plasma donor in China

AIM: To evaluate the efficacy of a new hepatitis C virus (HCV) core antigen assay developed in China.

METHODS: After the determination of HCV infection, 49 serial samples were selected from 11 regular plasma donors in 5 different plasma stations. To compare the performance of HCV core antigen detection and HCV PCR, these samples were genotyped, and each specimen was analyzed by ELISA for the detection of HCV core antigen and by qualitative HCV PCR.

RESULTS: Among all of the sequential samples, the original 13 specimens were HCV RNA-negative, and 36 samples were HCV RNA-positive. Twenty-seven samples (75%) were HCV core antigen-positive from these HCV RNA-positive specimens. Conversely, 27 samples (93.1%) were found HCV RNA-positive in HCV core antigen-positive samples. Intervals between HCV RNA and HCV core antigen-positive, as well as between HCV core antigen-positive and HCV antibody-positive were 36.0 and 32.8 d, respectively.

CONCLUSION: This HCV core antigen assay, developed in China, is able to detect much of anti-HCV-negative, HCV RNA-positive preseroconversion window period (PWP) plasma donations.

Hepatitis C virus core protein recruits nucleolar phosphoprotein B23 and coactivator p300 to relieve the repression effect of transcriptional factor YY1 on B23 gene expression

Hepatitis C virus (HCV) core has a pleiotropic effect on various promoters. In this study, we found that the expression of nucleolar phosphoprotein B23 was enhanced in HCV core-expressing cells and, moreover, HCV core interacts directly with the C-terminal end of B23. Using sucrose gradient centrifugation analysis and immunoprecipitation assays, HCV core was found in a large complex containing B23 and its interacting partner transcription factor YY1. Both B23 and HCV core associated with YY1 in the central GA/GK-rich and C-terminal zinc finger domain. These physical interactions between core, B23, and YY1 led to ternary complex formation that was bound to the YY1 response element. In a transient cotransfection experiment, relief of the trans-suppression activity of YY1 on the YY1-response element-driven reporter by core and B23 was found. This is also true when examining the effects of these three constructs on the B23 promoter-driven reporter. Additionally, chromatin immunoprecipitation assays indicated that a transcriptional activation complex consisting of core, together with B23, p300, and YY1, was recruited to the YY1 response element of B23 promoter, and this probably occurred through complex formation between core and these three cellular transcription regulators. This is different from the situation in the absence of core, where YY1 and histone deacetylase 1, but not B23 and p300, were associated on the YY1 element as the transcription repression complex. Together, our results indicate that HCV core can recruit B23 and p300 to relieve the repression effect of YY1 on B23 promoter activity, a property that requires the intrinsic histone acetyltransferase activity of p300. Thus, because these three core-associated cellular transcription regulators have a multitude of cellular interacting proteins and are involved in a versatility of cellular processes, the complex formation described here may partially account for the pleiotropic effects of core protein on gene expression and cellular function in HCV-infected cells.

Interaction between hepatitis B and C viruses in hepatocellular carcinogenesis

Although hepatitis B (HBV) and C viruses (HCV) are, individually, major causes of hepatocellular carcinoma, the interaction, if any, between the carcinogenic effects of the two viruses is uncertain. Equal numbers of published studies have reported no risk interaction or a synergistic risk interaction. These conflicting results are explained by the rarity of concurrent infection with HBV and HCV in individuals without clinically evident liver disease, which severely limits the ability to accurately estimate the hepatocarcinogenic risk of dual infection compared with that of either infection alone. In an attempt to circumvent this difficulty, two meta-analyses have been performed, one based on studies published from a number of countries and the other on studies confined to Chinese patients. Both analyses concluded that a synergistic carcinogenic interaction existed between the two viruses and that the increased risk was super-additive but not multiplicative. If confirmed, this risk interaction will occur against a background of negative confounding effects on viral replication between HBV and HCV, which may be reciprocal. The mechanisms responsible for the carcinogenic interaction between the viruses are unknown. One possibility is that the increased incidence of cirrhosis with concurrent HBV and HCV infections acts as an even more potent tumour promoter than occurs with either virus alone. Synergism between the direct hepatocarcinogenic effects of the two viruses is another possible mechanism, but proof will have to await a fuller understanding of the pathogenetic mechanisms involved with the individual viruses.

Is an assay for simultaneous detection of hepatitis C virus core antigen and antibody a valuable alternative to nucleic acid testing?

BACKGROUND

A new enzyme immunoassay based on the simultaneous detection of nucleocapsid proteins of hepatitis C virus (HCV) and anti-HCV (Monolisa HCV antigen-antibody Ultra, Bio-Rad) was evaluated as an alternative to nucleic acid testing (NAT) for the diagnosis of HCV infection during the window period in blood donations.

STUDY DESIGN AND METHODS

The study included 107 sequential samples from 10 HCV seroconversion commercial panels; 81 samples were in the preseroconversion phase, and 26 were collected after seroconversion. All samples were tested with HCV antigen-antibody assay and the two minipool (MP) NAT procedures that are routinely used in France (transcription-mediated amplification in pools of 8 and COBAS AmpliScreen HCV test [Roche Diagnostic] in pools of 24 donations).

RESULTS

From the 44 samples collected during window period that were MP-NAT-positive, 31 (70.5%) were also positive with the Monolisa HCV antigen-antibody assay. The mean delay in detecting HCV infection between these two methods was 5.1 days (range, 0-24 days). The Monolisa HCV antigen-antibody assay led to a reduction in the window period of 26.8 days (range, 0-72 days). All samples collected after seroconversion were detected with the HCV antigen-antibody assay. The specificity analyzed in 2503 consecutive blood donations was estimated at 99.88 percent.

CONCLUSION

This new developed assay presents an improvement for the detection of HCV infection, especially in the early phase of infection when antibodies are undetectable. Although less sensitive than NAT, this assay could be a suitable solution for blood screening in developing countries where NAT (or HCV core antigen-specific assay) is not affordable or its implementation is not feasible.

Hepatitis C virus core variants isolated from liver tumor but not from adjacent non-tumor tissue interact with Smad3 and inhibit the TGF-beta pathway

Hepatitis C virus (HCV) is a major risk factor for human hepatocellular carcinoma (HCC) but the mechanisms underlying HCV-induced carcinogenesis are still poorly understood. We have hypothesized that viral variants, selected during long-term infection, might contribute to cellular transformation. To address this issue, we have investigated the effect of natural HCV core variants isolated from liver tumors (T), or their non-tumor (NT) counterparts, on the tumor growth factor-beta (TGF-beta) pathway, a major regulator of cellular proliferation, differentiation and apoptosis. We have found a significant reduction in TGF-beta reporter gene activity with the expression of core sequences isolated from liver tumors. In contrast, moderate or no effects were observed with non-tumor mutants or a core reference sequence. The molecular mechanisms have been characterized and involved the inhibition, by tumor-derived cores, of the DNA-binding activity of the Smad3/4 transcription factors complex. This inhibition occurs through a direct interaction between the central domain (amino acids 59-126) of tumor-derived core and the MH1 DNA-binding domain of Smad3, thus preventing its binding to DNA. We have therefore identified a new cell-signaling pathway targeted by HCV core and inhibited by tumor-derived core sequences. These results suggest that during chronic infection, there is selection of viral variants that may promote cell transformation by providing, to clonally expanding cells, resistance to TGF-beta antiproliferative effects.

Proteomic profiling of cellular proteins interacting with the hepatitis C virus core protein

Hepatitis C virus (HCV) is a causative agent of chronic hepatitis and hepatocellular carcinoma. The core protein of HCV packages the viral RNA genome to form a nucleocapsid. In addition to its function as a structural protein, core protein is involved in regulation of cellular transcription, virus-induced transformation, and pathogenesis. To gain insights into cellular functions of the core protein by identification of cellular proteins interacting with the core protein, we employed a proteomic approach. Hepatocytes soluble cytoplasmic proteins were applied to the core proteins immobilized on Ni-nitrilotriacetic resin and total bound cellular proteins were resolved by 2-DE. Analyses of interacting proteins by matrix-assisted laser desorption/ionization-time of flight mass spectrometry allowed identification of 14 cellular proteins binding to the core protein. These proteins include DEAD-box polypeptide 5, similar in function to a known protein identified previously by yeast two-hybrid screening and 13 newly identified cellular proteins. Interestingly, nine protein spots were identified as intermediate microfilament proteins, including cytokeratins (five spots for cytokeratin 8, two for cytokeratin 19, and one for cytokeratin 18) and vimentin. Cytokeratin 8 and vimentin, which were previously shown to be involved in the infection processes of other viruses, were further analyzed to confirm their in vivo interactions with the core protein by immunoblotting and immunofluorescence microscopy. We discuss the functional implications of the interactions of the core protein with newly identified cellular proteins in HCV infection and pathogenesis.

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 assay using total hepatitis C virus (HCV) core antigen quantification for diagnosis of HCV infection in dialysis patients

Dialysis patients remain a high-risk group for hepatitis C virus (HCV) infection. The current diagnosis of HCV infection among dialysis patients includes serological assays and nucleic acid amplification technology (NAT) for assessing serum anti-HCV antibody and HCV viremia, respectively. However, current NAT techniques are expensive and labor-intensive and often lack standardization. An assay prototype designed to detect and quantify total HCV core antigen (total HCV core Ag) protein in serum and plasma in the presence or absence of anti-HCV antibodies has been recently developed. A comparison between a total anti-HCV core Ag enzyme-linked immunosorbent assay (ELISA) and a quantitative HCV RNA assay based on reverse transcription-PCR (RT-PCR) (Amplicor HCV Monitor test) was performed using a large (n = 305) cohort of ELISA HCV 3.0 HCV-negative and -positive patients on maintenance dialysis. The concentrations of HCV core Ag and HCV RNA levels (measured by RT-PCR) were significantly correlated (r = 0.471, P = 0.0001) over a wide range of HCV RNA levels and were maintained among different HCV genotypes (HCV genotype 1, r = 0.862, P = 0.0001; HCV genotype 2, r = 0.691, P = 0.0001). We estimated that 1 pg of total HCV core Ag per ml is equivalent to approximately 19.952 IU of HCV RNA per ml, even if the wide range in the ratio of core Ag to HCV RNA (95% confidence intervals, 2.8 x 10(3) to 1.6 x 10(5) IU/ml) precluded definitive conclusions. In summary, total HCV core Ag proved to be useful for performing HCV RNA measurement among dialysis patients in routine laboratories without the need for special equipment or training. The present study supports the use of the total anti-HCV core Ag ELISA for assessing viral load among dialysis patients with HCV infection.

Hepatitis C viral proteins interact with Smad3 and differentially regulate TGF-beta/Smad3-mediated transcriptional activation

Transforming growth factor-beta (TGF-beta) is a pleiotropic cytokine implicated as a pathogenic mediator in various liver diseases. Enhanced TGF-beta production and lack of TGF-beta responses are often observed during hepatitis C virus (HCV) infection. In this study, we demonstrate that TGF-beta-mediated transactivation is decreased in cells exogenously expressing the intact HCV polyprotein. Among 10 viral products of HCV, only core and nonstructural protein 3 (NS3) physically interact with the MH1 (Mad homology 1) region of the Smad3 and block TGF-beta/Smad3-mediated transcriptional activation through interference with the DNA-binding ability of Smad3, not the nuclear translocation. However, the interactive domain of NS3 extends to the MH2 (Mad homology 2) region of Smad3 and a distinction is found between effects mediated, respectively, by these two viral proteins. HCV core, in the presence or absence of TGF-beta, has a stronger suppressive effect on the DNA-binding and transactivation ability of Smad3 than NS3. Although HCV core, NS3, and the HCV subgenomic replicon all attenuate TGF-beta/Smad3-mediated apoptosis, only HCV core represses TGF-beta-induced G1 phase arrest through downregulation of the TGF-beta-induced p21 promoter activation. Along with this, HCV core, rather than NS3, exhibits a significant inhibitory effect on the binding of Smad3/Sp1 complex to the proximal p21 promoter in response to TGF-beta. In conclusion, HCV viral proteins interact with the TGF-beta signaling mediator Smad3 and differentially impair TGF-beta/Smad3-mediated transactivation and growth inhibition. This functional counteraction of TGF-beta responses provides insights into possible mechanisms, whereby the HCV oncogenic proteins antagonize the host defenses during hepatocarcinogenesis.

Membrane binding properties and terminal residues of the mature hepatitis C virus capsid protein in insect cells

The immature core protein (p23, residues 1 to 191) of hepatitis C virus undergoes posttranslational modifications including intramembranous proteolysis within its C-terminal signal sequence by signal peptide peptidase to generate the mature form (p21). In this study, we analyzed the cleavage site and other amino acid modifications that occur on the core protein. To produce the posttranslationally modified core protein, we used a baculovirus-insect cell expression model system. As previously reported, p23 is processed to form p21 in insect as well as in mammalian cells. p21 was found to be associated with the cytoplasmic membrane, and its significant portion behaved as an integral membrane protein. The protein was purified from the membrane by a simple and unique procedure on the basis of its membrane-binding properties and solubility in detergents. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of purified p21 showed that the average molecular mass (m/z 19,307) of its single-charged ion differs by m/z 1,457 from that calculated for p23. To determine the posttranslational modifications, tryptic p21 peptides were analyzed by MALDI-TOF MS. We found three peptides that did not match the theoretically derived peptides of p23. Analysis of these peptides by MALDI-TOF tandem MS revealed that they correspond to N-terminal peptides (residues 2 to 9 and 2 to 10) starting with alpha-N-acetylserine and C-terminal peptide (residues 150 to 177) ending with phenylalanine. These results suggest that the mature core protein (molecular mass of 19,306 Da) includes residues 2 to 177 and that its N terminus is blocked with an acetyl group.

Enhanced apoptosis of peripheral CD5-negative B lymphocytes from chronically hepatitis C virus-infected patients: reversal after antiviral treatment

Whereas enhanced peripheral T-cell apoptosis and its association with autoimmunity have recently been reported, the apoptotic status of peripheral B cells in chronic hepatitis C virus (HCV) infection remains ambiguous. We therefore sought to investigate the sensitivity of peripheral B cells to apoptosis and to assess the possible benefits of antiviral treatment in mitigating these effects. Spontaneous apoptosis, the extent of apoptosis rescue, and NF-kappaB expression in peripheral B cells were studied in patients with chronic HCV infections (group 1), in sustained responders after antiviral treatment (group 2), and in healthy controls (group 3). For group 1, spontaneous B-cell apoptosis was increased (26% +/- 4.6%) and apoptosis rescue was altered (39%) compared to group 3 (18% +/- 5% and 50%, respectively; P = 0.001). In contrast, apoptosis and apoptosis rescue were similar for groups 2 and 3. Enhanced B-cell apoptosis was associated with decreased NF-kappaB expression and was found only in CD5-negative (CD5(neg)) B cells, whereas CD5(pos) cells were apoptosis resistant. Chronic HCV infection is associated with enhanced peripheral B-cell apoptosis and decreased apoptosis rescue. Successful antiviral treatment reverses these abnormalities to the levels seen in healthy individuals. The relative resistance of the CD5(pos) B-cell subpopulation to apoptosis may play a role in HCV-related autoimmunity and lymphoproliferation.

Modulation of p53 transcription regulatory activity and post-translational modification by hepatitis C virus core protein

Oncogenic virus proteins often target to tumor suppressor p53 during virus life cycle. In the case of hepatitis C virus (HCV) core protein, it has been shown to affect p53-dependent transcription. Here, we further characterized the in vitro and in vivo interactions between HCV core protein and p53 and showed that these two proteins colocalized in subnuclear granular structures and the perinuclear area. By use of a reporter assay, we observed that while low level of HCV core protein enhanced the transactivational activity of p53, high level of HCV core protein inhibited this activity. In both cases, however, HCV core protein increased the p53 DNA-binding affinity in gel retardation analyses, likely due to the hyperacetylation of p53 Lys(373) and Lys(382) residues. Additionally, HCV core protein, depending on its expression level, had differential effects on the Ser(15) phosphorylation of p53. Moreover, HCV core protein could rescue p53-mediated suppressive effects on both RNA polymerase I and III transcriptions. Collectively, our results indicate that HCV core protein targets to p53 pathway via at least three means: physical interaction, modulation of p53 gene regulatory activity and post-translational modification. This feature of HCV core protein, may potentially contribute to the HCV-associated pathogenesis.

Domain I of nucleocapsid protein of murine hepatitis virus strain 3 upregulates transcription of mfgl2 prothrimbinase/fibroleukin gene

AIM: To investigate the responsible domain(s) of N protein and the I gene within the N gene of MHV-3 or MHV-A59 in the activation of mfgl2.

METHODS: To investigate the responsible domain(s) of N protein of MHV-3 or MHV-A59 in the activation of fgl2 gene, four ways comparison of the N protein was carried out and the site directed mutated N gene expression constructs within domain I and domain III were cotransfected respectively with mfgl2 promoter/luciferase reporter gene in CHO cells. Macrophages from Balb/cJ mice were infected with I gene mutated MHV virus Alb110 and its isogenic Alb111 for 8-10 hours, procoagulant activity (PCA) were measured. MHV-A59 I gene expression construct was cotransfected with mfgl2 promoter-reporter gene in Chinese hamster ovary (CHO) cells, and luciferase activity was detected for the assessment of promoter function.

RESULTS: Mutations of residues Gly-12, Pro-38, Asn-40, Gln-41 and Asn42 within domain I of the N protein of MHV-A59 to their corresponding residues were found in MHV-2 abrogated mfgl2 transcription, whereas mutation of other N protein domain III did not affect mfgl2 gene transcription. Alb 110 and Alb 111 infected macrophages showed a remarkable increasing in PCA activity compared with no virus or MHV-2 or MHV-JHM infected macrophages. There was no significant difference in PCA activity between Alb 110, Alb 111 infected group and MHV-A59 group. Cotransfection I gene expression construct with a reporter construct containing mfgl2 promoter in CHO cells displayed no significant difference in luciferase activity compared with nontransfected CHO cells.

CONCLUSION: Domain I of nucleocapsid protein of murine hepatitis virus strain 3 upregulates the transcription of mfgl2 prothrimbinase/fibroleukin gene. The MHV-A59 I gene is not essential for activation of mfgl2 gene. Our study may shed lights on the investigation of current worldwide-distributed disease, severe acute respiratory syndrome (SARS).

Induction of FAS ligand expression in a human hepatoblastoma cell line by HCV core protein

Tumour cells and virus infected cells expressing Fas ligand (FasL) can evade immune surveillance by inducing apoptosis in T cells expressing Fas. In order to characterise a possible role of hepatitis C virus (HCV) core protein in similar mechanisms during HCV infection, we investigated Fas ligand expression and activity in a human hepatoblastoma cell line (HepG2) constitutively expressing this protein. Strong FasL induction was detected by immunoblotting and flow cytometry analysis in the core expressing cell lines Hep39. In contrast, vector transfected cells or cell lines expressing HCV E1-E2 proteins did not show FasL expression. Co-cultivation experiments of Hep39 cells with a Fas-sensitive T cell line indicated that FasL induced by the core protein had apoptotic activity toward target cells. Effect of the core protein on induction of FasL promoter was further examined by co-transfection of HepG2 cells with core-bearing plasmid and a vector in which luciferase gene expression is driven by human FasL promoter. Results of the luciferase assay indicated a positive regulation of FasL promoter by the core protein. In conclusion, HCV core protein plays a role in the induction of functional FasL in hepatoblastoma cell line and apoptosis in a target T cell line expressing Fas. Similar mechanisms may contribute, in vivo, to establishment of chronic infection and development of hepatocellular carcinoma (HCC).

Structural biology of hepatitis C virus

Hepatitis C virus (HCV) causes acute and chronic liver disease in humans, including chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Studies of this virus have been hampered by the lack of a productive cell culture system; most information thus has been obtained from analysis of the HCV genome, heterologous expression systems, in vitro and in vivo models, and structural analyses. Structural analyses of HCV components provide an essential framework for understanding of the molecular mechanisms of HCV polyprotein processing, RNA replication, and virion assembly and may contribute to a better understanding of the pathogenesis of hepatitis C. Moreover, these analyses should allow the identification of novel targets for antiviral intervention and development of new strategies to prevent and combat viral hepatitis. This article reviews the current knowledge of HCV structural biology.

Alcohol and hepatitis C virus core protein additively increase lipid peroxidation and synergistically trigger hepatic cytokine expression in a transgenic mouse model

BACKGROUND/AIMS

Alcohol consumption accelerates the appearance of liver fibrosis and hepatocellular carcinoma in patients with chronic hepatitis C virus (HCV) infection, but the mechanisms of these interactions are unknown. We therefore investigated the effects of chronic ethanol consumption in HCV core protein-expressing transgenic mice.

METHODS

Ethanol was progressively added (up to 20%) to the drinking water that was given ad libidum.

RESULTS

In vivo fatty acid oxidation was not inhibited by ethanol consumption and/or HCV core expression. Both chronic ethanol consumption and HCV core expression decreased hepatic lipoprotein secretion and caused steatosis, but had no additive effects on lipoprotein secretion or steatosis. However, chronic ethanol consumption and HCV core protein additively increased lipid peroxidation and acted synergistically to increase the hepatic expression of transforming growth factor-beta (TGF-beta) and, to a less extent, tumor necrosis factor-alpha (TNF-alpha).

CONCLUSIONS

HCV core protein expression and chronic alcohol consumption have no effects on in vivo fatty acid oxidation and do not additively impair hepatic lipoprotein secretion, but additively increase hepatic lipid peroxidation and synergistically increase hepatic TNF-alpha and TGF-beta expression. These effects may be involved in the activation of fibrogenesis and the development of hepatocellular carcinoma in patients cumulating alcohol abuse and HCV infection.

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.

Triple decoding of hepatitis C virus RNA by programmed translational frameshifting

Ribosomes can be programmed to shift from one reading frame to another during translation. Hepatitis C virus (HCV) uses such a mechanism to produce F protein from the -2/+1 reading frame. We now report that the HCV frameshift signal can mediate the synthesis of the core protein of the zero frame, the F protein of the -2/+1 frame, and a 1.5-kDa protein of the -1/+2 frame. This triple decoding function does not require sequences flanking the frameshift signal and is apparently independent of membranes and the synthesis of the HCV polyprotein. Two consensus -1 frameshift sequences in the HCV type 1 frameshift signal facilitate ribosomal frameshifts into both overlapping reading frames. A sequence which is located immediately downstream of the frameshift signal and has the potential to form a double stem-loop structure can significantly enhance translational frameshifting in the presence of the peptidyl-transferase inhibitor puromycin. Based on these results, a model is proposed to explain the triple decoding activities of the HCV ribosomal frameshift signal.

Structural biology of hepatitis C virus

Structural analyses of hepatitis C virus (HCV) components provide an essential framework for understanding the molecular mechanisms of HCV polyprotein processing, RNA replication, and virion assembly. They are central, moreover, to the elucidation of interactions of HCV proteins with the host cell and may contribute to a better understanding of the pathogenesis of hepatitis C. Ultimately, these analyses should allow for identifying novel targets for antiviral intervention and for developing new strategies to prevent and combat viral hepatitis.

Hepatitis C virus--cell interactions and their role in pathogenesis

In summary, HCV-cell interactions include those directly involved with the HCV life cycle such as virus attachment, entry, and replication. Included within this broad area of research are the interactions of HCV proteins with the IFN system, cytokine and chemokine pathways such as IL-8, and various other cellular proteins and pathways. The plethora of contradictory and sometimes confusing accessory HCV-host interactions defies precise predictions of their role in HCV biology. It is clear that these virus-cell interactions affect HCV replication, antiviral resistance, persistence, and pathogenesis. Because HCV-host interactions are initiated immediately on infection, they are operative during acute HCV infection, whereby HCV interacts with innate cellular antiviral and immune systems. The magnitude and duration of these HCV-host interactions therefore may influence the development of acquired immunity. Because HCV exists as a quasispecies in all infected individuals, heterogeneity in biological responses to HCV-host interactions is predicted, revealing opportunities for the development of various genotypic and phenotypic prognostic indicators. With the model systems in place, these hypotheses can be tested. The challenge for the future is to determine if there is a hierarchical importance to these interactions, to delineate how these virus-cell interactions affect the patient infected with HCV, and to determine whether any of these interactions represents a target for therapeutic intervention.

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.

Lack of in vivo blockade of Fas- and TNFR1-mediated hepatocyte apoptosis by the hepatitis C virus

In vitro data have shown that the hepatitis C virus (HCV) core protein binds to protein members of the tumour necrosis factor receptor (TNFR) superfamily. Since this interaction could be relevant to HCV persistence and oncogenesis, this study assessed whether HCV may interfere with the apoptotic cascade in vivo. Apoptosis (by TUNEL) and Fas and TNFR1 expression (by immunohistochemistry) were scored in the liver of 60 chronic hepatitis C patients. Results were compared with the liver disease grading and staging scores and the HCV replication level in serum and liver. Apoptotic hepatocytes were stained in 29 cases. Fas was expressed in 35 cases and TNFR1 in 21, 15 patients (25%) being negative for both receptors. Overall, the numbers of TUNEL-, Fas- and TNFR-positive hepatocytes did not correlate with the extent of intrahepatic CD8+ T-lymphocyte infiltration, the grading and staging of liver disease, or the serum or liver HCV RNA levels. Furthermore, when patients expressing either Fas or TNFR1 were stratified according to serum HCV RNA levels, cases with detectable hepatocyte apoptosis had higher HCV viraemias. In conclusion, an HCV-mediated, in vivo blockade of hepatocyte apoptosis via the Fas- or TNFR1-dependent pathways seems unlikely.

Clinical utility of total HCV core antigen quantification: a new indirect marker of HCV replication

Hepatitis C virus (HCV) RNA detection, viral load quantification, and HCV genotyping are widely used in clinical practice. Recently, the availability of an anticore antigen (Ag) monoclonal antibody allowed development of an enzyme-linked immunosorbent assay (ELISA) detecting and quantifying total HCV core Ag in peripheral blood of HCV-infected patients. The aims of the present study were to investigate the biologic significance of this new marker in HCV infection, to establish the intrinsic performance of the current assay, and to determine its potential utility in the management of HCV-infected patients. A panel of infected sera calibrated to the World Health Organization International Standard and 657 serum samples from infected patients receiving antiviral treatment were studied. We showed that total HCV core Ag quantification is an accurate, precise, and specific indirect marker of HCV replication. We estimated that 1 pg/mL of total HCV core Ag is equivalent to approximately 8,000 HCV RNA international units (IU)/mL, although minor between-patient differences may exist. In conclusion, total HCV core Ag quantification can be used in the various indications of viral load monitoring, including the evaluation of baseline viral load before therapy, the assessment of the virologic response to antiviral treatment, and the study of early viral kinetics during therapy. Nevertheless, the total HCV core Ag assay cannot be used as a marker of viral replication for HCV RNA values below 20,000 IU/mL, limiting its use in the monitoring of late events during and after antiviral treatment.

Hepatitis C virus core protein inhibits microsomal triglyceride transfer protein activity and very low density lipoprotein secretion: a model of viral-related steatosis

Liver steatosis, which involves accumulation of intracytoplasmic lipid droplets, is characteristic of hepatitis C virus (HCV) infection. By use of an in vivo transgenic murine model, we demonstrate that hepatic overexpression of HCV core protein interferes with the hepatic assembly and secretion of triglyceride-rich very low density lipoproteins (VLDL). Core expression led to reduction in microsomal triglyceride transfer protein (MTP) activity and in the particle size of nascent hepatic VLDL without affecting accumulation of MTP and protein disulfide isomerase. Hepatic human apolipoprotein AII (apo AII) expression in double-core/apo AII transgenic mice diminished intrahepatic core protein accumulation and abrogated its effects on VLDL production. Apo AII and HCV core colocalized in human HCV-infected liver biopsies, thus testifying to the relevance of this interaction in productive HCV infection. Our results lead us to propose a new pathophysiological animal model for induction of viral-related steatosis whereby the core protein of HCV targets microsomal triglyceride transfer protein activity and modifies hepatic VLDL assembly and secretion.

Enhanced peripheral T-cell apoptosis in chronic hepatitis C virus infection: association with liver disease severity

BACKGROUND/AIMS

It has been suggested that enhanced T-cell apoptosis in hepatitis C virus (HCV) infection may lead to down-regulation of their cellular immune response, thus contributing to the persistency of HCV infection. In the present study we have investigated the role of bcl-2 and nuclear factor kappa B (NFkappaB) in dexamethasone-induced apoptosis of peripheral T cells in chronic HCV infection.

METHODS

The expression of bcl-2 and NFkappaB in peripheral T cells as well as spontaneous and dexamethasone-induced T-cell apoptosis were studied in HCV-infected patients (n=21), hepatitis B virus (HBV)-infected patients (n=14) and healthy individuals (n=19). These parameters were correlated with markers of autoimmunity and disease severity.

RESULTS

NFkappaB, but not bcl-2 expression, was significantly decreased in the HCV-infected patients. This decrease was associated with the presence of mixed cryoglobulins (MC) and rheumatoid factor and was positively correlated with alanine aminotransferase (ALT) levels and histological activity index (HAI). Both spontaneous and dexamethasone-induced T-cell apoptosis were enhanced in HCV-infected patients; however, only the latter was correlated with the presence of MC, ALT levels and HAI.

CONCLUSIONS

We confirm previous reports that enhanced T-cell apoptosis in HCV infection may play an important role in disease severity. Decreased expression of NFkappaB is important in the development of peripheral T-cell apoptosis, thus contributing to viral persistence and autoimmunity in these patients.

Recent advances in the molecular biology of hepatitis C virus

The Hepatitis C virus is a positive-stranded RNA virus which is the causal agent for a chronic liver infection afflicting more than 170,000,000 people world-wide. The HCV genome is approximately 9.6 kb in length and the proteome encoded is a polyprotein of a little more than 3000 amino acid residues. This polyprotein is processed by a combination of host and viral proteases into structural and non-structural proteins. The functions of most of these proteins have been established by analogy to other viruses and by sequence homology to known proteins, as well as subsequent biochemical analysis. Two of the non-structural proteins, NS4b and NS5a, are still of unknown function. The development of antivirals for this infectious agent has been hampered by the lack of robust and economical cell culture and animal infection systems. Recent progress in the molecular virology of HCV has come about due to the definition of molecular clones, which are infectious in the chimpanzee, the development of a subgenomic replicon system in Huh7 cells, and the description of a transgenic mouse model for HCV infection. Recent progress in the structural biology of the virus has led to the determination of high resolution three-dimensional structures of a number of the key virally encoded enzymes, including the NS3 protease, NS3 helicase, and NS5b RNA-dependent RNA polymerase. In some cases these structures have been determined in complex with substrates, co-factors (NS4a), and inhibitors. Finally, a variety of techniques have been used to define host factors, which may be required for HCV replication, although this work is just beginning.

Activation of the interferon-inducible protein kinase PKR by hepatocellular carcinoma derived-hepatitis C virus core protein

Hepatitis C virus (HCV) is a major etiological agent of chronic liver disease and hepatocellular carcinoma (HCC). We demonstrate herewith that HCV core proteins encoded by sequences isolated from HCC tumor tissues, but not those derived from their non-tumor counterparts in the same liver, co-localise in vitro and in vivo and co-immunoprecipitate with PKR in hepatocytic Huh7 cells. We show that this association in fact augments the autophosphorylation of PKR and the phosphorylation of the translation initiation factor eIF2alpha, which are two markers of PKR activity. The present study therefore identifies a novel model of virus-cell interactions whereby a viral protein, the HCV core, activates PKR activity.

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.