Differential activation of interferon-inducible genes by hepatitis C virus core protein mediated by the interferon stimulated response element

Hepatitis C virus NS5B triggers an MDA5-mediated innate immune response by producing dsRNA without the replication of viral genomes

During the replication of viral genomes, RNA viruses produce double-stranded RNA (dsRNA), through the activity of their RNA-dependent RNA polymerases (RdRps) as viral replication intermediates. Recognition of viral dsRNA by host pattern recognition receptors - such as retinoic acid-induced gene-I (RIG-I)-like receptors and Toll-like receptor 3 - triggers the production of interferon (IFN)-β via the activation of IFN regulatory factor (IRF)-3. It has been proposed that, during the replication of viral genomes, each of RIG-I and melanoma differentiation-associated gene 5 (MDA5) form homodimers for the efficient activation of a downstream signalling pathway in host cells. We previously reported that, in the non-neoplastic human hepatocyte line PH5CH8, the RdRp NS5B derived from hepatitis C virus (HCV) could induce IFN-β expression by its RdRp activity without the actual replication of viral genomes. However, the exact mechanism by which HCV NS5B produced IFN-β remained unknown. In the present study, we first showed that NS5B derived from another Flaviviridae family member, GB virus B (GBV-B), also possessed the ability to induce IFN-β in PH5CH8 cells. Similarly, HCV NS5B, but not its G317V mutant, which lacks RdRp activity, induced the dimerization of MDA5 and subsequently the activation of IRF-3. Interestingly, immunofluorescence analysis showed that HCV NS5B produced dsRNA. Like HCV NS5B, GBV-B NS5B also triggered the production of dsRNA and subsequently the dimerization of MDA5. Taken together, our results show that HCV NS5B triggers an MDA5-mediated innate immune response by producing dsRNA without the replication of viral genomes in human hepatocytes.

Antiviral mechanism of preclinical antimalarial compounds possessing multiple antiviral activities

We previously found that N‐89 and its derivative, N‐251, which are being developed as antimalarial compounds, showed multiple antiviral activities including hepatitis C virus (HCV). In this study, we focused on the most characterized anti‐HCV activity of N‐89(N‐251) to clarify their antiviral mechanisms. We first prepared cells exhibiting resistance to N‐89(N‐251) than the parental cells by serial treatment of HCV–RNA‐replicating parental cells with N‐89(N‐251). Then, we newly generated HCV–RNA‐replicating cells with the replacement of HCV–RNAs derived from N‐89(N‐251)‐resistant cells and parental cells. Using these cells, we examined the degree of inhibition of HCV–RNA replication by N‐89(N‐251) and found that the host and viral factors contributed almost equally to the resistance to N‐89(N‐251). To further examine the contribution of the host factors, we selected several candidate genes by cDNA microarray analysis and found that the upregulated expression of at least RAC2 and CKMT1B genes independently and differently contributed to the acquisition of an N‐89(N‐251)‐resistant phenotype. For the viral factors, we selected several mutation candidates by the genetic comparative analysis of HCV–RNAs and showed that at least one M414I mutation in the HCV NS5B contributed to the resistance to N‐89. Moreover, we demonstrated that the combination of host factors (RAC2 and/or CKMT1B) and a viral factor (M414I mutation) additively increased the resistance to N‐89. In summary, we identified the host and viral factors contributing to the acquisition of N‐89(N‐251)‐resistance in HCV–RNA replication. These findings will be useful for clarification of the antiviral mechanism of N‐89(N‐251).

Genotypic Regulation of Type I Interferon Induction Pathways by Frameshift (F) Proteins of Hepatitis C Virus

Hepatitis C virus (HCV) has evolved mechanisms to evade innate immunity that are leading to chronic infections. The immunological function of the HCV frameshift (F) protein, which is a frameshift product of core coding sequences, has not been well characterized. The HCV F protein is produced during natural HCV infections and is found most commonly in genotype 1 HCV. In this study, we investigated whether the F protein plays a role in type I interferon (IFN) induction pathways. We engineered F expression constructs from core coding sequences of 4 genotypes (1a, 2a, 3a, and 4a) of HCV as well as the sequences which would only be able to produce core proteins. The peptide lengths and amino acids sequences of F proteins are highly variable. We hypothesized that F proteins from different genotypes might control the type I IFN production and response differently. We found that both IFN-beta (IFN-β) promoter activities are significantly higher in genotype 1a F protein (F1a)-expressing cells. Conversely, the IFN-β promoter activities are lower in genotype 2a F (F2a) protein-expressing cells. We also used real-time PCR to confirm IFN-β mRNA expression levels. By generating chimera F proteins, we discovered that the effects of F proteins were determined by the amino acid sequence 40 to 57 of genotype 1a. The regulation of type I IFN induction pathway is related but not limited to the activity of F1a to interact with proteasome subunits and to disturb the proteasome activity. Further molecular mechanisms of how F proteins from different genotypes of HCV control these pathways differently remain to be investigated.IMPORTANCE Although naturally present in HCV infection patient serum, the virological or immunological functions of the HCV F protein, which is a frameshift product of core coding sequences, remain unclear. Here, we report the effects of the HCV F protein between genotypes and discuss a potential explanation for the differential responses to type I IFN-based therapy among patients infected with different genotypes of HCV. Our study provides one step forward to understanding the host response during HCV infection and new insights for the prediction of the outcome of IFN-based therapy in HCV patients.

High-level expression of STING restricts susceptibility to HBV by mediating type III IFN induction

Hepatitis B virus (HBV) is a hepatotropic DNA virus causing hepatic diseases such as chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. To study HBV, human hepatoma HepG2 cells are currently used as an HBV infectious cell culture model worldwide. HepG2 cells exhibit susceptibility to HBV by exogenously expressing sodium taurocholate cotransporting polypeptide (NTCP). We herein demonstrated that human immortalized hepatocyte NKNT-3 cells exhibited susceptibility to HBV by exogenously expressing NTCP (NKNT-3/NTCP cells). By comparing cyclic GMP-AMP synthetase (cGAS)-stimulator of interferon genes (STING) signaling pathway in several NKNT-3/NTCP cell-derived cell clones, we found that STING was highly expressed in cell clones exhibiting resistance but not susceptibility to HBV. High-level expression of STING was implicated in HBV-triggered induction of type III IFN and a pro-inflammatory cytokine, IL-6. In contrast, RNAi-mediated knockdown of STING inhibited type III IFN induction and restored the levels of HBV total transcript in an HBV-infected cell clone exhibiting resistance to HBV. These results suggest that STING regulates susceptibility to HBV by its expression levels. STING may thus be a novel target for anti-HBV strategies.

The cyclic GMP-AMP synthetase-STING signaling pathway is required for both the innate immune response against HBV and the suppression of HBV assembly

During viral replication, the innate immune response is induced through the recognition of viral replication intermediates by host factor(s). One of these host factors, cyclic GMP-AMP synthetase (cGAS), was recently reported to be involved in the recognition of viral DNA derived from DNA viruses. However, it is uncertain whether cGAS is involved in the recognition of hepatitis B virus (HBV), which is a hepatotropic DNA virus. In the present study, we demonstrated that HBV genome-derived double-stranded DNA induced the innate immune response through cGAS and its adaptor protein, stimulator of interferon genes (STING), in human hepatoma Li23 cells expressing high levels of cGAS. In addition, we demonstrated that HBV infection induced ISG56 through the cGAS-STING signaling pathway. This signaling pathway also showed an antiviral response towards HBV through the suppression of viral assembly. From these results, we conclude that the cGAS-STING signaling pathway is required for not only the innate immune response against HBV but also the suppression of HBV assembly. The cGAS-STING signaling pathway may thus be a novel target for anti-HBV strategies.

Rab18 is required for viral assembly of hepatitis C virus through trafficking of the core protein to lipid droplets

During persistent infection of HCV, the HCV core protein (HCV-JFH-1 strain of genotype 2a) is recruited to lipid droplets (LDs) for viral assembly, but the mechanism of recruitment of the HCV core protein is uncertain. Here, we demonstrated that one of the Ras-related small GTPases, Rab18, was required for trafficking of the core protein around LDs. The knockdown of Rab18 reduced intracellular and extracellular viral infectivity, but not intracellular viral replication in HCV-JFH-1-infected RSc cells (an HuH-7-derived cell line). Exogenous expression of Rab18 increased extracellular viral infectivity almost two-fold. Furthermore, Rab18 was co-localized with the core protein in HCV-JFH-1-infected RSc cells, and the knockdown of Rab18 blocked recruitment of the HCV-JFH-1 core protein to LDs. These results suggest that Rab18 has an important role in viral assembly through the trafficking of the core protein to LDs.

Adenosine kinase is a key determinant for the anti-HCV activity of ribavirin

Ribavirin (RBV) is often used in conjunction with interferon-based therapy for patients with chronic hepatitis C. There is a drastic difference in the anti-hepatitis C virus (HCV) activity of RBV between the HuH-7-derived assay system, OR6, possessing the RBV-resistant phenotype (50% effective concentration [EC50 ]: >100 µM) and the recently discovered Li23-derived assay system, ORL8, possessing the RBV-sensitive phenotype (EC50 : 8 µM; clinically achievable concentration). This is because the anti-HCV activity of RBV was mediated by the inhibition of inosine monophosphate dehydrogenase in RBV-sensitive ORL8 cells harboring HCV RNA. By means of comparative analyses using RBV-resistant OR6 cells and RBV-sensitive ORL8 cells, we tried to identify host factor(s) determining the anti-HCV activity of RBV. We found that the expression of adenosine kinase (ADK) in ORL8 cells was significantly higher than that in RBV-resistant OR6 cells harboring HCV RNA. Ectopic ADK expression in OR6 cells converted them from an RBV-resistant to an RBV-sensitive phenotype, and inhibition of ADK abolished the activity of RBV. We showed that the differential ADK expression between ORL8 and OR6 cells was not the result of genetic polymorphisms in the ADK gene promoter region and was not mediated by a microRNA control mechanism. We found that the 5' untranslated region (UTR) of ADK messenger RNA in ORL8 cells was longer than that in OR6 cells, and that only a long 5' UTR possessed internal ribosome entry site (IRES) activity. Finally, we demonstrated that the long 5' UTR functioned as an IRES in primary human hepatocytes.

CONCLUSION

These results indicate that ADK acts as a determinant for the activity of RBV and provide new insight into the molecular mechanism underlying differential drug sensitivity.

Class A scavenger receptor 1 (MSR1) restricts hepatitis C virus replication by mediating toll-like receptor 3 recognition of viral RNAs produced in neighboring cells

Persistent infections with hepatitis C virus (HCV) may result in life-threatening liver disease, including cirrhosis and cancer, and impose an important burden on human health. Understanding how the virus is capable of achieving persistence in the majority of those infected is thus an important goal. Although HCV has evolved multiple mechanisms to disrupt and block cellular signaling pathways involved in the induction of interferon (IFN) responses, IFN-stimulated gene (ISG) expression is typically prominent in the HCV-infected liver. Here, we show that Toll-like receptor 3 (TLR3) expressed within uninfected hepatocytes is capable of sensing infection in adjacent cells, initiating a local antiviral response that partially restricts HCV replication. We demonstrate that this is dependent upon the expression of class A scavenger receptor type 1 (MSR1). MSR1 binds extracellular dsRNA, mediating its endocytosis and transport toward the endosome where it is engaged by TLR3, thereby triggering IFN responses in both infected and uninfected cells. RNAi-mediated knockdown of MSR1 expression blocks TLR3 sensing of HCV in infected hepatocyte cultures, leading to increased cellular permissiveness to virus infection. Exogenous expression of Myc-MSR1 restores TLR3 signaling in MSR1-depleted cells with subsequent induction of an antiviral state. A series of conserved basic residues within the carboxy-terminus of the collagen superfamily domain of MSR1 are required for binding and transport of dsRNA, and likely facilitate acidification-dependent release of dsRNA at the site of TLR3 expression in the endosome. Our findings reveal MSR1 to be a critical component of a TLR3-mediated pattern recognition receptor response that exerts an antiviral state in both infected and uninfected hepatocytes, thereby limiting the impact of HCV proteins that disrupt IFN signaling in infected cells and restricting the spread of HCV within the liver.

Persistent hepatitis C virus (HCV) infection is an important cause of fatal cirrhosis and liver cancer in humans. While viral disruption of interferon (IFN) signaling pathways may contribute to the persistence of HCV, IFN-stimulated gene (ISG) expression is often prominent within the infected liver. We show here that this is due, at least in part, to Toll-like receptor 3 sensing of HCV mediated by class A scavenger receptor type 1 (MSR1)-dependent endocytosis and transport of extracellular viral double-stranded RNA (dsRNA) allowing it to be engaged by TLR3 in the late endosome. TLR3 expressed within uninfected cells is capable of sensing HCV infection in neighboring infected cells in a process that is dependent upon the dsRNA-scavenging activity of MSR1, resulting in the induction of a localized functional antiviral response. This contributes to the ISG expression that typifies the chronically-infected liver, as it occurs within cells that do not express HCV proteins that disrupt IFN signaling. TLR3 signaling thus limits the spread of virus within the liver, potentially explaining why only a small fraction of hepatocytes are infected with HCV in vivo.

Anti-ulcer agent teprenone inhibits hepatitis C virus replication: potential treatment for hepatitis C

BACKGROUND

Previously we reported that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, statins, inhibited hepatitis C virus (HCV) RNA replication. Furthermore, recent reports revealed that the statins are associated with a reduced risk of hepatocellular carcinoma and lower portal pressure in patients with cirrhosis. The statins exhibited anti-HCV activity by inhibiting geranylgeranylation of host proteins essential for HCV RNA replication. Geranylgeranyl pyrophosphate (GGPP) is a substrate for geranylgeranyltransferase. Therefore, we examined the potential of geranyl compounds with chemical structures similar to those of GGPP to inhibit HCV RNA replication.

METHODS

We tested geranyl compounds [geranylgeraniol, geranylgeranoic acid, vitamin K(2) and teprenone (Selbex)] for their effects on HCV RNA replication using genome-length HCV RNA-replicating cells (the OR6 assay system) and a JFH-1 infection cell culture system. Teprenone is the major component of the anti-ulcer agent, Selbex. We also examined the anti-HCV activities of the geranyl compounds in combination with interferon (IFN)-α or statins.

RESULTS

Among the geranyl compounds tested, only teprenone exhibited anti-HCV activity at a clinically achievable concentration. However, other anti-ulcer agents tested had no inhibitory effect on HCV RNA replication. The combination of teprenone and IFN-α exhibited a strong inhibitory effect on HCV RNA replication. Although teprenone alone did not inhibit geranylgeranylation, surprisingly, statins' inhibitory action against geranylgeranylation was enhanced by cotreatment with teprenone.

CONCLUSIONS

The anti-ulcer agent teprenone inhibited HCV RNA replication and enhanced statins' inhibitory action against geranylgeranylation. This newly discovered function of teprenone may improve the treatment of HCV-associated liver diseases as an adjuvant to statins.

Hepatitis B virus X protein enhances COX-2 expression in human liver cell line L-02

AIM: To investigate the effect of hepatitis B virus X protein (HBx) on COX-2 expression in human liver cell line L-02.

METHODS: HBx expression vector pIRES2-AcGFP-HBx was constructed and transfected into L-02 cells. The expression of COX-2 mRNA and protein was detected by RT-PCR and Western blot, respectively. The effect of HBx protein on cell division and proliferation was evaluated by plotting cell growth curve and analyzing cell cycle. Moreover, pGL3-COX-2 plasmid, in which the COX-2 promoter has been linked to the luciferase reporter gene, was transfected into L-02 cells and luciferase activities were measured.

RESULTS: RT-PCR results revealed that HBx mRNA was expressed only in cells transfected with the HBx gene, and that COX-2 mRNA expression in cells transfected with the HBx gene was higher than that in cells untranfected or transfected with an empty vector (0.76 ± 0.12 vs 0.28 ± 0.04, 0.25 ± 0.03, both P < 0.01). Western blot analysis showed that HBx protein was expressed only in cells transfected with the HBx gene, and COX-2 protein expression in this group was higher than that in the two control groups. The proliferation of cells transfected with the HBx gene was faster than that of control cells (both P < 0.05). The numbers of cells in S and G2-M phases significantly increased while those in G₀-G₁ phase decreased in cells transfected with the HBx gene compared to control cells (all P < 0.05). The luciferase activity in cells transfected with the HBx gene was higher than that in control cells (1 675.2 ± 84.9 vs 657.7 ± 34.7, 739.3 ± 45.3, both P < 0.05).

CONCLUSION: HBx protein can enhance COX-2 expression by up-regulating the activity of COX-2 promoter and promote cell growth, division and proliferation in human liver cell line L-02.

Mechanism of action of ribavirin in a novel hepatitis C virus replication cell system

Ribavirin (RBV) is a potential partner of interferon (IFN)-based therapy for patients with chronic hepatitis C. However, to date, its anti-hepatitis C virus (HCV) mechanism remains ambiguous due to the marginal activity of RBV on HCV RNA replication in HuH-7-derived cells, which are currently used as the only cell culture system for robust HCV replication. We investigated the anti-HCV activity of RBV using novel cell assay systems. The recently discovered human hepatoma cell line, Li23, which enables robust HCV replication, and the recently developed Li23-derived drug assay systems (ORL8 and ORL11), in which the genome-length HCV RNA (O strain of genotype 1b) encoding renilla luciferase efficiently replicates, were used for this study. At clinically achievable concentrations, RBV unexpectedly inhibited HCV RNA replication in ORL8 and ORL11 systems, but not in OR6 (an HuH-7-derived assay system). The anti-HCV activity of RBV was almost cancelled by an inhibitor of equilibrative nucleoside transporters. The evaluation of the anti-HCV mechanisms of RBV proposed to date using ORL8 ruled out the possibility that RBV induces error catastrophe, the IFN-signaling pathway or oxidative stress. However, we found that the anti-HCV activity of RBV was efficiently cancelled with guanosine, and demonstrated that HCV RNA replication was notably suppressed in inosine monophosphate dehydrogenase (IMPDH)-knockdown cells, suggesting that the antiviral activity of RBV is mediated through the inhibition of IMPDH. In conclusion, we demonstrated for the first time that inhibition of IMPDH is a major antiviral target by which RBV at clinically achievable concentrations inhibits HCV RNA replication.

Amino acid substitutions of hepatitis C virus core protein are not associated with intracellular antiviral response to interferon-α in vitro

BACKGROUND

Studies on patients with hepatitis C virus (HCV) of genotype 1b have suggested that amino acids (aa) 70 and/or 91 of the HCV core protein affect the outcome of interferon (IFN)-α and ribavirin (RBV) therapy, although there are no clear supporting data in vitro.

AIMS

This study was designed to determine the differences among the antiviral activities of HCV core proteins with various substitutions at aa70 and/or aa91.

METHODS

The retroviral vectors expressing the HCV core proteins with substitutions of arginine/leucine, arginine/methionine, glutamine/leucine or glutamine/methionine at aa70/aa91 were transiently transfected or stably transducted into an immortalized hepatocyte line (PH5CH8), hepatoma cell lines and an HCV-RNA replicating cell line (sOR) to evaluate antiviral responses to IFN-α or IFN-α/RBV. Sequence analysis was performed using genome-length HCV-RNA replicating cells (OR6 and AH1) to evaluate HCV core mutations during IFN-α treatment.

RESULTS

The promoter activity levels of IFN-stimulated genes in the transiently transfected cells or the mRNA levels of 2'-5'-oligoadenylate synthetase in the stably transducted PH5CH8 cells were not associated with the HCV core aa70 and/or aa91 substitutions during IFN-α treatment. Antiviral responses to IFN-α or IFN-α/RBV treatment were enhanced in sOR cells stably transducted with the HCV core, although there were no differences in antiviral responses among the cells expressing different core types. Sequence analysis showed no aa mutations after IFN-α treatment.

CONCLUSIONS

Antiviral activities were enhanced by HCV core transduction, but they were not associated with the HCV core aa70 and/or aa91 substitutions by in vitro analysis.

Cell cycle progression or translation control is not essential for vesicular stomatitis virus oncolysis of hepatocellular carcinoma

The intrinsic oncolytic specificity of vesicular stomatitis virus (VSV) is currently being exploited to develop alternative therapeutic strategies for hepatocellular carcinoma (HCC). Identifying key regulators in diverse transduction pathways that define VSV oncolysis in cancer cells represents a fundamental prerequisite to engineering more effective oncolytic viral vectors and adjusting combination therapies. After having identified defects in the signalling cascade of type I interferon induction, responsible for attenuated antiviral responses in human HCC cell lines, we have now investigated the role of cell proliferation and translation initiation. Cell cycle progression and translation initiation factors eIF4E and eIF2Bε have been recently identified as key regulators of VSV permissiveness in T-lymphocytes and immortalized mouse embryonic fibroblasts, respectively. Here, we show that in HCC, decrease of cell proliferation by cell cycle inhibitors or siRNA-mediated reduction of G(1) cyclin-dependent kinase activities (CDK4) or cyclin D1 protein expression, do not significantly alter viral growth. Additionally, we demonstrate that translation initiation factors eIF4E and eIF2Bε are negligible in sustaining VSV replication in HCC. Taken together, these results indicate that cellular proliferation and the initiation phase of cellular protein synthesis are not essential for successful VSV oncolysis of HCC. Moreover, our observations indicate the importance of cell-type specificity for VSV oncolysis, an important aspect to be considered in virotherapy applications in the future.

The wild-type hepatitis C virus core inhibits initiation of antigen-specific T- and B-cell immune responses in BALB/c mice

In this study, the effects of wild-type and deletion mutant hepatitis C virus (HCV) core proteins on the induction of immune responses in BALB/c mice were assessed. p2HA-C145-S23, encoding a core protein with the C-terminal 46 amino acids truncated, significantly produced stronger antibody and cellular responses than p2HA-C191-S23. The induction of immune responses by p2HA-C145-S23 was dose dependent. However, increasing the doses or repeated administration did not enhance immune responses by the wild-type core protein. In addition, p2HA-C191-S23 was apparently able to interfere with the priming of specific immune responses by p2HA-C145-S23 when the two were coadministered. These results demonstrated that the wild-type HCV core protein itself could inhibit the priming of immune responses in the course of a DNA vaccination, whereas the truncated HCV core protein could provide potential applications for the development of DNA- and peptide-based HCV vaccines.

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

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

HCV genotype 1b chimeric replicon with NS5B of JFH-1 exhibited resistance to cyclosporine A

Cyclosporine A (CsA) is a well-characterized anti-HCV reagent. Recently it was reported that the genotype 2a JFH-1 strain was more resistant than genotype 1 HCV strains to CsA in a cell culture system. However, the JFH-1 responsible region for the resistance to CsA remains unclear. It was also demonstrated that in genotype 1b HCVs, NS5B interacts with cyclophilin (CyP). To clarify whether or not NS5B of JFH-1 is significant for CsA resistance, we developed a chimeric replicon with NS5B of JFH-1 in the genotype 1b backbone. The chimeric replicon was more resistant to CsA than the parental genotype 1b replicon. Furthermore, reduction of CyPA had a greater effect on HCV RNA replication and sensitivity to CsA than reduction of CyPB. Here, we demonstrated that NS5B of JFH-1 contributed to this strain's CsA-resistant phenotype. NS5B and CyPA are significant for determining HCV's sensitivity to CsA.

Development of a hepatitis C virus relapse model using genome-length hepatitis C virus ribonucleic acid-harboring cells possessing the interferon-alpha-resistance phenotype

AIM

The cure rate of current interferon (IFN) therapy is limited to approximately 50% and most of the relapses after therapy are caused by genotype-1. To develop a relapse model in cell culture, we attempted to obtain genome-length hepatitis C virus ribonucleic acid (HCV RNA) harboring cells possessing the IFN-alpha-resistance phenotype from previously established OR6 cells, which enabled the luciferase reporter assay for monitoring of HCV RNA replication.

METHODS

The IFN-alpha-resistant HCV RNA-harboring cells and control cells were obtained by the treatment of OR6 cells with and without IFN-alpha, respectively. Then, we examined the relapse of HCV in IFN-alpha-resistant HCV RNA-harboring cells.

RESULTS

Only type I IFN (alpha and beta) showed significantly different anti-HCV activity between IFN-alpha-resistant HCV RNA-harboring cells and control cells. There was no significant difference in the anti-HCV activity of IFN-gamma, fluvastatin, or cyclosporine A between the two types of cells. Furthermore, we showed that fluvastatin or cyclosporine A in combination with IFN-alpha could prevent the relapse after therapy in the IFN-alpha-resistant HCV RNA-harboring cells.

CONCLUSION

We developed a HCV relapse model in cell culture using IFN-alpha-resistant HCV RNA-harboring cells. Thus anti-HCV reagents, which have a mechanism different from IFN-alpha, were shown to be useful for preventing a relapse of IFN-alpha-resistant HCV.

Double-stranded RNA-induced interferon-beta and inflammatory cytokine production modulated by hepatitis C virus serine proteases derived from patients with hepatic diseases

We previously demonstrated that hepatitis C virus (HCV) serine protease NS3-4A was unable to cleave TRIF (adaptor protein of Toll-like receptor 3), resulting in a lack of suppression of the TRIF-mediated pathway, whereas NS3-4A cleaved Cardif (adaptor protein of retinoic acid-inducible gene I or melanoma differentiation-associated gene-5), resulting in an interruption of the Cardif-mediated pathway in non-neoplastic human hepatocyte PH5CH8 cells. To elucidate these observations, we examined the cleavage potential of NS3-4A for TRIF in PH5CH8 cells, genome-length HCV RNA-replicating O cells, and HCV-infected cells, and we demonstrated that NS3-4A lacked the ability to cleave endogenous TRIF, regardless of HCV strains derived from patients with different stages of hepatic disease. Furthermore, we demonstrated that inflammatory cytokine production by NF-kappaB activation via the TRIF-mediated pathway also remained unsuppressed by NS3-4A. These results suggest that the inhibitory effects of NS3-4A on antiviral signaling pathways are limited to the Cardif-mediated pathway in human hepatocytes.

Oncostatin M synergistically inhibits HCV RNA replication in combination with interferon-alpha

Oncostatin M (OSM), a member of the interleukin-6 family, possesses various functions, including hepatocyte differentiation and suppression of melanoma cell growth. Here, we report anti-hepatitis C virus (HCV) activity of OSM as a new function of this cytokine. OSM possessed marked anti-HCV activity (50% effective concentration: 0.71 ng/ml) in an HCV RNA replication cell culture system. The most striking finding is that OSM exhibited synergistic inhibitory activity on interferon (IFN)-alpha even at a low concentration with weak anti-HCV activity, such as 25 pg/ml. OSM is a candidate anti-HCV reagent and may improve the current IFN therapy for patients with chronic hepatitis C.

Hepatitis C virus and ethanol alter antigen presentation in liver cells

Alcoholic patients have a high incidence of hepatitis C virus (HCV) infection. Alcohol consumption enhances the severity of the HCV disease course and worsens the outcome of chronic hepatitis C. The accumulation of virally infected cells in the liver is related to the HCV-induced inability of the immune system to recognize infected cells and to develop the immune responses. This review covers the effects of HCV proteins and ethanol on major histocompatibility complex (MHC) class I- and class II-restricted antigen presentation. Here, we discuss the liver which functions as an immune privilege organ; factors, which affect cleavage and loading of antigenic peptides onto MHC class I and class II in hepatocytes and dendritic cells, and the modulating effects of ethanol and HCV on antigen presentation by liver cells. Altered antigen presentation in the liver limits the ability of the immune system to clear HCV and infected cells and contributes to disease progression. HCV by itself affects dendritic cell function, switching their cytokine profile to the suppressive phenotype of interleukin-10 (IL-10) and transforming growth factor beta (TGFβ) predominance, preventing cell maturation and allostimulation capacity. The synergistic action of ethanol with HCV results in the suppression of MHC class II-restricted antigen presentation. In addition, ethanol metabolism and HCV proteins reduce proteasome function and interferon signaling, thereby suppressing the generation of peptides for MHC class I-restricted antigen presentation. Collectively, ethanol exposure further impairs antigen presentation in HCV-infected liver cells, which may provide a partial explanation for exacerbations and the poor outcome of HCV infection in alcoholics.

A new living cell-based assay system for monitoring genome-length hepatitis C virus RNA replication

We previously developed a cell-based luciferase reporter assay system for monitoring genome-length hepatitis C virus (HCV) RNA replication (OR6 assay system). Here, we aimed to develop a new living cell-based reporter assay system using enhanced green fluorescent protein (EGFP). Genome-length HCV RNAs encoding EGFP were introduced into a subline of HuH-7 cells and G418 selection was performed. One cloned cell line, OGF7, was successfully selected from among the several G418-resistant cell lines obtained, and the robust expression of HCV RNA and proteins in OGF7 cells was confirmed. The fluorescent intensity of OGF7 cells was decreased by interferon-alpha treatment in a dose-dependent manner, and it correlated well with the HCV RNA concentration. We demonstrated that the interferon-alpha sensitivity in the OGF7 assay system measuring the fluorescent intensity was equivalent to that of the OR6 assay system, and that the OGF7 assay system was useful for quantitative evaluation of anti-HCV reagents. The OGF7 assay system is expected to be the most time-saving and inexpensive assay system for high-throughput screening of anti-HCV reagents.

Role of hepatitis C virus proteins (C, NS3, NS5A) in hepatic oncogenesis

In recent years, the effects of hepatitis C virus (HCV) proteins on hepatocarcinogenesis have undergone intense investigations. The potentially oncogenic proteins include at least three HCV proteins: core (C) protein, NS3, and NS5A. Several authors indicated relationships between subcellular localization, concentration, a specific molecular form of the proteins (full length, truncated, phosphorylated), the presence of specific domains (the nuclear localization signal homologous to e.g. Bcl-2) and their effects on the mechanisms linked to oncogenesis. The involvement of all the proteins has been described as being in control of the cell cycle, through interactions with key proteins of the process (p53, p21, cyclins, proliferating cell nuclear antigen), transcription factors, proto-oncogenes, growth factors/cytokines and their receptors, and proteins linked to the apoptotic process. Untilnow, the involvement of the core protein of HCV in liver carcinogenesis is the most recognized. One of the most common proteins affected by HCV proteins is the p53 tumor-suppressor protein. The p21/WAF1 gene is a major target of p53, and the effect of HCV proteins on the gene is frequently considered in parallel. The results of studies on the effects of HCV proteins on the apoptotic process are controversial. This work summarizes the information collected thus far in the field of HCV molecular virology and principal intracellular signaling pathways in which HCV oncogenic proteins are involved.

Modulation of host metabolism as a target of new antivirals

The therapy for chronic hepatitis C (CH-C) started with interferon (IFN) monotherapy in the early 1990s and this therapy was considered effective in about 10% of cases. The present standard therapy of pegylated IFN with ribavirin achieves a sustained virologic response in about 50% of patients. However, about half of the CH-C patients are still at risk of fatal liver cirrhosis and hepatocellular carcinoma. The other significant event in hepatitis C virus (HCV) research has been the development of a cell culture system. The subgenomic replicon system enables robust HCV RNA replication in hepatoma cells. And recently, the complete life cycle of HCV has been achieved using a genotype 2a strain, JFH1. These hallmarks have provided much information about the mechanisms of HCV replication, including information on the host molecules required for the replication. Anti-HCV reagents targeting HCV proteins have been developed, and some of them are now in clinical trials. However, the RNA-dependent RNA polymerase frequently causes mutations in the HCV genome, which lead to the emergence of drug-resistant HCV mutants. Some of the cellular proteins essential for HCV RNA replication have already been discovered using the HCV cell culture system. These host molecules are also candidate targets for antivirals. Here, we describe the recent progress regarding the anti-HCV reagents targeting host metabolism.

Limited suppression of the interferon-beta production by hepatitis C virus serine protease in cultured human hepatocytes

Toll-like receptors and RNA helicase family members [retinoic acid-inducible gene I (RIG-I) and melanoma differentiation associated gene-5 (MDA5)] play important roles in the induction of interferon-beta as a major event in innate immune responses after virus infection. TRIF (adaptor protein of Toll-like receptor 3)-mediated and Cardif (adaptor protein of RIG-I or MDA5)-mediated signaling pathways contribute rapid induction of interferon-beta through the activation of interferon regulatory factor-3 (IRF-3). Previously, it has been reported that the hepatitis C virus NS3-4A serine protease blocks virus-induced activation of IRF-3 in the human hepatoma cell line HuH-7, and that NS3-4A cleaves TRIF and Cardif molecules, resulting in the interruption of antiviral signaling pathways. On the other hand, it has recently been reported that non-neoplastic human hepatocyte PH5CH8 cells retain robust TRIF- and Cardif-mediated pathways, unlike HuH-7 cells, which lack a TRIF-mediated pathway. In the present study, we further investigated the effect of NS3-4A on antiviral signaling pathways. Although we confirmed that PH5CH8 cells were much more effective than HuH-7 cells for the induction of interferon-beta, we obtained the unexpected result that NS3-4A could not suppress the interferon-beta production induced by the TRIF-mediated pathway, although it suppressed the Cardif-mediated pathway by cleaving Cardif at the Cys508 residue. Using PH5CH8, HeLa, and HuH-7-derived cells, we further showed that NS3-4A could not cleave TRIF, in disagreement with a previous report describing the cleavage of TRIF by NS3-4A. Taken together, our findings suggest that the blocking of the interferon production by NS3-4A is not sufficient in HCV-infected hepatocyte cells.

Different anti-HCV profiles of statins and their potential for combination therapy with interferon

We recently developed a genome-length hepatitis C virus (HCV) RNA replication system (OR6) with luciferase as a reporter. The OR6 assay system has enabled prompt and precise quantification of HCV RNA replication. Pegylated interferon (IFN) and ribavirin combination therapy is the world standard for chronic hepatitis C, but its effectiveness is limited to about 55% of patients. Newer therapeutic approaches are needed. In the present study, we used the OR6 assay system to evaluate the anti-HCV activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, called statins, and their effects in combination with IFN-alpha. Five types of statins (atorvastatin, fluvastatin, lovastatin, pravastatin, and simvastatin) were examined for their anti-HCV activities. Fluvastatin exhibited the strongest anti-HCV activity (IC50: 0.9 micromol/L), whereas atorvastatin and simvastatin showed moderate inhibitory effects. However, lovastatin, reported recently as an inhibitor of HCV replication, was shown to exhibit the weakest anti-HCV activity. The anti-HCV activities of statins were reversed by the addition of mevalonate or geranylgeraniol. Surprisingly, however, pravastatin exhibited no anti-HCV activity, although it worked as an inhibitor for HMG-CoA reductase. The combination of IFN and the statins (except for pravastatin) exhibited strong inhibitory effects on HCV RNA replication. In combination with IFN, fluvastatin also exhibited a synergistic inhibitory effect. In conclusion, statins, especially fluvastatin, could be potentially useful as new anti-HCV reagents in combination with IFN.

Epigenetic silencing of interferon-inducible genes is implicated in interferon resistance of hepatitis C virus replicon-harboring cells

BACKGROUND/AIMS

We previously established hepatitis C virus (HCV) replicon-harboring cell lines possessing two interferon (IFN)-resistant phenotypes: a partially resistant phenotype (alphaR series) and a severely resistant phenotype (betaR series). We recently found that the severe IFN resistance of the betaR-series cells is caused by the functional disruption of type I IFN receptors. Here, we aimed to clarify the mechanism(s) underlying the partial IFN resistance of the alphaR-series cells.

METHODS

alphaR-series cells were pre-treated with 5-azacytidine to evaluate the effects of DNA demethylation on IFN resistance. cDNA microarray analysis was carried out in order to compare 1alphaR cells, which belong to the alphaR series, treated with both 5-azacytidine and IFN-alpha with cells treated with 5-azacytidine or IFN-alpha alone.

RESULTS

We found that the IFN-resistant phenotype of alphaR-series cells was impaired by treatment with 5-azacytidine. cDNA microarray analysis identified seven IFN-stimulated genes, which were up-regulated by 5-azacytidine treatment. We demonstrated here that the ectopic expression of each of these seven genes in 1alphaR cells frequently weakened the IFN resistance of these cells.

CONCLUSIONS

The present results suggest that the epigenetic silencing of IFN-stimulated genes is implicated in the acquisition of a partially IFN-resistant phenotype of HCV replicon-harboring cells.

Treatment of chronic hepatitis C in non-responsive patients with pegylated interferon associated with ribavirin and thalidomide: report of six cases of total remission

Hepatitis C virus (HCV) infection is an important public health issue worldwide. It is estimated that over 170 million people are infected with the virus. The present study reports six cases in which patients did not respond to combination therapy with pegylated interferon and ribavirin. However, after the addition of thalidomide to the therapy, the patients presented negative RNA PCR. The use of thalidomide combined with pegylated interferon and ribavirin for the treatment of hepatitis C is described here for the first time in the related literature.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Hepatitis C virus NS5B delays cell cycle progression by inducing interferon-beta via Toll-like receptor 3 signaling pathway without replicating viral genomes

To clarify the pathogenesis of hepatitis C virus (HCV), we have studied the effects of HCV proteins using human hepatocytes. Here, we found that HCV NS5B, an RNA-dependent RNA polymerase, delayed cell cycle progression through the S phase in PH5CH8 immortalized human hepatocyte cells. Since treatment with anti-interferon (IFN)-beta neutralizing antibody restored the cell cycle delay, IFN-beta was deemed responsible for the cell cycle delay in NS5B-expressing PH5CH8 cells. The induction of IFN-beta and the cell cycle delay were overridden by the down-regulation of Toll-like receptor 3 (TLR3) through RNA interference in NS5B-expressing PH5CH8 cells. Moreover, the NS5B full form was required for the cell cycle delay, the induction of IFN-beta, and the activation of the IFN-beta signaling pathway. Our findings revealed that NS5B induced IFN-beta through the TLR3 signaling pathway in immortalized human hepatocytes even without replicating viral genomes.

Hepatitis C virus proteins exhibit conflicting effects on the interferon system in human hepatocyte cells

We previously found that hepatitis C virus (HCV) core protein (Core) activated the interferon (IFN)-inducible 40/46 kDa 2'-5'-oligoadenylate synthetase (2'-5'-OAS) gene through an IFN-stimulated response element (ISRE) in non-neoplastic human hepatocyte PH5CH8 cells. Here, we found that Core and NS5B synergistically enhanced the 2'-5'-OAS gene promoter activity through ISRE. Further analysis revealed that amino acid positions 12 and/or 13 of Core and RNA-dependent RNA polymerase activity of NS5B were essential for the activation of the 2'-5'-OAS gene promoter. Interestingly, we observed that the activation by Core or NS5B was still partially enhanced by even the NS5B or Core mutant lacking the activating ability, respectively, suggesting an indirect interaction between Core and NS5B. Furthermore, we showed that the activation by NS5B could be explained by NS5B's induction of IFN-beta, however, IFN-beta was not induced by Core. Moreover, we showed that the synergistic effect of Core and NS5B was not invalidated by NS3-4A, although NS3-4A significantly inhibited the activation by combination of Core and NS5B. Taken together, our findings reveal that NS5B/Core and NS3-4A exhibit conflicting effects (activation and inhibition) on the IFN system in PH5CH8 cells, and suggest that such effects may promote the distraction of the host defense system to lead to persistent infection.

Thr 446 phosphorylation of PKR by HCV core protein deregulates G2/M phase in HCC cells

Hepatitis C virus (HCV) is the major causative viral agent of cirrhosis and hepatocarcinoma (HCC). HCV core protein affects cell homeostasis, playing an important role in viral pathogenesis of HCC. We investigate the effects of HCV core protein expression on cell growth in HCC cell lines. Cell cycle distribution analysis of HepG2 polyclonal core positive cells reveals a peculiar accumulation of cells in G2/M phase. Different pathways mediate G2/M arrest: such as p53 and double strand RNA protein kinase (PKR). Flow cytometry in p53-null cells demonstrates that p53 plays only a marginal role in inducing HCV core-dependent G2/M phase accumulation that seems to be significantly affected by the functional inactivation of PKR. HCC core positive cells are characterized by a significant PKR phosphorylation in Thr 446 residue, which leads deregulation of mitosis. Moreover, we observe that the overexpression of the viral protein induces an upregulation of PKR activity, which does not correlate with an increased eIF-2 phosphorylation. This uncommon behavior of PKR suggests that its activation by HCV core protein could involve alternative PKR-dependent pathways, implicated in core-dependent G2/M accumulation. The described biological effects of HCV core protein on cell cycle could be an additional viral mechanism for both HCV resistance to interferon (IFN) and HCC HCV-related pathogenesis.

Consensus proposals for a unified system of nomenclature of hepatitis C virus genotypes

International standardization and coordination of the nomenclature of variants of hepatitis C virus (HCV) is increasingly needed as more is discovered about the scale of HCV-related liver disease and important biological and antigenic differences that exist between variants. A group of scientists expert in the field of HCV genetic variability, and those involved in development of HCV sequence databases, the Hepatitis Virus Database (Japan), euHCVdb (France), and Los Alamos (United States), met to re-examine the status of HCV genotype nomenclature, resolve conflicting genotype or subtype names among described variants of HCV, and draw up revised criteria for the assignment of new genotypes as they are discovered in the future. A comprehensive listing of all currently classified variants of HCV incorporates a number of agreed genotype and subtype name re-assignments to create consistency in nomenclature. The paper also contains consensus proposals for the classification of new variants into genotypes and subtypes, which recognizes and incorporates new knowledge of HCV genetic diversity and epidemiology. A proposal was made that HCV variants be classified into 6 genotypes (representing the 6 genetic groups defined by phylogenetic analysis). Subtype name assignment will be either confirmed or provisional, depending on the availability of complete or partial nucleotide sequence data, or remain unassigned where fewer than 3 examples of a new subtype have been described. In conclusion, these proposals provide the framework by which the HCV databases store and provide access to data on HCV, which will internationally coordinate the assignment of new genotypes and subtypes in the future.

Interferon resistance of hepatitis C virus replicon-harbouring cells is caused by functional disruption of type I interferon receptors

Hepatitis C virus (HCV) replicon-harbouring cell lines possessing interferon (IFN)-resistant phenotypes have recently been established. These were divided into two classes: partially IFN resistant and highly IFN resistant. Here, the viral and cellular factors contributing to the IFN resistance of HCV replicon-harbouring cells were evaluated. The results revealed that cellular factors rather than viral factors contributed to a highly IFN-resistant phenotype. The possibility of genetic abnormality of the factors involved in IFN signalling was investigated. As a result, nonsense mutations and deletions in type I IFN receptor genes (IFNAR1 and IFNAR2c) were found in replicon-harbouring cells showing a highly IFN-resistant phenotype, but rarely appeared in cells showing a partially IFN-resistant phenotype. Furthermore, similar genetic alterations were also found in IFN-resistant phenotype, replicon-harbouring cell lines obtained additionally by IFN-β treatment. Moreover, it was shown that ectopic expression of wild-type IFNAR1 in IFN-resistant phenotype, replicon-harbouring cells possessing the IFNAR1 mutant restored type I IFN signalling.

Activation of Interferon-Stimulated Response Element in Huh-7 Cells Replicating Hepatitis C Virus Subgenomic RNA

Interferon-alpha (IFN(alpha)) binds to receptors on the cell surface, which initiate a cascade of signal transduction pathways that leads to transcription of selected genes. This transduction pathway involves binding of transcription factors to a common cis-acting DNA sequence called IFN-stimulated response element (ISRE). To test whether these signaling pathways are functional in hepatitis C virus (HCV)-replicating cells, we studied the regulation of ISRE-mediated transcription of firefly luciferase gene in stable replicon cell lines. A plasmid construct was prepared (pISRELuc) which contains four tandem repeats of 9-27 ISRE sequences positioned directly upstream of the herpes virus 1 thymidine kinase promoter TATA box that drives the expression of firefly luciferase. Regulation of ISRE-mediated expression of firefly luciferase by IFN(alpha) was studied by transfecting this clone into Huh-7 cells replicating HCV subgenomic HCV RNA. The significance of ISRE-mediated transcriptional activation was studied in a replicon cell line by pretreatment of cells with actinomycin D, which inhibits cellular DNA-dependent RNA transcription. IFN treatment activates ISRE-mediated expression of luciferase, indicating that this pathway is functional in Huh-7 cells. Activation of ISRE-mediated transcription of luciferase is relatively high in two Huh-7 stable cell lines replicating HCV subgenomic RNA. Inhibition of ISRE-mediated transcription of luciferase by actinomycin D also makes HCV replication totally resistant to IFN(alpha). These in vitro studies suggest that activation of IFN-inducible genes is important in mounting a successful antiviral response against HCV.

Sensitivity of hepatitis C virus RNA to the antiviral enzyme ribonuclease L is determined by a subset of efficient cleavage sites

Ribonuclease L (RNase L) cleaves RNA predominantly at single-stranded UA and UU dinucleotides. Intriguingly, hepatitis C virus (HCV) RNAs have a paucity of UA and UU dinucleotides, and relatively interferon (IFN)-resistant strains have fewer UA and UU dinucleotides than do more IFN-sensitive strains. In this study, we found that contextual features of UA and UU dinucleotides dramatically affected the efficiency of RNase L cleavage in HCV RNA. HCV genotype la RNA was cleaved by RNase L into fragments 200-1000 bases in length, consistent with 10-50 RNase L cleavage sites within the 9650-base long viral RNA. Using primer extension, we found that HCV RNA structures with multiple single-stranded UA and UU dinucleotides were cleaved most efficiently by RNase L. UA and UU dinucleotides with 3' proximal C or G residues were cleaved infrequently, whereas UA and UU dinucleotides within dsRNA structures were not cleaved. 5'-GUAC-3' and 5'-CUUC-3' were particularly unfavorable contexts for cleavage by RNase L. More than 60% of the UA and UU dinucleotides in HCV la RNA were not cleaved by RNase L because of these contextual features. The 10-30 most efficiently cleaved sites were responsible for approximately 50%-85% of all RNase L cleavage events. Our data indicate that a relatively small number of the UA and UU dinucleotides in HCV RNA mediate the overall sensitivity of HCV RNA to cleavage by RNase L.

Effects of the hepatitis C virus core protein on innate cellular defense pathways

The hepatitis C virus (HCV) core protein is thought to contribute to HCV pathogenesis through its interaction with various signal transduction pathways. In this study, we explored the interaction of the core protein with innate defense pathways (interferon [IFN] regulatory factor [IRF], Jak-Stat, and inducible nitric oxide synthase [iNOS]) in HeLa and Huh7 human cell lines. Expression of a patient-derived genotype 1b core protein activated human IRF-1 and guanylate-binding protein-2 (GBP-2) promoters, induced IRF-1 mRNA, but failed to induce IRF-3 phosphorylation. HCV core protein caused dose-dependent induction of the IFN-beta promoter and IFN-beta mRNA but not the IFN-alpha1 and IFN-alpha4 promoters. In the presence of IFN-alpha, core expression was associated with increased IFN-stimulated gene factor 3 (ISGF3) binding to the IFN-stimulated response element (ISRE) and tyrosine phosphorylation of Stat1. Core expression resulted in dose-dependent activation of the ISRE and gamma activated sequence (GAS) promoters, in both the absence and the presence of either IFN-alpha or IFN-gamma. Core stimulated the human iNOS promoter and induced iNOS protein. The data indicate that HCV core can modulate IRF, Jak-Stat, and iNOS pathways and suggest mechanisms by which core could affect HCV persistence and pathogenesis.

STAT3 induces anti-hepatitis C viral activity in liver cells

Hepatitis C virus (HCV) infection is a leading cause a of chronic liver disease worldwide. The main therapeutic regimen is the combination of interferon alpha (IFN) and the nucleoside analog, Ribavirin. IFN initiates an intracellular antiviral state by the JAK-STAT signaling pathway, including a presumed role for STAT1 and STAT2. We have previously shown that the STAT3 activation occurs during IFN treatment of human hepatoma cells, suggesting that the STAT3-mediated pathway is relevant to IFN-induced antiviral activity. In this study, we investigate the role of activated STAT3 in the induction of anti-HCV activity in human hepatoma cells. We demonstrate that the STAT3 activation is involved in efficient IFN-induced anti-HCV activity. Using an inducible, cytokine-independent, STAT3 activation system, in which the entire coding region of STAT3 is fused with the ligand-binding domain of the estrogen receptor, we demonstrate that: activated STAT3 is tightly regulated in a stably transfected cell line by an estrogen analog, 4-HT; activated STAT3 initiates efficient anti-HCV activity in a HCV subgenomic replicon cell line; and activation of STAT3 is associated with the induction of a potential antiviral gene, 1-8U. In addition, we show that the cytokine IL-6, a potent STAT3 activator, inhibits HCV subgenomic RNA replication through STAT3 activation and ERK pathway. These results strongly suggest that STAT3 activation is capable of initiating intracellular antiviral pathways.

Establishment of hepatitis C virus replicon cell lines possessing interferon-resistant phenotype

To clarify the mechanism underlying resistance to interferon (IFN) by the hepatitis C virus (HCV) in patients with chronic hepatitis, we attempted to develop an IFN-resistant HCV replicon from the IFN-sensitive 50-1 replicon established previously. By treating 50-1 replicon cells with a prolonged low-dose treatment of IFN-alpha and then transfecting the total RNA derived from the IFN-alpha-treated replicon cells, we successfully obtained four clones (named 1, 3, 4, and 5) of HCV replicon cells that survived against IFN-alpha (200 IU/ml). These cloned cells were further treated with IFN-alpha or IFN-beta (increased gradually to 2000 or 1000 IU/ml, respectively). This led to four replicon cell lines (alphaR series) possessing the IFN-alpha-resistant phenotype and four replicon cell lines (betaR series) possessing the IFN-beta-resistant phenotype. Furthermore, we obtained an additional replicon cell line (alphaRmix) possessing the IFN-alpha-resistant phenotype by two rounds of prolonged treatment with IFN-alpha and RNA transfection as mentioned above. Characterization of these obtained HCV replicon cell lines revealed that the betaR series were highly resistant to both IFN-alpha and IFN-beta, although the alphaR series containing alphaRmix were only partially resistant to both IFN-alpha and IFN-beta. Genetic analysis of these HCV replicons found one common amino acid substitution in the NS4B and several additional amino acid substitutions in the NS5A of the betaR series, suggesting that these genetic alterations are involved in the IFN resistance of these HCV replicons. These newly established HCV replicon cell lines possessing IFN-resistant phenotypes are the first useful tools for understanding the mechanisms by which HCV acquires IFN resistance in vivo.

Promotion of microsatellite instability by hepatitis C virus core protein in human non-neoplastic hepatocyte cells

Hepatitis C virus proteins exert an effect on a variety of cellular functions, including gene expression, signal transduction, and apoptosis, and because they possess oncogenic potentials, they have also been suggested to play an important role in hepatocarcinogenesis. Although the mechanisms of hepatocarcinogenesis remain poorly understood, we hypothesized that the disease may arise because of a disturbance of the DNA repair system by hepatitis C virus proteins. To test this hypothesis, we developed a reproducible microsatellite instability assay system for mismatch-repair using human-cultured cells transducted with pCXpur retrovirus expression vector, in which the puromycin resistance gene was rendered out-of-frame by insertion of a (CA)(17) dinucleotide repeat tract immediately following the ATG start codon. Using several human cancer cell lines known to be replication error positive or negative, we demonstrated that this assay system was useful for monitoring the propensity for mismatch-repair in the cells. This assay system was applicable to non-neoplastic human PH5CH8 hepatocytes, which could support hepatitis C virus replication. Using PH5CH8 cells, in which hepatitis C virus proteins were stably expressed by the retrovirus-mediated gene transfer, we found that the core protein promoted microsatellite instability in PH5CH8 cells. Interestingly, such promotion by the core protein only occurred in cells having the core protein belonging to genotype 1b or 2a and did not occur in cells having the core protein belonging to genotype 1a, 2b, or 3a. This is the first report to demonstrate that the core protein may disturb the DNA repair system.