Hepatitis C Virus Protein Expression Research Articles

Hepatitis C virus (HCV) protein expression enhances hepatic fibrosis in HCV transgenic mice exposed to a fibrogenic agent

During chronic HCV infection, activation of fibrogenesis appears to be principally related to local inflammation. However, the direct role of hepatic HCV protein expression in fibrogenesis remains unknown. We used transgenic mice expressing the full length HCV open reading frame exposed to a 'second hit' of the fibrogenic agent carbon tetrachloride (CCl(4)). Both acute and chronic liver injuries were induced in these mice by CCl(4) injections. Liver injury, expression of matrix re-modeling genes, reactive oxygen species (ROS), inflammation, hepatocyte proliferation, ductular reaction and hepatic progenitor cells (HPC) expansion were examined. After CCl(4) treatment, HCV transgenic mice exhibited enhanced liver fibrosis, significant changes in matrix re-modeling genes and increased ROS production compared to wild type littermates despite no differences in the degree of local inflammation. This increase was accompanied by a decrease in hepatocyte proliferation, which appeared to be due to delayed hepatocyte entry into the S phase. A prominent ductular reaction and hepatic progenitor cell compartment expansion were observed in transgenic animals. These observations closely mirror those previously made in HCV-infected individuals. Together, these results demonstrate that expression of the HCV proteins in hepatocytes contributes to the development of hepatic fibrosis in the presence of other fibrogenic agents. In the presence of CCl(4), HCV transgenic mice display an intra-hepatic re-organization of several key cellular actors in the fibrogenic process.

(−)-Epigallocatechin-3-gallate inhibits the replication cycle of hepatitis C virus

(-)-Epigallocatechin-3-gallate (EGCG) is the most abundant catechin in green tea. In this study, we found that hepatitis C virus (HCV) infection was significantly suppressed by EGCG in an HCV cell culture (HCVcc) system using a JFH1-GFP chimeric virus, with a 50 % effective concentration (EC(50)) of 17.9 μM. The inhibitory activity of EGCG was confirmed by monitoring HCV RNA and protein expression levels in Huh7.5.1 cells infected with the JFH1 virus. Moreover, we demonstrated that the inhibitory mechanisms of EGCG were attributable to the suppression of both the HCV entry and RNA replication steps, although EGCG had little effect on translation directed by the viral internal ribosome entry site (IRES). Furthermore, HCV could be rapidly eliminated from cell cultures after two and five passages in the presence of 50 and 25 μM EGCG, respectively. These results indicate that EGCG is a potential candidate as a preventive and antiviral drug for HCV infection.

Lipid metabolite profiling identifies desmosterol metabolism as a new antiviral target for hepatitis C virus.

Hepatitis C virus (HCV) infection has been clinically associated with serum lipid abnormalities, yet our understanding of the effects of HCV on host lipid metabolism and conversely the function of individual lipids in HCV replication remains incomplete. Using liquid chromatography-mass spectrometry metabolite profiling of the HCV JFH1 cell culture infection model, we identified a significant steady-state accumulation of desmosterol, an immediate precursor to cholesterol. Pharmacological inhibition or RNAi-mediated depletion of DHCR7 significantly reduced steady-state HCV protein expression and viral genomic RNA. Moreover, this effect was reversed when cultures were supplemented with exogenous desmosterol. Together, these observations suggest an intimate connection between HCV replication and desmosterol homeostasis and that the enzymes responsible for synthesis of desmosterol may be novel targets for antiviral design.

Hepatitis C Virus Stimulates the Phosphatidylinositol 4-Kinase III Alpha-Dependent Phosphatidylinositol 4-Phosphate Production That Is Essential for Its Replication

Phosphatidylinositol 4-kinase III alpha (PI4KA) is an essential cofactor of hepatitis C virus (HCV) replication. We initiated this study to determine whether HCV directly engages PI4KA to establish its replication. PI4KA kinase activity was found to be absolutely required for HCV replication using a small interfering RNA transcomplementation assay. Moreover, HCV infection or subgenomic HCV replicons produced a dramatic increase in phosphatidylinositol 4-phosphate (PI4P) accumulation throughout the cytoplasm, which partially colocalized with the endoplasmic reticulum. In contrast, the majority of PI4P accumulated at the Golgi bodies in uninfected cells. The increase in PI4P was not observed after infection with UV-inactivated HCV and did not reflect changes in PI4KA protein or RNA abundance. In an analysis of U2OS cell lines with inducible expression of the HCV polyprotein or individual viral proteins, viral polyprotein expression resulted in enhanced cytoplasmic PI4P production. Increased PI4P accumulation following HCV protein expression was precluded by silencing the expression of PI4KA, but not the related PI4KB. Silencing PI4KA also resulted in aberrant agglomeration of viral replicase proteins, including NS5A, NS5B, and NS3. NS5A alone, but not other viral proteins, stimulated PI4P production in vivo and enhanced PI4KA kinase activity in vitro. Lastly, PI4KA coimmunoprecipitated with NS5A from infected Huh-7.5 cells and from dually transfected 293T cells. In sum, these results suggest that HCV NS5A modulation of PI4KA-dependent PI4P production influences replication complex formation.

Down-regulation of IRES containing 5'UTR of HCV genotype 3a using siRNAs

BackgroundHepatitis C virus (HCV) is a major causative agent of liver associated diseases leading to the development of hepatocellular carcinoma (HCC) all over the world and genotype-3a responsible for most of the cases in Pakistan. Due to the limited efficiency of current chemotherapy of interferon-α (IFN-α) and ribavirin against HCV infection alternative options are desperately needed out of which the recently discovered RNAi represent a powerful silencing approach for molecular therapeutics through a sequence-specific RNA degradation process to silence virus infection or replication. HCV translation is mediated by a highly conserved internal ribosome entry site (IRES) within the 5'UTR region making it a relevant target for new drug development.Materials and methodsThe present study was proposed to assess and explore the possibility of HCV silencing using siRNA targeting 5'UTR. For this analysis full length HCV 5'UTR of HCV-3a (pCR3.1/5'UTR) was tagged with GFP protein for in vitro analysis in Huh-7 cells. siRNA targeting 5'UTR were designed, and tested against constructed vector in Huh-7 cell line both at RNA and Protein levels. Furthermore, the effect of these siRNAs was confirmed in HCV-3a serum infected Huh-7 cell line.ResultsThe expression of 5'UTR-GFP was dramatically reduced both at mRNA and protein levels as compared with Mock transfected and control siRNAs treated cells using siRNAs against IRES of HCV-3a genotype. The potential of siRNAs specificity to inhibit HCV-3a replication in serum-infected Huh-7 cells was also investigated; upon treatment with siRNAs a significant decrease in HCV viral copy number and protein expression was observed.ConclusionsOverall, the present work of siRNAs against HCV 5'UTR inhibits HCV-3a expression and represents effective future therapeutic opportunities against HCV-3a genotype.

HMG CoA Reductase Inhibitors Inhibit HCV RNA Replication of HCV Genotype 1b but Not 2a

Replication of hepatitis C virus (HCV) is regulated by statin, one of 3-hydroxy-3-methylglutaryl CoA reducatase (HMG CoA reductase) inhibitors that block mevalonate pathway and cholesterol biosyntheis, which has been used usefully for health improvement and disease control in clinic. In order to know which statin can be used to inhibit HCV replication, we examined the effects of HCV genotype 1b replication by 6 kinds of statins with different structure. We treated six statins to HCV genotype 1b replicon cell. Atorvastatin, simvastatin, fluvastatin, mevastatin, and lovastatin inhibited HCV RNA replication and HCV protein expression in HCV genotype 1b replicon cells, though pravastatin did not affect HCV replication. In order to know whether inhibition of HCV replication by statin is depended on HCV genotype, we treated the statins to HCV genotype 2a producing cells, and investigated HCV RNA replication and HCV protein expression. HCV RNA replication and protein expression was not affected in HCV genotype 2a producing cells by treatment of statins and cholesterol inhibitor. These results suggest that HMG-CoA reductase and cholesterol inhibitors might be used depending on HCV genotype. In addition, inhibition of HCV genotype 1b replication by statins has been depended on structure of various statins which should be seriously selected for HCV clinic. In future, we will study on inhibition of another HCV genotype replication by HMG-CoA reductase and cholesterol inhibitors.

874 EPIGENETIC MODULATION OF TUMOUR SUPPRESSOR GADD45 BETA EXPRESSION BY HCV LEADS TO DEFECTIVE CELL CYCLE ARREST AND MAY PLAY A ROLE IN LIVER CARCINOGENESIS

Background and Aims: Chronic hepatitis C virus (HCV) infection is a major risk factor of hepatocellular carcinoma (HCC). Sustained oxidative stress and elevated DNA damage are considered major contributors to HCC. Gadd45b is a major mediator of the cellular response to DNA damage. Our goal was to study the effect of chronic HCV infection on Gadd45b expression. Methods: Gadd45b expression were analyzed by western blotting or quantitative RT-PCR in: (a) paired non-tumoral and tumoral human liver samples from uninfected patients, and patients chronically infected with hepatitis B virus (HBV) or HCV; (b) Huh7 cell cultures harboring the HCV genotype 1b replicon and the JFH1 infectious strain; (c) liver tissues from 18 month old wild-type (wt) and transgenic mice expressing the full-length HCV open reading frame (FL-N/35). Primary hepatocytes were isolated from 7 month old mice. Promoter hypermethylation was assessed by the effect of 5-azacytidine (a DNA methyltransferase inhibitor) on Gadd45b mRNA expression. Cell cycle arrest and mitotic indices were assessed by the presence of phospho-histone H3 after UV-C irradiation. Results: Gadd45b expression was abrogated in tumoral tissue from HBV-positive or -negative patients, whereas it was found at normal levels in non-tumoral tissues. In contrast, in HCV-infected individuals, Gadd45b was absent from both tumoral and nontumoral tissues. Gadd45b expression was also reduced in Huh7 cells exhibiting HCVRNA replication (although these cells originate from a liver tumor). A 2-fold decrease in levels of Gadd45b mRNA was observed in livers of FL-N/35 mice compared to controls, whereas amounts of related Gadd family members remained unaffected. Activation of the Gadd45b promoter was inhibited in the presence of HCV, with cells isolated from FL-N/35 mice demonstrating a 2-fold reduction in promoter activity compared to wt controls. Reduced murine Gadd45b expression was associated with decreased cell cycle arrest in response to DNA damage, and both Gadd45b expression and cell cycle arrest were restored to wt levels by treatment with 5-azacytidine. Conclusions: These data demonstrate that HCV protein expression is associated with inhibition of Gadd45b expression through hypermethylation of its promoter, adversely altering the DNA damage response and potentially promoting liver carcinogenesis.

The hepatitis C virus core protein indirectly induces alpha-smooth muscle actin expression in hepatic stellate cells via interleukin-8

Progressive deposition of liver fibrosis is a common feature of chronic hepatitis associated with hepatitis C virus (HCV) infection, and it may eventually lead to cirrhosis and liver failure. Although this fibrogenic process appears to be linked to HCV protein expression and replication via indirect mechanisms, i.e., to be mediated by virally-driven inflammation, a direct role of HCV in inducing fibrosis deposition has never been entirely excluded. We established an in vitro system in which the human hepatic stellate cell line LX-2 was cultured in the presence of conditioned medium from human hepatoma Huh-7 cells transduced with a lentiviral vector expressing HCV core proteins of different genotypes. Treatment of LX-2 cells, with conditioned medium from Huh-7 cells expressing HCV core protein, led to the activation of alpha-smooth muscle actin expression. Among the chemokines secreted by cells transduced with HCV core, interleukin-8 was identified as the strongest inducer of alpha-smooth muscle actin expression in LX-2 and primary hepatic stellate cells. This effect was accompanied by a decrease in cell migration and increased focal contact organisation. The expression of the HCV core in hepatocytes may contribute to the establishment of a profibrogenic microenvironment.

Immunohistochemical detection of hepatitis C virus (genotype 4) in B-cell NHL in an Egyptian population: correlation with serum HCV-RNA.

Retrospective evaluation of hepatitis C virus (HCV) prevalence in lymphoma tissues has important applications in clarifying the contribution of viral factors to the pathogenesis. Trials for detection of HCV at the cellular level in lymphoma tissues are, so far, minimal with unsatisfactory results. We aimed to study the detection and localization of HCV in the tissues of B-cell non-Hodgkin lymphoma (NHL) patients. We performed immunohistochemistry to detect the HCV nonstructural 3 protein in paraffin-embedded tissue specimens of B-cell NHL patients, in 39 serum HCV-RNA positive samples and 35 serum HCV-RNA negative samples as controls. The serum analysis was carried out for HCV antibodies using enzyme-linked immunoassay and for HCV-RNA using reverse transcription-polymerase chain reaction. Reverse transcription-polymerase chain reaction was used to detect the HCV-RNA in tissues in immunohistochemically positive cases. We correlated the results with the clinicopathologic characteristics of the patients. A diffuse cytoplasmic immunohistochemical staining for HCV in the lymphoid cells was detected in 8 of 39 serum positive cases (20.5%), all of which were genotype 4, which is the most prevalent HCV genotype in Egypt. Only 2 out of 35 serum negative control samples showed positive staining and in 1 of them HCV-RNA was detected in tissue. No significant correlation was detected between HCV positive cases and the clinicopathologic features of the patients. Immunohistochemical detection of HCV proteins in lymphoma tissues supports a potential role of viral replication in lymphomagenesis. The low number of cases showing expression of viral proteins may represent a low viral load in lymphoid tissue and/or restriction of HCV protein expression to certain subtypes of B-cell NHL. Immunohistochemistry can be used as a complementary tool for specific HCV detection in the paraffin-embedded material of lymphoma tissues not suitable for RNA analysis.

The Isomerase Active Site of Cyclophilin A Is Critical for Hepatitis C Virus Replication

Cyclosporine A and nonimmunosuppressive cyclophilin (Cyp) inhibitors such as Debio 025, NIM811, and SCY-635 block hepatitis C virus (HCV) replication in vitro. This effect was recently confirmed in HCV-infected patients where Debio 025 treatment dramatically decreased HCV viral load, suggesting that Cyps inhibitors represent a novel class of anti-HCV agents. However, it remains unclear how these compounds control HCV replication. Recent studies suggest that Cyps are important for HCV replication. However, a profound disagreement currently exists as to the respective roles of Cyp members in HCV replication. In this study, we analyzed the respective contribution of Cyp members to HCV replication by specifically knocking down their expression by both transient and stable small RNA interference. Only the CypA knockdown drastically decreased HCV replication. The re-expression of an exogenous CypA escape protein, which contains escape mutations at the small RNA interference recognition site, restored HCV replication, demonstrating the specificity for the CypA requirement. We then mutated residues that reside in the hydrophobic pocket of CypA where proline-containing peptide substrates and cyclosporine A bind and that are vital for the enzymatic or the hydrophobic pocket binding activity of CypA. Remarkably, these CypA mutants fail to restore HCV replication, suggesting for the first time that HCV exploits either the isomerase or the chaperone activity of CypA to replicate in hepatocytes and that CypA is the principal mediator of the Cyp inhibitor anti-HCV activity. Moreover, we demonstrated that the HCV NS5B polymerase associates with CypA via its enzymatic pocket. The study of the roles of Cyps in HCV replication should lead to the identification of new targets for the development of alternate anti-HCV therapies.

Effects of silymarin on hepatitis C virus and haem oxygenase‐1 gene expression in human hepatoma cells

Hepatitis C virus (HCV) infection is a global medical problem. The current standard treatment of chronic hepatitis C (CHC), pegylated interferon plus ribavirin, is prolonged, expensive, has serious side effects and, at best, is only 50% effective. Silymarin (SI) is a natural antioxidant often used by patients with CHC, although its efficacy for decreasing HCV levels or ameliorating CHC remains uncertain. HCV infection is associated with increased hepatic oxidative stress, and one of the antioxidant enzymes that protect cells against this stress is haem oxygenase-1 (HO-1). We investigated effects of SI on HCV and HO-1 gene expression in Huh-7 cells, CNS3 and 9-13 cells (the latter two stably expressing HCV-proteins). Silymarin significantly downregulated HCV core mRNA (by 20%-36%) and protein (by 30%-60%) in CNS3 cells. In contrast, SI did not decrease HCV NS5A mRNA or protein expression in 9-13 cells. HO-1 mRNA was upregulated (60%-400%) by SI in Huh-7, CNS3 and 9-13 cells, whereas BTB and CNC homology 1 and nuclear factor erythroid related factor 2 mRNA levels were not affected. The effect of SI to downregulate HCV core was not related to changes in the Janus-activated tyrosine kinases-signal transducer and activators of transcription signalling pathway. Silymarin may be of benefit in CHC, although prospective, randomized, controlled trials are needed to be certain.

Differential Expression of the CXCR3 Ligands in Chronic Hepatitis C Virus (HCV) Infection and Their Modulation by HCV In Vitro

To investigate chemokine expression networks in chronic hepatitis C virus (HCV) infection, we used microarray analysis to determine chemokine expression in human infection and in chimpanzees experimentally infected with HCV. The CXCR3 chemokine family was highly expressed in both human and chimpanzee infection. CXCL10 was the only CXCR3 chemokine elevated in the serum, suggesting that it may neutralize any CXCR3 chemokine gradient established between the periphery and liver by CXCL11 and CXCL9. Thus, CXCR3 chemokines may not be responsible for recruitment of T lymphocytes but may play a role in positioning these cells within the liver. The importance of the CXCR3 chemokines, in particular CXCL11, was highlighted by replicating HCV (JFH-1) to selectively upregulate its expression in response to gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). This selective upregulation was confirmed at the transcriptional level by using the CXCL11 promoter driving the luciferase reporter gene. This synergistic increase in expression was not a result of HCV protein expression but the nonspecific innate response to double-stranded RNA (dsRNA), as both in vitro-transcribed HCV RNA and the dsRNA analogue poly(I:C) increased CXCL11 expression and promoter activity. Furthermore, we show that CXCL11 is an IRF3 (interferon regulatory factor 3) response gene whose expression is selectively enhanced by IFN-gamma and TNF-alpha. In conclusion, the CXCR3 chemokines are the most significantly expressed chemokines in chronic hepatitis C and most likely play a role in positioning T cells in the liver. Furthermore, HCV can selectively increase CXCL11 expression in response to IFN-gamma and TNF-alpha stimulation that may play a role in the pathogenesis of HCV-related liver disease.

Reply

Our article1 reported that viral RNA could not be detected in the peripheral blood mononuclear cells (PBMCs) of aviremic seropositive blood donors, a conclusion supported by another recent article which also concluded that there was no evidence for persistent hepatitis C virus (HCV) infection in PBMCs after clearance of viremia in plasma.2 Decreasing or disappearing anti-HCV antibody titers in aviremic subjects also argue against continued HCV protein expression.3 Whether other reservoirs of HCV RNA, such as hepatocytes, exist in aviremic subjects remains unclear with some4-6 although not all7, 8 studies finding no HCV RNA in the liver of treated sustained viral responders. We clearly acknowledged1 that in chronically viremic subjects, PBMCs could be a site of HCV replication and that in vitro mitogen plus cytokine treatment might increase PBMC-associated HCV levels.8-10 With respect to the relative sensitivities of the HCV RNA assays used, we performed two different tests for HCV RNA in PBMCs (cell-associated transcription-mediated amplification [CA-TMA] and reverse transcription nested polymerase chain reaction [RT-nPCR]). We demonstrated a sensitivity of 2-50 HCV RNAs in 5 million PBMCs for the CA-TMA assay and 15-150 HCV RNAs in 5 million cells using RT-nPCR (adjusted from a sensitivity of 1-10 HCV RNAs for RT-nPCR, because only a fraction of total PBMC RNA and derived complementary DNA is sampled).1 Pham et al. report a sensitivity for their RT-nPCR-NAH (nucleic acid hybridization) assay of <10 viral genome equivalent (vge)/mL for serum (and in their letter, <5 vge/million PBMCs). We quantified the sensitivities of our assays using serial dilutions of plasma samples of known viral loads (prequantified using a commercial viral load assay) in the presence of total cellular RNA, as well as of total RNA from the PBMC of viremic subjects and showed the actual replicate assay results.1 Pham et al. used dilutions of a plasmid without interfering cellular nucleic acids for “semiquantitative estimation” in a “preliminary experiment” whose results where not shown.10 The fraction of total complementary DNA derived from PBMCs or 250 μL serum they used as input for their nPCR was not specified.10 With regard to the total number of cell equivalents analyzed in respective assays, we indeed analyzed only 0.16 million PBMCs by RT-nPCR but in parallel, and with consistent results, also used CA-TMA on 2.5 million PBMCs,1 slightly more than the 1 million to 2 million PBMCs Pham and Michalak reported in their letter. We agree with Pham and Michalak that difference in assay sensitivity is a likely explanation for the reported discrepancy but feel that the more relevant assay is that used for detecting HCV RNA in plasma. In our case, we used an extensively validated plasma HCV RNA assay used for blood-donation screening (Transcription mediated amplification, Procleix human immunodeficieny virus-1/HCV assay, Gen-probe, with a 95% detection sensitivity of 30 HCV RNA/mL).11-13 This TMA assay was used in duplicate assays (consuming a total of 1 mL plasma) to identify a total of 69 plasma aviremic blood donors, none of whom possessed detectable PBMC-associated HCV RNA.1 Pham et al. analyzed and found HCV RNA in the PBMCs of two aviremic subjects (so classified using their RT-nPCR-NAH).10 We suspect that further testing of the plasma from these two subjects using TMA assays might have detected a low-level viremia. Also, mostly consistent with our results, Pham et al. reported in 2008 detecting HCV RNA in only one of 10 PBMCs from aviremic subjects (although stimulation with interleukin-2 plus mitogen and testing of purified immune cell subsets lead to the detection of HCV RNA in all 10 PBMCs).14 Our selection criterion for the absence of plasma viremia (based on a highly sensitive, extensively validated assay used in duplicate tests to increase sensitivity) may therefore have been more stringent than that used by Pham et al. and account for the discrepant results seen in PBMCs. Ultimately, we agree with Pham and Michalak that the question of a residual HCV reservoir in the PBMCs of truly aviremic subjects will best be resolved using the demonstrably most sensitive detection assays for HCV RNA in both plasma and PBMC. The use of the same HCV RNA quantitation standards15 by different groups will help compare assay sensitivities. Eric Delwart Ph.D.*, * Blood Systems Research Institute, Department of Laboratory Medicine, University of California, San Francisco, San Francisco CA.

Differential expression of genes related to transcription in cultured hepatoma cells with intact genome of hepatitis C virus

To investigate the effects of hepatitis C virus (HCV) on transcription regulation genes of host cells by gene chip assays in cultured cells with intact HCV genome. Huh-7 hepatoma cells were cultured and infected with in vitro constructed HCV. The total RNAs, proteins and cell culture supernatants of HCV infected cells and control cells were isolated. Proteins and cell culture supernatants were used to detect the HCV replication and protein expression in cell culture system. The HCV protein expression was detected with Western blotting. Released HCV from infected cells was analyzed by real-time fluorescence quantitative PCR. Total RNA was qualified using 10 g/L agarose gel electrophoresis. cRNA was synthesized, fluorescence labeled and purified, then hybridized with Agilent oligo microarray (20173 probes). Differential expression of genes related to transcription in cell culture system was analyzed. HCV was positive in cell culture supernatants and HCV protein expression was also positive according to Western blotting results. Eleven up-regulated and 11 down-regulated genes related to transcription were found after Agilent gene chip screening. Intact hepatitis C virus cell culture system provides an useful tool for study on the affects of HCV infection on transcription regulation genes in host cells.

Hepatitis C virus structural proteins do not prevent human dendritic cell maturation

Infection with hepatitis C virus (HCV) results in chronic hepatitis in more than 70% of cases. Alterations in the maturation of dendritic cells (DC) might play a role in the immune system's inability to eliminate the virus, although viral factors that could be involved have not been identified. This study in vitro investigated whether HCV structural proteins affect maturation of monocyte-derived DC. HCV proteins (core, E1, E2) were expressed by transduction with recombinant adenoviruses of immature DC. The ability of these transduced DC to respond to a maturation stimulus was evaluated by measuring cell surface markers, allogenic lymphocyte stimulation and interleukin (IL)-12 production. Expression of HCV structural proteins did not modify DC maturation in the presence of lipopolysaccharide, as determined by their phenotype and stimulatory functioning. IL-12 secretion was not affected by HCV protein expression in mature DC. Our results suggest that HCV structural proteins do not affect maturation of monocyte-derived DC by lipopolysaccharide. These findings are important for further studies to clarify the pathogenesis of chronic HCV infection and towards the rational design of cellular vaccine approaches for immunotherapy against hepatitis C.

Responses of Nontransformed Human Hepatocytes to Conditional Expression of Full-Length Hepatitis C Virus Open Reading Frame

Hepatitis C virus (HCV) is a major cause of chronic hepatitis that can lead to cirrhosis and hepatocellular carcinoma. To study the effects of HCV protein expression on host cells, we established conditional expression of the full-length open reading frame (ORF) of an infectious cDNA clone of HCV (genotype 1a, H77 strain) in the nontransformed human hepatocyte line cell HH4 using the ecdysone receptor regulatory system. Treatment with the ecdysone analog ponasterone-A induced tightly regulated and dose-dependent full-length HCV ORF expression and properly processed HCV proteins. HCV Core, NS3, and NS5A colocalized in perinuclear regions and associated with the early endosomal protein EEA1. HCV ORF expression caused marked growth inhibition, increased intracellular reactive oxygen species, up-regulation of glutamate-l-cysteine ligase activity, increased glutathione level, and activation of nuclear factor kappaB. Although it was not directly cytotoxic, HCV ORF expression sensitized HH4 cells to Fas at certain concentrations but not to tumor necrosis factor-related apoptosis-inducing ligand. HCV ORF expression in HH4 cells up-regulated genes involved in innate immune response/inflammation and oxidative stress responses and down-regulated cell growth-related genes. Expression of HCV ORF in host cells may contribute to HCV pathogenesis by producing oxidative stress and increasing the expression of genes related to the innate immune response and inflammation.

Cre-estrogen receptor-mediated hepatitis C virus structural protein expression in mice

Hepatocyte apoptosis is an important feature of liver injury in hepatitis C virus (HCV) infection. However, the mechanism of apoptosis and consequences on disease progression in vivo have not been investigated fully in part due to the lack of adequate small animal models. In this study, transgenic (tg) mice were produced that express conditionally HCV structural proteins (core, E1, E2 and p7) in the liver following Cre-mediated DNA recombination. Using a novel Cre-estrogen receptor fusion protein (Cre-ER) induction strategy, tamoxifen was injected intraperitoneally (i.p.), which induced Cre nuclear translocation, transgene recombination and HCV protein expression in the liver. Hepatic expression of HCV core and envelope proteins resulted in increased hepatocyte apoptosis, detected by the TUNEL assay, between 7 and 33 days after induction. These results were confirmed by the presence of increased levels of apoptosis-associated cytokeratin 18 (CK-18) in the sera of the same animals. The presence of cleaved caspase-3 and elevated levels of CHOP/GADD153 in the liver suggests an endoplasmic reticulum (ER) stress-associated apoptosis mechanism. This study suggests an in vivo correlation between HCV structural protein expression, ER stress and hepatocyte apoptosis, implicating a potentially important mechanism of HCV pathogenesis.

Hepatitis C virus expression and interferon antiviral action is dependent on PKR expression

Interferon (IFN)-inducible double-stranded RNA-activated protein kinase (PKR) is thought to play a key antiviral role against hepatitis C virus (HCV). However, demonstrating the importance of PKR expression on HCV protein synthesis in the presence or absence of IFN has proven difficult in vivo. In the present experiment, full-length HCV constructs were transiently transfected into two cell lines stably expressing T7 RNA polymerase. HCV expression was monitored under conditions of upregulated or downregulated PKR expression. In addition, IFN was monitored during downregulation of PKR. HCV expression effectively increased PKR expression, as well as that of its regulated proteins. PKR was obviously knocked down by PKR-specific siRNA, which resulted in significantly increased HCV core protein levels. Conversely, over-expression of PKR significantly suppressed HCV core levels in both cell lines. Furthermore, IFN induced high levels of PKR, whereas downregulation of PKR reversed IFN's antiviral effects and increased HCV core levels. Based on these results, it appears that HCV protein expression is directly dependent on PKR expression. PKR is antiviral toward HCV and responsible for IFN's effect against HCV.

Hepatitis C virus protein expression causes calcium-mediated mitochondrial bioenergetic dysfunction and nitro-oxidative stress

Hepatitis C virus (HCV) infection induces a state of oxidative stress that is more pronounced than that in many other inflammatory diseases. In this study we used well-characterized cell lines inducibly expressing the entire HCV open-reading frame to investigate the impact of viral protein expression on cell bioenergetics. It was shown that HCV protein expression has a profound effect on cell oxidative metabolism, with specific inhibition of complex I activity, depression of mitochondrial membrane potential and oxidative phosphorylation coupling efficiency, increased production of reactive oxygen and nitrogen species, as well as loss of the Pasteur effect. Importantly, all these effects were causally related to mitochondrial calcium overload, as inhibition of mitochondrial calcium uptake completely reversed the observed bioenergetic alterations. Expression of HCV proteins causes deregulation of mitochondrial calcium homeostasis. This event occurs upstream of further mitochondrial dysfunction, leading to alterations in the bioenergetic balance and nitro-oxidative stress. These observations provide new insights into the pathogenesis of hepatitis C and may offer new opportunities for therapeutic intervention.

In vitro antiviral activity of SCH446211 (SCH6), a novel inhibitor of the hepatitis C virus NS3 serine protease

Current hepatitis C virus (HCV) therapies may cure approximately 60% of infections. They are often contraindicated or poorly tolerated, underscoring the need for safer and more effective drugs. A novel, alpha-ketoamide-derived, substrate-based inhibitor of the HCV serine protease (SCH446211) was developed. Compared with earlier reported inhibitors of similar chemical class, it has a P1'-P2' extension which provides extended interaction with the protease active site. The aim of this study was to evaluate the in vitro antiviral activity of SCH446211. Binding constant of SCH446211 to HCV NS3 protease was measured with the chromogenic substrate in vitro cleavage assay. Cell-based activity of SCH446211 was evaluated in replicon cells, which are Huh-7 hepatoma cells stably transfected with a subgenomic HCV RNA as reported previously. After 72 h of incubation with SCH446211, viral transcription and protein expression were measured by real-time RT-PCR (TaqMan), quantitative in situ hybridization, immunoblot and indirect immunofluorescence. The binding constant of SCH446211 to HCV NS3 protease was 3.8 +/- 0.4 nM. HCV replication and protein expression were inhibited by SCH446211 in replicon cells as consistently shown by four techniques. In particular, based on quantitative real-time RT-PCR measurements, the IC50 and IC90 of SCH446211 were estimated to be 40 +/- 20 and 100 +/- 20 nM (n = 17), respectively. Long-term culture of replicon cells with SCH446211 reduced replicon RNA to <0.1 copy per cell. SCH446211 did not show cellular toxicity at concentrations up to 50 microM. SCH446211 is a potent inhibitor of HCV protease in vitro. Its extended interaction with the HCV NS3 protease active site is associated with potent in vitro antiviral activity. This observation is potentially a useful guide for development of future potent inhibitors against HCV NS3 protease.