Host factors involved in the replication of hepatitis C virus

CRISPR/Cas9 as a New Antiviral Strategy for Treating Hepatitis Viral Infections

Hepatitis is an inflammatory liver disease primarily caused by hepatitis A (HAV), B (HBV), C (HCV), D (HDV), and E (HEV) viruses. The chronic forms of hepatitis resulting from HBV and HCV infections can progress to cirrhosis or hepatocellular carcinoma (HCC), while acute hepatitis can lead to acute liver failure, sometimes resulting in fatality. Viral hepatitis was responsible for over 1 million reported deaths annually. The treatment of hepatitis caused by viral infections currently involves the use of interferon-α (IFN-α), nucleoside inhibitors, and reverse transcriptase inhibitors (for HBV). However, these methods do not always lead to a complete cure for viral infections, and chronic forms of the disease pose significant treatment challenges. These facts underscore the urgent need to explore novel drug developments for the treatment of viral hepatitis. The discovery of the CRISPR/Cas9 system and the subsequent development of various modifications of this system have represented a groundbreaking advance in the quest for innovative strategies in the treatment of viral infections. This technology enables the targeted disruption of specific regions of the genome of infectious agents or the direct manipulation of cellular factors involved in viral replication by introducing a double-strand DNA break, which is targeted by guide RNA (spacer). This review provides a comprehensive summary of our current knowledge regarding the application of the CRISPR/Cas system in the regulation of viral infections caused by HAV, HBV, and HCV. It also highlights new strategies for drug development aimed at addressing both acute and chronic forms of viral hepatitis.

Effect of P-body component Mov10 on HCV virus production and infectivity

Mov10 is a processing body (P-body) protein and an interferon-stimulated gene that can affect replication of retroviruses, hepatitis B virus, and hepatitis C virus (HCV). The mechanism of HCV inhibition by Mov10 is unknown. Here, we investigate the effect of Mov10 on HCV infection and determine the virus life cycle steps affected by changes in Mov10 overexpression. Mov10 overexpression suppresses HCV RNA in both infectious virus and subgenomic replicon systems. Additionally, Mov10 overexpression decreases the infectivity of released virus, unlike control P-body protein DCP1a that has no effect on HCV RNA production or infectivity of progeny virus. Confocal imaging of uninfected cells shows endogenous Mov10 localized at P-bodies. However, in HCV-infected cells, Mov10 localizes in circular structures surrounding cytoplasmic lipid droplets with NS5A and core protein. Mutagenesis experiments show that the RNA binding activity of Mov10 is required for HCV inhibition, while its P-body localization, helicase, and ATP-binding functions are not required. Unexpectedly, endogenous Mov10 promotes HCV replication, as CRISPR-Cas9-based Mov10 depletion decreases HCV replication and infection levels. Our data reveal an important and complex role for Mov10 in HCV replication, which can be perturbed by excess or insufficient Mov10.

Serum and exosomal miR-122 and miR-199a as a biomarker to predict therapeutic efficacy of hepatitis C patients

MicroRNA (miRNA), which has been shown to correlate with liver functions, has been proposed as a new biomarker reflecting liver injury. The aim of the study was to investigate miRNA-122 (miR-122) and mir-RNA-199a (miR-199a) as a biomarker for predicting therapeutic efficacy in hepatitis C (HepC) patients. A total of 47 HepC 1b patients and 16 healthy subjects were enrolled in the study. Serum and exosomal mir-RNAs and other conventional biomarkers reflecting liver function were evaluated. The miR-122 levels in serum (miR-122_ser ) and exosomes (miR-122_exo ) were significantly lower in the Hepatitis C virus (HCV) genotype 1b patients than in the normal controls, but these levels were higher compared to the non-genotype 1b group. The mean miR-122_ser level in the sustained virological response (SVR) group was significantly higher than that in the non-response (NR) group (P < 0.01), and the miR-122_exo level in the SVR group was also higher than that in the NR group (P > 0.05), although this difference was not significant. miR-199a levels showed similar trends with the miR-122 levels in serum and exosomes. HCV RNA_ser was negatively correlated with the miR-122_ser (r = -0.473, P = 0.004) and miR-122_exo (r = -0.424, P = 0.009) levels. miR-122_ser levels were positively associated with miR-199a_ser levels (r = 0.453, P = 0.002)_. Univariate and multivariate regression analyses reveal that the miR-122_ser levels and ALT/AST ratio demonstrated a predictive value in evaluating patient outcomes. Serum miR-122 and miR-199a are potential biomarkers that reflect therapeutic efficacy.

Two-amino acids change in the nsp4 of SARS coronavirus abolishes viral replication

Infection with coronavirus rearranges the host cell membrane to assemble a replication/transcription complex in which replication of the viral genome and transcription of viral mRNA occur. Although coexistence of nsp3 and nsp4 is known to cause membrane rearrangement, the mechanisms underlying the interaction of these two proteins remain unclear. We demonstrated that binding of nsp4 with nsp3 is essential for membrane rearrangement and identified amino acid residues in nsp4 responsible for the interaction with nsp3. In addition, we revealed that the nsp3-nsp4 interaction is not sufficient to induce membrane rearrangement, suggesting the participation of other factors such as host proteins. Finally, we showed that loss of the nsp3-nsp4 interaction eliminated viral replication by using an infectious cDNA clone and replicon system of SARS-CoV. These findings provide clues to the mechanism of the replication/transcription complex assembly of SARS-CoV and could reveal an antiviral target for the treatment of betacoronavirus infection.

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H120 and F121 in the lumenal loop in nsp4 are essential for binding to nsp3.

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H120&F121 substitutions in nsp4 cause defect in membrane rearrangement function.

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Interaction with nsp3 through H120&F121 in nsp4 is crucial for viral propagation.

Inhibition of hepatitis C virus using siRNA targeted to the virus and Hsp90

Hepatitis C (HCV) is a viral disease affecting millions of people worldwide, and persistent HCV infection can lead to progressive liver disease with the development of liver cirrhosis and hepatocellular carcinoma. During treatment for hepatitis C, the occurrence of viral resistance is common. To reduce the occurrence of resistance, new viral treatments should target both viral and cellular factors. Many interactions occur between viral and host proteins during the HCV replication cycle and might be used for the development of new therapies against hepatitis C. Heat shock protein 90 (Hsp90) plays a role in the folding of cellular and viral proteins and also interacts with HCV proteins. In the present study, we knocked down the expression of the Hsp90 gene and inhibited viral replication using siRNA molecules. Reducing the expression of Hsp90 successfully decreased HCV replication. All siRNA molecules specific to the viral genome showed the efficient inhibition of viral replication, particularly siRNA targeted to the 5'UTR region. The combination of siRNAs targeting the viral genome and Hsp90 mRNA also successfully reduced HCV replication and reduced the occurrence of viral resistance. Moreover, these results suggest that an approach based on the combination of cellular and viral siRNAs can be used as an effective alternative for hepatitis C viral suppression.

Expanding the proteome of an RNA virus by phosphorylation of an intrinsically disordered viral protein

The human proteome contains myriad intrinsically disordered proteins. Within intrinsically disordered proteins, polyproline-II motifs are often located near sites of phosphorylation. We have used an unconventional experimental paradigm to discover that phosphorylation by protein kinase A (PKA) occurs in the intrinsically disordered domain of hepatitis C virus non-structural protein 5A (NS5A) on Thr-2332 near one of its polyproline-II motifs. Phosphorylation shifts the conformational ensemble of the NS5A intrinsically disordered domain to a state that permits detection of the polyproline motif by using (15)N-, (13)C-based multidimensional NMR spectroscopy. PKA-dependent proline resonances were lost in the presence of the Src homology 3 domain of c-Src, consistent with formation of a complex. Changing Thr-2332 to alanine in hepatitis C virus genotype 1b reduced the steady-state level of RNA by 10-fold; this change was lethal for genotype 2a. The lethal phenotype could be rescued by changing Thr-2332 to glutamic acid, a phosphomimetic substitution. Immunofluorescence and transmission electron microscopy showed that the inability to produce Thr(P)-2332-NS5A caused loss of integrity of the virus-induced membranous web/replication organelle. An even more extreme phenotype was observed in the presence of small molecule inhibitors of PKA. We conclude that the PKA-phosphorylated form of NS5A exhibits unique structure and function relative to the unphosphorylated protein. We suggest that post-translational modification of viral proteins containing intrinsic disorder may be a general mechanism to expand the viral proteome without a corresponding expansion of the genome.

Hepatitis C virus RNA replication

Genome replication is a crucial step in the life cycle of any virus. HCV is a positive strand RNA virus and requires a set of nonstructural proteins (NS3, 4A, 4B, 5A, and 5B) as well as cis-acting replication elements at the genome termini for amplification of the viral RNA. All nonstructural proteins are tightly associated with membranes derived from the endoplasmic reticulum and induce vesicular membrane alterations designated the membranous web, harboring the viral replication sites. The viral RNA-dependent RNA polymerase NS5B is the key enzyme of RNA synthesis. Structural, biochemical, and reverse genetic studies have revealed important insights into the mode of action of NS5B and the mechanism governing RNA replication. Although a comprehensive understanding of the regulation of RNA synthesis is still missing, a number of important viral and host determinants have been defined. This chapter summarizes our current knowledge on the role of viral and host cell proteins as well as cis-acting replication elements involved in the biogenesis of the membranous web and in viral RNA synthesis.

Ca(2+) /S100 proteins regulate HCV virus NS5A-FKBP8/FKBP38 interaction and HCV virus RNA replication

BACKGROUND & AIM

FKBP8/FKBP38 is a unique FK506-binding protein with a C-terminal membrane anchor and localizes at the outer membranes of mitochondria and the endoplasmic reticulum. Similar to some immunophilins, such as FKBP51, FKBP52 and Cyclophilin 40, FKBP8/FKBP38 contain a putative Calmodulin-binding domain and a tetratricopeptide-repeat (TPR) domain for the binding of Hsp90. Both Hsp90 and the non-structural protein 5A (NS5A) of the hepatitis C virus (HCV) interact specifically with FKBP8/FKBP38 through its TPR domain, and the ternary complex formation plays a critical role in HCV RNA replication. The goal of this study is to evaluate that the host factor inhibits the ternary complex formation and the replication of HCV in vitro and in vivo.

METHODS

S100 proteins, FKBP38, FKBP8, HCV NS5A, Hsp90, and calmodulin were expressed in E.coli and purified. In vitro binding studies were performed by GST pull-down, S-tag pull-down and surface plasmon resonance analyses. The effect of S100 proteins on HCV replication was analysed by Western blotting using an HCV NS3 antibody following transfection of S100 proteins into the HCV replicon harbouring cell line (sO cells).

RESULTS

In vitro binding studies showed that S100A1, S100A2, S100A6, S100B and S100P directly interacted with FKBP8/FKBP38 in a Ca(2+) -dependent manner and inhibited the FKBP8/FKBP38-Hsp90 and FKBP8/FKBP38-NS5A interactions. Furthermore, overexpression of S100A1, S100A2 and S100A6 in sO cells resulted in the efficient inhibition of HCV replication.

CONCLUSION

The association of the S100 proteins with FKBP8/FKBP38 provides a novel Ca(2+) -dependent regulatory role in HCV replication through the NS5A-host protein interaction.

Sigma-1 receptor regulates early steps of viral RNA replication at the onset of hepatitis C virus infection

Hepatitis C virus (HCV) genome replication is thought to occur in a membranous cellular compartment derived from the endoplasmic reticulum (ER). The molecular mechanisms by which these membrane-associated replication complexes are formed during HCV infection are only starting to be unraveled, and both viral and cellular factors contribute to their formation. In this study, we describe the discovery of nonopioid sigma-1 receptor (S1R) as a cellular factor that mediates the early steps of viral RNA replication. S1R is a cholesterol-binding protein that resides in lipid-rich areas of the ER and in mitochondrion-associated ER membranes (MAMs). Several functions have been ascribed to this ER-resident chaperone, many of which are related to Ca(2+) signaling at the MAMs and lipid storage and trafficking. Downregulation of S1R expression by RNA interference (RNAi) in Huh-7 cells leads to a proportional decrease in susceptibility to HCV infection, as shown by reduced HCV RNA accumulation and intra- and extracellular infectivity in single-cycle infection experiments. Similar RNAi studies in persistently infected cells indicate that S1R expression is not rate limiting for persistent HCV RNA replication, as marked reduction in S1R in these cells does not lead to any decrease in HCV RNA or viral protein expression. However, subgenomic replicon transfection experiments indicate that S1R expression is rate limiting for HCV RNA replication without impairing primary translation. Overall, our data indicate that the initial steps of HCV infection are regulated by S1R, a key component of MAMs, suggesting that these structures could serve as platforms for initial RNA replication during HCV infection.

[miR-122 participates in the cell tropism of hepatitis C virus]

Hepatitis C virus (HCV) exhibits a narrow host range and a specific tissue tropism. Studies on HCV life cycle have been progressed by the developments of in vitro replication and infection systems and an HCV laboratory strain (HCVcc) capable of propagating in human hepatoma cell line, Huh7 cells. Mice expressing four human entry receptor candidates for HCV permit entry of HCVcc, therefore tissue tropism of HCV was believed to be rely on the expression of the entry receptors. However, HCV infection is often associated with extra-hepatic manifestations and the determinants for cell tropism of HCV remain elusive. Recently, we have shown that several nonhepatic cell lines permit HCV-RNA replication through an expression of a liver-specific microRNA, miR-122, upon infection with HCVcc, while no infectious particle was produced. In the nonhepatic cells, only small numbers of lipid droplets and low levels of VLDL-associated proteins were observed in compared with Huh7 cells, suggesting that expression of miR-122 and functional lipid metabolism participates in the replication and assembly of HCVcc, respectively In this review, we would like to discuss about involvement of miR-122 and functional lipid metabolism in the determination of HCV cell tropism.

Structures of hepatitis C virus nonstructural proteins required for replicase assembly and function

Approximately 3% of the world population is infected with hepatitis C virus (HCV), causing a serious public health burden. Like other positive-strand RNA viruses, HCV assembles replicase complexes in association with cellular membranes and produces progeny RNA genomes through negative-strand intermediates. The viral proteins required for RNA replication are nonstructural (NS) proteins NS3 to NS5B. Owing to many obstacles and limitations in structural characterization of proteins and complexes with multiple transmembrane segments, attempts to understand the assembly and action of the HCV replicase complex have been challenging. Nevertheless, great progress has been made in obtaining structural information for several replicase components, providing insights into some aspects of the viral genome replication machinery.

Hepatitis C virus replication is modulated by the interaction of nonstructural protein NS5B and fatty acid synthase

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) is an RNA-dependent RNA polymerase (RdRp) that acts as a key player in the HCV replication complex. Understanding the interplay between the viral and cellular components of the HCV replication complex could provide new insight for prevention of the progression of HCV-associated hepatocellular carcinoma (HCC). In this study, the NS5B protein was used as the bait in a pulldown assay to screen for NS5B-interacting proteins that are present in Huh7 hepatoma cell lysates. After mass spectrophotometric analysis, fatty acid synthase (FASN) was found to interact with NS5B. Coimmunoprecipitation and double staining assays further confirmed the direct binding between NS5B and FASN. The domain of NS5B that interacts with FASN was also determined. Moreover, FASN was associated with detergent-resistant lipid rafts and colocalized with NS5B in active HCV replication complexes. In addition, overexpression of FASN enhanced HCV expression in Huh7/Rep-Feo cells, while transfection of FASN small interfering RNA (siRNA) or treatment with FASN-specific inhibitors decreased HCV replication and viral production. Notably, FASN directly increased HCV NS5B RdRp activity in vitro. These results together indicate that FASN interacts with NS5B and modulates HCV replication through a direct increase of NS5B RdRp activity. FASN may thereby serve as a target for the treatment of HCV infection and the prevention of HCV-associated HCC progression.

Role of miR-122 and lipid metabolism in HCV infection

Hepatitis C virus (HCV) exhibits a narrow host range and a specific tissue tropism. Mice expressing major entry receptors for HCV permit viral entry, and therefore the species tropism of HCV infection is considered to be reliant on the expression of the entry receptors. However, HCV receptor candidates are expressed and replication of HCV-RNA can be detected in several nonhepatic cell lines, suggesting that nonhepatic cells are also susceptible to HCV infection. Recently it was shown that the exogenous expression of a liver-specific microRNA, miR-122, facilitated the efficient replication of HCV not only in hepatic cell lines, including Hep3B and HepG2 cells, but also in nonhepatic cell lines, including Hec1B and HEK-293T cells, suggesting that miR-122 is required for the efficient replication of HCV in cultured cells. However, no infectious particle was detected in the nonhepatic cell lines, in spite of the efficient replication of HCV-RNA. In the nonhepatic cells, only small numbers of lipid droplets and low levels of very-low-density lipoprotein-associated proteins were observed compared with findings in the hepatic cell lines, suggesting that functional lipid metabolism participates in the assembly of HCV. Taken together, these findings indicate that miR-122 and functional lipid metabolism are involved in the tissue tropism of HCV infection. In this review, we would like to focus on the role of miR-122 and lipid metabolism in the cell tropism of HCV.

Inhibition of hepatitis C virus replication and viral helicase by ethyl acetate extract of the marine feather star Alloeocomatella polycladia

Hepatitis C virus (HCV) is a causative agent of acute and chronic hepatitis, leading to the development of hepatic cirrhosis and hepatocellular carcinoma. We prepared extracts from 61 marine organisms and screened them by an in vitro fluorescence assay targeting the viral helicase (NS3), which plays an important role in HCV replication, to identify effective candidates for anti-HCV agents. An ethyl acetate-soluble fraction of the feather star Alloeocomatella polycladia exhibited the strongest inhibition of NS3 helicase activity, with an IC(50) of 11.7 µg/mL. The extract of A. polycladia inhibited interaction between NS3 and RNA but not ATPase of NS3. Furthermore, the replication of the replicons derived from three HCV strains of genotype 1b in cultured cells was suppressed by the extract with an EC(50) value of 23 to 44 µg/mL, which is similar to the IC(50) value of the NS3 helicase assay. The extract did not induce interferon or inhibit cell growth. These results suggest that the unknown compound(s) included in A. polycladia can inhibit HCV replication by suppressing the helicase activity of HCV NS3. This study may present a new approach toward the development of a novel therapy for chronic hepatitis C.

Establishment of a novel permissive cell line for the propagation of hepatitis C virus by expression of microRNA miR122

The robust cell culture systems for hepatitis C virus (HCV) are limited to those using cell culture-adapted clones (HCV in cell culture [HCVcc]) and cells derived from the human hepatoma cell line Huh7. However, accumulating data suggest that host factors, including innate immunity and gene polymorphisms, contribute to the variation in host response to HCV infection. Therefore, the existing in vitro systems for HCV propagation are not sufficient to elucidate the life cycle of HCV. A liver-specific microRNA, miR122, has been shown to participate in the efficient replication of HCV. In this study, we examined the possibility of establishing a new permissive cell line for HCV propagation by the expression of miR122. A high level of miR122 was expressed by a lentiviral vector placed into human liver cell lines at a level comparable to the endogenous level in Huh7 cells. Among the cell lines that we examined, Hep3B cells stably expressing miR122 (Hep3B/miR122) exhibited a significant enhancement of HCVcc propagation. Surprisingly, the levels of production of infectious particles in Hep3B/miR122 cells upon infection with HCVcc were comparable to those in Huh7 cells. Furthermore, a line of "cured" cells, established by elimination of HCV RNA from the Hep3B/miR122 replicon cells, exhibited an enhanced expression of miR122 and a continuous increase of infectious titers of HCVcc in every passage. The establishment of the new permissive cell line for HCVcc will have significant implications not only for basic HCV research but also for the development of new therapeutics.

Dysfunction of autophagy participates in vacuole formation and cell death in cells replicating hepatitis C virus

Hepatitis C virus (HCV) is a major cause of chronic liver diseases. A high risk of chronicity is the major concern of HCV infection, since chronic HCV infection often leads to liver cirrhosis and hepatocellular carcinoma. Infection with the HCV genotype 1 in particular is considered a clinical risk factor for the development of hepatocellular carcinoma, although the molecular mechanisms of the pathogenesis are largely unknown. Autophagy is involved in the degradation of cellular organelles and the elimination of invasive microorganisms. In addition, disruption of autophagy often leads to several protein deposition diseases. Although recent reports suggest that HCV exploits the autophagy pathway for viral propagation, the biological significance of the autophagy to the life cycle of HCV is still uncertain. Here, we show that replication of HCV RNA induces autophagy to inhibit cell death. Cells harboring an HCV replicon RNA of genotype 1b strain Con1 but not of genotype 2a strain JFH1 exhibited an incomplete acidification of the autolysosome due to a lysosomal defect, leading to the enhanced secretion of immature cathepsin B. The suppression of autophagy in the Con1 HCV replicon cells induced severe cytoplasmic vacuolation and cell death. These results suggest that HCV harnesses autophagy to circumvent the harmful vacuole formation and to maintain a persistent infection. These findings reveal a unique survival strategy of HCV and provide new insights into the genotype-specific pathogenicity of HCV.

Characterization of thiobarbituric acid derivatives as inhibitors of hepatitis C virus NS5B polymerase

In an effort to find chemicals inhibiting the enzymatic activity of the hepatitis C virus (HCV) NS5B polymerase, a series of thiobarbituric acid derivatives were selected from a library provided by Korea Research Institute of Chemical Technology and characterized. The selected compounds exhibited IC50 values ranging from 1.7 to 3.8 μM, and EC50 values ranging from 12.3 to 20.7 μM against NS5B polymerase of type 1b strain. They showed little effect against type 2a polymerase. One of the compounds, G05, was selected and further characterized. It inhibited the synthesis of RNA by recombinant HCV NS5B polymerase in a dose dependent manner. The CC50 value was 77 μM. The inhibition was in a noncompetitive manner with the substrate UTP. The compound did not inhibit the elongation step of RNA synthesis in a single-cycle processive polymerization assay. It inhibited the binding of NS5B polymerase to the template RNA in a dose-dependent manner.

A novel class of geldanamycin derivatives as HCV replication inhibitors targeting on Hsp90: synthesis, structure-activity relationships and anti-HCV activity in GS4.3 replicon cells

A novel class of geldanamycin (GA) derivatives as hepatitis C virus (HCV) replication inhibitors has been synthesized and their anti-HCV activities were evaluated in GS4.3 HCV replicon cells. Most of the synthesized compounds demonstrated potential activities against HCV in vitro. Substitution with an aliphatic cyclic group (2b) and polar phosphate group (2f) at the 17 position of GA resulted in more potent inhibitory activity. The configurations of the tetrahydrofurfurylamino (THFM) substituents obviously affected their antiviral activities. The 2b with a 2'-(R)-THFM group at the 17 position showed much potent activity and higher selectivity than its 2'-(S) and 2'-(R, S) epimers. In the tested GA derivatives, 2b and 2f show the most potential leading compounds for development of novel anti-HCV agents.

Chaperonin TRiC/CCT participates in replication of hepatitis C virus genome via interaction with the viral NS5B protein

To identify the host factors implicated in the regulation of hepatitis C virus (HCV) genome replication, we performed comparative proteome analyses of HCV replication complex (RC)-rich membrane fractions prepared from cells harboring genome-length bicistronic HCV RNA at the exponential and stationary growth phases. We found that the eukaryotic chaperonin T-complex polypeptide 1 (TCP1)-ring complex/chaperonin-containing TCP1 (TRiC/CCT) plays a role in the replication possibly through an interaction between subunit CCT5 and the viral RNA polymerase NS5B. siRNA-mediated knockdown of CCT5 suppressed RNA replication and production of the infectious virus. Gain-of-function activity was shown following co-transfection with whole eight TRiC/CCT subunits. HCV RNA synthesis was inhibited by an anti-CCT5 antibody in a cell-free assay. These suggest that recruitment of the chaperonin by the viral nonstructural proteins to the RC, which potentially facilitate folding of the RC component(s) into the mature active form, may be important for efficient replication of the HCV genome.

Pathology of chronic hepatitis B and chronic hepatitis C

Histologic evaluation of the liver is a major component in the medical management and treatment algorithm of patients with chronic hepatitis B (HBV) and chronic hepatitis C (HCV). Liver biopsy in these patients remains the gold standard, and decisions on treatment are often predicated on the degree of damage and stage of fibrosis. This article outlines the clinical course and serologic diagnosis of HBV and HCV for the clinician and the pathologist, who together have a close working relationship in managing patients with acute and chronic liver disease. The salient histologic features are elucidated in an attempt to provide the clinician with an understanding of the basic histopathology underlying chronic HCV and HBV.

Hepatitis C virus core protein induces neuroimmune activation and potentiates Human Immunodeficiency Virus-1 neurotoxicity

Background

Hepatitis C virus (HCV) genomes and proteins are present in human brain tissues although the impact of HIV/HCV co-infection on neuropathogenesis remains unclear. Herein, we investigate HCV infectivity and effects on neuronal survival and neuroinflammation in conjunction with HIV infection.

Methodology

Human microglia, astrocyte and neuron cultures were infected with cell culture-derived HCV or exposed to HCV core protein with or without HIV-1 infection or HIV-1 Viral Protein R (Vpr) exposure. Host immune gene expression and cell viability were measured. Patch-clamp studies of human neurons were performed in the presence or absence of HCV core protein. Neurobehavioral performance and neuropathology were examined in HIV-1 Vpr-transgenic mice in which stereotaxic intrastriatal implants of HCV core protein were performed.

Principal Findings

HCV-encoded RNA as well as HCV core and non-structural 3 (NS3) proteins were detectable in human microglia and astrocytes infected with HCV. HCV core protein exposure induced expression of pro-inflammatory cytokines including interleukin-1β, interleukin-6 and tumor necrosis factor-α in microglia (p<0.05) but not in astrocytes while increased chemokine (e.g. CXCL10 and interleukin-8) expression was observed in both microglia and astrocytes (p<0.05). HCV core protein modulated neuronal membrane currents and reduced both β-III-tubulin and lipidated LC3-II expression (p<0.05). Neurons exposed to supernatants from HCV core-activated microglia exhibited reduced β-III-tubulin expression (p<0.05). HCV core protein neurotoxicity and interleukin-6 induction were potentiated by HIV-1 Vpr protein (p<0.05). HIV-1 Vpr transgenic mice implanted with HCV core protein showed gliosis, reduced neuronal counts together with diminished LC3 immunoreactivity. HCV core-implanted animals displayed neurobehavioral deficits at days 7 and 14 post-implantation (p<0.05).

Conclusions

HCV core protein exposure caused neuronal injury through suppression of neuronal autophagy in addition to neuroimmune activation. The additive neurotoxic effects of HCV- and HIV-encoded proteins highlight extrahepatic mechanisms by which HCV infection worsens the disease course of HIV infection.

Involvement of PA28gamma in the propagation of hepatitis C virus

We have reported previously that the proteasome activator PA28gamma participates not only in degradation of hepatitis C virus (HCV) core protein in the nucleus but also in the pathogenesis in transgenic mice expressing HCV core protein. However, the biological significance of PA28gamma in the propagation of HCV has not been clarified. PA28gamma is an activator of proteasome responsible for ubiquitin-independent degradation of substrates in the nucleus. In the present study, knockdown of PA28gamma in cells preinfection or postinfection with the JFH-1 strain of HCV impaired viral particle production but exhibited no effect on viral RNA replication. The particle production of HCV in PA28gamma knockdown cells was restored by the expression of an small interfering RNA (siRNA)-resistant PA28gamma. Although viral proteins were detected in the cytoplasm of cells infected with HCV, suppression of PA28gamma expression induced accumulation of HCV core protein in the nucleus. HCV core protein was also degraded in the cytoplasm after ubiquitination by an E3 ubiquitin ligase, E6AP. Knockdown of PA28gamma enhanced ubiquitination of core protein and impaired virus production, whereas that of E6AP reduced ubiquitination of core protein and enhanced virus production. Furthermore, virus production in the PA28gamma knockdown cells was restored through knockdown of E6AP or expression of the siRNA-resistant wild-type but not mutant PA28gamma incapable of activating proteasome activity.

CONCLUSION

Our results suggest that PA28gamma participates not only in the pathogenesis but also in the propagation of HCV by regulating the degradation of the core protein in both a ubiquitin-dependent and ubiquitin-independent manner.

Replication of subgenomic hepatitis C virus replicons in mouse fibroblasts is facilitated by deletion of interferon regulatory factor 3 and expression of liver-specific microRNA 122

Hepatitis C virus (HCV) infection causes significant morbidity, and efficient mouse models would greatly facilitate virus studies and the development of effective vaccines and new therapeutic agents. Entry factors, innate immunity, and host factors needed for viral replication represent the initial barriers that restrict HCV infection of mouse cells. Experiments in this paper consider early postentry steps of viral infection and investigate the roles of interferon regulatory factors (IRF-3 and IRF-9) and microRNA (miR-122) in promoting HCV replication in mouse embryo fibroblasts (MEFs) that contain viral subgenomic replicons. While wild-type murine fibroblasts are restricted for HCV RNA replication, deletion of IRF-3 alone can facilitate replicon activity in these cells. This effect is thought to be related to the inactivation of the type I interferon synthesis mediated by IRF-3. Additional deletion of IRF-9 to yield IRF-3(-/-) IRF-9(-/-) MEFs, which have blocked type I interferon signaling, did not increase HCV replication. Expression of liver-specific miR-122 in MEFs further stimulated the synthesis of HCV replicons in the rodent fibroblasts. The combined effects of miR-122 expression and deletion of IRF-3 produced a cooperative stimulation of HCV subgenome replication. miR-122 and IRF-3 are independent host factors that are capable of influencing HCV replication, and our findings could help to establish mouse models and other cell systems that support HCV growth and particle formation.

Identification of a structural element of the hepatitis C virus minus strand RNA involved in the initiation of RNA synthesis

The replication of the genomic RNA of the hepatitis C virus (HCV) of positive polarity involves the synthesis of a replication intermediate of negative polarity by the viral RNA-dependent RNA polymerase (NS5B). In vitro and likely in vivo, the NS5B initiates RNA synthesis without primers. This de novo mechanism needs specific interactions between the polymerase and viral RNA elements. Cis-acting elements involved in the initiation of (–) RNA synthesis have been identified in the 3′ non-coding region and in the NS5B coding region of the HCV RNA. However, the detailed contribution of sequences and/or structures of (–) RNA involved in the initiation of (+) RNA synthesis has been less studied. In this report, we identified an RNA element localized between nucleotides 177 and 222 from the 3′-end of the (–) RNA that is necessary for efficient initiation of RNA synthesis by the recombinant NS5B. By site-directed mutagenesis experiments, we demonstrate that the structure rather than the primary sequence of this domain is important for RNA synthesis. We also demonstrate that the intact structure of this RNA element is also needed for efficient RNA synthesis when the viral NS5B functions in association with other viral and cellular proteins in cultured hepatic cells.

Synthesis and Biological Evaluation of Heat-Shock Protein 90 Inhibitors: Geldanamycin Derivatives with Broad Antiviral Activities

Background:

Previous studies have suggested that geldanamycin (GA) inhibits the replication of several viruses in vitro. Here, we aimed to synthesize and evaluate the antiviral activity of 17-amino-17-demethoxygeldanamycin derivatives.

Methods:

A series of 17-substituted and 17-,19-disubstituted GA derivatives were screened for antiviral activities against eight different viral strains, including herpesvirus, hepatitis virus, retrovirus and picornavirus.

Results:

Most of the tested compounds showed inhibitory activity against the viruses and showed reduced cytotoxicity in vitro as compared with the parent compound GA. In vivo efficacy evaluation results showed that compound 6 noticeably inhibited duckling hepatitis B virus DNA replication in duckling serum after oral administration. Viral rebound did not occur after termination of the treatment. The modified GA derivatives also showed median lethal dose values that were higher than that of the parent GA in mice intraperitoneally treated with the study compounds.

Conclusions:

Targeting heat-shock protein 90 could be a new antiviral approach that is not prone to the development of drug resistance. The 17-amino-17-demethoxygeldanamycin derivatives could be novel agents with potential antiviral activity.

Hepatitis C virus NS2/3 protease regulates HCV IRES-dependent translation and NS5B RdRp activity

Chronic hepatitis C virus (HCV) infection often leads to liver cancer. NS2/3 protease is the first of two virally encoded proteases required for HCV polyprotein processing. In this report, we investigated the function of NS2/3 protease on HCV replication and translation. Cells transfected with plasmids encoding wild-type or mutant NS2/3 and a dual-luciferase reporter construct containing an HCV internal ribosome entry site (IRES) were used to examine the effect of NS2/3 protease on translation of HCV RNA. Cells transfected with plasmids encoding wild-type or mutant NS2/3, pcDNA-NS5B and a reporter plasmid were used to examine the effect of NS2/3 protease on HCV replication. The results showed that both autocleavage processing and the uncleaved form of NS2/3 protease specifically decrease HCV IRES-directed translation, while the uncleaved form of NS2/3 protease decreases HCV NS5B RdRp activity (replication), indicating that autoregulation by NS2/3 protease of HCV replication and translation may play an important role in persistent HCV infection.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Human VAP-C negatively regulates hepatitis C virus propagation

Human vesicle-associated membrane protein-associated protein (VAP) subtype A (VAP-A) and subtype B (VAP-B) are involved in the regulation of membrane trafficking, lipid transport and metabolism, and the unfolded protein response. VAP-A and VAP-B consist of the major sperm protein (MSP) domain, the coiled-coil motif, and the C-terminal transmembrane anchor and form homo- and heterodimers through the transmembrane domain. VAP-A and VAP-B interact with NS5B and NS5A of hepatitis C virus (HCV) through the MSP domain and the coiled-coil motif, respectively, and participate in the replication of HCV. VAP-C is a splicing variant of VAP-B consisting of the N-terminal half of the MSP domain of VAP-B followed by the subtype-specific frameshift sequences, and its biological function has not been well characterized. In this study, we have examined the biological functions of VAP-C in the propagation of HCV. VAP-C interacted with NS5B but not with VAP-A, VAP-B, or NS5A in immunoprecipitation analyses, and the expression of VAP-C inhibited the interaction of NS5B with VAP-A or VAP-B. Overexpression of VAP-C impaired the RNA replication of the HCV replicon and the propagation of the HCV JFH1 strain, whereas overexpression of VAP-A and VAP-B enhanced the replication. Furthermore, the expression of VAP-C was observed in various tissues, whereas it was barely detected in the liver. These results suggest that VAP-C acts as a negative regulator of HCV propagation and that the expression of VAP-C may participate in the determination of tissue tropism of HCV propagation.

Nonstructural 3/4A protease of hepatitis C virus activates epithelial growth factor-induced signal transduction by cleavage of the T-cell protein tyrosine phosphatase

The hepatitis C virus (HCV) is a worldwide major cause of chronic liver disease with a high tendency to establish a persistent infection. To permit persistent replication of viral genomes through the cellular translation machinery without affecting host cell viability, viruses must have developed mechanisms to control cellular cascades required for sufficient viral replication, on the one hand, and to adapt viral replication to the cellular requirements on the other hand. The present study aimed to further elucidate mechanisms by which HCV targets growth factor signaling of the host cell and their implications for viral replication. The study describes a novel mechanism by which HCV influences the activation of the epithelial growth factor receptor/Akt pathway through a nonstructural (NS)3/4A-dependent down-regulation of the ubiquitously expressed tyrosine phosphatase T cell protein tyrosine phosphatase (TC-PTP). NS3/4A is demonstrated to cleave TC-PTP protease-dependently in vitro at two cleavage sites. The in vivo relevance of this finding is supported by the fact that down-regulation of TC-PTP protein expression could also be demonstrated in HCV-infected individuals and in transgenic mice with intrahepatic expression of NS3/4A.

CONCLUSION

This down-regulation of TC-PTP results in an enhancement of epithelial growth factor (EGF)-induced signal transduction and increases basal activity of Akt, which is demonstrated to be essential for the maintenance of sufficient viral replication. Hence, therapeutic targeting of NS3/4A may not only disturb viral replication by blocking the processing of the viral polyprotein but also exerts unforeseen indirect antiviral effects, further diminishing viral replication.

[Processing and pathogenicity of HCV core protein]

Hepatitis C virus (HCV) is a major causative agent of blood-borne hepatitis. Most of the HCV-positive individuals have been chronically infected with the virus for decades, leading to development of steatosis, cirrhosis and ultimately hepatocellular carcinoma. In addition, cryoglobulinemia and type 2 diabetes mellitus are associated with a chronic infection with HCV. Hepatocellular carcinoma induced by HCV infection is not caused by only the repeated inflammations but also the biological activity of HCV proteins. HCV core protein has been reported as a component of the viral nucleocapsid as well as the pathogenic factor that could induce the production of oxidative stress and progression of cell growth. In this review, we summarize the current status of our knowledge regarding to the processing and pathogenicity of HCV core protein.

Modification of intracellular membrane structures for virus replication

Plus-stranded RNA viruses induce large membrane structures that might support the replication of their genomes. Similarly, cytoplasmic replication of poxviruses (large DNA viruses) occurs in associated membranes. These membranes originate from the endoplasmic reticulum (ER) or endosomes.

Membrane vesicles that support viral replication are induced by a number of RNA viruses. Similarly, the poxvirus replication site is surrounded by a double-membraned cisterna that is derived from the ER.

Analogies to autophagy have been proposed since the finding that autophagy cellular processes involve the formation of double-membrane vesicles. However, molecular evidence to support this hypothesis is lacking.

Membrane association of the viral replication complex is mediated by the presence of one or more viral proteins that contain sequences which associate with, or integrate into, membranes.

Replication-competent membranes might contain viral or cellular proteins that contain amphipathic helices, which could mediate the membrane bending that is required to form spherical vesicles.

Whereas poxvirus DNA replication occurs inside the ER-enclosed site, for most RNA viruses the topology of replication is not clear. Preliminary results for some RNA viruses suggest that their replication could also occur inside double-membrane vesicles.

We speculate that cytoplasmic replication might occur inside sites that are 'enwrapped' by an ER-derived cisterna, and that these cisternae are open to the cytoplasm. Thus, RNA and DNA viruses could use a common mechanism for replication that involves membrane wrapping by cellular cisternal membranes.

We propose that three-dimensional analyses using high-resolution electron-microscopy techniques could be useful for addressing this issue. High-throughput small-interfering-RNA screens should also shed light on molecular requirements for virus-induced membrane modifications.

Many viruses induce the formation of altered membrane structures upon replication in host cells. This Review examines how viruses modify intracellular membranes, highlights similarities between the structures that are induced by viruses from different families and discusses how these structures could be formed.

Viruses are intracellular parasites that use the host cell they infect to produce new infectious progeny. Distinct steps of the virus life cycle occur in association with the cytoskeleton or cytoplasmic membranes, which are often modified during infection. Plus-stranded RNA viruses induce membrane proliferations that support the replication of their genomes. Similarly, cytoplasmic replication of some DNA viruses occurs in association with modified cellular membranes. We describe how viruses modify intracellular membranes, highlight similarities between the structures that are induced by viruses of different families and discuss how these structures could be formed.