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The spliceosome factor SART1 exerts its anti-HCV action through mRNA splicing. - Journal of hepatology
The broadly used antiviral cytokine interferon-Î± (IFNÎ±)'s mechanisms of action against HCV infection are not well understood. We previously identified SART1, a host protein involved in RNA splicing and pre-mRNA processing, as a regulator of IFN's antiviral effects. We hypothesized that SART1 regulates antiviral IFN effector genes (IEGs) through mRNA processing and splicing.We performed siRNA knockdown in HuH7.5.1 cells and mRNA-sequencing with or without IFN treatment. Selected gene mRNA variants and their proteins, together with HCV replication, were monitored by qRT-PCR and Western blot in HCV OR6 replicon cells and the JFH1 HCV infectious model.We identified 419 genes with a greater than 2-fold expression difference between Neg siRNA and SART1 siRNA treated cells in the presence or absence of IFN. Bioinformatic analysis identified at least 10 functional pathways. SART1 knockdown reduced classical IFN stimulating genes (ISG) mRNA transcription including MX1 and OAS3. However, SART1 did not affect JAK-STAT pathway gene mRNA expression and IFN stimulated response element (ISRE) signaling. We identified alternative mRNA splicing events for several genes, including EIF4G3, GORASP2, ZFAND6, and RAB6A that contribute to their antiviral effects. EIF4G3 and GORASP2 were also confirmed to have anti-HCV effect.The spliceosome factor SART1 is not IFN-inducible but is an IEG. SART1 exerts its anti-HCV action through direct transcriptional regulation for some ISGs and alternative splicing for others, including EIF4G3, GORASP2. SART1 does not have an effect on IFN receptor or canonical signal transduction components. Thus, SART1 regulates ISGs using a novel, non-classical mechanism.Copyright Â© 2014 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
Entry inhibitors and future treatment of hepatitis C. - Antiviral research
Hepatitis C virus (HCV) is a major cause of liver cirrhosis and hepatocellular carcinoma. Furthermore, HCV-induced liver disease is the leading indication for liver transplantation. The recent introduction of direct-acting antivirals (DAAs) has revolutionized HCV treatment by making possible the cure of the majority of patients. However, their efficacy and safety in difficult-to-treat patients such as patients receiving immunosuppression, those with advanced liver disease, co-morbidity and HIV/HCV-co-infection remain to be determined. Furthermore, prevention of liver graft infection remains a pressing issue. HCV entry inhibitors target the very first step of the HCV life cycle and efficiently inhibit cell-cell transmission - a key prerequisite for viral spread. Because of their unique mechanism of action on cell-cell transmission they may provide a promising and simple perspective for prevention of liver graft infection. A high genetic barrier to resistance and complementary mechanism of action compared to DAAs makes entry inhibitors attractive as a new strategy for treatment of multi-resistant or difficult-to-treat patients. Clinical studies are needed to determine the future role of entry inhibitors in the arsenal of antivirals to combat HCV infection. This article forms part of a symposium in Antiviral Research on "Hepatitis C: next steps toward global eradication."Copyright Â© 2014. Published by Elsevier B.V.
Kinetic differences in the induction of interferon stimulated genes by interferon-Î± and interleukin 28B are altered by infection with hepatitis C virus. - Hepatology (Baltimore, Md.)
Several genome-wide association studies (GWAS) have identified a genetic polymorphism associated with the gene locus for interleukin 28B (IL28B), a type III interferon (IFN), as a major predictor of clinical outcome in hepatitis C. Antiviral effects of the type III IFN family have previously been shown against several viruses, including hepatitis C virus (HCV), and resemble the function of type I IFN including utilization of the intracellular Janus kinase signal transducer and activator of transcription (JAK-STAT) pathway. Effects unique to IL28B that would distinguish it from IFN-Î± are not well defined. By analyzing the transcriptomes of primary human hepatocytes (PHH) treated with IFN-Î± or IL28B, we sought to identify functional differences between IFN-Î± and IL28B to better understand the roles of these cytokines in the innate immune response. Although our data did not reveal distinct gene signatures, we detected striking kinetic differences between IFN-Î± and IL28B stimulation for interferon stimulated genes (ISGs). While gene induction was rapid and peaked at 8 hours of stimulation with IFN-Î± in PHH, IL28B produced a slower, but more sustained increase in gene expression. We confirmed these findings in the human hepatoma cell line Huh7.5.1. Interestingly, in HCV-infected cells the rapid response after stimulation with IFN-Î± was blunted, and the induction pattern resembled that caused by IL28B.The kinetics of gene induction are fundamentally different for stimulations with either IFN-Î± or IL28B in hepatocytes, suggesting distinct roles of these cytokines within the immune response. Furthermore, the observed differences are substantially altered by infection with HCV.Â© 2014 by the American Association for the Study of Liver Diseases.
The AMPK-related kinase SNARK regulates hepatitis C virus replication and pathogenesis through enhancement of TGF-Î² signaling. - Journal of hepatology
Hepatitis C virus (HCV) is a major cause of chronic liver disease worldwide. The biological and therapeutic importance of host cellular cofactors for viral replication has been recently appreciated. Here we examined the roles of SNF1/AMP kinase-related kinase (SNARK) in HCV replication and pathogenesis.The JFH1 infection system and the full-length HCV replicon OR6 cell line were used. Gene expression was knocked down by siRNAs. SNARK mutants were created by site-directed mutagenesis. Intracellular mRNA levels were measured by qRT-PCR. Endogenous and overexpressed proteins were detected by Western blot analysis and immunofluorescence. Transforming growth factor (TGF)-Î² signaling was monitored by a luciferase reporter construct. Liver biopsy samples from HCV-infected patients were analyzed for SNARK expression.Knockdown of SNARK impaired viral replication, which was rescued by wild type SNARK but not by unphosphorylated or kinase-deficient mutants. Knockdown and overexpression studies demonstrated that SNARK promoted TGF-Î² signaling in a manner dependent on both its phosphorylation and kinase activity. In turn, chronic HCV replication upregulated the expression of SNARK in patients. Further, the SNARK kinase inhibitor metformin suppressed both HCV replication and SNARK-mediated enhancement of TGF-Î² signaling.Thus reciprocal regulation between HCV and SNARK promotes TGF-Î² signaling, a major driver of hepatic fibrogenesis. These findings suggest that SNARK will be an attractive target for the design of novel host-directed antiviral and antifibrotic drugs.Copyright Â© 2013 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
A genetic screen identifies interferon-Î± effector genes required to suppress hepatitis C virus replication. - Gastroenterology
Hepatitis C virus (HCV) infection is a leading cause of end-stage liver disease. Interferon-Î± (IFNÎ±) is an important component of anti-HCV therapy; it up-regulates transcription of IFN-stimulated genes, many of which have been investigated for their antiviral effects. However, all of the genes required for the antiviral function of IFNÎ± (IFN effector genes [IEGs]) are not known. IEGs include not only IFN-stimulated genes, but other nontranscriptionally induced genes that are required for the antiviral effect of IFNÎ±. In contrast to candidate approaches based on analyses of messenger RNA (mRNA) expression, identification of IEGs requires a broad functional approach.We performed an unbiased genome-wide small interfering RNA screen to identify IEGs that inhibit HCV. Huh7.5.1 hepatoma cells were transfected with small interfering RNAs incubated with IFNÎ± and then infected with JFH1 HCV. Cells were stained using HCV core antibody, imaged, and analyzed to determine the percent infection. Candidate IEGs detected in the screen were validated and analyzed further.The screen identified 120 previously unreported IEGs. From these, we more fully evaluated the following: asparagine-linked glycosylation 10 homolog (yeast, Î±-1,2-glucosyltransferase); butyrylcholinesterase; dipeptidyl-peptidase 4 (CD26, adenosine deaminase complexing protein 2); glucokinase (hexokinase 4) regulator; guanylate cyclase 1, soluble, Î² 3; MYST histone acetyltransferase 1; protein phosphatase 3 (formerly 2B), catalytic subunit, Î² isoform; peroxisomal proliferator-activated receptor-Î³-DBD-interacting protein 1; and solute carrier family 27 (fatty acid transporter), member 2; and demonstrated that they enabled IFNÎ±-mediated suppression of HCV at multiple steps of its life cycle. Expression of these genes had more potent effects against flaviviridae because a subset was required for IFNÎ± to suppress dengue virus but not influenza A virus. In addition, many of the host genes detected in this screen (92%) were not transcriptionally stimulated by IFNÎ±; these genes represent a heretofore unknown class of non-IFN-stimulated gene IEGs.We performed a whole-genome loss-of-function screen to identify genes that mediate the effects of IFNÎ± against human pathogenic viruses. We found that IFNÎ± restricts HCV via actions of general and specific IEGs.Copyright Â© 2013 AGA Institute. Published by Elsevier Inc. All rights reserved.
SOCS1 abrogates IFN's antiviral effect on hepatitis C virus replication. - Antiviral research
Suppressor of cytokine signaling 1 (SOCS1) and suppressor of cytokine signaling 3 (SOCS3) have been thought to block type I interferon (IFN) signaling. We have previously reported that SOCS3 suppresses HCV replication in an mTOR-dependent manner. However, the relationship between SOCS1 and HCV replication remains unclear. Here, we found that overexpression of SOCS1 alone did not have an effect on HCV RNA replication. However, suppression of HCV replication by IFN-Î± was rescued by SOCS1 overexpression. The upregulation of HCV replication by SOCS1 overexpression in the presence of IFN is likely a result of the impairment of IFN signaling by SOCS1 and subsequent induction of ISGs. Knockdown of SOCS1 alone with specific shRNA enhanced the antiviral effect of IFN compared with negative control. Thus, SOCS1 acts as a suppressor of type I IFN function against HCV.Copyright Â© 2012 Elsevier B.V. All rights reserved.
Hepatitis C virus NS5A disrupts STAT1 phosphorylation and suppresses type I interferon signaling. - Journal of virology
Responses to alpha interferon (IFN-Î±)-based treatment are dependent on both host and viral factors and vary markedly among patients infected with different hepatitis C virus (HCV) genotypes (GTs). Patients infected with GT3 viruses consistently respond better to IFN treatment than do patients infected with GT1 viruses. The mechanisms underlying this difference are not well understood. In this study, we sought to determine the effects of HCV NS5A proteins from different genotypes on IFN signaling. We found that the overexpression of either GT1 or GT3 NS5A proteins significantly inhibited IFN-induced IFN-stimulated response element (ISRE) signaling, phosphorylated STAT1 (P-STAT1) levels, and IFN-stimulated gene (ISG) expression compared to controls. GT1 NS5A protein expression exhibited stronger inhibitory effects on IFN signaling than did GT3 NS5A protein expression. Furthermore, GT1 NS5A bound to STAT1 with a higher affinity than did GT3 NS5A. Domain mapping revealed that the C-terminal region of NS5A conferred these inhibitory effects on IFN signaling. The overexpression of HCV NS5A increased HCV replication levels in JFH1-infected cells through the further reduction of levels of P-STAT1, ISRE signaling, and downstream ISG responses. We demonstrated that the overexpression of GT1 NS5A proteins resulted in less IFN responsiveness than did the expression of GT3 NS5A proteins through stronger binding to STAT1. We confirmed that GT1 NS5A proteins exerted stronger IFN signaling inhibition than did GT3 NS5A proteins in an infectious recombinant JFH1 virus. The potent antiviral NS5A inhibitor BMS-790052 did not block NS5A-mediated IFN signaling suppression in an overexpression model, suggesting that NS5A's contributions to replication are independent of its subversive action on IFN. We propose a model in which the binding of the C-terminal region of NS5A to STAT1 leads to decreased levels of P-STAT1, ISRE signaling, and ISG transcription and, ultimately, to preferential GT1 resistance to IFN treatment.
A functional genomic screen reveals novel host genes that mediate interferon-alpha's effects against hepatitis C virus. - Journal of hepatology
The precise mechanisms by which IFN exerts its antiviral effect against HCV have not yet been elucidated. We sought to identify host genes that mediate the antiviral effect of IFN-Î± by conducting a whole-genome siRNA library screen.High throughput screening was performed using an HCV genotype 1b replicon, pRep-Feo. Those pools with replicate robust Z scores â‰¥2.0 entered secondary validation in full-length OR6 replicon cells. Huh7.5.1 cells infected with JFH1 were then used to validate the rescue efficacy of selected genes for HCV replication under IFN-Î± treatment.We identified and confirmed 93 human genes involved in the IFN-Î± anti-HCV effect using a whole-genome siRNA library. Gene ontology analysis revealed that mRNA processing (23 genes, p=2.756e-22), translation initiation (nine genes, p=2.42e-6), and IFN signaling (five genes, p=1.00e-3) were the most enriched functional groups. Nine genes were components of U4/U6.U5 tri-snRNP. We confirmed that silencing squamous cell carcinoma antigen recognized by T cells (SART1), a specific factor of tri-snRNP, abrogates IFN-Î±'s suppressive effects against HCV in both replicon cells and JFH1 infectious cells. We further found that SART1 was not IFN-Î± inducible, and its anti-HCV effector in the JFH1 infectious model was through regulation of interferon stimulated genes (ISGs) with or without IFN-Î±.We identified 93 genes that mediate the anti-HCV effect of IFN-Î± through genome-wide siRNA screening; 23 and nine genes were involved in mRNA processing and translation initiation, respectively. These findings reveal an unexpected role for mRNA processing in generation of the antiviral state, and suggest a new avenue for therapeutic development in HCV.Copyright Â© 2011 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
IL28B inhibits hepatitis C virus replication through the JAK-STAT pathway. - Journal of hepatology
The combination of pegylated interferon (IFN) Î± and ribavirin (RBV) is the standard therapy for patients with chronic HCV infection. However, it produces a sustained virologic response (SVR) in only half of the treated individuals and is associated with significant side effects. Recently, several single-nucleotide polymorphisms (SNPs) near the IL28B locus, also known as IFNÎ»3, were identified to be strong predictors of SVR in patients receiving PEG-IFN and RBV. We sought to determine whether IL28B was capable of inhibiting HCV replication and to determine the pathway by which IL28B exhibits anti-HCV activity.Using the full-length HCV replicon OR6 and the infectious HCV clones JFH1 and Jc1, we assessed the anti-HCV effect of IL28B on HCV and characterized the key steps of the JAK-STAT pathway by real time PCR, luciferase assay, and Western blot. Finally, we evaluated the anti-HCV effect of IL28B in the presence of JAK-STAT pathway inhibitors such as blocking antibodies, a pharmacological inhibitor, and siRNAs.We found that IL28B inhibits HCV replication in a dose- and time-dependent manner. Like IFNÎ±, IL28B induces the phosphorylation of STAT1 and STAT2, ISRE-driven transcription, and expression of known ISGs. The anti-HCV effects of IL28A, IL28B, and IL29 were abrogated by an IL10R2 blocking antibody, a pharmacological inhibitor of JAK1/TYK2, and by siRNA against IL28R1, STAT1, STAT2, and IRF9.Our data demonstrate that IL28A, IL28B, and IL29 signal through the JAK-STAT pathway to inhibit HCV. These data suggest possible applications of new approaches in HCV treatment.Copyright Â© 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
HIV infection increases HCV-induced hepatocyte apoptosis. - Journal of hepatology
HCV related liver disease is one of the most important complications in persons with HIV, with accelerated fibrosis progression in coinfected persons compared to those with HCV alone. We hypothesized that HCV-HIV coinfection increases HCV related hepatocyte apoptosis and that HCV and HIV influence TRAIL signaling in hepatocytes.We analyzed the effect of HIV in JFH1-infected Huh7.5.1 cells. Apoptosis was measured by Caspase-Glo 3/7 assay and Western blotting for cleaved PARP. TRAIL, TRAIL receptor 1 (DR4), and 2 (DR5) mRNA and protein levels were assessed by real-time PCR and Western blot, respectively. We also investigated activation of caspase pathways using caspase inhibitors and assessed expression of Bid and cytochrome C.We found increased caspase 3/7 activity and cleaved PARP in JFH1 HCV-infected Huh7.5.1 cells in the presence of heat-inactivated HIV, compared to Huh7.5.1 cells infected with JFH1 or exposed to heat-inactivated HIV alone. Both DR4 and DR5 mRNA and protein expression were increased in JFH1-infected cells in the presence of inactivated HIV compared to Huh7.5.1 cells infected with JFH1 or exposed to heat-inactivated HIV alone. Pancaspase, caspase-8, and caspase-9 inhibition blocked apoptosis induced by HCV, inactivated HIV, and HCV plus inactivated HIV. A caspase-9 inhibitor blocked apoptosis induced by HCV, HIV, and HCV-HIV comparably to pancaspase and caspase-8 inhibitors. HCV induced the activation of Bid cleavage and cytochrome C release. The addition of HIV substantially augmented this induction.Our findings indicate that hepatocyte apoptosis is increased in the presence of HCV and HIV compared to HCV or HIV alone, and that this increase is mediated by DR4 and DR5 up-regulation. These results provide an additional mechanism for the accelerated liver disease progression observed in HCV-HIV co-infection.Copyright Â© 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
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Massachusetts General Hospital 55 Fruit St. Boston, MA 02114
Massachusetts General Hospital 55 Fruit Street
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Massachusetts General Hospital 55 Fruit Street
Massachusetts General Hospital 55 Fruit Street
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Massachusetts General Hospital 55 Fruit Street
Massachusetts General Hospital 55 Fruit St.