scholarly journals Hepatitis C virus infection is inhibited by a non-canonical antiviral signaling pathway targeted by NS3-NS4A

2019 ◽  
Author(s):  
Christine Vazquez ◽  
Chin Yee Tan ◽  
Stacy M. Horner

AbstractThe hepatitis C virus (HCV) NS3-NS4A protease complex is required for viral replication and is the major viral innate immune evasion factor. NS3-NS4A evades antiviral innate immunity by inactivating several proteins, including MAVS, the signaling adaptor for RIG-I and MDA5, and Riplet, an E3 ubiquitin ligase that activates RIG-I. Here, we identified a Tyr-16-Phe (Y16F) change in the NS4A transmembrane domain that prevents NS3-NS4A targeting of Riplet but not MAVS. This Y16F substitution reduces HCV replication in Huh7 cells, but not in Huh-7.5 cells, known to lack RIG-I signaling. Surprisingly, deletion of RIG-I in Huh7 cells did not restore Y16F viral replication. Rather, we found that Huh-7.5 cells lack Riplet expression and that addition of Riplet to these cells reduced HCV Y16F replication. In addition, IRF3 deletion in Huh7 cells was sufficient to restore HCV Y16F replication, and the Y16F protease lacked the ability to prevent IRF3 activation or interferon induction. Taken together, these data reveal that the NS4A Y16 residue regulates a non-canonical Riplet-IRF3-dependent, but RIG-I-MAVS-independent, signaling pathway that limits HCV infection.ImportanceThe HCV NS3-NS4A protease complex facilitates viral replication by cleaving and inactivating the antiviral innate immune signaling proteins MAVS and Riplet, which are essential for RIG-I activation. NS3-NS4A therefore prevents IRF3 activation and interferon induction during HCV infection. Here, we uncover an amino acid residue within the NS4A transmembrane domain that is essential for inactivation of Riplet, but does not affect MAVS cleavage by NS3-NS4A. Our study reveals that Riplet is involved in a RIG-I- and MAVS-independent signaling pathway that activates IRF3 and that this pathway is normally inactivated by NS3-NS4A during HCV infection. Our study selectively uncouples these distinct regulatory mechanisms within NS3-NS4A and defines a new role for Riplet in the antiviral response to HCV. As Riplet is known to be inhibited by other RNA viruses, such as such influenza A virus, this innate immune signaling pathway may also be important in controlling other RNA virus infections.

2019 ◽  
Vol 93 (23) ◽  
Author(s):  
Christine Vazquez ◽  
Chin Yee Tan ◽  
Stacy M. Horner

ABSTRACT The hepatitis C virus (HCV) NS3-NS4A protease complex is required for viral replication and is the major viral innate immune evasion factor. NS3-NS4A evades antiviral innate immunity by inactivating several proteins, including MAVS, the signaling adaptor for RIG-I and MDA5, and Riplet, an E3 ubiquitin ligase that activates RIG-I. Here, we identified a Tyr-16-Phe (Y16F) change in the NS4A transmembrane domain that prevents NS3-NS4A targeting of Riplet but not MAVS. This Y16F substitution reduces HCV replication in Huh7 cells, but not in Huh-7.5 cells, known to lack RIG-I signaling. Surprisingly, deletion of RIG-I in Huh7 cells did not restore Y16F viral replication. Rather, we found that Huh-7.5 cells lack Riplet expression and that the addition of Riplet to these cells reduced HCV Y16F replication, whereas the addition of Riplet lacking the RING domain restored HCV Y16F replication. In addition, TBK1 inhibition or IRF3 deletion in Huh7 cells was sufficient to restore HCV Y16F replication, and the Y16F protease lacked the ability to prevent IRF3 activation or interferon induction. Taken together, these data reveal that the NS4A Y16 residue regulates a noncanonical Riplet-TBK1-IRF3-dependent, but RIG-I-MAVS-independent, signaling pathway that limits HCV infection. IMPORTANCE The HCV NS3-NS4A protease complex facilitates viral replication by cleaving and inactivating the antiviral innate immune signaling proteins MAVS and Riplet, which are essential for RIG-I activation. NS3-NS4A therefore prevents IRF3 activation and interferon induction during HCV infection. Here, we uncover an amino acid residue within the NS4A transmembrane domain that is essential for inactivation of Riplet but does not affect MAVS cleavage by NS3-NS4A. Our study reveals that Riplet is involved in a RIG-I- and MAVS-independent signaling pathway that activates IRF3 and that this pathway is normally inactivated by NS3-NS4A during HCV infection. Our study selectively uncouples these distinct regulatory mechanisms within NS3-NS4A and defines a new role for Riplet in the antiviral response to HCV. Since Riplet is known to be inhibited by other RNA viruses, such as such influenza A virus, this innate immune signaling pathway may also be important in controlling other RNA virus infections.


2015 ◽  
Vol 89 (21) ◽  
pp. 11056-11068 ◽  
Author(s):  
Alison Kell ◽  
Mark Stoddard ◽  
Hui Li ◽  
Joe Marcotrigiano ◽  
George M. Shaw ◽  
...  

ABSTRACTDespite the introduction of direct-acting antiviral (DAA) drugs against hepatitis C virus (HCV), infection remains a major public health concern because DAA therapeutics do not prevent reinfection and patients can still progress to chronic liver disease. Chronic HCV infection is supported by a variety of viral immune evasion strategies, but, remarkably, 20% to 30% of acute infections spontaneously clear prior to development of adaptive immune responses, thus implicating innate immunity in resolving acute HCV infection. However, the virus-host interactions regulating acute infection are unknown. Transmission of HCV involves one or a few transmitted/founder (T/F) variants. In infected hepatocytes, the retinoic acid-inducible gene I (RIG-I) protein recognizes 5′ triphosphate (5′ppp) of the HCV RNA and a pathogen-associated molecular pattern (PAMP) motif located within the 3′ untranslated region consisting of poly-U/UC. PAMP binding activates RIG-I to induce innate immune signaling and type 1 interferon antiviral defenses. HCV poly-U/UC sequences can differ in length and complexity, suggesting that PAMP diversity in T/F genomes could regulate innate immune control of acute HCV infection. Using 14 unique poly-U/UC sequences from HCV T/F genomes recovered from acute-infection patients, we tested whether RIG-I recognition and innate immune activation correlate with PAMP sequence characteristics. We show that T/F variants are recognized by RIG-I in a manner dependent on length of the U-core motif of the poly-U/UC PAMP and are recognized by RIG-I to induce innate immune responses that restrict acute infection. PAMP recognition of T/F HCV variants by RIG-I may therefore impart innate immune signaling and HCV restriction to impact acute-phase-to-chronic-phase transition.IMPORTANCERecognition of nonself molecular patterns such as those seen with viral nucleic acids is an essential step in triggering the immune response to virus infection. Innate immunity is induced by hepatitis C virus infection through the recognition of viral RNA by the cellular RIG-I protein, where RIG-I recognizes a poly-uridine/cytosine motif in the viral genome. Variation within this motif may provide an immune evasion strategy for transmitted/founder viruses during acute infection. Using 14 unique poly-U/UC sequences from HCV T/F genomes recovered from acutely infected HCV patients, we demonstrate that RIG-I binding and activation of innate immunity depend primarily on the length of the uridine core within this motif. T/F variants found in acute infection contained longer U cores within the motif and could activate RIG-I and induce innate immune signaling sufficient to restrict viral infection. Thus, recognition of T/F variants by RIG-I could significantly impact the transition from acute to chronic infection.


2015 ◽  
Vol 89 (13) ◽  
pp. 6608-6618 ◽  
Author(s):  
Chuanlong Zhu ◽  
Fei Xiao ◽  
Jian Hong ◽  
Kun Wang ◽  
Xiao Liu ◽  
...  

ABSTRACTThe elongation factor Tu GTP binding domain-containing protein 2 (EFTUD2) was identified as an anti-hepatitis C virus (HCV) host factor in our recent genome-wide small interfering RNA (siRNA) screen. In this study, we sought to further determine EFTUD2's role in HCV infection and investigate the interaction between EFTUD2 and other regulators involved in HCV innate immune (RIG-I, MDA5, TBK1, and IRF3) and JAK-STAT1 pathways. We found that HCV infection decreased the expression of EFTUD2 and the viral RNA sensors RIG-I and MDA5 in HCV-infected Huh7 and Huh7.5.1 cells and in liver tissue from in HCV-infected patients, suggesting that HCV infection downregulated EFTUD2 expression to circumvent the innate immune response. EFTUD2 inhibited HCV infection by inducing expression of the interferon (IFN)-stimulated genes (ISGs) in Huh7 cells. However, its impact on HCV infection was absent in both RIG-I knockdown Huh7 cells and RIG-I-defective Huh7.5.1 cells, indicating that the antiviral effect of EFTUD2 is dependent on RIG-I. Furthermore, EFTUD2 upregulated the expression of the RIG-I-like receptors (RLRs) RIG-I and MDA5 to enhance the innate immune response by gene splicing. Functional experiments revealed that EFTUD2-induced expression of ISGs was mediated through interaction of the EFTUD2 downstream regulators RIG-I, MDA5, TBK1, and IRF3. Interestingly, the EFTUD2-induced antiviral effect was independent of the classical IFN-induced JAK-STAT pathway. Our data demonstrate that EFTUD2 restricts HCV infection mainly through an RIG-I/MDA5-mediated, JAK-STAT-independent pathway, thereby revealing the participation of EFTUD2 as a novel innate immune regulator and suggesting a potentially targetable antiviral pathway.IMPORTANCEInnate immunity is the first line defense against HCV and determines the outcome of HCV infection. Based on a recent high-throughput whole-genome siRNA library screen revealing a network of host factors mediating antiviral effects against HCV, we identified EFTUD2 as a novel innate immune regulator against HCV in the infectious HCV cell culture model and confirmed that its expression in HCV-infected liver tissue is inversely related to HCV infection. Furthermore, we determined that EFTUD2 exerts its antiviral activity mainly through governing its downstream regulators RIG-I and MDA5 by gene splicing to activate IRF3 and induce classical ISG expression independent of the JAT-STAT signaling pathway. This study broadens our understanding of the HCV innate immune response and provides a possible new antiviral strategy targeting this novel regulator of the innate response.


2017 ◽  
Vol 91 (23) ◽  
Author(s):  
Yuwen Qin ◽  
Binbin Xue ◽  
Chunyan Liu ◽  
Xiaohong Wang ◽  
Renyun Tian ◽  
...  

ABSTRACT Activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. However, attenuation or termination of signaling is also necessary for preventing immune-mediated tissue damage and spontaneous autoimmunity. Here, we identify nucleotide binding oligomerization domain (NOD)-like receptor X1 (NLRX1) as a negative regulator of the mitochondrial antiviral signaling protein (MAVS)-mediated signaling pathway during hepatitis C virus (HCV) infection. The depletion of NLRX1 enhances the HCV-triggered activation of interferon (IFN) signaling and causes the suppression of HCV propagation in hepatocytes. NLRX1, a HCV-inducible protein, interacts with MAVS and mediates the K48-linked polyubiquitination and subsequent degradation of MAVS via the proteasomal pathway. Moreover, poly(rC) binding protein 2 (PCBP2) interacts with NLRX1 to participate in the NLRX1-induced degradation of MAVS and the inhibition of antiviral responses during HCV infection. Mutagenic analyses further revealed that the NOD of NLRX1 is essential for NLRX1 to interact with PCBP2 and subsequently induce MAVS degradation. Our study unlocks a key mechanism of the fine-tuning of innate immunity by which NLRX1 restrains the retinoic acid-inducible gene I-like receptor (RLR)-MAVS signaling cascade by recruiting PCBP2 to MAVS for inducing MAVS degradation through the proteasomal pathway. NLRX1, a negative regulator of innate immunity, is a pivotal host factor for HCV to establish persistent infection. IMPORTANCE Innate immunity needs to be tightly regulated to maximize the antiviral response and minimize immune-mediated pathology, but the underlying mechanisms are poorly understood. In this study, we report that NLRX1 is a proviral host factor for HCV infection and functions as a negative regulator of the HCV-triggered innate immune response. NLRX1 recruits PCBP2 to MAVS and induces the K48-linked polyubiquitination and degradation of MAVS, leading to the negative regulation of the IFN signaling pathway and promoting HCV infection. Overall, this study provides intriguing insights into how innate immunity is regulated during viral infection.


2006 ◽  
Vol 80 (2) ◽  
pp. 866-874 ◽  
Author(s):  
Keigo Machida ◽  
Kevin T. H. Cheng ◽  
Vicky M.-H. Sung ◽  
Alexandra M. Levine ◽  
Steven Foung ◽  
...  

ABSTRACT Hepatitis C virus (HCV) induces inflammatory signals, leading to hepatitis, hepatocellular carcinomas, and lymphomas. The mechanism of HCV involvement in the host's innate immune responses has not been well characterized. In this study, we analyzed expression and regulation of the entire panel of toll-like receptors (TLRs) in human B cells following HCV infection in vitro. Among all of the TLRs (TLRs 1 to 10) examined, only TLR4 showed an altered expression (a three- to sevenfold up-regulation) after HCV infection. Peripheral blood mononuclear cells from HCV-infected individuals also showed a higher expression level of TLR4 compared with those of healthy individuals. HCV infection significantly increased beta interferon (IFN-β) and interleukin-6 (IL-6) secretion from B cells, particularly after lipopolysaccharide stimulation. The increased IFN-β and IL-6 production was mediated by TLR4 induction, since the introduction of the small interfering RNA against TLR4 specifically inhibited the HCV-induced cytokine production. Among all of the viral proteins, only NS5A caused TLR4 induction in hepatocytes and B cells. NS5A specifically activated the promoter of the TLR4 gene in both hepatocytes and B cells. In conclusion, HCV infection directly induces TLR4 expression and thereby activates B cells, which may contribute to the host's innate immune responses.


Author(s):  
Luis Jesuino Oliveira Andrade ◽  
Luisa Correia Matos de Oliveira ◽  
Gabriela Correia Matos de Oliveira

Introduction: The mechanisms by which hepatitis C virus (HCV) infection induces autoimmune thyroiditis (AIT) have been studied, and it was suggested that inflammatory cytokines during HCV infection would change the thyroperoxidase (TPO) signaling cascade and thyroglobulin (Tg) determining autoimmune thyroid disease.Objective: To show the signaling pathway, of TPO and Tg, and their potential targets mediated HCV in individuals with hepatitis C.Methods: The mapping of the signaling pathway was based on a review study approach and performed using the automatic annotation server of the Kyoto and Genome Encyclopedia (KEGG). PathVisio is free software for analysis and design of open source routes, and was used for the graphic representation of the signaling pathway.Results: The contigs were extracted from the KEGG database and their mapped transcription represents the signaling pathway of the main biomolecules that triggers the AIT. The action of HCV, or its treatment can trigger AIT that is characterized by the presence of autoantibodies against TPO and Tg. In AIT, autoreactive CD4 + T lymphocytes recruit B cells and CD8 + T cells in the thyroid. The progression of the disease leads to the death of thyroid cellsand hypothyroidism.Conclusion: HCV or its treatment activates several signaling pathways with thyroid cells damage resulting in AIT and secondary hypothyroidism to cellular apoptosis.


2020 ◽  
Vol 26 (26) ◽  
pp. 3085-3095 ◽  
Author(s):  
Yuanjin Gong ◽  
Chang Chang ◽  
Xi Liu ◽  
Yan He ◽  
Yiqi Wu ◽  
...  

Stimulator of interferon genes is an important innate immune signaling molecule in the body and is involved in the innate immune signal transduction pathway induced by pathogen-associated molecular patterns or damage-associated molecular patterns. Stimulator of interferon genes promotes the production of type I interferon and thus plays an important role in the innate immune response to infection. In addition, according to a recent study, the stimulator of interferon genes pathway also contributes to anti-inflammatory and anti-tumor reactions. In this paper, current researches on the Stimulator of interferon genes signaling pathway and its relationship with tumor immunity are reviewed. Meanwhile, a series of critical problems to be addressed in subsequent studies are discussed as well.


Cytokine ◽  
2011 ◽  
Vol 56 (1) ◽  
pp. 108
Author(s):  
Marjolein Kikkert ◽  
Puck B. van Kasteren ◽  
Corrine Beugeling ◽  
Dennis Ninaber ◽  
Sander van Boheemen ◽  
...  

2010 ◽  
Vol 2010 ◽  
pp. 1-8 ◽  
Author(s):  
Helene Minyi Liu ◽  
Michael Gale

Exposure to hepatitis C virus (HCV) usually results in persistent infection that often develops into chronic liver disease. Interferon-alpha (IFN) treatment comprises the foundation of current approved therapy for chronic HCV infection but is limited in overall efficacy. IFN is a major effector of innate antiviral immunity and is naturally produced in response to viral infection when viral pathogen-associated molecular patterns (PAMPs) are recognized as nonself and are bound by cellular pathogen recognition receptors (PRRs), including Toll-like receptors (TLRs) and the RIG-I-like receptors (RLRs). Within hepatocytes, RIG-I is a major PRR of HCV infection wherein PAMP interactions serve to trigger intracellular signaling cascades in the infected hepatocyte to drive IFN production and the expression of interferon-stimulated genes (ISGs). ISGs function to limit virus replication, modulate the immune system, and to suppress virus spread. However, studies of HCV-host interactions have revealed several mechanisms of innate immune regulation and evasion that feature virus control of PRR signaling and regulation of hepatic innate immune programs that may provide a molecular basis for viral persistence.


2017 ◽  
Vol 91 (18) ◽  
Author(s):  
Hong-Lei Zhang ◽  
Han-Qing Ye ◽  
Si-Qing Liu ◽  
Cheng-Lin Deng ◽  
Xiao-Dan Li ◽  
...  

ABSTRACT West Nile virus (WNV) is a mosquito-borne flavivirus that causes epidemics of encephalitis and viscerotropic disease worldwide. This virus has spread rapidly and has posed a significant public health threat since the outbreak in New York City in 1999. The interferon (IFN)-mediated antiviral response represents an important component of virus-host interactions and plays an essential role in regulating viral replication. Previous studies have suggested that multifunctional nonstructural proteins encoded by flaviviruses antagonize the host IFN response via various means in order to establish efficient viral replication. In this study, we demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes IFN-β production, most likely through suppression of retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) activation. In a dual-luciferase reporter assay, WNV NS1 significantly inhibited the activation of the IFN-β promoter after Sendai virus infection or poly(I·C) treatment. NS1 also suppressed the activation of the IFN-β promoter when it was stimulated by interferon regulatory factor 3 (IRF3)/5D or its upstream molecules in the RLR signaling pathway. Furthermore, NS1 blocked the phosphorylation and nuclear translocation of IRF3 upon stimulation by various inducers. Mechanistically, WNV NS1 targets RIG-I and melanoma differentiation-associated gene 5 (MDA5) by interacting with them and subsequently causing their degradation by the proteasome. Furthermore, WNV NS1 inhibits the K63-linked polyubiquitination of RIG-I, thereby inhibiting the activation of downstream sensors in the RLR signaling pathway. Taken together, our results reveal a novel mechanism by which WNV NS1 interferes with the host antiviral response. IMPORTANCE WNV Nile virus (WNV) has received increased attention since its introduction to the United States. However, the pathogenesis of this virus is poorly understood. This study demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes the induction of interferon beta (IFN-β) by interacting with and degrading retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5), which are crucial viral sensors in the host innate immune system. Further experiments suggested that NS1-mediated inhibition of the RIG-I-like receptor (RLR) signaling pathway involves inhibition of RIG-I K63-linked polyubiquitination and that the proteasome plays a role in RIG-I degradation. This study provides new insights into the regulation of WNV NS1 in the RLR signaling pathway and reveals a novel mechanism by which WNV evades the host innate immune response. The novel findings may guide us to discover new therapeutic targets and develop effective vaccines for WNV infections.


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