Showing papers on "Interferon published in 2013"
TL;DR: Results indicate that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP, which belongs to the nucleotidyltransferase family.
Abstract: The presence of DNA in the cytoplasm of mammalian cells is a danger signal that triggers host immune responses such as the production of type I interferons. Cytosolic DNA induces interferons through the production of cyclic guanosine monophosphate–adenosine monophosphate (cyclic GMP-AMP, or cGAMP), which binds to and activates the adaptor protein STING. Through biochemical fractionation and quantitative mass spectrometry, we identified a cGAMP synthase (cGAS), which belongs to the nucleotidyltransferase family. Overexpression of cGAS activated the transcription factor IRF3 and induced interferon-β in a STING-dependent manner. Knockdown of cGAS inhibited IRF3 activation and interferon-β induction by DNA transfection or DNA virus infection. cGAS bound to DNA in the cytoplasm and catalyzed cGAMP synthesis. These results indicate that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP.
3,096 citations
TL;DR: Two broad categories of tumor escape based on cellular and molecular characteristics of the tumor microenvironment are suggested, which appear to resist immune attack through immune system exclusion or ignorance and may require distinct immunotherapeutic interventions for maximal therapeutic effect.
Abstract: Most tumor cells express antigens that can mediate recognition by host CD8(+) T cells. Cancers that are detected clinically must have evaded antitumor immune responses to grow progressively. Recent work has suggested two broad categories of tumor escape based on cellular and molecular characteristics of the tumor microenvironment. One major subset shows a T cell-inflamed phenotype consisting of infiltrating T cells, a broad chemokine profile and a type I interferon signature indicative of innate immune activation. These tumors appear to resist immune attack through the dominant inhibitory effects of immune system-suppressive pathways. The other major phenotype lacks this T cell-inflamed phenotype and appears to resist immune attack through immune system exclusion or ignorance. These two major phenotypes of tumor microenvironment may require distinct immunotherapeutic interventions for maximal therapeutic effect.
2,939 citations
TL;DR: The frequency of the ILC1 subset was much higher in inflamed intestine of people with Crohn's disease, which indicated a role for these IFN-γ-producing I LC1 cells in the pathogenesis of gut mucosal inflammation.
Abstract: Innate lymphoid cells (ILCs) are effectors of innate immunity and regulators of tissue modeling Recently identified ILC populations have a cytokine expression pattern that resembles that of the helper T cell subsets T(H)2, T(H)17 and T(H)22 Here we describe a distinct ILC subset similar to T(H)1 cells, which we call 'ILC1' ILC1 cells expressed the transcription factor T-bet and responded to interleukin 12 (IL-12) by producing interferon-γ (IFN-γ) ILC1 cells were distinct from natural killer (NK) cells as they lacked perforin, granzyme B and the NK cell markers CD56, CD16 and CD94, and could develop from RORγt(+) ILC3 under the influence of IL-12 The frequency of the ILC1 subset was much higher in inflamed intestine of people with Crohn's disease, which indicated a role for these IFN-γ-producing ILC1 cells in the pathogenesis of gut mucosal inflammation
858 citations
National Institutes of Health1, Center for Drug Evaluation and Research2, Silver Spring Networks3, Johns Hopkins University4, Carolinas Medical Center5, Cornell University6, National Development and Research Institutes7, University of Maryland, Baltimore8, University of California, Irvine9, Veterans Health Administration10
TL;DR: RNA sequencing in primary human hepatocytes activated with synthetic double-stranded RNA to mimic HCV infection provides new insights into the genetic regulation of HCV clearance and its clinical management.
Abstract: Chronic infection with hepatitis C virus (HCV) is a common cause of liver cirrhosis and cancer. We performed RNA sequencing in primary human hepatocytes activated with synthetic double-stranded RNA to mimic HCV infection. Upstream of IFNL3 (IL28B) on chromosome 19q13.13, we discovered a new transiently induced region that harbors a dinucleotide variant ss469415590 (TT or ΔG), which is in high linkage disequilibrium with rs12979860, a genetic marker strongly associated with HCV clearance. ss469415590[ΔG] is a frameshift variant that creates a novel gene, designated IFNL4, encoding the interferon-λ4 protein (IFNL4), which is moderately similar to IFNL3. Compared to rs12979860, ss469415590 is more strongly associated with HCV clearance in individuals of African ancestry, although it provides comparable information in Europeans and Asians. Transient overexpression of IFNL4 in a hepatoma cell line induced STAT1 and STAT2 phosphorylation and the expression of interferon-stimulated genes. Our findings provide new insights into the genetic regulation of HCV clearance and its clinical management.
844 citations
01 Jan 2013
TL;DR: Sofosbuvir plus ribavirin for 12 weeks may be effective in previously untreated patients with HCV genotype 1, 2, or 3 infection, and the rate of sustained virologic response 24 weeks after therapy is reported.
Abstract: BACKGROUND The standard treatment for hepatitis C virus (HCV) infection is interferon, which is administered subcutaneously and can have troublesome side effects. We evaluated so fos bu vir, an oral nucleotide inhibitor of HCV polymerase, in interferon-sparing and interferon-free regimens for the treatment of HCV infection. METHODS
671 citations
TL;DR: A direct causal link between IFN-I signaling, immune activation, negative immune regulator expression, lymphoid tissue disorganization, and virus persistence is demonstrated and the results suggest that therapies targeting IFn-I may help control persistent virus infections.
Abstract: During persistent viral infections, chronic immune activation, negative immune regulator expression, an elevated interferon signature, and lymphoid tissue destruction correlate with disease progression. We demonstrated that blockade of type I interferon (IFN-I) signaling using an IFN-I receptor neutralizing antibody reduced immune system activation, decreased expression of negative immune regulatory molecules, and restored lymphoid architecture in mice persistently infected with lymphocytic choriomeningitis virus. IFN-I blockade before and after establishment of persistent virus infection resulted in enhanced virus clearance and was CD4 T cell–dependent. Hence, we demonstrate a direct causal link between IFN-I signaling, immune activation, negative immune regulator expression, lymphoid tissue disorganization, and virus persistence. Our results suggest that therapies targeting IFN-I may help control persistent virus infections.
651 citations
TL;DR: It is demonstrated in mice that blockade of IFN-I signaling diminished chronic immune activation and immune suppression, restored lymphoid tissue architecture, and increased immune parameters associated with control of virus replication, ultimately facilitating clearance of the persistent infection.
Abstract: Type I interferons (IFN-I) are critical for antiviral immunity; however, chronic IFN-I signaling is associated with hyperimmune activation and disease progression in persistent infections. We demonstrated in mice that blockade of IFN-I signaling diminished chronic immune activation and immune suppression, restored lymphoid tissue architecture, and increased immune parameters associated with control of virus replication, ultimately facilitating clearance of the persistent infection. The accelerated control of persistent infection induced by blocking IFN-I signaling required CD4 T cells and was associated with enhanced IFN-γ production. Thus, we demonstrated that interfering with chronic IFN-I signaling during persistent infection redirects the immune environment to enable control of infection.
629 citations
TL;DR: Human MX2 is a cell-autonomous, anti-HIV-1 resistance factor whose purposeful mobilization may represent a new therapeutic approach for the treatment of HIV/AIDS.
Abstract: Here, a protein known as MX2 is shown to be a major effector of interferon-α-mediated resistance to HIV-1 infection: susceptibility of the HIV-1 virus to inhibition by MX2 is dictated by the Capsid region of the viral Gag protein, and inhibition occurs at a late post-entry step of infection. Two groups report in this issue of Nature that the human interferon-induced GTP-binding protein MX2 is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) and a number of other lentiviruses. For some years it had been known that the related protein MX1 can inhibit HIV-1 replication in humans, but MX2 was thought to be devoid of antiviral activity. The anti-HIV-1 action of MX2 is much less dependent on GTPase activity than is the broader antiviral activity of MX1, pointing to possible mechanistic differences between them. Animal cells harbour multiple innate effector mechanisms that inhibit virus replication. For the pathogenic retrovirus human immunodeficiency virus type 1 (HIV-1), these include widely expressed restriction factors1, such as APOBEC3 proteins2, TRIM5-α3, BST2 (refs 4, 5) and SAMHD1 (refs 6, 7), as well as additional factors that are stimulated by type 1 interferon (IFN)8,9,10,11,12,13,14. Here we use both ectopic expression and gene-silencing experiments to define the human dynamin-like, IFN-induced myxovirus resistance 2 (MX2, also known as MXB) protein as a potent inhibitor of HIV-1 infection and as a key effector of IFN-α-mediated resistance to HIV-1 infection. MX2 suppresses infection by all HIV-1 strains tested, has equivalent or reduced effects on divergent simian immunodeficiency viruses, and does not inhibit other retroviruses such as murine leukaemia virus. The Capsid region of the viral Gag protein dictates susceptibility to MX2, and the block to infection occurs at a late post-entry step, with both the nuclear accumulation and chromosomal integration of nascent viral complementary DNA suppressed. Finally, human MX1 (also known as MXA), a closely related protein that has long been recognized as a broadly acting inhibitor of RNA and DNA viruses, including the orthomyxovirus influenza A virus15,16, does not affect HIV-1, whereas MX2 is ineffective against influenza virus. MX2 is therefore a cell-autonomous, anti-HIV-1 resistance factor whose purposeful mobilization may represent a new therapeutic approach for the treatment of HIV/AIDS.
511 citations
TL;DR: The studies demonstrate a unique mechanism by which IFN achieves its antiviral state through the production of a natural oxysterol to inhibit viral entry and implicate membrane-modifying oxysterols as potential antiviral therapeutics.
505 citations
TL;DR: Overall, these findings indicate that MX2 is an effector of the anti-HIV-1 activity of type-I IFN, and suggest thatMX2 inhibits HIV-1 infection by inhibiting capsid-dependent nuclear import of subviral complexes.
Abstract: HIV-1 replication can be inhibited by type I interferon (IFN), and the expression of a number of gene products with anti-HIV-1 activity is induced by type I IFN. However, none of the known antiretroviral proteins can account for the ability of type I IFN to inhibit early, preintegration phases of the HIV-1 replication cycle in human cells. Here, by comparing gene expression profiles in cell lines that differ in their ability to support the inhibitory action of IFN-α at early steps of the HIV-1 replication cycle, we identify myxovirus resistance 2 (MX2) as an interferon-induced inhibitor of HIV-1 infection. Expression of MX2 reduces permissiveness to a variety of lentiviruses, whereas depletion of MX2 using RNA interference reduces the anti-HIV-1 potency of IFN-α. HIV-1 reverse transcription proceeds normally in MX2-expressing cells, but 2-long terminal repeat circular forms of HIV-1 DNA are less abundant, suggesting that MX2 inhibits HIV-1 nuclear import, or destabilizes nuclear HIV-1 DNA. Consistent with this notion, mutations in the HIV-1 capsid protein that are known, or suspected, to alter the nuclear import pathways used by HIV-1 confer resistance to MX2, whereas preventing cell division increases MX2 potency. Overall, these findings indicate that MX2 is an effector of the anti-HIV-1 activity of type-I IFN, and suggest that MX2 inhibits HIV-1 infection by inhibiting capsid-dependent nuclear import of subviral complexes.
434 citations
TL;DR: The small molecule GS-9620 activates Toll-like receptor 7 signaling in immune cells of chimpanzees to induce clearance of HBV-infected cells and might be developed for treatment of patients with chronic HBV infection.
TL;DR: In cultured cells, type I interferon and its downstream signaling cascade inhibited the antimicrobial response induced by type II interferons, providing a potential explanation for why robust disease rather than protection is seen in some cases of infection.
Abstract: Type I interferons (IFN-α and IFN-β) are important for protection against many viral infections, whereas type II interferon (IFN-γ) is essential for host defense against some bacterial and parasitic pathogens Study of IFN responses in human leprosy revealed an inverse correlation between IFN-β and IFN-γ gene expression programs IFN-γ and its downstream vitamin D-dependent antimicrobial genes were preferentially expressed in self-healing tuberculoid lesions and mediated antimicrobial activity against the pathogen Mycobacterium leprae in vitro In contrast, IFN-β and its downstream genes, including interleukin-10 (IL-10), were induced in monocytes by M leprae in vitro and preferentially expressed in disseminated and progressive lepromatous lesions The IFN-γ-induced macrophage vitamin D-dependent antimicrobial peptide response was inhibited by IFN-β and by IL-10, suggesting that the differential production of IFNs contributes to protection versus pathogenesis in some human bacterial infections
University of Manchester1, Université libre de Bruxelles2, Blackpool Victoria Hospital3, Lancashire Teaching Hospitals NHS Foundation Trust4, Coventry Health Care5, University of Pavia6, Necker-Enfants Malades Hospital7, Montreal Children's Hospital8, Paris Descartes University9, Central Manchester University Hospitals NHS Foundation Trust10, University Hospitals of Leicester NHS Trust11, Children's Hospital at Westmead12, University of Brescia13, University of Tartu14, Guy's and St Thomas' NHS Foundation Trust15, Leeds General Infirmary16, University of São Paulo17, Oslo University Hospital18, French Institute of Health and Medical Research19, George Washington University20, Rappaport Faculty of Medicine21, University of Utah22, Boston Children's Hospital23, University of Birmingham24, Nottingham University Hospitals NHS Trust25, Mater Dei Hospital26
TL;DR: AGS is consistently associated with an interferon signature, which is apparently sustained over time and can thus be used to differentiate patients with AGS from controls, and neutralisation assays suggested that measurable antiviral activity was related toInterferon α production.
Abstract: Summary Background Aicardi-Goutieres syndrome (AGS) is an inflammatory disorder caused by mutations in any of six genes ( TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1 , and ADAR ). The disease is severe and effective treatments are urgently needed. We investigated the status of interferon-related biomarkers in patients with AGS with a view to future use in diagnosis and clinical trials. Methods In this case-control study, samples were collected prospectively from patients with mutation-proven AGS. The expression of six interferon-stimulated genes (ISGs) was measured by quantitative PCR, and the median fold change, when compared with the median of healthy controls, was used to create an interferon score for each patient. Scores higher than the mean of controls plus two SD (>2·466) were designated as positive. Additionally, we collated historical data for interferon activity, measured with a viral cytopathic assay, in CSF and serum from mutation-positive patients with AGS. We also undertook neutralisation assays of interferon activity in serum, and looked for the presence of autoantibodies against a panel of interferon proteins. Findings 74 (90%) of 82 patients had a positive interferon score (median 12·90, IQR 6·14–20·41) compared with two (7%) of 29 controls (median 0·93, IQR 0·57–1·30). Of the eight patients with a negative interferon score, seven had mutations in RNASEH2B (seven [27%] of all 26 patients with mutations in this gene). Repeat sampling in 16 patients was consistent for the presence or absence of an interferon signature on 39 of 41 occasions. Interferon activity (tested in 147 patients) was negatively correlated with age (CSF, r =−0·604; serum, r =−0·289), and was higher in CSF than in serum in 104 of 136 paired samples. Neutralisation assays suggested that measurable antiviral activity was related to interferon α production. We did not record significantly increased concentrations of autoantibodies to interferon subtypes in patients with AGS, or an association between the presence of autoantibodies and interferon score or serum interferon activity. Interpretation AGS is consistently associated with an interferon signature, which is apparently sustained over time and can thus be used to differentiate patients with AGS from controls. If future studies show that interferon status is a reactive biomarker, the measurement of an interferon score might prove useful in the assessment of treatment efficacy in clinical trials. Funding European Union's Seventh Framework Programme; European Research Council.
TL;DR: A cellular antiviral role for macrophage production of 25-hydroxycholesterol as a component of the sterol metabolic network linked to the IFN response via Stat1 is reported, and 25HC is described as a sterol-lipid effector of an innate immune pathway.
TL;DR: A recently uncovered role for host type I IFNs for antitumor immunity has important fundamental and clinical implications.
TL;DR: Recent insights into how HCV regulates innate immune signaling within the liver reveal a complex interaction of patient genetic background with viral and host factors of innate immune triggering and control that imparts the outcome of HCV infection and immunity.
Abstract: Hepatitis C virus (HCV) is a global public health problem involving chronic infection of the liver, which can cause liver disease and is linked with liver cancer. Viral innate immune evasion strategies and human genetic determinants underlie the transition of acute HCV infection to viral persistence and the support of chronic infection. Host genetic factors, such as sequence polymorphisms in IFNL3, a gene in the host interferon system, can influence both the outcome of the infection and the response to antiviral therapy. Recent insights into how HCV regulates innate immune signaling within the liver reveal a complex interaction of patient genetic background with viral and host factors of innate immune triggering and control that imparts the outcome of HCV infection and immunity.
TL;DR: IRF-3, -5, and -7 are established as the key transcription factors responsible for mediating the type I IFN and ISG response in mDC during WNV infection and a novel signaling link between MAVS and IRF-5 is suggested.
Abstract: Although the transcription factors IRF-3 and IRF-7 are considered master regulators of type I interferon (IFN) induction and IFN stimulated gene (ISG) expression, Irf3−/−×Irf7−/− double knockout (DKO) myeloid dendritic cells (mDC) produce relatively normal levels of IFN-β after viral infection. We generated Irf3−/−×Irf5−/−×Irf7−/− triple knockout (TKO) mice to test whether IRF-5 was the source of the residual induction of IFN-β and ISGs in mDCs. In pathogenesis studies with two unrelated positive-sense RNA viruses (West Nile virus (WNV) and murine norovirus), TKO mice succumbed at rates greater than DKO mice and equal to or approaching those of mice lacking the type I IFN receptor (Ifnar−/−). In ex vivo studies, after WNV infection or exposure to Toll-like receptor agonists, TKO mDCs failed to produce IFN-β or express ISGs. In contrast, this response was sustained in TKO macrophages following WNV infection. To define IRF-regulated gene signatures, we performed microarray analysis on WNV-infected mDC from wild type (WT), DKO, TKO, or Ifnar−/− mice, as well as from mice lacking the RIG-I like receptor adaptor protein MAVS. Whereas the gene induction pattern in DKO mDC was similar to WT cells, remarkably, almost no ISG induction was detected in TKO or Mavs−/− mDC. The relative equivalence of TKO and Mavs−/− responses suggested that MAVS dominantly regulates ISG induction in mDC. Moreover, we showed that MAVS-dependent induction of ISGs can occur through an IRF-5-dependent yet IRF-3 and IRF-7-independent pathway. Our results establish IRF-3, -5, and -7 as the key transcription factors responsible for mediating the type I IFN and ISG response in mDC during WNV infection and suggest a novel signaling link between MAVS and IRF-5.
TL;DR: The observed IFN signature in several autoimmune diseases is a biomarker of active disease and is investigated as a tool when selecting treatment for individual patients.
Abstract: Purpose of reviewAn increased expression of type I interferon (IFN) regulated genes (an IFN signature) has been reported in blood and tissue cells from patients with SLE and other autoimmune diseases. We review the possible mechanisms behind the IFN signature as well as clinical and therapeutic cons
TL;DR: It is shown that MDA5 signaling activity is regulated by a dynamic balance between phosphorylation and dephosphorylation of its caspase recruitment domains (CARDs) and that PP1α and PP1γ are regulators of antiviral innate immune responses to various RNA viruses.
TL;DR: The cultivation of alveolar type II cells at an air-liquid interface provides primary cultures in which to study the pulmonary innate immune responses to infection with SARS-CoV, and to explore possible therapeutic approaches to modulating these innate immune responds.
Abstract: Severe acute respiratory syndrome (SARS)-coronavirus (CoV) produces a devastating primary viral pneumonia with diffuse alveolar damage and a marked increase in circulating cytokines One of the major cell types to be infected is the alveolar type II cell However, the innate immune response of primary human alveolar epithelial cells infected with SARS-CoV has not been defined Our objectives included developing a culture system permissive for SARS-CoV infection in primary human type II cells and defining their innate immune response Culturing primary human alveolar type II cells at an air-liquid interface (A/L) improved their differentiation and greatly increased their susceptibility to infection, allowing us to define their primary interferon and chemokine responses Viral antigens were detected in the cytoplasm of infected type II cells, electron micrographs demonstrated secretory vesicles filled with virions, virus RNA concentrations increased with time, and infectious virions were released by exocytosis from the apical surface of polarized type II cells A marked increase was evident in the mRNA concentrations of interferon-β and interferon-λ (IL-29) and in a large number of proinflammatory cytokines and chemokines A surprising finding involved the variability of expression of angiotensin-converting enzyme-2, the SARS-CoV receptor, in type II cells from different donors In conclusion, the cultivation of alveolar type II cells at an air-liquid interface provides primary cultures in which to study the pulmonary innate immune responses to infection with SARS-CoV, and to explore possible therapeutic approaches to modulating these innate immune responses
TL;DR: It is demonstrated that subcutaneous immunization of mice with mRNA encoding the HIV-1 antigen Gag complexed with DOTAP/DOPE elicits antigen-specific, functional T cell responses resulting in specific killing of Gag peptide-pulsed cells and the induction of humoral responses.
01 Jan 2013
TL;DR: The goal of this review is to give an overview of the different facets of the inflammatory process that show regulatory input by IFN/STAT.
Abstract: Interferons (IFN) are subdivided into type I IFN (IFN-I, here synonymous with IFN-α/β), type II (IFN-γ) and type III IFN (IFN-III/IFN-λ) that reprogram nuclear gene expression through STATs 1 and 2 by forming STAT1 dimers (mainly IFN-γ) or the ISGF3 complex, a STAT1-STAT2-IRF9 heterotrimer (IFN-I and IFN-III) Dominant IFN activities in the immune system are to protect cells from viral replication and to activate macrophages for enhanced effector function However, the impact of IFN and their STATs on the immune system stretches far beyond these activities and includes the control of inflammation The goal of this review is to give an overview of the different facets of the inflammatory process that show regulatory input by IFN/STAT
TL;DR: These findings attribute a novel immunological plasticity to the choroid plexus epithelium, allowing it to serve, through interferon-γ signalling, as a tightly regulated entry gate into the central nervous system for circulating leucocytes immune surveillance under physiological conditions, and for repair following acute injury.
Abstract: Infiltrating T cells and monocyte-derived macrophages support central nervous system repair. Although infiltration of leucocytes to the injured central nervous system has recently been shown to be orchestrated by the brain's choroid plexus, the immunological mechanism that maintains this barrier and regulates its activity as a selective gate is poorly understood. Here, we hypothesized that CD4(+) effector memory T cells, recently shown to reside at the choroid plexus stroma, regulate leucocyte trafficking through this portal through their interactions with the choroid plexus epithelium. We found that the naive choroid plexus is populated by T helper 1, T helper 2 and regulatory T cells, but not by encephalitogenic T cells. In vitro findings revealed that the expression of immune cell trafficking determinants by the choroid plexus epithelium is specifically induced by interferon-γ. Tumour necrosis factor-α and interferon-γ reciprocally controlled the expression of their receptors by the choroid plexus epithelium, and had a synergistic effect in inducing the epithelial expression of trafficking molecules. In vivo, interferon-γ-dependent signalling controlled trafficking through the choroid plexus; interferon-γ receptor knockout mice exhibited reduced levels of T cells and monocyte entry to the cerebrospinal fluid and impaired recovery following spinal cord injury. Moreover, reduced expression of trafficking molecules by the choroid plexus was correlated with reduced CD4(+) T cells in the choroid plexus and cerebrospinal fluid of interferon-γ receptor knockout mice. Similar effect on the expression of trafficking molecules by the choroid plexus was found in bone-marrow chimeric mice lacking interferon-γ receptor in the central nervous system, or reciprocally, lacking interferon-γ in the circulation. Collectively, our findings attribute a novel immunological plasticity to the choroid plexus epithelium, allowing it to serve, through interferon-γ signalling, as a tightly regulated entry gate into the central nervous system for circulating leucocytes immune surveillance under physiological conditions, and for repair following acute injury.
TL;DR: The current state of the field of ISG15, the viruses against which ISg15 mediates protection, and the mechanisms by which ISG 15 exerts antiviral activity are reviewed.
TL;DR: It is revealed that the ORF 4a protein of MERS-CoV has the most potential to counteract the antiviral effects of IFN via the inhibition of both the interferon production and ISRE promoter element signaling pathways.
Abstract: The newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic respiratory virus with pathogenic mechanisms that may be driven by innate immune pathways. The goal of this study is to characterize the expression of the structural (S, E, M, N) and accessory (ORF 3, ORF 4a, ORF 4b, ORF 5) proteins of MERS-CoV and to determine whether any of these proteins acts as an interferon antagonist. Individual structural and accessory protein-coding plasmids with an N-terminal HA tag were constructed and transiently transfected into cells, and their native expression and subcellular localization were assessed using Wes tern blotting and indirect immunofluorescence. While ORF 4b demonstrated majorly nuclear localization, all of the other proteins demonstrated cytoplasmic localization. In addition, for the first time, our experiments revealed that the M, ORF 4a, ORF 4b, and ORF 5 proteins are potent interferon antagonists. Further examination revealed that the ORF 4a protein of MERS-CoV has the most potential to counteract the antiviral effects of IFN via the inhibition of both the interferon production (IFN-β promoter activity, IRF-3/7 and NF-κB activation) and ISRE promoter element signaling pathways. Together, our results provide new insights into the function and pathogenic role of the structural and accessory proteins of MERS-CoV.
TL;DR: It is demonstrated that HCV infection upregulates miR-21, which in turn suppresses HCV-triggered type I IFN production, thus promoting HCV replication and may be a potential therapeutic target for antiviral intervention.
Abstract: Upon recognition of viral components by pattern recognition receptors, such as the toll-like receptors (TLRs) and retinoic acid-inducible gene I (RIG-I)-like helicases, cells are activated to produce type I interferon (IFN) and proinflammatory cytokines. These pathways are tightly regulated by the host to prevent an inappropriate cellular response, but viruses can modulate these pathways to proliferate and spread. In this study, we revealed a novel mechanism in which hepatitis C virus (HCV) evades the immune surveillance system to proliferate by activating microRNA-21 (miR-21). We demonstrated that HCV infection upregulates miR-21, which in turn suppresses HCV-triggered type I IFN production, thus promoting HCV replication. Furthermore, we demonstrated that miR-21 targets two important factors in the TLR signaling pathway, myeloid differentiation factor 88 (MyD88) and interleukin-1 receptor-associated kinase 1 (IRAK1), which are involved in HCV-induced type I IFN production. HCV-mediated activation of miR-21 expression requires viral proteins and several signaling components. Moreover, we identified a transcription factor, activating protein-1 (AP-1), which is partly responsible for miR-21 induction in response to HCV infection through PKCe/JNK/c-Jun and PKCα/ERK/c-Fos cascades. Taken together, our results indicate that miR-21 is upregulated during HCV infection and negatively regulates IFN-α signaling through MyD88 and IRAK1 and may be a potential therapeutic target for antiviral intervention.
TL;DR: Evidence is provided that Chlamydia synthesizes cyclic di-AMP (c-di-AMP), a nucleic acid metabolite not previously identified in Gram-negative bacteria, and that this metabolite is a prominent ligand for STING-mediated activation of IFN responses during infection.
Abstract: STING (stimulator of interferon (IFN) genes) initiates type I IFN responses in mammalian cells through the detection of microbial nucleic acids The membrane-bound obligate intracellular bacterium Chlamydia trachomatis induces a STING- dependent type I IFN response in infected cells, yet the IFN-inducing ligand remains unknown In this report, we provide evi- dence thatChlamydiasynthesizes cyclic di-AMP (c-di-AMP), a nucleic acid metabolite not previously identified in Gram- negative bacteria, and that this metabolite is a prominent ligand for STING-mediated activation of IFN responses during infection We used primary mouse lungfibroblasts and HEK293T cells to compare IFN-responses toChlamydia infection, c-di-AMP, and other type I IFN-inducing stimuli Chlamydiainfection and c-di-AMP treatment induced type I IFN responses in cells expressing STING but not in cells expressing STING variants that cannot sense cyclic dinucleotides but still respond to cy- toplasmic DNA The failure to induce a type I IFN response to Chlamydia and c-di-AMP correlated with the inability of STING to relocalize from the endoplasmic reticulum to cytoplasmic punctate signaling complexes required for IFN activation We con- clude thatChlamydia induces STING-mediated IFN responses through the detection of c-di-AMP in the host cell cytosol and propose that c-di-AMP is the ligand predominantly responsible for inducing such a response in Chlamydia-infected cells IMPORTANCE This study shows that the Gram-negative obligate pathogen Chlamydia trachomatis, a major cause of pelvic in- flammatory disease and infertility, synthesizes cyclic di-AMP (c-di-AMP), a nucleic acid metabolite that thus far has been de- scribed only in Gram-positive bacteria We further provide evidence that the host cell employs an endoplasmic reticulum (ER)- localized cytoplasmic sensor, STING (stimulator of interferon (IFN) genes), to detect c-di-AMP synthesized by Chlamydiaand induce a protective IFN response This detection occurs even though Chlamydia is confined to a membrane-bound vacuole This raises the possibility that the ER, an organelle that innervates the entire cytoplasm, is equipped with pattern recognition recep- tors that can directly survey membrane-bound pathogen-containing vacuoles for leaking microbe-specific metabolites to mount type I IFN responses required to control microbial infections
Journal Article•
TL;DR: In this article, the authors identify the helicase, DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41) as the pattern recognition receptor (PRR) that senses both cyclic-di-GMP and cyclic -di-AMP.
Abstract: Cytosolic detection of bacterially derived secondary messengers cyclic-di-GMP (c-di-GMP) or cyclic -di-AMP (c-di-AMP) by the host immune system activates an innate immune response characterized by the induction of type I interferons (IFNs) Induction of IFN by c-di-GMP or c-di-AMP has been shown to be dependent on a stimulator of IFN genes-TANK binding kinase 1-IFN regulatory factor 3 (STING-TBK1-IRF3) signaling axis Although STING has been shown to interact with c-di-GMP, an upstream sensor of these cyclic dinucleotides is unknown Here we identify the helicase, DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41) as the pattern recognition receptor (PRR) that senses both c-di-GMP and c-di-AMP DDX41 specifically and directly interacts with c-di-GMP Knockdown of DDX41 via shRNA in murine or human immune cells inhibits the induction of innate immune genes and results in defective STING, TBK1 and IRF3 activation in response to c-di-GMP or c-di-AMP Our findings suggest a mechanism whereby c-di-GMP and c-di-AMP molecules are detected by the DDX41 PRR, which complexes with the STING adaptor to signal to TBK1-IRF3 and activate the IFN response
TL;DR: Although many viruses enter the body through the respiratory and gastrointestinal tracts, this article has focused the discussion on influenza A virus, respiratory syncytial virus, and rotavirus, three ubiquitous human pathogens that target the epithelial lining and are associated with a major disease burden.
Abstract: Interferons (IFNs) are produced in response to virus infection and induce an antiviral state in virtually all cell types. In addition to upregulating the transcription of genes that inhibit virus replication, type I (or -α/β) IFNs also act to orchestrate the adaptive immune response to virus infection. Recently a new family of antiviral cytokines, the type III (or -λ) IFNs, has been identified that activate the same antiviral pathways via a distinct receptor. Although the identical transcription factor, IFN-stimulated gene factor 3 is activated by either IFN-α/β or IFN-λ signaling, differences in the induction and action of these two cytokine families are beginning to be appreciated. In this article, we review this emerging body of literature on the differing roles these cytokines play in host defense of the mucosal surface. Although many viruses enter the body through the respiratory and gastrointestinal tracts, we have focused the discussion on influenza A virus, respiratory syncytial virus, and rotavirus, three ubiquitous human pathogens that target the epithelial lining and are associated with a major disease burden.
TL;DR: It is shown that EV71 inhibits anti-viral type I interferon (IFN) responses by targeting the mitochondrial anti-Viral signaling (MAVS) protein—a unique adaptor molecule activated upon retinoic acid induced gene-I and melanoma differentiation associated gene (MDA-5) viral recognition receptor signaling—upstream of type Iinterferon production.
Abstract: Enterovirus 71 (EV71) is the major causative pathogen of hand, foot, and mouth disease (HFMD). Its pathogenicity is not fully understood, but innate immune evasion is likely a key factor. Strategies to circumvent the initiation and effector phases of anti-viral innate immunity are well known; less well known is whether EV71 evades the signal transduction phase regulated by a sophisticated interplay of cellular and viral proteins. Here, we show that EV71 inhibits anti-viral type I interferon (IFN) responses by targeting the mitochondrial anti-viral signaling (MAVS) protein—a unique adaptor molecule activated upon retinoic acid induced gene-I (RIG-I) and melanoma differentiation associated gene (MDA-5) viral recognition receptor signaling—upstream of type I interferon production. MAVS was cleaved and released from mitochondria during EV71 infection. An in vitro cleavage assay demonstrated that the viral 2A protease (2Apro), but not the mutant 2Apro (2Apro-110) containing an inactivated catalytic site, cleaved MAVS. The Protease-Glo assay revealed that MAVS was cleaved at 3 residues between the proline-rich and transmembrane domains, and the resulting fragmentation effectively inactivated downstream signaling. In addition to MAVS cleavage, we found that EV71 infection also induced morphologic and functional changes to the mitochondria. The EV71 structural protein VP1 was detected on purified mitochondria, suggesting not only a novel role for mitochondria in the EV71 replication cycle but also an explanation of how EV71-derived 2Apro could approach MAVS. Taken together, our findings reveal a novel strategy employed by EV71 to escape host anti-viral innate immunity that complements the known EV71-mediated immune-evasion mechanisms.