151
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Viral RNA detection by RIG-I-like receptors. Curr Opin Immunol 2015; 32:48-53. [PMID: 25594890 DOI: 10.1016/j.coi.2014.12.012] [Citation(s) in RCA: 334] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Revised: 12/17/2014] [Accepted: 12/30/2014] [Indexed: 12/12/2022]
Abstract
In higher vertebrates, recognition of the non-self signature of invading viruses by genome-encoded pattern recognition receptors initiates antiviral innate immunity. Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) detect viral RNA as a non-self pattern in the cytoplasm and activate downstream signaling. Detection of viral RNA also activates stress responses resulting in stress granule-like aggregates, which facilitate RLR-mediated antiviral immunity. Among the three RLR family members RIG-I and melanoma differentiation-associated gene 5 (MDA5) recognize distinct viral RNA species with differential molecular machinery and activate signaling through mitochondrial antiviral signaling (MAVS, also known as IPS-1/VISA/Cardif), which leads to the expression of cytokines including type I and III interferons (IFNs) to restrict viral propagation. In this review, we summarize recent knowledge regarding RNA recognition and signal transduction by RLRs and MAVS/IPS-1.
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152
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Bryant CE, Orr S, Ferguson B, Symmons MF, Boyle JP, Monie TP. International Union of Basic and Clinical Pharmacology. XCVI. Pattern recognition receptors in health and disease. Pharmacol Rev 2015; 67:462-504. [PMID: 25829385 PMCID: PMC4394686 DOI: 10.1124/pr.114.009928] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Since the discovery of Toll, in the fruit fly Drosophila melanogaster, as the first described pattern recognition receptor (PRR) in 1996, many families of these receptors have been discovered and characterized. PRRs play critically important roles in pathogen recognition to initiate innate immune responses that ultimately link to the generation of adaptive immunity. Activation of PRRs leads to the induction of immune and inflammatory genes, including proinflammatory cytokines and chemokines. It is increasingly clear that many PRRs are linked to a range of inflammatory, infectious, immune, and chronic degenerative diseases. Several drugs to modulate PRR activity are already in clinical trials and many more are likely to appear in the near future. Here, we review the different families of mammalian PRRs, the ligands they recognize, the mechanisms of activation, their role in disease, and the potential of targeting these proteins to develop the anti-inflammatory therapeutics of the future.
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Affiliation(s)
- Clare E Bryant
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
| | - Selinda Orr
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
| | - Brian Ferguson
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
| | - Martyn F Symmons
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
| | - Joseph P Boyle
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
| | - Tom P Monie
- Departments of Veterinary Medicine (C.E.B., J.P.B., T.P.M.), Pathology (B.F.), and Biochemistry (M.F.S., J.P.B.), University of Cambridge, Cambridge, United Kingdom; and Institute of Infection and Immunity, Cardiff University, Cardiff, United Kingdom (S.O.)
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153
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Zheng J, Yong HY, Panutdaporn N, Liu C, Tang K, Luo D. High-resolution HDX-MS reveals distinct mechanisms of RNA recognition and activation by RIG-I and MDA5. Nucleic Acids Res 2015; 43:1216-30. [PMID: 25539915 PMCID: PMC4333383 DOI: 10.1093/nar/gku1329] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 12/07/2014] [Accepted: 12/09/2014] [Indexed: 12/25/2022] Open
Abstract
RIG-I and MDA5 are the major intracellular immune receptors that recognize viral RNA species and undergo a series of conformational transitions leading to the activation of the interferon-mediated antiviral response. However, to date, full-length RLRs have resisted crystallographic efforts and a molecular description of their activation pathways remains hypothetical. Here we employ hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS) to probe the apo states of RIG-I and MDA5 and to dissect the molecular details with respect to distinct RNA species recognition, ATP binding and hydrolysis and CARDs activation. We show that human RIG-I maintains an auto-inhibited resting state owing to the intra-molecular HEL2i-CARD2 interactions while apo MDA5 lacks the analogous intra-molecular interactions and therefore adopts an extended conformation. Our work demonstrates that RIG-I binds and responds differently to short triphosphorylated RNA and long duplex RNA and that sequential addition of RNA and ATP triggers specific allosteric effects leading to RIG-I CARDs activation. We also present a high-resolution protein surface mapping technique that refines the cooperative oligomerization model of neighboring MDA5 molecules on long duplex RNA. Taken together, our data provide a high-resolution view of RLR activation in solution and offer new evidence for the molecular mechanism of RLR activation.
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Affiliation(s)
- Jie Zheng
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Hui Yee Yong
- Lee Kong Chian School of Medicine, Nanyang Technological University, 61 Biopolis Drive, Proteos Building, #07-03, 138673, Singapore
| | - Nantika Panutdaporn
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Chuanfa Liu
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Kai Tang
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Dahai Luo
- Lee Kong Chian School of Medicine, Nanyang Technological University, 61 Biopolis Drive, Proteos Building, #07-03, 138673, Singapore
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154
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Alcorn JF, Sarkar SN. What is the oligoadenylate synthetases-like protein and does it have therapeutic potential for influenza? Expert Rev Respir Med 2014; 9:1-3. [PMID: 25544107 DOI: 10.1586/17476348.2015.994608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Besides its pandemic potential, seasonal influenza infection is associated with an estimated 250,000 to 500,000 deaths worldwide every year. Part of this virulence of influenza virus can be attributed to its ability to evade the host innate immune response. Here, we discuss the possibility of using a recently described mechanism of boosting the innate immunity by oligoadenylate synthetase-like protein, to combat influenza infections.
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Affiliation(s)
- John F Alcorn
- Department of Pediatrics, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA, USA
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155
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Abstract
Cell proliferation and cell death are integral elements in maintaining homeostatic balance in metazoans. Disease pathologies ensue when these processes are disturbed. A plethora of evidence indicates that malfunction of cell death can lead to inflammation, autoimmunity, or immunodeficiency. Programmed necrosis or necroptosis is a form of nonapoptotic cell death driven by the receptor interacting protein kinase 3 (RIPK3) and its substrate, mixed lineage kinase domain-like (MLKL). RIPK3 partners with its upstream adaptors RIPK1, TRIF, or DAI to signal for necroptosis in response to death receptor or Toll-like receptor stimulation, pathogen infection, or sterile cell injury. Necroptosis promotes inflammation through leakage of cellular contents from damaged plasma membranes. Intriguingly, many of the signal adaptors of necroptosis have dual functions in innate immune signaling. This unique signature illustrates the cooperative nature of necroptosis and innate inflammatory signaling pathways in managing cell and organismal stresses from pathogen infection and sterile tissue injury.
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Affiliation(s)
- Francis Ka-Ming Chan
- Department of Pathology, Immunology and Microbiology Program, University of Massachusetts Medical School, Worcester, Massachusetts 01605;
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156
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Kagan JC, Magupalli VG, Wu H. SMOCs: supramolecular organizing centres that control innate immunity. Nat Rev Immunol 2014; 14:821-6. [PMID: 25359439 PMCID: PMC4373346 DOI: 10.1038/nri3757] [Citation(s) in RCA: 219] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The diverse receptor families of the innate immune system activate signal transduction pathways that are important for host defence, but common themes to explain the operation of these pathways remain undefined. In this Opinion article, we propose--on the basis of recent structural and cell biological studies--the concept of supramolecular organizing centres (SMOCs) as location-specific higher-order signalling complexes in which increased local concentrations of signalling components promote the intrinsically weak allosteric interactions that are required for enzyme activation. We suggest that SMOCs are assembled on various membrane-bound organelles or other intracellular sites, which may assist signal amplification to reach a response threshold and potentially define the specificity of cellular responses that are induced in response to infectious and non-infectious insults.
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Affiliation(s)
- Jonathan C Kagan
- Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02446, USA
| | - Venkat Giri Magupalli
- Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02446, USA
| | - Hao Wu
- Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02446, USA
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157
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Gokhale NS, Vazquez C, Horner SM. Hepatitis C Virus. Strategies to Evade Antiviral Responses. Future Virol 2014; 9:1061-1075. [PMID: 25983854 DOI: 10.2217/fvl.14.89] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hepatitis C virus (HCV) causes chronic liver disease and poses a major clinical and economic burden worldwide. HCV is an RNA virus that is sensed as non-self in the infected liver by host pattern recognition receptors, triggering downstream signaling to interferons (IFNs). The type III IFNs play an important role in immunity to HCV, and human genetic variation in their gene loci is associated with differential HCV infection outcomes. HCV evades host antiviral innate immune responses to mediate a persistent infection in the liver. This review focuses on anti-HCV innate immune sensing, innate signaling and effectors, and the processes and proteins used by HCV to evade and regulate host innate immunity.
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Affiliation(s)
- Nandan S Gokhale
- Department of Molecular Genetics & Microbiology, Duke University Medical Center, Durham, NC 27710
| | - Christine Vazquez
- Department of Molecular Genetics & Microbiology, Duke University Medical Center, Durham, NC 27710
| | - Stacy M Horner
- Department of Molecular Genetics & Microbiology, Duke University Medical Center, Durham, NC 27710 ; Department of Medicine, Duke University Medical Center, Durham, NC 27710
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158
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Kagan JC, Barton GM. Emerging principles governing signal transduction by pattern-recognition receptors. Cold Spring Harb Perspect Biol 2014; 7:a016253. [PMID: 25395297 PMCID: PMC4355268 DOI: 10.1101/cshperspect.a016253] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The problem of recognizing and disposing of non-self-organisms, whether for nutrients or defense, predates the evolution of multicellularity. Accordingly, the function of the innate immune system is often intimately associated with fundamental aspects of cell biology. Here, we review our current understanding of the links between cell biology and pattern-recognition receptors of the innate immune system. We highlight the importance of receptor localization for the detection of microbes and for the initiation of antimicrobial signaling pathways. We discuss examples that illustrate how pattern-recognition receptors influence, and are influenced by, the general membrane trafficking machinery of mammalian cells. In the future, cell biological analysis likely will rival pure genetic analysis as a tool to uncover fundamental principles that govern host-microbe interactions.
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Affiliation(s)
- Jonathan C Kagan
- Harvard Medical School and Division of Gastroenterology, Boston Children's Hospital, Boston, Massachusetts 02115
| | - Gregory M Barton
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, California 94720-3200
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159
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Cai X, Chen ZJ. Prion-like polymerization as a signaling mechanism. Trends Immunol 2014; 35:622-630. [PMID: 25457352 DOI: 10.1016/j.it.2014.10.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 10/14/2014] [Accepted: 10/15/2014] [Indexed: 12/25/2022]
Abstract
The innate immune system uses pattern recognition receptors such as RIG-I and NLRP3 to sense pathogen invasion and other danger signals. Activation of these receptors induces robust signal transduction cascades that trigger the production of cytokines important for host protection. MAVS and ASC are essential adaptor proteins downstream of RIG-I and NLRP3, respectively, and both contain N-terminal domains belonging to the death domain superfamily. Recent studies suggest that both MAVS and ASC form functional prion-like fibers through their respective death domains to propagate downstream signaling. Here, we review these findings, and in this context discuss the emerging concept of prion-like polymerization in signal transduction. We further examine the potential benefits of this signaling strategy, including signal amplification, host evolutionary advantage, and molecular memory.
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Affiliation(s)
- Xin Cai
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA.
| | - Zhijian J Chen
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA.
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160
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Narita R, Takahasi K, Murakami E, Hirano E, Yamamoto SP, Yoneyama M, Kato H, Fujita T. A novel function of human Pumilio proteins in cytoplasmic sensing of viral infection. PLoS Pathog 2014; 10:e1004417. [PMID: 25340845 PMCID: PMC4207803 DOI: 10.1371/journal.ppat.1004417] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 08/21/2014] [Indexed: 12/24/2022] Open
Abstract
RIG-I-like receptor (RLR) plays a pivotal role in the detection of invading pathogens to initiate type I interferon (IFN) gene transcription. Since aberrant IFN production is harmful, RLR signaling is strictly regulated. However, the regulatory mechanisms are not fully understood. By expression cloning, we identified Pumilio proteins, PUM1 and PUM2, as candidate positive regulators of RIG-I signaling. Overexpression of Pumilio proteins and their knockdown augmented and diminished IFN-β promoter activity induced by Newcastle disease virus (NDV), respectively. Both proteins showed a specific association with LGP2, but not with RIG-I or MDA5. Furthermore, all of these components were recruited to NDV-induced antiviral stress granules. Interestingly, biochemical analyses revealed that Pumilio increased double-stranded (ds) RNA binding affinity of LGP2; however, Pumilio was absent in the dsRNA-LGP2 complex, suggesting that Pumilio facilitates viral RNA recognition by LGP2 through its chaperon-like function. Collectively, our results demonstrate an unknown function of Pumilio in viral recognition by LGP2. Mammals utilize innate immune system to counteract viral infections. The host pattern-recognition receptors, such as RIG-I-like receptors (RLRs), sense invading pathogens and initiate innate immune responses. RLRs are composed of three RNA helicases, RIG-I, MDA5 and LGP2, and detect a series of RNA viruses, such as influenza or hepatitis C virus, in the cytoplasm. Upon RNA virus infection, RLRs transmit signals through mitochondrial adaptor protein, IPS-1, to activate transcription factor IRF-3/7, resulting in the production of type I interferon (IFN). Type I IFN plays a crucial role in innate immune system by inducing a hundreds of interferon-stimulated genes and its induction is tightly controlled at transcriptional and translational steps. Pumilio proteins are originally identified as translational repressor through direct binding to specific sequence motifs in the 3′ untranslated regions of specific mRNA, and regulate critical biological processes, such as development and differentiation. In this report, we identified human Pumilio proteins, PUM1 and PUM2, as candidate regulators of IFN signaling. Our results demonstrated an unknown function of Pumilio in viral recognition by LGP2.
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Affiliation(s)
- Ryo Narita
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Kiyohiro Takahasi
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
- Institute for Innovative NanoBio Drug Discovery and Development, Graduate School of Pharmaceutical Science, Kyoto University, Kyoto, Japan
| | - Etsu Murakami
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Emi Hirano
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Seiji P. Yamamoto
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Mitsutoshi Yoneyama
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, Chiba, Japan
| | - Hiroki Kato
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
- Laboratory of Molecular Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan
| | - Takashi Fujita
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto, Japan
- Laboratory of Molecular Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan
- * E-mail:
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161
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Rawling DC, Kohlway AS, Luo D, Ding SC, Pyle AM. The RIG-I ATPase core has evolved a functional requirement for allosteric stabilization by the Pincer domain. Nucleic Acids Res 2014; 42:11601-11. [PMID: 25217590 PMCID: PMC4191399 DOI: 10.1093/nar/gku817] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 08/16/2014] [Accepted: 08/29/2014] [Indexed: 12/24/2022] Open
Abstract
Retinoic acid-inducible gene I (RIG-I) is a pattern recognition receptor expressed in metazoan cells that is responsible for eliciting the production of type I interferons and pro-inflammatory cytokines upon detection of intracellular, non-self RNA. Structural studies of RIG-I have identified a novel Pincer domain composed of two alpha helices that physically tethers the C-terminal domain to the SF2 helicase core. We find that the Pincer plays an important role in mediating the enzymatic and signaling activities of RIG-I. We identify a series of mutations that additively decouple the Pincer motif from the ATPase core and show that this decoupling results in impaired signaling. Through enzymological and biophysical analysis, we further show that the Pincer domain controls coupled enzymatic activity of the protein through allosteric control of the ATPase core. Further, we show that select regions of the HEL1 domain have evolved to potentiate interactions with the Pincer domain, resulting in an adapted ATPase cleft that is now responsive to adjacent domains that selectively bind viral RNA.
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Affiliation(s)
- David C Rawling
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Andrew S Kohlway
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Dahai Luo
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA Department of Chemistry, Yale University, New Haven, CT 06520, USA
| | - Steve C Ding
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA Department of Chemistry, Yale University, New Haven, CT 06520, USA
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162
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Patel JR, GarcÃa-Sastre A. Activation and regulation of pathogen sensor RIG-I. Cytokine Growth Factor Rev 2014; 25:513-23. [PMID: 25212896 DOI: 10.1016/j.cytogfr.2014.08.005] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 08/15/2014] [Indexed: 12/24/2022]
Abstract
Cells are equipped with a large set of pattern recognition receptors or sensors that detect foreign molecules such as pathogenic nucleic acids and initiate proinflammatory and antimicrobial innate immune responses. RIG-I is a cytosolic sensor that detects 5'-triphosphate double-stranded RNAs produced during infection. RIG-I is responsible for mounting an antimicrobial response against a variety of viruses and intracellular bacteria. RIG-I contains an intricate structural architecture that allows for efficient signaling downstream in the pathway and autoregulation. The RIG-I-mediated antimicrobial pathway is highly regulated in cells requiring various cofactors, negative regulators, and posttranslational modifications. Modulation of RIG-I and RIG-I-mediated signaling in cells by pathogens to evade recognition and activation of the antimicrobial pathway highlights the essential nature of RIG-I in the innate immune response.
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Affiliation(s)
- Jenish R Patel
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
| | - Adolfo GarcÃa-Sastre
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of Medicine, Division of Infectious Diseases, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
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163
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Louber J, Kowalinski E, Bloyet LM, Brunel J, Cusack S, Gerlier D. RIG-I self-oligomerization is either dispensable or very transient for signal transduction. PLoS One 2014; 9:e108770. [PMID: 25259935 PMCID: PMC4178188 DOI: 10.1371/journal.pone.0108770] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 09/04/2014] [Indexed: 01/01/2023] Open
Abstract
Effective host defence against viruses depends on the rapid triggering of innate immunity through the induction of a type I interferon (IFN) response. To this end, microbe-associated molecular patterns are detected by dedicated receptors. Among them, the RIG-I-like receptors RIG-I and MDA5 activate IFN gene expression upon sensing viral RNA in the cytoplasm. While MDA5 forms long filaments in vitro upon activation, RIG-I is believed to oligomerize after RNA binding in order to transduce a signal. Here, we show that in vitro binding of synthetic RNA mimicking that of Mononegavirales (Ebola, rabies and measles viruses) leader sequences to purified RIG-I does not induce RIG-I oligomerization. Furthermore, in cells devoid of endogenous functional RIG-I-like receptors, after activation of exogenous Flag-RIG-I by a 62-mer-5'ppp-dsRNA or by polyinosinic:polycytidylic acid, a dsRNA analogue, or by measles virus infection, anti-Flag immunoprecipitation and specific elution with Flag peptide indicated a monomeric form of RIG-I. Accordingly, when using the Gaussia Luciferase-Based Protein Complementation Assay (PCA), a more sensitive in cellula assay, no RIG-I oligomerization could be detected upon RNA stimulation. Altogether our data indicate that the need for self-oligomerization of RIG-I for signal transduction is either dispensable or very transient.
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Affiliation(s)
- Jade Louber
- Centre International de Recherche en Infectiologie, INSERM, U1111, CNRS, UMR5308, Université Lyon 1, ENS Lyon, Lyon, France
| | - Eva Kowalinski
- European Molecular Biology Laboratory, Grenoble Outstation, Grenoble Cedex 9, France
- Unit of Virus Host-Cell Interactions, UJF-EMBL-CNRS, UMI 3265, Grenoble Cedex 9, France
| | - Louis-Marie Bloyet
- Centre International de Recherche en Infectiologie, INSERM, U1111, CNRS, UMR5308, Université Lyon 1, ENS Lyon, Lyon, France
| | - Joanna Brunel
- Centre International de Recherche en Infectiologie, INSERM, U1111, CNRS, UMR5308, Université Lyon 1, ENS Lyon, Lyon, France
| | - Stephen Cusack
- European Molecular Biology Laboratory, Grenoble Outstation, Grenoble Cedex 9, France
- Unit of Virus Host-Cell Interactions, UJF-EMBL-CNRS, UMI 3265, Grenoble Cedex 9, France
| | - Denis Gerlier
- Centre International de Recherche en Infectiologie, INSERM, U1111, CNRS, UMR5308, Université Lyon 1, ENS Lyon, Lyon, France
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164
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Onomoto K, Yoneyama M, Fung G, Kato H, Fujita T. Antiviral innate immunity and stress granule responses. Trends Immunol 2014; 35:420-8. [PMID: 25153707 PMCID: PMC7185371 DOI: 10.1016/j.it.2014.07.006] [Citation(s) in RCA: 180] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2014] [Revised: 07/16/2014] [Accepted: 07/16/2014] [Indexed: 12/13/2022]
Abstract
Viral infection triggers the activation of antiviral innate immune responses in mammalian cells. Viral RNA in the cytoplasm activates signaling pathways that result in the production of interferons (IFNs) and IFN-stimulated genes. Some viral infections have been shown to induce cytoplasmic granular aggregates similar to the dynamic ribonucleoprotein aggregates termed stress granules (SGs), suggesting that these viruses may utilize this stress response for their own benefit. By contrast, some viruses actively inhibit SG formation, suggesting an antiviral function for these structures. We review here the relationship between different viral infections and SG formation. We examine the evidence for antiviral functions for SGs and highlight important areas of inquiry towards understanding cellular stress responses to viral infection.
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Affiliation(s)
- Koji Onomoto
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, Chiba 260-8673, Japan
| | - Mitsutoshi Yoneyama
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, Chiba 260-8673, Japan
| | - Gabriel Fung
- University of British Columbia (UBC) James Hogg Research Center, Providence Heart and Lung Institute, St. Paul's Hospital and Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Hiroki Kato
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan; Laboratory of Molecular Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan
| | - Takashi Fujita
- Laboratory of Molecular Genetics, Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan; Laboratory of Molecular Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan.
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165
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Schmitz ML, Kracht M, Saul VV. The intricate interplay between RNA viruses and NF-κB. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:2754-2764. [PMID: 25116307 PMCID: PMC7114235 DOI: 10.1016/j.bbamcr.2014.08.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2014] [Revised: 08/01/2014] [Accepted: 08/02/2014] [Indexed: 12/19/2022]
Abstract
RNA viruses have rapidly evolving genomes which often allow cross-species transmission and frequently generate new virus variants with altered pathogenic properties. Therefore infections by RNA viruses are a major threat to human health. The infected host cell detects trace amounts of viral RNA and the last years have revealed common principles in the biochemical mechanisms leading to signal amplification that is required for mounting of a powerful antiviral response. Components of the RNA sensing and signaling machinery such as RIG-I-like proteins, MAVS and the inflammasome inducibly form large oligomers or even fibers that exhibit hallmarks of prions. Following a nucleation event triggered by detection of viral RNA, these energetically favorable and irreversible polymerization events trigger signaling cascades leading to the induction of antiviral and inflammatory responses, mediated by interferon and NF-κB pathways. Viruses have evolved sophisticated strategies to manipulate these host cell signaling pathways in order to ensure their replication. We will discuss at the examples of influenza and HTLV-1 viruses how a fascinating diversity of biochemical mechanisms is employed by viral proteins to control the NF-κB pathway at all levels.
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Affiliation(s)
- M Lienhard Schmitz
- Institute of Biochemistry, Medical Faculty, Friedrichstrasse 24, Justus-Liebig-University, 35392 Giessen, Germany.
| | - Michael Kracht
- Rudolf-Buchheim-Institute of Pharmacology, Justus-Liebig-University Giessen, D-35392 Giessen, Germany
| | - Vera V Saul
- Institute of Biochemistry, Medical Faculty, Friedrichstrasse 24, Justus-Liebig-University, 35392 Giessen, Germany
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166
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The innate immune sensor LGP2 activates antiviral signaling by regulating MDA5-RNA interaction and filament assembly. Mol Cell 2014; 55:771-81. [PMID: 25127512 DOI: 10.1016/j.molcel.2014.07.003] [Citation(s) in RCA: 196] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 06/11/2014] [Accepted: 07/03/2014] [Indexed: 12/24/2022]
Abstract
Cytoplasmic pattern recognition receptors detect non-self RNAs during virus infections and initiate antiviral signaling. One receptor, MDA5, possesses essential signaling domains, but weak RNA binding. A second receptor, LGP2, rapidly detects diverse dsRNA species, but lacks signaling domains. Accumulating evidence suggests LGP2 and MDA5 work together to detect viral RNA and generate a complete antiviral response, but the basis for their cooperation has been elusive. Experiments presented here address this gap in antiviral signaling, revealing that LGP2 assists MDA5-RNA interactions leading to enhanced MDA5-mediated antiviral signaling. LGP2 increases the initial rate of MDA5-RNA interaction and regulates MDA5 filament assembly, resulting in the formation of more numerous, shorter MDA5 filaments that are shown to generate equivalent or greater signaling activity in vivo than the longer filaments containing only MDA5. These findings provide a mechanism for LGP2 coactivation of MDA5 and a biological context for MDA5-RNA filaments in antiviral responses.
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167
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Reikine S, Nguyen JB, Modis Y. Pattern Recognition and Signaling Mechanisms of RIG-I and MDA5. Front Immunol 2014; 5:342. [PMID: 25101084 PMCID: PMC4107945 DOI: 10.3389/fimmu.2014.00342] [Citation(s) in RCA: 299] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 07/05/2014] [Indexed: 12/25/2022] Open
Abstract
Most organisms rely on innate immune receptors to recognize conserved molecular structures from invading microbes. Two essential innate immune receptors, RIG-I and MDA5, detect viral double-stranded RNA in the cytoplasm. The inflammatory response triggered by these RIG-I-like receptors (RLRs) is one of the first and most important lines of defense against infection. RIG-I recognizes short RNA ligands with 5′-triphosphate caps. MDA5 recognizes long kilobase-scale genomic RNA and replication intermediates. Ligand binding induces conformational changes and oligomerization of RLRs that activate the signaling partner MAVS on the mitochondrial and peroxisomal membranes. This signaling process is under tight regulation, dependent on post-translational modifications of RIG-I and MDA5, and on regulatory proteins including unanchored ubiquitin chains and a third RLR, LGP2. Here, we review recent advances that have shifted the paradigm of RLR signaling away from the conventional linear signaling cascade. In the emerging RLR signaling model, large multimeric signaling platforms generate a highly cooperative, self-propagating, and context-dependent signal, which varies with the subcellular localization of the signaling platform.
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Affiliation(s)
- Stephanie Reikine
- Department of Molecular Biophysics and Biochemistry, Yale University , New Haven, CT , USA
| | - Jennifer B Nguyen
- Department of Molecular Biophysics and Biochemistry, Yale University , New Haven, CT , USA
| | - Yorgo Modis
- Department of Molecular Biophysics and Biochemistry, Yale University , New Haven, CT , USA
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168
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Bruns AM, Horvath CM. Antiviral RNA recognition and assembly by RLR family innate immune sensors. Cytokine Growth Factor Rev 2014; 25:507-12. [PMID: 25081315 DOI: 10.1016/j.cytogfr.2014.07.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 07/03/2014] [Indexed: 12/24/2022]
Abstract
Virus-encoded molecular signatures, such as cytosolic double-stranded or otherwise biochemically distinct RNA species, trigger cellular antiviral signaling. Cytoplasmic proteins recognize these non-self RNAs and activate signal transduction pathways that drive the expression of virus-induced genes, including the primary antiviral cytokine, IFNβ, and diverse direct and indirect antiviral effectors. One important group of cytosolic RNA sensors known as the RIG-I-like receptors (RLRs) is comprised of three proteins that are similar in structure and function. The RLR proteins, RIG-I, MDA5, and LGP2, share the ability to recognize nucleic acid signatures produced by virus infections and activate antiviral signaling. Emerging evidence indicates that RNA detection by RLRs culminates in the assembly of dynamic multimeric ribonucleoprotein (RNP) complexes. These RNPs can act as signaling platforms that are capable of propagating and amplifying antiviral signaling responses. Despite their common domain structures and similar abilities to induce antiviral responses, the RLRs differ in their enzymatic properties, their intrinsic abilities to recognize RNA, and their ability to assemble into filamentous complexes. This molecular specialization has enabled the RLRs to recognize and respond to diverse virus infections, and to mediate both unique and overlapping functions in immune regulation.
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Affiliation(s)
- Annie M Bruns
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA
| | - Curt M Horvath
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
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169
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Wu B, Peisley A, Tetrault D, Li Z, Egelman EH, Magor KE, Walz T, Penczek PA, Hur S. Molecular imprinting as a signal-activation mechanism of the viral RNA sensor RIG-I. Mol Cell 2014; 55:511-23. [PMID: 25018021 DOI: 10.1016/j.molcel.2014.06.010] [Citation(s) in RCA: 191] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Revised: 05/12/2014] [Accepted: 06/02/2014] [Indexed: 12/24/2022]
Abstract
RIG-I activates interferon signaling pathways by promoting filament formation of the adaptor molecule, MAVS. Assembly of the MAVS filament is mediated by its CARD domain (CARD(MAVS)), and requires its interaction with the tandem CARDs of RIG-I (2CARD(RIG-I)). However, the precise nature of the interaction between 2CARD(RIG-I) and CARD(MAVS), and how this interaction leads to CARD(MAVS) filament assembly, has been unclear. Here we report a 3.6 Ã… electron microscopy structure of the CARD(MAVS) filament and a 3.4 Ã… crystal structure of the 2CARD(RIG-I):CARD(MAVS) complex, representing 2CARD(RIG-I) "caught in the act" of nucleating the CARD(MAVS) filament. These structures, together with functional analyses, show that 2CARD(RIG-I) acts as a template for the CARD(MAVS) filament assembly, by forming a helical tetrameric structure and recruiting CARD(MAVS) along its helical trajectory. Our work thus reveals that signal activation by RIG-I occurs by imprinting its helical assembly architecture on MAVS, a previously uncharacterized mechanism of signal transmission.
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Affiliation(s)
- Bin Wu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, MA 02115, USA
| | - Alys Peisley
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, MA 02115, USA
| | - David Tetrault
- Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Zongli Li
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA
| | - Katharine E Magor
- Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Thomas Walz
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Pawel A Penczek
- Department of Biochemistry and Molecular Biology, The University of Texas-Houston Medical School, Houston, TX 77030, USA
| | - Sun Hur
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, MA 02115, USA.
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170
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Sensing viral invasion by RIG-I like receptors. Curr Opin Microbiol 2014; 20:131-8. [PMID: 24968321 DOI: 10.1016/j.mib.2014.05.011] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 05/08/2014] [Accepted: 05/19/2014] [Indexed: 11/20/2022]
Abstract
Cellular responses to pathogen invasion are crucial for maintaining cell homeostasis and survival. The interferon (IFN) system is one of the most effective cellular responses to viral intrusion in mammals. Viral recognition by innate immune sensors activates the antiviral IFN system. Retinoic acid-inducible gene I (RIG-I) like receptors (RLRs) are DExD/H box RNA helicases that sense viral invasion. RLRs recognize cytoplasmic viral RNAs and trigger antiviral responses, resulting in production of type I IFN and inflammatory cytokines. Unique and common sensing mechanisms among RLRs have been reported. In this review, recent progress in the understanding of antiviral responses by RLRs is summarized and discussed.
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171
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Zhu J, Zhang Y, Ghosh A, Cuevas RA, Forero A, Dhar J, Ibsen MS, Schmid-Burgk JL, Schmidt T, Ganapathiraju MK, Fujita T, Hartmann R, Barik S, Hornung V, Coyne CB, Sarkar SN. Antiviral activity of human OASL protein is mediated by enhancing signaling of the RIG-I RNA sensor. Immunity 2014; 40:936-48. [PMID: 24931123 PMCID: PMC4101812 DOI: 10.1016/j.immuni.2014.05.007] [Citation(s) in RCA: 205] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2013] [Accepted: 04/28/2014] [Indexed: 02/07/2023]
Abstract
Virus infection is sensed in the cytoplasm by retinoic acid-inducible gene I (RIG-I, also known as DDX58), which requires RNA and polyubiquitin binding to induce type I interferon (IFN) and activate cellular innate immunity. We show that the human IFN-inducible oligoadenylate synthetases-like (OASL) protein has antiviral activity and mediates RIG-I activation by mimicking polyubiquitin. Loss of OASL expression reduced RIG-I signaling and enhanced virus replication in human cells. Conversely, OASL expression suppressed replication of a number of viruses in a RIG-I-dependent manner and enhanced RIG-I-mediated IFN induction. OASL interacted and colocalized with RIG-I, and through its C-terminal ubiquitin-like domain specifically enhanced RIG-I signaling. Bone-marrow-derived macrophages from mice deficient for Oasl2 showed that among the two mouse orthologs of human OASL, Oasl2 is functionally similar to human OASL. Our findings show a mechanism by which human OASL contributes to host antiviral responses by enhancing RIG-I activation.
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Affiliation(s)
- Jianzhong Zhu
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Yugen Zhang
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Arundhati Ghosh
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Rolando A Cuevas
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Adriana Forero
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Jayeeta Dhar
- Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA
| | - Mikkel Søes Ibsen
- Department of Molecular Biology, Aarhus University, Aarhus 8000, Denmark
| | | | - Tobias Schmidt
- Institute for Clinical Chemistry and Clinical Pharmacology, University of Bonn, Bonn 53127, Germany
| | - Madhavi K Ganapathiraju
- Department of Biomedical Informatics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Takashi Fujita
- Laboratory of Molecular Genetics, Kyoto University, Kyoto 606-8507, Japan
| | - Rune Hartmann
- Department of Molecular Biology, Aarhus University, Aarhus 8000, Denmark
| | - Sailen Barik
- Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA
| | - Veit Hornung
- Institute for Clinical Chemistry and Clinical Pharmacology, University of Bonn, Bonn 53127, Germany
| | - Carolyn B Coyne
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Saumendra N Sarkar
- Cancer Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA; Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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172
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MDA5 and LGP2: accomplices and antagonists of antiviral signal transduction. J Virol 2014; 88:8194-200. [PMID: 24850739 DOI: 10.1128/jvi.00640-14] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Mammalian cells have the ability to recognize virus infection and mount a powerful antiviral transcriptional response that provides an initial barrier to replication and impacts both innate and adaptive immune responses. Retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) proteins mediate intracellular virus recognition and are activated by viral RNA ligands to induce antiviral signal transduction. While the mechanisms of RIG-I regulation are already well understood, less is known about the more enigmatic melanoma differentiation-associated 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2). Emerging evidence suggests that these two RLRs are intimately associated as both accomplices and antagonists of antiviral signal transduction.
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173
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Abstract
RIG-I belongs to a type of intracellular pattern recognition receptors involved in the recognition of viral RNA by the innate immune system. A report by Peisley et al. published in Nature provides the crystal structure of human RIG-I revealing a tetrameric architecture of the RIG-I 2-CARD domain bound by three K63-linked ubiquitin chains, uncovering its activation mechanism for downstream signaling.
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174
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Peisley A, Wu B, Xu H, Chen ZJ, Hur S. Structural basis for ubiquitin-mediated antiviral signal activation by RIG-I. Nature 2014; 509:110-4. [PMID: 24590070 PMCID: PMC6136653 DOI: 10.1038/nature13140] [Citation(s) in RCA: 274] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 02/11/2014] [Indexed: 12/20/2022]
Abstract
Ubiquitin (Ub) has important roles in a wide range of intracellular signalling pathways. In the conventional view, ubiquitin alters the signalling activity of the target protein through covalent modification, but accumulating evidence points to the emerging role of non-covalent interaction between ubiquitin and the target. In the innate immune signalling pathway of a viral RNA sensor, RIG-I, both covalent and non-covalent interactions with K63-linked ubiquitin chains (K63-Ubn) were shown to occur in its signalling domain, a tandem caspase activation and recruitment domain (hereafter referred to as 2CARD). Non-covalent binding of K63-Ubn to 2CARD induces its tetramer formation, a requirement for downstream signal activation. Here we report the crystal structure of the tetramer of human RIG-I 2CARD bound by three chains of K63-Ub2. 2CARD assembles into a helical tetramer resembling a 'lock-washer', in which the tetrameric surface serves as a signalling platform for recruitment and activation of the downstream signalling molecule, MAVS. Ubiquitin chains are bound along the outer rim of the helical trajectory, bridging adjacent subunits of 2CARD and stabilizing the 2CARD tetramer. The combination of structural and functional analyses reveals that binding avidity dictates the K63-linkage and chain-length specificity of 2CARD, and that covalent ubiquitin conjugation of 2CARD further stabilizes the Ub-2CARD interaction and thus the 2CARD tetramer. Our work provides unique insights into the novel types of ubiquitin-mediated signal-activation mechanism, and previously unexpected synergism between the covalent and non-covalent ubiquitin interaction modes.
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Affiliation(s)
- Alys Peisley
- 1] Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115 USA [2] Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, Massachusetts 02115, USA
| | - Bin Wu
- 1] Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115 USA [2] Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, Massachusetts 02115, USA
| | - Hui Xu
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Zhijian J Chen
- 1] Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA [2] Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
| | - Sun Hur
- 1] Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115 USA [2] Program in Cellular and Molecular Medicine, Children's Hospital Boston, Boston, Massachusetts 02115, USA
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175
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Luo D. Toward a crystal-clear view of the viral RNA sensing and response by RIG-I-like receptors. RNA Biol 2014; 11:25-32. [PMID: 24457940 DOI: 10.4161/rna.27717] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The RIG-I-like receptors (RLRs)--RIG-I, MDA5, and LGP2--detect intracellular pathogenic RNA and elicit an antiviral immune response during viral infection. The protein architecture of the RLR family consists of multiple functional domains, including N-terminal Caspase Activation and Recruitment Domains (CARDs) for signaling initiation, a central RNA helicase core, and a C-terminal domain for RNA sensing. With these specialized sensing-and-responding modules, RLRs are able to selectively bind non-self RNA species and trigger downstream signaling events leading to interferon production. This article summarizes the recent progress toward defining the precise mechanisms of RNA recognition and subsequent signal induction by RLRs.
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Affiliation(s)
- Dahai Luo
- Lee Kong Chian School of Medicine; Nanyang Technological University; Singapore
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176
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Xu H, He X, Zheng H, Huang LJ, Hou F, Yu Z, de la Cruz MJ, Borkowski B, Zhang X, Chen ZJ, Jiang QX. Structural basis for the prion-like MAVS filaments in antiviral innate immunity. eLife 2014; 3:e01489. [PMID: 24569476 PMCID: PMC3932521 DOI: 10.7554/elife.01489] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mitochondrial antiviral signaling (MAVS) protein is required for innate immune responses against RNA viruses. In virus-infected cells MAVS forms prion-like aggregates to activate antiviral signaling cascades, but the underlying structural mechanism is unknown. Here we report cryo-electron microscopic structures of the helical filaments formed by both the N-terminal caspase activation and recruitment domain (CARD) of MAVS and a truncated MAVS lacking part of the proline-rich region and the C-terminal transmembrane domain. Both structures are left-handed three-stranded helical filaments, revealing specific interfaces between individual CARD subunits that are dictated by electrostatic interactions between neighboring strands and hydrophobic interactions within each strand. Point mutations at multiple locations of these two interfaces impaired filament formation and antiviral signaling. Super-resolution imaging of virus-infected cells revealed rod-shaped MAVS clusters on mitochondria. These results elucidate the structural mechanism of MAVS polymerization, and explain how an α-helical domain uses distinct chemical interactions to form self-perpetuating filaments. DOI:http://dx.doi.org/10.7554/eLife.01489.001 When infected by a virus, the body will generally launch an immune response to eliminate the infectious agent. Activation of the innate immune system–the first line of defense against infection—requires the host cells to recognize the presence of a pathogen and to sound the alarm once the invader is detected. Viruses can contain DNA or RNA, and when a virus containing double stranded RNA enters a cell, or starts replicating within the cytoplasm, proteins called RIG-I-like receptors (RLRs) will detect these RNA molecules. This will trigger a signaling cascade that results in the production of type I interferons, the proteins that activate cells of the innate immune system. Members of the RLR family of receptors, including RIG-I and MDA5, initiate the signaling cascade by interacting with the mitochondrial antiviral-signaling (MAVS) protein. Recent work revealed that upon activation by RIG-I or MDA5, MAVS proteins aggregate on the surface of mitochondria and form protein filaments. These filaments then activate inactive MAVS proteins, leading to the formation of more filaments. While a region of the MAVS protein called caspase activation and recruitment domain (CARD) is known to be involved in the formation of the filaments, the chemical interactions that govern the formation process have yet to be described. Now, using cryo-electron microscopy, Xu et al. have shown that these filaments are comprised of three-stranded helixes. This came as something of a surprise because other similar filaments known as prions are made of tightly packed beta sheets. Xu et al. went on to visualize full-length MAVS filaments in virus-infected cells, and to verify that mutations that impair the assembly of MAVS filaments also prevent RNA viruses from triggering the production of interferon. These results have the potential to inform future studies of the innate immune response, as well as investigations into the assembly of proteins to form prion-like filaments. DOI:http://dx.doi.org/10.7554/eLife.01489.002
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Affiliation(s)
- Hui Xu
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
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177
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Parts, assembly and operation of the RIG-I family of motors. Curr Opin Struct Biol 2013; 25:25-33. [PMID: 24878341 DOI: 10.1016/j.sbi.2013.11.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2013] [Revised: 11/26/2013] [Accepted: 11/28/2013] [Indexed: 11/21/2022]
Abstract
Host cell invasion is monitored by a series of pattern recognition receptors (PRRs) that activate the innate immune machinery upon detection of a cognate pathogen associated molecular pattern (PAMP). The RIG-I like receptor (RLR) family of PRRs includes three proteins--RIG-I, MDA5, and LGP2--responsible for the detection of intracellular pathogenic RNA. All RLR proteins are built around an ATPase core homologous to those found in canonical Superfamily 2 (SF2) RNA helicases, which has been modified through the addition of novel accessory domains to recognize duplex RNA. This review focuses on the structural bases for pathogen-specific dsRNA binding and ATPase activation in RLRs, differential RNA recognition by RLR family members, and implications for other duplex RNA activated ATPases, such as Dicer.
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178
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Chuenchor W, Jin T, Ravilious G, Xiao TS. Structures of pattern recognition receptors reveal molecular mechanisms of autoinhibition, ligand recognition and oligomerization. Curr Opin Immunol 2013; 26:14-20. [PMID: 24419035 DOI: 10.1016/j.coi.2013.10.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2013] [Accepted: 10/17/2013] [Indexed: 10/26/2022]
Abstract
Pattern recognition receptors (PRRs) are essential sentinels for pathogens or tissue damage and integral components of the innate immune system. Recent structural studies have provided unprecedented insights into the molecular mechanisms of ligand recognition and signal transduction by several PRR families at distinct subcellular compartments. Here we highlight some of the recent discoveries and summarize the common themes that are emerging from these exciting studies. Better mechanistic understanding of the structure and function of the PRRs will improve future prospects of therapeutic targeting of these important innate immune receptors.
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Affiliation(s)
- Watchalee Chuenchor
- Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA 20892-0430
| | - Tengchuan Jin
- Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA 20892-0430
| | - Geoffrey Ravilious
- Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA 20892-0430
| | - T Sam Xiao
- Structural Immunobiology Unit, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA 20892-0430
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