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Jarmoskaite I, Li JB. Multifaceted roles of RNA editing enzyme ADAR1 in innate immunity. RNA (NEW YORK, N.Y.) 2024; 30:500-511. [PMID: 38531645 PMCID: PMC11019752 DOI: 10.1261/rna.079953.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Accepted: 02/09/2024] [Indexed: 03/28/2024]
Abstract
Innate immunity must be tightly regulated to enable sensitive pathogen detection while averting autoimmunity triggered by pathogen-like host molecules. A hallmark of viral infection, double-stranded RNAs (dsRNAs) are also abundantly encoded in mammalian genomes, necessitating surveillance mechanisms to distinguish "self" from "nonself." ADAR1, an RNA editing enzyme, has emerged as an essential safeguard against dsRNA-induced autoimmunity. By converting adenosines to inosines (A-to-I) in long dsRNAs, ADAR1 covalently marks endogenous dsRNAs, thereby blocking the activation of the cytoplasmic dsRNA sensor MDA5. Moreover, beyond its editing function, ADAR1 binding to dsRNA impedes the activation of innate immune sensors PKR and ZBP1. Recent landmark studies underscore the utility of silencing ADAR1 for cancer immunotherapy, by exploiting the ADAR1-dependence developed by certain tumors to unleash an antitumor immune response. In this perspective, we summarize the genetic and mechanistic evidence for ADAR1's multipronged role in suppressing dsRNA-mediated autoimmunity and explore the evolving roles of ADAR1 as an immuno-oncology target.
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Affiliation(s)
- Inga Jarmoskaite
- Department of Genetics, Stanford University, Stanford, California 94305, USA
- AIRNA Corporation, Cambridge, Massachusetts 02142, USA
| | - Jin Billy Li
- Department of Genetics, Stanford University, Stanford, California 94305, USA
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Singh R, Wu Y, Herrero Del Valle A, Leigh KE, Mong S, Cheng MTK, Ferguson BJ, Modis Y. Contrasting functions of ATP hydrolysis by MDA5 and LGP2 in viral RNA sensing. J Biol Chem 2024; 300:105711. [PMID: 38309507 PMCID: PMC10909783 DOI: 10.1016/j.jbc.2024.105711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 01/16/2024] [Accepted: 01/24/2024] [Indexed: 02/05/2024] Open
Abstract
Cytosolic long dsRNA, among the most potent proinflammatory signals, is recognized by melanoma differentiation-associated protein 5 (MDA5). MDA5 binds dsRNA cooperatively forming helical filaments. ATP hydrolysis by MDA5 fulfills a proofreading function by promoting dissociation of shorter endogenous dsRNs from MDA5 while allowing longer viral dsRNAs to remain bound leading to activation of interferon-β responses. Here, we show that adjacent MDA5 subunits in MDA5-dsRNA filaments hydrolyze ATP cooperatively, inducing cooperative filament disassembly. Consecutive rounds of ATP hydrolysis amplify the filament footprint, displacing tightly bound proteins from dsRNA. Our electron microscopy and biochemical assays show that LGP2 binds to dsRNA at internal binding sites through noncooperative ATP hydrolysis. Unlike MDA5, LGP2 has low nucleic acid selectivity and can hydrolyze GTP and CTP as well as ATP. Binding of LGP2 to dsRNA promotes nucleation of MDA5 filament assembly resulting in shorter filaments. Molecular modeling identifies an internally bound MDA5-LGP2-RNA complex, with the LGP2 C-terminal tail forming the key contacts with MDA5. These contacts are specifically required for NTP-dependent internal RNA binding. We conclude that NTPase-dependent binding of LGP2 to internal dsRNA sites complements NTPase-independent binding to dsRNA ends, via distinct binding modes, to increase the number and signaling output of MDA5-dsRNA complexes.
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Affiliation(s)
- Rahul Singh
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK; Department of Pathology, University of Cambridge, Cambridge, UK
| | - Yuan Wu
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK
| | - Alba Herrero Del Valle
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK
| | - Kendra E Leigh
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK
| | - Sai Mong
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK
| | - Mark T K Cheng
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK
| | - Brian J Ferguson
- Department of Pathology, University of Cambridge, Cambridge, UK.
| | - Yorgo Modis
- Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, UK; Cambridge Institute of Therapeutic Immunology & Infectious Disease (CITIID), Department of Medicine, University of Cambridge, Cambridge, UK.
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Straub S, Sampaio NG. Activation of cytosolic RNA sensors by endogenous ligands: roles in disease pathogenesis. Front Immunol 2023; 14:1092790. [PMID: 37292201 PMCID: PMC10244536 DOI: 10.3389/fimmu.2023.1092790] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 05/15/2023] [Indexed: 06/10/2023] Open
Abstract
Early detection of infection is a central and critical component of our innate immune system. Mammalian cells have developed specialized receptors that detect RNA with unusual structures or of foreign origin - a hallmark of many virus infections. Activation of these receptors induces inflammatory responses and an antiviral state. However, it is increasingly appreciated that these RNA sensors can also be activated in the absence of infection, and that this 'self-activation' can be pathogenic and promote disease. Here, we review recent discoveries in sterile activation of the cytosolic innate immune receptors that bind RNA. We focus on new aspects of endogenous ligand recognition uncovered in these studies, and their roles in disease pathogenesis.
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Affiliation(s)
- Sarah Straub
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, VIC, Australia
- Department of Molecular and Translational Sciences, School of Clinical Sciences, Monash University, Clayton, VIC, Australia
| | - Natalia G. Sampaio
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, VIC, Australia
- Department of Molecular and Translational Sciences, School of Clinical Sciences, Monash University, Clayton, VIC, Australia
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Zheng J, Shi W, Yang Z, Chen J, Qi A, Yang Y, Deng Y, Yang D, Song N, Song B, Luo D. RIG-I-like receptors: Molecular mechanism of activation and signaling. Adv Immunol 2023; 158:1-74. [PMID: 37453753 DOI: 10.1016/bs.ai.2023.03.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2023]
Abstract
During RNA viral infection, RIG-I-like receptors (RLRs) recognize the intracellular pathogenic RNA species derived from viral replication and activate antiviral innate immune response by stimulating type 1 interferon expression. Three RLR members, namely, RIG-I, MDA5, and LGP2 are homologous and belong to a subgroup of superfamily 2 Helicase/ATPase that is preferably activated by double-stranded RNA. RLRs are significantly different in gene architecture, RNA ligand preference, activation, and molecular functions. As switchable macromolecular sensors, RLRs' activities are tightly regulated by RNA ligands, ATP, posttranslational modifications, and cellular cofactors. We provide a comprehensive review of the structure and function of the RLRs and summarize the molecular understanding of sensing and signaling events during the RLR activation process. The key roles RLR signaling play in both anti-infection and immune disease conditions highlight the therapeutic potential in targeting this important molecular pathway.
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Affiliation(s)
- Jie Zheng
- School of Pharmaceutical Science and Technology, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China; Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
| | - Wenjia Shi
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Ziqun Yang
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Jin Chen
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Ao Qi
- School of Pharmaceutical Science and Technology, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China; Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Yulin Yang
- School of Pharmaceutical Science and Technology, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China; Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Ying Deng
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Dongyuan Yang
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Ning Song
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Bin Song
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Dahai Luo
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore; NTU Institute of Structural Biology, Nanyang Technological University, Singapore, Singapore.
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Blum SI, Taylor JP, Barra JM, Burg AR, Shang Q, Qiu S, Shechter O, Hayes AR, Green TJ, Geurts AM, Chen YG, Tse HM. MDA5-dependent responses contribute to autoimmune diabetes progression and hindrance. JCI Insight 2023; 8:157929. [PMID: 36512407 PMCID: PMC9977297 DOI: 10.1172/jci.insight.157929] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 12/07/2022] [Indexed: 12/14/2022] Open
Abstract
Type 1 diabetes (T1D) is an autoimmune disease resulting in pancreatic β cell destruction. Coxsackievirus B3 (CVB3) infection and melanoma differentiation-associated protein 5-dependent (MDA5-dependent) antiviral responses are linked with T1D development. Mutations within IFIH1, coding for MDA5, are correlated with T1D susceptibility, but how these mutations contribute to T1D remains unclear. Utilizing nonobese diabetic (NOD) mice lacking Ifih1 expression (KO) or containing an in-frame deletion within the ATPase site of the helicase 1 domain of MDA5 (ΔHel1), we tested the hypothesis that partial or complete loss-of-function mutations in MDA5 would delay T1D by impairing proinflammatory pancreatic macrophage and T cell responses. Spontaneous T1D developed in female NOD and KO mice similarly, but was significantly delayed in ΔHel1 mice, which may be partly due to a concomitant increase in myeloid-derived suppressor cells. Interestingly, KO male mice had increased spontaneous T1D compared with NOD mice. Whereas NOD and KO mice developed CVB3-accelerated T1D, ΔHel1 mice were protected partly due to decreased type I IFNs, pancreatic infiltrating TNF+ macrophages, IFN-γ+CD4+ T cells, and perforin+CD8+ T cells. Furthermore, ΔHel1 MDA5 protein had reduced ATP hydrolysis compared with wild-type MDA5. Our results suggest that dampened MDA5 function delays T1D, yet loss of MDA5 promotes T1D.
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Affiliation(s)
- Samuel I. Blum
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Jared P. Taylor
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Jessie M. Barra
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Ashley R. Burg
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Qiao Shang
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Shihong Qiu
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Oren Shechter
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Aleah R. Hayes
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Todd J. Green
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | | | - Yi-Guang Chen
- Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Hubert M. Tse
- Department of Microbiology, Comprehensive Diabetes Center, The University of Alabama at Birmingham, Birmingham, Alabama, USA
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