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Hara M, Ariyoshi M, Sano T, Nozawa RS, Shinkai S, Onami S, Jansen I, Hirota T, Fukagawa T. Centromere/kinetochore is assembled through CENP-C oligomerization. Mol Cell 2023:S1097-2765(23)00379-9. [PMID: 37295434 DOI: 10.1016/j.molcel.2023.05.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 04/04/2023] [Accepted: 05/16/2023] [Indexed: 06/12/2023]
Abstract
Kinetochore is an essential protein complex required for accurate chromosome segregation. The constitutive centromere-associated network (CCAN), a subcomplex of the kinetochore, associates with centromeric chromatin and provides a platform for the kinetochore assembly. The CCAN protein CENP-C is thought to be a central hub for the centromere/kinetochore organization. However, the role of CENP-C in CCAN assembly needs to be elucidated. Here, we demonstrate that both the CCAN-binding domain and the C-terminal region that includes the Cupin domain of CENP-C are necessary and sufficient for chicken CENP-C function. Structural and biochemical analyses reveal self-oligomerization of the Cupin domains of chicken and human CENP-C. We find that the CENP-C Cupin domain oligomerization is vital for CENP-C function, centromeric localization of CCAN, and centromeric chromatin organization. These results suggest that CENP-C facilitates the centromere/kinetochore assembly through its oligomerization.
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Affiliation(s)
- Masatoshi Hara
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan.
| | - Mariko Ariyoshi
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Tomoki Sano
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Ryu-Suke Nozawa
- Division of Experimental Pathology, Cancer Institute of the Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan
| | - Soya Shinkai
- Laboratory for Developmental Dynamics, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
| | - Shuichi Onami
- Laboratory for Developmental Dynamics, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
| | | | - Toru Hirota
- Division of Experimental Pathology, Cancer Institute of the Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan
| | - Tatsuo Fukagawa
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan.
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2
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Zuo W, Wakimoto M, Kozaiwa N, Shirasaka Y, Oh SW, Fujiwara S, Miyachi H, Kogure A, Kato H, Fujita T. PKR and TLR3 trigger distinct signals that coordinate the induction of antiviral apoptosis. Cell Death Dis 2022; 13:707. [PMID: 35970851 PMCID: PMC9378677 DOI: 10.1038/s41419-022-05101-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Revised: 07/08/2022] [Accepted: 07/13/2022] [Indexed: 01/21/2023]
Abstract
RIG-I-like receptors (RLRs), protein kinase R (PKR), and endosomal Toll-like receptor 3 (TLR3) sense viral non-self RNA and are involved in cell fate determination. However, the mechanisms by which intracellular RNA induces apoptosis, particularly the role of each RNA sensor, remain unclear. We performed cytoplasmic injections of different types of RNA and elucidated the molecular mechanisms underlying viral dsRNA-induced apoptosis. The results obtained revealed that short 5'-triphosphate dsRNA, the sole ligand of RIG-I, induced slow apoptosis in a fraction of cells depending on IRF-3 transcriptional activity and IFN-I production. However, intracellular long dsRNA was sensed by PKR and TLR3, which activate distinct signals, and synergistically induced rapid apoptosis. PKR essentially induced translational arrest, resulting in reduced levels of cellular FLICE-like inhibitory protein and functioned in the TLR3/TRIF-dependent activation of caspase 8. The present results demonstrated that PKR and TLR3 were both essential for inducing the viral RNA-mediated apoptosis of infected cells and the arrest of viral production.
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Affiliation(s)
- Wenjie Zuo
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Mai Wakimoto
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Noriyasu Kozaiwa
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Yutaro Shirasaka
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Seong-Wook Oh
- grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Shiori Fujiwara
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Hitoshi Miyachi
- grid.258799.80000 0004 0372 2033Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Amane Kogure
- grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan
| | - Hiroki Kato
- grid.15090.3d0000 0000 8786 803XInstitute for Cardiovascular Immunology, University Hospital Bonn, Bonn, 53127 Germany
| | - Takashi Fujita
- grid.258799.80000 0004 0372 2033Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.258799.80000 0004 0372 2033Laboratory of Regulatory Information, Institute for Frontier Life and Medical Science, Kyoto University, Sakyo-ku, Kyoto, 606-8507 Japan ,grid.15090.3d0000 0000 8786 803XInstitute for Cardiovascular Immunology, University Hospital Bonn, Bonn, 53127 Germany
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3
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de Oliveira Mann CC, Orzalli MH, King DS, Kagan JC, Lee ASY, Kranzusch PJ. Modular Architecture of the STING C-Terminal Tail Allows Interferon and NF-κB Signaling Adaptation. Cell Rep 2020; 27:1165-1175.e5. [PMID: 31018131 PMCID: PMC7733315 DOI: 10.1016/j.celrep.2019.03.098] [Citation(s) in RCA: 125] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 02/15/2019] [Accepted: 03/26/2019] [Indexed: 01/28/2023] Open
Abstract
Stimulator of interferon genes (STING) is a key regulator of type I interferon and pro-inflammatory responses during infection, cellular stress, and cancer. Here, we reveal a mechanism for how STING balances activation of IRF3- and NF-κB-dependent transcription and discover that acquisition of discrete signaling modules in the vertebrate STING C-terminal tail (CTT) shapes downstream immunity. As a defining example, we identify a motif appended to the CTT of zebrafish STING that inverts the typical vertebrate signaling response and results in dramatic NF-κB activation and weak IRF3-interferon signaling. We determine a co-crystal structure that explains how this CTT sequence recruits TRAF6 as a new binding partner and demonstrate that the minimal motif is sufficient to reprogram human STING and immune activation in macrophage cells. Together, our results define the STING CTT as a linear signaling hub that can acquire modular motifs to readily adapt downstream immunity. de Oliveira Mann et al. define a mechanism that allows emergence of a signaling response in an innate immune pathway. Modular motifs in the STING CTT control the strength and specificity of downstream responses, and evolutionary acquisition of new signaling elements is facilitated by the linear arrangement of the CTT.
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Affiliation(s)
- Carina C de Oliveira Mann
- Department of Microbiology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Megan H Orzalli
- Division of Gastroenterology, Boston Children's Hospital and Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - David S King
- HHMI Mass Spectrometry Laboratory, University of California, Berkeley, Berkeley, California 94720, USA
| | - Jonathan C Kagan
- Division of Gastroenterology, Boston Children's Hospital and Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Amy S Y Lee
- Department of Biology, Brandeis University, Waltham, MA 02453, USA.
| | - Philip J Kranzusch
- Department of Microbiology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Parker Institute for Cancer Immunotherapy at Dana-Farber Cancer Institute, Boston, MA 02115, USA.
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4
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Zhao X, Xiao T, Jin S, Wang J, Wang J, Luo H, Li R, Sun T, Zou J, Li Y. Characterization and immune function of the interferon-β promoter stimulator-1 in the barbel chub, Squaliobarbus curriculus. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2020; 104:103571. [PMID: 31837379 DOI: 10.1016/j.dci.2019.103571] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 11/29/2019] [Accepted: 12/10/2019] [Indexed: 06/10/2023]
Abstract
To elucidate the immunity-protecting role of the interferon-β promoter stimulator-1 (ScIPS-1) in barbel chub Squaliobarbus curriculus, the full-length cDNA of ScIPS-1 was cloned and expression levels in response to stimulation were investigated. In addition, the function of ScIPS-1 and its domains were analyzed. The full-length cDNA of ScIPS-1 is 2524 bp and encodes 601 aa. The N-terminal caspase activation and recruitment domain, central proline-rich domain, C-terminal transmembrane domain, C2HC-zinc finger, and Cwf21 domains were identified. The mRNA level of ScIPS-1 was the highest in the kidney, whereas the highest protein level was observed in the liver. The ScIPS-1 expressions were significantly up-regulated after lipopolysaccharide and poly I:C treatment. The ScIPS-1 protein level was up-regulated at 12 h in the head kidney and was up-regulated at 12 h and then down-regulated from 12 to 48 h in the liver after grass carp reovirus (GCRV) infection. The CiIFN and CiMx transcription levels were significantly enhanced in pEGFP-C1-IPS-1 and pcDNA3.1-ΔCwf21 overexpressing cells after GCRV infection. The results indicate that ScIPS-1 may function in the immune response against pathogens and provide a basis for achieving resistance to diseases in fish breeding.
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Affiliation(s)
- Xin Zhao
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Tiaoyi Xiao
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Shengzhen Jin
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Jing'an Wang
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Junya Wang
- Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai, 201306, China
| | - Hong Luo
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Rui Li
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Tong Sun
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Jun Zou
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai, 201306, China
| | - Yaoguo Li
- Hunan Engineering Technology Research Center of Featured Aquatic Resources Utilization, Hunan Agricultural University, Changsha, 410128, China.
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5
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Identification of a new autoinhibitory domain of interferon-beta promoter stimulator-1 (IPS-1) for the tight regulation of oligomerization-driven signal activation. Biochem Biophys Res Commun 2019; 517:662-669. [PMID: 31395337 DOI: 10.1016/j.bbrc.2019.07.099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 07/26/2019] [Indexed: 12/20/2022]
Abstract
Upon viral infection, retinoic acid-inducible gene-I (RIG-I)-like receptors detect viral foreign RNAs and transmit anti-viral signals via direct interaction with the downstream mitochondrial adaptor molecule, interferon (IFN)-β promoter stimulator-1 (IPS-1), to inhibit viral replication. Although IPS-1 is known to form prion-like oligomers on mitochondria to activate signaling, the mechanisms that regulate oligomer formation remain unclear. Here, we identified an autoinhibitory domain (AD) at amino acids 180-349 to suppress oligomerization of IPS-1 in a resting state and regulate activation of downstream signaling. Size exclusion chromatography (SEC) analysis demonstrated that AD was required to suppress auto-oligomerization of the caspase recruitment domain (CARD) of IPS-1 via intramolecular interactions. This was supported by the observation that cleavage of a peptide bond between IPS-1 CARD and AD by Tobacco Etch virus (TEV) protease relieved autoinhibition. Conversely, deletion of this domain from IPS-1 enhanced signal activation in IFN-reporter assays, suggesting that IPS-1 AD played a critical role in the regulation of IPS-1-mediated anti-viral signal activation. These findings revealed novel molecular interactions involved in the tight regulation of innate anti-viral immunity.
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6
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Suzuki H, Kameyama T, Takaoka A. BinCARD2 as a positive regulator of interferon response in innate immunity. Biochem Biophys Res Commun 2019; 511:287-293. [PMID: 30795865 DOI: 10.1016/j.bbrc.2019.02.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2019] [Accepted: 02/06/2019] [Indexed: 10/27/2022]
Abstract
Innate immunity is a system that recognizes primarily and excludes pathogenic microorganism. MAVS/IPS-1/Cardif/Visa functions as an adapter protein for RIG-I like receptors (RLRs) and plays a key role in the production of antiviral proteins, interferons (IFNs), for RNA viruses. However, the activation mechanism is not fully understood. Here, we show that BinCARD isoform2 (BinCARD2), carrying CARD domain structure like MAVS, functions in innate immune response. Knockdown of BinCARD2 reduced the RLR ligand-induced expression of IFN-β mRNA and activation of the IFNB promoter. The activation of the IFNB promoter by overexpression of MAVS or TBK1 was suppressed by silencing of BinCARD2, but no effect on IFNB promoter activation by overexpression of TRIF or constitutive activated IRF-3. Furthermore, we confirmed that BinCARD2 protein associated with MAVS but not TBK1 by immunoprecipitation and colocalized with MAVS. Accordingly, we investigated whether BinCARD2 was involved in MAVS activation and showed that siBinCARD2 did not affect RIG-I/MAVS binding but impaired the MAVS oligomerization. Moreover, we infected A549 cells with vesicular stomatitis virus (VSV) and found that induction of IFN-β and IL-6 mRNA after VSV infection was decreased by BinCARD2 knockdown. Thus, these data may suggest that BinCARD2 associates with MAVS to positively modulate the oligomerization in the RIG-I like receptors pathway and activates innate immune response.
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Affiliation(s)
- Hiraku Suzuki
- Division of Signaling in Cancer and Immunology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0815, Japan; Oral Biochemistry and Molecular Biology, Graduate School of Dental Medicine, Hokkaido University, Sapporo, Hokkaido, 060-8586, Japan; Center for Medical Education, Graduate School of Medicine, Gunma University, Maebashi, Gunma, 371-8511, Japan.
| | - Takeshi Kameyama
- Division of Signaling in Cancer and Immunology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0815, Japan
| | - Akinori Takaoka
- Division of Signaling in Cancer and Immunology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0815, Japan
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7
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Human cytomegalovirus-encoded US9 targets MAVS and STING signaling to evade type I interferon immune responses. Nat Commun 2018; 9:125. [PMID: 29317664 PMCID: PMC5760629 DOI: 10.1038/s41467-017-02624-8] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 12/14/2017] [Indexed: 11/08/2022] Open
Abstract
Human cytomegalovirus (HCMV) has evolved sophisticated immune evasion mechanisms that target both the innate and adaptive immune responses. However, how HCMV encoded proteins are involved in this immune escape is not clear. Here, we show that HCMV glycoprotein US9 inhibits the IFN-β response by targeting the mitochondrial antiviral-signaling protein (MAVS) and stimulator of interferon genes (STING)-mediated signaling pathways. US9 accumulation in mitochondria attenuates the mitochondrial membrane potential, leading to promotion of MAVS leakage from the mitochondria. Furthermore, US9 disrupts STING oligomerization and STING–TBK1 association through competitive interaction. Intriguingly, US9 blocks interferon regulatory factor 3 (IRF3) nuclear translocation and its cytoplasmic domain is essential for inhibiting IRF3 activation. Mutant HCMV lacking US7-16 is impaired in antagonism of MAVS/STING-mediated IFN-β expression, an effect that is reversible by the introduction of US9. Our findings indicate that HCMV US9 is an antagonist of IFN signaling to persistently evade host innate antiviral responses. MAVS and STING signaling are central to interferon-inducing antiviral immunity. Here, the authors show how the human cytomegalovirus protein US9 can evade this immunity by antagonizing these pathways.
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Chen GA, Lin YR, Chung HT, Hwang LH. H-Ras Exerts Opposing Effects on Type I Interferon Responses Depending on Its Activation Status. Front Immunol 2017; 8:972. [PMID: 28848563 PMCID: PMC5554495 DOI: 10.3389/fimmu.2017.00972] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 07/31/2017] [Indexed: 12/25/2022] Open
Abstract
Using shRNA high-throughput screening, we identified H-Ras as a regulator of antiviral activity, whose depletion could enhance Sindbis virus replication. Further analyses indicated that depletion of H-Ras results in a robust increase in vesicular stomatitis virus infection and a decrease in Sendai virus (SeV)-induced retinoic acid-inducible gene-I-like receptor (RLR) signaling. Interestingly, however, ectopic expression of wild-type H-Ras results in a biphasic mode of RLR signaling regulation: while low-level expression of H-Ras enhances SeV-induced RLR signaling, high-level expression of H-Ras significantly inhibits this signaling. The inhibitory effects correlate with the activation status of H-Ras. As a result, oncogenic H-Ras, H-RasV12, strongly inhibits SeV-induced IFN-β promoter activity and type I interferon signaling. Conversely, the positive effects exerted by H-Ras on RLR signaling are independent of its signaling activity, as a constitutively inactive form of H-Ras, H-RasN17, also positively regulates RLR signaling. Mechanistically, we demonstrate that depletion of H-Ras reduces the formation of MAVS–TNF receptor-associated factor 3 signaling complexes. These results reveal that the H-Ras protein plays a role in promoting MAVS signalosome assembly in the mitochondria, whereas oncogenic H-Ras exerts a negative effect on type I IFN responses.
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Affiliation(s)
- Guann-An Chen
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan
| | - Yun-Ru Lin
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan
| | - Hai-Ting Chung
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan
| | - Lih-Hwa Hwang
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan
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9
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Multiple truncated isoforms of MAVS prevent its spontaneous aggregation in antiviral innate immune signalling. Nat Commun 2017; 8:15676. [PMID: 28607490 PMCID: PMC5474743 DOI: 10.1038/ncomms15676] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 04/19/2017] [Indexed: 12/18/2022] Open
Abstract
In response to virus infection, RIG-I-like receptors (RLRs) sense virus RNA and induce MAVS to form prion-like aggregates to further propagate antiviral signalling. Although monomeric MAVS recombinant protein can assemble into prion-like filaments spontaneously in vitro, endogenous MAVS in cells is prevented from aggregation until viral infection. The mechanism preventing cellular MAVS from spontaneous aggregation is unclear. Here we show that multiple N-terminal truncated isoforms of MAVS are essential in preventing full-length MAVS from spontaneous aggregation through transmembrane domain-mediated homotypic interaction. Without these shorter isoforms, full-length MAVS is prone to spontaneous aggregation and Nix-mediated mitophagic degradation. In the absence of N-terminally truncated forms, blocking Nix-mediated mitophagy stabilizes full-length MAVS, which aggregates spontaneously and induces the subsequent expression of type I interferon and other proinflammatory cytokines. Our data thus uncover an important mechanism preventing spontaneous aggregation of endogenous MAVS to avoid accidental activation of antiviral innate immune signalling.
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10
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Abstract
The mitochondrial anti-viral signaling protein (MAVS) plays an important role in the type I IFN response. In this study, two feline MAVS transcripts were cloned. Both transcripts have the same open reading frame encoding 523 amino acids. The putative protein shares 76.6 % similarity with canine and exhibits similarity to human, mouse, rat, bovine and porcine, ranging from 46.1 to 65.8 %. Deletion mutant analysis indicated that the transmembrane (TM) domain is necessary for localization in the mitochondrial membrane, and both the caspase activation and recruitment domain and TM domain are indispensible for activating the IFN-β response. Additionally, Sendai virus-induced IFN-β promoter activation was significantly inhibited by siRNA targeting MAVS. Finally, miniMAVS, a second protein encoded by MAVS mRNA, was identified, which interfered with the IFN-β response via the inhibition of NF-κB activation. The identification of MAVS will promote the understanding and control of feline infectious diseases.
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11
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Yoneyama M, Jogi M, Onomoto K. Regulation of antiviral innate immune signaling by stress-induced RNA granules. J Biochem 2016; 159:279-86. [PMID: 26748340 PMCID: PMC4763080 DOI: 10.1093/jb/mvv122] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 09/24/2015] [Indexed: 12/17/2022] Open
Abstract
Activation of antiviral innate immunity is triggered by cellular pattern recognition receptors. Retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs) detect viral non-self RNA in cytoplasm of virus-infected cells and play a critical role in the clearance of the invaded viruses through production of antiviral cytokines. Among the three known RLRs, RIG-I and melanoma differentiation-associated gene 5 recognize distinct non-self signatures of viral RNA and activate antiviral signaling. Recent reports have clearly described the molecular machinery underlying the activation of RLRs and interactions with the downstream adaptor, mitochondrial antiviral signaling protein (MAVS). RLRs and MAVS are thought to form large multimeric filaments around cytoplasmic organelles depending on the presence of Lys63-linked ubiquitin chains. Furthermore, RLRs have been shown to localize to stress-induced ribonucleoprotein aggregate known as stress granules and utilize them as a platform for recognition/activation of signaling. In this review, we will focus on the current understanding of RLR-mediated signal activation and the interactions with stress-induced RNA granules.
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Affiliation(s)
- Mitsutoshi Yoneyama
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8673, Japan
| | - Michihiko Jogi
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8673, Japan
| | - Koji Onomoto
- Division of Molecular Immunology, Medical Mycology Research Center, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8673, Japan
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12
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Looney BM, Xia CQ, Concannon P, Ostrov DA, Clare-Salzler MJ. Effects of type 1 diabetes-associated IFIH1 polymorphisms on MDA5 function and expression. Curr Diab Rep 2015; 15:96. [PMID: 26385483 DOI: 10.1007/s11892-015-0656-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Recent evidence has highlighted the role of the innate immune system in type 1 diabetes (T1D) pathogenesis. Specifically, aberrant activation of the interferon response prior to seroconversion of T1D-associated autoantibodies supports a role for the interferon response as a precipitating event toward activation of autoimmunity. Melanoma differentiation-associated protein 5 (MDA5), encoded by IFIH1, mediates the innate immune system's interferon response to certain viral species that form double-stranded RNA (dsRNA), the MDA5 ligand, during their life cycle. Extensive research has associated single nucleotide polymorphisms (SNPs) within the coding region of IFIH1 with T1D. This review discusses the different risk and protective IFIH1 alleles in the context of recent structural and functional analysis that relate to MDA5 regulation of interferon responses. These studies have provided a functional hypothesis for IFIH1 T1D-associated SNPs' effects on MDA5-mediated interferon responses as well as supporting the genome-wide association (GWA) studies that first associated IFIH1 with T1D.
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Affiliation(s)
- Benjamin M Looney
- Department of Pathology, Immunology and Laboratory Medicine, College of Medicine Interdisciplinary Program in Biomedical Sciences, University of Florida, 1600 SW Archer Rd., Gainesville, FL, 32610, USA.
| | - Chang-Qing Xia
- Department of Pathology, Immunology and Laboratory Medicine, College of Medicine, University of Florida, 1600 SW Archer Rd., Gainesville, FL, 32610, USA.
| | - Patrick Concannon
- University of Florida Genetics Institute, 2033 Mowry Rd., P.O. Box 103610, Gainesville, FL, 32611, USA.
| | - David A Ostrov
- Department of Pathology, Immunology and Laboratory Medicine, University of Florida, 2033 Mowry Rd., P.O. Box 103633, Gainesville, FL, 32611, USA.
| | - Michael J Clare-Salzler
- Department of Pathology, Immunology and Laboratory Medicine, University of Florida, 2033 Mowry Rd., P.O. Box 103633, Gainesville, FL, 32611, USA.
- Center for Immunology and Transplantation, University of Florida, 1600 SW Archer Rd., P.O. Box 100275, Gainesville, FL, 32610, USA.
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13
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Feng X, Zhang Y, Yang C, Liao L, Wang Y, Su J. Functional characterizations of IPS-1 in CIK cells: Potential roles in regulating IFN-I response dependent on IRF7 but not IRF3. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2015; 53:23-32. [PMID: 26111995 DOI: 10.1016/j.dci.2015.06.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 04/27/2015] [Accepted: 06/06/2015] [Indexed: 06/04/2023]
Abstract
IPS-1, as the sole adaptor of RIG-I and MDA5, plays a central role in innate antiviral immunity. In this study, we investigated potential roles of IPS-1 in innate immunity and the domain-requirement of IPS-1 for its signaling in grass carp (Ctenopharyngodon idella). Overexpression experiment showed that CiIPS-1 mediated IFN-I signal possibly dependent on CiIRF7 but not CiIRF3. Post GCRV challenge, CiIPS-1 could enhance antiviral immune responses. CARD and TM domains were crucial for antiviral function of CiIPS-1, and TRAF motif played an assistant role. PRO domain seemed as a negative regulator but was pivotal for the initiation of CiIFN-I and CiMx1. Post viral/bacterial PAMPs stimulation, CiIPS-1-mediated signaling was tightly controlled. CARD domain of CiIPS-1 could significantly elicit poly I:C/LPS/PGN-mediated signaling. PRO domain negatively regulated CiIRF7 and CiIFN-I but was indispensable for inductions of CiMx1 and CiIL-1β. TRAF motif and TM domain regulated the signaling presumably in a cooperative fashion. Post poly I:C stimulation, TRAF motif negatively regulated CiIRF7, CiIFN-I and CiIL-1β at a relative early time while TM domain functioned at a relative late time. TRAF motif was indispensable for the production of CiMx1, while TM domain slightly negatively regulated the expression. Post LPS and PGN stimulation, TRAF motif excited an assistant and persistent negative role on CiIFN-I, CiIRF7 and CiIL-1β induction, but was crucial for induction of CiMx1. TM domain slightly negatively regulated LPS- and PGN-triggered signaling. Taken together, CiIPS-1 not only exerted important functions in antiviral immune response but also participated in viral/bacterial PAMPs-triggered immune response which was tightly controlled to prevent harmful effects resulting from excessive activation. This study provided novel insights into the pivotal role of IPS-1 in innate immunity.
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Affiliation(s)
- Xiaoli Feng
- College of Animal Science and Technology, Northwest A&F University, Yangling 712100, China
| | - Yixuan Zhang
- College of Animal Science and Technology, Northwest A&F University, Yangling 712100, China
| | - Chunrong Yang
- College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China
| | - Lanjie Liao
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Yaping Wang
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Jianguo Su
- College of Animal Science and Technology, Northwest A&F University, Yangling 712100, China; College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China; Freshwater Aquaculture Collaborative Innovation Center of Hubei Province, Wuhan 430070, China.
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14
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Haynes LD, Verma S, McDonald B, Wu R, Tacke R, Nowyhed HN, Ekstein J, Feuvrier A, Benedict CA, Hedrick CC. Cardif (MAVS) Regulates the Maturation of NK Cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2015; 195:2157-67. [PMID: 26232430 PMCID: PMC4709023 DOI: 10.4049/jimmunol.1402060] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 06/18/2015] [Indexed: 01/12/2023]
Abstract
Cardif, also known as IPS-1, VISA, and MAVS, is an intracellular adaptor protein that functions downstream of the retinoic acid-inducible gene I family of pattern recognition receptors. Cardif is required for the production of type I IFNs and other inflammatory cytokines after retinoic acid-inducible gene I-like receptors recognize intracellular antigenic RNA. Studies have recently shown that Cardif may have other roles in the immune system in addition to its role in viral immunity. In this study, we find that the absence of Cardif alters normal NK cell development and maturation. Cardif(-/-) mice have a 35% loss of mature CD27(-)CD11b(+) NK cells in the periphery. In addition, Cardif(-/-) NK cells have altered surface marker expression, lower cytotoxicity, decreased intracellular STAT1 levels, increased apoptosis, and decreased proliferation compared with wild-type NK cells. Mixed chimeric mice revealed that the defective maturation and increased apoptotic rate of peripheral Cardif(-/-) NK cells is cell intrinsic. However, Cardif(-/-) mice showed enhanced control of mouse CMV (a DNA β-herpesvirus) by NK cells, commensurate with increased activation and IFN-γ production by these immature NK cell subsets. These results indicate that the skewed differentiation and altered STAT expression of Cardif(-/-) NK cells can result in their hyperresponsiveness in some settings and support recent findings that Cardif-dependent signaling can regulate aspects of immune cell development and/or function distinct from its well-characterized role in mediating cell-intrinsic defense to RNA viruses.
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MESH Headings
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/immunology
- Adaptor Proteins, Signal Transducing/metabolism
- Animals
- Apoptosis/genetics
- Apoptosis/immunology
- Blotting, Western
- Cell Differentiation/genetics
- Cell Differentiation/immunology
- Cell Proliferation
- Cells, Cultured
- Cytotoxicity, Immunologic/genetics
- Cytotoxicity, Immunologic/immunology
- Female
- Flow Cytometry
- Herpesviridae Infections/genetics
- Herpesviridae Infections/immunology
- Herpesviridae Infections/virology
- Interferon-gamma/biosynthesis
- Interferon-gamma/immunology
- Killer Cells, Natural/immunology
- Killer Cells, Natural/metabolism
- Liver/immunology
- Liver/metabolism
- Lymphocyte Count
- Male
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Mice, Knockout
- Muromegalovirus/immunology
- Muromegalovirus/physiology
- NIH 3T3 Cells
- STAT1 Transcription Factor/immunology
- STAT1 Transcription Factor/metabolism
- Spleen/immunology
- Spleen/metabolism
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Affiliation(s)
- LaTeira D Haynes
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Shilpi Verma
- Division of Immune Regulation, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037
| | - Bryan McDonald
- Division of Immune Regulation, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037
| | - Runpei Wu
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Robert Tacke
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Heba N Nowyhed
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Jennifer Ekstein
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Ariana Feuvrier
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
| | - Chris A Benedict
- Division of Immune Regulation, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037
| | - Catherine C Hedrick
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037; and
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15
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Wu B, Hur S. How RIG-I like receptors activate MAVS. Curr Opin Virol 2015; 12:91-8. [PMID: 25942693 PMCID: PMC4470786 DOI: 10.1016/j.coviro.2015.04.004] [Citation(s) in RCA: 153] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 03/26/2015] [Accepted: 04/16/2015] [Indexed: 12/22/2022]
Abstract
RIG-I and MDA5 are well-conserved cytoplasmic pattern recognition receptors that detect viral RNAs during infection and activate the type I interferon (IFN)-mediated antiviral immune response. While much is known about how these receptors recognize viral RNAs, how they interact with their common signaling adaptor molecule MAVS and activate the downstream signaling pathway had been less clear. Previous studies have shown that the signaling domains (tandem CARDs or 2CARDs) of RIG-I and MDA5 must form homo-oligomers in order to interact with MAVS, and that their interactions lead to filament formation of MAVS, a pre-requisite for downstream signal activation. More recent data suggest that multiple mechanisms synergistically promote tetramer formation of RIG-I 2CARD, and that this tetramer resembles a lock-washer, which serves as a helical template to nucleate the MAVS filament. We here summarize these recent findings and discuss the current understanding of the signal activation mechanisms of RIG-I and MDA5.
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Affiliation(s)
- Bin Wu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, United States; Program in Cellular and Molecular Medicine, Boston Children's Hospital, United States
| | - Sun Hur
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, United States; Program in Cellular and Molecular Medicine, Boston Children's Hospital, United States.
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16
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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: 324] [Impact Index Per Article: 36.0] [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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17
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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: 185] [Impact Index Per Article: 18.5] [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 Å electron microscopy structure of the CARD(MAVS) filament and a 3.4 Å 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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18
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Miranzo-Navarro D, Magor KE. Activation of duck RIG-I by TRIM25 is independent of anchored ubiquitin. PLoS One 2014; 9:e86968. [PMID: 24466302 PMCID: PMC3900705 DOI: 10.1371/journal.pone.0086968] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2013] [Accepted: 12/18/2013] [Indexed: 12/28/2022] Open
Abstract
Retinoic acid inducible gene I (RIG-I) is a viral RNA sensor crucial in defense against several viruses including measles, influenza A and hepatitis C. RIG-I activates type-I interferon signalling through the adaptor for mitochondrial antiviral signaling (MAVS). The E3 ubiquitin ligase, tripartite motif containing protein 25 (TRIM25), activates human RIG-I through generation of anchored K63-linked polyubiquitin chains attached to lysine 172, or alternatively, through the generation of unanchored K63-linked polyubiquitin chains that interact non-covalently with RIG-I CARD domains. Previously, we identified RIG-I of ducks, of interest because ducks are the host and natural reservoir of influenza viruses, and showed it initiates innate immune signaling leading to production of interferon-beta (IFN-β). We noted that K172 is not conserved in RIG-I of ducks and other avian species, or mouse. Because K172 is important for both mechanisms of activation of human RIG-I, we investigated whether duck RIG-I was activated by TRIM25, and if other residues were the sites for attachment of ubiquitin. Here we show duck RIG-I CARD domains are ubiquitinated for activation, and ubiquitination depends on interaction with TRIM25, as a splice variant that cannot interact with TRIM25 is not ubiquitinated, and cannot be activated. We expressed GST-fusion proteins of duck CARD domains and characterized TRIM25 modifications of CARD domains by mass spectrometry. We identified two sites that are ubiquitinated in duck CARD domains, K167 and K193, and detected K63 linked polyubiquitin chains. Site directed mutagenesis of each site alone, does not alter the ubiquitination profile of the duck CARD domains. However, mutation of both sites resulted in loss of all attached ubiquitin and polyubiquitin chains. Remarkably, the double mutant duck RIG-I CARD still interacts with TRIM25, and can still be activated. Our results demonstrate that anchored ubiquitin chains are not necessary for TRIM25 activation of duck RIG-I.
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Affiliation(s)
- Domingo Miranzo-Navarro
- Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alberta, Canada
| | - Katharine E. Magor
- Department of Biological Sciences and the Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alberta, Canada
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19
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Liu S, Chen J, Cai X, Wu J, Chen X, Wu YT, Sun L, Chen ZJ. MAVS recruits multiple ubiquitin E3 ligases to activate antiviral signaling cascades. eLife 2013; 2:e00785. [PMID: 23951545 PMCID: PMC3743401 DOI: 10.7554/elife.00785] [Citation(s) in RCA: 276] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 07/01/2013] [Indexed: 12/18/2022] Open
Abstract
RNA virus infections are detected by the RIG-I family of receptors, which induce type-I interferons through the mitochondrial protein MAVS. MAVS forms large prion-like polymers that activate the cytosolic kinases IKK and TBK1, which in turn activate NF-κB and IRF3, respectively, to induce interferons. Here we show that MAVS polymers recruit several TRAF proteins, including TRAF2, TRAF5, and TRAF6, through distinct TRAF-binding motifs. Mutations of these motifs that disrupted MAVS binding to TRAFs abrogated its ability to activate IRF3. IRF3 activation was also abolished in cells lacking TRAF2, 5, and 6. These TRAF proteins promoted ubiquitination reactions that recruited NEMO to the MAVS signaling complex, leading to the activation of IKK and TBK1. These results delineate the mechanism of MAVS signaling and reveal that TRAF2, 5, and 6, which are normally associated with NF-κB activation, also play a crucial role in IRF3 activation in antiviral immune responses. DOI:http://dx.doi.org/10.7554/eLife.00785.001 The innate immune system can detect and destroy viruses, bacteria and other pathogens that enter the human body. In particular, inside cells, viral RNA can bind to and activate a protein called RIG-I. This protein switches on another protein, called MAVS, which can activate other copies of itself. These MAVS molecules then aggregate together on the membrane of mitochondria and send a signal that leads to the production of small proteins, called cytokines, which stimulate an inflammatory response and ultimately neutralize the virus. Although many of the proteins that are activated by MAVS in the innate immunity signaling pathway have been identified, precisely how MAVS transmits this signal is unknown. Now, Liu et al. explore how this protein can propagate signals in the innate immune response by monitoring activation of the transcription factors IRF3 and NF-κB, which transcribe cytokine genes. Previous studies have suggested that a protein known as ubiquitin is needed to activate RIG-I, and that this protein collaborates with MAVS to signal through the innate immunity pathway. Liu et al. found that a group of proteins including TRAF2, TRAF5, TRAF6 and LUBAC relay the antiviral signal by binding to MAVS. These so-called ‘E3 ligases’ string ubiquitin together in chains called polyubiquitin, which is essential for activating signaling after, or downstream of, MAVS; however, the association of these E3 ligases with MAVS also requires that multiple copies of MAVS cluster together. MAVS, the TRAF proteins and LUBAC collectively recruit other innate immunity pathway proteins to activate IRF3 and NF-κB, and thus transcription of the genes that control the innate immunity response. Together, these results show the intricate interplay of proteins needed to eliminate viruses from the body. DOI:http://dx.doi.org/10.7554/eLife.00785.002
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Affiliation(s)
- Siqi Liu
- Department of Molecular Biology , University of Texas Southwestern Medical Center , Dallas , United States
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