101
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Ratner D, Orning MPA, Lien E. Bacterial secretion systems and regulation of inflammasome activation. J Leukoc Biol 2016; 101:165-181. [PMID: 27810946 DOI: 10.1189/jlb.4mr0716-330r] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 09/19/2016] [Accepted: 09/20/2016] [Indexed: 01/03/2023] Open
Abstract
Innate immunity is critical for host defenses against pathogens, but many bacteria display complex ways of interacting with innate immune signaling, as they may both activate and evade certain pathways. Gram-negative bacteria can exhibit specialized nanomachine secretion systems for delivery of effector proteins into mammalian cells. Bacterial types III, IV, and VI secretion systems (T3SS, T4SS, and T6SS) are known for their impact on caspase-1-activating inflammasomes, necessary for producing bioactive inflammatory cytokines IL-1β and IL-18, key participants of anti-bacterial responses. Here, we discuss how these secretion systems can mediate triggering and inhibition of inflammasome signaling. We propose that a fine balance between secretion system-mediated activation and inhibition can determine net activation of inflammasome activity and control inflammation, clearance, or spread of the infection.
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Affiliation(s)
- Dmitry Ratner
- Program in Innate Immunity, Division of Infectious Diseases and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA; and
| | - M Pontus A Orning
- Program in Innate Immunity, Division of Infectious Diseases and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA; and.,Centre of Molecular Inflammation Research, Department of Cancer Research and Molecular Medicine, Norges Teknisk-Naturvitenskapelige Universitet, Trondheim, Norway
| | - Egil Lien
- Program in Innate Immunity, Division of Infectious Diseases and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA; and .,Centre of Molecular Inflammation Research, Department of Cancer Research and Molecular Medicine, Norges Teknisk-Naturvitenskapelige Universitet, Trondheim, Norway
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102
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Deviant Behavior: Tick-Borne Pathogens and Inflammasome Signaling. Vet Sci 2016; 3:vetsci3040027. [PMID: 29056735 PMCID: PMC5606592 DOI: 10.3390/vetsci3040027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 09/22/2016] [Accepted: 09/23/2016] [Indexed: 12/11/2022] Open
Abstract
In the face of an assault, host cells mount an immediate response orchestrated by innate immunity. Two of the best described innate immune signaling networks are the Toll- and the Nod-like receptor pathways. Extensive work has been done characterizing both signaling cascades with several recent advances on the forefront of inflammasome biology. In this review, we will discuss how more commonly-studied pathogens differ from tick-transmitted microbes in the context of Nod-like receptor signaling and inflammasome formation. Because pathogens transmitted by ticks have unique characteristics, we offer the opinion that these microbes can be used to uncover novel principles of Nod-like receptor biology.
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103
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Janowski AM, Colegio OR, Hornick EE, McNiff JM, Martin MD, Badovinac VP, Norian LA, Zhang W, Cassel SL, Sutterwala FS. NLRC4 suppresses melanoma tumor progression independently of inflammasome activation. J Clin Invest 2016; 126:3917-3928. [PMID: 27617861 DOI: 10.1172/jci86953] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 08/02/2016] [Indexed: 01/05/2023] Open
Abstract
Members of the NLR family can assemble inflammasome complexes with the adaptor protein ASC and caspase-1 that result in the activation of caspase-1 and the release of IL-1β and IL-18. Although the NLRC4 inflammasome is known to have a protective role in tumorigenesis, there is an increased appreciation for the inflammasome-independent actions of NLRC4. Here, we utilized a syngeneic subcutaneous murine model of B16F10 melanoma to explore the role of NLRC4 in tumor suppression. We found that NLRC4-deficient mice exhibited enhanced tumor growth that was independent of the inflammasome components ASC and caspase-1. Nlrc4 expression was critical for cytokine and chemokine production in tumor-associated macrophages and was necessary for the generation of protective IFN-γ-producing CD4+ and CD8+ T cells. Tumor progression was diminished when WT or caspase-1-deficient, but not NLRC4-deficient, macrophages were coinjected with B16F10 tumor cells in NLRC4-deficient mice. Finally, examination of human primary melanomas revealed the extensive presence of NLRC4+ tumor-associated macrophages. In contrast, there was a paucity of NLRC4+ tumor-associated macrophages observed in human metastatic melanoma, supporting the concept that NLRC4 expression controls tumor growth. These results reveal a critical role for NLRC4 in suppressing tumor growth in an inflammasome-independent manner.
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104
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Sun Q, Scott MJ. Caspase-1 as a multifunctional inflammatory mediator: noncytokine maturation roles. J Leukoc Biol 2016; 100:961-967. [PMID: 27450556 DOI: 10.1189/jlb.3mr0516-224r] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 07/07/2016] [Indexed: 12/19/2022] Open
Abstract
Caspase-1 is an inflammatory caspase that is activated through formation of inflammasome complexes in response to both pathogen-derived and endogenous mediators. The most well-known function of active caspase-1 is to cleave the proforms of inflammatory cytokines IL-1β and -18 into their active forms in response to inflammatory stimuli in immune cells. However, recent evidence suggests that caspase-1 has multiple functions in addition to this cytokine maturation role and that it is at the center of many cell responses to stress and inflammation. The current review focuses on roles for caspase-1, and the closely related caspase-11, in inflammatory forms of cell death and protein cleavage and also in protein secretion. These alternative caspase-1 functions can influence inflammatory responses, not just in immune cells but in other cell types, such as epithelia, where inflammatory cytokine production may not be a primary cell function.
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Affiliation(s)
- Qian Sun
- Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Melanie J Scott
- Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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105
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Kolb R, Sutterwala FS, Zhang W. Obesity and cancer: inflammation bridges the two. Curr Opin Pharmacol 2016; 29:77-89. [PMID: 27429211 DOI: 10.1016/j.coph.2016.07.005] [Citation(s) in RCA: 248] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 05/05/2016] [Accepted: 07/06/2016] [Indexed: 12/14/2022]
Abstract
Obesity is a growing public health problem and affects 35% US adults. Obesity increases the risk of many cancer types and is associated with poor outcomes. Clinical management of cancer patients has been essentially the same between normal weight and obese individuals. Understanding causal mechanisms by which obesity drives cancer initiation and progression is essential for the development of novel precision therapy for obese cancer patients. One caveat is that various mechanisms have been proposed for different cancer types for their progression under obesity. Since obesity is known to have global impact on inflammation, here we will summarize recent literature and discuss the potential of inflammation being the common causal mechanism to promote cancer promotion across cancer types.
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Affiliation(s)
- Ryan Kolb
- Department of Pathology, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| | - Fayyaz S Sutterwala
- Division of Infectious Diseases, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA
| | - Weizhou Zhang
- Department of Pathology, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Interdisciplinary Graduate Program in Immunology, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Medical Scientist Training Program, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Free Radical and Radiation Biology Program, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Cancer Genes and Pathway Holden Comprehensive Cancer Center, University of Iowa Carver College of Medicine, Iowa City, IA, USA.
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106
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Yang J, Liu Z, Xiao TS. Post-translational regulation of inflammasomes. Cell Mol Immunol 2016; 14:65-79. [PMID: 27345727 PMCID: PMC5214939 DOI: 10.1038/cmi.2016.29] [Citation(s) in RCA: 146] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Revised: 05/05/2016] [Accepted: 05/05/2016] [Indexed: 12/16/2022] Open
Abstract
Inflammasomes play essential roles in immune protection against microbial infections. However, excessive inflammation is implicated in various human diseases, including autoinflammatory syndromes, diabetes, multiple sclerosis, cardiovascular disorders and neurodegenerative diseases. Therefore, precise regulation of inflammasome activities is critical for adequate immune protection while limiting collateral tissue damage. In this review, we focus on the emerging roles of post-translational modifications (PTMs) that regulate activation of the NLRP3, NLRP1, NLRC4, AIM2 and IFI16 inflammasomes. We anticipate that these types of PTMs will be identified in other types of and less well-characterized inflammasomes. Because these highly diverse and versatile PTMs shape distinct inflammatory responses in response to infections and tissue damage, targeting the enzymes involved in these PTMs will undoubtedly offer opportunities for precise modulation of inflammasome activities under various pathophysiological conditions.
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Affiliation(s)
- Jie Yang
- Department of Pathology, Case Western Reserve University, Cleveland, OH 44106-7288, USA.,Graduate Program in Physiology and Biophysics, Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106-7288, USA
| | - Zhonghua Liu
- Department of Pathology, Case Western Reserve University, Cleveland, OH 44106-7288, USA
| | - Tsan Sam Xiao
- Department of Pathology, Case Western Reserve University, Cleveland, OH 44106-7288, USA
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107
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A molluscan calreticulin ortholog from Haliotis discus discus: Molecular characterization and transcriptional evidence for its role in host immunity. Biochem Biophys Res Commun 2016; 474:43-50. [PMID: 27086846 DOI: 10.1016/j.bbrc.2016.04.056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 12/15/2015] [Accepted: 04/12/2016] [Indexed: 11/20/2022]
Abstract
Calreticulin (CALR), a Ca(2+) binding chaperone of the endoplasmic reticulum (ER) and mainly involved in Ca(2+) storage and signaling. In this study, we report the molecular characterization and immune responses of CALR homolog from disk abalone (AbCALR). The full length AbCALR cDNA (1837 bp) had an ORF of 1224 bp. According to the multiple alignments analysis, N- and P-domains were highly conserved in all the selected members of CALRs. In contrast, the C-domain which terminated with the characteristic ER retrieval signal (HDEL) was relatively less conserved. The phylogenetic analysis showed that all the selected molluscan homologs clustered together. Genomic sequence of AbCALR revealed that cDNA sequence was dispersed into ten exons interconnected with nine introns. AbCALR mRNA expression shows the significant (P < 0.05) up-regulation of AbCALR transcripts in hemocytes upon bacterial (Listeria monocytogenes and Vibrio parahaemolyticus), viral (Viral haemorrhagic septicaemia virus; VHSV) and immune stimulants (LPS and poly I:C) challenges at middle and/or late phases. These results collectively implied that AbCALR is able to be stimulated by pathogenic signals and might play a potential role in host immunity.
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108
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Shin S. Innate Immunity to Intracellular Pathogens: Lessons Learned from Legionella pneumophila. ADVANCES IN APPLIED MICROBIOLOGY 2016; 79:43-71. [PMID: 22569517 DOI: 10.1016/b978-0-12-394318-7.00003-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Intracellular bacterial pathogens have the remarkable ability to manipulate host cell processes in order to establish a replicative niche within the host cell. In response, the host can initiate immune defenses that lead to the eventual restriction and clearance of intracellular infection. The bacterial pathogen Legionella pneumophila has evolved elaborate virulence mechanisms that allow for its survival inside protozoa within a specialized membrane-bound organelle. These strategies also enable L. pneumophila to survive and replicate within alveolar macrophages, and can result in the severe pneumonia Legionnaires' disease. Essential to L. pneumophila's intracellular lifestyle is a specialized type IV secretion system, termed Dot/Icm, that translocates bacterial effector proteins into host cells. The ease with which L. pneumophila can be genetically manipulated has facilitated the comparison of host responses to virulent and isogenic avirulent mutants lacking a functional Dot/Icm system. This has made L. pneumophila an excellent model for understanding how the host discriminates between pathogenic and nonpathogenic bacteria and for systematically dissecting host defense mechanisms against intracellular pathogens. In this chapter, I discuss a few examples demonstrating how the study of immune responses triggered specifically by the L. pneumophila type IV secretion system has provided unique insight into our understanding of host immunity against intracellular bacterial pathogens.
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Affiliation(s)
- Sunny Shin
- Department of Microbiology, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania, USA.
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109
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Krause K, Amer AO. Caspase Exploitation by Legionella pneumophila. Front Microbiol 2016; 7:515. [PMID: 27148204 PMCID: PMC4829591 DOI: 10.3389/fmicb.2016.00515] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 03/29/2016] [Indexed: 12/21/2022] Open
Abstract
Legionella pneumophila remains a major health concern, especially for hospitalized patients. L. pneumophila in the environment can survive extracellular or as protozoan parasite within amoeba. After human infection it efficiently replicates in alveolar macrophages without activating inflammasome assembly and cleavage of caspase-1. In contrast murine macrophages actively recognize intracellular L. pneumophila via inflammasome components which initiate pro-inflammatory cytokine secretion, phagosomal maturation and pyroptotic cell death thereby leading to bacterial restriction. During this process flagellin-dependent and -independent signaling pathways trigger the canonical as well as the non-canonical inflammasome. This review describes the current knowledge about L. pneumophila-induced inflammasome pathways in permissive and restrictive host cells.
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Affiliation(s)
- Kathrin Krause
- Department of Microbial Infection and Immunity, The Ohio State University Columbus, OH, USA
| | - Amal O Amer
- Department of Microbial Infection and Immunity, The Ohio State University Columbus, OH, USA
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110
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Primary Role for Toll-Like Receptor-Driven Tumor Necrosis Factor Rather than Cytosolic Immune Detection in Restricting Coxiella burnetii Phase II Replication within Mouse Macrophages. Infect Immun 2016; 84:998-1015. [PMID: 26787725 DOI: 10.1128/iai.01536-15] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 01/14/2016] [Indexed: 12/13/2022] Open
Abstract
Coxiella burnetii replicates within permissive host cells by employing a Dot/Icm type IV secretion system (T4SS) to translocate effector proteins that direct the formation of a parasitophorous vacuole. C57BL/6 mouse macrophages restrict the intracellular replication of the C. burnetii. Nine Mile phase II (NMII) strain. However, eliminating Toll-like receptor 2 (TLR2) permits bacterial replication, indicating that the restriction of bacterial replication is immune mediated. Here, we examined whether additional innate immune pathways are employed by C57BL/6 macrophages to sense and restrict NMII replication. In addition to the known role of TLR2 in detecting and restricting NMII infection, we found that TLR4 also contributes to cytokine responses but is not required to restrict bacterial replication. Furthermore, the TLR signaling adaptors MyD88 and Trif are required for cytokine responses and restricting bacterial replication. The C. burnetii NMII T4SS translocates bacterial products into C57BL/6 macrophages. However, there was little evidence of cytosolic immune sensing of NMII, as there was a lack of inflammasome activation, T4SS-dependent cytokine responses, and robust type I interferon (IFN) production, and these pathways were not required to restrict bacterial replication. Instead, endogenous tumor necrosis factor (TNF) produced upon TLR sensing of C. burnetii NMII was required to control bacterial replication. Therefore, our findings indicate a primary role for TNF produced upon immune detection of C. burnetii NMII by TLRs, rather than cytosolic PRRs, in enabling C57BL/6 macrophages to restrict bacterial replication.
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111
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Naujoks J, Tabeling C, Dill BD, Hoffmann C, Brown AS, Kunze M, Kempa S, Peter A, Mollenkopf HJ, Dorhoi A, Kershaw O, Gruber AD, Sander LE, Witzenrath M, Herold S, Nerlich A, Hocke AC, van Driel I, Suttorp N, Bedoui S, Hilbi H, Trost M, Opitz B. IFNs Modify the Proteome of Legionella-Containing Vacuoles and Restrict Infection Via IRG1-Derived Itaconic Acid. PLoS Pathog 2016; 12:e1005408. [PMID: 26829557 PMCID: PMC4734697 DOI: 10.1371/journal.ppat.1005408] [Citation(s) in RCA: 183] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 12/30/2015] [Indexed: 11/21/2022] Open
Abstract
Macrophages can be niches for bacterial pathogens or antibacterial effector cells depending on the pathogen and signals from the immune system. Here we show that type I and II IFNs are master regulators of gene expression during Legionella pneumophila infection, and activators of an alveolar macrophage-intrinsic immune response that restricts bacterial growth during pneumonia. Quantitative mass spectrometry revealed that both IFNs substantially modify Legionella-containing vacuoles, and comparative analyses reveal distinct subsets of transcriptionally and spatially IFN-regulated proteins. Immune-responsive gene (IRG)1 is induced by IFNs in mitochondria that closely associate with Legionella-containing vacuoles, and mediates production of itaconic acid. This metabolite is bactericidal against intravacuolar L. pneumophila as well as extracellular multidrug-resistant Gram-positive and -negative bacteria. Our study explores the overall role IFNs play in inducing substantial remodeling of bacterial vacuoles and in stimulating production of IRG1-derived itaconic acid which targets intravacuolar pathogens. IRG1 or its product itaconic acid might be therapeutically targetable to fight intracellular and drug-resistant bacteria. Numerous intracellular bacterial pathogens replicate in specialized vacuoles within macrophages. We systematically study the molecular mechanism and the impact of macrophage-intrinsic antibacterial defense. Using L. pneumophila, an important cause of pneumonia and model organism for intracellular bacteria, we found that type I and II interferons critically modify the proteome of bacterial vacuoles to restrict infection. We identify IRG1 and demonstrate a bactericidal activity of its metabolite itaconic acid on bacteria in their vacuole. Moreover, our study provides evidence for the impact of this cell-autonomous defense pathway in alveolar macrophages to restrict lung infection. We speculate that vacuolar IRG1 or its product itaconic acid could serve as future therapeutic targets to fight intracellular and drug-resistant bacteria.
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Affiliation(s)
- Jan Naujoks
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Christoph Tabeling
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Brian D. Dill
- MRC Protein Phosphorylation Unit, University of Dundee, Dundee, United Kingdom
| | - Christine Hoffmann
- Max-von-Pettenkofer Institute, Ludwig Maximilian University, Munich, Germany
| | - Andrew S. Brown
- The Department of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, Australia
| | - Mareike Kunze
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Stefan Kempa
- Integrative Metabolomics and Proteomics, Institute of Medical Systems Biology/Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Andrea Peter
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | | | - Anca Dorhoi
- Max Planck Institute for Infection Biology, Berlin, Germany
| | - Olivia Kershaw
- Department of Veterinary Pathology, Free University Berlin, Berlin, Germany
| | - Achim D. Gruber
- Department of Veterinary Pathology, Free University Berlin, Berlin, Germany
| | - Leif E. Sander
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Martin Witzenrath
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Susanne Herold
- Medizinische Klinik II, University Giessen and Marburg Lung Center, Justus-Liebig-University Giessen, Giessen, Germany
| | - Andreas Nerlich
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Andreas C. Hocke
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Ian van Driel
- The Department of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, Australia
| | - Norbert Suttorp
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
| | - Sammy Bedoui
- The Department of Microbiology and Immunology, The University of Melbourne, Melbourne, Australia
| | - Hubert Hilbi
- Max-von-Pettenkofer Institute, Ludwig Maximilian University, Munich, Germany
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Matthias Trost
- MRC Protein Phosphorylation Unit, University of Dundee, Dundee, United Kingdom
| | - Bastian Opitz
- Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité University Medicine Berlin, Berlin, Germany
- * E-mail:
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112
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Zhao Y, Shao F. The NAIP-NLRC4 inflammasome in innate immune detection of bacterial flagellin and type III secretion apparatus. Immunol Rev 2016; 265:85-102. [PMID: 25879286 DOI: 10.1111/imr.12293] [Citation(s) in RCA: 148] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Bacterial flagella and type III secretion system (T3SS) are evolutionarily related molecular transport machineries. Flagella mediate bacterial motility; the T3SS delivers virulence effectors to block host defenses. The inflammasome is a cytosolic multi-protein complex that activates caspase-1. Active caspase-1 triggers interleukin-1β (IL-1β)/IL-18 maturation and macrophage pyroptotic death to mount an inflammatory response. Central to the inflammasome is a pattern recognition receptor that activates caspase-1 either directly or through an adapter protein. Studies in the past 10 years have established a NAIP-NLRC4 inflammasome, in which NAIPs are cytosolic receptors for bacterial flagellin and T3SS rod/needle proteins, while NLRC4 acts as an adapter for caspase-1 activation. Given the wide presence of flagella and the T3SS in bacteria, the NAIP-NLRC4 inflammasome plays a critical role in anti-bacteria defenses. Here, we review the discovery of the NAIP-NLRC4 inflammasome and further discuss recent advances related to its biochemical mechanism and biological function as well as its connection to human autoinflammatory disease.
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Affiliation(s)
- Yue Zhao
- National Institute of Biological Sciences, Beijing, China
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113
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Abdelaziz DHA, Khalil H, Cormet-Boyaka E, Amer AO. The cooperation between the autophagy machinery and the inflammasome to implement an appropriate innate immune response: do they regulate each other? Immunol Rev 2016; 265:194-204. [PMID: 25879294 DOI: 10.1111/imr.12288] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Autophagy is originally described as the main catabolic pathway responsible for maintaining intracellular nutritional homeostasis that involves the formation of a unique vacuole, the autophagosome, and the interaction with the endosome-lysosome pathways. This conserved machinery plays a key role in immune-protection against different invaders, including pathogenic bacteria, intracellular parasites, and some viruses like herpes simplex and hepatitis C virus. Importantly, autophagy is linked to a number of human diseases and disorders including neurodegenerative disease, Crohn's disease, type II diabetes, tumorigenesis, cardiomyopathy, and fatty liver disease. On the other hand, inflammasomes are multiprotein platforms stimulated upon several environmental conditions and microbial infection. Once assembled, the inflammasomes mediate the maturation of pro-inflammatory cytokines and promote phagosome-lysosome fusion to sustain an innate immune response. The intersections between autophagy and inflammasome have been observed in various diseases and microbial infections. This review highlights the molecular aspects involved in autophagy and inflammasome interactions during different medical conditions and microbial infections.
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Affiliation(s)
- Dalia H A Abdelaziz
- Department of Biochemistry and Molecular Biology, Faculty of Pharmacy, Helwan University, Cairo, Egypt
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114
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Abstract
Inflammasomes are oligomeric signaling complexes that promote caspase activation and maturation of proinflammatory cytokines. Structural and biophysical studies have shed light on the mechanisms of nucleic acid recognition and signaling complex assembly involving the AIM2 (absent in myeloma 2) and IFI16 (γ-interferon-inducible protein 16) inflammasomes. However, our understanding of the mechanisms of the NLRP3 (nucleotide-binding oligomerization-like receptor family, pyrin domain-containing protein 3) activation, either by nucleic acids or by other reported stimuli, has remained elusive. Exciting recent progress on the filament formation by the ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) pyrin domain and the IFI16-double stranded DNA complex has established that the formation of higher order polymers is one of the general mechanisms for signaling platform assembly in innate immune system. The paradigm-changing discovery of the extracellular function of the NLRP3-ASC inflammasome has opened the door for therapeutic targeting the inflammasome filament formation for various clinical conditions. Future characterization of the canonical and non-canonical inflammasome complexes will undoubtedly reveal more surprises on their structure and function and enrich our understanding of the molecular mechanisms of ligand recognition, activation, and regulation.
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Affiliation(s)
- Tsan Sam Xiao
- Department of Pathology, Case Western Reserve University, Cleveland, OH, USA
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115
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Abstract
Inflammasome biology is one of the most exciting and rapidly growing areas in immunology. Over the past 10 years, inflammasomes have been recognized for their roles in the host defense against invading pathogens and in the development of cancer, auto-inflammatory, metabolic, and neurodegenerative diseases. Assembly of an inflammasome complex requires cytosolic sensing of pathogen-associated molecular patterns or danger-associated molecular patterns by a nucleotide-binding domain and leucine-rich repeat receptor (NLR) or absent in melanoma 2 (AIM2)-like receptors (ALR). NLRs and ALRs engage caspase-1, in most cases requiring the adapter protein apoptosis-associated speck-like protein containing a CARD (ASC), to catalyze proteolytic cleavage of pro-interleukin-1β (pro-IL-1β) and pro-IL-18 and drive pyroptosis. Recent studies indicate that caspase-8, caspase-11, IL-1R-associated kinases (IRAK), and receptor-interacting protein (RIP) kinases contribute to inflammasome functions. In addition, post-translational modifications, including ubiquitination, deubiquitination, phosphorylation, and degradation control almost every aspect of inflammasome activities. Genetic studies indicate that mutations in NLRP1, NLRP3, NLRC4, and AIM2 are linked with the development of auto-inflammatory diseases, enterocolitis, and cancer. Overall, these findings transform our understanding of the basic biology and clinical relevance of inflammasomes. In this review, we provide an overview of the latest development of inflammasome research and discuss how inflammasome activities govern health and disease.
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Affiliation(s)
- Si Ming Man
- Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN, USA
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116
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Jorgensen I, Miao EA. Pyroptotic cell death defends against intracellular pathogens. Immunol Rev 2016; 265:130-42. [PMID: 25879289 DOI: 10.1111/imr.12287] [Citation(s) in RCA: 732] [Impact Index Per Article: 91.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Inflammatory caspases play a central role in innate immunity by responding to cytosolic signals and initiating a twofold response. First, caspase-1 induces the activation and secretion of the two prominent pro-inflammatory cytokines, interleukin-1β (IL-1β) and IL-18. Second, either caspase-1 or caspase-11 can trigger a form of lytic, programmed cell death called pyroptosis. Pyroptosis operates to remove the replication niche of intracellular pathogens, making them susceptible to phagocytosis and killing by a secondary phagocyte. However, aberrant, systemic activation of pyroptosis in vivo may contribute to sepsis. Emphasizing the efficiency of inflammasome detection of microbial infections, many pathogens have evolved to avoid or subvert pyroptosis. This review focuses on molecular and morphological characteristics of pyroptosis and the individual inflammasomes and their contribution to defense against infection in mice and humans.
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Affiliation(s)
- Ine Jorgensen
- Department of Microbiology and Immunology, Center for Gastrointestinal Biology and Disease, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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117
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Abu Khweek A, Kanneganti A, C. Guttridge D D, Amer AO. The Sphingosine-1-Phosphate Lyase (LegS2) Contributes to the Restriction of Legionella pneumophila in Murine Macrophages. PLoS One 2016; 11:e0146410. [PMID: 26741365 PMCID: PMC4704736 DOI: 10.1371/journal.pone.0146410] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 12/16/2015] [Indexed: 12/16/2022] Open
Abstract
L. pneumophila is the causative agent of Legionnaires’ disease, a human illness characterized by severe pneumonia. In contrast to those derived from humans, macrophages derived from most mouse strains restrict L. pneumophila replication. The restriction of L. pneumophila replication has been shown to require bacterial flagellin, a component of the type IV secretion system as well as the cytosolic NOD-like receptor (NLR) Nlrc4/ Ipaf. These events lead to caspase-1 activation which, in turn, activates caspase-7. Following caspase-7 activation, the phagosome-containing L. pneumophila fuses with the lysosome, resulting in the restriction of L. pneumophila growth. The LegS2 effector is injected by the type IV secretion system and functions as a sphingosine 1-phosphate lyase. It is homologous to the eukaryotic sphingosine lyase (SPL), an enzyme required in the terminal steps of sphingolipid metabolism. Herein, we show that mice Bone Marrow-Derived Macrophages (BMDMs) and human Monocyte-Derived Macrophages (hMDMs) are more permissive to L. pneumophila legS2 mutants than wild-type (WT) strains. This permissiveness to L. pneumophila legS2 is neither attributed to abolished caspase-1, caspase-7 or caspase-3 activation, nor due to the impairment of phagosome-lysosome fusion. Instead, an infection with the legS2 mutant resulted in the reduction of some inflammatory cytokines and their corresponding mRNA; this effect is mediated by the inhibition of the nuclear transcription factor kappa-B (NF-κB). Moreover, BMDMs infected with L. pneumophila legS2 mutant showed elongated mitochondria that resembles mitochondrial fusion. Therefore, the absence of LegS2 effector is associated with reduced NF-κB activation and atypical morphology of mitochondria.
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Affiliation(s)
- Arwa Abu Khweek
- Birzeit University, Department of Biology and Biochemistry, West Bank, Palestine
- * E-mail:
| | - Apurva Kanneganti
- The Ohio State University, Department of Microbial Infection and Immunity, College of Medicine, Center for Microbial Interface Biology, Columbus, Ohio, United States of America
| | - Denis C. Guttridge D
- Human Cancer Genetics Program, Ohio State University, Columbus, Ohio, United States of America
| | - Amal O. Amer
- The Ohio State University, Department of Microbial Infection and Immunity, College of Medicine, Center for Microbial Interface Biology, Columbus, Ohio, United States of America
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118
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Abstract
The complementary actions of the innate and adaptive immune systems often provide effective host defense against microbial pathogens and harmful environmental agents. Germline-encoded pattern recognition receptors (PRRs) endow the innate immune system with the ability to detect and mount a rapid response against a given threat. Members of several intracellular PRR families, including the nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs), the AIM2-like receptors (ALRs), and the tripartite motif-containing (TRIM) protein Pyrin/TRIM20, nucleate the formation of inflammasomes. These cytosolic scaffolds serve to recruit and oligomerize the cysteine protease caspase-1 in filaments that promote its proximity-induced autoactivation. This oligomerization occurs either directly or indirectly through intervention of the bipartite adaptor protein ASC, apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD), which is needed for the domain interaction. Caspase-1 cleaves the precursors of the inflammatory cytokines interleukin (IL)-1β and IL-18 and triggers their release into the extracellular space, where they act on effector cells to promote both local and systemic immune responses. Additionally, inflammasome activation gives rise to a lytic mode of cell death, named pyroptosis, which is thought to contribute to initial host defense against infection by eliminating replication niches of intracellular pathogens and exposing them to the immune system. Inflammasome-induced host defense responses are the subject of intense investigation, and understanding their physiological roles during infection and the regulatory circuits that are involved is becoming increasingly detailed. Here, we discuss current understanding of the activation mechanisms and biological outcomes of inflammasome activation.
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Affiliation(s)
- Hanne Dubois
- NOD-like Receptor and Inflammasome Laboratory, Inflammation Research Center, VIB, 9052, Zwijnaarde, Belgium.,Department of Internal Medicine, Ghent University, 9000, Ghent, Belgium
| | - Andy Wullaert
- NOD-like Receptor and Inflammasome Laboratory, Inflammation Research Center, VIB, 9052, Zwijnaarde, Belgium.,Department of Internal Medicine, Ghent University, 9000, Ghent, Belgium
| | - Mohamed Lamkanfi
- NOD-like Receptor and Inflammasome Laboratory, Inflammation Research Center, VIB, 9052, Zwijnaarde, Belgium. .,Department of Internal Medicine, Ghent University, 9000, Ghent, Belgium.
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119
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Abstract
Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are pattern-recognition receptors similar to toll-like receptors (TLRs). While TLRs are transmembrane receptors, NLRs are cytoplasmic receptors that play a crucial role in the innate immune response by recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Based on their N-terminal domain, NLRs are divided into four subfamilies: NLRA, NLRB, NLRC, and NLRP. NLRs can also be divided into four broad functional categories: inflammasome assembly, signaling transduction, transcription activation, and autophagy. In addition to recognizing PAMPs and DAMPs, NLRs act as a key regulator of apoptosis and early development. Therefore, there are significant associations between NLRs and various diseases related to infection and immunity. NLR studies have recently begun to unveil the roles of NLRs in diseases such as gout, cryopyrin-associated periodic fever syndromes, and Crohn's disease. As these new associations between NRLs and diseases may improve our understanding of disease pathogenesis and lead to new approaches for the prevention and treatment of such diseases, NLRs are becoming increasingly relevant to clinicians. In this review, we provide a concise overview of NLRs and their role in infection, immunity, and disease, particularly from clinical perspectives.
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Affiliation(s)
- Young Keun Kim
- Department of Internal Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea
| | - Jeon Soo Shin
- Department of Microbiology, Yonsei University College of Medicine, Seoul, Korea
- Brain Korea 21 PLUS for Medical Science, Yonsei University College of Medicine, Seoul, Korea
- Severance Biomedical Science Institute and Institute for Immunology and Immunological Diseases, Yonsei University College of Medicine, Seoul, Korea
| | - Moon H Nahm
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL, USA.
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL, USA
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120
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The Orchestra and Its Maestro: Shigella's Fine-Tuning of the Inflammasome Platforms. Curr Top Microbiol Immunol 2016; 397:91-115. [PMID: 27460806 DOI: 10.1007/978-3-319-41171-2_5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Shigella spp. are the causative agents of bacillary dysentery, leading to extensive mortality and morbidity worldwide. These facultative intracellular bacteria invade the epithelium of the colon and the rectum, inducing a severe inflammatory response from which the symptoms of the disease originate. Shigella are human pathogens able to manipulate and subvert the innate immune system surveillance. Shigella dampens inflammasome activation in epithelial cells. In infected macrophages, inflammasome activation and IL-1β and IL-18 release lead to massive neutrophil recruitment and greatly contribute to inflammation. Here, we describe how Shigella hijacks and finely tunes inflammasome activation in the different cell populations involved in pathogenesis: epithelial cells, macrophages, neutrophils, DCs, and B and T lymphocytes. Shigella emerges as a "sly" pathogen that switches on/off the inflammasome mechanisms in order to optimize the interaction with the host and establish a successful infection.
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121
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Schell U, Simon S, Hilbi H. Inflammasome Recognition and Regulation of the Legionella Flagellum. Curr Top Microbiol Immunol 2016; 397:161-81. [PMID: 27460809 DOI: 10.1007/978-3-319-41171-2_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The Gram-negative bacterium Legionella pneumophila colonizes extracellular environmental niches and infects free-living protozoa. Upon inhalation into the human lung, the opportunistic pathogen grows in macrophages and causes a fulminant pneumonia termed Legionnaires' disease. L. pneumophila employs a biphasic life cycle, comprising a replicative, non-virulent, and a stationary, virulent form. In the latter phase, the pathogen produces a plethora of so-called effector proteins, which are injected into host cells, where they subvert pivotal processes and promote the formation of a distinct membrane-bound compartment, the Legionella-containing vacuole. In the stationary phase, the bacteria also produce a single monopolar flagellum and become motile. L. pneumophila flagellin is recognized by and triggers the host's NAIP5 (Birc1e)/NLRC4 (Ipaf) inflammasome, which leads to caspase-1 activation, pore formation, and pyroptosis. The production of L. pneumophila flagellin and pathogen-host interactions are controlled by a complex stationary phase regulatory network, detecting nutrient availability as well as the Legionella quorum sensing (Lqs) signaling compound LAI-1 (3-hydroxypentadecane-4-one). Thus, the small molecule LAI-1 coordinates L. pneumophila flagellin production and motility, inflammasome activation, and virulence.
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Affiliation(s)
- Ursula Schell
- Max von Pettenkofer Institute, Ludwig-Maximilians University, Pettenkoferstraße 9a, 80336, Munich, Germany
| | - Sylvia Simon
- Institute of Medical Microbiology, University of Zürich, Gloriastrasse 30/32, 8006, Zürich, Switzerland
| | - Hubert Hilbi
- Institute of Medical Microbiology, University of Zürich, Gloriastrasse 30/32, 8006, Zürich, Switzerland.
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Caution K, Gavrilin MA, Tazi M, Kanneganti A, Layman D, Hoque S, Krause K, Amer AO. Caspase-11 and caspase-1 differentially modulate actin polymerization via RhoA and Slingshot proteins to promote bacterial clearance. Sci Rep 2015; 5:18479. [PMID: 26686473 PMCID: PMC4685268 DOI: 10.1038/srep18479] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 11/18/2015] [Indexed: 01/19/2023] Open
Abstract
Inflammasomes are multiprotein complexes that include members of the NOD-like receptor family and caspase-1. Caspase-1 is required for the fusion of the Legionella vacuole with lysosomes. Caspase-11, independently of the inflammasome, also promotes phagolysosomal fusion. However, it is unclear how these proteases alter intracellular trafficking. Here, we show that caspase-11 and caspase-1 function in opposing manners to phosphorylate and dephosphorylate cofilin, respectively upon infection with Legionella. Caspase-11 targets cofilin via the RhoA GTPase, whereas caspase-1 engages the Slingshot phosphatase. The absence of either caspase-11 or caspase-1 maintains actin in the polymerized or depolymerized form, respectively and averts the fusion of pathogen-containing vacuoles with lysosomes. Therefore, caspase-11 and caspase-1 converge on the actin machinery with opposing effects to promote vesicular trafficking.
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Affiliation(s)
- Kyle Caution
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Mikhail A Gavrilin
- Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Mia Tazi
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Apurva Kanneganti
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Daniel Layman
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Sheshadri Hoque
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Kathrin Krause
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
| | - Amal O Amer
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus OH 43210.,Dorothy M. Davis Heart and Lung Research Institute, and The Ohio State University, Columbus OH 43210
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123
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Inhibition of inflammasome activation by Coxiella burnetii type IV secretion system effector IcaA. Nat Commun 2015; 6:10205. [PMID: 26687278 PMCID: PMC4703858 DOI: 10.1038/ncomms10205] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 11/13/2015] [Indexed: 02/01/2023] Open
Abstract
Coxiella burnetii is a highly infectious bacterium that promotes its own replication in macrophages by inhibiting several host cell responses. Here, we show that C. burnetii inhibits caspase-1 activation in primary mouse macrophages. By using co-infection experiments, we determine that the infection of macrophages with C. burnetii inhibits the caspase-11-mediated non-canonical activation of the NLRP3 inflammasome induced by subsequent infection with Escherichia coli or Legionella pneumophila. Genetic screening using flagellin mutants of L. pneumophila as a surrogate host, reveals a novel C. burnetii gene (IcaA) involved in the inhibition of caspase activation. Expression of IcaA in L. pneumophila inhibited the caspase-11 activation in macrophages. Moreover, icaA- mutants of C. burnetii failed to suppress the caspase-11-mediated inflammasome activation induced by L. pneumophila. Our data reveal IcaA as a novel C. burnetii effector protein that is secreted by the Dot/Icm type IV secretion system and interferes with the caspase-11-induced, non-canonical activation of the inflammasome. Coxiella burnetti primarily infects alveolar macrophages and causes an acute form of pneumonia called Q fever. Cunha et al. describe a type IV secretion effector, termed IcaA, expressed by Coxiella burnetii that inhibits inflammasome activation and therefore may contribute to innate immune evasion by bacteria.
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124
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Converging roles of caspases in inflammasome activation, cell death and innate immunity. Nat Rev Immunol 2015; 16:7-21. [PMID: 26655628 DOI: 10.1038/nri.2015.7] [Citation(s) in RCA: 455] [Impact Index Per Article: 50.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Inflammatory and apoptotic caspases are central players in inflammation and apoptosis, respectively. However, recent studies have revealed that these caspases have functions beyond their established roles. In addition to mediating cleavage of the inflammasome-associated cytokines interleukin-1β (IL-1β) and IL-18, inflammatory caspases modulate distinct forms of programmed cell death and coordinate cell-autonomous immunity and other fundamental cellular processes. Certain apoptotic caspases assemble structurally diverse and dynamic complexes that direct inflammasome and interferon responses to fine-tune inflammation. In this Review, we discuss the expanding and interconnected roles of caspases that highlight new aspects of this family of cysteine proteases in innate immunity.
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125
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Levy M, Thaiss CA, Elinav E. Metagenomic cross-talk: the regulatory interplay between immunogenomics and the microbiome. Genome Med 2015; 7:120. [PMID: 26589591 PMCID: PMC4654884 DOI: 10.1186/s13073-015-0249-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The human microbiome, often referred to as the 'second genome', encompasses up to 100-fold more genes than the host genome. In contrast to the human genome, the microbial genome is flexible and amenable to change during the host's lifetime. As the composition of the microbial metagenome has been associated with the development of human disease, the mechanisms controlling the composition and function of the metagenome are of considerable interest and therapeutic potential. In the past few years, studies have revealed how the host immune system is involved in determining the microbial metagenome, and, in turn, how the microbiota regulates gene expression in the immune system. This species-specific bidirectional interaction is required for homeostatic health, whereas aberrations in the tightly controlled regulatory circuits that link the host immunogenome and the microbial metagenome drive susceptibility to common human diseases. Here, we summarize some of the major principles orchestrating this cross-talk between microbial and host genomes, with a special focus on the interaction between the intestinal immune system and the gut microbiome. Understanding the reciprocal genetic and epigenetic control between host and microbiota will be an important step towards the development of novel therapies against microbiome-driven diseases.
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Affiliation(s)
- Maayan Levy
- Immunology Department, Weizmann Institute of Science, 100 Herzl Street, Rehovot, 76100, Israel
| | - Christoph A Thaiss
- Immunology Department, Weizmann Institute of Science, 100 Herzl Street, Rehovot, 76100, Israel
| | - Eran Elinav
- Immunology Department, Weizmann Institute of Science, 100 Herzl Street, Rehovot, 76100, Israel.
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126
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Abstract
Eukaryotes have evolved strategies to detect microbial intrusion and instruct immune responses to limit damage from infection. Recognition of microbes and cellular damage relies on the detection of microbe-associated molecular patterns (MAMPs, also called PAMPS, or pathogen-associated molecular patterns) and so-called "danger signals" by various families of host pattern recognition receptors (PRRs). Members of the recently identified protein family of nucleotide-binding domain andleucine-rich-repeat-containing proteins (NLR), including Nod1, Nod2, NLRP3, and NLRC4, have been shown to detect specific microbial motifs and danger signals for regulating host inflammatory responses. Moreover, with the discovery that polymorphisms in NOD1, NOD2, NLRP1, and NLRP3 are associated with susceptibility to chronic inflammatory disorders, the view has emerged that NLRs act not only as sensors butalso can serve as signaling platforms for instructing and balancing host immune responses. In this chapter, we explore the functions of these intracellular innate immune receptors and examine their implication in inflammatory diseases.
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127
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Simon S, Hilbi H. Subversion of Cell-Autonomous Immunity and Cell Migration by Legionella pneumophila Effectors. Front Immunol 2015; 6:447. [PMID: 26441958 PMCID: PMC4568765 DOI: 10.3389/fimmu.2015.00447] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 08/17/2015] [Indexed: 12/14/2022] Open
Abstract
Bacteria trigger host defense and inflammatory processes, such as cytokine production, pyroptosis, and the chemotactic migration of immune cells toward the source of infection. However, a number of pathogens interfere with these immune functions by producing specific so-called “effector” proteins, which are delivered to host cells via dedicated secretion systems. Air-borne Legionella pneumophila bacteria trigger an acute and potential fatal inflammation in the lung termed Legionnaires’ disease. The opportunistic pathogen L. pneumophila is a natural parasite of free-living amoebae, but also replicates in alveolar macrophages and accidentally infects humans. The bacteria employ the intracellular multiplication/defective for organelle trafficking (Icm/Dot) type IV secretion system and as many as 300 different effector proteins to govern host–cell interactions and establish in phagocytes an intracellular replication niche, the Legionella-containing vacuole. Some Icm/Dot-translocated effector proteins target cell-autonomous immunity or cell migration, i.e., they interfere with (i) endocytic, secretory, or retrograde vesicle trafficking pathways, (ii) organelle or cell motility, (iii) the inflammasome and programed cell death, or (iv) the transcription factor NF-κB. Here, we review recent mechanistic insights into the subversion of cellular immune functions by L. pneumophila.
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Affiliation(s)
- Sylvia Simon
- Institute of Medical Microbiology, University of Zürich , Zürich , Switzerland
| | - Hubert Hilbi
- Institute of Medical Microbiology, University of Zürich , Zürich , Switzerland ; Max von Pettenkofer Institute, Ludwig-Maximilians University , Munich , Germany
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128
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Cerqueira DM, Pereira MSF, Silva ALN, Cunha LD, Zamboni DS. Caspase-1 but Not Caspase-11 Is Required for NLRC4-Mediated Pyroptosis and Restriction of Infection by Flagellated Legionella Species in Mouse Macrophages and In Vivo. THE JOURNAL OF IMMUNOLOGY 2015; 195:2303-11. [PMID: 26232428 DOI: 10.4049/jimmunol.1501223] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 07/07/2015] [Indexed: 11/19/2022]
Abstract
Gram-negative bacteria from the Legionella genus are intracellular pathogens that cause a severe form of pneumonia called Legionnaires' disease. The bacteria replicate intracellularly in macrophages, and the restriction of bacterial replication by these cells is critical for host resistance. The activation of the NAIP5/NLRC4 inflammasome, which is readily triggered in response to bacterial flagellin, is essential for the restriction of bacterial replication in murine macrophages. Once activated, this inflammasome induces pore formation and pyroptosis and facilitates the restriction of bacterial replication in macrophages. Because investigations related to the NLRC4-mediated restriction of Legionella replication were performed using mice double deficient for caspase-1 and caspase-11, we assessed the participation of caspase-1 and caspase-11 in the functions of the NLRC4 inflammasome and the restriction of Legionella replication in macrophages and in vivo. By using several species of Legionella and mice singly deficient for caspase-1 or caspase-11, we demonstrated that caspase-1 but not caspase-11 was required for pore formation, pyroptosis, and restriction of Legionella replication in macrophages and in vivo. By generating F1 mice in a mixed 129 × C57BL/6 background deficient (129 × Casp-11(-/-) ) or sufficient (129 × C57BL/6) for caspase-11 expression, we found that caspase-11 was dispensable for the restriction of Legionella pneumophila replication in macrophages and in vivo. Thus, although caspase-11 participates in flagellin-independent noncanonical activation of the NLRP3 inflammasome, it is dispensable for the activities of the NLRC4 inflammasome. In contrast, functional caspase-1 is necessary and sufficient to trigger flagellin/NLRC4-mediated restriction of Legionella spp. infection in macrophages and in vivo.
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Affiliation(s)
- Daiane M Cerqueira
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Marcelo S F Pereira
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Alexandre L N Silva
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Larissa D Cunha
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Dario S Zamboni
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
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129
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Sellin ME, Maslowski KM, Maloy KJ, Hardt WD. Inflammasomes of the intestinal epithelium. Trends Immunol 2015; 36:442-50. [PMID: 26166583 DOI: 10.1016/j.it.2015.06.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 06/16/2015] [Accepted: 06/16/2015] [Indexed: 02/08/2023]
Abstract
While the functional importance of inflammasomes in blood-derived cell types is well established, it remains poorly understood how inflammasomes in nonhematopoietic cells contribute to mucosal immunity. Recent studies have revealed functional roles of inflammasomes - particularly NAIP/NLRC4, NLRP6, and noncanonical caspase-4 (caspase-11) - within epithelial cells of the gut in mucosal immune defense, inflammation, and tumorigenesis. Here, we review and discuss these findings in the broader context of tissue compartment-specific mucosal immunity. We propose several models whereby activities of the intestinal epithelial inflammasomes converge on mechanisms to remove compromised epithelial cells, maintain host-microbiota mutualism, and communicate with immune cells of the underlying lamina propria.
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Affiliation(s)
- Mikael E Sellin
- Institute of Microbiology, ETH Zürich, 8093 Zürich, Switzerland.
| | - Kendle M Maslowski
- Laboratory for Intestinal Ecosystem, RIKEN Center for Integrative Medical Sciences, Yokohama 230-0045, Japan
| | - Kevin J Maloy
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK
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130
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Motta V, Soares F, Sun T, Philpott DJ. NOD-like receptors: versatile cytosolic sentinels. Physiol Rev 2015; 95:149-78. [PMID: 25540141 DOI: 10.1152/physrev.00009.2014] [Citation(s) in RCA: 211] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Nucleotide binding oligomerization domain (NOD)-like receptors are cytoplasmic pattern-recognition receptors that together with RIG-I-like receptor (retinoic acid-inducible gene 1), Toll-like receptor (TLR), and C-type lectin families make up the innate pathogen pattern recognition system. There are 22 members of NLRs in humans, 34 in mice, and even a larger number in some invertebrates like sea urchins, which contain more than 200 receptors. Although initially described to respond to intracellular pathogens, NLRs have been shown to play important roles in distinct biological processes ranging from regulation of antigen presentation, sensing metabolic changes in the cell, modulation of inflammation, embryo development, cell death, and differentiation of the adaptive immune response. The diversity among NLR receptors is derived from ligand specificity conferred by the leucine-rich repeats and an NH2-terminal effector domain that triggers the activation of different biological pathways. Here, we describe NLR genes associated with different biological processes and the molecular mechanisms underlying their function. Furthermore, we discuss mutations in NLR genes that have been associated with human diseases.
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Affiliation(s)
- Vinicius Motta
- Departments of Immunology and of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
| | - Fraser Soares
- Departments of Immunology and of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
| | - Tian Sun
- Departments of Immunology and of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
| | - Dana J Philpott
- Departments of Immunology and of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
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131
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Flagellin-induced NLRC4 phosphorylation primes the inflammasome for activation by NAIP5. Proc Natl Acad Sci U S A 2015; 112:1541-6. [PMID: 25605939 DOI: 10.1073/pnas.1417945112] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The Nlrc4 inflammasome contributes to immunity against intracellular pathogens that express flagellin and type III secretion systems, and activating mutations in NLRC4 cause autoinflammation in patients. Both Naip5 and phosphorylation of Nlrc4 at Ser533 are required for flagellin-induced inflammasome activation, but how these events converge upon inflammasome activation is not known. Here, we showed that Nlrc4 phosphorylation occurs independently of Naip5 detection of flagellin because Naip5 deletion in macrophages abolished caspase-1 activation, interleukin (IL)-1β secretion, and pyroptosis, but not Nlrc4 phosphorylation by cytosolic flagellin of Salmonella Typhimurium and Yersinia enterocolitica. ASC speck formation and caspase-1 expression also were dispensable for Nlrc4 phosphorylation. Interestingly, Helicobacter pylori flagellin triggered robust Nlrc4 phosphorylation, but failed to elicit caspase-1 maturation, IL-1β secretion, and pyroptosis, suggesting that it retained Nlrc4 Ser533 phosphorylating-activity despite escaping Naip5 detection. In agreement, the flagellin D0 domain was required and sufficient for Nlrc4 phosphorylation, whereas deletion of the S. Typhimurium flagellin carboxy-terminus prevented caspase-1 maturation only. Collectively, this work suggests a biphasic activation mechanism for the Nlrc4 inflammasome in which Ser533 phosphorylation prepares Nlrc4 for subsequent activation by the flagellin sensor Naip5.
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132
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Netea MG, van de Veerdonk FL, van der Meer JWM, Dinarello CA, Joosten LAB. Inflammasome-independent regulation of IL-1-family cytokines. Annu Rev Immunol 2014; 33:49-77. [PMID: 25493334 DOI: 10.1146/annurev-immunol-032414-112306] [Citation(s) in RCA: 250] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Induction, production, and release of proinflammatory cytokines are essential steps to establish an effective host defense. Cytokines of the interleukin-1 (IL-1) family induce inflammation and regulate T lymphocyte responses while also displaying homeostatic and metabolic activities. With the exception of the IL-1 receptor antagonist, all IL-1 family cytokines lack a signal peptide and require proteolytic processing into an active molecule. One such unique protease is caspase-1, which is activated by protein platforms called the inflammasomes. However, increasing evidence suggests that inflammasomes and caspase-1 are not the only mechanism for processing IL-1 cytokines. IL-1 cytokines are often released as precursors and require extracellular processing for activity. Here we review the inflammasome-independent enzymatic processes that are able to activate IL-1 cytokines, paying special attention to neutrophil-derived serine proteases, which subsequently induce inflammation and modulate host defense. The inflammasome-independent processing of IL-1 cytokines has important consequences for understanding inflammatory diseases, and it impacts the design of IL-1-based modulatory therapies.
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133
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Cesari S, Bernoux M, Moncuquet P, Kroj T, Dodds PN. A novel conserved mechanism for plant NLR protein pairs: the "integrated decoy" hypothesis. FRONTIERS IN PLANT SCIENCE 2014; 5:606. [PMID: 25506347 DOI: 10.3389/fpls.2014.00606/abstract] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 10/17/2014] [Indexed: 05/26/2023]
Abstract
Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat receptors (NLR). Plant NLRs contain an N-terminal signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also describe an "integrated decoy" model for the function of these receptor complexes. In this model, a plant protein targeted by an effector has been duplicated and fused to one member of the NLR pair, where it acts as a bait to trigger defense signaling by the second NLR upon effector binding. This mechanism may be common to many other plant NLR pairs.
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Affiliation(s)
- Stella Cesari
- Institut National de la Recherche Agronomique, Unité Mixtes de Recherche Biology and Genetics of Plant-Pathogen Interactions Montpellier, France ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Unité Mixtes de Recherche Biology and Genetics of Plant-Pathogen Interactions Montpellier, France ; Agriculture Flagship, Commonwealth Scientific and Industrial Research Organisation Canberra, ACT, Australia
| | - Maud Bernoux
- Agriculture Flagship, Commonwealth Scientific and Industrial Research Organisation Canberra, ACT, Australia
| | - Philippe Moncuquet
- Commonwealth Scientific and Industrial Research Organisation, Digital Productivity and Service Canberra, ACT, Australia
| | - Thomas Kroj
- Institut National de la Recherche Agronomique, Unité Mixtes de Recherche Biology and Genetics of Plant-Pathogen Interactions Montpellier, France ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Unité Mixtes de Recherche Biology and Genetics of Plant-Pathogen Interactions Montpellier, France
| | - Peter N Dodds
- Agriculture Flagship, Commonwealth Scientific and Industrial Research Organisation Canberra, ACT, Australia
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134
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Khan RN, Hay DP. A clear and present danger: inflammasomes DAMPing down disorders of pregnancy. Hum Reprod Update 2014; 21:388-405. [PMID: 25403436 DOI: 10.1093/humupd/dmu059] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Accepted: 10/27/2014] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND When the normal progression of pregnancy is threatened, inflammatory processes are often amplified in order to minimize detrimental effects and eliminate noxious agents. Inflammasomes are unique, intracellular, multiprotein assemblies that enable caspase-1 mediated proteolytic processing of the proinflammatory cytokine interleukin-1β, levels of which are elevated in some forms of preterm birth and maternal metabolic disorders. METHODS A comprehensive review based on a search of PubMed and Medline for terms and combinations of terms incorporating 'inflammation', 'inflammasome', 'pregnancy', 'preterm birth', 'pre-eclampsia', 'interleukin-1', 'caspase-1' and others selected to capture key articles. RESULTS In the decade since the discovery of the inflammasome, between January 2002 and June 2014 over 2200 articles have been published. Articles in the reproductive field are scarce but there is clear evidence for a role of the inflammasome axis in pregnancy, preterm birth and the maternal metabolic syndrome. CONCLUSION Further investigations on the inflammasome in pregnancy are needed in order to elucidate the biology of this unique structure in reproduction. Coordination of maternal, fetal and placental aspects of inflammasome function will potentially yield new information on the detection and transduction of host and non-host signals in the inflammatory response.
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Affiliation(s)
- Raheela N Khan
- Division of Medical Sciences & Graduate Entry Medicine, School of Medicine, University of Nottingham, Royal Derby Hospital Centre, Uttoxeter Road, Derby DE22 3DT, UK
| | - Daniel P Hay
- Division of Medical Sciences & Graduate Entry Medicine, School of Medicine, University of Nottingham, Royal Derby Hospital Centre, Uttoxeter Road, Derby DE22 3DT, UK
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135
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Gurung P, Kanneganti TD. Novel roles for caspase-8 in IL-1β and inflammasome regulation. THE AMERICAN JOURNAL OF PATHOLOGY 2014; 185:17-25. [PMID: 25451151 DOI: 10.1016/j.ajpath.2014.08.025] [Citation(s) in RCA: 124] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 08/20/2014] [Accepted: 08/25/2014] [Indexed: 01/14/2023]
Abstract
Caspase-8 is an initiator and apical activator caspase that plays a central role in apoptosis. Caspase-8-deficient mice are embryonic lethal, which makes study of caspase-8 in primary immune cells difficult. Recent advances have rescued caspase-8-deficient mice by crossing them to mice deficient in receptor-interacting serine-threonine kinase 3 (RIPK3). These genetic tools have made it possible to study the role of caspase-8 in vivo and in primary immune cells. Several recent studies have identified novel roles for caspase-8 in modulating IL-1β and inflammation, showing that caspase-8 directly regulates IL-1β independent of inflammasomes or indirectly through the regulation of inflammasomes, depending on the stimulus or stimuli that initiate the signaling cascade. Here, we address recent findings on caspase-8 and its role in modulating IL-1β and inflammation.
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Affiliation(s)
- Prajwal Gurung
- Department of Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee
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136
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Dhariwala MO, Anderson DM. Bacterial programming of host responses: coordination between type I interferon and cell death. Front Microbiol 2014; 5:545. [PMID: 25389418 PMCID: PMC4211556 DOI: 10.3389/fmicb.2014.00545] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Accepted: 09/30/2014] [Indexed: 01/24/2023] Open
Abstract
During mammalian infection, bacteria induce cell death from an extracellular or intracellular niche that can protect or hurt the host. Data is accumulating that associate type I interferon (IFN) signaling activated by intracellular bacteria with programmed death of immune effector cells and enhanced virulence. Multiple pathways leading to IFN-dependent host cell death have been described, and in some cases it is becoming clear how these mechanisms contribute to virulence. Yet common mechanisms of IFN-enhanced bacterial pathogenesis are not obvious and no specific interferon stimulated genes have yet been identified that cause sensitivity to pathogen-induced cell death. In this review, we will summarize some bacterial infections caused by facultative intracellular pathogens and what is known about how type I IFN signaling may promote the replication of extracellular bacteria rather than stimulate protection. Each of these pathogens can survive phagocytosis but their intracellular life cycles are very different, they express distinct virulence factors and trigger different pathways of immune activation and crosstalk. These differences likely lead to widely varying amounts of type I IFN expression and a different inflammatory environment, but these may not be important to the pathologic effects on the host. Instead, each pathogen induces programmed cell death of key immune cells that have been sensitized by the activation of the type I IFN response. We will discuss how IFN-dependent host cell death may increase host susceptibility and try to understand common pathways of pathogenesis that lead to IFN-enhanced bacterial virulence.
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Affiliation(s)
- Miqdad O Dhariwala
- Department of Veterinary Pathobiology, University of Missouri Columbia, MO, USA
| | - Deborah M Anderson
- Department of Veterinary Pathobiology, University of Missouri Columbia, MO, USA
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137
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Abstract
Inflammasomes are large cytosolic multiprotein complexes that assemble in response to detection of infection- or stress-associated stimuli and lead to the activation of caspase-1-mediated inflammatory responses, including cleavage and unconventional secretion of the leaderless proinflammatory cytokines IL-1β and IL-18, and initiation of an inflammatory form of cell death referred to as pyroptosis. Inflammasome activation can be induced by a wide variety of microbial pathogens and generally mediates host defense through activation of rapid inflammatory responses and restriction of pathogen replication. In addition to its role in defense against pathogens, recent studies have suggested that the inflammasome is also a critical regulator of the commensal microbiota in the intestine. Finally, inflammasomes have been widely implicated in the development and progression of various chronic diseases, such as gout, atherosclerosis, and metabolic syndrome. In this perspective, we discuss the role of inflammasomes in infectious and noninfectious inflammation and highlight areas of interest for future studies of inflammasomes in host defense and chronic disease.
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Affiliation(s)
- Marcel R de Zoete
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Noah W Palm
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Shu Zhu
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Richard A Flavell
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520 Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520
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138
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Inflammasomes and the microbiota--partners in the preservation of mucosal homeostasis. Semin Immunopathol 2014; 37:39-46. [PMID: 25315349 DOI: 10.1007/s00281-014-0451-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 10/02/2014] [Indexed: 12/16/2022]
Abstract
Inflammasomes are multiprotein complexes that serve as signaling platforms initiating innate immune responses. These structures are assembled upon a large array of stimuli, sensing both microbial products and endogenous signals indicating loss of cellular homeostasis. As such, inflammasomes are regarded as sensors of cellular integrity and tissue health, which, upon disruption of homeostasis, provoke an inflammatory response by the release of potent cytokines. Recent evidence suggests that in addition to sensing cellular integrity, inflammasomes are involved in the homeostatic mutualism between the host and its indigenous microbiota. Here, we summarize the involvement of various inflammasomes in host-microbiota interactions and focus on the role of commensal as well as pathogenic bacteria in inflammasome signaling.
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139
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Copenhaver AM, Casson CN, Nguyen HT, Fung TC, Duda MM, Roy CR, Shin S. Alveolar macrophages and neutrophils are the primary reservoirs for Legionella pneumophila and mediate cytosolic surveillance of type IV secretion. Infect Immun 2014; 82:4325-36. [PMID: 25092908 PMCID: PMC4187856 DOI: 10.1128/iai.01891-14] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 07/24/2014] [Indexed: 02/07/2023] Open
Abstract
Legionella pneumophila, an intracellular pathogen responsible for the severe pneumonia Legionnaires' disease, uses its dot/icm-encoded type IV secretion system (T4SS) to translocate effector proteins that promote its survival and replication into the host cell cytosol. However, by introducing bacterial products into the host cytosol, L. pneumophila also activates cytosolic immunosurveillance pathways, thereby triggering robust proinflammatory responses that mediate the control of infection. Thus, the pulmonary cell types that L. pneumophila infects not only may act as an intracellular niche that facilitates its pathogenesis but also may contribute to the immune response against L. pneumophila. The identity of these host cells remains poorly understood. Here, we developed a strain of L. pneumophila producing a fusion protein consisting of β-lactamase fused to the T4SS-translocated effector RalF, which allowed us to track cells injected by the T4SS. Our data reveal that alveolar macrophages and neutrophils both are the primary recipients of T4SS-translocated effectors and harbor viable L. pneumophila during pulmonary infection of mice. Moreover, both alveolar macrophages and neutrophils from infected mice produced tumor necrosis factor and interleukin-1α in response to T4SS-sufficient, but not T4SS-deficient, L. pneumophila. Collectively, our data suggest that alveolar macrophages and neutrophils are both an intracellular reservoir for L. pneumophila and a source of proinflammatory cytokines that contribute to the host immune response against L. pneumophila during pulmonary infection.
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Affiliation(s)
- Alan M Copenhaver
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Cierra N Casson
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Hieu T Nguyen
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Thomas C Fung
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Matthew M Duda
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Craig R Roy
- Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sunny Shin
- Immunology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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140
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Shigella IpaH7.8 E3 ubiquitin ligase targets glomulin and activates inflammasomes to demolish macrophages. Proc Natl Acad Sci U S A 2014; 111:E4254-63. [PMID: 25246571 DOI: 10.1073/pnas.1324021111] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
When nucleotide-binding oligomerization domain-like receptors (NLRs) sense cytosolic-invading bacteria, they induce the formation of inflammasomes and initiate an innate immune response. In quiescent cells, inflammasome activity is tightly regulated to prevent excess inflammation and cell death. Many bacterial pathogens provoke inflammasome activity and induce inflammatory responses, including cell death, by delivering type III secreted effectors, the rod component flagellin, and toxins. Recent studies indicated that Shigella deploy multiple mechanisms to stimulate NLR inflammasomes through type III secretion during infection. Here, we show that Shigella induces rapid macrophage cell death by delivering the invasion plasmid antigen H7.8 (IpaH7.8) enzyme 3 (E3) ubiquitin ligase effector via the type III secretion system, thereby activating the NLR family pyrin domain-containing 3 (NLRP3) and NLR family CARD domain-containing 4 (NLRC4) inflammasomes and caspase-1 and leading to macrophage cell death in an IpaH7.8 E3 ligase-dependent manner. Mice infected with Shigella possessing IpaH7.8, but not with Shigella possessing an IpaH7.8 E3 ligase-null mutant, exhibited enhanced bacterial multiplication. We defined glomulin/flagellar-associated protein 68 (GLMN) as an IpaH7.8 target involved in IpaH7.8 E3 ligase-dependent inflammasome activation. This protein originally was identified through its association with glomuvenous malformations and more recently was described as a member of a Cullin ring ligase inhibitor. Modifying GLMN levels through overexpression or knockdown led to reduced or augmented inflammasome activation, respectively. Macrophages stimulated with lipopolysaccharide/ATP induced GLMN puncta that localized with the active form of caspase-1. Macrophages from GLMN(+/-) mice were more responsive to inflammasome activation than those from GLMN(+/+) mice. Together, these results highlight a unique bacterial adaptation that hijacks inflammasome activation via interactions between IpaH7.8 and GLMN.
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141
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Cunha LD, Zamboni DS. Recognition of Legionella pneumophila nucleic acids by innate immune receptors. Microbes Infect 2014; 16:985-90. [PMID: 25172398 DOI: 10.1016/j.micinf.2014.08.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 08/18/2014] [Indexed: 10/24/2022]
Abstract
Innate immune receptors evolved to sense conserved molecules that are present in microbes or are released during non-physiological conditions. Activation of these receptors is essential for early restriction of microbial infections and generation of adaptive immunity. Among the conserved molecules sensed by innate immune receptors are the nucleic acids, which are abundantly contained in all infectious organisms including virus, bacteria, fungi and parasites. In this review we focus in the innate immune proteins that function to sense nucleic acids from the intracellular bacterial pathogen Legionella pneumophila and the importance of these processes to the outcome of the infection.
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Affiliation(s)
- Larissa D Cunha
- Department of Cell Biology, Ribeirão Preto Medical School, University of São Paulo (FMRP/USP), Ribeirão Preto, SP 14049-900, Brazil
| | - Dario S Zamboni
- Department of Cell Biology, Ribeirão Preto Medical School, University of São Paulo (FMRP/USP), Ribeirão Preto, SP 14049-900, Brazil.
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142
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Mascarenhas DPA, Pereira MSF, Manin GZ, Hori JI, Zamboni DS. Interleukin 1 receptor-driven neutrophil recruitment accounts to MyD88-dependent pulmonary clearance of legionella pneumophila infection in vivo. J Infect Dis 2014; 211:322-30. [PMID: 25104770 DOI: 10.1093/infdis/jiu430] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Legionella pneumophila, the etiological agent of Legionnaires' disease, triggers activation of multiple innate immune pathways that lead to the restriction of bacterial replication in vivo. Despite the critical role for MyD88 in infection clearance, the receptors and mechanisms responsible for MyD88-mediated pulmonary bacterial clearance are still unclear. Here, we used flagellin mutants of L. pneumophila, which bypass the NAIP5/NLRC4-mediated restriction of bacterial replication, to assess the receptors involved in MyD88-mediated pulmonary bacterial clearance. By systematically comparing pulmonary clearance of L. pneumophila in C57BL/6 MyD88(-/-), TLR2(-/-), TLR3(-/-), TLR4(-/-), TLR9(-/-), IL-1R(-/-), and IL-18(-/-) mice, we found that, while the knockout of a single Toll-like receptor or interleukin 18 resulted only in minor impairment of bacterial clearance, deficiency in the interleukin 1 (IL-1) receptor led to a significant impairment. IL-1/MyD88-mediated pulmonary bacterial clearance occurs via processes involving the recruitment of neutrophils. Collectively, our data contribute to the understanding of the effector mechanisms involved in MyD88-mediated pulmonary bacterial clearance.
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Affiliation(s)
- Danielle P A Mascarenhas
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil
| | - Marcelo S F Pereira
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil
| | - Graziele Z Manin
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil
| | - Juliana I Hori
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil
| | - Dario S Zamboni
- Department of Cell Biology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil
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143
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Eltom S, Belvisi MG, Yew-Booth L, Dekkak B, Maher SA, Dubuis ED, Jones V, Fitzgerald KA, Birrell MA. TLR4 activation induces IL-1β release via an IPAF dependent but caspase 1/11/8 independent pathway in the lung. Respir Res 2014; 15:87. [PMID: 25085021 PMCID: PMC4347603 DOI: 10.1186/s12931-014-0087-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Accepted: 07/23/2014] [Indexed: 01/05/2023] Open
Abstract
Background The IL-1 family of cytokines is known to play an important role in inflammation therefore understanding the mechanism by which they are produced is paramount. Despite the recent plethora of publications dedicated to the study of these cytokines, the mechanism by which they are produced in the airway following endotoxin, Lipopolysaccharide (LPS), exposure is currently unclear. The aim was to determine the mechanism by which the IL-1 cytokines are produced after LPS inhaled challenge. Methods Mice were challenged with aerosolised LPS, and lung tissue and bronchiolar lavage fluid (BALF) collected. Targets were measured at the mRNA and protein level; caspase activity was determined using specific assays. Results BALF IL-1b/IL-18, but not IL-1a, was dependent on Ice Protease-Activating Factor (IPAF), and to a lesser extent Apoptosis-associated Speck-like protein containing a CARD (ASC). Interestingly, although we measured an increase in mRNA expression for caspase 1 and 11, we could not detect an increase in lung enzyme activity or a role for them in IL-1a/b production. Further investigations showed that whilst we could detect an increase in caspase 8 activity at later points in the time course (during resolution of inflammation), it appeared to play no role in the production of IL-1 cytokines in this model system. Conclusions TLR4 activation increases levels of BALF IL-1b/IL-18 via an IPAF dependent and caspase 1/11/8 independent pathway. Furthermore, it would appear that the presence of IL-1a in the BALF is independent of these pathways. This novel data sheds light on innate signalling pathways in the lung that control the production of these key inflammatory cytokines.
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Affiliation(s)
- Suffwan Eltom
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Maria G Belvisi
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Liang Yew-Booth
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Bilel Dekkak
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Sarah A Maher
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Eric D Dubuis
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Victoria Jones
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
| | - Kate A Fitzgerald
- University of Massachusetts, Division of Infectious Diseases & Immunology, Worcester, MA, 01605, USA.
| | - Mark A Birrell
- Respiratory Pharmacology, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
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144
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Lage SL, Longo C, Branco LM, da Costa TB, Buzzo CDL, Bortoluci KR. Emerging Concepts about NAIP/NLRC4 Inflammasomes. Front Immunol 2014; 5:309. [PMID: 25071770 PMCID: PMC4078251 DOI: 10.3389/fimmu.2014.00309] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 06/17/2014] [Indexed: 12/14/2022] Open
Abstract
Neuronal apoptosis inhibitory protein (NAIP)/NOD-like receptor (NLR) containing a caspase activating and recruitment domain (CARD) 4 (NLRC4) inflammasome complexes are activated in response to proteins from virulent bacteria that reach the cell cytosol. Specific NAIP proteins bind to the agonists and then physically associate with NLRC4 to form an inflammasome complex able to recruit and activate pro-caspase-1. NAIP5 and NAIP6 sense flagellin, component of flagella from motile bacteria, whereas NAIP1 and NAIP2 detect needle and rod components from bacterial type III secretion systems, respectively. Active caspase-1 mediates the maturation and secretion of the pro-inflammatory cytokines, IL-1β and IL-18, and is responsible for the induction of pyroptosis, a pro-inflammatory form of cell death. In addition to these well-known effector mechanisms, novel roles have been described for NAIP/NLRC4 inflammasomes, such as phagosomal maturation, activation of inducible nitric oxide synthase, regulation of autophagy, secretion of inflammatory mediators, antibody production, activation of T cells, among others. These effector mechanisms mediated by NAIP/NLRC4 inflammasomes have been extensively studied in the context of resistance of infections and the potential of their agonists has been exploited in therapeutic strategies to non-infectious pathologies, such as tumor protection. Thus, this review will discuss current knowledge about the activation of NAIP/NLRC4 inflammasomes and their effector mechanisms.
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Affiliation(s)
- Silvia Lucena Lage
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil
| | - Carla Longo
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil ; Departamento de Ciências Biológicas, Universidade Federal de São Paulo , São Paulo , Brazil
| | - Laura Migliari Branco
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil
| | - Thaís Boccia da Costa
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil
| | - Carina de Lima Buzzo
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil
| | - Karina Ramalho Bortoluci
- Centro de Terapia Celular e Molecular (CTC-Mol), Universidade Federal de São Paulo , São Paulo , Brazil ; Departamento de Ciências Biológicas, Universidade Federal de São Paulo , São Paulo , Brazil
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145
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NLRC4 expression in intestinal epithelial cells mediates protection against an enteric pathogen. Mucosal Immunol 2014; 7:775-85. [PMID: 24280936 PMCID: PMC4020766 DOI: 10.1038/mi.2013.95] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Accepted: 09/25/2013] [Indexed: 02/04/2023]
Abstract
The inflammasomes have an important role in connecting the detection of endogenous and microbial danger signals to caspase-1 activation and induction of protective immune responses. NLRC4 is a cytosolic NOD (nucleotide binding and oligomerization domain)-like receptor (NLR) that can trigger inflammasome formation in response to bacterial flagellin, an immunodominant antigen in the intestine. To characterize the role of NLRC4 in bacterially triggered intestinal inflammation, we used the murine pathogen Citrobacter rodentium, an extracellular, attaching/effacing bacterium similar to enterohemorrhagic Escherichia coli and enteropathogenic E. coli. Following infection with C. rodentium, we found that Nlrc4(-/-) mice developed more severe weight loss, increased bacterial colonization levels, and exacerbated intestinal inflammation compared with wild-type counterparts. Nlrc4(-/-) mice mounted robust adaptive immune responses but were unable to control early colonization by C. rodentium, suggesting that a defect in innate immunity was responsible. Experiments using bone marrow (BM) chimeras revealed that the protective effects of NLRC4 were dependent on its expression in non-hematopoietic cells, and quantitative PCR (Q-PCR) analyses revealed that NLRC4 was highly expressed in epithelial crypts but not in intestinal stroma. Thus, early NLRC4 sensing in intestinal epithelial cells regulates colonization by an extracellular bacterial pathogen and limits subsequent intestinal damage.
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146
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Brusselle GG, Provoost S, Bracke KR, Kuchmiy A, Lamkanfi M. Inflammasomes in respiratory disease: from bench to bedside. Chest 2014; 145:1121-1133. [PMID: 24798836 DOI: 10.1378/chest.13-1885] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The respiratory tract of human subjects is constantly exposed to harmful microbes and air pollutants. The immune system responds to these offenders to protect the host, but an unbalanced inflammatory response itself may promote tissue damage and ultimately lead to acute and chronic respiratory diseases. Deregulated inflammasome activation is emerging as a key modulator of respiratory infections and pathologic airway inflammation in patients with asthma, COPD, and pulmonary fibrosis. Assembly of these intracellular danger sensors in cells of the respiratory mucosa and alveolar compartment triggers a proinflammatory cell death mode termed pyroptosis and leads to secretion of bioactive IL-1β and IL-18. Here, we summarize and review the inflammasome and its downstream effectors as therapeutic targets for the treatment of respiratory diseases.
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Affiliation(s)
- Guy G Brusselle
- Laboratory for Translational Research of Obstructive Pulmonary Disease, Ghent University Hospital, Ghent, Belgium; Departments of Epidemiology and Respiratory Medicine, Erasmus MC, Rotterdam, The Netherlands.
| | - Sharen Provoost
- Laboratory for Translational Research of Obstructive Pulmonary Disease, Ghent University Hospital, Ghent, Belgium
| | - Ken R Bracke
- Laboratory for Translational Research of Obstructive Pulmonary Disease, Ghent University Hospital, Ghent, Belgium
| | - Anna Kuchmiy
- Department of Medical Protein Research, Flanders Institute for Biotechnology (VIB), Ghent, Belgium; Department of Biochemistry, Ghent University, Ghent, Belgium
| | - Mohamed Lamkanfi
- Laboratory for Translational Research of Obstructive Pulmonary Disease, Ghent University Hospital, Ghent, Belgium; Departments of Epidemiology and Respiratory Medicine, Erasmus MC, Rotterdam, The Netherlands
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147
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Edwardsiella tarda-Induced cytotoxicity depends on its type III secretion system and flagellin. Infect Immun 2014; 82:3436-45. [PMID: 24891103 DOI: 10.1128/iai.01065-13] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Many Gram-negative bacteria utilize a type III secretion system (T3SS) to translocate virulence proteins into host cells to cause diseases. In responding to infection, macrophages detect some of the translocated proteins to activate caspase-1-mediated cell death, called pyroptosis, and secretion of proinflammatory cytokines to control the infection. Edwardsiella tarda is a Gram-negative enteric pathogen that causes hemorrhagic septicemia in fish and both gastrointestinal and extraintestinal infections in humans. In this study, we report that the T3SS of E. tarda facilitates its survival and replication in murine bone marrow-derived macrophages, and E. tarda infection triggers pyroptosis of infected macrophages from mice and fish and increased secretion of the cytokine interleukin 1β in a T3SS-dependent manner. Deletion of the flagellin gene fliC of E. tarda results in decreased cytotoxicity for infected macrophages and does not attenuate its virulence in a fish model of infection, whereas upregulated expression of FliC in the fliC mutant strain reduces its virulence. We propose that the host controls E. tarda infection partially by detecting FliC translocated by the T3SS, whereas the bacteria downregulate the expression of FliC to evade innate immunity.
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148
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149
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Bast A, Krause K, Schmidt IHE, Pudla M, Brakopp S, Hopf V, Breitbach K, Steinmetz I. Caspase-1-dependent and -independent cell death pathways in Burkholderia pseudomallei infection of macrophages. PLoS Pathog 2014; 10:e1003986. [PMID: 24626296 PMCID: PMC3953413 DOI: 10.1371/journal.ppat.1003986] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2013] [Accepted: 01/25/2014] [Indexed: 12/19/2022] Open
Abstract
The cytosolic pathogen Burkholderia pseudomallei and causative agent of melioidosis has been shown to regulate IL-1β and IL-18 production through NOD-like receptor NLRP3 and pyroptosis via NLRC4. Downstream signalling pathways of those receptors and other cell death mechanisms induced during B. pseudomallei infection have not been addressed so far in detail. Furthermore, the role of B. pseudomallei factors in inflammasome activation is still ill defined. In the present study we show that caspase-1 processing and pyroptosis is exclusively dependent on NLRC4, but not on NLRP3 in the early phase of macrophage infection, whereas at later time points caspase-1 activation and cell death is NLRC4- independent. In the early phase we identified an activation pathway involving caspases-9, -7 and PARP downstream of NLRC4 and caspase-1. Analyses of caspase-1/11-deficient infected macrophages revealed a strong induction of apoptosis, which is dependent on activation of apoptotic initiator and effector caspases. The early activation pathway of caspase-1 in macrophages was markedly reduced or completely abolished after infection with a B. pseudomallei flagellin FliC or a T3SS3 BsaU mutant. Studies using cells transfected with the wild-type and mutated T3SS3 effector protein BopE indicated also a role of this protein in caspase-1 processing. A T3SS3 inner rod protein BsaK mutant failed to activate caspase-1, revealed higher intracellular counts, reduced cell death and IL-1β secretion during early but not during late macrophage infection compared to the wild-type. Intranasal infection of BALB/c mice with the BsaK mutant displayed a strongly decreased mortality, lower bacterial loads in organs, and reduced levels of IL-1β, myeloperoxidase and neutrophils in bronchoalveolar lavage fluid. In conclusion, our results indicate a major role for a functional T3SS3 in early NLRC4-mediated caspase-1 activation and pyroptosis and a contribution of late caspase-1-dependent and -independent cell death mechanisms in the pathogenesis of B. pseudomallei infection. Inflammasome activation is important for host defence against bacterial infection. Many gram-negative pathogens use secretion systems to inject bacterial proteins such as flagellin or structural components of the secretion machinery itself into the host cytosol leading to caspase-1 activation and pyroptotic cell death. However, little is known about the B. pseudomallei factors that trigger caspase-1 activation as well as downstream signalling pathways and effector mechanisms of caspase-1. Here, we identified the B. pseudomallei T3SS3 inner rod protein BsaK as an early activator of caspase-1-dependent cell death and IL-1β secretion in primary macrophages and as a virulence factor in murine melioidosis. We could show that upon infection of macrophages, caspase-7 is activated downstream of the NLRC4/caspase-1 inflammasome and requires caspase-9 processing. Although caspase-7 was essential for cleavage of the DNA damage sensor PARP during pyroptosis, it did neither contribute to cytokine production nor B. pseudomallei growth restriction by promoting early macrophage death. In addition to a rapid NLRC4/caspase-1- dependent induction of pyroptosis in wild-type macrophages, we observed a delayed activation of classical apoptosis in macrophages lacking caspase-1/11. Thus, initiation of different cell death pathways seems to be an effective strategy to limit intracellular B. pseudomallei infection.
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Affiliation(s)
- Antje Bast
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Kathrin Krause
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Imke H. E. Schmidt
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Matsayapan Pudla
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
- Department of Microbiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Stefanie Brakopp
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Verena Hopf
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Katrin Breitbach
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
| | - Ivo Steinmetz
- Friedrich Loeffler Institute of Medical Microbiology, University Medicine Greifswald, Greifswald, Germany
- * E-mail:
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Gaide O, Hoffman HM. Insight into the inflammasome and caspase-activating mechanisms. Expert Rev Clin Immunol 2014; 4:61-77. [DOI: 10.1586/1744666x.4.1.61] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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