Journal Article•
DDX41 recognizes bacterial secondary messengers cyclic di-GMP and cyclic di-AMP to activate a type I interferon immune response (P1375)
TL;DR: In this article, the authors identify the helicase, DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41) as the pattern recognition receptor (PRR) that senses both cyclic-di-GMP and cyclic -di-AMP.
Abstract: Cytosolic detection of bacterially derived secondary messengers cyclic-di-GMP (c-di-GMP) or cyclic -di-AMP (c-di-AMP) by the host immune system activates an innate immune response characterized by the induction of type I interferons (IFNs) Induction of IFN by c-di-GMP or c-di-AMP has been shown to be dependent on a stimulator of IFN genes-TANK binding kinase 1-IFN regulatory factor 3 (STING-TBK1-IRF3) signaling axis Although STING has been shown to interact with c-di-GMP, an upstream sensor of these cyclic dinucleotides is unknown Here we identify the helicase, DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41) as the pattern recognition receptor (PRR) that senses both c-di-GMP and c-di-AMP DDX41 specifically and directly interacts with c-di-GMP Knockdown of DDX41 via shRNA in murine or human immune cells inhibits the induction of innate immune genes and results in defective STING, TBK1 and IRF3 activation in response to c-di-GMP or c-di-AMP Our findings suggest a mechanism whereby c-di-GMP and c-di-AMP molecules are detected by the DDX41 PRR, which complexes with the STING adaptor to signal to TBK1-IRF3 and activate the IFN response
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TL;DR: Recent advances in understanding the mechanism of nucleic acid sensing and signaling in the cytosol of mammalian cells as well as the emerging role of cytosolic nucleic acids in autoimmunity are reviewed.
Abstract: The innate immune system utilizes pattern-recognition receptors (PRRs) to detect the invasion of pathogens and initiate host antimicrobial responses such as the production of type I interferons and proinflammatory cytokines. Nucleic acids, which are essential genetic information carriers for all living organisms including viral, bacterial, and eukaryotic pathogens, are major structures detected by the innate immune system. However, inappropriate detection of self nucleic acids can result in autoimmune diseases. PRRs that recognize nucleic acids in cells include several endosomal members of the Toll-like receptor family and several cytosolic sensors for DNA and RNA. Here, we review the recent advances in understanding the mechanism of nucleic acid sensing and signaling in the cytosol of mammalian cells as well as the emerging role of cytosolic nucleic acids in autoimmunity.
920 citations
TL;DR: The cGAS–STING pathway forms a major DNA-sensing mechanism in mammalian cells and emerging evidence of its role in monogenic inflammatory diseases and cancer and new therapeutic opportunities is highlighted.
Abstract: The detection of pathogens through nucleic acid sensors is a defining principle of innate immunity. RNA-sensing and DNA-sensing receptors sample subcellular compartments for foreign nucleic acids and, upon recognition, trigger immune signalling pathways for host defence. Over the past decade, our understanding of how the recognition of nucleic acids is coupled to immune gene expression has advanced considerably, particularly for the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signalling effector stimulator of interferon genes (STING), as well as the molecular components and regulation of this pathway. Moreover, the ability of self-DNA to engage cGAS has emerged as an important mechanism fuelling the development of inflammation and implicating the cGAS-STING pathway in human inflammatory diseases and cancer. This detailed mechanistic and biological understanding is paving the way for the development and clinical application of pharmacological agonists and antagonists in the treatment of chronic inflammation and cancer.
624 citations
TL;DR: One of the most exciting developments in the field of bacterial pathogenesis in recent years is the discovery that many pathogens utilize complex nanomachines to deliver bacterially encoded effector proteins into target eukaryotic cells.
Abstract: One of the most exciting developments in the field of bacterial pathogenesis in recent years is the discovery that many pathogens utilize complex nanomachines to deliver bacterially encoded effector proteins into target eukaryotic cells. These effector proteins modulate a variety of cellular functions for the pathogen's benefit. One of these protein-delivery machines is the type III secretion system (T3SS). T3SSs are widespread in nature and are encoded not only by bacteria pathogenic to vertebrates or plants but also by bacteria that are symbiotic to plants or insects. A central component of T3SSs is the needle complex, a supramolecular structure that mediates the passage of the secreted proteins across the bacterial envelope. Working in conjunction with several cytoplasmic components, the needle complex engages specific substrates in sequential order, moves them across the bacterial envelope, and ultimately delivers them into eukaryotic cells. The central role of T3SSs in pathogenesis makes them great targets for novel antimicrobial strategies.
437 citations
TL;DR: Stimulator of IFN gene (STING) is identified as a direct receptor for DMXAA leading to TANK-binding kinase 1 and IFN regulatory factor 3 signaling, revealing an unexpected species-specific role for STING as a receptor for an anticancer drug.
Abstract: Vascular disrupting agents such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA) represent a novel approach for cancer treatment. DMXAA has potent antitumor activity in mice and, despite significant preclinical promise, failed human clinical trials. The antitumor activity of DMXAA has been linked to its ability to induce type I IFNs in macrophages, although the molecular mechanisms involved are poorly understood. In this study, we identify stimulator of IFN gene (STING) as a direct receptor for DMXAA leading to TANK-binding kinase 1 and IFN regulatory factor 3 signaling. Remarkably, the ability to sense DMXAA was restricted to murine STING. Human STING failed to bind to or signal in response to DMXAA. Human STING also failed to signal in response to cyclic dinucleotides, conserved bacterial second messengers known to bind and activate murine STING signaling. Collectively, these findings detail an unexpected species-specific role for STING as a receptor for an anticancer drug and uncover important insights that may explain the failure of DMXAA in clinical trials for human cancer.
334 citations
TL;DR: This review presents the evidence for the various interferon-inducing DNA receptors proposed to date, and examines the hypotheses that might explain why so many different receptors appear to be involved in the innate immune recognition of intracellular DNA.
229 citations
References
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TL;DR: The mammalian immune system has innate and adaptive components, which cooperate to protect the host against microbial infections, and recent progress brings us closer to an integrated view of the immune system and its function in host defence.
Abstract: The mammalian immune system has innate and adaptive components, which cooperate to protect the host against microbial infections. The innate immune system consists of functionally distinct 'modules' that evolved to provide different forms of protection against pathogens. It senses pathogens through pattern-recognition receptors, which trigger the activation of antimicrobial defences and stimulate the adaptive immune response. The adaptive immune system, in turn, activates innate effector mechanisms in an antigen-specific manner. The connections between the various immune components are not fully understood, but recent progress brings us closer to an integrated view of the immune system and its function in host defence.
2,656 citations
TL;DR: It is shown that STING (stimulator of interferon genes) is critical for the induction of IFN by non-CpG intracellular DNA species produced by various DNA pathogens after infection.
Abstract: The innate immune system is critical for the early detection of invading pathogens and for initiating cellular host defence countermeasures, which include the production of type I interferon (IFN). However, little is known about how the innate immune system is galvanized to respond to DNA-based microbes. Here we show that STING (stimulator of interferon genes) is critical for the induction of IFN by non-CpG intracellular DNA species produced by various DNA pathogens after infection. Murine embryonic fibroblasts, as well as antigen presenting cells such as macrophages and dendritic cells (exposed to intracellular B-form DNA, the DNA virus herpes simplex virus 1 (HSV-1) or bacteria Listeria monocytogenes), were found to require STING to initiate effective IFN production. Accordingly, Sting-knockout mice were susceptible to lethal infection after exposure to HSV-1. The importance of STING in facilitating DNA-mediated innate immune responses was further evident because cytotoxic T-cell responses induced by plasmid DNA vaccination were reduced in Sting-deficient animals. In the presence of intracellular DNA, STING relocalized with TANK-binding kinase 1 (TBK1) from the endoplasmic reticulum to perinuclear vesicles containing the exocyst component Sec5 (also known as EXOC2). Collectively, our studies indicate that STING is essential for host defence against DNA pathogens such as HSV-1 and facilitates the adjuvant activity of DNA-based vaccines.
2,042 citations
TL;DR: In this review, a comprehensively review the recent progress in the field of PAMP recognition by PRRs and the signaling pathways activated byPRRs.
Abstract: Microbial infection initiates complex interactions between the pathogen and the host. Pathogens express several signature molecules, known as pathogen-associated molecular patterns (PAMPs), which are essential for survival and pathogenicity. PAMPs are sensed by evolutionarily conserved, germline-encoded host sensors known as pathogen recognition receptors (PRRs). Recognition of PAMPs by PRRs rapidly triggers an array of anti-microbial immune responses through the induction of various inflammatory cytokines, chemokines and type I interferons. These responses also initiate the development of pathogen-specific, long-lasting adaptive immunity through B and T lymphocytes. Several families of PRRs, including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs), and DNA receptors (cytosolic sensors for DNA), are known to play a crucial role in host defense. In this review, we comprehensively review the recent progress in the field of PAMP recognition by PRRs and the signaling pathways activated by PRRs.
1,896 citations
TL;DR: IFI16 (p204) is the first PYHIN protein to their knowledge shown to be involved in IFN-β induction and forms a new family of innate DNA sensors the authors call 'AIM2-like receptors' (ALRs).
Abstract: The detection of intracellular microbial DNA is critical to appropriate innate immune responses; however, knowledge of how such DNA is sensed is limited. Here we identify IFI16, a PYHIN protein, as an intracellular DNA sensor that mediates the induction of interferon-β (IFN-β). IFI16 directly associated with IFN-β-inducing viral DNA motifs. STING, a critical mediator of IFN-β responses to DNA, was recruited to IFI16 after DNA stimulation. Lowering the expression of IFI16 or its mouse ortholog p204 by RNA-mediated interference inhibited gene induction and activation of the transcription factors IRF3 and NF-κB induced by DNA and herpes simplex virus type 1 (HSV-1). IFI16 (p204) is the first PYHIN protein to our knowledge shown to be involved in IFN-β induction. Thus, the PYHIN proteins IFI16 and AIM2 form a new family of innate DNA sensors we call 'AIM2-like receptors' (ALRs).
1,440 citations
TL;DR: This Review focuses on emerging principles of c-di-GMP signalling using selected systems in different bacteria as examples.
Abstract: On the stage of bacterial signal transduction and regulation, bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) has long played the part of Sleeping Beauty. c-di-GMP was first described in 1987, but only recently was it recognized that the enzymes that 'make and break' it are not only ubiquitous in the bacterial world, but are found in many species in huge numbers. As a key player in the decision between the motile planktonic and sedentary biofilm-associated bacterial 'lifestyles', c-di-GMP binds to an unprecedented range of effector components and controls diverse targets, including transcription, the activities of enzymes and larger cellular structures. This Review focuses on emerging principles of c-di-GMP signalling using selected systems in different bacteria as examples.
1,337 citations