Activation of the stimulator of interferon genes (STING) pathway by microbial or self-DNA, as well as cyclic dinucleotides (CDNs), results in the induction of numerous genes that suppress pathogen ...replication and facilitate adaptive immunity. However, sustained gene transcription is rigidly prevented to avoid lethal STING-dependent proinflammatory disease by mechanisms that remain unknown. We demonstrate here that, after autophagy-dependent STING delivery of TANK-binding kinase 1 (TBK1) to endosomal/lysosomal compartments and activation of transcription factors interferon regulatory factor 3 (IRF3) and NF-κB, STING is subsequently phosphorylated by serine/threonine UNC-51-like kinase (ULK1/ATG1), and IRF3 function is suppressed. ULK1 activation occurred following disassociation from its repressor AMP activated protein kinase (AMPK) and was elicited by CDNs generated by the cGAMP synthase, cGAS. Thus, although CDNs may initially facilitate STING function, they subsequently trigger negative-feedback control of STING activity, thus preventing the persistent transcription of innate immune genes.
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•Cytosolic DNA-generated cyclic dinucleotides facilitate innate signaling via STING•Cyclic dinucleotides subsequently activate the AMPK/ULK1 (ATG1) pathway•Activated ULK1 targets STING on serine 366, suppressing IRF3 activity•Phosphorylation of STING averts sustained production of inflammatory cytokines
Cytosolic DNA-derived cyclic dinucleotides, known to activate the STING innate immune signaling pathway, are shown here to be required to shut down STING activity through a mechanism dependent on ULK1-mediated phosphorylation of STING, preventing sustained STING activation that could result in pathological proinflammatory responses.
The rapid detection of microbial agents is essential for the effective initiation of host defence mechanisms against infection. Understanding how cells detect cytosolic DNA to trigger innate immune ...gene transcription has important implications - not only for comprehending the immune response to pathogens but also for elucidating the causes of autoinflammatory disease involving the sensing of self-DNA and the generation of effective antitumour adaptive immunity. The discovery of the STING (stimulator of interferon genes)-controlled innate immune pathway, which mediates cytosolic DNA-induced signalling events, has recently provided important insights into these processes, opening the way for the development of novel immunization regimes, as well as therapies to treat autoinflammatory disease and cancer.
Highlights • Host responses to pathogen-derived DNA or CDNs are STING dependent. • Signaling downstream of STING involves genes involved in the autophagy pathway. • STING may control inflammatory ...conditions associated with responses to self-DNA. • Understanding STING function may facilitate vaccine development.
STING (stimulator of interferon genes) is known to control the induction of innate immune genes in response to the recognition of cytosolic DNA species, including the genomes of viruses such as ...herpes simplex virus 1 (HSV-1). However, while STING is essential for protection of the host against numerous DNA pathogens, sustained STING activity can lead to lethal inflammatory disease. It is known that STING utilizes interferon regulatory factor 3 (IRF3) and nuclear factor κB (NF-κB) pathways to exert its effects, although the signal transduction mechanisms remain to be clarified fully. Here we demonstrate that in addition to the activation of these pathways, potent induction of the Jun N-terminal protein kinase/stress-activated protein kinase (JNK/SAPK) pathway was similarly observed in response to STING activation by double-stranded DNA (dsDNA). Furthermore, TANK-binding kinase 1 (TBK1) associated with STING was found to facilitate dsDNA-mediated canonical activation of NF-κB as well as IRF3 to promote proinflammatory gene transcription. The triggering of NF-κB function was noted to require TRAF6 activation. Our findings detail a novel dsDNA-mediated NF-κB activation pathway facilitated through a STING-TRAF6-TBK1 axis and suggest a target for therapeutic intervention to plausibly stimulate antiviral activity or, alternatively, avert dsDNA-mediated inflammatory disease.
The IKK complex, which is composed of two catalytic subunits, IKKα and IKKβ, has been suggested to be essential for the activation of canonical NF-κB signaling in response to various stimuli, including cytokines (e.g., interleukin-1α IL-1α and tumor necrosis factor alpha TNF-α), Toll-like receptor (TLR) ligands (e.g., lipopolysaccharide LPS), and dsRNAs derived from viruses, or a synthetic analog. STING has been identified as a critical signaling molecule required for the detection of cytosolic dsDNAs derived from pathogens and viruses. However, little is known about how cytosolic dsDNA triggers NF-κB signaling. In the present study, we demonstrate that TBK1, identified as an IKK-related kinase, may predominantly control the activation of NF-κB in response to dsDNA signaling via STING through the IKKαβ activation loop. Thus, our results establish TBK1 as a downstream kinase controlling dsDNA-mediated IRF3 and NF-κB signaling dependent on STING.
The innate immune system is responsible for detecting microbial invasion of the cell and for stimulating host defense countermeasures. These anti‐pathogen procedures include the transcriptional ...activation of powerful antiviral genes such as the type I interferons (IFNs) or the triggering of inflammatory responses through interleukin‐1 (IL‐1) production. Over the past decade, key cellular sensors responsible for triggering innate immune signaling pathways and host defense have started to be resolved and include the Toll‐like receptor (TLR), RIG‐I‐like helicase, and the cytoplasmic nucleotide‐binding oligermerization domain‐like receptor families. These sensors recognize non‐self pathogen‐associated molecular patterns such as microbial lipopolysaccharides and nucleic acids. For example, TLR9 has evolved to detect CpG DNA commonly found in bacteria and viruses and to initiate the production of IFN and other cytokines. In contrast, AIM2 (absent in melanoma 2) has been shown to be essential for mediating inflammatory responses involving IL‐1β following the sensing of microbial DNA. Recently, a molecule referred to as STING (stimulator of IFN genes) was demonstrated as being vital for recognizing cytoplasmic DNA and for activating the production of innate immune genes in response to a variety of DNA pathogens and even certain RNA viruses. Comprehending the mechanisms of intracellular DNA‐mediated innate immune signaling may lead to the design of new adjuvant concepts that will facilitate vaccine development and may provide important information into the origins of autoimmune disease.
How the cell recognizes cytosolic DNA including DNA-based microbes to trigger host-defense-related gene activation remains to be fully resolved. Here, we demonstrate that STING (stimulator of ...interferon genes), an endoplasmic reticulum translocon-associated transmembrane protein, acts to detect cytoplasmic DNA species. STING homodimers were able to complex with self- (apoptotic, necrotic) or pathogen-related ssDNA and dsDNA and were indispensible for HSV-1-mediated transcriptional activation of a wide array of innate immune and proinflammatory genes in addition to type I IFN. Our data indicate that STING instigates cytoplasmic DNA-mediated cellular defense gene transcription and facilitates adoptive responses that are required for protection of the host. In contrast, chronic STING activation may manifest inflammatory responses and possibly autoimmune disease triggered by self-DNA.
► Activation of cytosolic DNA signaling by STING
The first line of host defense against infectious agents involves activation of innate immune signaling pathways that recognize specific pathogen-associated molecular patterns (PAMPs). Key triggers ...of innate immune signaling are now known to include microbial-specific nucleic acid, which is rapidly detected in the cytosol of the cell. For example, RIG-I-like receptors (RLRs) have evolved to detect viral RNA species and to activate the production of host defense molecules and cytokines that stimulate adaptive immune responses. In addition, host defense countermeasures, including the production of type I interferons (IFNs), can also be triggered by microbial DNA from bacteria, viruses and perhaps parasites and are regulated by the cytosolic sensor, stimulator of interferon genes (STING). STING-dependent signaling is initiated by cyclic dinucleotides (CDNs) generated by intracellular bacteria following infection. CDNs can also be synthesized by a cellular synthase, cGAS, following interaction with invasive cytosolic self-DNA or microbial DNA species. The importance of STING signaling in host defense is evident since numerous pathogens have developed strategies to prevent STING function. Here, we review the relevance of STING-controlled innate immune signaling in host defense against pathogen invasion, including microbial endeavors to subvert this critical process.
The early detection of microbes is the responsibility of the innate immune system which has evolved to sense pathogen derived molecules such as lipopolysaccharides and non-self nucleic acid, to ...trigger host defense countermeasures. These sensors include the RIG-I-like helicase (RLH) family that specifically recognizes viral RNA, as well as the cytoplasmic, nucleotide binding oligermerization domain (NOD)-like receptor and Toll-like receptor (TLR) pathways that sense a variety of microbial derived molecules. Comprehending how the cell senses foreign DNA, generated by certain viruses, bacteria and possibly parasites has proven elusive but is of significant importance since such information could shed insight into the causes of microbial related disease, including viral associated cancers and autoimmune disorders. Plasmacytoid dendritic cells are known to utilize TLR9 to detect pathogen-associated DNA and to trigger the production of type I interferon (IFN), as well as other cytokines, although alternate key DNA detecting sensors remain to be identified. Recently however, a molecule referred to as AIM2 (absent in melanoma 2) was found to be essential for mediating inflammatory reactions triggered by cytoplasmic DNA. In addition, an endoplasmic reticulum associated protein referred to as STING (for stimulator of interferon genes) was demonstrated as being pivotal for facilitating IFN production in response to intracellular DNA and a variety of DNA pathogens. Here, we review recent discoveries relating to the detection of foreign DNA, including the importance of the STING and AIM2 and the activation of innate signaling pathways.
The type I interferon (IFN) response initiated by detection of nucleic acids is important for antiviral defense but is also associated with specific autoimmune diseases. Mutations in the human 3′ ...repair exonuclease 1 (Trex1) gene cause Aicardi-Goutières syndrome (AGS), an IFN-associated autoimmune disease. However, the source of the type I IFN response and the precise mechanisms of disease in AGS remain unknown. Here, we demonstrate that Trex1 is an essential negative regulator of the STING-dependent antiviral response. We used an in vivo reporter of IFN activity in Trex1-deficient mice to localize the initiation of disease to nonhematopoietic cells. These IFNs drove T cell-mediated inflammation and an autoantibody response that targeted abundant, tissue-restricted autoantigens. However, B cells contributed to mortality independently of T cell-mediated tissue damage. These findings reveal a stepwise progression of autoimmune disease in Trex1-deficient mice, with implications for the treatment of AGS and related disorders.
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► Trex1 is an essential negative regulator of the STING-dependent antiviral response ► Nonhematopoietic cells initiate IFN-dependent autoimmunity in Trex1-deficient mice ► T cells are necessary and sufficient for autoimmune inflammation in Trex1−/− mice ► B cells contribute to mortality in Trex1−/− mice independently of inflammation
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