Alternative titles; symbols
HGNC Approved Gene Symbol: STING1
SNOMEDCT: 711164003;
Cytogenetic location: 5q31.2 Genomic coordinates (GRCh38) : 5:139,475,533-139,482,758 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 5q31.2 | STING-associated vasculopathy, infantile-onset | 615934 | Autosomal dominant | 3 |
The TMEM173 gene, also known as STING1, encodes an adaptor protein that mediates the production of beta-interferon (IFNB1; 147640). STING is a transmembrane protein in the endoplasmic reticulum (ER), where it forms a homodimer in response to the presence of cytosolic dsDNA (summary by Liu et al., 2014).
Using a functional screen to identify genes able to induce expression of IFN-beta, Ishikawa and Barber (2008) cloned STING, which they designated STING. The deduced 379-amino acid protein has a calculated molecular mass of 42.2 kD. It has 5 putative N-terminal transmembrane domains, a signal cleavage site in the first transmembrane domain, and a leucine-rich region that overlaps the first 4 transmembrane domains. Northern blot analysis detected STING expression in all tissues examined. Confocal microscopy and fractionation analysis of human embryonic kidney 293 cells revealed that STING predominantly associated with the ER. Western blot analysis of 293 cells detected endogenous STING at an apparent molecular mass of 42 kD.
Jin et al. (2008) cloned mouse Tmem173, which they called Mpys based on its N-terminal met-pro-tyr-ser amino acid sequence. They identified human MYPS by database analysis. Human and mouse MYPS share about 80% homology, and both contain 4 predicted N-terminal transmembrane domains and an extended C-terminal tail containing multiple signaling motifs, including immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Confocal microscopy showed that some Mpys localized to the cell surface of mouse B-lymphoma cells, but a large proportion localized to mitochondria. Western blot analysis of human and mouse cells showed higher MPYS expression in splenocytes than in thymocytes, and MYPS was also present in dendritic cells. MPYS was expressed throughout the B-cell lineage prior to the plasma cell stage, but it was expressed at highest levels in mature B cells. Cross-linking experiments suggested that Mpys exists as an 80-kD dimer within mouse cells.
Liu et al. (2014) found expression of the STING gene in human skin endothelial cells, alveolar type 2 pneumocytes, bronchial epithelium, and alveolar macrophages.
Cryoelectron Microscopy
Shang et al. (2019) presented the cryoelectron microscopy structures of full-length STING from human and chicken in the inactive dimeric state (about 80 kD in size), as well as cGAMP-bound chicken STING in both the dimeric and tetrameric states. The structures showed that the transmembrane and cytoplasmic regions interact to form an integrated, domain-swapped dimeric assembly. Closure of the ligand-binding domain, induced by cGAMP, leads to a 180-degree rotation of the ligand-binding domain relative to the transmembrane domain. This rotation is coupled to a conformational change in a loop on the side of the ligand-binding domain dimer, which leads to the formation of the STING tetramer and higher-order oligomers through side-by-side packing. Shang et al. (2019) concluded that this model of STING oligomerization and activation is supported by their structure-based mutational analyses.
Zhang et al. (2019) presented the cryoelectron microscopy structure of human TBK1 (604834) in complex with cGAMP-bound, full-length chicken STING. The structure revealed that the C-terminal tail of STING adopts a beta-strand-like conformation and inserts into a groove between the kinase domain of one TBK1 subunit and the scaffold and dimerization domain of the second subunit in the TBK1 dimer. In this binding mode, the phosphorylation site ser366 in the STING tail cannot reach the kinase-domain active site of bound TBK1, which suggests that STING phosphorylation by TBK1 requires the oligomerization of both proteins. Mutational analyses validated the interaction mode between TBK1 and STING and supported a model in which high-order oligomerization of STING and TBK1, induced by cGAMP, leads to STING phosphorylation by TBK1.
Crystal Structure
Zhao et al. (2019) showed that a conserved PLPLRT/SD motif within the C-terminal tail of STING mediates the recruitment and activation of TBK1. Crystal structures of TBK1 bound to STING revealed that the PLPLRT/SD motif binds to the dimer interface of TBK1. Cell-based studies confirmed that the direct interaction between TBK1 and STING is essential for induction of IFN-beta after cGAMP stimulation. Zhao et al. (2019) showed that full-length STING oligomerizes after it binds cGAMP, and highlighted this as an essential step in the activation of STING-mediated signaling.
Hartz (2008) mapped the STING gene to chromosome 5q31.2 based on an alignment of the STING sequence (GenBank BC047779) with the genomic sequence (build 36.1).
Ishikawa and Barber (2008) found that STING activated both the NF-kappa-B (see 164011) and IRF3 (603734) transcription pathways to induce expression of IFN-alpha (IFNA1; 147660) and IFN-beta and exert a potent antiviral effect. Yeast 2-hybrid and coimmunoprecipitation studies showed that STING interacted with RIGI (DDX58; 609631) and TRAP-beta (SSR2; 600867), a member of the translocon-associated protein (TRAP) complex required for translocation of nascent proteins across the ER membrane. Ablation of both TRAP-beta and SEC61-beta (SEC61B; 609214) via RNA interference inhibited the ability of STING to stimulate IFN-beta expression. Ishikawa and Barber (2008) concluded that STING and the translocon are involved in innate immune signaling.
Jin et al. (2008) found that antibody cross-linking of major histocompatibility complex (MHC) II (see 142857) in a mouse B-lymphoma cell line resulted in Mpys tyrosine phosphorylation, followed by association of Mpys with the phosphatases Shp1 (PTPN6; 176883) and Ship (INPP5D; 601582) and cell death via Erk (see MAPK3; 601795) activation. Knockdown of Mpys expression inhibited Erk activation and cell death in response to MHC II activation. Aggregation of Mpys in the absence of MHC II activation also led to cell death.
Ishikawa et al. (2009) demonstrated that STING 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; 604834) from the endoplasmic reticulum to perinuclear vesicles containing the exocyst component EXOC2 (Sec5; 615329). Ishikawa et al. (2009) concluded that STING is essential for host defense against DNA pathogens such as HSV-1 and facilitates the adjuvant activity of DNA-based vaccines.
Using a yeast 2-hybrid screen, Zhong et al. (2009) identified RNF5 (602677) as an MITA-interacting protein. Coimmunoprecipitation and mutation analyses showed that the RNF5 C terminus was required for the interaction, which was induced by viral infection. RNF5 ubiquitinated MITA at lys150, leading to MITA degradation and inhibition of virus-induced IRF3 activation, IFNB1 expression, and cellular antiviral response. Zhong et al. (2009) concluded that RNF5 negatively regulates virus-induced signaling by targeting MITA for ubiquitination and degradation at the mitochondria.
Sun et al. (2009) found that overexpression of STING, which they called ERIS, led to high type I IFN induction and expression of IFN-regulated genes. Suppression of ERIS via RNA interference reduced IFNB induction and increased susceptibility to viral infection. Fluorescence microscopy demonstrated perinuclear expression and localization of ERIS to the ER membrane, and mutation analysis revealed that RYR and RIR motifs in ERIS were necessary for ER retention. Coimmunoprecipitation experiments showed that ERIS could interact with TBK1 and IKKI (IKBKE; 605048), but not IRF3. Overexpression of TBK1 or IKKI, but not other kinases related to NFKB activation, caused ERIS modification, including dimerization and possibly hyperphosphorylation. Dimerization of ERIS, which was mediated through its transmembrane domains, led to type I IFN production, suggesting that dimerization is necessary for IFN production and antiviral activity. Sun et al. (2009) concluded that ERIS is an essential innate immune mediator.
Using coimmunoprecipitation experiments with virus-infected or transfected human 293 cells, Li et al. (2009) showed that ISG56 (147690) interacted with MITA. ISG56 overexpression inhibited virus-triggered activation of interferon-stimulated regulatory element (ISRE), a conserved enhancer motif recognized by activated IRF3, and the IFNB promoter. In contrast, ISG56 knockdown potentiated virus-induced activation of ISRE, NFKB, and IFNB. ISG56 interaction with MITA inhibited MITA interaction with VISA (MAVS; 609676) and TBK1. Li et al. (2009) proposed that ISG56 is a mediator of negative-feedback regulation of virus-triggered induction of type I IFNs and cellular antiviral responses.
Burdette et al. (2011) reported evidence that STING itself is an innate immune sensor of cyclic dinucleotides. They demonstrated that STING binds directly to radiolabelled cyclic diguanylate monophosphate (c-di-GMP), and showed that unlabeled cyclic dinucleotides, but not other nucleotides or nucleic acids, compete with c-di-GMP for binding to STING. Furthermore, Burdette et al. (2011) identified mutations in STING that selectively affect the response to cyclic dinucleotides without affecting the response to DNA. Thus, Burdette et al. (2011) concluded that STING seems to function as a direct sensor of cyclic dinucleotides, in addition to its established role as a signaling adaptor in the IFN response to cytosolic DNA.
Using human and mouse cells, Chen et al. (2011) found that viruses or cytoplasmic nucleic acids triggered STING to recruit STAT6 (601512) to the endoplasmic reticulum, where STAT6 was phosphorylated on ser407 by TBK1 and on tyr641 in a Janus kinase (see 147795)-independent manner. Phosphorylated STAT6 dimerized and translocated to the nucleus to induce genes involved in cell homing. Unlike the cell-type specific role of STAT6 in cytokine signaling, virus-induced STAT6 activation was detected in all cell types tested. Mice lacking Stat6 were susceptible to virus infection. Chen et al. (2011) concluded that STAT6 mediates immune signaling in response to cytokines at the plasma membrane and to virus infection at the endoplasmic reticulum.
Cytosolic DNA induces interferons through the production of cyclic guanosine monophosphate-adenosine monophosphate (cyclic GMP-AMP, or cGAMP), which binds to and activates the adaptor protein STING. Through biochemical fractionation and quantitative mass spectrometry, Sun et al. (2013) identified a cGAMP synthase (cGAS; 613973), which belongs to the nucleotidyltransferase family. Overexpression of cGAS activated the transcription factor IRF3 (603734) and induced interferon-beta (IFNB; 147640) in a STING-dependent manner. Knockdown of cGAS inhibited IRF3 activation and interferon-beta induction by DNA transfection or DNA virus infection. cGAS bound to DNA in the cytoplasm and catalyzed cGAMP synthesis. Sun et al. (2013) concluded that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP.
Wu et al. (2013) found that mammalian cytosolic extracts synthesized cGAMP in vitro from adenosine triphosphate (ATP) and guanosine triphosphate (GTP) in the presence of DNA but not RNA. DNA transfection or DNA virus infection of mammalian cells also triggered cGAMP production. cGAMP bound to STING, leading to the activation of IRF3 and induction of interferon-beta. Thus, Wu et al. (2013) concluded that cGAMP is present in metazoans and functions as an endogenous second messenger that triggers interferon production in response to cytosolic DNA.
Ablasser et al. (2013) found in murine and human cells that cGAS-synthesized cGAMP (2-prime-5-prime) is transferred from producing cells to neighboring cells through gap junctions, where it promotes STING activation and thus antiviral immunity independently of type I interferon signaling. In line with the limited cargo specificity of connexins, the proteins that assemble gap junction channels, most connexins tested were able to confer this bystander immunity, thus indicating a broad physiologic relevance of this local immune collaboration. Collectively, the observations of Ablasser et al. (2013) identified cGAS-triggered cGAMP (2-prime-5-prime) transfer as a novel host strategy that serves to rapidly convey antiviral immunity in a transcription-independent, horizontal manner.
You et al. (2013) observed enhanced susceptibility to West Nile Virus (WNV; see 610379), a single-stranded RNA virus, in mice with a loss-of-function mutation in Sting. Infection of HeLa cells with WNV, followed by immunoprecipitation analysis, identified ELF4 (300775) as an interacting partner of STING. Transfection of human or mouse ELF4 into human embryonic kidney cells induced expression of type I IFN (e.g., IFNB). Viral infection or stimulation with IFN induced ELF4 expression, which reduced viral replication, in human cells. Infection of Elf4 -/- mice with WNV resulted in enhanced viral burden and lethality and less circulating type I IFN compared with wildtype mice. Transfer of natural killer (NK) or NKT cells did not enable resistance to WNV infection. Mechanistic studies in human cells showed that ELF4 was involved in TLR signaling, was activated in parallel with IRFs after phosphorylation by TBK1, and bound to type I IFN promoters. You et al. (2013) concluded that ELF4 is a type of IRF that activates the innate immune response by promoting production of type I IFNs.
Zhang et al. (2014) found that Nlrc3 (615648) reduced Sting-dependent innate immune function in mouse cells in response to cytosolic DNA, cyclic di-GMP, and DNA viruses. Mouse embryonic fibroblasts lacking Nlrc3 produced more Ifnb and Il6 (147620) in response to cyclic di-GMP-producing bacteria. Pull-down experiments with recombinant human NLRC3 and STING showed direct interaction between the proteins. The nucleotide-binding domain of NLRC3 associated with membrane-bound STING. NLRC3 interacted with the N terminus of TBK1 (604834) and impeded STING-TBK1 interaction and downstream type I interferon production. NLRC3 prevented correct trafficking of STING to perinuclear and punctate regions. Zhang et al. (2014) concluded that interaction of the NLR and STING pathways fine tunes the host response to intracellular DNA, cyclic di-GMP, and DNA viruses.
Using biochemical and mouse cell- and human cell-based assays, Liu et al. (2015) found that both MAVS (609676) and STING interacted with IRF3 (603734) in a phosphorylation-dependent manner. The authors showed that both MAVS and STING are phosphorylated in response to stimulation at their respective C-terminal pLxIS consensus motifs (p, hydrophilic residue; x, any residue; S, phosphorylation site). This phosphorylation event then recruits IRF3 to the active adaptor protein and is essential for IRF3 activation. Point mutations that impair the phosphorylation of MAVS or STING at their consensus motif abrogated IRF3 binding and subsequent interferon (see 147660) induction. Liu et al. (2015) found that MAVS is phosphorylated by the kinases TBK1 and IKK, whereas STING is phosphorylated by TBK1. Phosphorylated MAVS and STING subsequently bind to conserved, positively charged surfaces of IRF3, thereby recruiting IRF3 for its phosphorylation and activation by TBK1. Liu et al. (2015) also showed that TRIF (607601)-mediated activation of IRF3 depends of TRIF phosphorylation at the pLxIS motif commonly found in MAVS, STING, and IRF3. The authors concluded that phosphorylation of innate immune adaptor proteins is an essential and conserved mechanism that selectively recruits IRF3 to activate type I interferon production.
West et al. (2015) showed that moderate mtDNA stress elicited by TFAM (600438) deficiency engages cytosolic antiviral signaling to enhance the expression of a subset of interferon-stimulated genes. Mechanistically, the authors found that aberrant mtDNA packaging promotes escape of mtDNA into the cytosol, where it engages the DNA sensor cGAS (613973) and promotes STING/IRF3-dependent signaling to elevate interferon-stimulated gene expression, potentiate type I interferon responses, and confer broad viral resistance. Furthermore, West et al. (2015) demonstrated that herpes viruses induce mtDNA stress, which enhances antiviral signaling and type I interferon responses during infection. West et al. (2015) concluded that their results further demonstrated that mitochondria are central participants in innate immunity, identified mtDNA stress as a cell-intrinsic trigger of antiviral signaling, and suggested that cellular monitoring of mtDNA homeostasis cooperates with canonical virus-sensing mechanisms to fully engage antiviral innate immunity.
Bridgeman et al. (2015) produced replication-incompetent human immunodeficiency virus (HIV)-1 (see 609423)-based lentiviruses expressing a vesicular stomatitis virus glycoprotein and GFP (HIV-1-GFP) in 293T cells, which do not endogenously express CGAS. Infection of HEK293 cells with HIV-1-GFP produced in the presence of exogenous wildtype mouse Cgas, but not catalytically inactive Cgas, induced IFN production in a STING-dependent manner through incorporation of cGAMP into HIV-1-GFP. Depletion of exosomes showed that most IFN-inducing activity was associated with virions. Subsequent experiments used other cell types and viruses and extended the findings to infectious viruses. Bridgeman et al. (2015) concluded that a signal for innate immunity, cGAMP, is transferred between cells, thus accelerating and broadening antiviral responses.
In experiments similar to those of Bridgeman et al. (2015), Gentili et al. (2015) independently found that transfer of CGAS-synthesized cGAMP by viruses activated innate immunity and antiviral responses in uninfected target cells in a STING-dependent manner.
Using human HEK293 and HeLa cells and immortalized mouse fibroblasts, Lau et al. (2015) showed that, unlike primary fibroblasts, these DNA tumor virus-generated cell lines failed to produce type I IFN in response to DNA, although they could respond to a triphosphate RNA ligand that activates RIGI. Further analysis identified viral oncogenes, including human papillomavirus E7 and adenovirus E1A, that were potent and specific inhibitors of the cGAS-STING pathway. The LxCxE motif of these oncoproteins, which is essential for blockade of RB1 (614041), was also important for antagonizing DNA sensing. E7 and E1A bound STING, and silencing of these oncogenes in human tumor cells restored the cGAS-STING pathway. Lau et al. (2015) concluded that DNA tumor virus oncoproteins are potent and specific antagonists of the DNA-activated antiviral response.
Harding et al. (2017) demonstrated that cell cycle progression through mitosis following double-stranded DNA breaks leads to the formation of micronuclei, which precede activation of inflammatory signaling and are a repository for the pattern-recognition receptor CGAS. Inhibiting progression through mitosis or loss of pattern recognition by STING-CGAS impaired interferon signaling. Moreover, STING loss prevented the regression of abscopal tumors in the context of ionizing radiation and immune checkpoint blockade in vivo. Harding et al. (2017) concluded that their findings implicated temporal modulation of the cell cycle as an important consideration in the context of therapeutic strategies that combine genotoxic agents with immune checkpoint blockade.
Dou et al. (2017) showed that cytoplasmic chromatin activates the innate immunity cytosolic DNA-sensing cGAS (613973)-STING pathway, leading both to short-term inflammation to restrain activated oncogenes and to chronic inflammation that associates with tissue destruction and cancer. The cytoplasmic chromatin-cGAS-STING pathway promoted the senescence-associated secretory phenotype in primary human cells and in mice. Mice deficient in STING showed impaired immunosurveillance of oncogenic RAS and reduced tissue inflammation upon ionizing radiation. Dou et al. (2017) showed that this pathway is activated in cancer cells, and correlates with proinflammatory gene expression in human cancers. Dou et al. (2017) concluded that genomic DNA serves as a reservoir to initiate a proinflammatory pathway in the cytoplasm in senescence and cancer.
Haag et al. (2018) reported the discovery and characterization of highly potent and selective small-molecule antagonists of the STING protein, a central signaling component of the intracellular DNA sensing pathway. Mechanistically, the identified compounds covalently target the predicted transmembrane cysteine-91 and thereby block the activation-induced palmitoylation of STING. Using these inhibitors, Haag et al. (2018) showed that the palmitoylation of STING is essential for its assembly into multimeric complexes at the Golgi apparatus and, in turn, for the recruitment of downstream signaling factors. The identified compounds and their derivatives reduced STING-mediated inflammatory cytokine production in both human and mouse cells. Furthermore, Haag et al. (2018) found that these small-molecule antagonists attenuated pathologic features of autoinflammatory disease in mice.
Gui et al. (2019) reported that STING can activate autophagy through a mechanism that is independent of TBK1 (604834) activation and interferon induction. Upon binding cGAMP, STING translocates to the endoplasmic reticulum-Golgi intermediate compartment and the Golgi in a process that is dependent on the COPII complex and ARF GTPases (see 103180). STING-containing endoplasmic reticulum-Golgi intermediate compartment serves as a membrane source for LC3 (see 601242) lipidation, which is a key step in autophagosome biogenesis. cGAMP induced LC3 lipidation through a pathway that is dependent on WIPI2 (609225) and ATG5 (604261) but independent of the ULK (see 603169) and VPS34 (602609)-beclin (604378) kinase complexes. Gui et al. (2019) also showed that cGAMP-induced autophagy is important for the clearance of DNA and viruses in the cytosol.
Eaglesham et al. (2019) developed a biochemical screen to analyze 24 mammalian viruses, and identified poxvirus immune nucleases (poxins) as a family of 2-prime,3-prime-cGAMP-degrading enzymes. Poxins cleave 2-prime,3-prime-cGAMP to restrict STING-dependent signaling, and deletion of the poxin gene attenuates vaccinia virus replication in vivo.
Wu et al. (2019) found that expression of human STING with an asn154-to-ser (N154S) gain-of-function mutation, corresponding to the mouse N153S mutation (see ANIMAL MODEL), at physiologic level in Jurkat T cells intrinsically primed the cells for apoptosis through ER stress when exposed to TCR signaling. Further examination revealed that TCR signaling-induced ER stress alone was not sufficient to cause immediate cell death, but expression of STING N154S exacerbated ER stress and thereby tipped the balance toward cell death. Structural and functional analyses demonstrated that expression of IFN and unfolded protein response (UPR) genes was mediated through distinct domains of STING. Furthermore, the UPR motif of STING, specifically residues arg331 and arg334, was required for N154S ER-to-Golgi translocation, which was critical for activation of UPR and T-cell death. Live-cell microscopic analysis showed that STING N154S disrupted ER calcium homeostasis and induced ER stress, thus resulting in T-cell death.
Motwani et al. (2019) found that heterozygous mutant mice carrying counterpart mutations (N153S and V154M) of the most common STING mutations in SAVI patients (N154S and V155M) spontaneously developed lung disease and had shortened life spans, with V154M mutant mice having more severe disease (lung fibrosis) and shorter life spans than the N153S strain. ELISA analysis showed that genes related to IFN signature and inflammation were upregulated in mutant mice, with V154M mutant protein being more stable, enabling higher expression of some of those genes compared with the N153S mutant. Analysis of the immune cell composition of spleens found that mutant mice of both strains had a reduced number of mature T and B cells compared to wildtype, with the V154M mutant presenting with more severe immune cell abnormalities than the N153S mutant, reflecting defects in lymphoid cell development. Reconstitution of lethally irradiated wildtype mice with mutant or wildtype bone marrow showed that V154M bone marrow transferred disease to the wildtype host, whereas the N153S did not.
Sliter et al. (2018) reported a strong inflammatory phenotype in both parkin-null (602544) and Pink1-null (608309) mice following exhaustive exercise, and in Prkn-null;mutator mice, which accumulate mutations in mitochondrial DNA (mtDNA). Inflammation resulting from either exhaustive exercise or mtDNA mutation was completely rescued by concurrent loss of Sting, a central regulator of the type I interferon response to cytosolic DNA. The loss of dopaminergic neurons from the substantia nigra pars compacta and the motor defect observed in aged Prkn-null;mutator mice were also rescued by loss of Sting, suggesting that inflammation facilitates this phenotype. Humans with mono- and biallelic PRKN mutations also displayed elevated cytokines. Sliter et al. (2018) concluded that their results supported a role for PINK1- and parkin-mediated mitophagy in restraining innate immunity.
Ran et al. (2019) found that YIPF5 (611483) positively regulated innate immune responses to DNA viruses in human and mouse immortalized cell lines and primary cells. YIPF5 specifically regulated viral infection-induced expression of type I IFNs and downstream IFN-stimulated genes. YIPF5 was also important for cellular antiviral responses against DNA but not RNA viruses. Immunoprecipitation analysis and confocal microscopy revealed that YIPF5 interacted and colocalized with STING in DNA virus-triggered pathways. The interaction was facilitated by the C-terminal transmembrane domains of YIPF5 and the fourth transmembrane domain of STING. YIPF5 mediated STING trafficking from ER to Golgi by recruiting it to COPII-coated vesicles, which were essential for the STING-mediated innate immune response to intracellular DNA.
Fang et al. (2023) identified ARMH3 (620867) as a regulator of STING activation, as deletion of ARMH3 abolished STING activation in HT1080 cells. ARMH3 interacted with the Golgi-localized protein PI4KB (602758) and functioned as an adaptor to bridge STING and PI4KB at the Golgi for STING activation. The kinase activity of PI4KB was required for STING activation because PI4KB recruited by ARMH3 synthesized PI4P around STING at the Golgi membrane. PI4P was essential for STING activation, as accumulated cellular PI4P caused CGAS-independent STING autoactivation, with the participation of PI4P-binding proteins in a lipid environment optimal for STING activation. Analysis of mouse lung fibroblasts with Armh3 deletion and of mice with macrophage-specific deletion of Armh3 indicated that Armh3 was required for the host defense against DNA virus, highlighting the importance of Armh3 in STING activation and innate immune responses.
In 6 unrelated patients with STING-associated vasculopathy with onset in infancy (SAVI; 615934), Liu et al. (2014) identified 3 different de novo heterozygous missense mutations in the TMEM173 gene (612374.0001-612374.0003). The mutation in the first patient was found by whole-exome sequencing, and mutations in the subsequent patients were found by Sanger sequencing. One of the patients was somatic mosaic for the mutation. Studies in patient cells as well as transfection studies in HEK293T cells indicated that the mutations resulted in a gain of function, with constitutive STAT1 (600555) phosphorylation and activation and increased IFNB1 activity. Exposure of control endothelial cells to cGAMP, which activates TMEM173, resulted in increased expression of genes that mediate inflammation, apoptosis, cell adhesion, and coagulation pathways, and caused endothelial activation and apoptosis. In vitro experiments in patient cells showed that inhibition of JAK1 (147795) resulted in decreased IFNB1 transcription and blockage of some interferon-response genes.
In 3 affected members of a 3-generation French family of mixed European descent with SAVI, Jeremiah et al. (2014) identified a heterozygous missense mutation in the STING gene (V155M; 612374.0002). The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing. In vitro functional expression assays showed that the mutation caused constitutive activation of the IFNB1 promoter, even in the absence of stimulation. Confocal microscopy of patient fibroblasts showed that mutant STING was present mainly in the Golgi and in perinuclear punctiform vesicles, suggestive of activation, whereas wildtype STING was uniformly expressed in the cytoplasm of control cells. Patient samples showed increased type 1 interferon activity and overexpression of downstream genes.
Morehouse et al. (2020) identified functional STING homologs encoded within prokaryotic defense islands, as well as a conserved mechanism of signal activation. Crystal structures of bacterial STING defined a minimal homodimeric scaffold that selectively responded to cyclic di-GMP synthesized by a neighbouring cGAS/DncV-like nucleotidyltransferase enzyme. Bacterial STING domains coupled the recognition of cyclic dinucleotides with formation of protein filaments to drive oligomerization of TIR effector domains and rapid NAD+ cleavage. Morehouse et al. (2020) reconstructed the evolutionary events that followed acquisition of STING into metazoan innate immunity and determined the structure of a full-length TIR-STING fusion from the Pacific oyster Crassostrea gigas. Comparative structural analysis demonstrated how metazoan-specific additions to the core STING scaffold enabled a switch from direct effector function to regulation of antiviral transcription. The findings explained the mechanism of STING-dependent signaling and revealed conservation of a functional cGAS-STING pathway in prokaryotic defense against bacteriophages.
Ishikawa and Barber (2008) obtained Sting -/- mice at a mendelian ratio, and the mutant animals developed and bred normally. Sting -/- mouse embryonic fibroblasts were extremely susceptible to negative-stranded virus infection, including vesicular stomatitis virus. Sting ablation abrogated the ability of intracellular B-form DNA, as well as members of the herpesvirus family, to induce Ifn-beta, but it did not significantly affect the Toll-like receptor pathway (see TLR1; 601194).
Zhu et al. (2014) noted that patients with inflammatory bowel disease (see 266600) have an increased risk of developing colorectal cancer (see 114500) and that pattern recognition receptors are involved in colitis-associated colorectal cancer development. They found that Sting -/- mice treated with dextran sulfate sodium to induce colitis showed high susceptibility to CRC, with significant intestinal damage and tumor development. Sting deficiency also resulted in failure to restrict activation of the Nfkb and Stat3 (102582) signaling pathways, leading to increased levels of the proinflammatory cytokines Il6 and Cxcl1 (155730). Zhu et al. (2014) concluded that STING has an important role in mediating protection against colorectal tumorigenesis.
Wu et al. (2019) noted that mice heterozygous for a knockin N153S gain-of-function mutation in Sting spontaneously develop lung inflammation, T-cell cytopenia, and premature death, mimicking the pathologic findings in patients with SAVI. Wu et al. (2019) found that TCR signaling in Sting N153S/+ mice resulted in T-cell activation and spontaneous T-cell death due to induced ER stress and UPR. Treatment of Sting N153S/+ mice with pharmacologic inhibitors of ER stress significantly increased T cells in peripheral blood. Crossing Sting N153S/+ mice with OT-1 mice, which carry an altered TCR locus in Cd8 (see 186910)-positive T cells, reduced ER stress and cell death and restored Cd8-positive T cells in Sting N153S/+ mice. Restoration of Cd8-positive T cells in Sting N1253S/+ mice by crossing them with OT-1 mice also led to reductions in inflammation and lung disease.
Wu et al. (2020) noted that phosphorylation of ser365 in mouse Sting (ser366 in human STING) is required for recruitment of Irf3 and subsequent activation of IFN signaling. They found that mice homozygous for a ser365-to-ala (S365A) mutation in Sting were born at the expected mendelian ratio and that adult mutant mice were healthy. However, analysis of bone marrow-derived macrophages (BMDMs) and T cells showed that IFN-dependent activities of Sting were abrogated in Sting S365A/S365A mice, whereas IFN-independent activities were preserved. Transcriptomic analysis revealed that many physiologically important Sting activities were Ifn independent, especially in T cells. Sting S365A/S365A mice were protected against HSV-1 infection predominantly through IFN-independent activities. Sting agonists showed differential dependency on IFN in inducing T-cell death, with some showing complete IFN independence and others showing partial IFN dependence. Using mouse tumor models, the authors found that tumors evaded immune response by inducing Sting-mediated T-cell death. Recruitment of T cells to tumors was largely IFN dependent, but once the T cells reached the tumor, Sting-mediated T-cell death was IFN independent.
DNase II (DNASE2; 126350) -/- mice show embryonic lethality accompanied by inflammation and anemia. Li et al. (2022) found that DNase II -/- mice homozygous for Sting mutations, including S365A, leu373 to ala (L373A), C-terminal tail deletion (delta-CTT), or 'goldenticket' (gt, which ablates Sting expression), were born normally. DNase II -/- mice homozygous for Sting S365A developed polyarthritis characterized by swelling of footpads starting at 10 to 12 weeks of age, whereas DNase II -/- mice homozygous for Sting L373A or delta-CTT did not. Since Sting S365A, unlike Sting L373A or delta-CTT, retains the ability to recruit Tbk1, the results suggested that Tbk1 recruitment to Sting mediates arthritis development in DNase II -/- mice. Further analysis with DNase II -/- mice homozygous for Sting S365A confirmed that Tbk1 recruitment to Sting caused inflammation in footpads, induced inflammatory cytokines, and increased blood monocytes. The authors found that Tnfa (191160) and Il6 mediated development of inflammatory arthritis in DNase II -/- mice homozygous for Sting S365A, and consequently, blocking Tnfa alleviated arthritis and reduced expression of inflammatory genes.
In 4 unrelated children with STING-associated vasculopathy with onset in infancy (SAVI; 615934), Liu et al. (2014) identified a de novo heterozygous c.461A-G transition in exon 5 of the TMEM173 gene, resulting in an asn154-to-ser (N154S) substitution at a highly conserved residue. The mutation, which was found by whole-exome sequencing in the first patient and by Sanger sequencing in subsequent patients, was not found in the dbSNP (build 137) or Exome Sequencing Project databases. One of the patients appeared to be somatic mosaic for the mutation. The patients were of French Canadian, European, and Turkish descent.
In a boy of European ancestry with STING-associated vasculopathy with onset in infancy (SAVI; 615934), Liu et al. (2014) identified a de novo heterozygous c.463G-A transition in exon 5 of the TMEM173 gene, resulting in a val155-to-met (V155M) substitution at a highly conserved residue. The mutation was not found in the dbSNP (build 137) or Exome Sequencing Project databases. The patient died of pulmonary disease at age 15 years.
Jeremiah et al. (2014) identified a heterozygous V155M mutation in the TMEM173 gene in 3 affected members of a nonconsanguineous family of mixed European descent with SAVI. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, occurred at a conserved residue in the first hydrophobic helix (alpha-5) that forms intermolecular interactions. Molecular modeling predicted that the mutation would stabilize the dimer and/or mimic the effect of ligand binding. In vitro functional expression assays showed that the mutation caused constitutive activation of the IFNB (147640) promoter, even in the absence of stimulation. Expression of the mutant protein was decreased compared to wildtype, suggesting that it is less stable, or more likely to be degraded. Confocal microscopy of patient fibroblasts showed that mutant STING was present mainly in the Golgi and in perinuclear punctiform vesicles, suggestive of activation, whereas wildtype STING was uniformly expressed in the cytoplasm of control cells. Patient samples showed increased type 1 interferon activity and overexpression of downstream genes. Jeremiah et al. (2014) noted that the phenotype in this family was less severe than that observed in the patient reported by Liu et al. (2014).
In a 9-year-old boy of Chilean ancestry with STING-associated vasculopathy with onset in infancy (SAVI; 615934), Liu et al. (2014) identified a de novo heterozygous c.439G-C transversion in exon 5 of the TMEM173 gene, resulting in a val147-to-leu (V147L) substitution The residue is conserved in most species, except the chicken (Gallus gallus), which carries a leucine at this codon. The mutation was not found in the dbSNP (build 137) or Exome Sequencing Project databases.
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