STING-deficient Mice Research Articles

Manganese Increases the Sensitivity of the cGAS-STING Pathway for Double-Stranded DNA and Is Required for the Host Defense against DNA Viruses

Manganese (Mn) is essential for many physiological processes, but its functions in innate immunity remain undefined. Here, we found that Mn2+ was required for the host defense against DNA viruses by increasing the sensitivity of the DNA sensor cGAS and its downstream adaptor protein STING. Mn2+ was released from membrane-enclosed organelles upon viral infection and accumulated in the cytosol where it bound directly to cGAS. Mn2+ enhanced the sensitivity of cGAS to double-stranded DNA (dsDNA) and its enzymatic activity, enabling cGAS to produce secondary messenger cGAMP inthe presence of low concentrations of dsDNA that would otherwise be non-stimulatory. Mn2+ alsoenhanced STING activity by augmenting cGAMP-STING binding affinity. Mn-deficient mice showed diminished cytokine production and were more vulnerable to DNA viruses, and Mn-deficient STING-deficient mice showed no increased susceptibility. These findings indicate that Mn is critically involved and required for the host defense against DNA viruses.

CGAS-mediated autophagy protects the liver from ischemia-reperfusion injury independently of STING.

Liver ischemia-reperfusion (I/R) injury occurs through induction of oxidative stress and release of damage-associated molecular patterns (DAMPs), including cytosolic DNA released from dysfunctional mitochondria or from the nucleus. Cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS) is a cytosolic DNA sensor known to trigger stimulator of interferon genes (STING) and downstream type 1 interferon (IFN-I) pathways, which are pivotal innate immune system responses to pathogen. However, little is known about the role of cGAS/STING in liver I/R injury. We subjected C57BL/6 (WT), cGAS knockout (cGAS-/-), and STING-deficient (STINGgt/gt) mice to warm liver I/R injury and that found cGAS-/- mice had significantly increased liver injury compared with WT or STINGgt/gt mice, suggesting a protective effect of cGAS independent of STING. Liver I/R upregulated cGAS in vivo and also in vitro in hepatocytes subjected to anoxia/reoxygenation (A/R). We confirmed a previously published finding that hepatocytes do not express STING under normoxic conditions or after A/R. Hepatocytes and liver from cGAS-/- mice had increased cell death and reduced induction of autophagy under hypoxic conditions as well as increased apoptosis. Protection could be restored in cGAS-/- hepatocytes by overexpression of cGAS or by pretreatment of mice with autophagy inducer rapamycin. Our findings indicate a novel protective role for cGAS in the regulation of autophagy during liver I/R injury that occurs independently of STING. NEW & NOTEWORTHY Our studies are the first to document the important role of cGAS in the acute setting of sterile injury induced by I/R. Specifically, we provide evidence that cGAS protects liver from I/R injury in a STING-independent manner.

E. fischeriana Root Compound Dpo Activates Antiviral Innate Immunity.

E. fischeriana has long been used as a traditional Chinese medicine. Recent studies reported that some compounds of E. fischeriana exhibited antimicrobial and immune enhance activity. Innate immune system is essential for the immune surveillance of inner and outer threats, initial host defense responses and immune modulation. The role of natural drug compounds, including E. fischeriana, in innate immune regulation is largely unknown. Here we demonstrated that E. fischeriana compound Dpo is involved in antiviral signaling. The genome wide RNA-seq analysis revealed that the induction of ISGs by viral infection could be synergized by Dpo. Consistently, Dpo enhanced the antiviral immune responses and protected the mice from death during viral infection. Dpo however was not able to rescue STING deficient mice lethality caused by HSV-1 infection. The enhancement of ISG15 by Dpo was also impaired in STING, IRF3, IRF7, or ELF4 deficient cells, demonstrating that Dpo activates innate immune responses in a STING/IRFs/ELF4 dependent way. The STING/IRFs/ELF4 axis is therefore important for Dpo induced ISGs expression, and can be used by host to counteract infection.

Uterotubal junction prevents chlamydial ascension via innate immunity.

Ascension to the oviduct is necessary for Chlamydia to induce tubal infertility. Using the Chlamydia muridarum induction of hydrosalpinx mouse model, we have demonstrated a significant role of the uterotubal junction in preventing chlamydial ascending infection. First, delivery of C. muridarum to either side of the uterotubal junction resulted in significant reduction in live organisms from the tissues on the opposite sides. However, the recovery yields remained similar among different sections of the uterine horn. These observations suggest that the uterotubal junction may function as a barrier between the uterine horn and oviduct. Second, deficiency in innate immunity signaling pathways mediated by either MyD88 or STING significantly compromised the uterotubal junction barrier function, permitting C. muridarum to spread freely between uterine horn and oviduct. Finally, transcervical inoculation of C. muridarum led to significantly higher incidence of bilateral hydrosalpinges in the STING-deficient mice while the same inoculation mainly induced unilateral hydrosalpinx in the wild type mice, suggesting that the STING pathway-dependent uterotubal junction plays a significant role in preventing tubal pathology. Thus, we have demonstrated for the first time that the uterotubal junction is a functional barrier for preventing tubal infection by a sexually transmitted agent, providing the first in vivo evidence for detecting chlamydial infection by the STING pathway.

RIG-I/MAVS and STING signaling promote gut integrity during irradiation- and immune-mediated tissue injury.

The molecular pathways that regulate the tissue repair function of type I interferon (IFN-I) during acute tissue damage are poorly understood. We describe a protective role for IFN-I and the RIG-I/MAVS signaling pathway during acute tissue damage in mice. Mice lacking mitochondrial antiviral-signaling protein (MAVS) were more sensitive to total body irradiation– and chemotherapy-induced intestinal barrier damage. These mice developed worse graft-versus-host disease (GVHD) in a preclinical model of allogeneic hematopoietic stem cell transplantation (allo-HSCT) than did wild-type mice. This phenotype was not associated with changes in the intestinal microbiota but was associated with reduced gut epithelial integrity. Conversely, targeted activation of the RIG-I pathway during tissue injury promoted gut barrier integrity and reduced GVHD. Recombinant IFN-I or IFN-I expression induced by RIG-I promoted growth of intestinal organoids in vitro and production of the antimicrobial peptide regenerating islet–derived protein 3 γ (RegIIIγ). Our findings were not confined to RIG-I/MAVS signaling because targeted engagement of the STING (stimulator of interferon genes) pathway also protected gut barrier function and reduced GVHD. Consistent with this, STING-deficient mice suffered worse GVHD after allo-HSCT than did wild-type mice. Overall, our data suggest that activation of either RIG-I/MAVS or STING pathways during acute intestinal tissue injury in mice resulted in IFN-I signaling that maintained gut epithelial barrier integrity and reduced GVHD severity. Targeting these pathways may help to prevent acute intestinal injury and GVHD during allogeneic transplantation.

Intratumoral administration of cGAMP transiently accumulates potent macrophages for anti-tumor immunity at a mouse tumor site.

Stimulator of IFN genes (STING) spontaneously contributes to anti-tumor immunity by inducing type I interferons (IFNs) following sensing of tumor-derived genomic DNAs in the tumor-bearing host. Although direct injection of STING ligands such as cyclic diguanylate monophosphate (c-di-GMP) and cyclic [G(2',5')pA(3',5')p] (cGAMP) into the tumor microenvironment exerts anti-tumor effects through strong induction of type I IFNs and activation of innate and adaptive immunity, the precise events caused by STING in the tumor microenvironment remain to be elucidated. We describe here our finding that a CD45+ CD11bmid Ly6C+ cell subset transiently accumulated in mouse tumor microenvironment of 4T1 breast cancer, squamous cell carcinomas, CT26 colon cancer, or B16F10 melanoma tissue after intratumoral injection of cGAMP. The accumulated cells displayed a macrophage (M ) phenotype since the cells were positive for F4/80 and MHC class II and negative for Ly6G. Intratumoral cGAMP treatment did not induce Mφ accumulation in STING-deficient mice. Depletion of CD8+ T cell using anti-CD8 mAb impaired the anti-tumor effects of cGAMP treatment. Depletion of the Mφ using clodronate liposomes impaired the anti-tumor effects of cGAMP treatment. Functional analysis indicated that the STING-triggered tumor-migrating Mφ exhibited phagocytic activity, production of tumor necrosis factor alpha TNFα), and high expression levels of T cell-recruiting chemokines, Cxcl10 and Cxcl11, IFN-induced molecules, MX dynamin-like GTPase 1 (Mx1) and 2'-5' oligoadenylate synthetase-like 1 (Oasl1), nitric oxide synthase 2 (Nos2), and interferon beta 1 (Ifnb1). These results indicate that the STING-triggered tumor-migrating Mφ participate in the anti-tumor effects of STING-activating compounds.

Endoplasmic Reticulum Stress-induced Hepatocellular Death Pathways Mediate Liver Injury and Fibrosis via Stimulator of Interferon Genes

Fibrosis, driven by inflammation, marks the transition from benign to progressive stages of chronic liver diseases. Although inflammation promotes fibrogenesis, it is not known whether other events, such as hepatocyte death, are required for the development of fibrosis. Interferon regulatory factor 3 (IRF3) regulates hepatocyte apoptosis and production of type I IFNs. In the liver, IRF3 is activated via Toll-like receptor 4 (TLR4) signaling or the endoplasmic reticulum (ER) adapter, stimulator of interferon genes (STING). We hypothesized that IRF3-mediated hepatocyte death is an independent determinant of chemically induced liver fibrogenesis. To test this, we performed acute or chronic CCl4 administration to WT and IRF3-, Toll/Interleukin-1R (TIR) domain-containing adapter-inducing interferon-β (TRIF)-, TRIF-related adaptor molecule (TRAM)-, and STING-deficient mice. We report that acute CCl4 administration to WT mice resulted in early ER stress, activation of IRF3, and type I IFNs, followed by hepatocyte apoptosis and liver injury, accompanied by liver fibrosis upon repeated administration of CCl4 Deficiency of IRF3 or STING prevented hepatocyte death and fibrosis both in acute or chronic CCl4 In contrast, mice deficient in type I IFN receptors or in TLR4 signaling adaptors, TRAM or TRIF, upstream of IRF3, were not protected from hepatocyte death and/or fibrosis, suggesting that the pro-apoptotic role of IRF3 is independent of TLR signaling in fibrosis. Hepatocyte death is required for liver fibrosis with causal involvement of STING and IRF3. Thus, our results identify that IRF3, by its association with STING in the presence of ER stress, couples hepatocyte apoptosis with liver fibrosis and indicate that innate immune signaling regulates outcomes of liver fibrosis via modulation of hepatocyte death in the liver.

Sensing of HSV-1 by the cGAS-STING pathway in microglia orchestrates antiviral defence in the CNS.

Herpes simplex encephalitis (HSE) is the most common form of acute viral encephalitis in industrialized countries. Type I interferon (IFN) is important for control of herpes simplex virus (HSV-1) in the central nervous system (CNS). Here we show that microglia are the main source of HSV-induced type I IFN expression in CNS cells and these cytokines are induced in a cGAS–STING-dependent manner. Consistently, mice defective in cGAS or STING are highly susceptible to acute HSE. Although STING is redundant for cell-autonomous antiviral resistance in astrocytes and neurons, viral replication is strongly increased in neurons in STING-deficient mice. Interestingly, HSV-infected microglia confer STING-dependent antiviral activities in neurons and prime type I IFN production in astrocytes through the TLR3 pathway. Thus, sensing of HSV-1 infection in the CNS by microglia through the cGAS–STING pathway orchestrates an antiviral program that includes type I IFNs and immune-priming of other cell types.

DNA sensing via STING regulates immune responses in a lung cancer model via IDO

Abstract The Stimulator of Interferon Genes (STING) is a signaling adaptor associated with the endoplasmic reticulum. STING is activated by cytosolic DNA sensors to stimulate IFN type I expression (IFN-I). Recent reports revealed that DNA sensing to activate STING in dendritic cells (DCs) that engulfed dying tumor cells impeded growth of immunogenic tumors and potentiated responses to therapy. Consistent with these findings, synthetic STING agonists enhanced tumor regression. Paradoxically, Lewis Lung Carcinoma (LLC) grew slower in STING-deficient mice, revealing that STING is required for optimal LLC growth. Mechanistically, STING ablation abolished upregulation of the immunoregulatory enzyme, indoleamine 2,3 dioxygenase (IDO) in DCs located in tumor draining lymph nodes during LLC growth. Also, expression of the regulatory cytokine IL-10 and infiltration of myeloid derived suppressor cells (MDSCs) into the tumor microenvironment (TME) was diminished in mice lacking STING. In contrast, STING was not required for optimal growth of LLC tumors expressing neo-antigens, revealing a pivotal role for tumor antigenicity in influencing responses to DNA in the TME. These findings support the hypothesis that DNA from dying cells are sensed in the TME to activate STING, which induces dominant regulatory responses via IDO when tumor antigenicity is low and dominant immunogenic responses when tumor antigenicity is enhanced. Thus, cytosolic DNA sensing to activate STING has dichotomous roles in the TME, and tumor antigenicity is a pivotal factor influencing immune responses to DNA at sites of chronic inflammation associated with tumor growth.

STING Promotes the Growth of Tumors Characterized by Low Antigenicity via IDO Activation.

Cytosolic DNA sensing is an important process during the innate immune response that activates the stimulator of interferon genes (STING) adaptor and induces IFN-I. STING incites spontaneous immunity during immunogenic tumor growth and accordingly, STING agonists induce regression of therapy-resistant tumors. However DNA, STING agonists, and apoptotic cells can also promote tolerogenic responses via STING by activating immunoregulatory mechanisms such as indoleamine 2,3 dioxygenase (IDO). Here, we show that IDO activity induced by STING activity in the tumor microenvironment (TME) promoted the growth of Lewis lung carcinoma (LLC). Although STING also induced IDO in tumor-draining lymph nodes (TDLN) during EL4 thymoma growth, this event was insufficient to promote tumorigenesis. In the LLC model, STING ablation enhanced CD8(+) T-cell infiltration and tumor cell killing while decreasing myeloid-derived suppressor cell infiltration and IL10 production in the TME. Depletion of CD8(+) T cells also eliminated the growth disadvantage of LLC tumors in STING-deficient mice, indicating that STING signaling attenuated CD8(+) T-cell effector functions during tumorigenesis. In contrast with native LLC tumors, STING signaling neither promoted growth of neoantigen-expressing LLC, nor did it induce IDO in TDLN. Similarly, STING failed to promote growth of B16 melanoma or to induce IDO activity in TDLN in this setting. Thus, our results show how STING-dependent DNA sensing can enhance tolerogenic states in tumors characterized by low antigenicity and how IDO inhibition can overcome this state by attenuating tumor tolerance. Furthermore, our results reveal a greater complexity in the role of STING signaling in cancer, underscoring how innate immune pathways in the TME modify tumorigenesis in distinct tumor settings, with implications for designing effective immunotherapy trials. Cancer Res; 76(8); 2076-81. ©2016 AACR.

Nucleic Acid-Sensing Receptors: Rheostats of Autoimmunity and Autoinflammation.

Distinct families of germline-encoded pattern recognition receptors can sense both microbial and endogenous nucleic acids. These DNA and RNA sensors include endosomal TLRs and cytosolic sensors upstream of stimulator of type I IFN genes (STING) and MAVS. The existence of overlapping specificities for both foreign and self nucleic acids suggests that, under optimal conditions, the activity of these receptors is finely tuned to effectively mediate host defense yet constrain pathogenic self-reactivity. This equilibrium becomes disrupted with the loss of either TLR9 or STING. To maintain immune protection, this loss can be counterbalanced by the elevated response of an alternative receptor(s). Unfortunately, this adjustment can lead to an increased risk for the development of systemic autoimmunity, as evidenced by the exacerbated clinical disease manifestations of TLR9-deficient and STING-deficient autoimmune-prone mice. These studies underscore the delicate balance normally maintained by tonic signals that prevent unchecked immune responses to nucleic acids released during infections and cellular duress or death.

STING protects against colitis-associated colorectal tumorigenesis by modulating intestinal inflammation (TUM7P.1018)

Abstract Stimulator of IFN genes (STING) is an innate immune sensor for cytosolic cyclic dinucleotides and also serves as an adaptor molecule for a number of intracellular DNA sensors. While STING has been shown to be critically involved in modulating immune responses during infections and autoimmune diseases, its physiological role in cancer remains largely unknown. In this study, we demonstrated that STING-deficient mice are highly susceptible to colitis-associated colorectal cancer with overt intestinal proliferation during early stages of tumorigenesis. Hyperactive NF-kB and STAT3 signaling was responsible for increased levels of proinflammatory cytokines observed in STING-deficient mice. Furthermore, intestinal tissues deficient in STING exhibited elevated level of DNA damage maker, γH2AX and a defect in caspase-1-mediated colonic IL-18 release, highlighting its fundamental functions in maintaining genomic integrity and activating inflammasome. Therefore, our results identify an unexpected and important role for STING in mediating protection against colorectal tumorigenesis.

STING-dependent sensing of polyomavirus infection (VIR9P.1158)

Abstract Polyomaviruses (PyV) are nonenveloped DNA viruses that persist as low-level asymptomatic infections in a variety of vertebrates, including humans. In immunosuppressed individuals, the human BK and JC PyVs may cause transplant-associated nephropathy and progressive multifocal leukoencephalopathy, respectively. Mouse polyomavirus (MPyV) allows investigation of PyV immunity in a natural host. After caveolae-/clathrin-mediated endocytosis, PyV virions traffic in microtubule-guided microvesicles from endosomes to the ER, where uncoating is initiated. Unknown is whether complete uncoating occurs in the cytosol, exposing the viral DNA to cytosolic DNA sensors, before it is transported to the nucleus where viral replication and assembly occur. Here, we report that persistent MPyV infection in mice is associated with chronically elevated IFN-β transcripts, and that WT primary mouse embryo fibroblasts (MEFs) infected with MPyV upregulate IFN-β, TNF-α and ISG (PKR and MDA-5) mRNAs. However, MPyV infection failed to induce expression for these transcripts in MEFs from STING-/- mice. Interestingly, MPyV acute infection activated NK cells in WT, but not in IFNαβR-/- mice or in STING-deficient (Goldenticket) mice. Together, these data suggest that MPyV-induced activation of NK cells requires Type I IFN and a STING-dependent cytosolic DNA sensing pathway(s). Moreover, these data provide strong evidence that PyV DNA is exposed in the cytosol and activate innate immune sensors.

Suppression of systemic autoimmunity by the innate immune adaptor STING

Cytosolic DNA-sensing pathways that signal via Stimulator of interferon genes (STING) mediate immunity to pathogens and also promote autoimmune pathology in DNaseII- and DNaseIII-deficient mice. In contrast, we report here that STING potently suppresses inflammation in a model of systemic lupus erythematosus (SLE). Lymphoid hypertrophy, autoantibody production, serum cytokine levels, and other indicators of immune activation were markedly increased in STING-deficient autoimmune-prone mice compared with STING-sufficient littermates. As a result, STING-deficient autoimmune-prone mice had significantly shorter lifespans than controls. Importantly, Toll-like receptor (TLR)-dependent systemic inflammation during 2,6,10,14-tetramethylpentadecane (TMPD)-mediated peritonitis was similarly aggravated in STING-deficient mice. Mechanistically, STING-deficient macrophages failed to express negative regulators of immune activation and thus were hyperresponsive to TLR ligands, producing abnormally high levels of proinflammatory cytokines. This hyperreactivity corresponds to dramatically elevated numbers of inflammatory macrophages and granulocytes in vivo. Collectively these findings reveal an unexpected negative regulatory role for STING, having important implications for STING-directed therapies.

Diverse roles of STING-dependent signaling on the development of cancer.

Stimulator of interferon genes (STING) is a cellular sensor that controls cytosolic DNA-activated innate immune signaling. We have previously demonstrated that STING-deficient mice are resistant to carcinogen-induced skin cancer, similar to myeloid differentiation primary response gene 88 (MyD88) deficient mice, since the production of STING-dependent DNA-damage-induced proinflammatory cytokines, that likely require MyD88 signaling to exert their growth-promoting activity, are prevented. In contrast, MyD88-deficient mice are sensitive to colitis-associated cancer (CAC), since selected cytokines generated following DNA-damage also activate repair pathways, which can help prevent tumor development. Here, we demonstrate that STING signaling facilitates wound repair processes and that analogous to MyD88-deficient mice, STING-deficient mice (SKO) are prone to CAC induced by DNA-damaging agents. SKO mice harboring tumors exhibited low levels of tumor-suppressive interleukin-22 binding protein (IL-22BP) compared to normal mice, a cytokine considered critical for preventing colon-related cancer. Our data indicate that STING constitutes a critical component of the host early response to intestinal damage and is essential for invigorating tissue repair pathways that may help prevent tumorigenesis.

Cutting edge: STING mediates protection against colorectal tumorigenesis by governing the magnitude of intestinal inflammation.

Stimulator of IFN genes (STING) is a cytoplasmic innate immune sensor for cyclic dinucleotides that also serves a dual role as an adaptor molecule for a number of intracellular DNA receptors. Although STING has important functions in the host defense against pathogens and autoimmune diseases, its physiological role in cancer is unknown. In this study, we show that STING-deficient mice are highly susceptible to colitis-associated colorectal cancer. Colons of STING-deficient mice exhibit significant intestinal damage and overt proliferation during early stages of tumorigenesis. Moreover, STING-deficient mice fail to restrict activation of the NF-κB- and STAT3-signaling pathways, which leads to increased levels of the proinflammatory cytokines IL-6 and KC. Therefore, our results identified an unexpected and important role for STING in mediating protection against colorectal tumorigenesis.

Entropy controls activity

743 Written by Ines Chen, Arianne Heinrichs & Michelle Montoya cellular membranes. The VLPs could induce an interferon response in both mouse and human cells without causing an inflammatory response. Using VLPs that lacked specific envelope glycoproteins, the authors established that viral membrane fusion is required to induce the interferon response. Other membrane-fusion events, such as cell-cell fusion or cationic liposome fusion, could cause a similar response. Using liposomes with different lipid composition, the authors could see a direct correlation between fusogenic potential and the level of cellular responses. They next investigated the signaling events involved in the cellular response to membrane fusion. Cells from STING-deficient mice did not show interferon responses upon treatment with VLPs or liposomes, implying that protein was needed for the response to membrane fusion. In addition, the roles of phospholipase C-γ and phosphatidylinositol-3-OH kinase, both involved in membraneproximal signaling, were also demonstrated by using specific inhibitors. The authors note that many membranefusion events occur as part of normal physiological processes (for example, ER-membrane fusion or natural syncytium formation) and do not induce immune responses. Thus, cells must be able to differentiate those events from ‘unscheduled’ membrane fusions that are sensed as danger signals. How exactly membrane fusion is sensed remains to be established, but this work uncovers a novel innate detection mechanism and extends the role of STING in immune responses. (Nat. Immunol. doi:10.1038/ni.2350, published online 17 June 2012) IC Entropy controls activity