STING Signaling Research Articles

STINGing CD4+ T cells to induce refractoriness to HIV infection

Abstract HIV rapidly infects CD4+ T cells where it can establish latent infection. Identifying immune mechanisms which can render CD4+ T cells refractory to infection represents a critical step in limiting infection and viral spread. Using purified memory CD4+ T cells from healthy donors, we found that activation of the STING signaling pathway with 0.5 mM of the STING agonist diABZI was sufficient to induce a state of refractoriness to in vitro HIV infection in memory CD4+ T cells, a major source of the HIV reservoir. We observed that STING activation in CD4+ T cells induces Type I IFN production and activates p-IRF3. CRISPR KD of STING in memory CD4+ T cells led to a significant increase in HIV infection, demonstrating a cell intrinsic role for STING signaling in limiting HIV infection/replication. Using proteomics, we identified that diABZI significantly and potently induces restriction factors and proteins involved in antiviral immunity and Type 1 IFN signaling. Importantly, proteins that were significantly reduced mapped to pathways including RNA processing and protein translation which are aspects of the host machinery which HIV needs to co-opt to replicate and produce infectious virions. Our data provide mechanistic insight into the STING pathway as a means to render CD4+ T cells refractory to HIV infection and highlights that this pathway lands a “1–2” punch by increasing expression of antiviral proteins that directly target the virus while suppressing the cellular machinery needed for the viral life cycle. The potential to use a STING agonist as a post-exposure therapeutic which directly limits viral infection while promoting global antiviral immunity represents a novel strategy that may stop HIV infection in its tracks.

Antigen-specific nanoparticle tolerance treatment actively induces regulatory mechanisms via the STING pathway

Abstract Antigen (Ag)-specific T cells are the underlying cause of many autoimmune diseases. T cells found at the site of tissue destruction not only in the exacerbation of disease, but contribute to the release of additiotnal self-epitopes resulting in the activation of spread eptitope-specific T cell populations perpetuating disease. Treatment with Ag-containingbiodegradable poly(lactide-co-glycolide) (PLGA) nanoparticles, i.e. tolerogenic immune-modifying particles (TIMP), has been shown to be both safe and induces Ag-specific tolerance in mouse models of autoimmunity and allergy, as well as in a celiac disease Phase I/IIa clinical trial. We are in the process of assessing if the mechanism of action between Ag-specific TIMP treatment and Ag-coupled cell treatment, to thereby identify self-tolerance mechanisms in common between the two highly efficacious therapies. The PLP 139-151TCR transgenic model system was utilized to determine the cellular and molecular mechanisms driving Ag-specific tolerance mediated by tolerogenic nanoparticle treatment. These data show Ag-specific TIMP treatment induced both FoxP3 +iTregs and IL-10 +Tr1 regulatory in both naïve mice and mice pre-primed with Ag/CFA. Additionally, the expression of STING is required for the induction of tolerance. The involvement of the STING pathway for both TIMP and Ag-coupled cell treatment was confirmed in MOG 35-55EAE. The data also show that Ag-specific tolerance induction requires both Type I IFNs and PD-1/PD-L1 expression, which are downstream of STING activation and signaling. Treatment thus activates various Ag-specific Treg subsets capable of regulating responses to disease-relevant autoepitopes via a STING/IFNAR/PD-1/PD-L1 pathway.

Induction of STING/IL-29 signaling in human lung adenocarcinoma/tumor-associated neutrophil cocultures

Abstract LKB1-mutant lung adenocarcinoma (LUAD), is an intractable form of lung cancer. LKB1-mutant LUAD is poor in T-cells and does not respond to checkpoint inhibitor therapy, and instead is enriched in tumor-infiltrating neutrophils (TINs). STING is a key innate sensor mediating anti-tumor responses that is inhibited in LKB1-mutant LUAD. However, the status of STING signaling and if it can be induced in TINs to antagonize tumors is unknown. Here, we developed a novel human LKB1-mutant LUAD/TIN model to tackle this question. Based on prior work from our lab (Dobosh, STAR Protoc. 2021), we grew the H1944 LKB1-mutant LUAD line at air-liquid interface on Alvetex scaffolds (Reprocell), followed by the transmigration of human blood neutrophils. The effect of the STING agonist MSA-2 was assessed in the model by a 20-plex immune mediator assay(Mesoscale). We successfully manufactured a LKB1-mutant LUAD/TIN model from H1944 cells and human blood neutrophils. MSA-2 treatment resulted in significant increases in the STING-regulated mediators IL-6, IP-10 and MIP-1beta. Most strikingly, MSA-2 treatment induced IL-29 (type III interferon) levels by 27-fold, while neither type I nor type II interferons were induced. The model showcased here mimics LKB1-mutant LUAD/TIN interplay and shows responsiveness to STING agonist treatment through induction of type III (but not type I and II) interferon and other immune mediators. Since IL-29 receptor expression is limited to epithelial and myeloid cells (including neutrophils) and IL-29 is known to mediate immunomodulatory and anti-tumor responses, future work will address if and how the large IL-29 increase observed upon MSA-2 treatment affects LUAD proliferation and TIN activation in this context.

High glucose-induced STING activation inhibits diabetic wound healing through promoting M1 polarization of macrophages

Diabetic wound (DW) is characterized by elevated pro-inflammatory cytokines and cellular dysfunction consistent with elevated reactive oxygen species (ROS) levels. Recent advances in immunology have dissected molecular pathways involved in the innate immune system where cytoplasmic DNA can trigger STING-dependent inflammatory responses and play an important role in metabolic-related diseases. We investigated whether STING regulates inflammation and cellular dysfunction in DW healing. We found that STING and M1 macrophages were increased in wound tissues from DW in patients and mice and delayed the wound closure. We also noticed that the massively released ROS in the High glucose (HG) environment activated STING signaling by inducing the escape of mtDNA to the cytoplasm, inducing macrophage polarization into a pro-inflammatory phenotype, releasing pro-inflammatory cytokines, and exacerbating endothelial cell dysfunction. In Conclusion, mtDNA-cGAS-STING pathway activation under diabetic metabolic stress is an important mechanism of DW refractory healing. While using STING gene-edited macrophages for wound treatment by cell therapy can induce the polarization of wound macrophages from pro-inflammatory M1 to anti-inflammatory M2, promote angiogenesis, and collagen deposition to accelerate DW healing. STING may be a promising therapeutic target for DW.

IL-33/ST2 antagonizes STING signal transduction via autophagy in response to acetaminophen-mediated toxicological immunity

BackgroundInterleukin-33 (IL-33), defined as "alarming", exert diverse functions through signaling via the suppression of tumorigenicity 2 (ST2). However, the physiological roles of IL-33/ST2 signaling during acetaminophen (APAP)-induced liver injury are still poorly understood by modern medicine (AILI). This research aims to explore the relationship between IL-33/ST2 and stimulator of interferon (IFN) response cGAMP interactor 1 (STING)-mediated signal transduction.MethodsC57BL/6N mice (WT) and IL-33-deficient mice (KO) were intraperitoneally injected with APAP (250 mg/kg). Recombinant IL-33 (500 ng/mouse) and the cGAS/STING inhibitor RU.521 (200 g/kg) were combined to treat AILI. For mechanistic research in vitro, CRISPR-mediated KD technology, immunoprecipitation, mass spectrometry, and immunofluorescence were utilized.ResultsWe discovered that IL-33 deficient mice had increased APAP-induced hepatotoxicity, DNA accumulation, and type 1 IFN production. Mechanistic analysis revealed that IL-33/ST2 enhanced the interaction between Beclin-1 and STING, disrupting STING dimerization, IRF3 phosphorylation, nuclear transport, and IFN-1 gene transcription in HepaRG and Huh7 cells. Beclin-1 interacted with the C-terminus of STING, causing Lys338 acetylation and autophagy degradation of STING. ST2 depletion increased STING signal transduction and IFN-1 promoter activity. Surprisingly, the cGAS/STING inhibitor RU.521 and recombinant IL-33 together improved AILI in vivo.ConclusionsThese results shed insight on the potential of inhibiting cGAS/STING as a therapy for AILI and emphasize the crucial role of IL-33/ST2 signaling in the regulation of APAP-induced STING signaling.7gSjYBv15HDd7Gp_h4w39CVideo Graphical

Human adenovirus infection induces pulmonary inflammatory damage by triggering noncanonical inflammasomes activation and macrophage pyroptosis.

Human adenovirus (HAdV) is a common respiratory virus, which can lead to severe pneumonia in children and immunocompromised persons, and canonical inflammasomes are reported to be involved in anti-HAdV defense. However, whether HAdV induced noncanonical inflammasome activation has not been explored. This study aims to explore the broad roles of noncanonical inflammasomes during HAdV infection to investigate the regulatory mechanism of HAdV-induced pulmonary inflammatory damage. We mined available data on GEO database and collected clinical samples from adenovirus pneumonia pediatric patients to investigate the expression of noncanonical inflammasome and its clinical relevance. An in vitro cell model was employed to investigate the roles of noncanonical inflammasomes in macrophages in response to HAdV infection. Bioinformatics analysis showed that inflammasome-related genes, including caspase-4 and caspase-5, were enriched in adenovirus pneumonia. Moreover, caspase-4 and caspase-5 expression levels were significantly increased in the cells isolated from peripheral blood and broncho-alveolar lavage fluid (BALF) of pediatric patients with adenovirus pneumonia, and positively correlated with clinical parameters of inflammatory damage. In vitro experiments revealed that HAdV infection promoted caspase-4/5 expression, activation and pyroptosis in differentiated THP-1 (dTHP-1) human macrophages via NF-κB, rather than STING signaling pathway. Interestingly, silencing of caspase-4 and caspase-5 in dTHP-1 cells suppressed HAdV-induced noncanonical inflammasome activation and macrophage pyroptosis, and dramatically decreased the HAdV titer in cell supernatants, by influencing virus release rather than other stages of virus life cycle. In conclusion, our study demonstrated that HAdV infection induced macrophage pyroptosis by triggering noncanonical inflammasome activation via a NF-kB-dependent manner, which may explore new perspectives on the pathogenesis of HAdV-induced inflammatory damage. And high expression levels of caspase-4 and caspase-5 may be a biomarker for predicting the severity of adenovirus pneumonia.

Abstract 1841: TAK-500 is a clinical stage immune-cell directed antibody drug conjugate (iADC) inducing STING activation in CCR2-expressing intratumor myeloid cells and favorable immunomodulation

Abstract Introduction: Myeloid cells are present in the tumor microenvironment (TME) of most human solid cancers, playing an essential role to influence local immunomodulatory functions. STING signaling in intratumor myeloid cells can enhance interferon (IFN) production leading to enhanced local innate and adaptive immunity, and synergism with other anti-tumor mechanisms. Here, we used a novel iADC, TAK-500, to selectively activate STING in CCR2-expressing cells. This approach enables systemic delivery and favors intratumor accumulation of a STING agonist to potentially achieve anti-tumor activity. Methods: TAK-500 and mTAK-500, a murine surrogate, were employed to study the immunomodulatory role and anti-tumor effects in preclinical models. CCR2 protein expression was characterized in the TME of >1,000 primary human tumors including non-small cell lung cancer (NSCLC, 2 cohorts, N= 411), colorectal carcinomas (CRC, 2 cohorts, N=350) and pancreatic ductal adenocarcinomas (PDAC, 1 cohort, N=228) represented in tissue microarrays using multiplexed quantitative immunofluorescence (mQIF). Results: TAK-500 triggered dose-dependent monocyte activation in vitro. mTAK-500 induced robust activation of innate and adaptive immune responses both in vitro and in vivo. In syngeneic mouse models with CCR2 expressing intratumoral myeloid cells, mTAK-500 treatment caused accumulation and activation of CD8+ effector T-cells in the TME resulting in prominent anti-tumor activity and enhanced survival. The baseline levels of CCR2-expressing mMDSCs in mouse models positively associated with anti-tumor response to mTAK-500. mQIF analysis of human tumors confirmed high expression of CCR2 in myeloid cells, lower expression in tumor infiltrating lymphocytes (TILs) and absence in tumor epithelial cells. Using an mQIF panel for simultaneous measurement of DAPI, CK, CCR2, CD11b and CD68, we identified CCR2 protein expression in 94% of NSCLCs, 87% CRCs and 89% PDACs. The levels of CCR2 protein were significantly higher in NSCLC than in CRC and PDAC. In NSCLC, high CCR2 protein in myeloid cells was associated with the presence of activating EGFR/KRAS mutations and increased CD8+ TILs and local PD-L1 expression. In CRC, higher levels of CCR2 in CD68+ macrophages were seen in tumors harboring microsatellite instability than in microsatellite stable carcinomas. Conclusion: The iADC TAK-500 and mTAK-500 induces CCR2-dependent immune cell activation and anti-tumor effect. CCR2 is highly expressed in intratumor myeloid cells from NSCLC. High CCR2 is associated with enhanced local adaptive immune responses and specific clinical/molecular tumor subsets. TAK-500 is currently being evaluated clinically as a single agent and in combination with pembrolizumab in adults with select locally advanced or metastatic solid tumors (NCT05070247). Citation Format: Kurt A. Schalper, Atsushi Matsuda, Michelle Ganno-Sherwood, Angel E. Maldonado-Lopez, Emily Rosentrater, Angelo Porciuncula, Dong Mei Zhang, Camilla L. Christensen, Samantha A. Merrigan, Tiquella Hatten, Hong Myung Lee, Min Young Lee, Linlin Dong, Jian Huang, Natasha Iartchouk, Jianing Wang, He Xu, Tomoki Yoneyama, Konstantin I. Piatkov, Carole E. Harbison, Alex Parent, Neil Lineberry, Adnan O. Abu-Yousif, Vicky Appleman. TAK-500 is a clinical stage immune-cell directed antibody drug conjugate (iADC) inducing STING activation in CCR2-expressing intratumor myeloid cells and favorable immunomodulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1841.

Abstract 5170: STING inflames NF1 malignancies for immunotherapy

Abstract Introduction: Neurofibromatosis Type 1 (NF1) is caused by mutations in the NF1 gene that encodes neurofibromin, a RAS GTPase-Activating Protein. Inactivating NF1 mutations result in hyperactivation of RAS-mediated signaling. NF1 patients develop benign tumors on the skin and along nerves in the spinal cord and brain, and ~10% of these progress to Malignant Peripheral Nerve Sheath Tumors (MPNST). Attempts to inhibit RAS-signaling to treat MPNST have not worked in clinical trials. Surgical removal is the only cure for MPNST, which is challenging due to large tumor size and/or proximity to nerves. MPNSTs often recur, metastasize, and respond poorly to chemo- and radiotherapy. As a result, MPNSTs are the leading cause of death in NF1 patients. Immune Checkpoint Blockade (ICB) is an approach to treat inoperable, undruggable cancers. Immune checkpoint proteins (ICPs) terminate normal immune responses to prevent collateral tissue damage. Cancer cells hijack this mechanism and express ICPs to avoid immune detection. ICB disrupts this process, enhancing antitumor immunity. Monoclonal antibodies (mABs) that disrupt the interaction between Programmed Cell Death Receptor 1 (PD-1) and its ligand Programmed Cell Death Ligand 1 (PD-L1) are a widely used ICB therapy. Having a T cell-enriched hot tumor microenvironment (TME) is required for successful ICB. However, MPNSTs lack a T cell-inflamed TME and respond poorly to ICB therapy. Activation of the protein “stimulator of interferon genes” (STING) enhances anti-tumor immunity via induction of pro-inflammatory cytokines, thus increasing T cell infiltration into the TME. We hypothesized that reprogramming the MPNST TME by STING pathway activation would turn cold MPNSTs into hot tumors amenable to ICB. Methods: We treated mouse MPNSTs with STING agonist or STING agonist + anti-PD-1/anti-PD-L1 mAb. Tumor size was measured throughout treatment. The mice were sacrificed and tumor tissue was analyzed for STING pathway activation, T cell infiltration, cell proliferation, and apoptosis. MPNST allograft tumors in athymic mice were controls. Results: STING pathway activation and increased T cell presence was observed in STING agonist-treated MPNSTs compared to vehicle-treated. MPNSTs treated with STING agonist alone or STING agonist + PD-1/PD-L1 mAbs showed less tumor growth relative to vehicle. Importantly, STING agonist + PD-1/PD-L1 mAb-treated tumors showed significant cell death increase while cell proliferation remained unchanged. Interestingly, tumors in athymic mice continued to grow despite treatment suggesting the antitumor effects seen in immunocompetent mice were mediated by T cells. Conclusions: Our data show that MPNSTs can become T cell-rich tumors by activating STING signaling. Reprogramming the TME made MPNSTs susceptible to immune destruction by ICB therapy. Our studies support this novel treatment strategy for MPNST, an aggressive, deadly tumor for which no molecular therapy currently exists. Citation Format: Nipunika Somatilaka, Laasya Madana, Ali Sadek, Renee M. McKay, Lu Q. Le. STING inflames NF1 malignancies for immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5170.

Abstract 4423: XMT-2056, a HER2-targeted STING agonist antibody-drug conjugate, exhibits ADCC function that synergizes with STING pathway activation and contributes to anti-tumor responses

Abstract XMT-2056 is a systemically administered Immunosynthen STING agonist antibody-drug conjugate (ADC) that targets a novel HER2 epitope and induces complete tumor regressions with a single dose in multiple tumor models. We have previously shown that XMT-2056 delivers its STING agonist payload into tumor cells and FcγRI (CD64)-expressing myeloid cells, activating STING signaling in both cell types, leading to type I interferon (IFN) and anti-tumor innate immune responses. Here, we demonstrate that XMT-2056 exhibits ADCC (antibody-dependent cell-mediated cytotoxicity) function, which synergizes with STING pathway activation and induces potent cancer cell-killing activity in co-cultures of HER2-expressing cancer cells and FcγRIII+ (CD16+) immune cells. We show that both XMT-2056 and HT-19 (the unconjugated parental antibody) retain significant cancer cell-killing activity in an Fc-dependent manner in PBMC co-cultures depleted of FcγRI-expressing myeloid cells. This activity is abrogated by co-depletion of FcγRIII+ immune cells, illustrating the ADCC function of XMT-2056. In this setting, XMT-2056 cancer cell-killing activity was significantly increased compared to HT-19, suggesting that the STING payload contributes to the differential activity observed with XMT-2056 treatment. Indeed, co-treatment of cancer cell and immune cell co-cultures with HT-19 and free STING agonist payload enhanced the anti-tumor responses, although to a lesser extent than XMT-2056, suggesting a synergy between the ADCC function and STING pathway activation. Consistently, XMT-2056 treatment of HER2-expressing cancer cells co-cultured with unstimulated CD56+/FcγRIII+ NK cells induced granzyme b and IFN-γ cytokine production, expression of NK cell activation markers, and cancer cell-killing activity. The ADCC activity of HT-19 was comparable to that of trastuzumab in NK cell co-cultures. Finally, we found that depletion of FcγRI+ cells inhibited the cancer cell-killing activity of XMT-2056 in cancer cell and PBMC co-cultures more substantially compared to depletion of FcγRIII+ cells or CD56+ NK cells, indicating a greater contribution of myeloid cells to the XMT-2056 mechanism of action in this setting. Notably, XMT-2056 was capable of engaging both FcγRI+ myeloid cells and FcγRIII+ NK cells, activating both STING-mediated innate immune responses and ADCC function in triple cultures with HER2-expressing cancer cells. Collectively, our data reveal a synergy between ADCC function and STING pathway induction both mediated by XMT-2056, which enhances the cancer cell-killing activity of FcγRIII+ cells. This additional mechanism of action of XMT-2056 can potentially impact the overall anti-tumor immune responses in tumors infiltrated by FcγRIII+ cells. Citation Format: Jahna Soomer-James, Marc Damelin, Naniye Malli. XMT-2056, a HER2-targeted STING agonist antibody-drug conjugate, exhibits ADCC function that synergizes with STING pathway activation and contributes to anti-tumor responses. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4423.

Abstract 6397: Eribulin acts as an immune adjuvant to enhance the antitumor efficacy of STING agonists in triple-negative breast cancer models

Abstract Triple-negative breast cancer (TNBC) is a heterogenous subtype of breast cancer lacking effective targeted treatment options. However, TNBC typically has a higher mutational burden and greater degree of immunogenicity than other breast tumors, making immunotherapy a viable strategy for effective treatment. Strategies to improve the response of TNBC patients to immunotherapy include the upregulation of the cGAS-STING innate immune sensing pathway and STING agonists are in clinical development. We previously showed that eribulin, a microtubule destabilizer used in the treatment of TNBC, functions as an indirect STING agonist because it promotes the release of mitochondrial DNA into the cytoplasm. In separate studies, we demonstrated that eribulin also significantly enhances type I interferon expression induced by STING agonists through a second TBK1-dependent mechanism downstream of STING activation. Both mechanisms of eribulin-mediated activation of interferon expression occur in immune and TNBC cells and are shared with other microtubule destabilizers but not with the microtubule stabilizer paclitaxel. Our current studies demonstrate the in vivo immunological effects of the microtubule destabilizer eribulin with the STING agonist ADU-S100 that lead to a significant decrease in tumor growth in the spontaneous MMTV-PyVT mammary tumor model upon combination treatment. The immunostimulatory effects of eribulin with or without concurrent administration of a STING agonist were determined in the spleen, tumor draining lymph nodes, and tumors with distinct effects observed in the activation of innate and adaptive responses. We further demonstrate the immunological and antitumor efficacy of combinations of eribulin and ADU-S100 in the syngeneic 4T1 model that is resistant to the antimitotic effects of eribulin as a single agent. Even in the absence of direct antimitotic effects on the tumor, eribulin was sufficient to promote activation of CD4+CD25− effector T-cells in the spleen and lymph nodes specifically in tumored animals but not untumored controls. Additionally, eribulin was able to promote a similar increase in the activation of CD4+ effector T-cells even in untumored animals when administered in combination with a STING agonist. Together, these data contribute to accumulating evidence that there are important mechanistic differences between the microtubule targeted chemotherapeutics currently used in the treatment of TNBC that could inform on their more rational use in the clinic as single agents or as chemotherapeutic backbones in combination with targeted therapy, including immunotherapeutics. More specifically, our data demonstrate that eribulin can act as an immune adjuvant to promote STING signaling and T-cell activation in multiple in vivo TNBC models in addition to its well established anti-mitotic effects to enhance antitumor efficacy. Citation Format: Leila Takahashi-Ruiz, Charles S. Fermaintt, Nancy Wilkinson, Peter Y. Chan, Susan L. Mooberry, April L. Risinger. Eribulin acts as an immune adjuvant to enhance the antitumor efficacy of STING agonists in triple-negative breast cancer models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6397.

Glycolysis drives STING signaling to facilitate dendritic cell antitumor function.

Activation of STING signaling in DCs promotes antitumor immunity. Aerobic glycolysis is a metabolic hallmark of activated DCs, but how the glycolytic pathway intersects with STING signaling in tumor-infiltrating DCs remains elusive. Here, we show that glycolysis drives STING signaling to facilitate DC-mediated antitumor immune responses. Tumor-infiltrating DCs exhibited elevated glycolysis, and blockade of glycolysis by DC-specific Ldha/Ldhb double deletion resulted in defective antitumor immunity. Mechanistically, glycolysis augmented ATP production to boost STING activation and STING-dependent DC antitumor functions. Moreover, DC-intrinsic STING activation accelerated HIF-1α-mediated glycolysis and established a positive feedback loop. Importantly, glycolysis facilitated STING-dependent DC activity in tissue samples from patients with non-small cell lung cancer. Our results provide mechanistic insight into how the crosstalk of glycolytic metabolism and STING signaling enhances DC antitumor activity and can be harnessed to improve cancer therapies.

Interplay between RNA viruses and cGAS/STING axis in innate immunity.

While the function of cGAS/STING signalling axis in the innate immune response to DNA viruses is well deciphered, increasing evidence demonstrates its significant contribution in the control of RNA virus infections. After the first evidence of cGAS/STING antagonism by flaviviruses, STING activation has been detected following infection by various enveloped RNA viruses. It has been discovered that numerous viral families have implemented advanced strategies to antagonize STING pathway through their evolutionary path. This review summarizes the characterized cGAS/STING escape strategies to date, together with the proposed mechanisms of STING signalling activation perpetrated by RNA viruses and discusses possible therapeutic approaches. Further studies regarding the interaction between RNA viruses and cGAS/STING-mediated immunity could lead to major discoveries important for the understanding of immunopathogenesis and for the treatment of RNA viral infections.

SARS-CoV-2 NSP8 suppresses type I and III IFN responses by modulating the RIG-I/MDA5, TRIF, and STING signaling pathways.

SARS-CoV-2 has developed a variety of approaches to counteract host innate antiviral immunity to facilitate its infection, replication and pathogenesis, but the molecular mechanisms that it employs are still not been fully understood. Here, we found that SARS-CoV-2 NSP8 inhibited the production of type I and III IFNs by acting on RIG-I/MDA5 and the signaling molecules TRIF and STING. Overexpression of NSP8 downregulated the expression of type I and III IFNs stimulated by poly (I:C) transfection and infection with SeV and SARS-CoV-2. In addition, NSP8 impaired IFN expression triggered by overexpression of the signaling molecules RIG-I, MDA5, and MAVS, instead of TBK1 and IRF3-5D, an active form of IRF3. From a mechanistic view, NSP8 interacts with RIG-I and MDA5, and thereby prevents the assembly of the RIG-I/MDA5-MAVS signalosome, resulting in the impaired phosphorylation and nuclear translocation of IRF3. NSP8 also suppressed the TRIF- and STING- induced IFN expression by directly interacting with them. Moreover, ectopic expression of NSP8 promoted virus replications. Taken together, SARS-CoV-2 NSP8 suppresses type I and III IFN responses by disturbing the RIG-I/MDA5-MAVS complex formation and targeting TRIF and STING signaling transduction. These results provide new insights into the pathogenesis of COVID-19. This article is protected by copyright. All rights reserved.

The cGAS-STING pathway in diabetic retinopathy and age-related macular degeneration.

Diabetic retinopathy and age-related macular degenerationare common retinal diseases with shared pathophysiology, including oxidative stress-induced inflammation. Cellular mechanisms responsible for converting oxidative stress into retinal damage are ill-defined but have begun to clarify. One common outcome of retinal oxidative stress is mitochondrial damage and subsequent release of mitochondrial DNA into the cytosol. This leads to activation of the cGAS-STING pathway, resulting in interferon release and disease-amplifying inflammation. This review summarizes the evolving link between aberrant cGAS-STING signaling and inflammation in common retinal diseases and provides prospective for targeting this system in diabetic retinopathy and age-related macular degeneration. Further defining the roles of this system in the retina is expected to reveal new disease pathology and novel therapeutic approaches.

The ubiquitin E3 ligase TRIM10 promotes STING aggregation and activation in the Golgi apparatus

STING is an endoplasmic reticulum-resident protein regulating innate immunity. After binding with cyclic guanosine monophosphate-AMP (cGAMP), STING translocates from the endoplasmic reticulum (ER) to the Golgi apparatus to stimulate TBK1 and IRF3 activation, leading to expression of type I interferon. However, the exact mechanism concerning STING activation remains largely enigmatic. Here, we identify tripartite motif 10 (TRIM10) as a positive regulator of STING signaling. TRIM10-deficient macrophages exhibit reduced type I interferon production upon double-stranded DNA (dsDNA) or cGAMP stimulation and decreased resistance to herpes simplex virus 1 (HSV-1) infection. Additionally, TRIM10-deficient mice are more susceptible to HSV-1 infection and exhibit faster melanoma growth. Mechanistically, TRIM10 associates with STING and catalyzes K27- and K29-linked polyubiquitination of STING at K289 and K370, which promotes STING trafficking from the ER to the Golgi apparatus, formation of STING aggregates, and recruitment of TBK1 to STING, ultimately enhancing the STING-dependent type I interferon response. Our study defines TRIM10 as a critical activator in cGAS-STING-mediated antiviral and antitumor immunity.

Epigenetic state determines the in vivo efficacy of STING agonist therapy

While STING-activating agents have shown limited efficacy in early-phase clinical trials, multiple lines of evidence suggest the importance of tumor cell-intrinsic STING function in mediating antitumor immune responses. Although STING signaling is impaired in human melanoma, its restoration through epigenetic reprogramming can augment its antigenicity and T cell recognition. In this study, we show that reversal of methylation silencing of STING in murine melanoma cell lines using a clinically available DNA methylation inhibitor can improve agonist-induced STING activation and type-I IFN induction, which, in tumor-bearing mice, can induce tumor regression through a CD8+ T cell-dependent immune response. These findings not only provide mechanistic insight into how STING signaling dysfunction in tumor cells can contribute to impaired responses to STING agonist therapy, but also suggest that pharmacological restoration of STING signaling through epigenetic reprogramming might improve the therapeutic efficacy of STING agonists.

Flavonoid derivative DMXAA attenuates cisplatin-induced acute kidney injury independent of STING signaling.

Cisplatin-induced nephrotoxicity is the main adverse effect of cisplatin-based chemotherapy and highly limits its clinical use. DMXAA, a flavonoid derivative, is a promising vascular disrupting agent and known as an agonist of STING. Although cGAS-STING activation has been demonstrated to mediate cisplatin-induced acute kidney injury (AKI), the role of DMXAA in this condition is unclear. Here, we defined an unexpected and critical role of DMXAA in improving renal function, ameliorating renal tubular injury and cell apoptosis, and suppressing inflammation in cisplatin-induced AKI. Moreover, we confirmed that DMXAA combated AKI in a STING-independent manner, as evidenced by its protective effect in STING global knockout mice subjected to cisplatin. Furthermore, we compared the role of DMXAA with another STING agonist SR717 in cisplatin-treated mice and found that DMXAA but not SR717 protected animals against AKI. To better evaluate the role of DMXAA, we performed transcriptome analyses and observed that both inflammatory and metabolic pathways were altered by DMXAA treatment. Due to the established role of metabolic disorders in AKI, which contributes to kidney injury and recovery, we also performed metabolomics using kidney tissues from cisplatin-induced AKI mice with or without DMXAA treatment. Strikingly, our results revealed that DMXAA improved the metabolic disorders in kidneys of AKI mice, especially regulated the tryptophan metabolism. Collectively, therapeutic administration of DMXAA ameliorates cisplatin-induced AKI independent of STING, suggesting a promising potential for preventing nephrotoxicity induced by cisplatin-based chemotherapy.

Synthetic enforcement of STING signaling in cancer cells appropriates the immune microenvironment for checkpoint inhibitor therapy

Immune checkpoint inhibitors (ICIs) enhance anticancer immunity by releasing repressive signals into tumor microenvironments (TMEs). To be effective, ICIs require preexisting immunologically "hot" niches for tumor antigen presentation and lymphocyte recruitment. How the mutational landscape of cancer cells shapes these immunological niches remains poorly defined. We found in human and murine colorectal cancer (CRC) models that the superior antitumor immune response of mismatch repair (MMR)-deficient CRC required tumor cell-intrinsic activation of cGAS-STING signaling triggered by genomic instability. Subsequently, we synthetically enforced STING signaling in CRC cells with intact MMR signaling using constitutively active STING variants. Even in MMR-proficient CRC, genetically encoded gain-of-function STING was sufficient to induce cancer cell-intrinsic interferon signaling, local activation of antigen-presenting cells, recruitment of effector lymphocytes, and sensitization of previously "cold" TMEs to ICI therapy in vivo. Thus, our results introduce a rational strategy for modulating cancer cell-intrinsic programs via engineered STING enforcement to sensitize resistant tumors to ICI responsiveness.

PP2Ac/STRN4 negatively regulates STING-type I IFN signaling in tumor-associated macrophages.

Stimulator of IFN genes type I (STING-Type I) IFN signaling in myeloid cells plays a critical role in effective antitumor immune responses, but STING agonists as monotherapy have shown limited efficacy in clinical trials. The mechanisms that downregulate STING signaling are not fully understood. Here, we report that protein phosphatase 2A (PP2A), with its specific B regulatory subunit Striatin 4 (STRN4), negatively regulated STING-Type I IFN in macrophages. Mice with macrophage PP2A deficiency exhibited reduced tumor progression. The tumor microenvironment showed decreased immunosuppressive and increased IFN-activated macrophages and CD8+ T cells. Mechanistically, we demonstrated that Hippo kinase MST1/2 was required for STING activation. STING agonists induced dissociation of PP2A from MST1/2 in normal macrophages, but not in tumor conditioned macrophages. Furthermore, our data showed that STRN4 mediated PP2A binding to and dephosphorylation of Hippo kinase MST1/2, resulting in stabilization of YAP/TAZ to antagonize STING activation. In human patients with glioblastoma (GBM), YAP/TAZ was highly expressed in tumor-associated macrophages but not in nontumor macrophages. We also demonstrated that PP2A/STRN4 deficiency in macrophages reduced YAP/TAZ expression and sensitized tumor-conditioned macrophages to STING stimulation. In summary, we demonstrated that PP2A/STRN4-YAP/TAZ has, in our opinion, been an unappreciated mechanism that mediates immunosuppression in tumor-associated macrophages, and targeting the PP2A/STRN4-YAP/TAZ axis can sensitize tumors to immunotherapy.

CGAS-STING signalling in cancer: striking a balance with chromosomal instability.

Chromosomal instability (CIN) is a hallmark of cancer that drives tumour evolution. It is now recognised that CIN in cancer leads to the constitutive production of misplaced DNA in the form of micronuclei and chromatin bridges. These structures are detected by the nucleic acid sensor cGAS, leading to the production of the second messenger 2'3'-cGAMP and activation of the critical hub of innate immune signalling STING. Activation of this immune pathway should instigate the influx and activation of immune cells, resulting in the eradication of cancer cells. That this does not universally occur in the context of CIN remains an unanswered paradox in cancer. Instead, CIN-high cancers are notably adept at immune evasion and are highly metastatic with typically poor outcomes. In this review, we discuss the diverse facets of the cGAS-STING signalling pathway, including emerging roles in homeostatic processes and their intersection with genome stability regulation, its role as a driver of chronic pro-tumour inflammation, and crosstalk with the tumour microenvironment, which may collectively underlie its apparent maintenance in cancers. A better understanding of the mechanisms whereby this immune surveillance pathway is commandeered by chromosomally unstable cancers is critical to the identification of new vulnerabilities for therapeutic exploitation.