Human STING is a proton channel

Synthesis and structure-activity evaluation of a series of novel tricyclic STING activators

A novel small molecule tricyclic series of STING activators was designed, synthesized and evaluated for human STING activity. These STING agonists were optimized from an initial set of structures with low potency through iterative cycles of design, synthesis and biological evaluation to yield compounds with potent human STING activity. The binding and functional properties of 68, an exemplar from the series were determined. Further, while 68 activated major variants of human STING it did not activate murine STING. Treatment of human PBMCs led to pathway engagement and the release of pro-inflammatory cytokines. When administered intra-tumorally, 68 caused robust retardation in the growth of MCA205 mouse fibrosarcoma tumors in human STING knock-in mice.

TRIM23 mediates cGAS-induced autophagy in anti-HSV defense

The cGAS-STING pathway, well-known to elicit interferon (IFN) responses, is also a key inducer of autophagy upon virus infection or other stimuli. Whereas the mediators for cGAS-induced IFN responses are well characterized, much less is known about how cGAS elicits autophagy. Here, we report that TRIM23, a unique TRIM protein harboring both ubiquitin E3 ligase and GTPase activity, is crucial for cGAS-STING-dependent antiviral autophagy. Genetic ablation of TRIM23 impairs autophagic control of HSV-1 infection. HSV-1 infection or cGAS-STING stimulation induces TBK1-mediated TRIM23 phosphorylation at S39, which triggers TRIM23 autoubiquitination and GTPase activity and ultimately elicits autophagy. Fibroblasts from a patient with herpes simplex encephalitis heterozygous for a dominant-negative, kinase-inactivating TBK1 mutation fail to activate autophagy by TRIM23 and cGAS-STING. Our results thus identify the cGAS-STING-TBK1-TRIM23 axis as a key autophagy defense pathway and may stimulate new therapeutic interventions for viral or inflammatory diseases.

STING agonist-based ER-targeting molecules boost antigen cross-presentation

CD8+ T cell immune responses are critical for combating infectious diseases and tumours1-3. Antigen cross-presentation, primarily occurring at the endoplasmic reticulum (ER) of dendritic cells, is essential for protein-based vaccines to induce CD8+ T cell responses4. Current efforts have focused on antigen delivery at the tissue and cellular levels, whereas subcellular delivery has been limited to facilitating antigen escape from lysosomes into the cytosol. In the absence of a small-sized high-affinity ER-targeting molecule, the importance of the 'last mile' from the cytosol to the ER remains elusive. Here we developed stimulator of interferon genes (STING) agonist-based ER-targeting molecules (SABER), which effectively deliver antigens to the ER and cluster key machinery in cross-presentation to form microreactors by folding the ER membrane. Conjugation of SABER to various antigens substantially enhances the induction of CD8+ T cell immune responses to tumour neoantigens and conserved viral epitopes, far exceeding that achieved by mixtures of antigens with STING agonists or conventional adjuvants. SABER also retains a potent adjuvant effect, effectively enhancing the ability of a SARS-CoV-2 subunit vaccine to induce broadly neutralizing antibodies. This study provides a high-affinity ER-targeting delivery system and vaccine adjuvant, demonstrating that precise subcellular delivery targeting the last mile of cross-presentation can lead to a qualitative leap.

cGAS-STING: mechanisms and therapeutic opportunities

The cGAS-STING pathway plays a crucial role in the innate immune system by detecting mislocalized double-stranded DNA (dsDNA) in the cytoplasm and triggering downstream signal transduction. Understanding the mechanisms by which cGAS and STING operate is vital for gaining insights into the biology of this pathway. This review provides a detailed examination of the structural features of cGAS and STING proteins, with a particular emphasis on their activation and inhibition mechanisms. We also discuss the novel discovery of STING functioning as an ion channel. Furthermore, we offer an overview of key agonists and antagonists of cGAS and STING, shedding light on their mechanisms of action. Deciphering the molecular intricacies of the cGAS-STING pathway holds significant promise for the development of targeted therapies aimed at maintaining immune homeostasis within both innate and adaptive immunity.

Lysosomal Repair in Health and Disease

Lysosomes are essential organelles degrading a wide range of substrates, maintaining cellular homeostasis, and regulating cell growth through nutrient and metabolic signaling. A key vulnerability of lysosomes is their membrane permeabilization (LMP), a process tightly linked to diseases including aging, neurodegeneration, lysosomal storage disorders, and cardiovascular disease. Research progress in the past few years has greatly improved our understanding of lysosomal repair mechanisms. Upon LMP, cells activate multiple membrane remodeling processes to restore lysosomal integrity, such as membrane invagination, tubulation, lipid patching, and membrane stabilization. These repair pathways are critical in preserving cellular stress tolerance and preventing deleterious inflammation and cell death triggered by lysosomal damage. This review focuses on the expanding mechanistic insights of lysosomal repair, highlighting its crucial role in maintaining cellular health and the implications for disease pathogenesis and therapeutic strategies.

Antibody-Drug Conjugates (ADCs): current and future biopharmaceuticals

Antibody-drug conjugates (ADCs) represent a novel class of biopharmaceuticals comprising monoclonal antibodies covalently conjugated to cytotoxic agents via engineered chemical linkers. This combination enables targeted delivery of cytotoxic agents to tumor site through recognizing target antigens by antibody while minimizing off-target effects on healthy tissues. Clinically, ADCs overcome the limitations of traditional chemotherapy, which lacks target specificity, and enhance the therapeutic efficacy of monoclonal antibodies, providing higher efficacy and fewer toxicity anti-tumor biopharmaceuticals. ADCs have ushered in a new era of targeted cancer therapy, with 15 drugs currently approved for clinical use. Additionally, ADCs are being investigated as potential therapeutic candidates for autoimmune diseases, persistent bacterial infections, and other challenging indications. Despite their therapeutic benefits, the development and application of ADCs face significant challenges, including antibody immunogenicity, linker instability, and inadequate control over the release of cytotoxic agent. How can ADCs be designed to be safer and more efficient? What is the future development direction of ADCs? This review provides a comprehensive overview of ADCs, summarizing the structural and functional characteristics of the three core components, antibody, linker, and payload. Furthermore, we systematically assess the advancements and challenges associated with the 15 approved ADCs in cancer therapy, while also exploring the future directions and ongoing challenges. We hope that this work will provide valuable insights into the design and optimization of next-generation ADCs for wider clinical applications.

STING: a multifaced player in cellular homeostasis

The stimulator of interferon gene (STING) is an important innate immune mediator of the cytoplasmic DNA sensing pathway. As a mediator known for its role in the immune response to infections, STING is also surprisingly at the center of a variety of non-infectious human diseases, including cancer, autoimmune diseases and neurodegenerative diseases. Recent studies have shown that STING has many signaling activities, including type I interferon (IFN-I) and other IFN-independent activities, many of which are poorly understood. STING also has the unique property of being continuous transported from the ER to the Golgi then to the lysosome. Mutations of STING or trafficking cofactors are associated with human diseases affecting multiple immune and non-immune organs. Here, we review recent advances in STING trafficking and signaling mechanisms based in part on studies of STING-associated monogenic inborn error diseases.

STING aggravates ferroptosis-dependent myocardial ischemia-reperfusion injury by targeting GPX4 for autophagic degradation

Despite advancements in interventional coronary reperfusion technologies following myocardial infarction, a notable portion of patients continue to experience elevated mortality rates as a result of myocardial ischemia-reperfusion (MI/R) injury. An in-depth understanding of the mechanisms underlying MI/R injury is crucial for devising strategies to minimize myocardial damage and enhance patient survival. Here, it is discovered that during MI/R, double-stranded DNA (dsDNA)-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signal accumulates, accompanied by high rates of myocardial ferroptosis. The specific deletion of cgas or Sting in cardiomyocytes, resulting in the inhibition of oxidative stress, has been shown to mitigate ferroptosis and I/R injury. Conversely, activation of STING exacerbates ferroptosis and I/R injury. Mechanistically, STING directly targets glutathione peroxidase 4 (GPX4) to facilitate its degradation through autophagy, by promoting the fusion of autophagosomes and lysosomes. This STING-GPX4 axis contributes to cardiomyocyte ferroptosis and forms a positive feedback circuit. Blocking the STING-GPX4 interaction through mutations in T267 of STING or N146 of GPX4 stabilizes GPX4. Therapeutically, AAV-mediated GPX4 administration alleviates ferroptosis induced by STING, resulting in enhanced cardiac functional recovery from MI/R injury. Additionally, the inhibition of STING by H-151 stabilizes GPX4 to reverse GPX4-induced ferroptosis and alleviate MI/R injury. Collectively, a novel autophagy-dependent ferroptosis mechanism is identified in this study. Specifically, STING autophagy induced by anoxia or ischemia-reperfusion leads to GPX4 degradation, thereby presenting a promising therapeutic target for heart diseases associated with I/R.

TFEB and TFE3 regulate STING1-dependent immune responses by controlling type I interferon signaling

STING1 is an essential component of the innate immune defense against a wide variety of pathogens. Whereas induction of type I interferon (IFN) responses is one of the best-defined functions of STING1, our transcriptomic analysis revealed IFN-independent activities of STING1 in macrophages, including transcriptional upregulation of numerous lysosomal and autophagic genes. This upregulation was mediated by the STING1-induced activation of the transcription factors TFEB and TFE3, and led to increased autophagy, lysosomal biogenesis, and lysosomal acidification. TFEB and TFE3 also modulated IFN-dependent STING1 signaling by controlling IRF3 activation. IFN production and cell death were increased in TFEB- and TFE3-depleted iBMDMs. Conversely, TFEB overexpression led to reduced IRF3 activation and an almost complete inhibition of IFN synthesis and secretion, resulting in decreased CASP3 activation and increased cell survival. Our study reveals a key role of TFEB and TFE3 as regulators of STING1-mediated innate antiviral immunity.Abbreviation: ACOD1/IRG1, aconitate decarboxylase 1; cGAMP, cyclic guanosine monophosphate-adenosine monophosphate; CGAS, cyclic GMP-AMP synthase; DMXAA, 5,6-dimethylxanthenone-4-acetic acid; EIF4EBP1, eukaryotic translation initiation factor 4E binding protein 1; GABARAP, GABA type A receptor-associated protein; HSV-1, herpes simplex virus type; iBMDMs, immortalized bone marrow-derived macrophages; IFN, type I interferon; IFNB, interferon beta; IKBKE, inhibitor of nuclear factor kappa B kinase subunit epsilon; IRF3, interferon regulatory factor 3; LAMP1, lysosomal associated membrane protein 1; LAMP2, lysosomal associated membrane protein 2; MTORC1, mechanistic target of rapamycin kinase complex 1; RPS6, ribosomal protein S6; STING1, stimulator of interferon response cGAMP interactor 1; TBK1, TANK binding kinase 1; TFE3, transcription factor binding to IGHM enhancer 3; TFEB, transcription factor EB.

STING mediates lysosomal quality control and recovery through its proton channel function and TFEB activation in lysosomal storage disorders

Lysosomes are essential organelles for cellular homeostasis. Defective lysosomes are associated with diseases like lysosomal storage disorders (LSDs). How lysosomal defects are detected and lysosomal function restored remain incompletely understood. Here, we show that STING mediates a neuroinflammatory gene signature in three distinct LSD mouse models, Galctwi/twi, Ppt1-/-, and Cln7-/-. Transcriptomic analysis of Galctwi/twi mouse brain tissue revealed that STING also mediates the expression of lysosomal genes that are regulated by transcriptional factor EB (TFEB). Immunohistochemical and single-nucleus RNA-sequencing (snRNA-seq) analysis show that STING regulates lysosomal gene expression in microglia. Mechanistically, we show that STING activation leads to TFEB dephosphorylation, nuclear translocation, and expression of lysosomal genes. This process requires STING's proton channel function, the V-ATPase-ATG5-ATG8 cascade, and is independent of immune signaling. Furthermore, we show that the STING-TFEB axis facilitates lysosomal repair. Together, our data identify STING-TFEB as a lysosomal quality control mechanism that responds to lysosomal dysfunction.

Bioinspired Chloride-Assisted Protein Channels: Enhancing Proton Transport for Sustainable Energy Harvesting from Acidic Wastewater

Highly efficient proton transfer in biological processes has driven the pursuit of synthetic analogs; however, replicating high proton permeance in natural systems remains a significant challenge. Herein, inspired by the function of the ClC-ec1 protein, we report the design of Cl--assisted proton transport channels within a hybrid membrane composed of covalent organic frameworks (COFs) integrated with aramid nanofibers (ANFs). By leveraging buffer layer-mediated interfacial polymerization and the flocculation behavior of ANF in aqueous environments, we establish robust hydrogen-bonding interactions between COFs and ANFs. The hydride material enables Cl- binding, significantly accelerating proton transport in a manner similar to that of the ClC-ec1 protein channel. In the presence of a small concentration of Cl- ions (0.1% of the proton concentration), the proton permeation rate is enhanced approximately by 3 times, reaching 9.8 mol m-2 h-2. Notably, the membrane facilitates sustainable osmotic power generation from acidic wastewater, delivering an output power density of 434.8 W m-2. Theoretical calculations revealed that ANF preferentially binds Cl-, promoting proton hopping and lowering the energy barrier for proton transport. This study establishes a new paradigm for bioinspired ion-assisted proton transport, presenting an approach for sustainable energy harvesting from acidic wastewater.

Distinct oligomeric assemblies of STING induced by non-nucleotide agonists

STING plays essential roles coordinating innate immune responses to processes that range from pathogenic infection to genomic instability. Its adaptor function is activated by cyclic dinucleotide (CDN) secondary messengers originating from self (2'3'-cGAMP) or bacterial sources (3'3'-CDNs). Different classes of CDNs possess distinct binding modes, stabilizing STING's ligand-binding domain (LBD) in either a closed or open conformation. The closed conformation, induced by the endogenous ligand 2'3'-cGAMP, has been extensively studied using cryo-EM. However, significant questions remain regarding the structural basis of STING activation by open conformation-inducing ligands. Using cryo-EM, we investigate potential differences in conformational changes and oligomeric assemblies of STING for closed and open conformation-inducing synthetic agonists. While we observe a characteristic 180° rotation for both classes, the open-LBD inducing agonist diABZI-3 uniquely induces a quaternary structure reminiscent but distinct from the reported autoinhibited state of apo-STING. Additionally, we observe slower rates of activation for this ligand class in functional assays, which collectively suggests the existence of a potential additional regulatory mechanism for open conformation-inducing ligands that involves head-to-head interactions and restriction of curved oligomer formation. These observations have potential implications in the selection of an optimal class of STING agonist in the context of a defined therapeutic application.

LRRK2, lysosome damage, and Parkinson's disease

Limited understanding of regulatory mechanisms controlling LRRK2 kinase activity has hindered insights into both its normal biology and how its dysregulation contributes to Parkinson's disease. Fortunately, recent years have yielded an increased understanding of how LRRK2 kinase activity is dynamically regulated by recruitment to endolysosomal membranes. Notably, multiple small GTPases from the Rab family act as both activators and substrates of LRRK2. Additionally, it was recently discovered that LRRK2 is recruited to, and activated at, stressed or damaged lysosomes through an interaction with GABARAP via the CASM (conjugation of ATG8 to single membranes) pathway. These discoveries position LRRK2 within the rapidly growing field of lysosomal damage and repair mechanisms, offering important insights into lysosome biology and the pathogenesis of Parkinson's disease.

Regulation of the cGAS-STING Pathway

The cGAS-cGAMP-STING pathway is essential for immune defense against pathogens. Upon binding DNA, cGAS synthesizes cGAMP, which activates STING, leading to potent innate immune effector responses. However, lacking specific features to distinguish between self and nonself DNA, cGAS-STING immunity requires precise regulation to prevent aberrant activation. Several safeguard mechanisms acting on different levels have evolved to maintain tolerance to self DNA and ensure immune homeostasis under normal conditions. Disruption of these safeguards can lead to erroneous activation by self DNA, resulting in inflammatory conditions but also favorable antitumor immunity. Insights into structural and cellular checkpoints that control and terminate cGAS-STING signaling are essential for comprehending and manipulating DNA-triggered innate immunity in health and disease.

STING Activation in Various Cell Types in Metabolic Dysfunction-Associated Steatotic Liver Disease

BACKGROUND

During the hepatic histological progression in metabolic dysfunction-associated steatotic liver disease (MASLD), the immunological mechanisms play a the pivotal role, especially when progressing to metabolic dysfunction-associated steatohepatitis (MASH). The discovery of the stimulator of interferon genes (STING) marked a significant advancement in understanding the immune system.

METHODS

We searched literature on STING involved in MASLD in PubMed to summarise the role of intrahepatic or extrahepatic STING signal pathways and the potential agonists or inhibitors of STING in MASLD.

RESULTS

Besides inflammation and type I interferon response induced by STING activation in the intrahepatic or extrahepatic immune cells, STING activation in hepatocytes leads to protein aggregates and lipid deposition. STING activation in hepatic macrophages inhibits autophagy in hepatocytes and promotes hepatic stellate cells (HSCs) activation. STING activation in HSCs promotes HSC activation and exacerbates liver sinusoidal endothelial cells (LSECs) impairment. However, it was also reported that STING activation in hepatic macrophages promotes lipophagy in hepatocytes and STING activation in HSCs leads to HSC senescence. STING activation in LSEC, inhibits angiogenesis. For extrahepatic tissue, STING signalling participates in the regulation of the intestinal permeability, intestinal microecology and insulin action in adipocytes, which were all involved in the pathogenesis of MASLD.

CONCLUSION

There're plenty of STING ligands in MASLD. How STING activation affects the intercellular conversation in MASLD deserves thorough investigation.

An Injectable Multifunctional Nanosweeper Eliminates Cardiac Mitochondrial DNA to Reduce Inflammation

Myocarditis, a leading cause of sudden cardiac death and heart transplantation, poses significant treatment challenges. The study of clinical samples from myocarditis patients reveals a correlation between the pathogenesis of myocarditis and cardiomyocyte mitochondrial DNA (mtDNA). During inflammation, the concentration of mtDNA in cardiomyocytes increases. Hence, it is hypothesized that the combined clearance of mtDNA and its downstream STING pathway can treat myocarditis. However, clearing mtDNA is problematic. An innovative mtDNA scavenger is introduced, Nanosweeper (NS), which utilizes its nanostructure to facilitate the transport of NS-mtDNA co-assemblies for degradation, achieving mtDNA clearance. The fluorescent mtDNA probe on NS, bound to functional peptides, enhances the stability of NS. NS also exhibits robust stability in human plasma with a half-life of up to 10 hours. In a murine myocarditis model, NS serves as a drug delivery vehicle, targeting the delivery of the STING pathway inhibitor C-176 to the myocardium. This approach synergistically modulates the cGAS-STING axis with NS, effectively attenuating myocarditis- associated inflammatory cascade. This evaluation of NS in porcine models corroborated its superior biosafety profile and cardiac targeting capability. This strategic approach of targeted mtDNA clearance couple with STING pathway inhibition, significantly augments therapeutic efficacy against myocarditis, outperforming the conventional drug C-176, indicating its clinical potential.

Extracellular vesicles in cancer progression: mechanisms and significance

Tumor recurrence, metastasis, clinical drug resistance, and immune evasion are critical events in cancer progression, characterized by significant spatiotemporal heterogeneity and plasticity. Intercellular communication between tumor cells and other cells within the tumor microenvironment plays a pivotal role in these processes. Extracellular vesicles (EVs), heterogeneous secretory messengers carrying bioactive molecules, facilitate this cell-to-cell communication, thereby dynamically influencing cancer progression. Deciphering the mechanisms of EV formation and regulatory pathways and identifying key networks and targets in tumor metastasis, drug resistance, and immune response mediated by EVs will provide new insights into the understanding of cancer progression patterns and offer innovative strategies for cancer diagnosis and therapy.

ArfGAP2 promotes STING proton channel activity, cytokine transit, and autoinflammation

Stimulator of interferon genes (STING) transmits signals downstream of the cytosolic DNA sensor cyclic guanosine monophosphate-AMP synthase (cGAS), leading to transcriptional upregulation of cytokines. However, components of the STING signaling pathway, such as IRF3 and IFNAR1, are not essential for autoinflammatory disease in STING gain-of-function (STING-associated vasculopathy with onset in infancy [SAVI]) mice. Recent discoveries revealed that STING also functions as a proton channel that deacidifies the Golgi apparatus. Because pH impacts Golgi enzyme activity, protein maturation, and trafficking, we hypothesized that STING proton channel activity influences multiple Golgi functions. Here, we show that STING-mediated proton efflux non-transcriptionally regulates Golgi trafficking of protein cargos. This process requires the Golgi-associated protein ArfGAP2, a cell-type-specific dual regulator of STING-mediated proton efflux and signaling. Deletion of ArfGAP2 in hematopoietic and endothelial cells markedly reduces STING-mediated cytokine and chemokine secretion, immune cell activation, and autoinflammatory pathology in SAVI mice. Thus, ArfGAP2 facilitates STING-mediated signaling and cytokine release in hematopoietic cells, significantly contributing to autoinflammatory disease pathogenesis.

Comparative Molecular, Innate, and Adaptive Impacts of Chemically Diverse STING Agonists

Pharmacologic activation of the innate immune response is being actively being pursued for numerous clinical purposes including enhancement of vaccine potency and potentiation of anti-cancer immunotherapy. Pattern recognition receptors (PRRs) represent especially useful targets for these efforts as their engagement by agonists can trigger signaling pathways that associate with phenotypes desirable for specific immune outcomes. Stimulator of interferon genes (STING) is an ER-resident PRR reactive to cyclic dinucleotides such as those synthesized endogenously in response to cytosolic dsDNA. STING activation leads to transient generation of type I interferon (IFN-I) and proinflammatory responses that augment immunologically relevant effects including antiviral responses, antigen presentation, immune cell trafficking, and immunogenic cell death. In recent years engineered cyclic dinucleotides and small molecules have been discovered that induce STING and safely confer clinically useful outcomes in animal models such as adjuvanticity of anti-microbial vaccines and tumor clearance. Unfortunately, clinical trials examining the efficacy of STING agonists have thus far failed to satisfactorily recapitulate these positive outcomes and this has prevented their translational advancement. A likely relevant yet perplexingly under investigated aspect of pharmacologic STING activation is the diversity of molecular and immune responses that associate with chemical properties of the agonist. Based on this, a comparative survey of these was undertaken using unrelated STING-activating molecules to characterize the molecular, innate, cellular, and immune outcomes they elicit. This was done to inform and direct future studies aimed at designing and selecting agonists appropriate for desired clinical goals. This revealed demonstrable differences between the agonists in potency, transcriptomes, cytokine secretion profiles, immune cell trafficking, and antigen-directed humoral and cell mediated immune responses. As such, this work illustrates that phenotypes deriving from activation of a protein target can be linked to chemical properties of the engaging agonist and thus heightened scrutiny is necessary when selecting molecules to generate specific in vivo effects.

STING-induced noncanonical autophagy regulates endolysosomal homeostasis

The cGAS-STING pathway mediates innate immune responses to cytosolic DNA. In addition to its well-established role in inducing inflammatory cytokines, activation of the cGAS-STING pathway also induces noncanonical autophagy, a process involving the conjugation of the ATG8 family of ubiquitin-like proteins to membranes of the endolysosomal system. The mechanisms and functions of STING-induced autophagy remain poorly understood. In this study, we demonstrated that STING activation induced formation of pH-elevated Golgi-derived vesicles that led to ATG16L1 and V-ATPase-dependent noncanonical autophagy. We showed that STING-induced noncanonical autophagy resulted in activation of the MiT/TFE family of transcription factors (TFEB, TFE3, and MITF), which regulate lysosome biogenesis. We found that lipidation of the ATG8 proteins, particularly GABARAPs, inhibited phosphorylation of MiT/TFE transcription factors by mTORC1. The lipidated GABARAPs bound to the Folliculin-interacting proteins (FNIPs), thereby sequestering the FNIP-folliculin protein complexes from activating mTORC1, resulting in dephosphorylation and nuclear translocation of MiT/TFE transcription factors. Furthermore, we found that STING-induced autophagy activated Leucine-rich repeat kinase 2 (LRRK2), a protein implicated in Parkinson's disease, through GABARAPs lipidation. We further showed that STING-induced autophagy induced ALIX-mediated ESCRT machinery recruitment to mitigate endolysosomal perturbation. These results reveal the multifaceted functions of STING-induced noncanonical autophagy in regulating endolysosomal homeostasis.

ARIES domains: functional signaling units of type I interferon responses

The innate immune system relies on a network of signaling proteins classified by shared domains, which serve as functional units that orchestrate inflammatory and host defensive activities. Within type I interferon (IFN) responses, the stimulator of interferon genes protein (STING), mitochondrial antiviral-signaling protein (MAVS), Toll-IL-1 receptor-resistance protein domain-containing adapter-inducing interferon-β (TRIF), Toll-like receptor adapter interacting with SLC15A4 on the lysosome (TASL), insulin receptor tyrosine kinase substrate protein of 53 kDa (IRSp53), and GEM interacting protein (GMIP) utilize a conserved pLxIS motif to recruit IRF family transcription factors. Notably, the pLxIS motif functions within a larger signaling unit, which is referred to here as an Activator of Interferon Expression via a pLxIS motif (ARIES) domain. ARIES domains consist of the pLxIS motif and adjacent kinase activation motifs that together drive IFN responses. This review explores how ARIES domains promote immune responses via shared and distinct signaling mechanisms, protein localization, and regulation of metabolic shifts, underscoring their evolutionary conservation and critical role in host defense.

ATG8 in single membranes: Fresh players of endocytosis and acidic organelle quality control in cancer, neurodegeneration, and inflammation

Ubiquitin-like autophagy-related gene ATG8 proteins are typically associated with degradative quality control via canonical double-membrane macro-autophagosomes in the cell. ATG8 proteins have now stepped forward in non-canonical pathways in single membrane organelles. The growing interest in non-canonical ATG8 roles has been stimulated by recent links to human conditions, especially in the regulation of inflammation, neurodegeneration and cancers. Here, we summarize the evidence linking non-canonical ATG8s to human pathologies and the quality control of acidic V-ATPase-regulated organelles in the cell.

The cGAS-STING pathway activates transcription factor TFEB to stimulate lysosome biogenesis and pathogen clearance

Induction of autophagy is an ancient function of the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway through which autophagic cargoes are delivered to lysosomes for degradation. However, whether lysosome function is also modulated by the cGAS-STING pathway remains unknown. Here, we discovered that the cGAS-STING pathway upregulated lysosomal activity by stimulating lysosome biogenesis independently of the downstream protein kinase TANK-binding kinase 1 (TBK1). STING activation enhanced lysosome biogenesis through inducing the nuclear translocation of transcription factor EB (TFEB) as well as its paralogs transcription factor E3 (TFE3) and microphthalmia-associated transcription factor (MITF). STING-induced lipidation of GABA type A receptor-associated protein (GABARAP), an autophagy-related protein, on STING vesicles was responsible for TFEB activation. Membrane-bound GABARAP sequestered the GTPase-activating protein folliculin (FLCN) and FLCN-interacting protein (FNIP) complex to block its function toward the Rag GTPases Ras-related GTP-binding C and D (RagC and RagD), abolishing mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent phosphorylation and inactivation of TFEB. Functionally, STING-induced lysosome biogenesis within cells facilitated the clearance of cytoplasmic DNA and invading pathogens. Thus, our findings reveal that induction of lysosome biogenesis is another important function of the cGAS-STING pathway.

Next generation lysosome: Brought to you by cGAS-STING

Renowned for driving interferon responses, the cGAS-STING pathway reveals a surprising role: lysosomal biogenesis. In this issue of Immunity, Xu et al. uncover how STING activates the transcription factor TFEB, linking innate immune sensing to enhanced pathogen clearance through lysosomal activity.

A STING-CASM-GABARAP pathway activates LRRK2 at lysosomes

Mutations that increase LRRK2 kinase activity have been linked to Parkinson's disease and Crohn's disease. LRRK2 is also activated by lysosome damage. However, the endogenous cellular mechanisms that control LRRK2 kinase activity are not well understood. In this study, we identify signaling through stimulator of interferon genes (STING) as an activator of LRRK2 via the conjugation of ATG8 to single membranes (CASM) pathway. We furthermore establish that multiple chemical stimuli that perturb lysosomal homeostasis also converge on CASM to activate LRRK2. Although CASM results in the lipidation of multiple ATG8 protein family members, we establish that LRRK2 lysosome recruitment and kinase activation are highly dependent on interactions with the GABARAP member of this family. Collectively, these results define a pathway that integrates multiple stimuli at lysosomes to control the kinase activity of LRRK2. Aberrant activation of LRRK2 via this pathway may be of relevance in both Parkinson's and Crohn's diseases.

The Stimulator of Interferon Genes Deficiency Attenuates Diabetic Myopathy Through Inhibiting NLRP3-Mediated Pyroptosis

BACKGROUND

Diabetic myopathy is characterized by the loss of skeletal muscle mass and function. NOD-like receptor family pyrin domain containing 3 (NLRP3)-mediated pyroptosis is a type of proinflammatory cell death, which can exacerbate significant muscle cell loss and adverse remodelling. The stimulator of interferon genes (STING) is an essential molecule involved in the regulation of inflammation and immune responses across various diseases. The regulatory mechanism by which STING affects muscle pyroptosis in diabetic myopathy remains unclear.

METHODS

STING-knockout and wild-type (WT) mice underwent intraperitoneal injection of streptozotocin (STZ). STING small interfering RNA (siRNA) was transfected into fully differentiated C2C12 myotubes prior to glucose treatment. Muscle function tests, body composition analysis, transmission electron microscopy, scanning electron microscopy, western blotting, immunofluorescence, immunohistochemistry, histology, enzyme-linked immunosorbent assay, and reverse transcription polymerase chain reaction were performed. Co-immunoprecipitation assays were employed to investigate the interaction between STING and NLRP3.

RESULTS

STING expression was elevated in the gastrocnemius muscle (GM) tissues of WT diabetic mice. STING-deficient diabetic mice exhibited pronounced hyperglycaemia accompanied by hypoinsulinaemia, with no significant difference compared with WT diabetic mice. However, STING-deficient diabetic mice demonstrated a significantly increased body weight and lean mass. A significant decrease in muscle weight, myofibrillar diameter and area, muscle function, and the expression of genes related to muscle atrophy (MuRF1, Atrogin1) were observed in WT diabetic mice, which was mitigated in STING-deficient diabetic mice. STING deficiency reduced the number of GSDMD-N formed pores and pyroptosis-related components (NLRP3, caspase-1, cle-caspase-1, GSDMD, and GSDMD-N) in the GM tissues and was associated with a reduction in inflammatory chemokines. Similar changes were observed in vitro with glucose-induced myotube atrophy and pyroptosis as seen in vivo. Activation of STING by the agonist diABZI exacerbated muscle atrophy and pyroptosis in C2C12 myotubes. Co-localization of STING and NLRP3 was observed, and the interaction between STING and NLRP3 was enhanced in GM tissues from WT diabetic mice. We also found that STING could activate NLRP3 dependent on its channel activity, which can be attenuated by treated with C53 (an inhibitor of STING's ion-channel function).

CONCLUSIONS

In conclusion, our results indicate that STING-induced activation of the NLRP3 inflammasome leads to pyroptosis, resulting in muscle atrophy and dysfunction. These findings not only elucidate the mechanism of STING-induced pyroptosis but also identify STING as a potential therapeutic target for diabetic myopathy.

The STING signaling pathways and bacterial infection

As antibiotic-resistant bacteria continue to emerge frequently, bacterial infections have become a significant and pressing challenge to global public health. Innate immunity triggers the activation of host responses by sensing "non-self" components through various pattern recognition receptors (PRRs), serving as the first line of antibacterial defense. Stimulator of interferon genes (STING) is a PRR that binds with cyclic dinucleotides (CDN) to exert effects against bacteria, viruses, and cancer by inducing the production of type I interferon and inflammatory cytokines, and facilitating regulated cell death. Currently, drugs targeting the STING signaling pathway are predominantly applied in the fields of modulating host immune defense against cancer and viral infections, with relatively limited application in treating bacterial infections. Given the significant immunomodulatory functions of STING in the interaction between bacteria and hosts, this review summarizes the research progress on STING signaling pathways and their roles in bacterial infection, as well as the novel functions of STING modulators, aiming to offer insights for the development of antibacterial drugs.

The critical role of endoplasmic reticulum stress and the stimulator of interferon genes (STING) pathway in kidney fibrosis

Endoplasmic reticulum (ER) stress is a condition in which the ER is overwhelmed and unable to manage its protein load properly. The precise activation mechanisms and role of ER stress in kidney disease remain unclear. To study this, we performed unbiased transcriptomics analysis to demonstrate ER stress in kidneys of patients with chronic kidney disease and in mouse models of acute and chronic kidney injury (cisplatin and unilateral ureteral obstruction and reanalyzed previously published data on folic acid and mitochondrial transcription factor A(TFAM) knockout mice). Inhibiting the protein kinase RNA-like ER kinase (PERK) arm of ER stress but not activating transcription factor 6 or inositol-requiring enzyme 1, protected mice from kidney fibrosis. The stimulator of interferon genes (STING) was identified as an important upstream activator of ER stress in kidney tubule cells. STING and PERK were found to physically interact, and STING agonists induced PERK activation in kidney tubule cells. Mice with a STING activating mutation presented with ER stress and kidney fibroinflammation. We also generated mice with a tubule specific STING deletion that were resistant to ER stress and kidney fibrosis. Human kidney spatial transcriptomics highlighted a spatial correlation between STING, ER stress and fibrotic gene expression. Thus, our results indicate that STING is an important upstream regulator of PERK and ER stress in tubule cells during kidney fibrosis development.

Mechanisms and roles of membrane-anchored ATG8s

Autophagy-related protein 8 (ATG8) family proteins, including LC3 and GABARAP subfamilies, are pivotal in canonical autophagy, driving autophagosome formation, cargo selection, and lysosomal fusion. However, recent studies have identified non-canonical roles for lipidated ATG8 in processes such as LC3-associated phagocytosis (LAP), LC3-associated endocytosis (LANDO), and lipidated ATG8-mediated secretory autophagy. These pathways expand ATG8's functional repertoire in immune regulation, membrane repair, and pathogen clearance, as ATG8 becomes conjugated to single-membrane structures (e.g., phagosomes and lysosomes). This review examines the molecular mechanisms of ATG8 lipidation, focusing on its selective conjugation to phosphatidylethanolamine (PE) in autophagy and phosphatidylserine (PS) in CASM. We highlight LIR-based probes and LC3/GABARAP-specific deconjugases as critical tools that allow precise tracking and manipulation of ATG8 in autophagic and non-autophagic contexts. These advancements hold therapeutic promise for treating autophagy-related diseases, including cancer and neurodegenerative disorders, by targeting ATG8-driven pathways that maintain cellular homeostasis.

Regulation of cGAS-STING signalling and its diversity of cellular outcomes

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling pathway, which recognizes both pathogen DNA and host-derived DNA, has emerged as a crucial component of the innate immune system, having important roles in antimicrobial defence, inflammatory disease, ageing, autoimmunity and cancer. Recent work suggests that the regulation of cGAS-STING signalling is complex and sophisticated. In this Review, we describe recent insights from structural studies that have helped to elucidate the molecular mechanisms of the cGAS-STING signalling cascade and we discuss how the cGAS-STING pathway is regulated by both activating and inhibitory factors. Furthermore, we summarize the newly emerging understanding of crosstalk between cGAS-STING signalling and other signalling pathways and provide examples to highlight the wide variety of cellular processes in which cGAS-STING signalling is involved, including autophagy, metabolism, ageing, inflammation and tumorigenesis.

Emerging concepts and treatments in autoinflammatory interferonopathies and monogenic systemic lupus erythematosus

Over the past two decades, the number of genetically defined autoinflammatory interferonopathies has steadily increased. Aicardi-Goutières syndrome and proteasome-associated autoinflammatory syndromes (PRAAS, also known as CANDLE) are caused by genetic defects that impair homeostatic intracellular nucleic acid and protein processing respectively. Research into these genetic defects revealed intracellular sensors that activate type I interferon production. In SAVI and COPA syndrome, genetic defects that cause chronic activation of the dinucleotide sensor stimulator of interferon genes (STING) share features of lung inflammation and fibrosis; and selected mutations that amplify interferon-α/β receptor signalling cause central nervous system manifestations resembling Aicardi-Goutières syndrome. Research into the monogenic causes of childhood-onset systemic lupus erythematosus (SLE) demonstrates the pathogenic role of autoantibodies to particle-bound extracellular nucleic acids that distinguishes monogenic SLE from the autoinflammatory interferonopathies. This Review introduces a classification for autoinflammatory interferonopathies and discusses the divergent and shared pathomechanisms of interferon production and signalling in these diseases. Early success with drugs that block type I interferon signalling, new insights into the roles of cytoplasmic DNA or RNA sensors, pathways in type I interferon production and organ-specific pathology of the autoinflammatory interferonopathies and monogenic SLE, reveal novel drug targets that could personalize treatment approaches.

Adaptor-Mediated Trafficking of Tank Binding Kinase 1 During Diverse Cellular Processes

The serine/threonine kinase, Tank Binding Kinase 1 (TBK1), drives distinct cellular processes like innate immune signaling, selective autophagy, and mitosis. It is suggested that the translocation and activation of TBK1 at different subcellular locations within the cell, downstream of diverse stimuli, are driven by TBK1 adaptor proteins forming a complex directly or indirectly with TBK1. Various TBK1 adaptors and associated proteins like NAP1, TANK, SINTBAD, p62, optineurin (OPTN), TAX1BP1, STING, and NDP52 have been identified in facilitating TBK1 activation and recruitment with varying overlapping redundancy. This review focuses on what is known about these proteins, their interactions with TBK1, and the functional consequences of these associations. We shed light on underexplored areas of research on these TBK1 binding partners while emphasizing how future research is required to understand the function and flexibility of TBK1 signaling and crosstalk or regulation between different biological processes.

STING induces HOIP-mediated synthesis of M1 ubiquitin chains to stimulate NF-κB signaling

STING activation by cyclic dinucleotides induces IRF3- and NF-κB-mediated gene expression in mammals, as well as lipidation of LC3B at Golgi-related membranes. While mechanisms of the IRF3 response are well understood, the mechanisms of NF-κB activation via STING remain unclear. We report here that STING activation induces linear/M1-linked ubiquitin chain (M1-Ub) formation and recruitment of the LUBAC E3 ligase, HOIP, to LC3B-associated Golgi membranes where ubiquitin is also localized. Loss of HOIP prevents formation of M1-Ub chains and reduces STING-induced NF-κB and IRF3 signaling in human THP1 monocytes and mouse bone marrow-derived macrophages, without affecting STING activation. STING-induced LC3B lipidation is not required for M1-Ub chain formation or for immune-related gene expression, but the recently reported STING function in neutralizing Golgi pH may be involved. Thus, LUBAC synthesis of M1-linked ubiquitin chains mediates STING-induced innate immune signaling.

Potential therapeutic strategies for colitis and colon cancer: bidirectional targeting STING pathway

The cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) pathway has emerged as a promising therapeutic target for colitis and colon cancers. Notably, inhibiting STING may mitigate the progression of colitis, whereas activating STING can enhance anti-tumor immune responses against colon cancer. This duality suggests that the development of STING agonists and inhibitors possesses significant clinical translational potential. In this review, we provide a comprehensive overview of STING inhibitors/agonists that have been systematically evaluated in the contexts of colitis and colon cancer and their specific molecular mechanisms. Other well-characterized STING inhibitors/agonists may also hold considerable promise for the treatment of these conditions, although efficacy validation remain necessary. Additionally, we delve into the latest advances concerning STING oligomerization, degradation and phase separation-dependent self-regulation, proposing potential druggable targets that could inspire the development of novel STING agonists or inhibitors. In Summary, targeting STING appears to be a promising strategy for the treatment of colitis and colon cancer.

The intricate interactions between inflammasomes and bacterial pathogens: Roles, mechanisms, and therapeutic potentials

Inflammasomes are intracellular multiprotein complexes that consist of a sensor, an adaptor, and a caspase enzyme to cleave interleukin (IL)-1β and IL-18 into their mature forms. In addition, caspase-1 and -11 activation results in the cleavage of gasdermin D to form pores, thereby inducing pyroptosis. Activation of the inflammasome and pyroptosis promotes host defense against pathogens, whereas dysregulation of the inflammasome can result in various pathologies. Inflammasomes exhibit versatile microbial signal detection, directly or indirectly, through cellular processes, such as ion fluctuations, reactive oxygen species generation, and the disruption of intracellular organelle function; however, bacteria have adaptive strategies to manipulate the inflammasome by altering microbe-associated molecular patterns, intercepting innate pathways with secreted effectors, and attenuating inflammatory and cell death responses. In this review, we summarize recent advances in the diverse roles of the inflammasome during bacterial infections and discuss how bacteria exploit inflammasome pathways to establish infections or persistence. In addition, we highlight the therapeutic potential of harnessing bacterial immune subversion strategies against acute and chronic bacterial infections. A more comprehensive understanding of the significance of inflammasomes in immunity and their intricate roles in the battle between bacterial pathogens and hosts will lead to the development of innovative strategies to address emerging threats posed by the expansion of drug-resistant bacterial infections.

Application of Proteomics Technology Based on LC-MS Combined with Western Blotting and Co-IP in Antiviral Innate Immunity

As an interferon-stimulating factor protein, STING plays a role in the response and downstream liaison in antiviral natural immunity. Upon viral invasion, the immediate response of STING protein leads to a series of changes in downstream proteins, which ultimately leads to an antiviral immune response in the form of proinflammatory cytokines and type I interferons, thus triggering an innate immune response, an adaptive immune response in vivo, and long-term protection of the host. In the field of antiviral natural immunity, it is particularly important to rigorously and sequentially probe the dynamic changes in the antiviral natural immunity connector protein STING caused by the entire anti-inflammatory and anti-pathway mechanism and the differences in upstream and downstream proteins. Traditionally, proteomics technology has been validated by detecting proteins in a 2D platform, for which it is difficult to sensitively identify changes in the nature and abundance of target proteins. With the development of mass spectrometry (MS) technology, MS-based proteomics has made important contributions to characterizing the dynamic changes in the natural immune proteome induced by viral infections. MS analytical techniques have several advantages, such as high throughput, rapidity, sensitivity, accuracy, and automation. The most common techniques for detecting complex proteomes are liquid chromatography (LC) and mass spectrometry (MS). LC-MS (Liquid Chromatography-Mass Spectrometry), which combines the physical separation capability of LC and the mass analysis capability of MS, is a powerful technique mainly used for analyzing the proteome of cells, tissues, and body fluids. To explore the combination of traditional proteomics techniques such as Western blotting, Co-IP (co-Immunoprecipitation), and the latest LC-MS methods to probe the anti-inflammatory pathway and the differential changes in upstream and downstream proteins induced by the antiviral natural immune junction protein STING.

Homogeneous and bioluminescent biochemical and cellular assay for monitoring cGAMP and enzymes that generate and degrade cGAMP

The cyclic GMP-AMP synthase-stimulator of the interferon gene (cGAS-STING) signaling pathway is considered an essential pattern recognition and effector pathway in the natural immune system and is mainly responsible for recognizing DNA molecules present in the cytoplasm and activating downstream signaling pathways to generate type I interferons (IFN-I) and other inflammatory factors. STING, a crucial junction protein in the innate immune system, exerts an essential role in host resistance to external pathogen invasion. The DNA introduced by pathogens or tumors is recognized by the cytoplasmic nucleic acid receptor cGAS, and a second messenger, cGAMP, is generated using intracellular guanosine triphosphate (GTP) and adenosine triphosphate (ATP). Furthermore, cellular and extracellular cGAMP concentrations are also controlled by ENPP1, an enzyme that breaks down cGAMP to AMP and GMP. Therefore, the role of the cGAS-STING signaling pathway has generated great interest in inflammatory and cancer research. To advance our understanding of innate immune system and in particular the STING pathway, we have developed a homogeneous, bioluminescent cGAMP detection assay that is very sensitive and highly selective against other nucleotides, cyclic nucleotides, and dicyclic nucleotides. The assay can be also used to monitor the activity of cGAS and ENPP1 to enable the development of inhibitors of both enzymes which might be used for therapeutic applications.

Classification and functional characterization of regulators of intracellular STING trafficking identified by genome-wide optical pooled screening

Stimulator of interferon genes (STING) traffics across intracellular compartments to trigger innate responses. Mutations in factors regulating this process lead to inflammatory disorders. To systematically identify factors involved in STING trafficking, we performed a genome-wide optical pooled screen (OPS). Based on the subcellular localization of STING in 45 million cells, we defined 464 clusters of gene perturbations based on their cellular phenotypes. A secondary, higher-dimensional OPS identified 73 finer clusters. We show that the loss of the gene of unknown function C19orf25, which clustered with USE1, a protein involved in Golgi-to-endoplasmic reticulum (ER) transport, enhances STING signaling. Additionally, HOPS deficiency delayed STING degradation and consequently increased signaling. Similarly, GARP/RIC1-RGP1 loss increased STING signaling by delaying STING Golgi exit. Our findings demonstrate that genome-wide genotype-phenotype maps based on high-content cell imaging outperform other screening approaches and provide a community resource for mining factors that impact STING trafficking and other cellular processes.

TFEB links the cGAS-STING pathway to lysosome biogenesis

The cGAS-STING pathway senses the level of double-stranded (ds)DNA in the cytosol, and is required for innate immunity through its effector, TBK1. A recent study by Lv et al. reports that STING activation also simultaneously promotes lysosomal biogenesis by inducing nuclear translocation of the transcription factors TFEB/TFE3 independent of TBK1.

How Does African Swine Fever Virus Evade the cGAS-STING Pathway?

African swine fever (ASF), a highly infectious and devastating disease affecting both domestic pigs and wild boars, is caused by the African swine fever virus (ASFV). ASF has resulted in rapid global spread of the disease, leading to significant economic losses within the swine industry. A significant obstacle to the creation of safe and effective ASF vaccines is the existing knowledge gap regarding the pathogenesis of ASFV and its mechanisms of immune evasion. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a major pathway mediating type I interferon (IFN) antiviral immune response against infections by diverse classes of pathogens that contain DNA or generate DNA in their life cycles. To evade the host's innate immune response, ASFV encodes many proteins that inhibit the production of type I IFN by antagonizing the cGAS-STING signaling pathway. Multiple proteins of ASFV are involved in promoting viral replication by protein-protein interaction during ASFV infection. The protein QP383R could impair the function of cGAS. The proteins EP364R, C129R and B175L could disturb the function of cyclic guanosine monophosphate-adenosine monophosphate (cGAMP). The proteins E248R, L83L, MGF505-11L, MGF505-7R, H240R, CD2v, E184L, B175L and p17 could interfere with the function of STING. The proteins MGF360-11L, MGF505-7R, I215L, DP96R, A151R and S273R could affect the function of TANK Binding Kinase 1 (TBK1) and IκB kinase ε (IKKε). The proteins MGF360-14L, M1249L, E120R, S273R, D129L, E301R, DP96R, MGF505-7R and I226R could inhibit the function of Interferon Regulatory Factor 3 (IRF3). The proteins MGF360-12L, MGF505-7R/A528R, UBCv1 and A238L could inhibit the function of nuclear factor kappa B (NF-Κb).

DNA-sensing pathways in health, autoinflammatory and autoimmune diseases

Detection of microbial DNA is a primary means of host defense. In mammalian cells, DNA-sensing pathways induce robust anti-microbial responses and initiation of adaptive immunity, leading to the eventual clearance of the infectious agent. However, while conferring the advantage of broad detection capability, the sequence-independent recognition mechanisms of most DNA sensors pose a significant challenge for mammalian cells to maintain ignorance to self-DNA under homeostatic conditions. In this Review, we summarize the fundamentals of DNA-sensing pathways and the intricate regulatory networks that keep these pathways in check. In addition, we describe how regulatory restraints can be defective and underlie human autoinflammatory and autoimmune diseases. Further, we discuss therapies in development that limit inflammation fueled by self-DNA or inappropriate activation of DNA-sensing pathways.

A TBK1-independent primordial function of STING in lysosomal biogenesis

Stimulator of interferon genes (STING) is activated in many pathophysiological conditions, leading to TBK1-dependent interferon production in higher organisms. However, primordial functions of STING independent of TBK1 are poorly understood. Here, through proteomics and bioinformatics approaches, we identify lysosomal biogenesis as an unexpected function of STING. Transcription factor EB (TFEB), an evolutionarily conserved regulator of lysosomal biogenesis and host defense, is activated by STING from multiple species, including humans, mice, and frogs. STING-mediated TFEB activation is independent of TBK1, but it requires STING trafficking and its conserved proton channel. GABARAP lipidation, stimulated by the channel of STING, is key for STING-dependent TFEB activation. STING stimulates global upregulation of TFEB-target genes, mediating lysosomal biogenesis and autophagy. TFEB supports cell survival during chronic sterile STING activation, a common condition in aging and age-related diseases. These results reveal a primordial function of STING in the biogenesis of lysosomes, essential organelles in immunity and cellular stress resistance.

ER: a critical hub for STING signaling regulation

The Stimulator of Interferon Genes (STING) has a crucial role in mediating the immune response against cytosolic double-stranded DNA (dsDNA) and its activation is critically involved in various diseases. STING is synthesized, modified, and resides in the endoplasmic reticulum (ER), and its ER exit is intimately connected with its signaling. The ER, primarily known for its roles in protein folding, lipid synthesis, and calcium storage, has been identified as a pivotal platform for the regulation of a wide range of STING functions. In this review, we discuss the emerging factors that regulate STING in the ER and examine the interplay between STING signaling and ER pathways, highlighting the impacts of such regulations on immune responses and their potential implications in STING-related disorders.

STING induces HOIP-mediated synthesis of M1 ubiquitin chains to stimulate NFκB signaling

STING activation by cyclic dinucleotides in mammals induces IRF3- and NFκB -mediated gene expression, and the lipidation of LC3B at Golgi-related membranes. While mechanisms of the IRF3 response are well understood, the mechanisms of NFκB activation mediated by STING remain unclear. We report that STING activation induces linear/M1-linked ubiquitin chain (M1-Ub) formation and recruitment of the LUBAC E3 ligase, HOIP, to LC3B-associated Golgi membranes where ubiquitin is also localized. Loss of HOIP prevents formation of M1-Ub ubiquitin chains and reduces STING-induced NFκB and IRF3-mediated signaling in human monocytic THP1 cells and mouse bone marrow derived macrophages, without affecting STING activation. STING-induced LC3B lipidation is not required for M1-Ub chain formation or the immune-related gene expression, however the recently reported function of STING to neutralize the pH of the Golgi may be involved. Thus, LUBAC synthesis of M1 ubiquitin chains mediates STING-induced innate immune signaling.

Advances in the prerequisite and consequence of STING downstream signalosomes

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is an evolving DNA-sensing mechanism involved in innate immunity and pathogen defense that has been optimized while remaining conserved. Aside from recognizing pathogens through conserved motifs, these receptors also detect aberrant or misplaced self-molecules as possible signs of perturbed homeostasis. Upon binding external or self-derived DNA, a mobile secondary messenger 2'3'-cyclic GMP-AMP (cGAMP) is produced by cGAS and in turn activates its adapter STING in the endoplasmic reticulum (ER). Resting-state or activated STING protein is finely restricted by multiple degradation machineries. The post-translational changes of the STING protein, along with the regulatory machinery of the secret routes, limit the onset, strength and sustention of STING signal. STING experiences a conformational shift and relocates with TBK1 from the ER to perinuclear vesicles containing transcription factors, provoking the transcription activity of IRF3/IFN-I and NF-κB pathways, as well as to initiate a number of cellular processes that have been shown to alter the immune landscape in cancer, such as autophagy, NLRP3 inflammasome, ER stress, and cell death. STING signal thus serves as a potent activator for immune mobilization yet also triggers immune-mediated pathology in tissues. Recent advances have established the vital role of STING in immune surveillance as well as tumorigenic process. This review provides an overview of the disparate outcomes of cancer attributed to the actions of pleiotropic and coordinated STING downstream signalosomes, along with the underlying mechanisms of STING function in pathologies, providing therapeutic implications for new approaches in hunt for the next generation of cancer immunotherapy base on STING.

IKKɛ induces STING non-IFN immune responses via a mechanism analogous to TBK1

The cGAS-STING pathway responds to cytosolic DNA to elicit host immunity to infection. The activation of stimulator of interferon genes (STING) can trigger a number of critical cellular responses including inflammation, noncanonical autophagy, lipid metabolism, senescence, and cell death. STING-mediated immunity through the production of type I interferons (IFNs) and nuclear factor kappa B (NF-κB)-driven proinflammatory cytokines is primarily driven via the effector protein TBK1. We have previously found that IκBα kinase epsilon (IKKε), a homolog of TBK1, can also facilitate STING-NF-κB responses. Therefore, a thorough understanding of how IKKε participates in STING signaling is essential. Here, we used a combination of genetic and biochemical approaches to provide mechanistic details into how IKKε confers non-IFN (e.g., NF-κB and MAPK) STING responses in macrophages, including in the absence of TBK1. We demonstrate a conserved mechanism of STING binding between TBK1 and IKKε. These findings strengthen our understanding of cGAS-STING signaling and the preservation of host immunity in cases of TBK1-deficiency.

Protein-protein interactions in cGAS-STING pathway: a medicinal chemistry perspective

Protein-protein interactions (PPIs) play pivotal roles in biological processes and are closely linked with human diseases. Research on small molecule inhibitors targeting PPIs provides valuable insights and guidance for novel drug development. The cGAS-STING pathway plays a crucial role in regulating human innate immunity and is implicated in various pathological conditions. Therefore, modulators of the cGAS-STING pathway have garnered extensive attention. Given that this pathway involves multiple PPIs, modulating PPIs associated with the cGAS-STING pathway has emerged as a promising strategy for modulating this pathway. In this review, we summarize an overview of recent advancements in medicinal chemistry insights into cGAS-STING PPI-based modulators and propose alternative strategies for further drug discovery based on the cGAS-STING pathway.

Microglial cGAS-STING signaling underlies glaucoma pathogenesis

Characterized by progressive degeneration of retinal ganglion cells (RGCs) and vision loss, glaucoma is the primary cause of irreversible blindness, incurable and affecting over 78 million patients. However, pathogenic mechanisms leading to glaucoma-induced RGC loss are incompletely understood. Unexpectedly, we found that cGAS-STING (2'3'-cyclic GMP-AMP-stimulator of interferon genes) signaling, which surveils displaced double-stranded DNA (dsDNA) in the cytosol and initiates innate immune responses, was robustly activated during glaucoma in retinal microglia in distinct murine models. Global or microglial deletion of STING markedly relieved glaucoma symptoms and protected RGC degeneration and vision loss, while mice bearing genetic cGAS-STING supersensitivity aggravated retinal neuroinflammation and RGC loss. Mechanistically, dsDNA from tissue injury activated microglial cGAS-STING signaling, causing deleterious macroglia reactivity in retinas by cytokine-mediated microglia-macroglia interactions, progressively driving apoptotic death of RGCs. Remarkably, preclinical investigations of targeting cGAS-STING signaling by intraocular injection of TBK1i or anti-IFNAR1 antibody prevented glaucoma-induced losses of RGCs and vision. Therefore, we unravel an essential role of cGAS-STING signaling underlying glaucoma pathogenesis and suggest promising therapeutic strategies for treating this devastating disease.

A novel STING variant triggers endothelial toxicity and SAVI disease

Gain-of-function mutations in STING cause STING-associated vasculopathy with onset in infancy (SAVI) characterized by early-onset systemic inflammation, skin vasculopathy, and interstitial lung disease. Here, we report and characterize a novel STING variant (F269S) identified in a SAVI patient. Single-cell transcriptomics of patient bone marrow revealed spontaneous activation of interferon (IFN) and inflammatory pathways across cell types and a striking prevalence of circulating naïve T cells was observed. Inducible STING F269S expression conferred enhanced signaling through ligand-independent translocation of the protein to the Golgi, protecting cells from viral infections but preventing their efficient immune priming. Additionally, endothelial cell activation was promoted and further exacerbated by cytokine secretion by SAVI immune cells, resulting in inflammation and endothelial damage. Our findings identify STING F269S mutation as a novel pathogenic variant causing SAVI, highlight the importance of the crosstalk between endothelial and immune cells in the context of lung disease, and contribute to a better understanding of how aberrant STING activation can cause pathology.

Crosstalk between inflammasome sensors and DNA damage response pathways

Eukaryotic cells encounter diverse threats jeopardizing their integrity, prompting the development of defense mechanisms against these stressors. Among these mechanisms, inflammasomes are well-known for their roles in coordinating the inflammatory response against infections. Extensive research has unveiled their multifaceted involvement in cellular processes beyond inflammation. Recent studies emphasize the intricate relationship between the inflammasome and the DNA damage response (DDR). They highlight how the DDR participates in inflammasome activation and the reciprocal impact of inflammasome on DDR and genome integrity preservation. Moreover, novel functions of inflammasome sensors in DDR pathways have emerged, broadening our understanding of their roles. Finally, this review delves into identifying common signals that drive the activation of inflammasome sensors alongside activation cues for the DNA damage response, offering potential insights into shared regulatory pathways between these critical cellular processes.