Deficiency in coatomer complex I causes aberrant activation of STING signalling

Flavonoid extracted from Epimedium attenuate cGAS-STING-mediated diseases by targeting the formation of functional STING signalosome

Hyperactivation of the cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling pathway has been shown to be associated with the development of a variety of inflammatory diseases, and the discovery of an inhibitor of the cGAS-STING signalling pathway holds great promise in the therapeutic interventions. Epimedium flavonoid (EF), a major active ingredient isolated from the medicinal plant Epimedium, has been reported to have good anti-inflammatory activity, but its exact mechanism of action remains unclear. In the present study, we found that EF in mouse bone marrow-derived macrophages (BMDMs), THP-1 (Tohoku Hospital Pediatrics-1) as well as in human peripheral blood mononuclear cells (hPBMC) inhibited the activation of the cGAS-STING signalling pathway, which subsequently led to a decrease in the expression of type I interferon (IFN-β, CXCL10 and ISG15) and pro-inflammatory cytokines (IL-6 and TNF-α). Mechanistically, EF does not affect STING oligomerization, but inhibits the formation of functional STING signalosome by attenuating the interaction of interferon regulatory factor 3 (IRF3) with STING and TANK-binding kinase 1 (TBK1). Importantly, in vivo experiments, EF has shown promising therapeutic effects on inflammatory diseases mediated by the cGAS-STING pathway, which include the agonist model induced by DMXAA stimulation, the autoimmune inflammatory disease model induced by three prime repair exonuclease 1 (Trex1) deficiency, and the non-alcoholic steatohepatitis (NASH) model induced by a pathogenic amino acid and choline deficiency diet (MCD). To summarize, our study suggests that EF is a potent potential inhibitor component of the cGAS-STING signalling pathway for the treatment of inflammatory diseases mediated by the cGAS-STING signalling pathway.

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

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

STING is an innate immune sensor that traffics across many cellular compartments to carry out its function of detecting cyclic di-nucleotides and triggering defense processes. Mutations in factors that regulate this process are often linked to STING-dependent human inflammatory disorders. To systematically identify factors involved in STING trafficking, we performed a genome-wide optical pooled screen and examined the impact of genetic perturbations on intracellular STING localization. Based on subcellular imaging of STING protein and trafficking markers in 45 million cells perturbed with sgRNAs, we defined 464 clusters of gene perturbations with similar cellular phenotypes. A higher-dimensional focused optical pooled screen on 262 perturbed genes which assayed 11 imaging channels identified 73 finer phenotypic clusters. In a cluster containing USE1, a protein that mediates Golgi to ER transport, we found a gene of unknown function, C19orf25. Consistent with the known role of USE1, loss of C19orf25 enhanced STING signaling. Other clusters contained subunits of the HOPS, GARP and RIC1-RGP1 complexes. We show that HOPS deficiency delayed STING degradation and consequently increased signaling. Similarly, GARP/RIC1-RGP1 loss increased STING signaling by delaying STING exit from the Golgi. 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 for factors that impact STING trafficking as well as other cellular processes observable in our dataset.

Development of STING degrader with double covalent ligands

Stimulator of interferon genes (STING), a homodimeric membrane receptor localized in the endoplasmic reticulum, plays a pivotal role in signaling innate immune responses. Inhibitors and proteolysis-targeting chimeras (PROTACs) targeting STING are promising compounds for addressing autoinflammatory and autoimmune disorders. In this study, we used a minimal covalent handle recently developed as the ligand portion of an E3 ligase. The engineered STING degrader with a low molecular weight compound covalently binds to STING and E3 ligase. Degrader 2 showed sustained STING degradation activity at lower concentrations (3 µM, 48 h, about 75 % degradation) compared to a reported STING PROTAC, SP23. This discovery holds significance for its potential in treating autoinflammatory and autoimmune diseases, offering promising avenues for developing more efficacious STING-targeted therapies.

Interferon lambda in respiratory viral infection: immunomodulatory functions and antiviral effects in epithelium

Type III interferon (IFN-λ), a new member of the IFN family, was initially considered to possess antiviral functions similar to those of type I interferon, both of which are induced via the JAK/STAT pathway. Nevertheless, recent findings demonstrated that IFN-λ exerts a nonredundant antiviral function at the mucosal surface, preferentially produced in epithelial cells in contrast to type I interferon, and its function cannot be replaced by type I interferon. This review summarizes recent studies showing that IFN-λ inhibits the spread of viruses from the cell surface to the body. Further studies have found that the role of IFN-λ is not only limited to the abovementioned functions, but it can also can exert direct and/or indirect effects on immune cells in virus-induced inflammation. This review focuses on the antiviral activity of IFN-λ in the mucosal epithelial cells and its action on immune cells and summarizes the pathways by which IFN-λ exerts its action and differentiates it from other interferons in terms of mechanism. Finally, we conclude that IFN-λ is a potent epidermal antiviral factor that enhances the respiratory mucosal immune response and has excellent therapeutic potential in combating respiratory viral infections.

IUPHAR ECR review: The cGAS-STING pathway: Novel functions beyond innate immune and emerging therapeutic opportunities

Stimulator of interferon genes (STING) is a crucial innate immune sensor responsible for distinguishing pathogens and cytosolic DNA, mediating innate immune signaling pathways to defend the host. Recent studies have revealed additional regulatory functions of STING beyond its innate immune-related activities, including the regulation of cellular metabolism, DNA repair, cellular senescence, autophagy and various cell deaths. These findings highlight the broader implications of STING in cellular physiology beyond its role in innate immunity. Currently, approximately 10 STING agonists have entered the clinical stage. Unlike inhibitors, which have a maximum inhibition limit, agonists have the potential for infinite amplification. STING signaling is a complex process that requires precise regulation of STING to ensure balanced immune responses and prevent detrimental autoinflammation. Recent research on the structural mechanism of STING autoinhibition and its negative regulation by adaptor protein complex 1 (AP-1) provides valuable insights into its different effects under physiological and pathological conditions, offering a new perspective for developing immune regulatory drugs. Herein, we present a comprehensive overview of the regulatory functions and molecular mechanisms of STING beyond innate immune regulation, along with updated details of its structural mechanisms. We discuss the implications of these complex regulations in various diseases, emphasizing the importance and feasibility of targeting the immunity-dependent or immunity-independent functions of STING. Moreover, we highlight the current trend in drug development and key points for clinical research, basic research, and translational research related to STING.

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 signaling in the brain: Molecular threats, signaling activities, and therapeutic challenges

Stimulator of interferon genes (STING) is an innate immune signaling protein critical to infections, autoimmunity, and cancer. STING signaling is also emerging as an exciting and integral part of many neurological diseases. Here, we discuss recent advances in STING signaling in the brain. We summarize how molecular threats activate STING signaling in the diseased brain and how STING signaling activities in glial and neuronal cells cause neuropathology. We also review human studies of STING neurobiology and consider therapeutic challenges in targeting STING to treat neurological diseases.

Single-molecule localization microscopy reveals STING clustering at the trans-Golgi network through palmitoylation-dependent accumulation of cholesterol

Stimulator of interferon genes (STING) is critical for the type I interferon response to pathogen- or self-derived DNA in the cytosol. STING may function as a scaffold to activate TANK-binding kinase 1 (TBK1), but direct cellular evidence remains lacking. Here we show, using single-molecule imaging of STING with enhanced time resolutions down to 5 ms, that STING becomes clustered at the trans-Golgi network (about 20 STING molecules per cluster). The clustering requires STING palmitoylation and the Golgi lipid order defined by cholesterol. Single-molecule imaging of TBK1 reveals that STING clustering enhances the association with TBK1. We thus provide quantitative proof-of-principle for the signaling STING scaffold, reveal the mechanistic role of STING palmitoylation in the STING activation, and resolve the long-standing question of the requirement of STING translocation for triggering the innate immune signaling.

Clinical efficacy, pharmacodynamic components, and molecular mechanisms of antiviral granules in the treatment of influenza: A systematic review

ETHNOPHARMACOLOGICAL RELEVANCE

The Antiviral Granules (AG) are derived from the classical famous prescription, which is composed of 9 traditional Chinese medicines, namely Radix Isatidis (called Banlangen, BLG in Chinese), Forsythiae Fructus (called Lianqiao, LQ in Chinese), Gypsum fibrosum, Anemarrhenae Rhizoma (called Zhimu, ZM in Chinese), Phragmitis Rhizoma (called Lugen, LG in Chinese), Rehmanniae Radix (called Dihuang, DH in Chinese), Pogostemonis Herba (called Guanghuoxiang, GHX in Chinese), Acori Tatarinowii Rhizoma (called Shichangpu, SCP in Chinese), and Curcumae Radix (called Yujin, YJ in Chinese), and has shown an excellent therapeutic effect in clinical treatment of influenza. However, there are few studies on the anti-influenza mechanism of AG, and the mechanism of action is still unclear.

AIM OF THE STUDY

The purpose is to provide the latest information about the clinical efficacy, pharmacodynamic composition and mechanism of AG based on scientific literature, so as to enhance the utilization of AG in the treatment of influenza and related diseases, and promote the development and innovation of novel anti-influenza drugs targeting the influenza virus.

MATERIALS AND METHODS

Enter the data retrieval room, search for Antiviral Granules, as well as the scientific names, common names, and Chinese names of each Chinese medicine. Additionally, search for the relevant clinical applications, pharmacodynamic composition, pharmacological action, and molecular mechanism of both Antiviral Granules and single-ingredient medicines. Keywords includes terms such as "antiviral granules", "influenza", "Isatis indigotica Fort.", "Radix Isatidis", "Banlangeng", "pharmacology", "clinical application", "pharmacologic action", etc. and their combinations. Obtain results from the Web of Science, PubMed, Google Scholar, Sci Finder Scholar, CNKI and other resources.

RESULTS

AG is effective in the treatment of influenza and is often used in combination with other drugs to treat viral diseases. Its chemical composition is complex, including alkaloids, polysaccharides, volatile oils, steroid saponins, phenylpropanoids, terpenoids and other compounds. These compounds have a variety of pharmacological activities, which can interfere with the replication cycle of the influenza virus, regulate RIG-I-MAVS, JAK/STAT, TLRs/MyD88, NF-κB signaling pathways and related cytokines, regulate intestinal microorganisms, and protect both the lungs and extrapulmonary organs.

CONCLUSIONS

AG can overcome the limitations of traditional antiviral drug therapy, play a synergistic role in fighting influenza virus with the characteristics of multi-component, multi-pathway and multi-target therapy, and reverse the bodily function damage caused by influenza virus. AG may be a potential drug in the prevention and treatment of influenza and related diseases.

Heterozygous mutations in the C-terminal domain of COPA underlie a complex autoinflammatory syndrome

Mutations in the N-terminal WD40 domain of coatomer protein complex subunit α (COPA) cause a type I interferonopathy, typically characterized by alveolar hemorrhage, arthritis, and nephritis. We described 3 heterozygous mutations in the C-terminal domain (CTD) of COPA (p.C1013S, p.R1058C, and p.R1142X) in 6 children from 3 unrelated families with a similar syndrome of autoinflammation and autoimmunity. We showed that these CTD COPA mutations disrupt the integrity and the function of coat protein complex I (COPI). In COPAR1142X and COPAR1058C fibroblasts, we demonstrated that COPI dysfunction causes both an anterograde ER-to-Golgi and a retrograde Golgi-to-ER trafficking defect. The disturbed intracellular trafficking resulted in a cGAS/STING-dependent upregulation of the type I IFN signaling in patients and patient-derived cell lines, albeit through a distinct molecular mechanism in comparison with mutations in the WD40 domain of COPA. We showed that CTD COPA mutations induce an activation of ER stress and NF-κB signaling in patient-derived primary cell lines. These results demonstrate the importance of the integrity of the CTD of COPA for COPI function and homeostatic intracellular trafficking, essential to ER homeostasis. CTD COPA mutations result in disease by increased ER stress, disturbed intracellular transport, and increased proinflammatory signaling.

Chemical Biology Perspectives on STING Agonists as Tumor Immunotherapy

Stimulator of interferon genes (STING) is a crucial adaptor protein in the innate immune response. STING activation triggers cytokine secretion, including type I interferon and initiates T cell-mediated adaptive immunity. The activated immune system converts "cold tumors" into "hot tumors" that are highly responsive to T cells by recruiting them to the tumor microenvironment, ultimately leading to potent and long-lasting antitumor effects. Unlike most immune checkpoint inhibitors, STING agonists represent a groundbreaking class of innate immune agonists that hold great potential for effectively targeting various cancer populations and are poised to become a blockbuster in tumor immunotherapy. This review will focus on the correlation between the STING signaling pathway and tumor immunity, as well as explore the impact of STING activation on other biological processes. Ultimately, we will summarize the development and optimization of STING agonists from a medicinal chemistry perspective, evaluate their potential in cancer therapy, and identify possible challenges for future advancement.

Membrane traffic governs the STING inflammatory signalling

The cGAS-STING innate immune pathway has recently emerged as a critical driver of inflammation in a variety of settings, such as virus infection, cellular stress and tissue damage. The pathway detects microbial and host-derived double-stranded DNA (dsDNA) in the cytosol, and triggers the production of the type I interferons through the activation of IRF3. The detailed mechanistic and biochemical understanding of the pathway has enabled the development of pharmacological agents for the treatment of chronic inflammation and cancer. STING is an endoplasmic reticulum (ER)-localized transmembrane protein. Upon emergence of cytosolic dsDNA, STING exits the ER and migrates sequentially to the Golgi, recycling endosomes and lysosomes. Importantly, the intracellular translocation of STING is essential for the activation and inactivation of the STING signalling. In this review, I summarize the recent insights into the regulators of the membrane traffic of STING and STING-associated autoinflammatory diseases.

COPI coatomer subunit α-COP interacts with the RNA binding protein Nucleolin via a C-terminal dilysine motif

The COPI coatomer subunit α-COP has been shown to co-precipitate mRNA in multiple settings, but it was unclear whether the interaction with mRNA was direct or mediated by interaction with an adapter protein. The COPI complex often interacts with proteins via C-terminal dilysine domains. A search for candidate RNA binding proteins with C-terminal dilysine motifs yielded Nucleolin, which terminates in a KKxKxx sequence. This protein was an especially intriguing candidate as it has been identified as an interacting partner for Survival Motor Neuron protein (SMN). Loss of SMN causes the neurodegenerative disease Spinal Muscular Atrophy. We have previously shown that SMN and α-COP interact and co-migrate in axons, and that overexpression of α-COP reduced phenotypic severity in cell culture and animal models of SMA. We show here that in an mRNA independent manner, endogenous Nucleolin co-precipitates endogenous α-COP and ε-COP but not β-COP which may reflect an interaction with the so-called B-subcomplex rather a complete COPI heptamer. The ability of Nucleolin to bind to α-COP requires the presence of the C-terminal KKxKxx domain of Nucleolin. Furthermore, we have generated a point mutant in the WD40 domain of α-COP which eliminates its ability to co-precipitate Nucleolin but does not interfere with precipitation of partners mediated by non-KKxKxx motifs such as the kainate receptor subunit 2. We propose that via interaction between the C-terminal dilysine motif of Nucleolin and the WD40 domain of α-COP, Nucleolin acts an adaptor to allow α-COP to interact with a population of mRNA.

ARF1 prevents aberrant type I interferon induction by regulating STING activation and recycling

Type I interferon (IFN) signalling is tightly controlled. Upon recognition of DNA by cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING) translocates along the endoplasmic reticulum (ER)-Golgi axis to induce IFN signalling. Termination is achieved through autophagic degradation or recycling of STING by retrograde Golgi-to-ER transport. Here, we identify the GTPase ADP-ribosylation factor 1 (ARF1) as a crucial negative regulator of cGAS-STING signalling. Heterozygous ARF1 missense mutations cause a previously unrecognized type I interferonopathy associated with enhanced IFN-stimulated gene expression. Disease-associated, GTPase-defective ARF1 increases cGAS-STING dependent type I IFN signalling in cell lines and primary patient cells. Mechanistically, mutated ARF1 perturbs mitochondrial morphology, causing cGAS activation by aberrant mitochondrial DNA release, and leads to accumulation of active STING at the Golgi/ERGIC due to defective retrograde transport. Our data show an unexpected dual role of ARF1 in maintaining cGAS-STING homeostasis, through promotion of mitochondrial integrity and STING recycling.

COPA Syndrome from Diagnosis to Treatment: A Clinician's Guide

COPA syndrome is a recently described autosomal dominant inborn error of immunity characterized by high titer autoantibodies and interstitial lung disease, with many individuals also having arthritis and nephritis. Onset is usually in early childhood, with unique disease features including alveolar hemorrhage, which can be insidious, pulmonary cyst formation, and progressive pulmonary fibrosis in nonspecific interstitial pneumonia or lymphocytic interstitial pneumonia patterns. This review explores the clinical presentation, genetics, molecular mechanisms, organ manifestations, and treatment approaches for COPA syndrome, and presents a diagnostic framework of suggested indications for patient testing.

Golgi retention and oncogenic KIT signaling via PLCγ2-PKD2-PI4KIIIβ activation in gastrointestinal stromal tumor cells

Most gastrointestinal stromal tumors (GISTs) develop due to gain-of-function mutations in the tyrosine kinase gene, KIT. We recently showed that mutant KIT mislocalizes to the Golgi area and initiates uncontrolled signaling. However, the molecular mechanisms underlying its Golgi retention remain unknown. Here, we show that protein kinase D2 (PKD2) is activated by the mutant, which causes Golgi retention of KIT. In PKD2-inhibited cells, KIT migrates from the Golgi region to lysosomes and subsequently undergoes degradation. Importantly, delocalized KIT cannot trigger downstream activation. In the Golgi/trans-Golgi network (TGN), KIT activates the PKD2-phosphatidylinositol 4-kinase IIIβ (PKD2-PI4KIIIβ) pathway through phospholipase Cγ2 (PLCγ2) to generate a PI4P-rich membrane domain, where the AP1-GGA1 complex is aberrantly recruited. Disruption of any factors in this cascade results in the release of KIT from the Golgi/TGN. Our findings show the molecular mechanisms underlying KIT mislocalization and provide evidence for a strategy for inhibition of oncogenic signaling.

cGAS-STING pathway in ischemia-reperfusion injury: a potential target to improve transplantation outcomes

Transplantation is an important life-saving therapeutic choice for patients with organ or tissue failure once all other treatment options are exhausted. However, most allografts become damaged over an extended period, and post-transplantation survival is limited. Ischemia reperfusion injury (IRI) tends to be associated with a poor prognosis; resultant severe primary graft dysfunction is the main cause of transplant failure. Targeting the cGAS-STING pathway has recently been shown to be an effective approach for improving transplantation outcomes, when activated or inhibited cGAS-STING pathway, IRI can be alleviated by regulating inflammatory response and programmed cell death. Thus, continuing efforts to develop selective agonists and antagonists may bring great hopes to post-transplant patient. In this mini-review, we reviewed the role of the cGAS-STING pathway in transplantation, and summarized the crosstalk between this pathway and inflammatory response and programmed cell death during IRI, aiming to provide novel insights into the development of therapies to improve patient outcome after transplantation.

Regulation of cGAS and STING signaling during inflammation and infection

Stimulator of interferon genes (STING) is a sensor of cyclic dinucleotides including cyclic GMP-AMP, which is produced by cyclic GMP-AMP synthase (cGAS) in response to cytosolic DNA. The cGAS-STING signaling pathway regulates both innate and adaptive immune responses, as well as fundamental cellular functions such as autophagy, senescence, and apoptosis. Mutations leading to constitutive activation of STING cause devastating human diseases. Thus, the cGAS-STING pathway is of great interest because of its role in diverse cellular processes and because of the potential therapeutic implications of targeting cGAS and STING. Here, we review molecular and cellular mechanisms of STING signaling, and we propose a framework for understanding the immunological and other cellular functions of STING in the context of disease.

The proteomic landscape of soft tissue sarcomas

Soft tissue sarcomas (STS) are rare and diverse mesenchymal cancers with limited treatment options. Here we undertake comprehensive proteomic profiling of tumour specimens from 321 STS patients representing 11 histological subtypes. Within leiomyosarcomas, we identify three proteomic subtypes with distinct myogenesis and immune features, anatomical site distribution and survival outcomes. Characterisation of undifferentiated pleomorphic sarcomas and dedifferentiated liposarcomas with low infiltrating CD3 + T-lymphocyte levels nominates the complement cascade as a candidate immunotherapeutic target. Comparative analysis of proteomic and transcriptomic profiles highlights the proteomic-specific features for optimal risk stratification in angiosarcomas. Finally, we define functional signatures termed Sarcoma Proteomic Modules which transcend histological subtype classification and show that a vesicle transport protein signature is an independent prognostic factor for distant metastasis. Our study highlights the utility of proteomics for identifying molecular subgroups with implications for risk stratification and therapy selection and provides a rich resource for future sarcoma research.

Termination of STING responses is mediated via ESCRT-dependent degradation

cGAS-STING signalling is induced by detection of foreign or mislocalised host double-stranded (ds)DNA within the cytosol. STING acts as the major signalling hub, where it controls production of type I interferons and inflammatory cytokines. Basally, STING resides on the ER membrane. Following activation STING traffics to the Golgi to initiate downstream signalling and subsequently to endolysosomal compartments for degradation and termination of signalling. While STING is known to be degraded within lysosomes, the mechanisms controlling its delivery remain poorly defined. Here we utilised a proteomics-based approach to assess phosphorylation changes in primary murine macrophages following STING activation. This identified numerous phosphorylation events in proteins involved in intracellular and vesicular transport. We utilised high-temporal microscopy to track STING vesicular transport in live macrophages. We subsequently identified that the endosomal complexes required for transport (ESCRT) pathway detects ubiquitinated STING on vesicles, which facilitates the degradation of STING in murine macrophages. Disruption of ESCRT functionality greatly enhanced STING signalling and cytokine production, thus characterising a mechanism controlling effective termination of STING signalling.

PERK-STING-RIPK3 pathway facilitates cognitive impairment by inducing neuronal necroptosis in sepsis-associated encephalopathy

AIMS

Sepsis-associated encephalopathy (SAE) is a common but serious complication in septic survivors and often causes long-term cognitive impairments. The role of RIPK3-participated necroptosis in SAE remains obscured. STING is a key molecule in regulating necroptosis and apoptosis. However, there is uncertainty as to the mechanisms of STING in CLP-induced SAE. The aim of this study was to investigate whether STING is involved in the underlying mechanism of SAE.

METHODS

The contextual fear conditioning test (CFCT) assesses cognitive impairment. A transmission electron microscope (TEM) was used to notice the necroptosis. Western blotting and immunofluorescence labeling were applied for the observation of related proteins.

RESULTS

The phosphorylated STING in the hippocampal neuron of SAE mice was significantly elevated. Knocking down STING inhibited necroptosis and attenuated cognitive impairment in SAE mice. Moreover, RIPK3^-/- mice had less cognitive deficit in the SAE model. However, STING overexpression did not deteriorate cognitive impairment in RIPK3^-/- mice with SAE, indicating that STING is upstream involved in necroptosis. Furthermore, PERK inhibition ameliorated cognitive deficits through a STING-dependent pathway in SAE mice.

CONCLUSION

PERK-STING-RIPK3 pathway facilitates cognitive impairment by inducing neuronal necroptosis in the pathology of SAE, which provided a new therapeutic target in SAE treatment.

A path towards personalized medicine for autoinflammatory and related diseases

The human genome project led to the advancement of genetic technologies and genomic medicine for a variety of human diseases, including monogenic autoimmune and autoinflammatory diseases. As a result, the genome of an individual can now be rapidly sequenced at a low cost, and this technology is beginning to change the practice of rheumatology. In this Perspective, we describe how new sequencing technologies combined with careful clinical phenotyping have led to the discovery of rare rheumatic diseases and their corresponding disease-causing mutations. Additionally, we explore ways in which single-gene mutations, including somatic mutations, are creating opportunities to develop personalized medicines. To illustrate this idea, we focus on diseases affecting the TREX1-cGAS-STING pathway, which is associated with monogenic autoinflammatory diseases and vasculopathies. For many of the affected patients and families, there is an urgent, unmet need for the development of personalized therapies. New innovations related to small molecular inhibitors and gene therapies have the potential to benefit these families, and might help drive further innovations that could prove useful for patients with more common forms of autoimmunity and autoinflammation.

A non-nucleotide agonist that binds covalently to cysteine residues of STING

Stimulator of interferon genes (STING) is an ER-localized transmembrane protein and the receptor for 2',3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP), which is a second messenger produced by cGAMP synthase (cGAS), a cytosolic double-stranded DNA sensor. The cGAS-STING pathway plays a critical role in the innate immune response to infection of a variety of DNA pathogens through the induction of the type I interferons. Pharmacological activation of STING is a promising therapeutic strategy for cancer, thus the development of potent and selective STING agonists has been pursued. Here we report that mouse STING can be activated by phenylarsine oxide (PAO), a membrane permeable trivalent arsenic compound that preferentially reacts with thiol group of cysteine residue (Cys). The activation of STING with PAO does not require cGAS or cGAMP. Mass spectrometric analysis of the peptides generated by trypsin and chymotrypsin digestion of STING identifies several PAO adducts, suggesting that PAO covalently binds to STING. Screening of STING variants with single Cys to serine residues (Ser) reveals that Cys88 and Cys291 are critical to the response to PAO. STING activation with PAO, as with cGAMP, requires the ER-to-Golgi traffic and palmitoylation of STING. Our results identify a non-nucleotide STING agonist that does not target the cGAMP-binding pocket, and demonstrate that Cys of STING can be a novel target for the development of STING agonist.Key words: STING agonist, cysteine modification, innate immunity, phenylarsine oxide.

ESCRT-dependent STING degradation inhibits steady-state and cGAMP-induced signalling

Stimulator of interferon genes (STING) is an intracellular sensor of cyclic di-nucleotides involved in the innate immune response against pathogen- or self-derived DNA. STING trafficking is tightly linked to its function, and its dysregulation can lead to disease. Here, we systematically characterize genes regulating STING trafficking and examine their impact on STING-mediated responses. Using proximity-ligation proteomics and genetic screens, we demonstrate that an endosomal sorting complex required for transport (ESCRT) complex containing HGS, VPS37A and UBAP1 promotes STING degradation, thereby terminating STING-mediated signaling. Mechanistically, STING oligomerization increases its ubiquitination by UBE2N, forming a platform for ESCRT recruitment at the endosome that terminates STING signaling via sorting in the lysosome. Finally, we show that expression of a UBAP1 mutant identified in patients with hereditary spastic paraplegia and associated with disrupted ESCRT function, increases steady-state STING-dependent type I IFN responses in healthy primary monocyte-derived dendritic cells and fibroblasts. Based on these findings, we propose that STING is subject to a tonic degradative flux and that the ESCRT complex acts as a homeostatic regulator of STING signaling.

STING trafficking as a new dimension of immune signaling

The cGAS-STING pathway is an evolutionarily conserved immune signaling pathway critical for microbial defense. Unlike other innate immune pathways that largely rely on stationary cascades of signaling events, STING is highly mobile in the cell. STING is activated on the ER, but only signals after it arrives on the Golgi, and then it is quickly degraded by the lysosome. Each step of STING trafficking through the secretory pathway is regulated by host factors. Homeostatic STING trafficking via COPI-, COPII-, and clathrin-coated vesicles is important for maintaining baseline tissue and cellular immunity. Aberrant vesicular trafficking or lysosomal dysfunction produces an immune signal through STING, which often leads to tissue pathology in mice and humans. Many trafficking-mediated diseases of STING signaling appear to impact the central nervous system, leading to neurodegeneration. Therefore, STING trafficking introduces a new dimension of immune signaling that likely has broad implications in human disease.

HPV is a cargo for the COPI sorting complex during virus entry

During entry, human papillomavirus (HPV) traffics from the cell surface to the endosome and then to the trans-Golgi network (TGN) and Golgi apparatus. HPV must transit across the TGN/Golgi and exit these compartments to reach the nucleus to cause infection, although how these steps are accomplished is unclear. Combining cellular fractionation, unbiased proteomics, and gene knockdown strategies, we identified the coat protein complex I (COPI), a highly conserved protein complex that facilitates retrograde trafficking of cellular cargos, as a host factor required for HPV infection. Upon TGN/Golgi arrival, the cytoplasmic segment of HPV L2 binds directly to COPI. COPI depletion causes the accumulation of HPV in the TGN/Golgi, resembling the fate of a COPI binding-defective L2 mutant. We propose that the L2-COPI interaction drives HPV trafficking through the TGN and Golgi stacks during virus entry. This shows that an incoming virus is a cargo of the COPI complex.

Multifaceted functions of STING in human health and disease: from molecular mechanism to targeted strategy

Since the discovery of Stimulator of Interferon Genes (STING) as an important pivot for cytosolic DNA sensation and interferon (IFN) induction, intensive efforts have been endeavored to clarify the molecular mechanism of its activation, its physiological function as a ubiquitously expressed protein, and to explore its potential as a therapeutic target in a wide range of immune-related diseases. With its orthodox ligand 2'3'-cyclic GMP-AMP (2'3'-cGAMP) and the upstream sensor 2'3'-cGAMP synthase (cGAS) to be found, STING acquires its central functionality in the best-studied signaling cascade, namely the cGAS-STING-IFN pathway. However, recently updated research through structural research, genetic screening, and biochemical assay greatly extends the current knowledge of STING biology. A second ligand pocket was recently discovered in the transmembrane domain for a synthetic agonist. On its downstream outputs, accumulating studies sketch primordial and multifaceted roles of STING beyond its cytokine-inducing function, such as autophagy, cell death, metabolic modulation, endoplasmic reticulum (ER) stress, and RNA virus restriction. Furthermore, with the expansion of the STING interactome, the details of STING trafficking also get clearer. After retrospecting the brief history of viral interference and the milestone events since the discovery of STING, we present a vivid panorama of STING biology taking into account the details of the biochemical assay and structural information, especially its versatile outputs and functions beyond IFN induction. We also summarize the roles of STING in the pathogenesis of various diseases and highlight the development of small-molecular compounds targeting STING for disease treatment in combination with the latest research. Finally, we discuss the open questions imperative to answer.

Genetics in Idiopathic Pulmonary Fibrosis: A Clinical Perspective

BACKGROUND

Unraveling the genetic background in a significant proportion of patients with both sporadic and familial IPF provided new insights into the pathogenic pathways of pulmonary fibrosis.

AIM

The aim of the present study is to overview the clinical significance of genetics in IPF.

PERSPECTIVE

It is fascinating to realize the so-far underestimated but dynamically increasing impact that genetics has on aspects related to the pathophysiology, accurate and early diagnosis, and treatment and prevention of this devastating disease. Genetics in IPF have contributed as no other in unchaining the disease from the dogma of a "a sporadic entity of the elderly, limited to the lungs" and allowed all scientists, but mostly clinicians, all over the world to consider its many aspects and "faces" in all age groups, including its co-existence with several extra pulmonary conditions from cutaneous albinism to bone-marrow and liver failure.

CONCLUSION

By providing additional evidence for unsuspected characteristics such as immunodeficiency, impaired mucus, and surfactant and telomere maintenance that very often co-exist through the interaction of common and rare genetic variants in the same patient, genetics have created a generous and pluralistic yet unifying platform that could lead to the understanding of the injurious and pro-fibrotic effects of many seemingly unrelated extrinsic and intrinsic offending factors. The same platform constantly instructs us about our limitations as well as about the heritability, the knowledge and the wisdom that is still missing.

Interruption of post-Golgi STING trafficking activates tonic interferon signaling

Activation of the cGAS-STING pathway is traditionally considered a "trigger-release" mechanism where detection of microbial DNA or cyclic di-nucleotides sets off the type I interferon response. Whether this pathway can be activated without pathogenic ligand exposure is less well understood. Here we show that loss of Golgi-to-lysosome STING cofactors, but not ER-to-Golgi cofactors, selectively activates tonic interferon signalling. Impairment of post-Golgi trafficking extends STING Golgi-dwell time, resulting in elevated immune signalling and protection against infection. Mechanistically, trans-Golgi coiled coil protein GCC2 and several RAB GTPases act as key regulators of STING post-Golgi trafficking. Genomic deletion of these factors potently activates cGAS-STING signalling without instigating any pathogenic trigger for cGAS. Gcc2-/- mice develop STING-dependent serologic autoimmunity. Gcc2-deleted or Rab14-deleted cancer cells induce T-cell and IFN-dependent anti-tumour immunity and inhibit tumour growth in mice. In summary, we present a "basal flux" mechanism for tonic cGAS-STING signalling, regulated at the level of post-Golgi STING trafficking, which could be exploited for cancer immunotherapy.

STING Targeting in Lung Diseases

The cGAS-STING pathway displays important functions in the regulation of innate and adaptive immunity following the detection of microbial and host-derived DNA. Here, we briefly summarize biological functions of STING and review recent literature highlighting its important contribution in the context of respiratory diseases. Over the last years, tremendous progress has been made in our understanding of STING activation, which has favored the development of STING agonists or antagonists with potential therapeutic benefits. Antagonists might alleviate STING-associated chronic inflammation and autoimmunity. Furthermore, pharmacological activation of STING displays strong antiviral properties, as recently shown in the context of SARS-CoV-2 infection. STING agonists also elicit potent stimulatory activities when used as an adjuvant promoting antitumor responses and vaccines efficacy.

The activity of disease-causative STING variants can be suppressed by wild-type STING through heterocomplex formation

Stimulator of interferon genes (STING) is essential for the type I interferon response induced by microbial DNA from viruses or self-DNA from mitochondria/nuclei. Recently, gain-of-function mutations in STING have been identified in patients with STING-associated vasculopathy with onset in infancy (SAVI). The SAVI patients exhibit complex systemic vascular inflammation and interstitial lung disease, resulting in pulmonary fibrosis and respiratory failure. SAVI mouse models have recently developed, harbouring common SAVI mutations, such as N153S and V154M, which correspond to the human N154S and V155M, respectively. Interestingly, crosses of heterozygous SAVI mice did not yield homozygous SAVI mice as of embryonic day 14, indicating that homozygous SAVI embryos were not viable and that wild-type (WT) allele would function dominantly over SAVI alleles in terms of viability. However, the molecular mechanism underlying the dominance has not been understood. In the present study, we show that STING (WT) and STING (SAVI) can form heterocomplex. The heterocomplex localized primarily in the endoplasmic reticulum (ER) and failed to reach the trans-Golgi network (TGN), where STING activates the downstream kinase TBK1. SURF4 is the essential protein functioning in the retrieval of STING from the Golgi to the ER. The amount of SURF4 bound to STING (SAVI) significantly increased in the presence of STING (WT). These results suggest that STING (WT) can suppress the activity of STING (SAVI) by tethering STING (SAVI) to the ER through heterocomplex formation. The dormant heterocomplex formation may underlie, at least in part, the dominance of STING WT allele over SAVI alleles in the STING-triggered inflammatory response.

Recent advances in the development of STING inhibitors: an updated patent review

INTRODUCTION

STING is at the center of the cGAS-STING signaling and acts as the hub of the innate immune system. Hyper-activation of STING has been observed in various severe autoimmune diseases, such as AGS, SLE, and many other diseases including neurological and metabolic disorders. Therefore, STING has been considered as a promising target. In recent years, several STING inhibitors have been claimed in patents.

AREAS COVERED

Small-molecule STING inhibitors reported in patents (disclosed before May 2022 through the public database at https://worldwide.espacenet.com) were summarized in this review and the available structure-activity relationships (SARs) and molecular mechanisms of action were presented.

EXPERT OPINION

Compared with STING agonists, the development of STING inhibitors is still in its infancy and no candidates have entered clinical investigation stage. Fortunately, patent applications are appearing at an increasing rate and a few of them have been validated in vivo, thus providing valuable insights for further structural optimization. More efforts are urgently needed since it is not clear yet that inhibitors targeting STING can solely exert sufficient therapeutic effects on autoimmune diseases, and the toxicity profile of such inhibitors is unknown as well. Therefore, it is extremely important to identify a selective and efficacious STING inhibitor for clinical evaluation to provide proof-of-concept for this approach.

MITA/STING-mediated antiviral immunity and autoimmunity: the evolution, mechanism, and intervention

Mediator of IRF3 activation (MITA, also known as stimulator of interferon genes (STING) and endoplasmic reticulum interferon stimulator (ERIS)) is an ER-associated protein that senses cellular and bacterium-derived cyclic dinucleotide (CDN), leading to induction of type-I interferons (IFNs) and innate immune responses against viruses and bacteria. Recently, it has become clear that sensing of CDN and induction of autophagy are two evolutionarily conserved functions of MITA, predating its role in mediating type-I IFN induction. Studies have shown that MITA-mediated signaling promotes a number of autoimmune disorders caused by gene mutations in human. Here, we summarize the most recent progress on MITA-mediated signaling in a view of evolution and highlight the roles of MITA in human inflammatory disorders caused by gene mutations and in genetically modified mouse models. We also briefly introduce the chemicals targeting MITA and discuss their potential in treatment of MITA-mediated inflammatory diseases. Finally, we propose several key questions that should be addressed for targeting MITA for treatment of related autoimmune diseases.

Clathrin-associated AP-1 controls termination of STING signalling

Stimulator of interferon genes (STING) functions downstream of cyclic GMP-AMP synthase in DNA sensing or as a direct receptor for bacterial cyclic dinucleotides and small molecules to activate immunity during infection, cancer and immunotherapy1-10. Precise regulation of STING is essential to ensure balanced immune responses and prevent detrimental autoinflammation11-16. After activation, STING, a transmembrane protein, traffics from the endoplasmic reticulum to the Golgi, where its phosphorylation by the protein kinase TBK1 enables signal transduction17-20. The mechanism that ends STING signalling at the Golgi remains unknown. Here we show that adaptor protein complex 1 (AP-1) controls the termination of STING-dependent immune activation. We find that AP-1 sorts phosphorylated STING into clathrin-coated transport vesicles for delivery to the endolysosomal system, where STING is degraded21. We identify a highly conserved dileucine motif in the cytosolic C-terminal tail (CTT) of STING that, together with TBK1-dependent CTT phosphorylation, dictates the AP-1 engagement of STING. A cryo-electron microscopy structure of AP-1 in complex with phosphorylated STING explains the enhanced recognition of TBK1-activated STING. We show that suppression of AP-1 exacerbates STING-induced immune responses. Our results reveal a structural mechanism of negative regulation of STING and establish that the initiation of signalling is inextricably associated with its termination to enable transient activation of immunity.

Inhibitory targeting cGAS-STING-TBK1 axis: Emerging strategies for autoimmune diseases therapy

The cGAS-STING signaling plays an integral role in the host immune response, and the abnormal activation of cGAS-STING is highly related to various autoimmune diseases. Therefore, targeting the cGAS-STING-TBK1 axis has become a promising strategy in therapy of autoimmune diseases. Herein, we summarized the key pathways mediated by the cGAS-STING-TBK1 axis and various cGAS-STING-TBK1 related autoimmune diseases, as well as the recent development of cGAS, STING, or TBK1 selective inhibitors and their potential application in therapy of cGAS-STING-TBK1 related autoimmune diseases. Overall, the review highlights that inhibiting cGAS-STING-TBK1 signaling is an attractive strategy for autoimmune disease therapy.