Activation of STING requires palmitoylation at the Golgi

Design and syntheses of a bimolecular STING agonist based on the covalent STING antagonist

Cyclic GMP-AMP synthase and stimulator of interferon genes (cGAS-STING) signaling stimulators, an essential innate immunity component, monitor invading pathogen DNA and damaged self-DNA, making them an appealing target for drug development. The natural STING agonist, 2'3'-cGAMP, mounts and stabilizes the STING homodimer to trigger an antiviral or antitumor immune responses. However, cyclic-dinucleotide-based STING agonists show limited clinical effects owing to their short half-lives. To explore whether STING-dimer stabilizers could trigger STING signaling instead of cyclic dinucleotide-based molecules, we analyzed the structural characteristics of STING to design and synthesize a series of compounds based on the covalent STING inhibitor C-170, three of which were 23, 26, and 27, exhibited STING-dependent immune activation, both in vitro and in vivo. Compound 23 could act synergistically with cGAMP and other STING agonists as a promising moderate STING agonist. This indicates that promoting STING dimerization is a promising strategy for designing next-generation STING agonists.

ROS-dependent palmitoylation is an obligate licensing modification for GSDMD pore formation

Gasdermin D (GSDMD) is the common effector for cytokine secretion and pyroptosis downstream of inflammasome activation by forming large transmembrane pores upon cleavage by inflammatory caspases. Here we report the surprising finding that GSDMD cleavage is not sufficient for its pore formation. Instead, GSDMD is lipidated by S-palmitoylation at Cys191 upon inflammasome activation, and only palmitoylated GSDMD N-terminal domain (GSDMD-NT) is capable of membrane translocation and pore formation, suggesting that palmitoylation licenses GSDMD activation. Treatment by the palmitoylation inhibitor 2-bromopalmitate and alanine mutation of Cys191 abrogate GSDMD membrane localization, cytokine secretion, and cell death, without affecting GSDMD cleavage. Because palmitoylation is formed by a reversible thioester bond sensitive to free thiols, we tested if GSDMD palmitoylation is regulated by cellular redox state. Lipopolysaccharide (LPS) mildly and LPS plus the NLRP3 inflammasome activator nigericin markedly elevate reactive oxygen species (ROS) and GSDMD palmitoylation, suggesting that these two processes are coupled. Manipulation of cellular ROS by its activators and quenchers augment and abolish, respectively, GSDMD palmitoylation, GSDMD pore formation and cell death. We discover that zDHHC5 and zDHHC9 are the major palmitoyl transferases that mediate GSDMD palmitoylation, and when cleaved, recombinant and partly palmitoylated GSDMD is 10-fold more active in pore formation than bacterially expressed, unpalmitoylated GSDMD, evidenced by liposome leakage assay. Finally, other GSDM family members are also palmitoylated, suggesting that ROS stress and palmitoylation may be a general switch for the activation of this pore-forming family.

One-Sentence Summary

GSDMD palmitoylation is induced by ROS and required for pore formation.

Combining targeted DNA repair inhibition and immune-oncology approaches for enhanced tumor control

Targeted therapy and immunotherapy have revolutionized cancer treatment. However, the ability of cancer to evade the immune system remains a major barrier for effective treatment. Related to this, several targeted DNA-damage response inhibitors (DDRis) are being tested in the clinic and have been shown to potentiate anti-tumor immune responses. Seminal studies have shown that these agents are highly effective in a pan-cancer class of tumors with genetic defects in key DNA repair genes such as BRCA1/2, BRCA-related genes, ataxia telangiectasia mutated (ATM), and others. Here, we review the molecular consequences of targeted DDR inhibition, from tumor cell death to increased engagement of the anti-tumor immune response. Additionally, we discuss mechanistic and clinical rationale for pairing targeted DDRis with immunotherapy for enhanced tumor control. We also review biomarkers for patient selection and promising new immunotherapy approaches poised to form the foundation of next-generation DDRi and immunotherapy combinations.

cGAMP-activated cGAS-STING signaling: its bacterial origins and evolutionary adaptation by metazoans

The metazoan cGAMP-activated cGAS-STING innate immunity pathway is triggered in response to genomic instability and DNA damage, thereby providing host defense against microbial pathogens. This pathway also impacts on autophagy, cellular senescence and antitumor immunity, while its overactivation triggers autoimmune and inflammatory diseases. Metazoan cGAS generates cGAMP containing distinct combinations of 3'-5' and 2'-5' linkages, which target the adaptor protein STING and activate the innate immune response through a signaling cascade leading to upregulation of cytokine and interferon production. This Review highlights a structure-based mechanistic perspective of recent advances in cGAMP-activated cGAS-STING innate immune signaling by focusing on the cGAS sensor, cGAMP second messenger and STING adaptor components, thereby elucidating the specificity, activation, regulation and signal transduction features of the pathway. In addition, the Review addresses progress towards identification of inhibitors and activators targeting cGAS and STING, as well as strategies developed by pathogens to evade cGAS-STING immunity. Most importantly, it highlights cyclic nucleotide second messengers as ancient signaling molecules that elicit a potent innate immune response that originated in bacteria and evolved through evolutionary adaptation to metazoans.

Targeting STING to promote antitumor immunity

Pharmacology-based methods that promote antitumor immunity have the potential to be highly efficacious while avoiding the systemic cytotoxicity associated with traditional chemotherapies. Activation of type I interferon (IFN) signaling in antigen-presenting cell types [e.g., macrophages and dendritic cells (DCs)] is critical, if not essential, for inducing a tumor-specific adaptive immune response, including the activation of cytolytic CD8 T cells. In the context of promoting antitumor immunity, the cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway has emerged as a principal regulator of essential type I IFN signaling. As such, STING represents a highly attractive target for developing a first-in-class immunotherapy, albeit one with a potential for significant cell type- and downstream pathway-dependent on-target toxicities, as well as conceivable pharmacogenomic liabilities.

STING signalling is terminated through ESCRT-dependent microautophagy of vesicles originating from recycling endosomes

Stimulator of interferon genes (STING) is essential for the type I interferon response against a variety of DNA pathogens. Upon emergence of cytosolic DNA, STING translocates from the endoplasmic reticulum to the Golgi where STING activates the downstream kinase TBK1, then to lysosome through recycling endosomes (REs) for its degradation. Although the molecular machinery of STING activation is extensively studied and defined, the one underlying STING degradation and inactivation has not yet been fully elucidated. Here we show that STING is degraded by the endosomal sorting complexes required for transport (ESCRT)-driven microautophagy. Airyscan super-resolution microscopy and correlative light/electron microscopy suggest that STING-positive vesicles of an RE origin are directly encapsulated into Lamp1-positive compartments. Screening of mammalian Vps genes, the yeast homologues of which regulate Golgi-to-vacuole transport, shows that ESCRT proteins are essential for the STING encapsulation into Lamp1-positive compartments. Knockdown of Tsg101 and Vps4, components of ESCRT, results in the accumulation of STING vesicles in the cytosol, leading to the sustained type I interferon response. Knockdown of Tsg101 in human primary T cells leads to an increase the expression of interferon-stimulated genes. STING undergoes K63-linked ubiquitination at lysine 288 during its transit through the Golgi/REs, and this ubiquitination is required for STING degradation. Our results reveal a molecular mechanism that prevents hyperactivation of innate immune signalling, which operates at REs.

4-octyl itaconate as a metabolite derivative inhibits inflammation via alkylation of STING

The Krebs cycle-derived metabolite itaconate, whose production is catalyzed by immune response gene 1 (IRG1), has potential to link immunity and metabolism in activated macrophages through alkylation or competitive inhibition of target proteins. In support of this, our previous study demonstrated that the stimulator of interferon genes (STING) signaling platform functions as a hub in macrophage immunity and has a profound impact on the prognosis of sepsis. Interestingly, we find that itaconate, an endogenous immunomodulator, can significantly inhibit the activation of STING signaling. Moreover, 4-octyl itaconate (4-OI), which is a permeable itaconate derivative, can alkylate cysteine sites 65, 71, 88, and 147 of STING, thereby inhibiting its phosphorylation. Furthermore, itaconate and 4-OI inhibit the production of inflammatory factors in sepsis models. Our results broaden the knowledge on the role of the IRG1-itaconate axis in immunomodulation and highlight itaconate and its derivatives as potential therapeutic agents in sepsis.

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.

Single High-Dose Irradiation-Induced iRhom2 Upregulation Promotes Macrophage Antitumor Activity Through cGAS/STING Signaling

PURPOSE

The clinical application of stereotactic body radiation therapy (SBRT) allows a high dose of radiation to be safely delivered to extracranial targets within the body; however, a high dose per fraction (hypofractionation) has opened the radiation oncology field to new questions on a variety of dose-fractionation schedules, especially the immunomodulatory effects of radiation therapy, which can change after various dose-fractionation schedules. We investigated the immunomodulatory effects of different fractionation schedules.

METHODS AND MATERIALS

We established a subcutaneous tumor model in wild-type C57BL/6J mice and STING (stimulator of interferon genes)-deficient mice. We then compared the tumor control efficacy of 3 different fractionation schedules: 2 Gy × 8, 4.5 Gy × 3, and 10 Gy × 1, which are similar biologically effective doses.

RESULTS

We found the fractionation schedule of 10 Gy × 1 had a significantly higher antitumor effect, suggesting that a single high dose induced enhanced antitumor immunity compared with conventional fractionation (2 Gy × 8) and moderate hypofractionation (4.5 Gy × 3). However, in STING-deficient mice, differential tumor control was not observed among the 3 dose-fractionation schedules, suggesting that cGAS (cyclic GMP-AMP synthase)/STING signaling is involved in the antitumor immune effects of single high-dose schedules. Mechanistically, we found that conventional fractionation induced apoptosis; by comparison, a single high dose was more attuned to induced necroptosis, leading to the release of intracellular irradiation-induced double-stranded DNA (dsDNA) due to the loss of plasma membrane integrity, which then activated the dsDNA sensing signaling cGAS/STING in the recruited macrophage. Furthermore, iRhom2, a member of the conserved family of inhibitory rhomboid-like pseudoproteases, was upregulated in infiltrated macrophages in the single high-dose irradiation microenvironment. Therefore, iRhom2 positively regulates STING and directly promotes tumor necrosis factor α secretion. This exacerbates necroptosis of irradiated tumor cells, leading to continuous dsDNA release and enhancement of cGAS/STING signaling antitumor immunity in a positive feedback loop.

CONCLUSIONS

iRhom2 amplifies antitumor signaling in a positive feedback loop mediated by cGAS/STING signaling and tumor necrosis factor-driven necroptosis after single high-dose radiation.

Myristic acid as a checkpoint to regulate STING-dependent autophagy and interferon responses by promoting N-myristoylation

Stimulator of interferon gene (STING)-triggered autophagy is crucial for the host to eliminate invading pathogens and serves as a self-limiting mechanism of STING-induced interferon (IFN) responses. Thus, the mechanisms that ensure the beneficial effects of STING activation are of particular importance. Herein, we show that myristic acid, a type of long-chain saturated fatty acid (SFA), specifically attenuates cGAS-STING-induced IFN responses in macrophages, while enhancing STING-dependent autophagy. Myristic acid inhibits HSV-1 infection-induced innate antiviral immune responses and promotes HSV-1 replication in mice in vivo. Mechanistically, myristic acid enhances N-myristoylation of ARF1, a master regulator that controls STING membrane trafficking. Consequently, myristic acid facilitates STING activation-triggered autophagy degradation of the STING complex. Thus, our work identifies myristic acid as a metabolic checkpoint that contributes to immune homeostasis by balancing STING-dependent autophagy and IFN responses. This suggests that myristic acid and N-myristoylation are promising targets for the treatment of diseases caused by aberrant STING activation.

Function and regulation of cGAS-STING signaling in infectious diseases

The efficacious detection of pathogens and prompt induction of innate immune signaling serve as a crucial component of immune defense against infectious pathogens. Over the past decade, DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signaling adaptor stimulator of interferon genes (STING) have emerged as key mediators of type I interferon (IFN) and nuclear factor-κB (NF-κB) responses in health and infection diseases. Moreover, both cGAS-STING pathway and pathogens have developed delicate strategies to resist each other for their survival. The mechanistic and functional comprehension of the interplay between cGAS-STING pathway and pathogens is opening the way for the development and application of pharmacological agonists and antagonists in the treatment of infectious diseases. Here, we briefly review the current knowledge of DNA sensing through the cGAS-STING pathway, and emphatically highlight the potent undertaking of cGAS-STING signaling pathway in the host against infectious pathogenic organisms.

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.

Encapsulation of Platinum Prodrugs into PC7A Polymeric Nanoparticles Combined with Immune Checkpoint Inhibitors for Therapeutically Enhanced Multimodal Chemotherapy and Immunotherapy by Activation of the STING Pathway

Tumor immunotherapy has emerged as one of the most promising therapeutic methods to treat cancer. Despite its clinical application, the immunosuppressive tumor microenvironment compromises the therapeutic efficiency of this technique. To overcome this limitation, many research efforts have been devoted to the development of agents that reprogram the immunosuppressive tumor microenvironment through novel mechanisms. Over the last decade, compounds that intervene through the immunogenic stimulator of interferon genes (STING) pathway have emerged with potential for clinical development. Herein, the encapsulation of chemotherapeutic platinum complexes with a polymer with a cyclic seven-membered ring (PC7A)-based polymer into pH-responsive nanoparticles for multimodal therapeutically enhanced chemotherapy and immunotherapy is presented. This study represents the first nanomaterial with a dual activation mechanism of the STING pathway through DNA fragmentation as well as PC7A binding. The combination of these nanoparticles with immune checkpoint inhibitors demonstrates to nearly fully eradicate a colorectal tumor inside the mouse model by chemotherapy and immunotherapy using the STING pathway.

Genomic instability caused by Arp2/3 complex inactivation results in micronucleus biogenesis and cellular senescence

The Arp2/3 complex is an actin nucleator with well-characterized activities in cell morphogenesis and movement, but its roles in nuclear processes are relatively understudied. We investigated how the Arp2/3 complex affects genomic integrity and cell cycle progression using mouse fibroblasts containing an inducible knockout (iKO) of the ArpC2 subunit. We show that permanent Arp2/3 complex ablation results in DNA damage, the formation of cytosolic micronuclei, and cellular senescence. Micronuclei arise in ArpC2 iKO cells due to chromatin segregation defects during mitosis and premature mitotic exits. Such phenotypes are explained by the presence of damaged DNA fragments that fail to attach to the mitotic spindle, abnormalities in actin assembly during metaphase, and asymmetric microtubule architecture during anaphase. In the nuclei of Arp2/3-depleted cells, the tumor suppressor p53 is activated and the cell cycle inhibitor Cdkn1a/p21 mediates a G1 arrest. In the cytosol, micronuclei are recognized by the DNA sensor cGAS, which is important for stimulating a STING- and IRF3-associated interferon response. These studies establish functional requirements for the mammalian Arp2/3 complex in mitotic spindle organization and genome stability. They also expand our understanding of the mechanisms leading to senescence and suggest that cytoskeletal dysfunction is an underlying factor in biological aging.

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.

Palmitoylation prevents sustained inflammation by limiting NLRP3 inflammasome activation through chaperone-mediated autophagy

As a key component of the inflammasome, NLRP3 is a critical intracellular danger sensor emerging as an important clinical target in inflammatory diseases. However, little is known about the mechanisms that determine the kinetics of NLRP3 inflammasome stability and activity to ensure effective and controllable inflammatory responses. Here, we show that S-palmitoylation acts as a brake to turn NLRP3 inflammasome off. zDHHC12 is identified as the S-acyltransferase for NLRP3 palmitoylation, which promotes its degradation through the chaperone-mediated autophagy pathway. Zdhhc12 deficiency in mice enhances inflammatory symptoms and lethality following alum-induced peritonitis and LPS-induced endotoxic shock. Notably, several disease-associated mutations in NLRP3 are associated with defective palmitoylation, resulting in overt NLRP3 inflammasome activation. Thus, our findings identify zDHHC12 as a repressor of NLRP3 inflammasome activation and uncover a previously unknown regulatory mechanism by which the inflammasome pathway is tightly controlled by the dynamic palmitoylation of NLRP3.

Metabolic enzyme UAP1 mediates IRF3 pyrophosphorylation to facilitate innate immune response

Post-translational modifications (PTMs) of proteins are crucial to guarantee the proper biological functions in immune responses. Although protein phosphorylation has been extensively studied, our current knowledge of protein pyrophosphorylation, which occurs based on phosphorylation, is very limited. Protein pyrophosphorylation is originally considered to be a non-enzymatic process, and its function in immune signaling is unknown. Here, we identify a metabolic enzyme, UDP-N-acetylglucosamine pyrophosphorylase 1 (UAP1), as a pyrophosphorylase for protein serine pyrophosphorylation, by catalyzing the pyrophosphorylation of interferon regulatory factor 3 (IRF3) at serine (Ser) 386 to promote robust type I interferon (IFN) responses. Uap1 deficiency significantly impairs the activation of both DNA- and RNA-viruse-induced type I IFN pathways, and the Uap1-deficient mice are highly susceptible to lethal viral infection. Our findings demonstrate the function of protein pyrophosphorylation in the regulation of antiviral responses and provide insights into the crosstalk between metabolism and innate immunity.

Mechanism and effects of STING-IFN-I pathway on nociception: A narrative review

Since the discovery of STING in 2008, numerous studies have investigated its functions in immunity, inflammation, and cancer. STING activates downstream molecules including IFN-I, NLRP3, and NF-κB. The STING-IFN-I pathway plays a vital role in nociception. After receiving the upstream signal, STING is activated and induces the expression of IFN-I, and after paracrine and autocrine signaling, IFN-I binds to IFN receptors. Subsequently, the activity of ion channels is inhibited by TYK2, which induces an acute antinociceptive effect. JAK activates PIK3 and MAPK-MNK-eIF4E pathways, which sensitize nociceptors in the peripheral nervous system. In the mid-late stage, the STING-IFN-I pathway activates STAT, increases pro-inflammatory and anti-inflammatory cytokines, inhibits ER-phagy, and promotes microglial M1-polarization in the central nervous system, leading to central sensitization. Thus, the STING-IFN-I pathway may exert complex effects on nociception at various stages, and these effects require further comprehensive elucidation. Therefore, in this review, we systematically summarized the mechanisms of the STING-IFN-I pathway and discussed its function in nociception.

ZDHHC11 Suppresses Zika Virus Infections by Palmitoylating the Envelope Protein

Zika virus (ZIKV) is an RNA-enveloped virus that belongs to the Flavivirus genus, and ZIKV infections potentially induce severe neurodegenerative diseases and impair male fertility. Palmitoylation is an important post-translational modification of proteins that is mediated by a series of DHHC-palmitoyl transferases, which are implicated in various biological processes and viral infections. However, it remains to be investigated whether palmitoylation regulates ZIKV infections. In this study, we initially observed that the inhibition of palmitoylation by 2-bromopalmitate (2-BP) enhanced ZIKV infections, and determined that the envelope protein of ZIKV is palmitoylated at Cys308. ZDHHC11 was identified as the predominant enzyme that interacts with the ZIKV envelope protein and catalyzes its palmitoylation. Notably, ZDHHC11 suppressed ZIKV infections in an enzymatic activity-dependent manner and ZDHHC11 knockdown promoted ZIKV infection. In conclusion, we proposed that the envelope protein of ZIKV undergoes a novel post-translational modification and identified a distinct mechanism in which ZDHHC11 suppresses ZIKV infections via palmitoylation of the ZIKV envelope protein.

STING Suppresses Mitochondrial VDAC2 to Govern RCC Growth Independent of Innate Immunity

STING is an innate immune sensor for immune surveillance of viral/bacterial infection and maintenance of an immune-friendly microenvironment to prevent tumorigenesis. However, if and how STING exerts innate immunity-independent function remains elusive. Here, the authors report that STING expression is increased in renal cell carcinoma (RCC) patients and governs tumor growth through non-canonical innate immune signaling involving mitochondrial ROS maintenance and calcium homeostasis. Mitochondrial voltage-dependent anion channel VDAC2 is identified as a new STING binding partner. STING depletion potentiates VDAC2/GRP75-mediated MERC (mitochondria-ER contact) formation to increase mitochondrial ROS/calcium levels, impairs mitochondria function, and suppresses mTORC1/S6K signaling leading to RCC growth retardation. STING interaction with VDAC2 occurs through STING-C88/C91 palmitoylation and inhibiting STING palmitoyl-transferases ZDHHCs by 2-BP significantly impedes RCC cell growth alone or in combination with sorafenib. Together, these studies reveal an innate immunity-independent function of STING in regulating mitochondrial function and growth in RCC, providing a rationale to target the STING/VDAC2 interaction in treating RCC.

Host M-CSF induced gene expression drives changes in susceptible and resistant mice-derived BMdMs upon Leishmania major infection

Leishmaniases are a group of diseases with different clinical manifestations. Macrophage-Leishmania interactions are central to the course of the infection. The outcome of the disease depends not only on the pathogenicity and virulence of the parasite, but also on the activation state, the genetic background, and the underlying complex interaction networks operative in the host macrophages. Mouse models, with mice strains having contrasting behavior in response to parasite infection, have been very helpful in exploring the mechanisms underlying differences in disease progression. We here analyzed previously generated dynamic transcriptome data obtained from Leishmania major (L. major) infected bone marrow derived macrophages (BMdMs) from resistant and susceptible mouse. We first identified differentially expressed genes (DEGs) between the M-CSF differentiated macrophages derived from the two hosts, and found a differential basal transcriptome profile independent of Leishmania infection. These host signatures, in which 75% of the genes are directly or indirectly related to the immune system, may account for the differences in the immune response to infection between the two strains. To gain further insights into the underlying biological processes induced by L. major infection driven by the M-CSF DEGs, we mapped the time-resolved expression profiles onto a large protein-protein interaction (PPI) network and performed network propagation to identify modules of interacting proteins that agglomerate infection response signals for each strain. This analysis revealed profound differences in the resulting responses networks related to immune signaling and metabolism that were validated by qRT-PCR time series experiments leading to plausible and provable hypotheses for the differences in disease pathophysiology. In summary, we demonstrate that the host's gene expression background determines to a large degree its response to L. major infection, and that the gene expression analysis combined with network propagation is an effective approach to help identifying dynamically altered mouse strain-specific networks that hold mechanistic information about these contrasting responses to infection.

Crosstalk between cGAS-STING pathway and autophagy in cancer immunity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is critical in cancer immunity. Autophagy is a highly conserved process that is responsible for the degradation of cytoplasmic material and is involved in both innate and adaptive immunity. Recently, cGAS-STING and autophagy have been shown to be interconnected, which may influence the progression of cancer. Although cGAS-STING and autophagy have been shown to be interrelated in innate immunity, little has been reported about cancer immunity. As cancer immunity is key to treating tumors, it is essential to summarize the relationship and interactions between the two. Based on this, we systematically sorted out the recent findings of cGAS-STING and autophagy in cancer immunity and explored the interactions between cGAS-STING and autophagy, although these interactions have not been extensively studied. Lastly, we provide an outlook on how cGAS-STING and autophagy can be combined, with the hope that our research can help people better understand their potential roles in cancer immunity and bring light to the treatment of cancer.

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.

Manganese-coordinated mRNA vaccines with enhanced mRNA expression and immunogenicity induce robust immune responses against SARS-CoV-2 variants

It is urgent to develop more effective mRNA vaccines against the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants owing to the immune escape. Here, we constructed a novel mRNA delivery system [IC8/Mn lipid nanoparticles (IC8/Mn LNPs)]with high immunogenicity, via introducing a stimulator of interferon genes (STING) agonist [manganese (Mn)] based on a newly synthesized ionizable lipid (IC8). It was found that Mn can not only promote maturation of antigen-presenting cells via activating STING pathway but also improve mRNA expression by facilitating lysosomal escape for the first time. Subsequently, IC8/Mn LNPs loaded with mRNA encoding the Spike protein of SARS-CoV-2 Delta or Omicron variant (IC8/Mn@D or IC8/Mn@O) were prepared. Both mRNA vaccines induced substantial specific immunoglobulin G responses against Delta or Omicron. IC8/Mn@D displayed strong pseudovirus neutralization ability, T helper 1-biased immune responses, and good safety. It can be concluded that IC8/Mn LNPs have great potential for developing Mn-coordinated mRNA vaccines with robust immunogenicity and good safety.

Research advances in cGAS-stimulator of interferon genes pathway and central nervous system diseases: Focus on new therapeutic approaches

Cyclic GMP-AMP synthase (cGAS), a crucial innate immune sensor, recognizes cytosolic DNA and induces stimulator of interferon genes (STING) to produce type I interferon and other proinflammatory cytokines, thereby mediating innate immune signaling. The cGAS-STING pathway is involved in the regulation of infectious diseases, anti-tumor immunity, and autoimmune diseases; in addition, it plays a key role in the development of central nervous system (CNS) diseases. Therapeutics targeting the modulation of cGAS-STING have promising clinical applications. Here, we summarize the cGAS-STING signaling mechanism and the recent research on its role in CNS diseases.

ABHD16A Negatively Regulates the Palmitoylation and Antiviral Function of IFITM Proteins

Interferon-inducible transmembrane (IFITM) proteins are small homologous proteins that are encoded by the interferon-stimulated genes (ISGs), which can be strongly induced by interferon (IFN) and provide resistance to invasion by a variety of viral pathogens. However, the exact molecular mechanisms underlying this function have remained elusive. The antiviral activity of IFITMs from different species depends on S-palmitoylation at conserved cysteine residues. However, specific enzymes involved in the dynamic palmitoylation cycle of IFITMs, especially depalmitoylase, have not yet been reported. Here, we demonstrate that α/-hydrolase domain-containing 16A (ABHD16A) is a depalmitoylase and a negative regulator of IFITM protein that can catalyze the depalmitoyl reaction of S-palmitoylated IFITM proteins, thereby decreasing their antiviral activities on RNA viruses. Using the acyl-PEGyl exchange gel shift (APEGS) assay, we identified ABHD16A proteins from humans, pigs, and mice that can directly participate in the palmitoylation/depalmitoylation cycles of IFITMs in the constructed abhd16a^-/- cells and ABHD16A-overexpressing cells. Furthermore, we showed that ABHD16A functions as a regulator of subcellular localization of IFITM proteins and is related to the immune system. It is tempting to suggest that pharmacological intervention in IFITMs and ABHD16A can be achieved either through controlling their expression or regulating their activity, thereby providing a broad-spectrum therapeutic strategy for animal viral diseases. IMPORTANCE IFITM protein is the cells first line of antiviral defense that blocks early stages of viral replication; the underlying mechanism might be associated with the proper distribution in cells. The palmitoylation/depalmitoylation cycle can dynamically regulate protein localization, stability, and function. This work is the first one that found the critical enzyme that participates in the palmitoylation/depalmitoylation cycle of IFITM, and this type of palmitoyl loss may be an essential regulation mode for balancing the antiviral functions of the IFN pathway. These findings imply that the pharmacological intervention in IFITM and ABHD16A, either through controlling their expression or regulating their activities, could provide a broad-spectrum therapeutic strategy for animal viral diseases and complications linked to interferon elevation.

The Golgi-resident protein ACBD3 concentrates STING at ER-Golgi contact sites to drive export from the ER

STING, an endoplasmic reticulum (ER)-resident receptor for cyclic di-nucleotides (CDNs), is essential for innate immune responses. Upon CDN binding, STING moves from the ER to the Golgi, where it activates downstream type-I interferon (IFN) signaling. General cargo proteins exit from the ER via concentration at ER exit sites. However, the mechanism of STING concentration is poorly understood. Here, we visualize the ER exit sites of STING by blocking its transport at low temperature or by live-cell imaging with the cell-permeable ligand bis-^pivSATE-2'F-c-di-dAMP, which we have developed. After ligand binding, STING forms punctate foci at non-canonical ER exit sites. Unbiased proteomic screens and super-resolution microscopy show that the Golgi-resident protein ACBD3/GCP60 recognizes and concentrates ligand-bound STING at specialized ER-Golgi contact sites. Depletion of ACBD3 impairs STING ER-to-Golgi trafficking and type-I IFN responses. Our results identify the ACBD3-mediated non-canonical cargo concentration system that drives the ER exit of STING.

The emerging roles of TLR and cGAS signaling in tumorigenesis and progression of ovarian cancer

Ovarian cancer is fatal to women and has a high mortality rate. Although on-going efforts are never stopped in identifying diagnostic and intervention strategies, the disease is so far unable to be well managed. The most important reason for this is the complexity of pathogenesis for OC, and therefore, uncovering the essential molecular biomarkers accompanied with OC progression takes the privilege for OC remission. Inflammation has been reported to participate in the initiation and progression of OC. Both microenvironmental and tumor cell intrinsic inflammatory signals contribute to the malignancy of OC. Inflammation responses can be triggered by various kinds of stimulus, including endogenous damages and exogenous pathogens, which are initially recognized and orchestrated by a series of innate immune system related receptors, especially Toll like receptors, and cyclic GMP-AMP synthase. In this review, we will discuss the roles of innate immune system related receptors, including TLRs and cGAS, and responses both intrinsic and exogenetic in the development and treatment of OC.

cGAS in nucleus: The link between immune response and DNA damage repair

As the first barrier of host defense, innate immunity sets up the parclose to keep out external microbial or virus attacks. Depending on the type of pathogens, several cytoplasm pattern recognition receptors exist to sense the attacks from either foreign or host origins, triggering the immune response to battle with the infections. Among them, cGAS-STING is the major pathway that mainly responds to microbial DNA, DNA virus infections, or self-DNA, which mainly comes from genome instability by-product or released DNA from the mitochondria. cGAS was initially found functional in the cytoplasm, although intriguing evidence indicates that cGAS exists in the nucleus where it is involved in the DNA damage repair process. Because the close connection between DNA damage response and immune response and cGAS recognizes DNA in length-dependent but DNA sequence-independent manners, it is urgent to clear the function balance of cGAS in the nucleus versus cytoplasm and how it is shielded from recognizing the host origin DNA. Here, we outline the current conception of immune response and the regulation mechanism of cGAS in the nucleus. Furthermore, we will shed light on the potential mechanisms that are restricted to be taken away from self-DNA recognition, especially how post-translational modification regulates cGAS functions.

The effect of the cyclic GMP-AMP synthase-stimulator of interferon genes signaling pathway on organ inflammatory injury and fibrosis

The cyclic GMP-AMP synthase-stimulator of interferon genes signal transduction pathway is critical in innate immunity, infection, and inflammation. In response to pathogenic microbial infections and other conditions, cyclic GMP-AMP synthase (cGAS) recognizes abnormal DNA and initiates a downstream type I interferon response. This paper reviews the pathogenic mechanisms of stimulator of interferon genes (STING) in different organs, including changes in fibrosis-related biomarkers, intending to systematically investigate the effect of the cyclic GMP-AMP synthase-stimulator of interferon genes signal transduction in inflammation and fibrosis processes. The effects of stimulator of interferon genes in related auto-inflammatory and neurodegenerative diseases are described in this article, in addition to the application of stimulator of interferon genes-related drugs in treating fibrosis.

The Microtubule Destabilizer Eribulin Synergizes with STING Agonists to Promote Antitumor Efficacy in Triple-Negative Breast Cancer Models

Eribulin is a microtubule destabilizer used in the treatment of triple-negative breast cancer (TNBC). Eribulin and other microtubule targeted drugs, such as the taxanes, have shared antimitotic effects, but differ in their mechanism of microtubule disruption, leading to diverse effects on cellular signaling and trafficking. Herein, we demonstrate that eribulin is unique from paclitaxel in its ability to enhance expression of the immunogenic cytokine interferon beta (IFNβ) in combination with STING agonists in both immune cells and TNBC models, including profound synergism with ADU-S100 and E7766, which are currently undergoing clinical trials. The mechanism by which eribulin enhances STING signaling is downstream of microtubule disruption and independent of the eribulin-dependent release of mitochondrial DNA. Eribulin did not override the requirement of ER exit for STING activation and did not inhibit subsequent STING degradation; however, eribulin significantly enhanced IRF3 phosphorylation and IFNβ production downstream of the RNA sensing pathway that converges on this transcription factor. Additionally, we found that eribulin enhanced the population of activated CD4⁺ T-cells in vivo when combined with either a STING agonist or tumor, demonstrating the ability to function as an immune adjuvant. We further interrogated the combination of eribulin with ADU-S100 in the MMTV-PyVT spontaneous murine mammary tumor model where we observed significant antitumor efficacy with combination treatment. Together, our findings demonstrate that microtubule targeted chemotherapeutics have distinct immunological effects and that eribulin's ability to enhance innate immune sensing pathways supports its use in combination with immunotherapies, such as STING agonists, for the more effective treatment of TNBC and other malignancies.

The Relationship between Reactive Oxygen Species and the cGAS/STING Signaling Pathway in the Inflammaging Process

During Inflammaging, a dysregulation of the immune cell functions is generated, and these cells acquire a senescent phenotype with an increase in pro-inflammatory cytokines and ROS. This increase in pro-inflammatory molecules contributes to the chronic inflammation and oxidative damage of biomolecules, classically observed in the Inflammaging process. One of the most critical oxidative damages is generated to the host DNA. Damaged DNA is located out of the natural compartments, such as the nucleus and mitochondria, and is present in the cell's cytoplasm. This DNA localization activates some DNA sensors, such as the cGAS/STING signaling pathway, that induce transcriptional factors involved in increasing inflammatory molecules. Some of the targets of this signaling pathway are the SASPs. SASPs are secreted pro-inflammatory molecules characteristic of the senescent cells and inducers of ROS production. It has been suggested that oxidative damage to nuclear and mitochondrial DNA generates activation of the cGAS/STING pathway, increasing ROS levels induced by SASPs. These additional ROS increase oxidative DNA damage, causing a loop during the Inflammaging. However, the relationship between the cGAS/STING pathway and the increase in ROS during Inflammaging has not been clarified. This review attempt to describe the potential connection between the cGAS/STING pathway and ROS during the Inflammaging process, based on the current literature, as a contribution to the knowledge of the molecular mechanisms that occur and contribute to the development of the considered adaptative Inflammaging process during aging.

The cGAS-STING pathway and cancer

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway has emerged as a critical innate immune pathway that, following engagement by DNA, promotes distinct immune effector responses that can impact virtually all aspects of tumorigenesis, from malignant cell transformation to metastasis. Here we address how natural tumor-associated processes and traditional cancer therapies are shaped by cGAS-STING signaling, and how this contributes to beneficial or detrimental outcomes of cancer. We consider current efforts to target the cGAS-STING axis in tumors and highlight new frontiers in cGAS-STING biology to inspire thinking about their connection to cancer.

MPYS Modulates Fatty Acid Metabolism and Immune Tolerance at Homeostasis Independent of Type I IFNs

MPYS/STING (stimulator of IFN genes) senses cyclic dinucleotides (CDNs), generates type I IFNs, and plays a critical role in infection, inflammation, and cancer. In this study, analyzing genotype and haplotype data from the 1000 Genomes Project, we found that the R71H-G230A-R293Q (HAQ) MPYS allele frequency increased 57-fold in East Asians compared with sub-Saharan Africans. Meanwhile, the G230A-R293Q (AQ) allele frequency decreased by 98% in East Asians compared with sub-Saharan Africans. We propose that the HAQ and AQ alleles underwent a natural selection during the out-of-Africa migration. We used mouse models of HAQ and AQ to investigate the underlying mechanism. We found that the mice carrying the AQ allele, which disappeared in East Asians, had normal CDN-type I IFN responses. Adult AQ mice, however, had less fat mass than did HAQ or wild-type mice on a chow diet. AQ epididymal adipose tissue had increased regulatory T cells and M2 macrophages with protein expression associated with enhanced fatty acid oxidation. Conditional knockout mice and adoptive cell transfer indicate a macrophage and regulatory T cell-intrinsic role of MPYS in fatty acid metabolism. Mechanistically, AQ/IFNAR1-/- mice had a similar lean phenotype as for the AQ mice. MPYS intrinsic tryptophan fluorescence revealed that the R71H change increased MPYS hydrophilicity. Lastly, we found that the second transmembrane (TM) and the TM2-TM3 linker region of MPYS interact with activated fatty acid, fatty acyl-CoA. In summary, studying the evolution of the human MPYS gene revealed an MPYS function in modulating fatty acid metabolism that may be critical during the out-of-Africa migration.

The cGAS-STING pathway: Post-translational modifications and functional implications in diseases

Recent studies have illustrated the functional significance of DNA recognition in the activation of innate immune responses among a variety of diseases. The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has been found to be modulated by post-translational modifications and can regulate the immune response via type I IFNs. Accumulating evidence indicates a pivotal role of cGAS-STING signaling, being protective or pathogenic, in the development of diseases. Thus, a comprehensive understanding of the post-translational modifications of cGAS-STING pathway and their role in disease development will provide insights in predicting individual disease outcomes and developing appropriate therapies. In this review, we will discuss the regulation of the cGAS-STING pathway and its implications in disease pathologies, as well as pharmacologic strategies to target the cGAS-STING pathway for therapeutic intervention.

Alternative pathways driven by STING: From innate immunity to lipid metabolism

The Stimulator of Interferon Genes (STING) is a major adaptor protein that is central to the initiation of type I interferon responses and proinflammatory signalling. STING-dependent signalling is triggered by the presence of cytosolic nucleic acids that are generated following pathogen infection or cellular stress. Beyond this central role in controlling immune responses through the production of cytokines and chemokines, recent reports have uncovered inflammation-independent STING functions. Amongst these, a rapidly growing body of evidence demonstrates a key role of STING in controlling metabolic pathways at several levels. Since immunity and metabolic homeostasis are tightly interconnected, these findings deepen our understanding of the involvement of STING in human pathologies. Here, we discuss these findings and reflect on their impact on our current understanding of how nucleic acid immunity controls homeostasis and promotes pathological outcomes.

MITA oligomerization upon viral infection is dependent on its N-glycosylation mediated by DDOST

The mediator of IRF3 activation (MITA, also named STING) is critical for immune responses to abnormal cytosolic DNA and has been considered an important drug target in the clinical therapy of tumors and autoimmune diseases. In the present study, we report that MITA undergoes DDOST-mediated N-glycosylation in the endoplasmic reticulum (ER) upon DNA viral infection. Selective mutation of DDOST-dependent N-glycosylated residues abolished MITA oligomerization and thereby its immune functions. Moreover, increasing the expression of Ddost in the mouse brain effectively strengthens the local immune response to herpes simplex virus-1 (HSV-1) and prolongs the survival time of mice with HSV encephalitis (HSE). Our findings reveal the dependence of N-glycosylation on MITA activation and provide a new perspective on the pathogenesis of HSE.

Anlotinib enhances the antitumor immunity of radiotherapy by activating cGAS/STING in non-small cell lung cancer

Radiation resistance and unsatisfactory efficacy of radioimmunotherapy are important barriers to non-small cell lung cancer (NSCLC) treatment. The impacts of anlotinib on radiation and tumor immune microenvironment (TIME) in NSCLC remain to be resolved. Here, we find anlotinib enhances radiosensitivity, and further increases radiotherapy-stimulated CD8+ T cell infiltration and activation via triggering cGAS/STING pathway. Moreover, anlotinib shows significant effects on radioimmunotherapy (radiotherapy plus anti-PD-L1). The addition of anlotinib alleviates CD8+ T cell exhaustion, promotes the cytotoxicity and proliferation of CD8+ T cells, and boosts immune memory activation. Our work reveals the crucial role of anlotinib in antitumor immunity, and provides preclinical evidence for the application of anlotinib combined with radioimmunotherapy in NSCLC treatment.

Extended Applications of Small-Molecule Covalent Inhibitors toward Novel Therapeutic Targets

Recently, small-molecule covalent inhibitors have been accepted as a practical tool for targeting previously "undruggable" proteins. The high target selectivity of modern covalent inhibitors is now alleviating toxicity concerns regarding the covalent modifications of proteins. However, despite the tremendous clinical success of current covalent inhibitors, there are still unmet medical needs that covalent inhibitors have not yet addressed. This review categorized representative covalent inhibitors based on their mechanism of covalent inhibition: conventional covalent inhibitors, targeted covalent inhibitors (TCIs), and expanded TCIs. By reviewing both Food and Drug Administration (FDA)-approved drugs and drug candidates from recent literature, we provide insight into the future direction of covalent inhibitor development.

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.

SARS-CoV-2 ORF10 antagonizes STING-dependent interferon activation and autophagy

A characteristic feature of COVID-19, the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, is the dysregulated immune response with impaired type I and III interferon (IFN) expression and an overwhelming inflammatory cytokine storm. RIG-I-like receptors (RLRs) and cGAS-STING signaling pathways are responsible for sensing viral infection and inducing IFN production to combat invading viruses. Multiple proteins of SARS-CoV-2 have been reported to modulate the RLR signaling pathways to achieve immune evasion. Although SARS-CoV-2 infection also activates the cGAS-STING signaling by stimulating micronuclei formation during the process of syncytia, whether SARS-CoV-2 modulates the cGAS-STING pathway requires further investigation. Here, we screened 29 SARS-CoV-2-encoded viral proteins to explore the viral proteins that affect the cGAS-STING signaling pathway and found that SARS-CoV-2 open reading frame 10 (ORF10) targets STING to antagonize IFN activation. Overexpression of ORF10 inhibits cGAS-STING-induced interferon regulatory factor 3 phosphorylation, translocation, and subsequent IFN induction. Mechanistically, ORF10 interacts with STING, attenuates the STING-TBK1 association, and impairs STING oligomerization and aggregation and STING-mediated autophagy; ORF10 also prevents the endoplasmic reticulum (ER)-to-Golgi trafficking of STING by anchoring STING in the ER. Taken together, these findings suggest that SARS-CoV-2 ORF10 impairs the cGAS-STING signaling by blocking the translocation of STING and the interaction between STING and TBK1 to antagonize innate antiviral immunity.

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.

Recent advances in the activation and regulation of the cGAS-STING pathway

The cGAS-STING pathway is responsible for cytoplasmic double-stranded DNA (dsDNA) -triggered innate immunity and involved in the pathology of various diseases including infection, autoimmune diseases, neurodegeneration and cancer. Understanding the activation and regulatory mechanisms of this pathway is critical to develop therapeutic strategies toward these diseases. Here, we review the signal transduction, cellular functions and regulations of cGAS and STING, particularly highlighting the latest understandings on the activation of cGAS by dsDNA and/or Manganese (Mn²⁺), STING trafficking, sulfated glycosaminoglycans (sGAGs)-induced STING polymerization and activation, and also regulation of the cGAS-STING pathway by different biocondensates formed via phase separation of proteins from host cells and viruses.

The STING in Non-Alcoholic Fatty Liver Diseases: Potential Therapeutic Targets in Inflammation-Carcinogenesis Pathway

Non-alcoholic fatty liver disease (NAFLD), an important chronic disease, is one of the major causes of high mortality and creates a substantial financial burden worldwide. The various immune cells in the liver, including macrophages, NK cells, dendritic cells, and the neutrophils involved in the innate immune response, trigger inflammation after recognizing the damage signaled from infection or injured cells and tissues. The stimulator of interferon genes (STING) is a critical molecule that binds to the cyclic dinucleotides (CDNs) generated by the cyclic GMP-AMP synthase (cGAS) to initiate the innate immune response against infection. Previous studies have demonstrated that the cGAS-STING pathway plays a critical role in inflammatory, auto-immune, and anti-viral immune responses. Recently, studies have focused on the role of STING in liver diseases, the results implying that alterations in its activity may be involved in the pathogenesis of liver disorders. Here, we summarize the function of STING in the development of NAFLD and present the current inhibitors and agonists targeting STING.

Fatty acid metabolism in T-cell function and differentiation

Immunometabolism has recently emerged as a field of study examining the intersection between immunology and metabolism. Studies in this area have yielded new findings on the roles of a diverse range of metabolic pathways and metabolites, which have been found to control many aspects of T-cell biology, including cell differentiation, function and fate. A particularly important finding has been the discovery that to meet the energy requirements associated with their proliferation, activation and specific functions, T cells switch their metabolic signatures during differentiation. For example, whereas the induction of de novo fatty acid biosynthesis and fatty acid uptake programs are required for antigen-stimulation-induced proliferation and differentiation of effector T cells, fatty acid catabolism via β-oxidation is essential for the generation of memory T cells and the differentiation of regulatory T cells. In this review, we discuss recent advances in our understanding of the metabolism in different stages of T cells and how fatty acid metabolism in these cells controls their specific functions.

Emerging role of STING signalling in CNS injury: inflammation, autophagy, necroptosis, ferroptosis and pyroptosis

Stimulator of interferons genes (STING), which is crucial for the secretion of type I interferons and proinflammatory cytokines in response to cytosolic nucleic acids, plays a key role in the innate immune system. Studies have revealed the participation of the STING pathway in unregulated inflammatory processes, traumatic brain injury (TBI), spinal cord injury (SCI), subarachnoid haemorrhage (SAH) and hypoxic–ischaemic encephalopathy (HIE). STING signalling is markedly increased in CNS injury, and STING agonists might facilitate the pathogenesis of CNS injury. However, the effects of STING-regulated signalling activation in CNS injury are not well understood. Aberrant activation of STING increases inflammatory events, type I interferon responses, and cell death. cGAS is the primary pathway that induces STING activation. Herein, we provide a comprehensive review of the latest findings related to STING signalling and the cGAS–STING pathway and highlight the control mechanisms and their functions in CNS injury. Furthermore, we summarize and explore the most recent advances toward obtaining an understanding of the involvement of STING signalling in programmed cell death (autophagy, necroptosis, ferroptosis and pyroptosis) during CNS injury. We also review potential therapeutic agents that are capable of regulating the cGAS–STING signalling pathway, which facilitates our understanding of cGAS–STING signalling functions in CNS injury and the potential value of this signalling pathway as a treatment target.

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.