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

The RIG-I-like receptor signaling pathway triggered by Staphylococcus aureus promotes breast cancer metastasis

Host microbes are increasingly recognized as key components in various types of cancer, although their exact impact remains unclear. This study investigated the functional significance of Staphylococcus aureus (S. aureus) in breast cancer tumorigenesis and progression. We found that S. aureus invasion resulted in a compromised DNA damage response process, as evidenced by the absence of G1-phase arrest and apoptosis in breast cells in the background of double strand breaks production and the activation of the ataxia-telangiectasia mutated (ATM)-p53 signaling pathway. The high-throughput mRNA sequencing, bioinformatics analysis and pharmacological studies revealed that S. aureus facilitates breast cell metastasis through the innate immune pathway, particularly in cancer cells. During metastasis, S. aureus initially induced the expression of RIG-I-like receptors (RIG-I in normal breast cells, RIG-I and MDA5 in breast cancer cells), which in turn activated NF-κB p65 expression. We further showed that NF-κB p65 activated the CCL5-CCR5 pathway, contributing to breast cell metastasis. Our study provides novel evidence that the innate immune system, triggered by bacterial infection, plays a role in bacterial-driven cancer metastasis.

PROTAC based STING degrader attenuates acute colitis by inhibiting macrophage M1 polarization and intestinal epithelial cells pyroptosis mediated by STING-NLRP3 axis

Inflammatory bowel diseases (IBDs) are chronic, relapsing, and inflammatory disorders of the gastrointestinal tract characterized by abnormal immune responses. Recently, STING has emerged as a promising therapeutic target for various autoinflammatory diseases. However, few STING-selective small molecules have been investigated as novel strategies for IBD. In this study, we sought to examine the effects of PROTAC-based STING degrader SP23 on acute colitis and explore its underlying mechanism. SP23 treatment notably alleviates dextran sulfate sodium (DSS)-induced colitis. Pharmacological degradation of STING significantly reduced the production of inflammatory cytokines, such as TNF-α, IL-1β, and IL-6, and inhibited macrophage polarization towards the M1 type. Furthermore, SP23 administration decreased the loss of tight junction proteins, including ZO-1, occludin, and claudin-1, and downregulated STING and NLRP3 signaling pathways in intestinal inflammation. In vitro, STING activated NLRP3 inflammasome-mediated pyroptosis in intestinal epithelial cells, which could be abrogated by SP23 and STING siRNA intervention. In conclusion, these findings provide new evidence for STING as a novel therapeutic target for IBD, and reveal that hyperactivation of STING could exaggerate colitis by inducing NLRP3/Caspase-1/GSDMD axis mediated intestinal epithelial cells pyroptosis.

Butyrate attenuates intestinal inflammation in Crohn's disease by suppressing pyroptosis of intestinal epithelial cells via the cGSA-STING-NLRP3 axis

Butyrate can strengthen the intestinal epithelial barrier. However, the mechanisms by which butyrate affects intestinal epithelial cells (IECs) pyroptosis in Crohn's disease (CD) remain unclear. In this study, we collected colonic biopsy samples from CD patients and healthy controls to assess pyroptosis levels. Our findings indicated elevated expression of pyroptosis markers in CD patients, alongside distinct morphological evidence of pyroptosis in IECs. We further investigated the effects of tributyrin on pyroptosis and the cGAS-STING pathway in a trinitrobenzene sulfonic acid-induced colitis rat model. Tributyrin significantly mitigated intestinal inflammation, reduced pathological progression, and inhibited pyroptosis and cGAS-STING pathway activation in the colitis rat model. Similarly, in an in vitro model of IECs pyroptosis, sodium butyrate inhibited pyroptosis and cGAS-STING pathway activation in HT-29 cells. Co-treatment with a cGAS-STING pathway activator and butyrate demonstrated that the activator reversed the inhibitory effects of butyrate on pyroptosis and cGAS-STING pathway activation in both the colitis rat model and HT-29 cells. Mechanistically, the cGAS-STING pathway was found to interact with NLRP3. Taken together, butyrate may mitigate intestinal inflammation in CD by suppressing cGAS-STING-NLRP3 axis-mediated IECs pyroptosis. These findings offer new insights into potential therapeutic strategies for managing CD.

Innate immune sensing of cell death in disease and therapeutics

Innate immunity, cell death and inflammation underpin many aspects of health and disease. Upon sensing pathogens, pathogen-associated molecular patterns or damage-associated molecular patterns, the innate immune system activates lytic, inflammatory cell death, such as pyroptosis and PANoptosis. These genetically defined, regulated cell death pathways not only contribute to the host defence against infectious disease, but also promote pathological manifestations leading to cancer and inflammatory diseases. Our understanding of the underlying mechanisms has grown rapidly in recent years. However, how dying cells, cell corpses and their liberated cytokines, chemokines and inflammatory signalling molecules are further sensed by innate immune cells, and their contribution to further amplify inflammation, trigger antigen presentation and activate adaptive immunity, is less clear. Here, we discuss how pattern-recognition and PANoptosome sensors in innate immune cells recognize and respond to cell-death signatures. We also highlight molecular targets of the innate immune response for potential therapeutic development.

Breaking the Tumor Chronic Inflammation Balance with a Programmable Release and Multi-Stimulation Engineering Scaffold for Potent Immunotherapy

Tumor-associated chronic inflammation severely restricts the efficacy of immunotherapy in cold tumors. Here, a programmable release hydrogel-based engineering scaffold with multi-stimulation and reactive oxygen species (ROS)-response (PHOENIX) is demonstrated to break the chronic inflammatory balance in cold tumors to induce potent immunity. PHOENIX can undergo programmable release of resiquimod and anti-OX40 under ROS. Resiquimod is first released, leading to antigen-presenting cell maturation and the transformation of myeloid-derived suppressor cells and M2 macrophages into an antitumor immune phenotype. Subsequently, anti-OX40 is transported into the tumor microenvironment, leading to effector T-cell activation and inhibition of Treg function. PHOENIX consequently breaks the chronic inflammation in the tumor microenvironment and leads to a potent immune response. In mice bearing subcutaneous triple-negative breast cancer and metastasis models, PHOENIX effectively inhibited 80% and 60% of tumor growth, respectively. Moreover, PHOENIX protected 100% of the mice against TNBC tumor rechallenge by electing a robust long-term antigen-specific immune response. An excellent inhibition and prolonged survival in PHOENIX-treated mice with colorectal cancer and melanoma is also observed. This work presents a potent therapeutic scaffold to improve immunotherapy efficiency, representing a generalizable and facile regimen for cold tumors.

Research progress of cGAS-STING signaling pathway in intestinal diseases

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signal has drawn much consideration due to its sensitivity to DNA in innate immune mechanisms. Activation of the cGAS-STIN signaling pathway induces the production of interferon and inflammatory cytokines, resulting in immune responses, or inflammatory diseases. The intestinal tract is a vital organ for the body's nutrition absorption, recent studies have had various points of view on the job of cGAS-STING pathway in various intestinal sicknesses. Therefore, understanding its role and mechanism in the intestinal environment can help to develop new strategies for the treatment of intestinal diseases. This article examines the mechanism of the cGAS-STING pathway and its function in inflammatory bowel disease, intestinal cancer, and long-injury ischemia-reperfusion, lists the current medications that target it for the treatment of intestinal diseases, and discusses the impact of intestinal flora on this signaling pathway, to offer a theoretical and scientific foundation for upcoming targeted therapies for intestinal disorders via the cGAS-STING pathway.

CircRNA Regulation of T Cells in Cancer: Unraveling Potential Targets

T lymphocytes play a critical role in antitumor immunity, but their exhaustion poses a significant challenge for immune evasion by malignant cells. Circular RNAs (circRNAs), characterized by their covalently closed looped structure, have emerged as pivotal regulators within the neoplastic landscape. Recent studies have highlighted their multifaceted roles in cellular processes, including gene expression modulation and protein function regulation, which are often disrupted in cancer. In this review, we systematically explore the intricate interplay between circRNAs and T cell modulation within the tumor microenvironment. By dissecting the regulatory mechanisms through which circRNAs impact T cell exhaustion, we aim to uncover pathways crucial for immune evasion and T cell dysfunction. These insights can inform innovative immunotherapeutic strategies targeting circRNA-mediated molecular pathways. Additionally, we discuss the translational potential of circRNAs as biomarkers for therapeutic response prediction and as intervention targets. Our comprehensive analysis aims to enhance the understanding of immune evasion dynamics in the tumor microenvironment by facilitating the development of precision immunotherapy.

Advances in molecular mechanisms of inflammatory bowel disease‑associated colorectal cancer (Review)

The link between inflammation and cancer is well documented and colonic inflammation caused by inflammatory bowel disease (IBD) is thought to be a high-risk factor for the development of colorectal cancer (CRC). The complex crosstalk between epithelial and inflammatory cells is thought to underlie the progression from inflammation to cancer. The present review collates and summarises recent advances in the understanding of the pathogenesis of IBD-associated CRC (IBD-CRC), including the oncogenic mechanisms of the main inflammatory signalling pathways and genetic alterations induced by oxidative stress during colonic inflammation, and discusses the crosstalk between the tumour microenvironment, intestinal flora and host immune factors during inflammatory oncogenesis in colitis-associated CRC. In addition, the therapeutic implications of anti-inflammatory therapy for IBD-CRC were discussed, intending to provide new insight into improve clinical practice.

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.

Extrachromosomal Circular DNA: An Emerging Potential Biomarker for Inflammatory Bowel Diseases?

Inflammatory bowel disease (IBD) comprising ulcerative colitis and Crohn's disease is a chronic immune-mediated disease which affects the gastrointestinal tract with a relapsing and remitting course, causing lifelong morbidity. IBD pathogenesis is determined by multiple factors including genetics, immune and microbial factors, and environmental factors. Although therapy options are expanding, remission rates are unsatisfiable, and together with the disease course, response to therapy remains unpredictable. Therefore, the identification of biomarkers that are predictive for the disease course and response to therapy is a significant challenge. Extrachromosomal circular DNA (eccDNA) fragments exist in all tissue tested so far. These fragments, ranging in length from a few hundreds of base pairs to mega base pairs, have recently gained more interest due to technological advances. Until now, eccDNA has mainly been studied in relation to cancer due to its ability to act as an amplification site for oncogenes and drug resistance genes. However, eccDNA could also play an important role in inflammation, expressed both locally in the- involved tissue and at distant sites. Here, we review the current evidence on the molecular mechanisms of eccDNA and its role in inflammation and IBD. Additionally, the potential of eccDNA as a tissue or plasma marker for disease severity and/or response to therapy is evaluated.

Harnessing innate immune pathways for therapeutic advancement in cancer

The innate immune pathway is receiving increasing attention in cancer therapy. This pathway is ubiquitous across various cell types, not only in innate immune cells but also in adaptive immune cells, tumor cells, and stromal cells. Agonists targeting the innate immune pathway have shown profound changes in the tumor microenvironment (TME) and improved tumor prognosis in preclinical studies. However, to date, the clinical success of drugs targeting the innate immune pathway remains limited. Interestingly, recent studies have shown that activation of the innate immune pathway can paradoxically promote tumor progression. The uncertainty surrounding the therapeutic effectiveness of targeted drugs for the innate immune pathway is a critical issue that needs immediate investigation. In this review, we observe that the role of the innate immune pathway demonstrates heterogeneity, linked to the tumor development stage, pathway status, and specific cell types. We propose that within the TME, the innate immune pathway exhibits multidimensional diversity. This diversity is fundamentally rooted in cellular heterogeneity and is manifested as a variety of signaling networks. The pro-tumor effect of innate immune pathway activation essentially reflects the suppression of classical pathways and the activation of potential pro-tumor alternative pathways. Refining our understanding of the tumor's innate immune pathway network and employing appropriate targeting strategies can enhance our ability to harness the anti-tumor potential of the innate immune pathway and ultimately bridge the gap from preclinical to clinical application.

Ku70 senses cytosolic DNA and assembles a tumor-suppressive signalosome

The innate immune response contributes to the development or attenuation of acute and chronic diseases, including cancer. Microbial DNA and mislocalized DNA from damaged host cells can activate different host responses that shape disease outcomes. Here, we show that mice and humans lacking a single allele of the DNA repair protein Ku70 had increased susceptibility to the development of intestinal cancer. Mechanistically, Ku70 translocates from the nucleus into the cytoplasm where it binds to cytosolic DNA and interacts with the GTPase Ras and the kinase Raf, forming a tripartite protein complex and docking at Rab5+Rab7+ early-late endosomes. This Ku70-Ras-Raf signalosome activates the MEK-ERK pathways, leading to impaired activation of cell cycle proteins Cdc25A and CDK1, reducing cell proliferation and tumorigenesis. We also identified the domains of Ku70, Ras, and Raf involved in activating the Ku70 signaling pathway. Therapeutics targeting components of the Ku70 signalosome could improve the treatment outcomes in cancer.

The NF-κB signaling system in the immunopathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is an idiopathic, chronic condition characterized by episodes of inflammation in the gastrointestinal tract. The nuclear factor κB (NF-κB) system describes a family of dimeric transcription factors. Canonical NF-κB signaling is stimulated by and enhances inflammation, whereas noncanonical NF-κB signaling contributes to immune organogenesis. Dysregulation of NF-κB factors drives various inflammatory pathologies, including IBD. Signals from many immune sensors activate NF-κB subunits in the intestine, which maintain an equilibrium between local microbiota and host responses. Genetic association studies of patients with IBD and preclinical mouse models confirm the importance of the NF-κB system in host defense in the gut. Other studies have investigated the roles of these factors in intestinal barrier function and in inflammatory gut pathologies associated with IBD. NF-κB signaling modulates innate and adaptive immune responses and the production of immunoregulatory proteins, anti-inflammatory cytokines, antimicrobial peptides, and other tolerogenic factors in the intestine. Furthermore, genetic studies have revealed critical cell type-specific roles for NF-κB proteins in intestinal immune homeostasis, inflammation, and restitution that contribute to the etiopathology of IBD-associated manifestations. Here, we summarize our knowledge of the roles of these NF-κB pathways, which are activated in different intestinal cell types by specific ligands, and their cross-talk, in fueling aberrant intestinal inflammation. We argue that an in-depth understanding of aberrant immune signaling mechanisms may hold the key to identifying predictive or prognostic biomarkers and developing better therapeutics against inflammatory gut pathologies.

Role of cGAS-STING in colorectal cancer: A new window for treatment strategies

Colorectal cancer (CRC) is a common and deadly form of cancer, leading to the need for new therapeutic targets and strategies for treatment. Recent studies have shown the cGAS-STING pathway to be a promising target for cancer therapy. The cGAS-STING pathway is a part of the innate immune system and serves to identify DNA damage and viral infection, promoting an immune response. Activation of this pathway leads to the production of immune mediators, such as type I interferons, that activate immune cells to attack cancer cells. Research has identified the cGAS-STING pathway as a frequently dysregulated component in CRC, promoting tumor growth and metastasis, or leading to chronic inflammation and tissue damage. The modulation of this pathway presents a potential therapeutic approach, either activating or inhibiting the pathway to enhance the immune response and prevent inflammation, respectively. Developing drugs that can modulate the cGAS-STING pathway offers promise for improving treatment outcomes for CRC patients. The present review explores recent research on the role of cGAS-STING in CRC and highlights the potential therapeutic benefits of targeting this pathway.

Harnessing the innate immune system by revolutionizing macrophage-mediated cancer immunotherapy

Immunotherapy is a promising and safer alternative to conventional cancer therapies. It involves adaptive T-cell therapy, cancer vaccines, monoclonal antibodies, immune checkpoint blockade (ICB), and chimeric antigen receptor (CAR) based therapies. However, most of these modalities encounter restrictions in solid tumours owing to a dense, highly hypoxic and immune-suppressive microenvironment as well as the heterogeneity of tumour antigens. The elevated intra-tumoural pressure and mutational rates within fastgrowing solid tumours present challenges in efficient drug targeting and delivery. The tumour microenvironment is a dynamic niche infiltrated by a variety of immune cells, most of which are macrophages. Since they form a part of the innate immune system, targeting macrophages has become a plausible immunotherapeutic approach. In this review, we discuss several versatile approaches (both at pre-clinical and clinical stages) such as the direct killing of tumour-associated macrophages, reprogramming pro-tumour macrophages to anti-tumour phenotypes, inhibition of macrophage recruitment into the tumour microenvironment, novel CAR macrophages, and genetically engineered macrophages that have been devised thus far. These strategies comprise a strong and adaptable macrophage-toolkit in the ongoing fight against cancer and by understanding their significance, we may unlock the full potential of these immune cells in cancer therapy.

FMT rescues mice from DSS-induced colitis in a STING-dependent manner

Fecal microbiota transplantation (FMT) is currently a promising therapy for inflammatory bowel disease (IBD). However, clinical studies have shown that there is an obvious individual difference in the efficacy of FMT. Therefore, it is a pressing issue to identify the factors that influence the efficacy of FMT and find ways to screen the most suitable patients for this therapy. In this work, we targeted the stimulator of interferon genes (STING), a DNA-sensing protein that regulates host-defense. By comparing the differential efficacy of FMT in mice with different expression level of STING, it is revealed that FMT therapy provides treatment for DSS-induced colitis in a STING-dependent manner. Mechanistically, FMT exerts a regulatory effect on the differentiation of intestinal Th17 cells and macrophages, splenic Th1 and Th2 cells, as well as Th1 cells of the mesenteric lymph nodes via STING, down-regulating the colonic M1/M2 and splenic Th1/Th2 cell ratios, thereby improving the imbalanced immune homeostasis in the inflamed intestine. Meanwhile, based on the 16SrDNA sequencing of mice fecal samples, STING was found to facilitate the donor strain colonization in recipients' gut, mainly Lactobacillales, thereby reshaping the gut microbiota disturbed by colitis. Consequently, we proposed that STING, as a key target of FMT therapy, is potentially a biomarker for screening the most suitable individuals for FMT to optimize treatment regimens and enhance clinical benefit.

Nuclear localization of STING1 competes with canonical signaling to activate AHR for commensal and intestinal homeostasis

Extensive studies demonstrate the importance of the STING1 (also known as STING) protein as a signaling hub that coordinates immune and autophagic responses to ectopic DNA in the cytoplasm. Here, we report a nuclear function of STING1 in driving the activation of the transcription factor aryl hydrocarbon receptor (AHR) to control gut microbiota composition and homeostasis. This function was independent of DNA sensing and autophagy and showed competitive inhibition with cytoplasmic cyclic guanosine monophosphate (GMP)-AMP synthase (CGAS)-STING1 signaling. Structurally, the cyclic dinucleotide binding domain of STING1 interacted with the AHR N-terminal domain. Proteomic analyses revealed that STING1-mediated transcriptional activation of AHR required additional nuclear partners, including positive and negative regulatory proteins. Although AHR ligands could rescue colitis pathology and dysbiosis in wild-type mice, this protection was abrogated by mutational inactivation of STING1. These findings establish a key framework for understanding the nuclear molecular crosstalk between the microbiota and the immune system.

cGAS-STING signaling pathway in intestinal homeostasis and diseases

The intestinal mucosa is constantly exposed to commensal microbes, opportunistic pathogens, toxins, luminal components and other environmental stimuli. The intestinal mucosa consists of multiple differentiated cellular and extracellular components that form a critical barrier, but is also equipped for efficient absorption of nutrients. Combination of genetic susceptibility and environmental factors are known as critical components involved in the pathogenesis of intestinal diseases. The innate immune system plays a critical role in the recognition and elimination of potential threats by detecting pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). This host defense is facilitated by pattern recognition receptors (PRRs), in which the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has gained attention due to its role in sensing host and foreign double-stranded DNA (dsDNA) as well as cyclic dinucleotides (CDNs) produced by bacteria. Upon binding with dsDNA, cGAS converts ATP and GTP to cyclic GMP-AMP (cGAMP), which binds to STING and activates TANK binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3), inducing type I interferon (IFN) and nuclear factor kappa B (NF-κB)-mediated pro-inflammatory cytokines, which have diverse effects on innate and adaptive immune cells and intestinal epithelial cells (IECs). However, opposite perspectives exist regarding the role of the cGAS-STING pathway in different intestinal diseases. Activation of cGAS-STING signaling is associated with worse clinical outcomes in inflammation-associated diseases, while it also plays a critical role in protection against tumorigenesis and certain infections. Therefore, understanding the context-dependent mechanisms of the cGAS-STING pathway in the physiopathology of the intestinal mucosa is crucial for developing therapeutic strategies targeting the cGAS-STING pathway. This review aims to provide insight into recent findings of the protective and detrimental roles of the cGAS-STING pathway in intestinal diseases.

STING Promotes Intestinal IgA Production by Regulating Acetate-producing Bacteria to Maintain Host-microbiota Mutualism

BACKGROUND

Intestinal Immunoglobulin A (IgA) is crucial in maintaining host-microbiota mutualism and gut homeostasis. It has been shown that many species of gut bacteria produce cyclic dinucleotides, along with an abundance of microbiota-derived DNA present within the intestinal lumen, which triggers the tonic activation of the cytosolic cGAS-STING pathway. However, the role of STING in intestinal IgA remains poorly understood. We further investigated whether and how STING affects intestinal IgA response.

METHODS

Intestinal IgA was determined between wild-type (WT) mice and Sting-/- mice in steady conditions and upon enteric Citrobacter rodentium infection. STING agonists were used to stimulating B cells or dendritic cells in vitro. Gut microbiota composition was examined by 16S ribosomal RNA gene sequencing. Bacteria metabolomics functional analyses was performed by PICRUSt2. Fecal short-chain fatty acid (SCFA) was determined by Mass spectrometry and Cedex Bio Analyzer. Gut bacteria from WT mice and Sting-/- mice were transferred into germ-free mice and antibiotic-pretreated mice.

RESULTS

Intestinal IgA response was impaired in Sting-/- mice. However, STING agonists did not directly stimulate B cells or dendritic cells to induce IgA. Interestingly, Sting-/- mice displayed altered gut microbiota composition with decreased SCFA-producing bacteria and downregulated SCFA fermentation pathways. Transfer of fecal bacteria from Sting-/- mice induced less IgA than that from WT mice in germ-free mice and antibiotic-pretreated mice, which is mediated by GPR43. Acetate, the dominant SCFA, was decreased in Sting-/- mice, and supplementation of acetate restored intestinal IgA production in Sting-/- mice.

CONCLUSIONS

STING promotes intestinal IgA by regulating acetate-producing gut bacteria.

The Many Ways to Deal with STING

The stimulator of interferon genes (STING) is an adaptor protein involved in the activation of IFN-β and many other genes associated with the immune response activation in vertebrates. STING induction has gained attention from different angles such as the potential to trigger an early immune response against different signs of infection and cell damage, or to be used as an adjuvant in cancer immune treatments. Pharmacological control of aberrant STING activation can be used to mitigate the pathology of some autoimmune diseases. The STING structure has a well-defined ligand binding site that can harbor natural ligands such as specific purine cyclic di-nucleotides (CDN). In addition to a canonical stimulation by CDNs, other non-canonical stimuli have also been described, whose exact mechanism has not been well defined. Understanding the molecular insights underlying the activation of STING is important to realize the different angles that need to be considered when designing new STING-binding molecules as therapeutic drugs since STING acts as a versatile platform for immune modulators. This review analyzes the different determinants of STING regulation from the structural, molecular, and cell biology points of view.

Role of stimulator of interferon genes (STING) in the enteric nervous system in health and disease

Stimulator of Interferon Genes (STING) is a crucial protein that controls the immune system's reaction to bacterial and viral infections. As a pattern-recognition receptor, STING is found in immune cells as well as in neurons and glia in the enteric nervous system (ENS). Recent studies have linked STING to the pathogenesis of several neurological disorders like multiple sclerosis (MS), Alzheimer's disease (AD), and gastrointestinal disorders, including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), which are characterized by chronic inflammation and dysregulation of the enteric nervous system (ENS) in the digestive tract. STING plays a crucial role in the pathway that induces the production of interferon in response to viral infection in the central nervous system (CNS). A new study by Dharshika et al. in the current issue of Neurogastroenterology and Motility has demonstrated distinct roles for STING in enteric neurons and glia, namely activation of STING leads to IFN-β production in enteric neurons but not in glia and reducing STING activation in enteric glia does not modulate the severity of Dextran sulfate sodium (DSS) colitis or subsequent loss of enteric neurons. Rather, the role of STING in enteric glia is related to enhancing autophagy. STING can influence gastrointestinal motility and barrier function and therefore be involved in the pathophysiology of IBS and IBD. This mini review highlights the current knowledge of STING in the pathophysiology of CNS and gastrointestinal diseases as well as these newly uncovered roles STING in enteric neurons and glia.

Dendritic cell subsets in cancer immunity and tumor antigen sensing

Dendritic cells (DCs) exhibit a specialized antigen-presenting function and play crucial roles in both innate and adaptive immune responses. Due to their ability to cross-present tumor cell-associated antigens to naïve T cells, DCs are instrumental in the generation of specific T-cell-mediated antitumor effector responses in the control of tumor growth and tumor cell dissemination. Within an immunosuppressive tumor microenvironment, DC antitumor functions can, however, be severely impaired. In this review, we focus on the mechanisms of DC capture and activation by tumor cell antigens and the role of the tumor microenvironment in shaping DC functions, taking advantage of recent studies showing the phenotype acquisition, transcriptional state and functional programs revealed by scRNA-seq analysis. The therapeutic potential of DC-mediated tumor antigen sensing in priming antitumor immunity is also discussed.

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

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

Intrinsic STING Switches off Pathogenetic Programs of Th1 Cells to Inhibit Colitis

BACKGROUND & AIMS

T helper 1 (Th1) effector cells are implicated in inflammatory bowel disease. The stimulator of interferon genes (STING), an intracellular DNA sensor, has been shown to regulate infection and various cancers. However, whether and how intrinsic STING signaling in Th1 cells regulates colitis is still unknown.

METHODS

Dextran sodium sulfate-induced colitis and wild-type/STING-deficient CD4+T cell adoptive transfer models were used to analyze the role of STING in regulating colitis. The effect of STING on Th1 cells was determined by flow cytometry, RNA sequencing, metabolic assays, and mitochondrial functions. 16S ribosomal RNA sequencing and germ-free mice were used to investigate whether the microbiota were involved. The in vivo effect of STING agonist in murine colitis was determined. The expression and role of STING in human T cells were also determined.

RESULTS

Activation of STING transformed proinflammatory IFNγ+Th1 cells into IL-10+IFNγ+Th1 cells, which were dramatically less pathogenic in inducing colitis. STING promoted Th1 interleukin (IL)-10 production by inducing STAT3 translocation into nuclear and mitochondria, which promoted Blimp1 expression and mitochondrial oxidation, respectively. Blockade of glucose or glutamine-derived oxidation, but not lipid-derived oxidation, suppressed STING induction of IL-10. Gut microbiota were changed in STING-/- mice, but the altered microbiota did not mediate STING effects on intestinal CD4+T cell production of IL-10. Translationally, STING agonists suppressed both acute and chronic colitis. Intestinal STING+ CD4+T cells were increased in inflammatory bowel disease patients, and STING agonists upregulated IL-10 production in human CD4+T cells.

CONCLUSIONS

These findings establish a crucial role of T cell-intrinsic STING in switching off the pathogenic programs of Th1 cells in intestinal inflammation.

The Role of cGAS-STING in Age-Related Diseases from Mechanisms to Therapies

With aging, the incidence of age-related diseases increases. Hence, age-related diseases are inevitable. However, the mechanisms by which aging leads to the onset and progression of age-related diseases remain unclear. It has been reported that inflammation is closely associated with age-related diseases and that the cGAS-STING signaling pathway, which can sense the aberrant presence of cytosolic DNA during aging and induce an inflammatory response, is an important mediator of inflammation in age-related diseases. With a better understanding of the structure and molecular biology of the cGAS-STING signaling axis, numerous selective inhibitors and agonists targeting the cGAS-STING pathway in human age-related diseases have been developed to modulate inflammatory responses. Here, we provide a narrative review of the activity of the cGAS- STING pathway in age-related diseases and discuss its general mechanisms in the onset and progression of age-related diseases. In addition, we outline treatments targeting the cGAS-STING pathway, which may constitute a potential therapeutic alternative for age-related diseases.

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.

STING/NF-κB/IL-6-Mediated Inflammation in Microglia Contributes to Spared Nerve Injury (SNI)-Induced Pain Initiation

Innate immune response acts as the first line of host defense against damage and is initiated following the recognition of pathogen-associated molecular patterns (PAMPs). For double-stranded DNA (dsDNA) sensing, interferon gene stimulator (STING) was discovered to be an integral sensor and could mediate the immune and inflammatory response. Selective STING antagonist C-176 was administered and pain behaviors were assessed following spared nerve injury (SNI)-induced neuropathic pain. The level of serum dsDNA following neuropathic pain was assessed using Elisa analysis. STING signaling pathway, microglia activation, and proinflammatory cytokines were assessed by qPCR, western blots, Elisa, and immunofluorescence staining. STING agonist DMXAA was introduced into BV-2 cells to assess the inflammatory response in microglial cells. dsDNA was significantly increased following SNI and STING/TANK-binding kinase 1 (TBK1)/nuclear factor-kappa B (NF-κB) pathway was activated in vivo and vitro. Early but not the late intrathecal injection of C-176 attenuated SNI-induced pain hypersensitivity, microglia activation, proinflammatory factors, and phosphorylated JAK2/STAT3 in the spinal cord dorsal horn, and the analgesic effect of C-176 was greatly abolished by recombinant IL-6 following SNI. We provided evidence clarifying dsDNA mediated activation of microglia STING signaling pathway, after which promoting expression of proinflammatory cytokines that are required for hyperalgesia initiation in the spinal cord dorsal horn of SNI model. Further analysis showed that microglial STING/TBK1/NF-κB may contribute to pain initiation via IL-6 signaling. Pharmacological blockade of STING may be a promising target in the treatment of initiation of neuropathic pain.

Low-dose ganciclovir ameliorates dextran sulfate sodium-induced ulcerative colitis through inhibiting macrophage STING activation in mice

Ganciclovir (GCV) is a prodrug nucleoside analogue and is clinically used as antiviral drug for the treatment of cytomegalovirus (CMV) and other infections. Based on the potential anti-inflammatory activity of GCV, this study aimed to investigate the therapeutic effects of ganciclovir on dextran sulfate sodium (DSS)-induced ulcerative colitis (UC), which may involve cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathways. Our results demonstrated that incubation of GCV (50 μM) inhibited cGAS-STING pathway in macrophage RAW264.7 cells. Then, it was found that intestinal cGAS-STING pathways were upregulated in UC patients, Crohn's disease colitis (CD) patients, and DSS-induced colitis mice. Intraperitoneal injection of low-dose GCV (10 mg/kg/day) attenuated DSS-induced colitis and abdominal pain in mice. GCV treatment significantly inhibited the upregulation of cGAS-STING pathway in DSS-induced colitis mice. Moreover, DSS-induced colitis and gut dysbiosis was markedly attenuated in STING deficient mice compared with that of wild-type (WT) mice. Finally, there was lacking therapeutic effect of GCV on DSS-induced colitis in STING deficient mice. Together, our results indicated that low-dose GCV ameliorated DSS-induced UC in mice, possibly through inhibiting STING signaling in colonic macrophages, indicating that GCV may be useful for the treatment of UC.

Clinical significance of STING expression and methylation in lung adenocarcinoma based on bioinformatics analysis

The role of stimulator of interferon genes [STING, also known as transmembrane protein 173 (TMEM173)] in various human cancers has begun to emerge. However, the clinical value of STING in lung adenocarcinoma (LUAD) remains elusive. This study aims to elucidate the clinical significance of STING expression and methylation in LUAD. Here, through analyzing data from public resources, we found that both the mRNA and protein expression of STING were reduced in lung cancer. Moreover, lower expression of STING was associated with a worse prognosis in LUAD, but not lung squamous cell carcinoma (LUSC). Of note, higher methylation of STING was found in LUAD and had the potential to distinguish LUAD tissues from adjacent non-tumor lung tissues and correlated with unfavorable outcomes. Furthermore, the methylation of STING could serve as an independent prognostic indicator for both the overall survival (OS) and disease-free survival (DFS) of LUAD patients. Additionally, the constructed nomogram exhibited a favorable predictive accuracy in predicting the probability of 1- and 2-year OS. Our findings suggest that the mRNA expression, and especially the DNA methylation of STING, have the potential to be prognostic indicators for LUAD patients.

Context-dependent functions of pattern recognition receptors in cancer

The immune system plays a critical role in shaping all facets of cancer, from the early initiation stage through to metastatic disease and resistance to therapy. Our understanding of the importance of the adaptive arm of the immune system in antitumour immunity has led to the implementation of immunotherapy with immune checkpoint inhibitors in numerous cancers, albeit with differing efficacy. By contrast, the clinical utility of innate immunity in cancer has not been exploited, despite dysregulated innate immunity being a feature of at least one-third of all cancers associated with tumour-promoting chronic inflammation. The past two decades have seen innate immune pattern recognition receptors (PRRs) emerge as critical regulators of the immune response to microbial infection and host tissue damage. More recently, it has become apparent that in many cancer types, PRRs play a central role in modulating a vast array of tumour-inhibiting and tumour-promoting cellular responses both in immune cells within the tumour microenvironment and directly in cancer cells. Herein, we provide a comprehensive overview of the fast-evolving field of PRRs in cancer, and discuss the potential to target PRRs for drug development and biomarker discovery in a wide range of oncology settings.

cGAS-STING signaling encourages immune cell overcoming of fibroblast barricades in pancreatic cancer

Immune checkpoint blockade (ICB) treatment improves the prognosis of several types of solid tumors, however, responsiveness to ICB therapy remains low in pancreatic ductal adenocarcinoma (PDACs), which has a rich tumor microenvironment (TME). The TME is composed of various stromal cells, including cancer-associated fibroblasts (CAFs), which contribute to the establishment of an immunosuppressive microenvironment. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is an innate immune pathway that results in the upregulation of immune cell recruiting-cytokines and anti-tumor efficacy. In this study, we aimed to investigate the impact of cGAS-STING expression and the presence of CAFs upon immune cell infiltration in PDACs. cGAS and STING co-expressing PDAC cases showed favorable survival, with many cytotoxic CD8 + T cell infiltrations from the stromal component adjacent to the cancer cells toward cancer cells, but not in cGAS-STING signaling defected PDAC cases. The signatures of tumor-restrain CAFs were expressed in tumors with cGAS-STING signaling. Finally, transwell co-culture experiments demonstrated that immune cell infiltration was impeded by the presence of CAFs, but not by activation of cGAS-STING signaling. In conclusion, pro-infiltration signals, such as cGAS-STING, and characterization of CAFs are crucial in defeating CAF barricades and encouraging immune cell infiltration in PDACs.

Genetic variants involved in the cGAS-STING pathway predict outcome in patients with metastatic colorectal cancer: Data from FIRE-3 and TRIBE trials

BACKGROUND

The activation of stimulator of interferon genes (STING) was reported to enhance cetuximab-mediated natural killer cell activation and dendritic cell maturation. Polymorphisms in genes in the cyclic GMP-AMP synthase (cGAS)-STING pathway may affect innate immune response. Therefore, we hypothesised that genetic variants in the cGAS-STING pathway may predict the efficacy of cetuximab-based treatment in patients with metastatic colorectal cancer.

METHODS

Genomic DNA from blood samples of patients enrolled in FIRE-3 (cetuximab arm, n = 129; bevacizumab arm, n = 107) and TRIBE (bevacizumab arm, n = 215) was genotyped using the OncoArray-500K bead chip panel. Seven selected single nucleotide polymorphisms in 3 genes (cGAS, STING and interferon B1 (IFNB1)) were analysed for the association with overall survival and progression-free survival.

RESULTS

In the cetuximab cohort, patients with STING rs1131769 any T allele showed significantly shorter overall survival (36.3 versus 56.1 months) than carriers of C/C in both univariate [hazard ratio (HR) = 2.08; 95% confidence interval (CI): 1.06-4.07; P = 0.03] and multivariate (HR = 2.98; 95% CI: 1.35-6.6; P = 0.0085) analyses; patients carrying IFNB1 rs1051922 G/A and A/A genotype showed a significantly shorter progression-free survival than carriers of G/G allele in both univariate (G/A versus G/G, 10.2 versus 14.1 months, HR = 1.84; 95% CI 1.23-2.76; A/A versus G/G, 10.7 versus 14.1 months, HR = 2.19; 95% CI 0.97-4.96; P = 0.0077) and multivariate analyses (G/A versus G/G, HR = 2; 95% CI 1.22-3.3; A/A versus G/G, HR = 2.19, 95% CI 0.92-5.26, P = 0.02). These associations were not observed in the bevacizumab arm of FIRE-3 or TRIBE.

CONCLUSION

These results suggest for the first time that germline polymorphisms in STING and IFNB1 genes may predict the outcomes of cetuximab-based treatment in patients with metastatic colorectal cancer.

STING-mediated Syk Signaling Attenuates Tumorigenesis of Colitis‑associated Colorectal Cancer Through Enhancing Intestinal Epithelium Pyroptosis

BACKGROUND

Stimulator of interferon genes (STING) has essential functions in the immune responses and can induce cancer cell apoptosis. However, it is not completely clear how STING plays a role in colitis-associated colorectal cancer (CAC) and whether it can trigger pyroptosis during the tumorigenesis of CAC.

METHODS

To investigate the role of STING-modulated pyroptosis in the development of CAC, STING knockout and Wild type mice were challenged with azoxymethane (AOM) and dextran sodium sulfate (DSS) to establish a murine CAC model. STING pharmacological agonist was used to further study the functions of STING signaling in the tumorigenesis. Moreover, STING endogenous ligand was employed to verify the effects of STING in human colon cancer cells.

RESULTS

STING deficiency mice were more susceptible to CAC by reducing pyroptosis of tumor cells, whereas overactivation of STING with the agonist suppressed tumorigenesis of CAC. STING also managed CAC development by modulating tumor cells proliferation, adhesion, and invasion, as well as inflammatory response. The ex vivo studies indicated that STING could induce pyroptosis via spleen tyrosine kinase (Syk), and Syk knockdown weakened such pyroptotic tumor cells death. In addition, the visible physical interaction between STING and Syk was observed in colorectal tumor samples of CAC patients.

CONCLUSIONS

STING-mediated Syk signaling may regulate the tumorigenesis of CAC by modulating pyroptosis of tumor cells, and modulation of STING/Syk serves as a novel therapeutic strategy for CAC therapy.

STING Agonists/Antagonists: Their Potential as Therapeutics and Future Developments

The cGAS STING pathway has received much attention in recent years, and it has been recognized as an important component of the innate immune response. Since the discovery of STING and that of cGAS, many observations based on preclinical models suggest that the faulty regulation of this pathway is involved in many type I IFN autoinflammatory disorders. Evidence has been accumulating that cGAS/STING might play an important role in pathologies beyond classical immune diseases, as in, for example, cardiac failure. Human genetic mutations that result in the activation of STING or that affect the activity of cGAS have been demonstrated as the drivers of rare interferonopathies affecting young children and young adults. Nevertheless, no data is available in the clinics demonstrating the therapeutic benefit in modulating the cGAS/STING pathway. This is due to the lack of STING/cGAS-specific low molecular weight modulators that would be qualified for clinical exploration. The early hopes to learn from STING agonists, which have reached the clinics in recent years for selected oncology indications, have not yet materialized since the initial trials are progressing very slowly. In addition, transforming STING agonists into potent selective antagonists has turned out to be more challenging than expected. Nevertheless, there has been progress in identifying novel low molecular weight compounds, in some cases with unexpected mode of action, that might soon move to clinical trials. This study gives an overview of some of the potential indications that might profit from modulation of the cGAS/STING pathway and a short overview of the efforts in identifying STING modulators (agonists and antagonists) suitable for clinical research and describing their potential as a "drug".

cGAS/STING cross-talks with cell cycle and potentiates cancer immunotherapy

The correct duplication and transfer of genetic material to daughter cells is the major event of cell division. Dysfunction of DNA replication or chromosome segregation presents challenges in cancer initiation and development as well as opportunities for cancer treatment. Cyclic GMP-AMP synthase (cGAS) of the innate immune system detects cytoplasmic DNA and mediates downstream immune responses through the molecule stimulator of interferon genes (STING). However, how cytosolic DNA sensor cGAS participates in guaranteeing accurate cell division and preventing tumorigenesis is still unclear. Recent evidence indicates malfunction of cGAS/STING pathway in cancer progression. Cell cycle-targeted therapy synergizes with immunotherapy via cGAS/STING activation, leading to promising therapeutic benefit. Here, we review the interactions between cell cycle regulation and cGAS/STING signaling, thus enabling us to understand the role of cGAS/STING in cancer initiation, development, and treatment.

Sensitizing immune unresponsive colorectal cancers to immune checkpoint inhibitors through MAVS overexpression

BACKGROUND

The majority of colorectal carcinomas (CRCs) are insensitive to programmed death protein-1/programmed death-ligand 1 (anti-PD-1/PD-L1) immune checkpoint inhibitor (ICI) antibodies. While there are many causes for ICI insensitivity, recent studies suggest that suppression of innate immune gene expression in tumor cells could be a root cause of this insensitivity and an important factor in the evolution of tumor immunosuppression.

METHODS

We first assessed the reduction of mitochondrial antiviral signaling gene (MAVS) and related RIG-I pathway gene expression in several patient RNA expression datasets. We then engineered MAVS expressing tumor cells and tested their ability to elicit innate and adaptive anti-tumor immunity using both in vitro and in vivo approaches, which we then confirmed using MAVS expressing viral vectors. Finally, we observed that MAVS stimulated PD-L1 expression in multiple cell types and then assessed the combination of PD-L1 ICI antibodies with MAVS tumor expression in vivo.

RESULTS

MAVS was significantly downregulated in CRCs, but its re-expression could stimulate broad cellular interferon-related responses, in both murine and patient-derived CRCs. In vivo, local MAVS expression elicited significant anti-tumor responses in both immune-sensitive and insensitive CRC models, through the stimulation of an interferon responsive axis that provoked tumor antigen-specific adaptive immunity. Critically, we found that tumor-intrinsic MAVS expression triggered systemic adaptive immune responses that enabled abscopal CD8 +T cell cytotoxicity against distant CRCs. As MAVS also induced PD-L1 expression, we further found synergistic anti-tumor responses in combination with anti-PD-L1 ICIs.

CONCLUSION

These data demonstrate that intratumoral MAVS expression results in local and systemic tumor antigen-specific T cell responses, which could be combined with PD-L1 ICI to permit effective anti-tumor immunotherapy in ICI resistant cancers.

Innate Lymphoid Cells and Intestinal Inflammatory Disorders

Innate lymphoid cells (ILCs) are a population of lymphoid cells that do not express T cell or B cell antigen-specific receptors. They are largely tissue-resident and enriched at mucosal sites to play a protective role against pathogens. ILCs mimic the functions of CD4 T helper (Th) subsets. Type 1 innate lymphoid cells (ILC1s) are defined by the expression of signature cytokine IFN-γ and the master transcription factor T-bet, involving in the type 1 immune response; ILC2s are characterized by the expression of signature cytokine IL-5/IL-13 and the master transcription factor GATA3, participating in the type 2 immune response; ILC3s are RORγt-expressing cells and are capable of producing IL-22 and IL-17 to maintain intestinal homeostasis. The discovery and investigation of ILCs over the past decades extends our knowledge beyond classical adaptive and innate immunology. In this review, we will focus on the roles of ILCs in intestinal inflammation and related disorders.

PARP mediated DNA damage response, genomic stability and immune responses

Poly (ADP-ribose) polymerase (PARP) enzymes, especially PARP1, play important roles in the DNA damage response and in the maintenance of genome stability, which makes PARPis a classic synthetic lethal therapy for BRCA-deficient tumors. Conventional mechanisms suggest that PARPis exert their effects via catalytic inhibition and PARP-DNA trapping. Recently, PARP1 has been found to play a role in the immune modulation of tumors. The blockade of PARP1 is able to induce innate immunity through a series of molecular mechanisms, thus allowing the prediction of the feasibility of PARPis combined with immune agents in the treatment of tumors. PARPis combined with immunomodulators may have a stronger tumor suppressive effect on inhibiting tumor growth and blocking immune escape. This article is protected by copyright. All rights reserved.

cGAS-STING signaling pathway in gastrointestinal inflammatory disease and cancers

Cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a key DNA-sensing machinery in innate immunity. Activation of cGAS-STING signaling pathway mediates the production of interferons and proinflammatory cytokines. Although cGAS-STING signaling pathway shows critical function in the maintenance of gut homeostasis, overactive cGAS-STING signaling pathway leads to gastrointestinal (GI) inflammation. Harnessing the effect and mechanism of the cGAS-STING signaling pathway could be beneficial for the development of novel strategies for the treatment of GI diseases. This review presents recent advances regarding the role of cGAS-STING signaling pathway in GI inflammatory disease and cancers and describes perspective therapeutic strategies targeting the signaling pathway.

Deficiency of cGAS signaling protects against sepsis-associated encephalopathy

Sepsis is a life-threatening inflammatory syndrome secondary to infection. Thanks to the advances of antibiotics and life-supporting techniques, the mortality of sepsis has been decreasing in recent decades. Nevertheless, sepsis-associated encephalopathy (SAE) is still common in septic patients, which promotes the mortality of septic patients and results in cognitive dysfunction in survivors. Full understanding and effective medicine in the treatment of SAE is currently scant. Here, we revealed a novel role of cGAS signaling in the pathogenesis of SAE. Deficiency of cGas significantly restored cognitive impairment in sepsis mice model. The restoration may attribute to the recovery of neo-neuron decline that associated with the decrease of activated microglia and astrocytes in the hippocampus of cGas-deficient mice. In addition, type I interferon (IFN) signaling, a downstream of cGAS pathway, was boosted in the hippocampus of septic mice, which was dramatically attenuated by deleting cGas. Moreover, administration of recombinant IFNβ markedly reversed the protection of ablation of cGas in the cognitive impairment in sepsis. Collectively, cGAS promotes the pathogenesis of SAE by up-regulating type I IFN signaling. Blocking cGAS may be a promising strategy for preventing encephalopathy in sepsis.

Extracts of Waste from Poplar Wood Processing Alleviate Experimental Dextran Sulfate-Induced Colitis by Ameliorating Oxidative Stress, Inhibiting the Th1/Th17 Response and Inducing Apoptosis in Inflammatory Lymphocytes

As a fast-growing tree, poplar is widely planted and typically used for wood processing in China. During poplar wood processing, a large amount of poplar sawdust (PS) and poplar leaves (PL) are produced and abandoned. To make full use of poplar resources and clarify the use of poplar as a feed additive, the active ingredients in PS and PL were extracted and isolated, and the anti-inflammatory effects of the extracts on mice with dextran sulfate sodium (DSS)-induced colitis were investigated. In vitro anti-inflammatory experiments showed that the ethyl acetate extract of PS and PL (PSE and PLE, respectively) could significantly inhibit the proliferation of concanavalin A (Con A)-activated lymphocytes. Salicortin, tremulacin and salireposide were identified in both PSE and PLE. Oral administration of PSE and PLE rescued DSS-induced colonic shortening, repaired tissue damage, and decreased the disease activity index (DAI). The antioxidant capacity, including the increased activities of glutathione peroxidase (GSH-Px), total superoxide dismutase (T-SOD and catalase (CAT) and decreased activity of myeloperoxidase (MPO), in the colons of mice with colitis was enhanced through the activation of ERK after treatment with PSE and PLE. The ratio of Th1 to Th17 cells, which can lead to inflammation in the spleen, was significantly decreased by the administration of PSE and PLE, while the phosphorylation of related transcription factors (p65, STAT1, and STAT3) was inhibited. Furthermore, PSE and PLE could induce apoptosis in Con A-activated lymphocytes, which may be associated with the increase in p-TBK1, as the molecular docking results also indicated that salireposide in PSE and PLE could interact with the TBK1 protein. Overall, our study provides a promising feed additive for improving intestinal inflammation in animals and a method for the full utilization of poplar resources.

cGAS restricts colon cancer development by protecting intestinal barrier integrity

The DNA-sensing enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) regulates inflammation and immune defense against pathogens and malignant cells. Although cGAS has been shown to exert antitumor effects in several mouse models harboring transplanted tumor cell lines, its role in tumors arising from endogenous tissues remains unknown. Here, we show that deletion of cGAS in mice exacerbated chemical-induced colitis and colitis-associated colon cancer (CAC). Interestingly, mice lacking cGAS were more susceptible to CAC than those lacking stimulator of interferon genes (STING) or type I interferon receptor under the same conditions. cGAS but not STING is highly expressed in intestinal stem cells. cGAS deficiency led to intestinal stem cell loss and compromised intestinal barrier integrity upon dextran sodium sulfate-induced acute injury. Loss of cGAS exacerbated inflammation, led to activation of STAT3, and accelerated proliferation of intestinal epithelial cells during CAC development. Mice lacking cGAS also accumulated myeloid-derived suppressive cells within the tumor, displayed enhanced Th17 differentiation, but reduced interleukin (IL)-10 production. These results indicate that cGAS plays an important role in controlling CAC development by defending the integrity of the intestinal mucosa.

Dysbiosis exacerbates colitis by promoting ubiquitination and accumulation of the innate immune adaptor STING in myeloid cells

Alterations in the cGAS-STING DNA-sensing pathway affect intestinal homeostasis. We sought to delineate the functional role of STING in intestinal inflammation. Increased STING expression was a feature of intestinal inflammation in mice with colitis and in humans afflicted with inflammatory bowel disease. Mice bearing an allele rendering STING constitutively active exhibited spontaneous colitis and dysbiosis, as well as progressive chronic intestinal inflammation and fibrosis. Bone marrow chimera experiments revealed STING accumulation in intestinal macrophages and monocytes as the initial driver of inflammation. Depletion of Gram-negative bacteria prevented STING accumulation in these cells and alleviated intestinal inflammation. STING accumulation occurred at the protein rather than transcript level, suggesting post-translational stabilization. We found that STING was ubiquitinated in myeloid cells, and this K63-linked ubiquitination could be elicited by bacterial products, including cyclic di-GMP. Our findings suggest a positive feedback loop wherein dysbiosis foments the accumulation of STING in intestinal myeloid cells, driving intestinal inflammation.

Microbial and genetic-based framework identifies drug targets in inflammatory bowel disease

Rationale: With increasing incidence and prevalence of inflammatory bowel disease (IBD), it has become one of the major public health threats, and there is an urgent need to develop new therapeutic agents. Although the pathogenesis of IBD is still unclear, previous research has provided evidence for complex interplays between genetic, immune, microbial, and environmental factors. Here, we constructed a gene-microbiota interaction-based framework to discover IBD biomarkers and therapeutics. Methods: We identified candidate biomarkers for IBD by analyzing the publicly available transcriptomic and microbiome data from IBD cohorts. Animal models of IBD and diarrhea were established. The inflammation-correlated microbial and genetic variants in gene knockout mice were identified by 16S rRNA sequences and PCR array. We performed bioinformatic analysis of microbiome functional prediction and drug repurposing. Our validation experiments with cells and animals confirmed anti-inflammatory properties of a drug candidate. Results: We identified the DNA-sensing enzyme cyclic GMP-AMP synthase (cGAS) as a potential biomarker for IBD in both patients and murine models. cGAS knockout mice were less susceptible to DSS-induced colitis. cGAS-associated gut microbiota and host genetic factors relating to IBD pathogenesis were also identified. Using a computational drug repurposing approach, we predicted 43 candidate drugs with high potency to reverse colitis-associated gene expression and validated that brefeldin-a mitigates inflammatory response in colitis mouse model and colon cancer cell lines. Conclusions: By integrating computational screening, microbiota interference, gene knockout techniques, and in vitro and in vivo validation, we built a framework for predicting biomarkers and host-microbe interaction targets and identifying repurposing drugs for IBD, which may be tested further for clinical application. This approach may also be a tool for repurposing drugs for treating other diseases.

Harnessing Genomic Stress for Antitumor Immunity

Significance: Genomic instability, a hallmark of cancer, renders cancer cells susceptible to genomic stress from both endogenous and exogenous origins, resulting in the increased tendency to accrue DNA damage, chromosomal instability, or aberrant DNA localization. Apart from the cell autonomous tumor-promoting effects, genomic stress in cancer cells could have a profound impact on the tumor microenvironment. Recent Advances: Recently, it is increasingly appreciated that harnessing genomic stress could provide a promising strategy to revive antitumor immunity, and thereby offer new therapeutic opportunities in cancer treatment. Critical Issues: Genomic stress is closely intertwined with antitumor immunity via mechanisms involving the direct crosstalk with DNA damage response components, upregulation of immune-stimulatory/inhibitory ligands, release of damage-associated molecular patterns, increase of neoantigen repertoire, and activation of DNA sensing pathways. A better understanding of these mechanisms will provide molecular basis for exploiting the genomic stress to boost antitumor immunity. Future Directions: Future research should pay attention to the heterogeneity between individual cancers in the genomic instability and the associated immune response, and how to balance the toxicity and benefit by specifying the types, potency, and treatment sequence of genomic stress inducer in therapeutic practice. Antioxid. Redox Signal. 34, 1128-1150.

Robotic retroperitoneal versus transperitoneal inferior vena cava thrombectomy: right-sided cases with level I-II tumor thrombus

OBJECTIVES

To compare the perioperative hemodynamic consequences and oncology outcomes of robotic retroperitoneal versus transperitoneal inferior vena cava(IVC) thrombectomy(IVCT) for right renal cell carcinoma(RCC) with IVC tumor thrombus(IVCTT) that located below the first porta hepatis.

PATIENTS AND METHODS

Between January 2018 and June 2019, 35 patients of right RCC with IVCTT that located below the first porta hepatis underwent robotic retroperitoneal IVCT(16 patients) or transperitoneal IVCT(19 patients). We have described the procedures of transperitoneal IVCT earlier. The main procedure of robotic retroperitoneal IVCT include circumferential dissection of the IVC, sequentially clamping subhepatic IVC, the left renal vein and the caudal IVC with vessel loops, IVCT, IVC repair, radical nephrectomy(RN). The following parameters were compared between the two groups: baselines characteristic, perioperative consequences and hemodynamic changes.

RESULTS

Retroperitoneal and transperitoneal cohorts were comparable in terms of IVC thrombus length(3.2 vs 4.0 cm), IVC block time (18 vs 16 min, p=0.64), postoperative hospital stay (6 vs 6 days, p= 0.67), postoperative complications (0 vs 0), and recurrence or metastasis rate(0 vs 0) for patients with similar baseline characteristic. The retroperitoneal cohort tended to less blood loss (160 vs 240ml,p=0.024), shorter operative time(130 vs 145min,p=0.003), lower central venous pressure(p＜0.05) and smaller diameter of IVC (p＜0.05).

CONCLUSIONS

Robotic retroperitoneal RN and IVCT is feasible for patients of right RCC with IVCTT located below the first porta hepatis and is superior to transperitoneal IVCT in terms of bleeding control and operation time for skilled surgeons.

Nucleic Acid Sensors as Therapeutic Targets for Human Disease

Innate immune sensors that detect nucleic acids are attractive targets for therapeutic intervention because of their diverse roles in many disease processes. In detecting RNA and DNA from either self or non-self, nucleic acid sensors mediate the pathogenesis of many autoimmune and inflammatory conditions. Despite promising pre-clinical data and investigational use in the clinic, relatively few drugs targeting nucleic acid sensors are approved for therapeutic use. Nevertheless, there is growing appreciation for the untapped potential of nucleic acid sensors as therapeutic targets, driven by the need for better therapies for cancer, infectious diseases, and autoimmune disorders. This review highlights the diverse mechanisms by which nucleic acid sensors are activated and exert their biological effects in the context of various disease settings. We discuss current therapeutic strategies utilizing agonists and antagonists targeting nucleic acid sensors to treat infectious disease, cancer, and autoimmune and inflammatory disorders.

cGAS promotes sepsis in radiotherapy of cancer by up-regulating caspase-11 signaling

Radiotherapy is the most common strategy in the treatment of cancer. However, radiation-induced acute complications, in particular sepsis, render patients in a life-threatening status or lead to delay of therapy that largely influences patients' overall responses. The understanding of sepsis in radiotherapy is currently scant and effective medicine is not available by far. Here, with WT mice as control, we challenged mice deficient to cGas, Caspase-11, Gsdmd or Asc with cecal ligation and puncture (CLP, a sepsis model) after a treatment of thorax irradiation. We found that radiation robustly upgraded caspase-11 pathway in irradiated region and consequently deteriorated lung injury and mortality in the sepsis model. cGas knockout markedly attenuated radiation-upgraded caspase-11 and restored sepsis. Deficiency of non-canonical inflammasome, caspase-11 and the downstream GSDMD, rather than an AIM2 inflammasome component, ASC, dramatically protected against radiation-promoted injury and mortality in septic mice. The protection may attribute to the inhibition of caspase-11-mediated pyroptosis in endothelial cells of the lung. Thus, blocking cGAS/caspase-11 signaling would be an adjuvant treatment strategy for preventing sepsis in radiotherapy of cancer.

Immune Regulation of the cGAS-STING Signaling Pathway in the Tumor Microenvironment and Its Clinical Application

As a DNA receptor in the cytoplasm, cyclic GMP-AMP synthase (cGAS) contributes to the recognition of abnormal DNA in the cytoplasm and contributes to the stimulator of interferon genes (STING) signaling pathway. cGAS could mediate the expression of interferon-related genes, inflammatory-related factors, and downstream chemokines, thus initiating the immune response. The STING protein is a key effector downstream of the DNA receptor pathway. It is widely expressed across cell types such as immune cells, tumor cells, and stromal cells and plays a role in signal transduction for cytoplasmic DNA sensing and immunity. STING agonists, as novel agonists, are used in preclinical research and in the treatment of various tumors via clinical trials and have displayed attractive application prospects. Studying the cGAS-STING signaling pathway will deepen our understanding of tumor immunity and provide a basis for the research and development of antitumor drugs.