Phosphorylation and chromatin tethering prevent cGAS activation during mitosis

Secrets of DNA-PKcs beyond DNA repair

The canonical role of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) in repairing DNA double-strand breaks combined with its reported dysregulation in several malignancies has driven the development of DNA-PKcs inhibitors as therapeutics. However, until recently the relationship between DNA-PKcs and tumorigenesis has been primarily investigated with regard to its role in non-homologous end joining (NHEJ) repair. Emerging research has uncovered non-canonical DNA-PKcs functions involved with transcriptional regulation, telomere maintenance, metabolic regulation, and immune signaling all of which may also impinge on tumorigenesis. This review mainly discusses these non-canonical roles of DNA-PKcs in cellular biology and their potential contribution to tumorigenesis, as well as evaluating the implications of targeting DNA-PKcs for cancer therapy.

Decrotonylation of cGAS K254 prompts homologous recombination repair by blocking its DNA binding and releasing PARP1

Cyclic GMP-AMP synthase (cGAS), a cytosolic DNA sensor, also exhibits nuclear genomic localization and is involved in DNA damage signaling. In this study, we investigated the impact of cGAS crotonylation on the regulation of the DNA damage response, particularly homologous recombination repair, following exposure to ionizing radiation (IR). Lysine 254 of cGAS is constitutively crotonylated by the CREB-binding protein; however, IR-induced DNA damage triggers sirtuin 3 (SIRT3)-mediated decrotonylation. Lysine 254 decrotonylation decreased the DNA-binding affinity of cGAS and inhibited its interaction with PARP1, promoting homologous recombination repair. Moreover, SIRT3 suppression led to homologous recombination repair inhibition and markedly sensitized cancer cells to IR and DNA-damaging chemicals, highlighting SIRT3 as a potential target for cancer therapy. Overall, this study revealed the crucial role of cGAS crotonylation in the DNA damage response. Furthermore, we propose that modulating cGAS and SIRT3 activities could be potential strategies for cancer therapy.

The role of cGAS in epithelial dysregulation in inflammatory bowel disease and gastrointestinal malignancies

The gastrointestinal tract is lined by an epithelial monolayer responsible for selective permeability and absorption, as well as protection against harmful luminal contents. Recognition of foreign or aberrant DNA within these epithelial cells is, in part, regulated by pattern recognition receptors such as cyclic GMP-AMP synthase (cGAS). cGAS binds double-stranded DNA from exogenous and endogenous sources, resulting in the activation of stimulator of interferon genes (STING) and a type 1 interferon response. cGAS is also implicated in non-canonical pathways involving the suppression of DNA repair and the upregulation of autophagy via interactions with PARP1 and Beclin-1, respectively. The importance of cGAS activation in the development and progression of inflammatory bowel disease and gastrointestinal cancers has been and continues to be explored. This review delves into the intricacies of the complex role of cGAS in intestinal epithelial inflammation and gastrointestinal malignancies, as well as recent therapeutic advances targeting cGAS pathways.

The balance of STING signaling orchestrates immunity in cancer

Over the past decade, it has become clear that the stimulator of interferon genes (STING) pathway is critical for a variety of immune responses. This endoplasmic reticulum-anchored adaptor protein has regulatory functions in host immunity across a spectrum of conditions, including infectious diseases, autoimmunity, neurobiology and cancer. In this Review, we outline the central importance of STING in immunological processes driven by expression of type I and III interferons, as well as inflammatory cytokines, and we look at therapeutic options for targeting STING. We also examine evidence that challenges the prevailing notion that STING activation is predominantly beneficial in combating cancer. Further exploration is imperative to discern whether STING activation in the tumor microenvironment confers true benefits or has detrimental effects. Research in this field is at a crossroads, as a clearer understanding of the nuanced functions of STING activation in cancer is required for the development of next-generation therapies.

Nuclear rupture induced by capillary constriction forces promotes differential effects on metastatic and normal breast cells

During metastatic dissemination, circulating tumour cells (CTCs) enter capillary beds, where they experience mechanical constriction forces. The transient and persistent effects of these forces on CTCs behaviour remain poorly understood. Here, we developed a high-throughput microfluidic platform mimicking human capillaries to investigate the impact of mechanical constriction forces on malignant and normal breast cell lines. We observed that capillary constrictions induced nuclear envelope rupture in both cancer and normal cells, leading to transient changes in nuclear and cytoplasmic area. Constriction forces transiently activated cGAS/STING and pathways involved in inflammation (NF-κB, STAT and IRF3), especially in the non-malignant cell line. Furthermore, the non-malignant cell line experienced transcriptional changes, particularly downregulation of epithelial markers, while the metastatic cell lines showed minimal alterations. These findings suggest that mechanical constriction forces within capillaries may promote differential effects in malignant and normal cell lines.

Identification of the cytoplasmic DNA-Sensing cGAS-STING pathway-mediated gene signatures and molecular subtypes in prostate cancer

BACKGROUND

Considering the age relevance of prostate cancer (PCa) and the involvement of the cGAS-STING pathway in aging and cancer, we aim to classify PCa into distinct molecular subtypes and identify key genes from the novel perspective of the cGAS-STING pathway. It is of significance to guide personalized intervention of cancer-targeting therapy based on genetic evidence.

METHODS

The 430 patients with PCa from the TCGA database were included. We integrated 29 key genes involved in cGAS-STING pathway and analyzed differentially expressed genes and biochemical recurrence (BCR)-free survival-related genes. The assessments of tumor stemness and heterogeneity and tumor microenvironment (TME) were conducted to reveal potential mechanisms.

RESULTS

PCa patients were classified into two distinct subtypes using AURKB, TREX1, and STAT6, and subtype 1 had a worse prognosis than subtype 2 (HR: 21.19, p < 0.001). The findings were validated in the MSKCC2010 cohort. Among subtype 1 and subtype 2, the top ten mutation genes were MUC5B, DNAH9, SLC5A10, ZNF462, USP31, SIPA1L3, PLEC, HRAS, MYOM1, and ITGB6. Gene set variation analysis revealed a high enrichment of the E2F target in subtype 1, and gene set enrichment analysis showed significant enrichment of base excision repair, cell cycle, and DNA replication in subtype 1. TME evaluation indicated that subtype 1 had a significantly higher level of T cells follicular helper and a lower level of plasma cells than subtype 2.

CONCLUSIONS

The molecular subtypes mediated by the cGAS-STING pathway and the genetic risk score may aid in identifying potentially high-risk PCa patients who may benefit from pharmacologic therapies targeting the cGAS-STING pathway.

Host Factors Modulate Virus-Induced IFN Production via Pattern Recognition Receptors

Innate immunity is the first line of defense in the human body, and it plays an important role in defending against viral infection. Viruses are identified by different pattern-recognition receptors (PRRs) that activate the mitochondrial antiviral signaling protein (MAVS) or transmembrane protein 173 (STING), which trigger multiple signaling cascades that cause nuclear factor-κB (NF-κB) and interferon regulatory factor 3 (IRF3) to produce inflammatory factors and interferons (IFNs). PRRs play a pivotal role as the first step in pathogen induction of interferon production. Interferon elicits antiviral activity by inducing the transcription of hundreds of IFN-stimulated genes (ISGs) via the janus kinase (JAK) - signal transducer and activator of transcription (STAT) pathway. An increasing number of studies have shown that environmental, pathogen and host factors regulate the IFN signaling pathway. Here, we summarize the mechanisms of host factor modulation in IFN production via pattern recognition receptors. These regulatory mechanisms maintain interferon levels in a normal state and clear viruses without inducing autoimmune disease.

Liquid-liquid phase separation in innate immunity

Intrinsic and innate immune responses are essential lines of defense in the body's constant surveillance of pathogens. The discovery of liquid-liquid phase separation (LLPS) as a key regulator of this primal response to infection brings an updated perspective to our understanding of cellular defense mechanisms. Here, we review the emerging multifaceted role of LLPS in diverse aspects of mammalian innate immunity, including DNA and RNA sensing and inflammasome activity. We discuss the intricate regulation of LLPS by post-translational modifications (PTMs), and the subversive tactics used by viruses to antagonize LLPS. This Review, therefore, underscores the significance of LLPS as a regulatory node that offers rapid and plastic control over host immune signaling, representing a promising target for future therapeutic strategies.

The STING agonist IMSA101 enhances chimeric antigen receptor T cell function by inducing IL-18 secretion

As a strategy to improve the therapeutic success of chimeric antigen receptor T cells (CART) directed against solid tumors, we here test the combinatorial use of CART and IMSA101, a newly developed stimulator of interferon genes (STING) agonist. In two syngeneic tumor models, improved overall survival is observed when mice are treated with intratumorally administered IMSA101 in addition to intravenous CART infusion. Transcriptomic analyses of CART isolated from tumors show elevated T cell activation, as well as upregulated cytokine pathway signatures, in particular IL-18, in the combination treatment group. Also, higher levels of IL-18 in serum and tumor are detected with IMSA101 treatment. Consistent with this, the use of IL-18 receptor negative CART impair anti-tumor responses in mice receiving combination treatment. In summary, we find that IMSA101 enhances CART function which is facilitated through STING agonist-induced IL-18 secretion.

Keeping cGAS in check: SPSB3 promotes nuclear cGAS degradation for maintaining immune homeostasis

In a recent publication in Nature, Xu et al.1 discovered a role of CRL5-SPSB3 ubiquitin ligase in promoting ubiquitination and degradation of nuclear cGAS, which prevents aberrant cGAS activation by genomic DNA and contributes to the maintenance of immune homeostasis.

DAMP sensing and sterile inflammation: intracellular, intercellular and inter-organ pathways

Damage-associated molecular patterns (DAMPs) are endogenous molecules that are released from host cells as a result of cell death or damage. The release of DAMPs in tissues is associated with loss of tissue homeostasis. Sensing of DAMPs by innate immune receptors triggers inflammation, which can be beneficial in initiating the processes that restore tissue homeostasis but can also drive inflammatory diseases. In recent years, the sensing of intracellular DAMPs has received extensive attention in the field of sterile inflammation. However, emerging studies have shown that DAMPs that originate from neighbouring cells, and even from distal tissues or organs, also mediate sterile inflammatory responses. This multi-level sensing of DAMPs is crucial for intercellular, trans-tissue and trans-organ communication. Here, we summarize how DAMP-sensing receptors detect DAMPs from intracellular, intercellular or distal tissue and organ sources to mediate sterile inflammation. We also discuss the possibility of targeting DAMPs or their corresponding receptors to treat inflammatory diseases.

New frontiers in the cGAS-STING intracellular DNA-sensing pathway

The cGAS-STING intracellular DNA-sensing pathway has emerged as a key element of innate antiviral immunity and a promising therapeutic target. The existence of an innate immune sensor that can be activated by any double-stranded DNA (dsDNA) of any origin raises fundamental questions about how cGAS is regulated and how it responds to "foreign" DNA while maintaining tolerance to ubiquitous self-DNA. In this review, we summarize recent evidence implicating important roles for cGAS in the detection of foreign and self-DNA. We describe two recent and surprising insights into cGAS-STING biology: that cGAS is tightly tethered to the nucleosome and that the cGAMP product of cGAS is an immunotransmitter acting at a distance to control innate immunity. We consider how these advances influence our understanding of the emerging roles of cGAS in the DNA damage response (DDR), senescence, aging, and cancer biology. Finally, we describe emerging approaches to harness cGAS-STING biology for therapeutic benefit.

The proteomic landscape of genotoxic stress-induced micronuclei

Micronuclei (MN) are induced by various genotoxic stressors and amass nuclear- and cytoplasmic-resident proteins, priming the cell for MN-driven signaling cascades. Here, we measured the proteome of micronuclear, cytoplasmic, and nuclear fractions from human cells exposed to a panel of six genotoxins, comprehensively profiling their MN protein landscape. We find that MN assemble a proteome distinct from both surrounding cytoplasm and parental nuclei, depleted of spliceosome and DNA damage repair components while enriched for a subset of the replisome. We show that the depletion of splicing machinery within transcriptionally active MN contributes to intra-MN DNA damage, a known precursor to chromothripsis. The presence of transcription machinery in MN is stress-dependent, causing a contextual induction of MN DNA damage through spliceosome deficiency. This dataset represents a unique resource detailing the global proteome of MN, guiding mechanistic studies of MN generation and MN-associated outcomes of genotoxic stress.

How enzyme-centered approaches are advancing research on cyclic oligo-nucleotides

Cyclic nucleotides are the most diversified category of second messengers and are found in all organisms modulating diverse pathways. While cAMP and cGMP have been studied over 50 years, cyclic di-nucleotide signaling in eukaryotes emerged only recently with the anti-viral molecule 2´3´cGAMP. Recent breakthrough discoveries have revealed not only the astonishing chemical diversity of cyclic nucleotides but also surprisingly deep-rooted evolutionary origins of cyclic oligo-nucleotide signaling pathways and structural conservation of the proteins involved in their synthesis and signaling. Here we discuss how enzyme-centered approaches have paved the way for the identification of several cyclic nucleotide signals, focusing on the advantages and challenges associated with deciphering the activation mechanisms of such enzymes.

Micronucleus is not a potent inducer of the cGAS/STING pathway

Micronuclei (MN) have been associated with the innate immune response. The abrupt rupture of MN membranes results in the accumulation of cGAS, potentially activating STING and downstream interferon-responsive genes. However, direct evidence connecting MN and cGAS activation has been lacking. We have developed the FuVis2 reporter system, which enables the visualization of the cell nucleus carrying a single sister chromatid fusion and, consequently, MN. Using this FuVis2 reporter equipped with cGAS and STING reporters, we rigorously assessed the potency of cGAS activation by MN in individual living cells. Our findings reveal that cGAS localization to membrane-ruptured MN during interphase is infrequent, with cGAS primarily capturing MN during mitosis and remaining bound to cytosolic chromatin. We found that cGAS accumulation during mitosis neither activates STING in the subsequent interphase nor triggers the interferon response. Gamma-ray irradiation activates STING independently of MN formation and cGAS localization to MN. These results suggest that cGAS accumulation in cytosolic MN is not a robust indicator of its activation and that MN are not the primary trigger of the cGAS/STING pathway.

HERC5-catalyzed ISGylation potentiates cGAS-mediated innate immunity

The cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) is essential to elicit type I interferon cascade response; thus, the activity of cGAS must be strictly regulated to boost the antiviral innate immunity. Here, we report that cGAS is responsible for the DNA-induced ISG15 conjugation system. The E3 HERC5 catalyzes the ISGylation of cytoplasmic cGAS at lysine 21, 187, 219, and 458, whereas Ubl carboxy-terminal hydrolase 18 removes the ISGylation of cGAS. The interaction of cGAS and HERC5 depends on the cGAS C-terminal domain and the RRC1-4 and RRC1-5 domains of HERC5. Mechanically, HERC5-catalyzed ISGylation promotes DNA-induced cGAS oligomerization and enhances cGAS enzymatic activity. Deficiency of ISGylation attenuates the downstream inflammatory gene expression induced by the cGAS-STING axis and the antiviral ability in mouse and human cells. Mice deficient in Isg15 or Herc6 are more vulnerable to herpes simplex virus 1 infection. Collectively, our study shows a positive feedback regulation of the cGAS-mediated innate immune pathway by ISGylation.

The efficient synthesis and purification of 2'3'- cGAMP from Escherichia coli

Agonists of the stimulator of interferon genes (STING) pathway are being explored as potential immunotherapeutics for the treatment of cancer and as vaccine adjuvants for infectious diseases. Although chemical synthesis of 2'3' - cyclic Guanosine Monophosphate-Adenosine Monophosphate (cGAMP) is commercially feasible, the process results in low yields and utilizes organic solvents. To pursue an efficient and environmentally friendly process for the production of cGAMP, we focused on the recombinant production of cGAMP via a whole-cell biocatalysis platform utilizing the murine cyclic Guanosine monophosphate-Adenosine monophosphate synthase (mcGAS). In E. coli BL21(DE3) cells, recombinant expression of mcGAS, a DNA-dependent enzyme, led to the secretion of cGAMP to the supernatants. By evaluating the: (1) media composition, (2) supplementation of divalent cations, (3) temperature of protein expression, and (4) amino acid substitutions pertaining to DNA binding; we showed that the maximum yield of cGAMP in the supernatants was improved by 30% from 146 mg/L to 186 ± 7 mg/mL under optimized conditions. To simplify the downstream processing, we developed and validated a single-step purification process for cGAMP using anion exchange chromatography. The method does not require protein affinity chromatography and it achieved a yield of 60 ± 2 mg/L cGAMP, with <20 EU/mL (<0.3 EU/μg) of endotoxin. Unlike chemical synthesis, our method provides a route for the recombinant production of cGAMP without the need for organic solvents and supports the goal of moving toward shorter, more sustainable, and more environmentally friendly processes.

cGAS: action in the nucleus

As a canonical cytoplasmic DNA sensor, cyclic GMP-AMP synthase (cGAS) plays a key role in innate immunity. In recent years, a growing number of studies have shown that cGAS can also be located in the nucleus and plays new functions such as regulating DNA damage repair, nuclear membrane repair, chromosome fusion, DNA replication, angiogenesis and other non-canonical functions. Meanwhile, the mechanisms underlying the nucleo-cytoplasmic transport and the regulation of cGAS activation have been revealed in recent years. Based on the current understanding of the structure, subcellular localization and canonical functions of cGAS, this review focuses on summarizing the mechanisms underlying nucleo-cytoplasmic transport, activity regulation and non-canonical functions of cGAS in the nucleus. We aim to provide insights into exploring the new functions of cGAS in the nucleus and advance its clinical translation.

The molecular mechanism of dsDNA sensing through the cGAS-STING pathway

Double stranded DNA (dsDNA) in the cytoplasm triggers the cGAS-STING innate immune pathway to defend against pathogenic infections, tissue damage and malignant cells. Extensive structural and functional studies over the last couple of years have enabled the molecular understanding of dsDNA induced activation of the cGAS-STING signaling pathway. This review highlights recent advances in the structural characterization of key molecules in the cGAS-STING signaling axis by focusing on the mechanism of cGAS activation by dsDNA, the regulation of cGAS activity, the mechanism of STING activation by cGAMP, the molecular basis of TBK1 recruitment and activation by STING, the structural basis of IRF3 recruitment by STING, and the mechanism of IRF3 activation upon phosphorylation by TBK1. These comprehensive structural studies provide a detailed picture of the mechanism of the cGAS-STING signaling pathway, establishing a molecular framework for the development of novel therapeutic strategies targeting this pathway.

Phase separation-mediated biomolecular condensates and their relationship to tumor

Phase separation is a cellular phenomenon where macromolecules aggregate or segregate, giving rise to biomolecular condensates resembling "droplets" and forming distinct, membrane-free compartments. This process is pervasive in biological cells, contributing to various essential cellular functions. However, when phase separation goes awry, leading to abnormal molecular aggregation, it can become a driving factor in the development of diseases, including tumor. Recent investigations have unveiled the intricate connection between dysregulated phase separation and tumor pathogenesis, highlighting its potential as a novel therapeutic target. This article provides an overview of recent phase separation research, with a particular emphasis on its role in tumor, its therapeutic implications, and outlines avenues for further exploration in this intriguing field.

Mechanisms of Immune Sensing of DNA Damage

Genomic stability relies on a multifaceted and evolutionarily conserved DNA damage response (DDR). In multicellular organisms, an integral facet of the DDR involves the activation of the immune system to eliminate cells with persistent DNA damage. Recent research has shed light on a complex array of nucleic acid sensors crucial for innate immune activation in response to oncogenic stress-associated DNA damage, a process vital for suppressing tumor formation. Yet, these immune sensing pathways may also be co-opted to foster tolerance of chromosomal instability, thereby driving cancer progression. This review aims to provide an updated overview of how the innate immune system detects and responds to DNA damage. An improved understanding of the regulatory intricacies governing this immune response may uncover new avenues for cancer prevention and therapeutic intervention.

The cGAS-STING pathway: a therapeutic target in diabetes and its complications

Diabetic wound healing (DWH) represents a major complication of diabetes where inflammation is a key impediment to proper healing. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a central mediator of inflammatory responses to cell stress and damage. However, the contribution of cGAS-STING activation to impaired healing in DWH remains understudied. In this review, we examine the evidence that cGAS-STING-driven inflammation is a critical factor underlying defective DWH. We summarize studies revealing upregulation of the cGAS-STING pathway in diabetic wounds and discuss how this exacerbates inflammation and senescence and disrupts cellular metabolism to block healing. Partial pharmaceutical inhibition of cGAS-STING has shown promise in damping inflammation and improving DWH in preclinical models. We highlight key knowledge gaps regarding cGAS-STING in DWH, including its relationships with endoplasmic reticulum stress and metal-ion signaling. Elucidating these mechanisms may unveil new therapeutic targets within the cGAS-STING pathway to improve healing outcomes in DWH. This review synthesizes current understanding of how cGAS-STING activation contributes to DWH pathology and proposes future research directions to exploit modulation of this pathway for therapeutic benefit.

Role of micronucleus-activated cGAS-STING signaling in antitumor immunity

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling is a significant component of the innate immune system and functions as a vital sentinel mechanism to monitor cellular and tissue aberrations in microbial invasion and organ injury. cGAS, a cytosolic DNA sensor, is specialized in recognizing abnormally localized cytoplasmic double-stranded DNA (dsDNA) and catalyzes the formation of a second messenger cyclic-GMP-AMP (cGAMP), which initiates a cascade of type Ⅰ interferon and inflammatory responses mediated by STING. Micronucleus, a byproduct of chromosomal missegregation during anaphase, is also a significant contributor to cytoplasmic dsDNA. These unstable subcellular structures are susceptible to irreversible nuclear envelope rupture, exposing genomic dsDNA to the cytoplasm, which potently recruits cGAS and activates STING-mediated innate immune signaling and its downstream activities, including type Ⅰ interferon and classical nuclear factor-κB (NF-κB) signaling pathways lead to senescence, apoptosis, autophagy activating anti-cancer immunity or directly killing tumor cells. However, sustained STING activation-induced endoplasmic reticulum stress, activated chronic type Ⅰ interferon and nonclassical NF-κB signaling pathways remodel immunosuppressive tumor microenvironment, leading to immune evasion and facilitating tumor metastasis. Therefore, activated cGAS-STING signaling plays a dual role of suppressing or facilitating tumor growth in tumorigenesis and therapy. This review elaborates on research advances in mechanisms of micronucleus inducing activation of cGAS-STING signaling and its implications in tumorigenesis and therapeutic strategies of malignant tumors.

Innate immune responses to RNA: sensing and signaling

Nucleic acids are among the most essential PAMPs (pathogen-associated molecular patterns). Animals have evolved numerous sensors to recognize nucleic acids and trigger immune signaling against pathogen replication, cellular stress and cancer. Many sensor proteins (e.g., cGAS, AIM2, and TLR9) recognize the molecular signature of infection or stress and are responsible for the innate immune response to DNA. Remarkably, recent evidence demonstrates that cGAS-like receptors acquire the ability to sense RNA in some forms of life. Compared with the nucleic-acid sensing by cGAS, innate immune responses to RNA are based on various RNA sensors, including RIG-I, MDA5, ADAR1, TLR3/7/8, OAS1, PKR, NLRP1/6, and ZBP1, via a broad-spectrum signaling axis. Importantly, new advances have brought to light the potential clinical application of targeting these signaling pathways. Here, we highlight the latest discoveries in the field. We also summarize the activation and regulatory mechanisms of RNA-sensing signaling. In addition, we discuss how RNA sensing is tightly controlled in cells and why the disruption of immune homeostasis is linked to disease.

MRE11 liberates cGAS from nucleosome sequestration during tumorigenesis

Oncogene-induced replication stress generates endogenous DNA damage that activates cGAS-STING-mediated signalling and tumour suppression1-3. However, the precise mechanism of cGAS activation by endogenous DNA damage remains enigmatic, particularly given that high-affinity histone acidic patch (AP) binding constitutively inhibits cGAS by sterically hindering its activation by double-stranded DNA (dsDNA)4-10. Here we report that the DNA double-strand break sensor MRE11 suppresses mammary tumorigenesis through a pivotal role in regulating cGAS activation. We demonstrate that binding of the MRE11-RAD50-NBN complex to nucleosome fragments is necessary to displace cGAS from acidic-patch-mediated sequestration, which enables its mobilization and activation by dsDNA. MRE11 is therefore essential for cGAS activation in response to oncogenic stress, cytosolic dsDNA and ionizing radiation. Furthermore, MRE11-dependent cGAS activation promotes ZBP1-RIPK3-MLKL-mediated necroptosis, which is essential to suppress oncogenic proliferation and breast tumorigenesis. Notably, downregulation of ZBP1 in human triple-negative breast cancer is associated with increased genome instability, immune suppression and poor patient prognosis. These findings establish MRE11 as a crucial mediator that links DNA damage and cGAS activation, resulting in tumour suppression through ZBP1-dependent necroptosis.

The entanglement of DNA damage and pattern recognition receptor signaling

Cells are under constant pressure to suppress DNA damage originating from both exogenous and endogenous sources. Cellular responses to DNA damage help to prevent mutagenesis and cell death that arises when DNA damage is either left unrepaired or repaired inaccurately. During the "acute phase" of DNA damage signaling, lesions are recognized, processed, and repaired to restore the primary DNA sequence whilst cell cycle checkpoints delay mitotic progression, cell death and the propagation of errors to daughter cells. Increasingly, there is recognition of a "chronic phase" of DNA damage signaling, exemplified by the secretion of dozens of cytokines days after the inciting damage event. In this review, we focus on the cellular origin of these chronic responses, the molecular pathways that control them and the increasing appreciation for the interconnection between acute and chronic DNA damage responses.

mRNAs encoding self-DNA reactive cGAS enhance the immunogenicity of lipid nanoparticle vaccines

IMPORTANCE

Nucleic acid-based vaccines hold promise in preventing infections and treating cancer. The most common use of this technology is to encode antigenic proteins on mRNAs that are delivered to cells via lipid nanoparticle (LNP) formulations. In this study, we discovered that immunostimulatory proteins can also be encoded on mRNAs in LNPs. We found that an active mutant of the enzyme cGAS, referred to as cGAS∆N, acts as a catalytic adjuvant in LNP-encapsulated mRNA vaccines. The delivery of cGAS∆N mRNA via LNPs in combination with antigen mRNA-LNPs led to durable antigen-specific IFNγ-producing T cells that exceeded the efficiency of antigen-LNPs similar to those currently used in the clinic. This strategy did not compromise B cell responses; rather it induced Th1-biased antibody isotypes. This work unveils new vaccine design strategies using mRNA-encoded catalytic adjuvants that could be ideal for generating CD8+ T cell and B cell responses for immunotherapies.

Nuclear cGAS restricts L1 retrotransposition by promoting TRIM41-mediated ORF2p ubiquitination and degradation

Cyclic GMP-AMP synthase (cGAS), initially identified as a cytosolic DNA sensor, detects DNA fragments to trigger an innate immune response. Recently, accumulating evidence reveals the presence of cGAS within the nucleus. However, the biological functions of nuclear cGAS are not fully understood. Here, we demonstrate that nuclear cGAS represses LINE-1 (L1) retrotransposition to preserve genome integrity in human cells. Mechanistically, the E3 ligase TRIM41 interacts with and ubiquitinates ORF2p to influence its stability, and cGAS enhances the association of ORF2p with TRIM41, thereby promoting TRIM41-mediated ORF2p degradation and the suppression of L1 retrotransposition. In response to DNA damage, cGAS is phosphorylated at serine residues 120 and 305 by CHK2, which promotes cGAS-TRIM41 association, facilitating TRIM41-mediated ORF2p degradation. Moreover, we show that nuclear cGAS mediates the repression of L1 retrotransposition in senescent cells induced by DNA damage agents. We also identify several cancer-associated cGAS mutations that abolish the suppressive effect on L1 retrotransposition by disrupting the CHK2-cGAS-TRIM41-ORF2p regulatory axis. Together, these findings indicate that nuclear cGAS exhibits an inhibitory function in L1 retrotransposition which could provide avenues for future interventions in both aging and tumorigenesis.

The odyssey of cGAS: From cytosol to nucleus

The cyclic GMP-AMP synthase (cGAS) is a widely recognized pattern recognition receptor responsible for detecting pathogenic DNA in the cytosol and inducing the production of type I interferon (IFN) to combat infections. The recently discovered nuclear localization of cGAS has changed the old dogma, illuminated a captivating dimension of innate immunity, and sparked many fundamental questions beyond the field of immunology. This review explores cGAS nuclear localization models, activation mechanisms, and biological significance. This expansion challenges the conventional understanding of cGAS and opens new avenues for scientific exploration, promising insights into cellular surveillance and potentially unveiling new therapeutic targets for immune disorders.

Polyamine metabolism controls B-to-Z DNA transition to orchestrate DNA sensor cGAS activity

Cyclic guanosine monophosphate (GMP)-AMP (cGAMP) synthase (cGAS) is a universal double-stranded DNA (dsDNA) sensor that recognizes foreign and self-DNA in the cytoplasm and initiates innate immune responses and has been implicated in various infectious and non-infectious contexts. cGAS binds to the backbone of dsDNA and generates the second messenger, cGAMP, which activates the stimulator of interferon genes (STING). Here, we show that the endogenous polyamines spermine and spermidine attenuated cGAS activity and innate immune responses. Mechanistically, spermine and spermidine induced the transition of B-form DNA to Z-form DNA (Z-DNA), thereby decreasing its binding affinity with cGAS. Spermidine/spermine N1-acetyltransferase 1 (SAT1), the rate-limiting enzyme in polyamine catabolism that decreases the cellular concentrations of spermine and spermidine, enhanced cGAS activation by inhibiting cellular Z-DNA accumulation; SAT1 deficiency promoted herpes simplex virus 1 (HSV-1) replication in vivo. The results indicate that spermine and spermidine induce dsDNA to adopt the Z-form conformation and that SAT1-mediated polyamine metabolism orchestrates cGAS activity.

2D and 3D multiplexed subcellular profiling of nuclear instability in human cancer

Nuclear atypia, including altered nuclear size, contour, and chromatin organization, is ubiquitous in cancer cells. Atypical primary nuclei and micronuclei can rupture during interphase; however, the frequency, causes, and consequences of nuclear rupture are unknown in most cancers. We demonstrate that nuclear envelope rupture is surprisingly common in many human cancers, particularly glioblastoma. Using highly-multiplexed 2D and super-resolution 3D-imaging of glioblastoma tissues and patient-derived xenografts and cells, we link primary nuclear rupture with reduced lamin A/C and micronuclear rupture with reduced lamin B1. Moreover, ruptured glioblastoma cells activate cGAS-STING-signaling involved in innate immunity. We observe that local patterning of cell states influences tumor spatial organization and is linked to both lamin expression and rupture frequency, with neural-progenitor-cell-like states exhibiting the lowest lamin A/C levels and greatest susceptibility to primary nuclear rupture. Our study reveals that nuclear instability is a core feature of cancer, and links nuclear integrity, cell state, and immune signaling.

Targeting LYPLAL1-mediated cGAS depalmitoylation enhances the response to anti-tumor immunotherapy

Cyclic GMP-AMP synthase (cGAS) binds pathogenic and other cytoplasmic double-stranded DNA (dsDNA) to catalyze the synthesis of cyclic GMP-AMP (cGAMP), which serves as the secondary messenger to activate the STING pathway and innate immune responses. Emerging evidence suggests that activation of the cGAS pathway is crucial for anti-tumor immunity; however, no effective intervention method targeting cGAS is currently available. Here we report that cGAS is palmitoylated by ZDHHC9 at cysteines 404/405, which promotes the dimerization and activation of cGAS. We further identified that lysophospholipase-like 1 (LYPLAL1) depalmitoylates cGAS to compromise its normal function. As such, inhibition of LYPLAL1 significantly enhances cGAS-mediated innate immune response, elevates PD-L1 expression, and enhances anti-tumor response to PD-1 blockade. Our results therefore reveal that targeting LYPLAL1-mediated cGAS depalmitoylation contributes to cGAS activation, providing a potential strategy to augment the efficacy of anti-tumor immunotherapy.

Targeting the loss of cGAS/STING signaling in cancer

The cGAS/STING pathway provides a key host defense mechanism by detecting the accumulation of cytoplasmic double-stranded DNA (dsDNA) and mediating innate and adaptive immune signaling. In addition to detecting pathogen-derived dsDNA, cGAS senses intrinsic dsDNA, such as those associated with defective cell cycle progression and mitophagy that has leaked from the nucleus or mitochondria, and subsequently evokes host immunity to eliminate pathogenic cells. In cancer cells, dysregulation of DNA repair and cell cycle caused at the DNA replication checkpoint and spindle assembly checkpoint results in aberrant cytoplasmic dsDNA accumulation, stimulating anti-tumor immunity. Therefore, the suppression of cGAS/STING signaling is beneficial for survival and frequently observed in cancer cells as a way to evade detection by the immune system, and is likely to be related to immune checkpoint blockade (ICB) resistance. Indeed, the mechanisms of ICB resistance overlap with those acquired in cancers during immunoediting to evade immune surveillance. This review highlights the current understanding of cGAS/STING suppression in cancer cells and discusses how to establish effective strategies to regenerate effective anti-tumor immunity through reactivation of the cGAS/STING pathway.

How Does cGAS Avoid Sensing Self-DNA under Normal Physiological Conditions?

cGAS is a cytosolic DNA sensor that activates innate immune responses by producing the second messenger 2'3'-cGAMP, which activates the adaptor STING. cGAS senses dsDNA in a length-dependent but sequence-independent manner, meaning it cannot discriminate self-DNA from foreign DNA. In normal physiological conditions, cellular DNA is sequestered in the nucleus by a nuclear envelope and in mitochondria by a mitochondrial membrane. When self-DNA leaks into the cytosol during cellular stress or mitosis, the cGAS can be exposed to self-DNA and activated. Recently, many studies have investigated how cGAS keeps inactive and avoids being aberrantly activated by self-DNA. Thus, this narrative review aims to summarize the mechanisms by which cGAS avoids sensing self-DNA under normal physiological conditions.

CBASS to cGAS-STING: The Origins and Mechanisms of Nucleotide Second Messenger Immune Signaling

Host defense against viral pathogens is an essential function for all living organisms. In cell-intrinsic innate immunity, dedicated sensor proteins recognize molecular signatures of infection and communicate to downstream adaptor or effector proteins to activate immune defense. Remarkably, recent evidence demonstrates that much of the core machinery of innate immunity is shared across eukaryotic and prokaryotic domains of life. Here, we review a pioneering example of evolutionary conservation in innate immunity: the animal cGAS-STING (cyclic GMP-AMP synthase-stimulator of interferon genes) signaling pathway and its ancestor in bacteria, CBASS (cyclic nucleotide-based antiphage signaling system) antiphage defense. We discuss the unique mechanism by which animal cGLRs (cGAS-like receptors) and bacterial CD-NTases (cGAS/dinucleotide-cyclase in Vibrio (DncV)-like nucleotidyltransferases) in these pathways link pathogen detection with immune activation using nucleotide second messenger signals. Comparing the biochemical, structural, and mechanistic details of cGAS-STING, cGLR signaling, and CBASS, we highlight emerging questions in the field and examine evolutionary pressures that may have shaped the origins of nucleotide second messenger signaling in antiviral defense.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Lem2 is essential for cardiac development by maintaining nuclear integrity

AIMS

Nuclear envelope integrity is essential for the compartmentalization of the nucleus and cytoplasm. Importantly, mutations in genes encoding nuclear envelope (NE) and associated proteins are the second highest cause of familial dilated cardiomyopathy. One such NE protein that causes cardiomyopathy in humans and affects mouse heart development is Lem2. However, its role in the heart remains poorly understood.

METHODS AND RESULTS

We generated mice in which Lem2 was specifically ablated either in embryonic cardiomyocytes (Lem2 cKO) or in adult cardiomyocytes (Lem2 iCKO) and carried out detailed physiological, tissue, and cellular analyses. High-resolution episcopic microscopy was used for three-dimensional reconstructions and detailed morphological analyses. RNA-sequencing and immunofluorescence identified altered pathways and cellular phenotypes, and cardiomyocytes were isolated to interrogate nuclear integrity in more detail. In addition, echocardiography provided a physiological assessment of Lem2 iCKO adult mice. We found that Lem2 was essential for cardiac development, and hearts from Lem2 cKO mice were morphologically and transcriptionally underdeveloped. Lem2 cKO hearts displayed high levels of DNA damage, nuclear rupture, and apoptosis. Crucially, we found that these defects were driven by muscle contraction as they were ameliorated by inhibiting myosin contraction and L-type calcium channels. Conversely, reducing Lem2 levels to ∼45% in adult cardiomyocytes did not lead to overt cardiac dysfunction up to 18 months of age.

CONCLUSIONS

Our data suggest that Lem2 is critical for integrity at the nascent NE in foetal hearts, and protects the nucleus from the mechanical forces of muscle contraction. In contrast, the adult heart is not detectably affected by partial Lem2 depletion, perhaps owing to a more established NE and increased adaptation to mechanical stress. Taken together, these data provide insights into mechanisms underlying cardiomyopathy in patients with mutations in Lem2 and cardio-laminopathies in general.

Tumor Cells Transmit Drug Resistance via Cisplatin-Induced Extracellular Vesicles

Cisplatin is a first-line clinical agent used for treating solid tumors. Cisplatin damages the DNA of tumor cells and induces the production of high levels of reactive oxygen species to achieve tumor killing. Tumor cells have evolved several ways to tolerate this damage. Extracellular vesicles (EVs) are an important mode of information transfer in tumor cells. EVs can be substantially activated under cisplatin treatment and mediate different responses of tumor cells under cisplatin treatment depending on their different cargoes. However, the mechanism of action of tumor-cell-derived EVs under cisplatin treatment and their potential cargoes are still unclear. This review considers recent advances in cisplatin-induced release of EVs from tumor cells, with the expectation of providing a new understanding of the mechanisms of cisplatin treatment and drug resistance, as well as strategies for the combined use of cisplatin and other drugs.

Role of cGAS-STING signaling pathway in cardiometabolic diseases

Cardiometabolic disease is a common clinical syndrome with exact causal relationship between the aberrant of glucose/lipid metabolism and cardiovascular disfunction, but its pathogenesis is unclear. Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon gene (STING) signaling pathway regulates the activation of innate immunity by sensing intracellular double stranded DNA. Metabolic risk factors drive the activation of cGAS-STING pathway through mitochondrial DNA, nuclear DNA and endoplasmic reticulum stress. In addition, the activation of the cGAS-STING pathway triggers chronic sterile inflammation, excessive activation of autophagy, senescence and apoptosis in related cells of cardiovascular system. These changes induced by cGAS-STING pathway might be implicated in the onset and deterioration of cardiometabolic disease. Therefore, the targeting intervention of cGAS-STING signaling pathway may emerge as a novel treatment for cardiometabolic disease.

IFI16 phase separation via multi-phosphorylation drives innate immune signaling

The interferon inducible protein 16 (IFI16) is a prominent sensor of nuclear pathogenic DNA, initiating innate immune signaling and suppressing viral transcription. However, little is known about mechanisms that initiate IFI16 antiviral functions or its regulation within the host DNA-filled nucleus. Here, we provide in vitro and in vivo evidence to establish that IFI16 undergoes liquid-liquid phase separation (LLPS) nucleated by DNA. IFI16 binding to viral DNA initiates LLPS and induction of cytokines during herpes simplex virus type 1 (HSV-1) infection. Multiple phosphorylation sites within an intrinsically disordered region (IDR) function combinatorially to activate IFI16 LLPS, facilitating filamentation. Regulated by CDK2 and GSK3β, IDR phosphorylation provides a toggle between active and inactive IFI16 and the decoupling of IFI16-mediated cytokine expression from repression of viral transcription. These findings show how IFI16 switch-like phase transitions are achieved with temporal resolution for immune signaling and, more broadly, the multi-layered regulation of nuclear DNA sensors.

HBV confers innate immune evasion through triggering HAT1/acetylation of H4K5/H4K12/miR-181a-5p or KPNA2/cGAS-STING/IFN-I signaling

Viral immune evasion is crucial to the pathogenesis of hepatitis B virus (HBV) infection. However, the role of HBV in the modulation of innate immune evasion is poorly understood. A liver-specific histone acetyltransferase 1 (Hat1) knockout (KO) mouse model and HAT1 KO cell line were established. Immunohistochemistry staining, Western blot analysis, Southern blot analysis, Northern blot analysis, immunofluorescence assays, enzyme-linked immunosorbent assay, reverse transcription-quantitative polymerase chain reaction, and chromatin immunoprecipitation assays were performed in the livers of mouse models, primary human hepatocytes, HepG2-NTCP, and Huh7 and HepG2 cell lines. HBV-elevated HAT1 increased the expression of miR-181a-5p targeting cyclic GMP-AMP synthase (cGAS) messenger RNA 3' untranslated regions through modulating acetylation of H4K5 and H4K12 in vitro and in vivo, leading to the inability of cGAS-stimulator of interferon genes (STING) pathway and type I interferon (IFN-I) signaling. Additionally, HBV-elevated HAT1 promoted the expression of KPNA2 through modulating acetylation of H4K5 and H4K12 in the system, resulting in nuclear translocation of cGAS, HBx was responsible for the events by HAT1, suggesting that HBV-elevated HAT1 controls the cGAS-STING pathway and IFN-I signaling to modulate viral innate immune evasion. HBV confers innate immune evasion through triggering HAT1/acetylation of H4K5/H4K12/miR-181a-5p or KPNA2/cGAS-STING/IFN-I signaling. Our finding provides new insights into the mechanism by which HBV drives viral innate immune evasion.

Harnessing the cooperation between DNA-PK and cGAS in cancer therapies: The cooperation between DNA-PK and cGAS shapes tumour immunogenicity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is central for the initiation of anti-tumoural immune responses. Enormous effort has been made to optimise the design and administration of STING agonists to stimulate tumour immunogenicity. However, in certain contexts the cGAS-STING axis fuels tumourigenesis. Here, we review recent findings on the regulation of cGAS expression and activity. We particularly focus our attention on the DNA-dependent protein kinase (DNA-PK) complex, that recently emerged as an activator of inflammatory responses in tumour cells. We propose that stratification analyses on cGAS and DNA-PK expression/activation status should be carried out to predict treatment efficacy. We herein also provide insights into non-canonical functions borne by cGAS and cGAMP, highlighting how they may influence tumourigenesis. All these parameters should be taken into consideration concertedly to choose strategies aiming to effectively boost tumour immunogenicity.

The proto-oncogene SRC phosphorylates cGAS to inhibit an antitumor immune response

Cyclic GMP-AMP synthase (cGAS) is a DNA sensor and responsible for inducing an antitumor immune response. Recent studies reveal that cGAS is frequently inhibited in cancer, and therapeutic targets to promote antitumor cGAS function remain elusive. SRC is a proto-oncogene tyrosine kinase and is expressed at elevated levels in numerous cancers. Here, we demonstrate that SRC expression in primary and metastatic bladder cancer negatively correlates with innate immune gene expression and immune cell infiltration. We determine that SRC restricts cGAS signaling in human cell lines through SRC small molecule inhibitors, depletion, and overexpression. cGAS and SRC interact in cells and in vitro, while SRC directly inhibits cGAS enzymatic activity and DNA binding in a kinase-dependent manner. SRC phosphorylates cGAS, and inhibition of cGAS Y248 phosphorylation partially reduces SRC inhibition. Collectively, our study demonstrates that cGAS antitumor signaling is hindered by the proto-oncogene SRC and describes how cancer-associated proteins can regulate the innate immune system.

Methionine restriction promotes cGAS activation and chromatin untethering through demethylation to enhance antitumor immunity

Cyclic GMP-AMP synthase (cGAS) is the major sensor for cytosolic DNA and activates type I interferon signaling and plays an essential role in antitumor immunity. However, it remains unclear whether the cGAS-mediated antitumor activity is affected by nutrient status. Here, our study reports that methionine deprivation enhances cGAS activity by blocking its methylation, which is catalyzed by methyltransferase SUV39H1. We further show that methylation enhances the chromatin sequestration of cGAS in a UHRF1-dependent manner. Blocking cGAS methylation enhances cGAS-mediated antitumor immunity and suppresses colorectal tumorigenesis. Clinically, cGAS methylation in human cancers correlates with poor prognosis. Thus, our results indicate that nutrient stress promotes cGAS activation via reversible methylation, and suggest a potential therapeutic strategy for targeting cGAS methylation in cancer treatment.

TRABID inhibition activates cGAS/STING-mediated anti-tumor immunity through mitosis and autophagy dysregulation

Activation of tumor-intrinsic innate immunity has been a major strategy for improving immunotherapy. Previously, we reported an autophagy-promoting function of the deubiquitinating enzyme TRABID. Here, we identify a critical role of TRABID in suppressing anti-tumor immunity. Mechanistically, TRABID is upregulated in mitosis and governs mitotic cell division by removing K29-linked polyubiquitin chain from Aurora B and Survivin, thereby stabilizing the entire chromosomal passenger complex. TRABID inhibition causes micronuclei through a combinatory defect in mitosis and autophagy and protects cGAS from autophagic degradation, thereby activating the cGAS/STING innate immunity pathway. Genetic or pharmacological inhibition of TRABID promotes anti-tumor immune surveillance and sensitizes tumors to anti-PD-1 therapy in preclinical cancer models in male mice. Clinically, TRABID expression in most solid cancer types correlates inversely with an interferon signature and infiltration of anti-tumor immune cells. Our study identifies a suppressive role of tumor-intrinsic TRABID in anti-tumor immunity and highlights TRABID as a promising target for sensitizing solid tumors to immunotherapy.

Vaccinia E5 is a major inhibitor of the DNA sensor cGAS

The DNA sensor cyclic GMP-AMP synthase (cGAS) is critical in host antiviral immunity. Vaccinia virus (VACV) is a large cytoplasmic DNA virus that belongs to the poxvirus family. How vaccinia virus antagonizes the cGAS-mediated cytosolic DNA-sensing pathway is not well understood. In this study, we screened 80 vaccinia genes to identify potential viral inhibitors of the cGAS/Stimulator of interferon gene (STING) pathway. We discovered that vaccinia E5 is a virulence factor and a major inhibitor of cGAS. E5 is responsible for abolishing cGAMP production during vaccinia virus (Western Reserve strain) infection of dendritic cells. E5 localizes to the cytoplasm and nucleus of infected cells. Cytosolic E5 triggers ubiquitination of cGAS and proteasome-dependent degradation via interacting with cGAS. Deleting the E5R gene from the Modified vaccinia virus Ankara (MVA) genome strongly induces type I IFN production by dendritic cells (DCs) and promotes DC maturation, and thereby improves antigen-specific T cell responses.

PRMT1 mediated methylation of cGAS suppresses anti-tumor immunity

Activation of the cGAS/STING innate immunity pathway is essential and effective for anti-tumor immunotherapy. However, it remains largely elusive how tumor-intrinsic cGAS signaling is suppressed to facilitate tumorigenesis by escaping immune surveillance. Here, we report that the protein arginine methyltransferase, PRMT1, methylates cGAS at the conserved Arg133 residue, which prevents cGAS dimerization and suppresses the cGAS/STING signaling in cancer cells. Notably, genetic or pharmaceutical ablation of PRMT1 leads to activation of cGAS/STING-dependent DNA sensing signaling, and robustly elevates the transcription of type I and II interferon response genes. As such, PRMT1 inhibition elevates tumor-infiltrating lymphocytes in a cGAS-dependent manner, and promotes tumoral PD-L1 expression. Thus, combination therapy of PRMT1 inhibitor with anti-PD-1 antibody augments the anti-tumor therapeutic efficacy in vivo. Our study therefore defines the PRMT1/cGAS/PD-L1 regulatory axis as a critical factor in determining immune surveillance efficacy, which serves as a promising therapeutic target for boosting tumor immunity.

RELA tunes innate-like interferon I/III responses in human T cells

In innate immune cells, intracellular sensors such as cGAS-STING stimulate type I/III interferon (IFN) expression, which promotes antiviral defense and immune activation. However, how IFN-I/III expression is controlled in adaptive cells is poorly understood. Here, we identify a transcriptional rheostat orchestrated by RELA that confers human T cells with innate-like abilities to produce IFN-I/III. Despite intact cGAS-STING signaling, IFN-I/III responses are stunted in CD4+ T cells compared with dendritic cells or macrophages. We find that lysine residues in RELA tune the IFN-I/III response at baseline and in response to STING stimulation in CD4+ T cells. This response requires positive feedback driven by cGAS and IRF7 expression. By combining RELA with IRF3 and DNA demethylation, IFN-I/III production in CD4+ T cells reaches levels observed in dendritic cells. IFN-I/III production provides self-protection of CD4+ T cells against HIV infection and enhances the elimination of tumor cells by CAR T cells. Therefore, innate-like functions can be tuned and leveraged in human T cells.

Regulation of cGAS-STING signalling in cancer: Approach for combination therapy

Innate immunity plays an important role not only during infection but also homeostatic role during stress conditions. Activation of the immune system including innate immune response plays a critical role in the initiation and progression of tumorigenesis. The innate immune sensor recognizes pathogen-associated molecular patterns (PAMPs) and activates cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) (cGAS-STING) and induces type-1 immune response during viral and bacterial infection. cGAS-STING is regulated differently in conditions like cellular senescence and DNA damage in normal and tumor cells and is implicated in the progression of tumors from different origins. cGAS binds to cytoplasmic dsDNA and synthesize cyclic GMP-AMP (2'3'-cGAMP), which selectively activates STING and downstream IFN and NF-κB activation. We here reviewed the cGAS-STING signalling pathway and its cross-talk with other pathways to modulate tumorigenesis. Further, the review also focused on emerging studies that targeted the cGAS-STING pathway for developing targeted therapeutics and combinatorial regimens for cancer of different origins.

Mitochondria-localized cGAS suppresses ferroptosis to promote cancer progression

A well-established role of cyclic GMP-AMP synthase (cGAS) is the recognition of cytosolic DNA, which is linked to the activation of host defense programs against pathogens via stimulator of interferon genes (STING)-dependent innate immune response. Recent advance has also revealed that cGAS may be involved in several noninfectious contexts by localizing to subcellular compartments other than the cytosol. However, the subcellular localization and function of cGAS in different biological conditions is unclear; in particular, its role in cancer progression remains poorly understood. Here we show that cGAS is localized to mitochondria and protects hepatocellular carcinoma cells from ferroptosis in vitro and in vivo. cGAS anchors to the outer mitochondrial membrane where it associates with dynamin-related protein 1 (DRP1) to facilitate its oligomerization. In the absence of cGAS or DRP1 oligomerization, mitochondrial ROS accumulation and ferroptosis increase, inhibiting tumor growth. Collectively, this previously unrecognized role for cGAS in orchestrating mitochondrial function and cancer progression suggests that cGAS interactions in mitochondria can serve as potential targets for new cancer interventions.