KAT5 acetylates cGAS to promote innate immune response to DNA virus

Unconventional posttranslational modification in innate immunity

Pattern recognition receptors (PRRs) play a crucial role in innate immunity, and a complex network tightly controls their signaling cascades to maintain immune homeostasis. Within the modification network, posttranslational modifications (PTMs) are at the core of signaling cascades. Conventional PTMs, which include phosphorylation and ubiquitination, have been extensively studied. The regulatory role of unconventional PTMs, involving unanchored ubiquitination, ISGylation, SUMOylation, NEDDylation, methylation, acetylation, palmitoylation, glycosylation, and myristylation, in the modulation of innate immune signaling pathways has been increasingly investigated. This comprehensive review delves into the emerging field of unconventional PTMs and highlights their pivotal role in innate immunity.

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.

Relationship between the cGAS-STING and NF-κB pathways-role in neurotoxicity

Neurotoxicity can cause a range of symptoms and disorders in humans, including neurodegenerative diseases, neurodevelopmental disorders, nerve conduction abnormalities, neuroinflammation, autoimmune disorders, and cognitive deficits. The cyclic guanosine-adenosine synthase (cGAS)-stimulator of interferon genes (STING) pathway and NF-κB pathway are two important signaling pathways involved in the innate immune response. The cGAS-STING pathway is activated by the recognition of intracellular DNA, which triggers the production of type I interferons and pro-inflammatory cytokines, such as tumor necrosis factor, IL-1β, and IL-6. These cytokines play a role in oxidative stress and mitochondrial dysfunction in neurons. The NF-κB pathway is activated by various stimuli, such as bacterial lipopolysaccharide, viral particle components, and neurotoxins. NF-κB activation may lead to the production of pro-inflammatory cytokines, which promote neuroinflammation and cause neuronal damage. A potential interaction exists between the cGAS-STING and NF-κB pathways, and NF-κB activation blocks STING degradation by inhibiting microtubule-mediated STING transport. This review examines the progress of research on the roles of these pathways in neurotoxicity and their interrelationships. Understanding the mechanisms of these pathways will provide valuable therapeutic insights for preventing and controlling neurotoxicity.

The multiple faces of cGAS-STING in antitumor immunity: prospects and challenges

As a key sensor of double-stranded DNA (dsDNA), cyclic GMP-AMP synthase (cGAS) detects cytosolic dsDNA and initiates the synthesis of 2'3' cyclic GMP-AMP (cGAMP) that activates the stimulator of interferon genes (STING). This finally promotes the production of type I interferons (IFN-I) that is crucial for bridging innate and adaptive immunity. Recent evidence show that several antitumor therapies, including radiotherapy (RT), chemotherapy, targeted therapies and immunotherapies, activate the cGAS-STING pathway to provoke the antitumor immunity. In the last decade, the development of STING agonists has been a major focus in both basic research and the pharmaceutical industry. However, up to now, none of STING agonists have been approved for clinical use. Considering the broad expression of STING in whole body and the direct lethal effect of STING agonists on immune cells in the draining lymph node (dLN), research on the optimal way to activate STING in tumor microenvironment (TME) appears to be a promising direction. Moreover, besides enhancing IFN-I signaling, the cGAS-STING pathway also plays roles in senescence, autophagy, apoptosis, mitotic arrest, and DNA repair, contributing to tumor development and metastasis. In this review, we summarize the recent advances on cGAS-STING pathway's response to antitumor therapies and the strategies involving this pathway for tumor treatment.

Substrate and Functional Diversity of Protein Lysine Post-translational Modifications

Lysine post-translational modifications (PTMs) are widespread and versatile protein PTMs that are involved in diverse biological processes by regulating the fundamental functions of histone and non-histone proteins. Dysregulation of lysine PTMs is implicated in many diseases, and targeting lysine PTM regulatory factors, including writers, erasers, and readers, has become an effective strategy for disease therapy. The continuing development of mass spectrometry (MS) technologies coupled with antibody-based affinity enrichment technologies greatly promotes the discovery and decoding of PTMs. The global characterization of lysine PTMs is crucial for deciphering the regulatory networks, molecular functions, and mechanisms of action of lysine PTMs. In this review, we focus on lysine PTMs, and provide a summary of the regulatory enzymes of diverse lysine PTMs and the proteomics advances in lysine PTMs by MS technologies. We also discuss the types and biological functions of lysine PTM crosstalks on histone and non-histone proteins and current druggable targets of lysine PTM regulatory factors for disease therapy.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.

STUB1 is acetylated by KAT5 and alleviates myocardial ischemia-reperfusion injury through LATS2-YAP-β-catenin axis

Myocardial ischemia-reperfusion injury (MIRI) is involved in the pathogenesis of multiple cardiovascular diseases. This study elucidated the biological function of lysine acetyltransferase 5 (KAT5) in cardiomyocyte pyroptosis during MIRI. Oxygen-glucose deprivation/reoxygenation and left anterior descending coronary artery ligation were used to establish MIRI models. Here we show, KAT5 and STIP1 homology and U-box-containing protein 1 (STUB1) were downregulated, while large tumor suppressor kinase 2 (LATS2) was upregulated in MIRI models. KAT5/STUB1 overexpression or LATS2 silencing repressed cardiomyocyte pyroptosis. Mechanistically, KAT5 promoted STUB1 transcription via acetylation modulation, and subsequently caused ubiquitination and degradation of LATS2, which activated YAP/β-catenin pathway. Notably, the inhibitory effect of STUB1 overexpression on cardiomyocyte pyroptosis was abolished by LATS2 overexpression or KAT5 depletion. Our findings suggest that KAT5 overexpression inhibits NLRP3-mediated cardiomyocyte pyroptosis to relieve MIRI through modulation of STUB1/LATS2/YAP/β-catenin axis, providing a potential therapeutic target for MIRI.

Acetylation is required for full activation of the NLRP3 inflammasome

Full activation of the NLRP3 inflammasome needs two sequential signals: a priming signal, followed by a second, assembly signal. Several studies have shown that the two signals trigger post-translational modification (PTM) of NLRP3, affecting activity of the inflammasome, however, the PTMs induced by the second signal are less well characterized. Here, we show that the assembly signal involves acetylation of NLRP3 at lysine 24, which is important for the oligomerization and the actual assembly of NLRP3 without affecting its recruitment to dispersed trans-Golgi network (dTGN). Accordingly, NLRP3 inflammasome activation is impaired in NLRP3-K24R knock-in mice. We identify KAT5 as an acetyltransferase able to acetylate NLRP3. KAT5 deficiency in myeloid cells and pharmacological inhibition of KAT5 enzymatic activity reduce activation of the NLRP3 inflammasome, both in vitro and in vivo. Thus, our study reveals a key mechanism for the oligomerization and full activation of NLRP3 and lays down the proof of principle for therapeutic targeting of the KAT5-NLRP3 axis.

Mitochondrial DNA-triggered innate immune response: mechanisms and diseases

Various cellular stress conditions trigger mitochondrial DNA (mtDNA) release from mitochondria into the cytosol. The released mtDNA is sensed by the cGAS-MITA/STING pathway, resulting in the induced expression of type I interferon and other effector genes. These processes contribute to the innate immune response to viral infection and other stress factors. The deregulation of these processes causes autoimmune diseases, inflammatory metabolic disorders and cancer. Therefore, the cGAS-MITA/STING pathway is a potential target for intervention in infectious, inflammatory and autoimmune diseases as well as cancer. In this review, we focus on the mechanisms underlying the mtDNA-triggered activation of the cGAS-MITA/STING pathway, the effects of the pathway under various physiological and pathological conditions, and advances in the development of drugs that target cGAS and MITA/STING.

Understanding nucleic acid sensing and its therapeutic applications

Nucleic acid sensing is involved in viral infections, immune response-related diseases, and therapeutics. Based on the composition of nucleic acids, nucleic acid sensors are defined as DNA or RNA sensors. Pathogen-associated nucleic acids are recognized by membrane-bound and intracellular receptors, known as pattern recognition receptors (PRRs), which induce innate immune-mediated antiviral responses. PRR activation is tightly regulated to eliminate infections and prevent abnormal or excessive immune responses. Nucleic acid sensing is an essential mechanism in tumor immunotherapy and gene therapies that target cancer and infectious diseases through genetically engineered immune cells or therapeutic nucleic acids. Nucleic acid sensing supports immune cells in priming desirable immune responses during tumor treatment. Recent studies have shown that nucleic acid sensing affects the efficiency of gene therapy by inhibiting translation. Suppression of innate immunity induced by nucleic acid sensing through small-molecule inhibitors, virus-derived proteins, and chemical modifications offers a potential therapeutic strategy. Herein, we review the mechanisms and regulation of nucleic acid sensing, specifically covering recent advances. Furthermore, we summarize and discuss recent research progress regarding the different effects of nucleic acid sensing on therapeutic efficacy. This study provides insights for the application of nucleic acid sensing in therapy.

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.

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.

IL-17 induces non-small cell lung cancer metastasis via GCN5-dependent SOX4 acetylation enhancing MMP9 gene transcription and expression

Interleukin-17 (IL-17), a potent proinflammatory cytokine, can trigger the metastasis of non-small cell lung cancer (NSCLC). However, the underlying mechanism involved in IL-17-induced NSCLC cell metastasis remains unclear. In this study, we found that not only the expression of IL-17, IL-17RA, and/or general control nonrepressed protein 5 (GCN5), SRY-related HMG-BOX gene 4 (SOX4), and matrix metalloproteinase 9 (MMP9) was increased in the NSCLC tissues and in the IL-17-stimulated NSCLC cells, but also IL-17 treatment could enhance NSCLC cell migration and invasion. Further mechanism exploration revealed that IL-17-upregulated GCN5 and SOX4 could bind to the same region (-915 to -712 nt) of downstream MMP9 gene promoter driving its gene transcription. In the process, GCN5 could mediate SOX4 acetylation at lysine 118 (K118, a newly identified site) boosting MMP9 gene expression as well as cell migration and invasion. Moreover, the SOX4 acetylation or MMP9 induction and metastatic nodule number in the lung tissues of the BALB/c nude mice inoculated with the NSCLC cells stably infected by corresponding LV-shGCN5 or LV-shSOX4, LV-shMMP9 plus IL-17 incubation were markedly reduced. Overall, our findings implicate that NSCLC metastasis is closely associated with IL-17-GCN5-SOX4-MMP9 axis.

The role of Mycobacterium tuberculosis acetyltransferase and protein acetylation modifications in tuberculosis

Tuberculosis (TB) is a widespread infectious disease caused by Mycobacterium tuberculosis (M. tb), which has been a significant burden for a long time. Post-translational modifications (PTMs) are essential for protein function in both eukaryotic and prokaryotic cells. This review focuses on the contribution of protein acetylation to the function of M. tb and its infected macrophages. The acetylation of M. tb proteins plays a critical role in virulence, drug resistance, regulation of metabolism, and host anti-TB immune response. Similarly, the PTMs of host proteins induced by M. tb are crucial for the development, treatment, and prevention of diseases. Host protein acetylation induced by M. tb is significant in regulating host immunity against TB, which substantially affects the disease's development. The review summarizes the functions and mechanisms of M. tb acetyltransferase in virulence and drug resistance. It also discusses the role and mechanism of M. tb in regulating host protein acetylation and immune response regulation. Furthermore, the current scenario of isoniazid usage in M. tb therapy treatment is examined. Overall, this review provides valuable information that can serve as a preliminary basis for studying pathogenic research, developing new drugs, exploring in-depth drug resistance mechanisms, and providing precise treatment for TB.

Oncolytic herpes simplex virus armed with a bacterial GBP1 degrader improves antitumor activity

Oncolytic viruses (OVs) encoding various transgenes are being evaluated for cancer immunotherapy. Diverse factors such as cytokines, immune checkpoint inhibitors, tumor-associated antigens, and T cell engagers have been exploited as transgenes. These modifications are primarily aimed to reverse the immunosuppressive tumor microenvironment. By contrast, antiviral restriction factors that inhibit the replication of OVs and result in suboptimal oncolytic activity have received far less attention. Here, we report that guanylate-binding protein 1 (GBP1) is potently induced during HSV-1 infection and restricts HSV-1 replication. Mechanistically, GBP1 remodels cytoskeletal organization to impede nuclear entry of HSV-1 genome. Previous studies have established that IpaH9.8, a bacterial E3 ubiquitin ligase, targets GBPs for proteasomal degradation. We therefore engineered an oncolytic HSV-1 to express IpaH9.8 and found that the modified OV effectively antagonized GBP1, replicated to a higher titer in vitro and showed superior antitumor activity in vivo. Our study features a strategy for improving the replication of OVs via targeting a restriction factor and achieving promising therapeutic efficacy.

Knockdown of KAT5/KIF11 induces autophagy and promotes apoptosis in anaplastic thyroid cancer cells

K (lysine) acetyltransferase (KAT) 5, which is a member of the KAT family of enzymes, has been found to act as a regulatory factor in various types of cancer. However, the role of KAT5 in anaplastic thyroid carcinoma (ATC) and its underlying mechanism is still elusive. The expression levels of KAT5 and kinesin family member 11 (KIF11) in ATC cells were assessed utilizing reverse transcription-quantitative PCR and western blot analyses. The cell proliferative ability was assessed via Cell Counting Kit-8 assay and using 5-ethynyl-2'-deoxyuridine staining. Flow cytometry and western blot analyses were applied for the assessment of cell apoptosis. Cell autophagy was investigated by employing western blot analysis and immunofluorescence staining. In addition, the enrichment of histone H3 lysine 27 acetylation (H3K27ac) and RNA polymerase II (RNA pol II) was analyzed by chromatin immunoprecipitation assay. It was shown that KAT5 expression was markedly increased in ATC cells. KAT5 depletion suppressed the cell proliferative capability but promoted the induction of apoptosis and autophagy. In addition, the autophagy inhibitor 3-methyladenine reversed the effects of KAT5 deficiency on the proliferative and apoptotic activities of 8505C cells. With regard to the mechanism, it was found that KAT5 inhibited the expression of KIF11 by repressing the enrichment of H3K27ac and RNA pol II. Upregulation of KIF11 expression reversed the effects of KAT5 silencing on the proliferative activity, apoptosis and autophagy of 8505C cells. In conclusion, the results indicated that KAT5 induced autophagy and promoted apoptosis of ATC cells by targeting KIF11, which may provide a promising target for the treatment of ATC.

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.

ZYG11B potentiates the antiviral innate immune response by enhancing cGAS-DNA binding and condensation

As a key dsDNA recognition receptor, cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) plays a vital role in innate immune responses. Activated cGAS, by sensing DNA, catalyzes the synthesis of the secondary messenger cyclic GMP-AMP (cGAMP), which subsequently activates downstream signaling to induce production of interferons and inflammatory cytokines. Here, we report Zyg-11 family member B (ZYG11B) as a potent amplifier in cGAS-mediated immune responses. Knockdown of ZYG11B impairs production of cGAMP and subsequent transcription of interferon and inflammatory cytokines. Mechanistically, ZYG11B enhances cGAS-DNA binding affinity, potentiates cGAS-DNA condensation, and stabilizes the cGAS-DNA condensed complex. Moreover, herpes simplex virus 1 (HSV-1) infection induces ZYG11B degradation in a cGAS-unrelated manner. Our findings not only reveal an important role of ZYG11B in the early stage of DNA-induced cGAS activation but also indicate a viral strategy to dampen the innate immune response.

p53 promotes peroxisomal fatty acid β-oxidation to repress purine biosynthesis and mediate tumor suppression

The metabolic pathways through which p53 functions as a potent tumor suppressor are incompletely understood. Here we report that, by associating with the Vitamin D receptor (VDR), p53 induces numerous genes encoding enzymes for peroxisomal fatty acid β-oxidation (FAO). This leads to increased cytosolic acetyl-CoA levels and acetylation of the enzyme 5-Aminoimidazole-4-Carboxamide Ribonucleotide Formyltransferase/IMP Cyclohydrolase (ATIC), which catalyzes the last two steps in the purine biosynthetic pathway. This acetylation step, mediated by lysine acetyltransferase 2B (KAT2B), occurs at ATIC Lys 266, dramatically inhibits ATIC activity, and inversely correlates with colorectal cancer (CRC) tumor growth in vitro and in vivo, and acetylation of ATIC is downregulated in human CRC samples. p53-deficient CRCs with high levels of ATIC is more susceptible to ATIC inhibition. Collectively, these findings link p53 to peroxisomal FAO, purine biosynthesis, and CRC pathogenesis in a manner that is regulated by the levels of ATIC acetylation.

Systematic pan-cancer analysis identifies cGAS as an immunological and prognostic biomarker

Background

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus causes novel coronavirus disease 2019 (COVID-19), which is characterized by pneumonia, cytokine storms, and lymphopenia. Due to immunosuppression, cancer patients may be more susceptible to SARS-CoV-2 and have more serious complications. According to recent research, cyclic GMP-AMP synthase (cGAS) could be a potential SARS-CoV-2 sensor. However, at present, no studies have been conducted on cGAS gene alterations in pan-cancer. This study aimed to discover therapeutic implications for COVID-19-infected tumor patients by performing a comprehensive analysis of cGAS in malignant tumors.

Methods

cGAS expression matrices were obtained from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Cancer Cell Line Encyclopedia (CCLE) databases, which were used to evaluate cGAS expression in various tumors, its prognostic value, and its relationship to the immune microenvironment, microsatellite instability (MSI), immune neoantigens, gene mutations, immune checkpoints, MSI, tumor mutational burden (TMB), mismatch repair (MMR) genes, and DNA methyltransferases (DNMT). We also used the cBioPortal, Human Protein Atlas (HPA), and GeneMANIA databases to explore the types of changes, gene networks and immunofluorescence localization, and protein expression of these genes.

Results

Compared to normal tissues, cGAS was highly expressed in 13 types of cancer (e.g., lung cancer) and lowly expressed in other cancers (e.g., pancreatic cancer). cGAS expression was associated with prognosis in nine cancers, such as renal clear cell carcinoma (P<0.05). Furthermore, deep deletion was the most common type of cGAS genomic mutation. DNMT, immune infiltration levels, TMB, MSI, MMR genes, neoantigens, and immune checkpoints were all correlated with cGAS expression. Moreover, we used the GSE30589 dataset to investigate the post-SARS-CoV infection changes in cGAS expression in vitro. Finally, mithramycin, MI219, AFP464, aminoflavone, kahalide F, AT13387, doxorubicin, and other drugs increased the sensitivity of cGAS expression. According to the evidence presented above, cGAS may become an important target for cancer therapy.

Conclusions

This study discovered that SARS-CoV-2-infected cancer patients might experience changes in their tumor environment as a result of cGAS, making patients with tumors expressing high cGAS more susceptible to COVID-19 and possibly a worsening prognosis. Furthermore, cGAS may be a novel biomarker for diagnosing and treating COVID-19-infected tumor patients.

Current understanding of the cGAS-STING signaling pathway: Structure, regulatory mechanisms, and related diseases

The innate immune system protects the host from external pathogens and internal damage in various ways. The cGAS-STING signaling pathway, comprised of cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), and downstream signaling adaptors, plays an essential role in protective immune defense against microbial DNA and internal damaged-associated DNA and is responsible for various immune-related diseases. After binding with DNA, cytosolic cGAS undergoes conformational change and DNA-linked liquid-liquid phase separation to produce 2'3'-cGAMP for the activation of endoplasmic reticulum (ER)-localized STING. However, further studies revealed that cGAS is predominantly expressed in the nucleus and strictly tethered to chromatin to prevent binding with nuclear DNA, and functions differently from cytosolic-localized cGAS. Detailed delineation of this pathway, including its structure, signaling, and regulatory mechanisms, is of great significance to fully understand the diversity of cGAS-STING activation and signaling and will be of benefit for the treatment of inflammatory diseases and cancer. Here, we review recent progress on the above-mentioned perspectives of the cGAS-STING signaling pathway and discuss new avenues for further study.

Protein acylation: mechanisms, biological functions and therapeutic targets

Metabolic reprogramming is involved in the pathogenesis of not only cancers but also neurodegenerative diseases, cardiovascular diseases, and infectious diseases. With the progress of metabonomics and proteomics, metabolites have been found to affect protein acylations through providing acyl groups or changing the activities of acyltransferases or deacylases. Reciprocally, protein acylation is involved in key cellular processes relevant to physiology and diseases, such as protein stability, protein subcellular localization, enzyme activity, transcriptional activity, protein-protein interactions and protein-DNA interactions. Herein, we summarize the functional diversity and mechanisms of eight kinds of nonhistone protein acylations in the physiological processes and progression of several diseases. We also highlight the recent progress in the development of inhibitors for acyltransferase, deacylase, and acylation reader proteins for their potential applications in drug discovery.

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

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

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

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

Mendelian randomization accounting for complex correlated horizontal pleiotropy while elucidating shared genetic etiology

Mendelian randomization (MR) harnesses genetic variants as instrumental variables (IVs) to study the causal effect of exposure on outcome using summary statistics from genome-wide association studies. Classic MR assumptions are violated when IVs are associated with unmeasured confounders, i.e., when correlated horizontal pleiotropy (CHP) arises. Such confounders could be a shared gene or inter-connected pathways underlying exposure and outcome. We propose MR-CUE (MR with Correlated horizontal pleiotropy Unraveling shared Etiology and confounding), for estimating causal effect while identifying IVs with CHP and accounting for estimation uncertainty. For those IVs, we map their cis-associated genes and enriched pathways to inform shared genetic etiology underlying exposure and outcome. We apply MR-CUE to study the effects of interleukin 6 on multiple traits/diseases and identify several S100 genes involved in shared genetic etiology. We assess the effects of multiple exposures on type 2 diabetes across European and East Asian populations.

The cGAS-STING-mediated NLRP3 inflammasome is involved in the neurotoxicity induced by manganese exposure

Heavy metal pollution has become a global health challenge. Exposure to heavy metals represents a major health risk. Manganese (Mn) is an essential trace element but also an environmental pollutant. Mn exposure can induce neurotoxicity and lead to neurodegenerative disease. Inflammation and Tau hyperphosphorylation are prominent hallmarks of neurodegenerative diseases induced by Mn exposure. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway can induce powerful innate immune defense programmes and has emerged as a key mediator of inflammation. In recent years, Mn²⁺ has been found to be the second activator of the cGAS-STING pathway in addition to double-stranded DNA (dsDNA). NLRP3 activation is upstream of Tau pathology, and NLRP3 activation induces Tau hyperphosphorylation and aggregation. Mn exposure-induced neurotoxicity may be associated with excessive activation of the cGAS-STING signaling pathway, leading to inflammation. The cGAS-STING/NLRP3 axis may be a promising option for revealing the mechanisms of neurotoxicity of Mn exposure in the future.

Post-Translational Modifications of cGAS-STING: A Critical Switch for Immune Regulation

Innate immune mechanisms initiate immune responses via pattern-recognition receptors (PRRs). Cyclic GMP-AMP synthase (cGAS), a member of the PRRs, senses diverse pathogenic or endogenous DNA and activates innate immune signaling pathways, including the expression of stimulator of interferon genes (STING), type I interferon, and other inflammatory cytokines, which, in turn, instructs the adaptive immune response development. This groundbreaking discovery has rapidly advanced research on host defense, cancer biology, and autoimmune disorders. Since cGAS/STING has enormous potential in eliciting an innate immune response, understanding its functional regulation is critical. As the most widespread and efficient regulatory mode of the cGAS-STING pathway, post-translational modifications (PTMs), such as the covalent linkage of functional groups to amino acid chains, are generally considered a regulatory mechanism for protein destruction or renewal. In this review, we discuss cGAS-STING signaling transduction and its mechanism in related diseases and focus on the current different regulatory modalities of PTMs in the control of the cGAS-STING-triggered innate immune and inflammatory responses.

Protein Acetylation Going Viral: Implications in Antiviral Immunity and Viral Infection

During viral infection, both host and viral proteins undergo post-translational modifications (PTMs), including phosphorylation, ubiquitination, methylation, and acetylation, which play critical roles in viral replication, pathogenesis, and host antiviral responses. Protein acetylation is one of the most important PTMs and is catalyzed by a series of acetyltransferases that divert acetyl groups from acetylated molecules to specific amino acid residues of substrates, affecting chromatin structure, transcription, and signal transduction, thereby participating in the cell cycle as well as in metabolic and other cellular processes. Acetylation of host and viral proteins has emerging roles in the processes of virus adsorption, invasion, synthesis, assembly, and release as well as in host antiviral responses. Methods to study protein acetylation have been gradually optimized in recent decades, providing new opportunities to investigate acetylation during viral infection. This review summarizes the classification of protein acetylation and the standard methods used to map this modification, with an emphasis on viral and host protein acetylation during viral infection.

Regulation of cGAS Activity and Downstream Signaling

Cyclic GMP-AMP synthase (cGAS) is a predominant and ubiquitously expressed cytosolic onfirmedDNA sensor that activates innate immune responses by producing a second messenger, cyclic GMP-AMP (cGAMP), and the stimulator of interferon genes (STING). cGAS contains a highly disordered N-terminus, which can sense genomic/chromatin DNA, while the C terminal of cGAS binds dsDNA liberated from various sources, including mitochondria, pathogens, and dead cells. Furthermore, cGAS cellular localization dictates its response to foreign versus self-DNA. Recent evidence has also highlighted the importance of dsDNA-induced post-translational modifications of cGAS in modulating inflammatory responses. This review summarizes and analyzes cGAS activity regulation based on structure, sub-cellular localization, post-translational mechanisms, and Ca²⁺ signaling. We also discussed the role of cGAS activation in different diseases and clinical outcomes.

Mechanisms of phase-separation-mediated cGAS activation revealed by dcFCCS

Cyclic GMP-AMP synthase (cGAS), as a DNA sensor, plays an important role in cGAS-STING pathway, which further induces expression of type I interferon as the innate immune response. Previous studies reported that liquid-liquid phase separation (LLPS) driven by cGAS and long DNA is essential to promote catalytic activity of cGAS to produce a second messenger, cyclic GMP-AMP (cGAMP). However, the molecular mechanism of LLPS promoting cGAS activity is still unclear. Here, we applied dual-color fluorescence cross-correlation spectroscopy (dcFCCS), a highly sensitive and quantitative method, to characterize phase separation driven by cGAS and DNA from miscible individual molecule to micronscale. Thus, we captured nanoscale condensates formed by cGAS at close-to-physiological concentration and quantified their sizes, molecular compositions and binding affinities within condensates. Our results pinpointed that interactions between DNA and cGAS at DNA binding sites A, B, and C and the dimerization of cGAS are the fundamental molecular basis to fully activate cGAS in vitro. Due to weak binding constants of these sites, endogenous cGAS cannot form stable interactions at these sites, leading to no activity in the absence of LLPS. Phase separation of cGAS and DNA enriches cGAS and DNA by 2 to 3 orders of magnitude to facilitate these interactions among cGAS and DNA and to promote cGAS activity as an on/off switch. Our discoveries not only shed lights on the molecular mechanisms of phase-separation-mediated cGAS activation, but also guided us to engineer a cGAS fusion, which can be activated by 15 bp short DNA without LLPS.

Control of innate immunity by the cGAS‐STING pathway

Within the cytoplasm of mammalian cells is a protein called cyclic GMP-AMP synthase (cGAS), which acts to defend against infection and other threats to the host. cGAS operates in this manner through its ability to detect a molecular occurrence that should not exist in healthy cells - the existence of DNA in the cytosol. Upon DNA binding, cGAS synthesizes cyclic GMP-AMP (cGAMP), a cyclic dinucleotide that activates the endoplasmic reticulum-localized protein stimulator of interferon genes (STING). STING-mediated signaling culminates in host defensive responses typified by inflammatory cytokine and interferon expression, and the induction of autophagy. Studies over the past several years have established a consensus in the field of the enzymatic activities of cGAS in vitro, as it relates to DNA-induced production of cGAMP. However, much additional work is needed to understand the regulation of cGAS functions within cells, where multiple sources of DNA can create a problem of self and non-self discrimination. In this review, we provide an overview of how the cGAS-STING pathway mediates innate immune responses during infection and other cellular stresses. We then highlight recent progress in the understanding of the increasingly diverse ways in which this DNA-sensing machinery is regulated inside cells, including how cGAS remains inactive to host-derived DNA under conditions of homeostasis.

Post-Translational Modifications of Proteins in Cytosolic Nucleic Acid Sensing Signaling Pathways

The innate immune response is the first-line host defense against pathogens. Cytosolic nucleic acids, including both DNA and RNA, represent a special type of danger signal to initiate an innate immune response. Activation of cytosolic nucleic acid sensors is tightly controlled in order to achieve the high sensitivity needed to combat infection while simultaneously preventing false activation that leads to pathologic inflammatory diseases. In this review, we focus on post-translational modifications of key cytosolic nucleic acid sensors that can reversibly or irreversibly control these sensor functions. We will describe phosphorylation, ubiquitination, SUMOylation, neddylation, acetylation, methylation, succinylation, glutamylation, amidation, palmitoylation, and oxidation modifications events (including modified residues, modifying enzymes, and modification function). Together, these post-translational regulatory modifications on key cytosolic DNA/RNA sensing pathway members reveal a complicated yet elegantly controlled multilayer regulator network to govern innate immune activation.

Opposing effects of deubiquitinase OTUD3 in innate immunity against RNA and DNA viruses

Retinoic acid-inducible-I (RIG-I), melanoma differentiation-associated gene 5 (MDA5), and cyclic GMP-AMP synthase (cGAS) genes encode essential cytosolic receptors mediating antiviral immunity against viruses. Here, we show that OTUD3 has opposing role in response to RNA and DNA virus infection by removing distinct types of RIG-I/MDA5 and cGAS polyubiquitination. OTUD3 binds to RIG-I and MDA5 and removes K63-linked ubiquitination. This serves to reduce the binding of RIG-I and MDA5 to viral RNA and the downstream adaptor MAVS, leading to the suppression of the RNA virus-triggered innate antiviral responses. Meanwhile, OTUD3 associates with cGAS and targets at Lys279 to deubiquitinate K48-linked ubiquitination, resulting in the enhancement of cGAS protein stability and DNA-binding ability. As a result, Otud3-deficient mice and zebrafish are more resistant to RNA virus infection but are more susceptible to DNA virus infection. These findings demonstrate that OTUD3 limits RNA virus-triggered innate immunity but promotes DNA virus-triggered innate immunity.

MARCH8 attenuates cGAS-mediated innate immune responses through ubiquitylation

Cyclic GMP-AMP synthase (cGAS) binds to microbial and self-DNA in the cytosol and synthesizes cyclic GMP-AMP (cGAMP), which activates stimulator of interferon genes (STING) and downstream mediators to elicit an innate immune response. Regulation of cGAS activity is essential for immune homeostasis. Here, we identified the E3 ubiquitin ligase MARCH8 (also known as MARCHF8, c-MIR, and RNF178) as a negative regulator of cGAS-mediated signaling. The immune response to double-stranded DNA was attenuated by overexpression of MARCH8 and enhanced by knockdown or knockout of MARCH8. MARCH8 interacted with the enzymatically active core of cGAS through its conserved RING-CH domain and catalyzed the lysine-63 (K63)-linked polyubiquitylation of cGAS at Lys⁴¹¹. This polyubiquitylation event inhibited the DNA binding ability of cGAS, impaired cGAMP production, and attenuated the downstream innate immune response. Furthermore, March8-deficient mice were less susceptible than their wild-type counterparts to herpes simplex virus 1 (HSV-1) infection. Together, our findings reveal a mechanism underlying the functional regulation of cGAS and the fine-tuning of the innate immune response.

The Protective Effects of KAT5 Inhibition on Ocular Inflammation by Mediating the PI3K/AKT Pathway in a Murine Model of Allergic Conjunctivitis

Purpose

We aimed to explore the effect of lysine acetyltransferase KAT5 on allergic conjunctivitis (AC).

Methods

The effect of KAT5 on inflammatory response during AC progression was analyzed in the experimental allergic conjunctivitis (EAC) mouse model.

Results

The clinical score, permeability, total IgE, ovalbumin (OVA)-specific IgE, and IgG1/IgG2a were induced in the EAC mice, in which the overexpression of KAT5 could further enhance but KAT5 inhibitor NU9056 reduce the phenotypes. The eosinophilic infiltration was induced in EAC mice, in which the overexpression of KAT5 was able to further promote but NU9056 attenuate the phenotype. The expression of Eotaxin and RANTES and the inflammatory factors were upregulated in EAC mice and KAT5 overexpression increased, but NU9056 decreased the expression in the model. Significantly, the CD11c+ dendritic cells and CD4+ T cells infiltration in the conjunctiva was enhanced in EAC mice, whereas KAT5 overexpression induced but NU9056 suppressed the effect in the model. Mechanically, the phosphorylation of PI3K and Akt and the levels of histone H3 lysine 27 acetylation (H3K27ac) were enhanced in EAC mice, whereas the overexpression of KAT5 promoted and NU9056 repressed the phenotype in the mice. The enrichment of KAT5 and H3K27ac on PI3K promoter was increased in EAC mice, and the overexpression of KAT5 further enhanced the enrichment in the mice. Significantly, we observed similar results in the KAT5 knockout mice as well. Moreover, PI3K/AKT signaling inhibitor LY294002 reversed KAT5 overexpression-mediated phenotypes and inflammatory response after induction AC in vivo.

Conclusions

Therefore we concluded that KAT5 inhibition protected against ocular inflammation by mediating the PI3K/AKT pathway in EAC mouse model.

The Emerging Role of the Serine Incorporator Protein Family in Regulating Viral Infection

Serine incorporator (SERINC) proteins 1–5 (SERINC1-5) are involved in the progression of several diseases. SERINC2-4 are carrier proteins that incorporate the polar amino acid serine into membranes to facilitate the synthesis of phosphatidylserine and sphingolipids. SERINC genes are also differentially expressed in tumors. Abnormal expression of SERINC proteins occurs in human cancers of the breast, lung, colon, liver, and various glands, as well as in mouse testes. SERINC proteins also affect cleft lip and palate and nerve-related diseases, such as seizure Parkinsonism and borderline personality. Moreover, SERINC proteins have garnered significant interest as retroviral restriction factors, spurring efforts to define their function and elucidate the mechanisms through which they operate when associated with viruses. Human SERINC proteins possess antiviral potential against human immunodeficiency virus (HIV), SARS-COV-2, murine leukemia virus (MLV), equine infectious anemia virus (EIAV), and hepatitis B virus (HBV). Furthermore, the crystal structure is known, and the critical residues of SERINC5 that act against HIV have been identified. In this review, we discuss the most prevalent mechanisms by which SERINC3 and SERINC5 antagonize viruses and focus on the potential therapeutic applications of SERINC5/3 against HIV.

PCBP2 maintains antiviral signaling homeostasis by regulating cGAS enzymatic activity via antagonizing its condensation

Cyclic GMP-AMP synthase (cGAS) plays a major role in detecting pathogenic DNA. It produces cyclic dinucleotide cGAMP, which subsequently binds to the adaptor protein STING and further triggers antiviral innate immune responses. However, the molecular mechanisms regulating cGAS enzyme activity remain largely unknown. Here, we characterize the cGAS-interacting protein Poly(rC)-binding protein 2 (PCBP2), which plays an important role in controlling cGAS enzyme activity, thereby mediating appropriate cGAS-STING signaling transduction. We find that PCBP2 overexpression reduces cGAS-STING antiviral signaling, whereas loss of PCBP2 significantly increases cGAS activity. Mechanistically, we show that PCBP2 negatively regulates anti-DNA viral signaling by specifically interacting with cGAS but not other components. Moreover, PCBP2 decreases cGAS enzyme activity by antagonizing cGAS condensation, thus ensuring the appropriate production of cGAMP and balancing cGAS-STING signal transduction. Collectively, our findings provide insight into how the cGAS-mediated antiviral signaling is regulated.

DNA Damage and Activation of cGAS/STING Pathway Induce Tumor Microenvironment Remodeling

DNA damage occurs throughout tumorigenesis and development. The immunogenicity of DNA makes it an immune stimulatory molecule that initiates strong inflammatory responses. The cGAS/STING pathway has been investigated as a critical receptor in both exogenous and endogenous DNA sensing to activate the innate immune response. Growing lines of evidence have indicated that activation of the cGAS/STING pathway is critical in antitumor immunity. Recent studies have demonstrated the outstanding advancement of this pathway in tumor-combined immunotherapy; accordingly, increased studies focus on exploration of STING pathway agonists and analogues. However, current studies propose the potential use of the cGAS/STING pathway in tumor initiation and metastasis. Here, we review the molecular mechanisms and activation of the cGAS/STING pathway, and the relationship between DNA damage and this pathway, particularly highlighting the remodeling of immune contexture in tumor environment (TME) triggered by cascade inflammatory signals. A detailed understanding of TME reprogramming initiated by this pathway may pave the way for the development of new therapeutic strategies and rational clinical application.

A Variety of Nucleic Acid Species Are Sensed by cGAS, Implications for Its Diverse Functions

Cyclic GMP-AMP synthase (cGAS) recognizes double-stranded DNA (dsDNA) derived from invading pathogens and induces an interferon response via activation of the key downstream adaptor protein stimulator of interferon genes (STING). This is the most classic biological function of the cGAS-STING signaling pathway and is critical for preventing pathogenic microorganism invasion. In addition, cGAS can interact with various types of nucleic acids, including cDNA, DNA : RNA hybrids, and circular RNA, to contribute to a diverse set of biological functions. An increasing number of studies have revealed an important relationship between the cGAS-STING signaling pathway and autophagy, cellular senescence, antitumor immunity, inflammation, and autoimmune diseases. This review details the mechanism of action of cGAS as it interacts with different types of nucleic acids, its rich biological functions, and the potential for targeting this pathway to treat various diseases.

Regulation and function of the cGAS-MITA/STING axis in health and disease

The innate immune systems detect pathogens via pattern-recognition receptors including nucleic acid sensors and non-nucleic acid sensors. Cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS, also known as MB21D1) is a cytosolic DNA sensor that recognizes double-stranded DNA (dsDNA) and catalyzes the synthesis of 2',3'-cGAMP. Subsequently, 2',3'-cGAMP binds to the adaptor protein mediator of IRF3 activation (MITA, also known as STING, MPYS, ERIS, and TMEM173) to activate downstream signaling cascades. The cGAS-MITA/STING signaling critically mediates immune responses against DNA viruses, retroviruses, bacteria, and protozoan parasites. In addition, recent discoveries have extended our understanding of the roles of the cGAS-MITA/STING pathway in autoimmune diseases and cancers. Here, we summarize the identification and activation of cGAS and MITA/STING, present the updated functions and regulatory mechanisms of cGAS-MITA/STING signaling and provide a comprehensive understanding of the cGAS-MITA/STING axis in autoimmune diseases and cancers.

The stress granule protein G3BP1 promotes pre-condensation of cGAS to allow rapid responses to DNA

Cyclic GMP-AMP synthase (cGAS) functions as a key sensor for microbial invasion and cellular damage by detecting emerging cytosolic DNA. Here, we report that GTPase-activating protein-(SH3 domain)-binding protein 1 (G3BP1) primes cGAS for its prompt activation by engaging cGAS in a primary liquid-phase condensation state. Using high-resolution microscopy, we show that in resting cells, cGAS exhibits particle-like morphological characteristics, which are markedly weakened when G3BP1 is deleted. Upon DNA challenge, the pre-condensed cGAS undergoes liquid-liquid phase separation (LLPS) more efficiently. Importantly, G3BP1 deficiency or its inhibition dramatically diminishes DNA-induced LLPS and the subsequent activation of cGAS. Interestingly, RNA, previously reported to form condensates with cGAS, does not activate cGAS. Accordingly, we find that DNA - but not RNA - treatment leads to the dissociation of G3BP1 from cGAS. Taken together, our study shows that the primary condensation state of cGAS is critical for its rapid response to DNA.

The Regulatory Network of Cyclic GMP-AMP Synthase-Stimulator of Interferon Genes Pathway in Viral Evasion

Virus infection has been consistently threatening public health. The cyclic GMP-AMP synthase (cGAS)-Stimulator of Interferon Genes (STING) pathway is a critical defender to sense various pathogens and trigger innate immunity of mammalian cells. cGAS recognizes the pathogenic DNA in the cytosol and then synthesizes 2'3'-cyclic GMP-AMP (2'3'cGAMP). As the second messenger, cGAMP activates STING and induces the following cascade to produce type I interferon (IFN-I) to protect against infections. However, viruses have evolved numerous strategies to hinder the cGAS-STING signal transduction, promoting their immune evasion. Here we outline the current status of the viral evasion mechanism underlying the regulation of the cGAS-STING pathway, focusing on how post-transcriptional modifications, viral proteins, and non-coding RNAs involve innate immunity during viral infection, attempting to inspire new targets discovery and uncover potential clinical antiviral treatments.

Cytosolic Self-DNA—A Potential Source of Chronic Inflammation in Aging

Aging is the consequence of a lifelong accumulation of stochastic damage to tissues and cellular components. Advancing age closely associates with elevated markers of innate immunity and low-grade chronic inflammation, probably reflecting steady increasing incidents of cellular and tissue damage over the life course. The DNA sensing cGAS-STING signaling pathway is activated by misplaced cytosolic self-DNA, which then initiates the innate immune responses. Here, we hypothesize that the stochastic release of various forms of DNA from the nucleus and mitochondria, e.g., because of DNA damage, altered nucleus integrity, and mitochondrial damage, can result in chronic activation of inflammatory responses that characterize the aging process. This cytosolic self-DNA-innate immunity axis may perturb tissue homeostasis and function that characterizes human aging and age-associated pathology. Proper techniques and experimental models are available to investigate this axis to develop therapeutic interventions.

Protein lysine acetylation and its role in different human pathologies: a proteomic approach

INTRODUCTION

Lysine acetylation is a reversible post-translational modification (PTM) regulated through the action of specific types of enzymes: lysine acetyltransferases (KATs) and lysine deacetylases (HDACs), in addition to bromodomains, which are a group of conserved domains which identify acetylated lysine residues, several of the players in the process of protein acetylation, including enzymes and bromodomain-containing proteins, have been related to the progression of several diseases. The combination of high-resolution mass spectrometry-based proteomics, and immunoprecipitation to enrich acetylated peptides has contributed in recent years to expand the knowledge about this PTM described initially in histones and nuclear proteins, and is currently reported in more than 5000 human proteins, that are regulated by this PTM.

AREAS COVERED

This review presents an overview of the main participant elements, the scenario in the development of protein lysine acetylation, and its role in different human pathologies.

EXPERT OPINION

Acetylation targets are practically all cellular processes in eukaryotes and prokaryotes organisms. Consequently, this modification has been linked to many pathologies like cancer, viral infection, obesity, diabetes, cardiovascular, and nervous system-associated diseases, to mention a few relevant examples. Accordingly, some intermediate mediators in the acetylation process have been projected as therapeutic targets.

Acetyl-CoA derived from hepatic mitochondrial fatty acid β-oxidation aggravates inflammation by enhancing p65 acetylation

Acetylation coordinates many biological processes to ensure cells respond appropriately to nutrients. However, how acetylation regulates lipid surplus-induced inflammation remains poorly understood. Here, we found that a high-fat diet (HFD) enhanced mitochondrial fatty acid β-oxidation, which enhanced acetyl-CoA levels in the liver of the large yellow croaker. The HFD activated ACLY to govern the "citrate transport" to transfer acetyl-CoA from the mitochondria to the nucleus. Elevated acetyl-CoA activated CBP to increase p65 acetylation and then aggravated inflammation. SIRT1 was deactivated with a decline in NAD+/NADH, which further aggravated inflammation. Therefore, acetylation-dependent regulation of transcription factor activity is an adaptation to proinflammatory stimuli under nutrient stress, which was also confirmed in AML12 hepatocytes. In vitro octanoate stimulation further verified that acetyl-CoA derived from fatty acid β-oxidation mediated acetylation homeostasis in the nucleus. The broad therapeutic prospects of intermediate metabolites and acetyltransferases/deacetylases might provide critical insights for the treatment of metabolic diseases in vertebrates.

A preliminary study of KAT2A on cGAS-related immunity in inflammation amplification of systemic lupus erythematosus

Previous studies demonstrated that cGAS pathway is related to the inflammation amplification in a variety of autoimmune diseases. Lysine acetyltransferase family (KATs) can regulate the nuclear transcription or cytoplasmic activation of cGAS through different mechanisms. However, its role and related immunity patterns in systemic lupus erythematosus (SLE) have not been explored. In this study, RNA-seq and scRNA-seq profiling were performed for peripheral blood mononuclear cells (PBMCs) from patients with SLE. R packages were used for bioinformatic analysis. Cell culture, RT-PCR, western blotting, immunofluorescence, immunohistochemistry, and ELISA were used to explore gene expression in vitro or clinical specimens. Plasmid transfection and mass spectrometry were used to detect protein modifications. Eight acetyltransferase and deacetylase family members with significantly differential expression in SLE were found. Among them, KAT2A was abnormally upregulated and positively correlated with disease activity index. Further, KAT2A-cGAS pathway was aberrantly expressed in specific immune cell subsets in SLE. In vitro studies showed KAT2A modulated cGAS through increasing expression and post-translational modification. Our research provides novel insights for accurately positioning specific immune-cell subgroups in which KAT2A-cGAS reaction mainly works and KAT2A regulation patterns.

cGAS- Stimulator of Interferon Genes Signaling in Central Nervous System Disorders

Cytosolic nucleic acid sensors contribute to the initiation of innate immune responses by playing a critical role in the detection of pathogens and endogenous nucleic acids. The cytosolic DNA sensor cyclic-GMP-AMP synthase (cGAS) and its downstream effector, stimulator of interferon genes (STING), mediate innate immune signaling by promoting the release of type I interferons (IFNs) and other inflammatory cytokines. These biomolecules are suggested to play critical roles in host defense, senescence, and tumor immunity. Recent studies have demonstrated that cGAS-STING signaling is strongly implicated in the pathogenesis of central nervous system (CNS) diseases which are underscored by neuroinflammatory-driven disease progression. Understanding and regulating the interactions between cGAS-STING signaling and the nervous system may thus provide an effective approach to prevent or delay late-onset CNS disorders. Here, we present a review of recent advances in the literature on cGAS-STING signaling and provide a comprehensive overview of the modulatory patterns of the cGAS-STING pathway in CNS disorders.

Mitotic inactivation of the cGAS‒MITA/STING pathways

The cyclic guanosine monophosphate‒adenosine monophosphate synthase (cGAS)‒mediator of interferon response factor 3 activation/stimulator of interferon genes (MITA/STING) axis has emerged as a major pathway, which senses microbial or mislocated cellular DNA in the cytosol to trigger innate immune responses. cGAS senses cytosolic DNA without a preference of self- or nonself-DNA. How the cGAS‒MITA/STING axis is inactivated upon nuclear envelope breakdown (NEBD) at mitotic entry in vertebrate cells to avoid self-DNA sensing remains unclear until very recently. In this review, we summarize the recent advances on how cGAS responds to chromosomes upon NEBD and the mechanisms involved in the inactivation of the cGAS‒MITA/STING pathways in mitosis.

cGAS-STING pathway: post-translational modifications and functions in sterile inflammatory diseases

Cytoplasmic microbial and host aberrant DNAs act as danger signals and trigger host immune responses. Upon recognition, the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) catalyzes the production of a second messenger 2'3'-cGAMP, which activates endoplasmic reticulum (ER)-associated stimulator of interferon (IFN) genes (STING) and ultimately leads to the induction of type I IFNs and inflammatory genes that collectively initiate host immune defense against microbial invasion. Inappropriate activation or suppression of this signaling pathway has been implicated in the development of some autoimmune diseases, sterile inflammation, and cancers. In this review, we describe how the activity of cGAS and STING is regulated by host post-translational modifications and summarize the recent advances of cell-specific cGAS-STING activation and its association in sterile inflammatory diseases. We also discuss key outstanding questions in the field, including how our knowledge of cGAS-STING pathway could be translated into clinical applications.

A delicate initiation: Lipolysis of lipid droplets fuels glioblastoma

Liu et al. (2021) demonstrate that CHKα2 is capable of promoting lipolysis of lipid droplets through mechanisms that require sequential steps of post-translational modifications after glucose deprivation. Intriguingly, the oxidation of fatty acids derived from lipid droplets is essential for the survival of tumor cells that informs clinical outcome among glioblastoma patients.