Cytosolic DNA sensing by cGAS/STING promotes TRPV2-mediated Ca2+ release to protect stressed replication forks

Inhibition of the cGAS-STING pathway: contributing to the treatment of cerebral ischemia-reperfusion injury

The cGAS-STING pathway plays an important role in ischemia-reperfusion injury in the heart, liver, brain, and kidney, but its role and mechanisms in cerebral ischemia-reperfusion injury have not been systematically reviewed. Here, we outline the components of the cGAS-STING pathway and then analyze its role in autophagy, ferroptosis, cellular pyroptosis, disequilibrium of calcium homeostasis, inflammatory responses, disruption of the blood-brain barrier, microglia transformation, and complement system activation following cerebral ischemia-reperfusion injury. We further analyze the value of cGAS-STING pathway inhibitors in the treatment of cerebral ischemia-reperfusion injury and conclude that the pathway can regulate cerebral ischemia-reperfusion injury through multiple mechanisms. Inhibition of the cGAS-STING pathway may be helpful in the treatment of cerebral ischemia-reperfusion injury.

Activated NETosis of bone marrow neutrophils up-regulates macrophage osteoclastogenesis via cGAS-STING/AKT2 pathway to promote osteoporosis

Bone marrow (BM) of postmenopausal osteoporosis has been found highly inflammatory, resulting from dysregulated immune cells induced by both estrogen efficiency and body aging. NETosis of neutrophils has been found aberrantly activated in age-related chronic inflammation, while their role in postmenopausal osteoporosis remains unclear. Here we found NETosis of BM neutrophils of OVX (ovariectomy) mice was significantly activated, and we verified NETs released by neutrophils induced M1 polarization and osteoclastogenesis of RAW264.7 macrophages. Further, we demonstrated effects of NETs on osteoclastogenesis was mediated by cGAS-STING/AKT2 pathway. Finally, we found in vivo NETs-clearance through GSK484 significantly inhibited osteoclastogenesis and attenuated osteoporosis of OVX mice. Our study highlights the role of neutrophil NETosis in activating osteoclastogenesis and bone resorption of postmenopausal osteoporosis, thereby providing novel targets for bone loss treatment.

MYO1F positions cGAS on the plasma membrane to ensure full and functional signaling

Cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS) detects viral or endogenous DNA, activating the innate immune response to infections and autoimmune diseases. Upon binding to double-stranded DNA, cGAS synthesizes 2'3' cGMP-AMP, which triggers type I interferon production. Besides its presence in the cytosol and nucleus, cGAS is found at the plasma membrane, although its significance remains unclear. Here, we report that cGAS associates with myosin 1F (MYO1F) at the plasma membrane of human and mouse macrophages. During viral infection, phosphorylation of MYO1F by spleen-associated tyrosine kinase (SYK) facilitates the recruitment of lysine acetyltransferase 2A (KAT2A), which acetylates cGAS at lysine residues 421, 292, and 131, essential for its activation. Moreover, membrane-localized cGAS is crucial for signaling activation and type I interferon production triggered by virus-cell fusion due to Mn2+ release from organelles. Our results highlight the importance of MYO1F-mediated cGAS localization for its full activation in response to viral infection.

Layered Double Hydroxides for Radium-223 Targeted Alpha Therapy with Elicitation of the Immune Response

Targeted Alpha therapy (TAT) has promising application prospects in tumor therapy. It is very appealing to design alpha-emitting radiopharmaceuticals that can modulate the immune microenvironment to overcome the limitations of immunotherapy. Herein, Mg/Al layered double hydroxide nanomaterials (LDH) are utilized to load the alpha-emitting nuclide Radium-223 (223Ra), achieving precise delivery of 223Ra to the tumor microenvironment. Dual-modal imaging is employed to dynamically monitor the in vivo distribution of 223Ra-LDH, ensuring its prolonged retention at the tumor site. In vitro experimentsshowed that ionizing radiation from alpha-emitting nuclides effectively reduced glutathione (GSH) and produced large amounts of reactive oxygen species (ROS), which damaged mitochondria and released free calcium (Ca2+), thereby aggravating tumor cell death. Additionally,  DNA double-strand breaks induced by alpha-emitting radiation triggered the STING signaling pathway, which in turn effectively induced immunogenic cell death (ICD) and promoted immune cell maturation and activation. The synergistic effect with immunotherapy triggered a powerful systemic antitumor immune response. Overall, this study develops a novel TAT therapeutic strategy with sufficient antitumor immunity.

The interferon response at the intersection of genome integrity and innate immunity

In recent years, numerous reports indicated that, besides pathogen infections, DNA replication stress and defective DNA repair can trigger the innate immune response by introducing a state of viral mimicry, due to cytosolic accumulation of the self-nucleic acid species, which culminates in the activation of type I interferon (IFN) pathway. In turn, IFN upregulates a variety of factors mutually implicated in immune- and genome-related mechanisms, shedding light on the unprecedented causality between genome stability and innate immunity. Intriguingly, in addition to being induced by replication stress, IFN-regulated factors can also promote it, pinpointing IFN signaling as both a consequence and a cause of replication stress. Here, we provide an overview of the factors and molecular mechanisms implicated in the evolutionary conserved crosstalk between genome maintenance and innate immunity, highlighting the role of the IFN-stimulated gene 15 (ISG15), which appears to be at the hub of this intersection. Moreover, we discuss the potential significance and clinical implications of the immune-mediated modulation of DNA replication and repair upon pathogen infection and in human diseases such as cancer and autoinflammatory syndromes. Finally, we discuss the relevant open questions and future directions.

Targeting Dlat-Trpv3 pathway by hyperforin elicits non-canonical promotion of adipose thermogenesis as an effective anti-obesity strategy

INTRODUCTION

Promoting adipose thermogenesis is considered as a promising therapeutic intervention in obesity. However, endeavors to develop anti-obesity medications by targeting the canonical thermogenesis regulatory pathway, particularly β3-adrenergic receptor (β3-AR)-dependent mechanism, have failed due to the off-target effects of β3-AR agonists, exacerbating the risk of cardiovascular disease. Hyperforin (HPF), a natural compound extracted from the traditional herbal St. John's Wort, binds to Dihydrolipoamide s-acetyltransferase (Dlat) and exerts effective anti-obesity properties through promoting adipose thermogenesis.

OBJECTIVES

The objective of this study was to investigate the oral efficacy and pharmacokinetics profile of HPF, and explore the detailed mechanism by which Dlat modulates HPF-mediated adipose thermogenesis.

METHODS

To assess the anti-obesity efficacy of orally administered HPF in vivo, Dlat heterozygous knockout (Dlat+/-) mice and wild-type (WT) mice, both fed a high-fat diet (HFD), underwent a validation process that involved the use of metabolic cages, NMR analysis, and infrared imaging. Sprague Dawley rats were employed to determine the pharmacokinetic parameters of HPF. Seahorse assays, JC-1 staining, qPCR, and immunoblotting were performed to evaluate cellular thermogenic efficacy of HPF and Dlat in vitro.

RESULTS

Our study uncovered a non-canonical thermogenesis pathway involving Dlat, transient receptor potential vanilloid 3 (Trpv3, a calcium channel) and AMPK. Dlat interacted with Trpv3 to activate it, resulting in an increase in intracellular calcium (Ca2+) and the activation of Camkkβ. Camkkβ then stimulated AMPK, leading to elevated Ucp1 expression and initiating adipose thermogenesis. HPF promoted thermogenesis in adipose tissues through enhancing the Dlat-Trpv3 interaction independently of β3-AR, causing minimal cardiac side effects. Notably, HPF's thermogenic effects were reduced in Dlat+/- mice. Moreover, HPF exerted favorable oral bioavailability, a relatively long half-life, and extensive distribution within adipose tissues.

CONCLUSION

In summary, our study demonstrates that HPF targets a novel mechanism for promoting adipose thermogenesis and exhibits potent and safe anti-obesity efficacy.

The metabolic sensor AMPK: Twelve enzymes in one

BACKGROUND

AMP-activated protein kinase (AMPK) is an evolutionarily conserved regulator of energy metabolism. AMPK is sensitive to acute perturbations to cellular energy status and leverages fundamental bioenergetic pathways to maintain cellular homeostasis. AMPK is a heterotrimer comprised of αβγ-subunits that in humans are encoded by seven individual genes (isoforms α1, α2, β1, β2, γ1, γ2 and γ3), permitting formation of at least 12 different complexes with personalised biochemical fingerprints and tissue expression patterns. While the canonical activation mechanisms of AMPK are well-defined, delineation of subtle, as well as substantial, differences in the regulation of heterogenous AMPK complexes remain poorly defined.

SCOPE OF REVIEW

Here, taking advantage of multidisciplinary findings, we dissect the many aspects of isoform-specific AMPK function and links to health and disease. These include, but are not limited to, allosteric activation by adenine nucleotides and small molecules, co-translational myristoylation and post-translational modifications (particularly phosphorylation), governance of subcellular localisation, and control of transcriptional networks. Finally, we delve into current debate over whether AMPK can form novel protein complexes (e.g., dimers lacking the α-subunit), altogether highlighting opportunities for future and impactful research.

MAJOR CONCLUSIONS

Baseline activity of α1-AMPK is higher than its α2 counterpart and is more sensitive to synergistic allosteric activation by metabolites and small molecules. α2 complexes however, show a greater response to energy stress (i.e., AMP production) and appear to be better substrates for LKB1 and mTORC1 upstream. These differences may explain to some extent why in certain cancers α1 is a tumour promoter and α2 a suppressor. β1-AMPK activity is toggled by a 'myristoyl-switch' mechanism that likely precedes a series of signalling events culminating in phosphorylation by ULK1 and sensitisation to small molecules or endogenous ligands like fatty acids. β2-AMPK, not entirely beholden to this myristoyl-switch, has a greater propensity to infiltrate the nucleus, which we suspect contributes to its oncogenicity in some cancers. Last, the unique N-terminal extensions of the γ2 and γ3 isoforms are major regulatory domains of AMPK. mTORC1 may directly phosphorylate this region in γ2, although whether this is inhibitory, especially in disease states, is unclear. Conversely, γ3 complexes might be preferentially regulated by mTORC1 in response to physical exercise.

The cGAS-STING pathway as a novel therapeutic strategy for pancreatic diseases

The Cyclic GMP-AMP synthase (cGAS)-Stimulator of interferon genes [1] signaling pathway has emerged as a pivotal immune response mechanism, activating immune defenses upon detection of both exogenous and endogenous DNA within cells. Its activation is intricately linked to various diseases and inflammatory processes, spanning autoimmune disorders, infectious ailments, and malignancies. Among pancreatic diseases, encompassing acute pancreatitis, chronic pancreatitis, and pancreatic cancer, current clinical treatment efficacy remains suboptimal. Here, we elucidate the molecular intricacies of the cGAS-STING signaling pathway and delineate its therapeutic potential in acute pancreatitis, chronic pancreatitis, and pancreatic cancer. Additionally, we offer an overview of recent advancements in STING agonists and antagonists, assessing their therapeutic potential in pancreatic-related disorders. In summary, by exploring the multifaceted roles of the cGAS-STING signaling pathway and its implications in pancreatic diseases, we aim to shed light on potential avenues for therapeutic intervention and management in these challenging clinical contexts.

Inhibition of O-GlcNAc transferase activates type I interferon-dependent antitumor immunity by bridging cGAS-STING pathway

The O-GlcNAc transferase (OGT) is an essential enzyme that mediates protein O-GlcNAcylation, a unique form of posttranslational modification of many nuclear and cytosolic proteins. Recent studies observed increased OGT and O-GlcNAcylation levels in a broad range of human cancer tissues compared to adjacent normal tissues, indicating a universal effect of OGT in promoting tumorigenesis. Here, we show that OGT is essential for tumor growth in immunocompetent mice by repressing the cyclic GMP-AMP synthase (cGAS)-dependent DNA sensing pathway. We found that deletion of OGT (Ogt-/-) caused a marked reduction in tumor growth in both syngeneic mice tumor models and a genetic mice colorectal cancer (CRC) model induced by mutation of the Apc gene (Apcmin). Pharmacological inhibition or genetic deletion of OGT induced a robust genomic instability (GIN), leading to cGAS-dependent production of the type I interferon (IFN-I) and IFN-stimulated genes (ISGs). As a result, deletion of Cgas or Sting from Ogt-/- cancer cells restored tumor growth, and this correlated with impaired CD8+ T-cell-mediated antitumor immunity. Mechanistically, we found that OGT-dependent cleavage of host cell factor C1 (HCF-1) is required for the avoidance of GIN and IFN-I production in tumors. In summary, our results identify OGT-mediated genomic stability and activate cGAS-STING pathway as an important tumor-cell-intrinsic mechanism to repress antitumor immunity.

ER: a critical hub for STING signaling regulation

The Stimulator of Interferon Genes (STING) has a crucial role in mediating the immune response against cytosolic double-stranded DNA (dsDNA) and its activation is critically involved in various diseases. STING is synthesized, modified, and resides in the endoplasmic reticulum (ER), and its ER exit is intimately connected with its signaling. The ER, primarily known for its roles in protein folding, lipid synthesis, and calcium storage, has been identified as a pivotal platform for the regulation of a wide range of STING functions. In this review, we discuss the emerging factors that regulate STING in the ER and examine the interplay between STING signaling and ER pathways, highlighting the impacts of such regulations on immune responses and their potential implications in STING-related disorders.

Inhibition of O-GlcNAc transferase activates type I interferon-dependent antitumor immunity by bridging cGAS-STING pathway

The O-GlcNAc transferase (OGT) is an essential enzyme that mediates protein O-GlcNAcylation, a unique form of posttranslational modification of many nuclear and cytosolic proteins. Recent studies observed increased OGT and O-GlcNAcylation levels in a broad range of human cancer tissues compared to adjacent normal tissues, indicating a universal effect of OGT in promoting tumorigenesis. Here, we show that OGT is essential for tumor growth in immunocompetent hosts by repressing the cyclic GMP-AMP synthase (cGAS)-dependent DNA sensing pathway. We found that deletion of OGT (Ogt -/- ) caused a marked reduction in tumor growth in both syngeneic tumor models and a genetic colorectal cancer (CRC) model induced by mutation of the Apc gene (Apc min ). Pharmacological inhibition or genetic deletion of OGT induced a robust genomic instability (GIN), leading to cGAS-dependent production of the type I interferon (IFN-I) and IFN-stimulated genes (ISGs). As a result, deletion of Cgas or Sting from Ogt -/- cancer cells restored tumor growth, and this correlated with impaired CD8+ T cell-mediated antitumor immunity. Mechanistically, we found that OGT-dependent cleavage of host cell factor C1 (HCF-1) is required for the avoidance of GIN and IFN-I production in tumors. In summary, our results identify OGT-mediated genomic stability and activate cGAS-STING pathway as an important tumor cell-intrinsic mechanism to repress antitumor immunity.

TCAF1 promotes TRPV2-mediated Ca2+ release in response to cytosolic DNA to protect stressed replication forks

The protection of the replication fork structure under stress conditions is essential for genome maintenance and cancer prevention. A key signaling pathway for fork protection involves TRPV2-mediated Ca2+ release from the ER, which is triggered after the generation of cytosolic DNA and the activation of cGAS/STING. This results in CaMKK2/AMPK activation and subsequent Exo1 phosphorylation, which prevent aberrant fork processing, thereby ensuring genome stability. However, it remains poorly understood how the TRPV2 channel is activated by the presence of cytosolic DNA. Here, through a genome-wide CRISPR-based screen, we identify TRPM8 channel-associated factor 1 (TCAF1) as a key factor promoting TRPV2-mediated Ca2+ release under replication stress or other conditions that activate cGAS/STING. Mechanistically, TCAF1 assists Ca2+ release by facilitating the dissociation of STING from TRPV2, thereby relieving TRPV2 repression. Consistent with this function, TCAF1 is required for fork protection, chromosomal stability, and cell survival after replication stress.

Viral infection and spread are inhibited by the polyubiquitination and downregulation of TRPV2 channel by the interferon-stimulated gene TRIM21

Interferon (IFN) contributes to the host's antiviral response by inducing IFN-stimulated genes (ISGs). However, their functional targets and the mechanism of action remain elusive. Here, we report that one such ISG, TRIM21, interacts with and degrades the TRPV2 channel in myeloid cells, reducing its expression and providing host protection against viral infections. Moreover, viral infection upregulates TRIM21 in paracrine and autocrine manners, downregulating TRPV2 in neighboring cells to prevent viral spread to uninfected cells. Consistently, the Trim21-/- mice are more susceptible to HSV-1 and VSV infection than the Trim21+/+ littermates, in which viral susceptibility is rescued by inhibition or deletion of TRPV2. Mechanistically, TRIM21 catalyzes the K48-linked ubiquitination of TRPV2 at Lys295. TRPV2K295R is resistant to viral-infection-induced TRIM21-dependent ubiquitination and degradation, promoting viral infection more profoundly than wild-type TRPV2 when reconstituted into Lyz2-Cre;Trpv2fl/fl myeloid cells. These findings characterize targeting the TRIM21-TRPV2 axis as a conducive strategy to control viral spread to bystander cells.

STIM1 translocation to the nucleus protects cells from DNA damage

DNA damage represents a challenge for cells, as this damage must be eliminated to preserve cell viability and the transmission of genetic information. To reduce or eliminate unscheduled chemical modifications in genomic DNA, an extensive signaling network, known as the DNA damage response (DDR) pathway, ensures this repair. In this work, and by means of a proteomic analysis aimed at studying the STIM1 protein interactome, we have found that STIM1 is closely related to the protection from endogenous DNA damage, replicative stress, as well as to the response to interstrand crosslinks (ICLs). Here we show that STIM1 has a nuclear localization signal that mediates its translocation to the nucleus, and that this translocation and the association of STIM1 to chromatin increases in response to mitomycin-C (MMC), an ICL-inducing agent. Consequently, STIM1-deficient cell lines show higher levels of basal DNA damage, replicative stress, and increased sensitivity to MMC. We show that STIM1 normalizes FANCD2 protein levels in the nucleus, which explains the increased sensitivity of STIM1-KO cells to MMC. This study not only unveils a previously unknown nuclear function for the endoplasmic reticulum protein STIM1 but also expands our understanding of the genes involved in DNA repair.

Dual deficiency of melatonin and dihydrotestosterone promotes stromal cell damage and mediates prostatitis via the cGAS-STING pathway in sleep-deprived mice

PURPOSE

Prostatitis is a highly prevalent condition that seriously affects men's physical and mental health. Although epidemiological investigations have provided evidence of a correlation between insufficient sleep and prostatitis, the pathogenesis of prostatitis remains unclear. We sought to identify the underlying mechanism involved and identify a promising therapeutic target.

METHODS

Sleep deprivation (SD) was utilized to establish a mouse model of insufficient sleep in a special device. Prostatitis was observed at different time points post-SD. The degree of prostatitis was evaluated by pathological section and behavioural tests. Using immunofluorescence, western blot, and proteomic analyses, the underlying mechanism of SD-related prostatitis was investigated, and the development and therapeutic target of prostatitis were elucidated.

RESULTS

SD, as an initial pathological trigger, resulted in a reduction in dihydrotestosterone and melatonin levels. Proteomic analysis revealed that the cGAS-STING pathway may play a significant role in inducing prostatitis. The subsequent results illustrated that the dual reduction in dihydrotestosterone and melatonin led to an accumulation of reactive oxygen species and the release of mitochondrial DNA (mt-DNA). The accumulation of mt-DNA activated the cGAS-STING pathway, which recruited inflammatory cells into the prostatic stroma through the secretion of interferon-β. Consequently, an inflammatory microenvironment was formed, ultimately promoting the development of prostatitis. Notably, mice with SD-induced prostatitis gradually recovered to a normal state within 7 days of recovery sleep. However, after being subjected to SD again, these mice tended to have a more pronounced manifestation of prostatitis within a shorter timeframe, which suggested that prostatitis is prone to relapse.

CONCLUSIONS

The cGAS-STING pathway activated by dual deficiency of dihydrotestosterone and melatonin plays a comprehensive inflammatory role in SD-related prostatitis. This research provides valuable insights into the pathogenesis, therapeutic targets, and prevention strategies of prostatitis.

TRPV: An emerging target in glaucoma and optic nerve damage

Transient receptor potential vanilloid (TRPV) channels are members of the TRP channel superfamily, which are ion channels that sense mechanical and osmotic stimuli and participate in Ca2+ signalling across the cell membrane. TRPV channels play important roles in maintaining the normal functions of an organism, and defects or abnormalities in TRPV channel function cause a range of diseases, including cardiovascular, neurological and urological disorders. Glaucoma is a group of chronic progressive optic nerve diseases with pathological changes that can occur in the tissues of the anterior and posterior segments of the eye, including the ciliary body, trabecular meshwork, Schlemm's canal, and retina. TRPV channels are expressed in these tissues and play various roles in glaucoma. In this article, we review various aspects of the pathogenesis of glaucoma, the structure and function of TRPV channels, the relationship between TRPV channels and systemic diseases, and the relationship between TRPV channels and ocular diseases, especially glaucoma, and we suggest future research directions. This information will help to further our understanding of TRPV channels and provide new ideas and targets for the treatment of glaucoma and optic nerve damage.

Potential cGAS-STING pathway functions in DNA damage responses, DNA replication and DNA repair

The major innate immune responder to the DNA of pathogens is the cyclic GMP-AMP (cGAMP) synthase (cGAS) - stimulator of interferon genes (STING) pathway. Most prominently, the outcome of cGAS signalling is the activation of inflammatory transcription through interferon regulatory factor 3 (IRF3) and nuclear factor kappa B (NF-kB). In addition, the cGAS-STING pathway can lead to the direct modulation of cellular processes independently of transcription, such as activation of autophagy. Under unperturbed conditions, several mechanisms are in place to prevent the activation of cGAS by self-DNA, chiefly its sequestration on chromatin, which interferes with binding to stimulatory DNA. However, under conditions of genotoxic stress and chromosomal instability, this inhibition breaks down, resulting in the activation of cGAS, which drives sterile inflammation, as well as cell fate and immune responses in cancer. Recently, several studies have suggested that cGAS, STING, or downstream pathway components can also regulate the DNA damage response, DNA damage checkpoint signalling, DNA repair and DNA replication. Here, I review these proposed mechanisms, and discuss some unanswered questions relating to them.

CaMKK2 and CHK1 phosphorylate human STN1 in response to replication stress to protect stalled forks from aberrant resection

Keeping replication fork stable is essential for safeguarding genome integrity; hence, its protection is highly regulated. The CTC1-STN1-TEN1 (CST) complex protects stalled forks from aberrant MRE11-mediated nascent strand DNA degradation (NSD). However, the activation mechanism for CST at forks is unknown. Here, we report that STN1 is phosphorylated in its intrinsic disordered region. Loss of STN1 phosphorylation reduces the replication stress-induced STN1 localization to stalled forks, elevates NSD, increases MRE11 access to stalled forks, and decreases RAD51 localization at forks, leading to increased genome instability under perturbed DNA replication condition. STN1 is phosphorylated by both the ATR-CHK1 and the calcium-sensing kinase CaMKK2 in response to hydroxyurea/aphidicolin treatment or elevated cytosolic calcium concentration. Cancer-associated STN1 variants impair STN1 phosphorylation, conferring inability of fork protection. Collectively, our study uncovers that CaMKK2 and ATR-CHK1 target STN1 to enable its fork protective function, and suggests an important role of STN1 phosphorylation in cancer development.

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.

Cadenza ad libitum: cGAS and STING showcase their versatile virtuosities in the Ca2+-dependent rescue of stalled replication forks

In this issue of Molecular Cell, Li et al. report that the cGAS-STING cytosolic dsDNA sensing pathway plays a crucial role in regulating the TRPV2 calcium channel to rescue replication forks.