Endocytosis triggers V-ATPase-SYK-mediated priming of cGAS activation and innate immune response

Antitumor and immunomodulatory activities of diphyllin and its derivatives

Immune surveillance plays a key role in controlling tumor formation and development, and immune cell-based therapies, such as chimeric antigen receptor (CAR)-T cells and CAR-natural killer (NK) cells, have become important for the treatment of cancer. The proton pump (PP), vacuolar H+-ATPase (V-ATPase), acidifies intracellular organelles, pumps protons across the cell plasma membranes, and regulates the activity of various signaling pathways, and thus has been regarded as a potential target for cancer treatment. In addition, V-ATPase plays an important role in cytotoxic T lymphocytes, extracellular vesicle (EV) endocytosis, innate immune responses (IIR), and phagocytosis and hence has the potential to function as a target for the enhancement of immunotherapy. As potent V-ATPase inhibitors, the arylnaphthalene lignans, diphyllin and its derivatives, have exhibited potent antitumor and immunomodulatory activities. The structurally related aryltetralin lignan, podophyllotoxin, has served as a lead compound for both etoposide and teniposide, which have been developed as effective anticancer agents. In the present review, the role of V-ATPase in cancer immunotherapy and the structure-activity relationships (SARs) of diphyllin and its cytotoxic and V-ATPase inhibitory activities and the mechanisms of action are discussed. Also, the promise of diphyllin and its derivatives in the development of new adjuvants for cancer immunotherapies has been proposed.

Extracellular vesicles from diverse fungal pathogens induce species-specific and endocytosis-dependent immunomodulation

Microbial pathogens generate extracellular vesicles (EVs) for intercellular communication and quorum sensing. Microbial EVs also induce inflammatory pathways within host innate immune cells. We previously demonstrated that EVs secreted by Candida albicans trigger type I interferon signaling in host cells specifically via the cGAS-STING innate immune signaling pathway. Here, we show that despite sharing similar properties of morphology and internal DNA content, the interactions between EVs and the innate immune system differ according to the parental fungal species. EVs secreted by C. albicans, Saccharomyces cerevisiae, Cryptococcus neoformans, and Aspergillus fumigatus are endocytosed at different rates by murine macrophages triggering varied cytokine responses, innate immune signaling, and subsequent immune cell recruitment. Notably, cell wall constituents that decorate C. neoformans and A. fumigatus EVs inhibit efficient internalization by macrophages and dampen innate immune activation. Our data uncover the transcriptional and functional consequences of the internalization of diverse fungal EVs by immune cells and reveal novel insights into the early innate immune response to distinct clinically significant fungal pathogens.

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.

Resolving the two-body problem: A postulated role for the V0 sector of the V0V1-ATPase in exosome biogenesis and multivesicular body fate

Because the discovery of the multivesicular body (MVB) as the origin of secreted vesicles or exosomes, the question arose and still looms-what distinguishes an MVB destined for fusion with the plasma membrane (EXO-MVB) facilitating exosome release from an MVB involved in transport of content to the lysosome (LYSO-MVB). Do they have independent origins? Hence, the two-body problem. We hypothesize that a key to this conundrum is the membrane spanning V0 sector of the proton pump, V0V1-ATPase. The V0V1-ATPase participates in the acidification of intracellular compartments, although V0 can function separately from V1 and different V0 isoforms are endowed with membrane binding capabilities that allow the V0V1-ATPase to selectively localize to different endocytic compartments including early and late endosomes and lysosomes. We propose that V0, in collaboration with cholesterol and phosphoinositides, plays a central role in the early endosome as a nucleation center to direct the de novo assembly of an EXO-MVB scaffold. The EXO-MVB scaffold may play multiple roles-operating as an assembly platform, participating in membrane fission as well as providing downstream navigational queues necessary for exosome secretion. Thus, V0 may represent an influential nexus, a starting point, in exosome biogenesis.

Liquid-liquid Phase Separation in Aging: Novel Insights in the Pathogenesis and Therapeutics

The intricate organization of distinct cellular compartments is paramount for the maintenance of normal biological functions and the orchestration of complex biochemical reactions. These compartments, whether membrane-bound organelles or membraneless structures like Cajal bodies and RNA transport granules, play crucial roles in cellular function. Liquid-liquid phase separation (LLPS) serves as a reversible process that elucidates the genesis of membranelles structures through the self-assembly of biomolecules. LLPS has been implicated in a myriad of physiological and pathological processes, encompassing immune response and tumor genesis. But the association between LLPS and aging has not been clearly clarified. A recent advancement in the realm of aging research involves the introduction of a new edition outlining the twelve hallmarks of aging, categorized into three distinct groups. By delving into the role and mechanism of LLPS in the formation of membraneless structures at a molecular level, this review encapsulates an exploration of the interaction between LLPS and these aging hallmarks, aiming to offer novel perspectives of the intricate mechanisms underlying the aging process and deeper insights into aging therapeutics.

Activation of the cGAS-STING-IRF3 Axis by Type I and II Interferons Contributes to Host Defense

Interferons (IFNs) activate JAK-STAT pathways to induce downstream effector genes for host defense against invaded pathogens and tumors. Here both type I (β) and II (γ) IFNs are shown that can activate the transcription factor IRF3 in parallel with STAT1. IRF3-deficiency impairs transcription of a subset of downstream effector genes induced by IFN-β and IFN-γ. Mechanistically, IFN-induced activation of IRF3 is dependent on the cGAS-STING-TBK1 axis. Both IFN-β and IFN-γ cause mitochondrial DNA release into the cytosol. In addition, IFNs induce JAK1-mediated tyrosine phosphorylation of cGAS at Y214/Y215, which is essential for its DNA binding activity and signaling. Furthermore, deficiency of cGAS, STING, or IRF3 impairs IFN-β- or IFN-γ-mediated antiviral and antitumor activities. The findings reveal a novel IRF3 activation pathway parallel with the canonical STAT1/2 activation pathways triggered by IFNs and provide an explanation for the pleiotropic roles of the cGAS-STING-IRF3 axis in host defense.

Defective Lamtor5 Leads to Autoimmunity by Deregulating v-ATPase and Lysosomal Acidification

Despite accumulating evidence linking defective lysosome function with autoimmune diseases, how the catabolic machinery is regulated to maintain immune homeostasis remains unknown. Late endosomal/lysosomal adaptor, MAPK and mTOR activator 5 (Lamtor5) is a subunit of the Ragulator mediating mechanistic target of rapamycin complex 1 (mTORC1) activation in response to amino acids, but its action mode and physiological role are still unclear. Here it is demonstrated that Lamtor5 level is markedly decreased in peripheral blood mononuclear cells (PBMCs) of patients with systemic lupus erythematosus (SLE). In parallel, the mice with myeloid Lamtor5 ablation developed SLE-like manifestation. Impaired lysosomal function and aberrant activation of mTORC1 are evidenced in Lamtor5 deficient macrophages and PBMCs of SLE patients, accompanied by blunted autolysosomal pathway and undesirable inflammatory responses. Mechanistically, it is shown that Lamtor5 is physically associated with ATP6V1A, an essential subunit of vacuolar H+-ATPase (v-ATPase), and promoted the V0/V1 holoenzyme assembly to facilitate lysosome acidification. The binding of Lamtor5 to v-ATPase affected the lysosomal tethering of Rag GTPase and weakened its interaction with mTORC1 for activation. Overall, Lamtor5 is identified as a critical factor for immune homeostasis by intergrading v-ATPase activity, lysosome function, and mTOR pathway. The findings provide a potential therapeutic target for SLE and/or other autoimmune diseases.

Compound sophora decoction alleviates ulcerative colitis by regulating macrophage polarization through cGAS inhibition: network pharmacology and experimental validation

INTRODUCTION

Ulcerative colitis (UC) is a refractory disease with complex pathogenesis, and its pathogenesis is not clear. The present study aimed to investigate the potential target and related mechanism of Compound Sophora Decoction (CSD) in treating UC.

METHODS

A network pharmacology approach predicted the components and targets of CSD to treat UC, and cell and animal experiments confirmed the findings of the approach and a new target for CSD treatment of UC.

RESULTS

A total of 155 potential targets were identified for CSD treatment of UC, with some related to macrophage polarization, such as nitric oxide synthase (NOS2), also known as inducible nitric oxide synthase (iNOS). GO and KEGG enrichment analysis indicated that oxidative stress response and multiple inflammatory signaling pathways such as TNF-α may play a significant role. In vitro experiments revealed that Interferon-stimulated DNA (ISD) interference can cause polarization imbalances in Raw 264.7 and bone marrow-derived macrophages (BMDMs). Flow cytometry demonstrated that polarization of macrophages in the intestine, spleen, and lymph nodes in vivo was also unbalanced after dextran sulfate sodium (DSS) modeling with pathological intestinal injury. Both in vitro and in vivo studies indicated that after inducing inflammation, the levels of macrophage polarization-related markers (iNOS and Arg1) and inflammation-related factors (CCL17, IL10, TNF-α, and CXCL10) changed, accompanied by increased expression of cGAS. However, CSD treatment based on inflammation can inhibit the expression of cGAS protein and mRNA, lower the level of inflammatory factors, promote the expression of anti-inflammatory factors, and regulate macrophage polarization.

CONCLUSION

We concluded that CSD alleviated DSS-induced UC by inhibiting cGAS, thus regulating macrophage polarization.

2',3' cyclic nucleotide 3' phosphodiesterase 1 functional isoform antagonizes HIV-1 particle assembly

IFN-stimulated gene 2',3' cyclic nucleotide 3' phosphodiesterase (CNP) comprises two isoforms: the short CNP1 and the long CNP2, featuring an additional N-terminal segment of 20 amino acids (N20aa) proposed as a mitochondrial targeting sequence. Notably, CNP1 can be produced by cleaving the N20aa segment from CNP2. Although previous investigations have recognized the HIV-1 particle assembly impairment capability of CNP2, the antiviral activity of CNP1 remains ambiguous. Our study clarifies that CNP1, as opposed to CNP2, serves as the primary isoform exerting anti-HIV-1 activity. Both CNP1 and CNP2 can localize to the cell membrane, but the N20aa segment of CNP2 impedes CNP2-HIV-1 Gag interaction. Cleavage of the N20aa segment from CNP2 results in the formation of a functional, truncated form known as CNP1. Intriguingly, this posttranslational processing of CNP2 N20aa occurs within the cytoplasmic matrix rather than the mitochondria. Regulated by CTII motif prenylation, CNP1 proteins translocate to the cell membrane and engage with HIV-1 Gag. In conclusion, our findings underscore the pivotal role of posttranslational modification in governing the inhibitory potential of CNP in HIV-1 replication.

Advancements in tyrosine kinase-mediated regulation of innate nucleic acid sensing

Innate nucleic acid sensing is a ubiquitous and highly conserved immunological process, which is pivotal for monitoring and responding to pathogenic invasion and cellular damage, and central to host defense, autoimmunity, cell fate determination and tumorigenesis. Tyrosine phosphorylation, a major type of post-translational modification, plays a critical regulatory role in innate immune sensing pathway. Core members of nucleic acid sensing signaling pathway, such as cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS), stimulator of interferon genes (STING), and TANK binding kinase 1 (TBK1), are all subject to activity regulation triggered by tyrosine phosphorylation, thereby affecting the host antiviral defense and anti-tumor immunity under physiological or pathological conditions. This review summarizes the recent advances in research on tyrosine kinases and tyrosine phosphorylation in regulation of nucleic acid sensing. The function and potential applications of targeting tyrosine phosphorylation in anti-tumor immunity is disussed to provide insights for understanding and expanding new anti-tumor strategies.

Aberrant Expressions of PSMD14 in Tumor Tissue are the Potential Prognostic Biomarkers for Hepatocellular Carcinoma after Curative Resection

Introduction

Hepatocellular carcinoma (HCC) has a high mortality rate, with curative resection being the primary treatment. However, HCC patients have a large possibility of recurrence within 5 years after curative resection.

Methods

Thus, identifying biomarkers to predict recurrence is crucial. In our study, we analyzed data from CCLE, GEO, and TCGA, identifying eight oncogenes associated with HCC. Subsequently, the expression of 8 genes was tested in 5 cases of tumor tissues and the adjacent non-tumor tissues. Then ATP6AP1, PSMD14 and HSP90AB1 were selected to verify the expression in 63 cases of tumor tissues and the adjacent non-tumor tissues. The results showed that ATP6AP1, PSMD14, HSP90AB1 were generally highly expressed in tumor tissues. A five-year follow-up of the 63 clinical cases, combined with Kaplan-Meier Plotter's relapse-free survival (RFS) analysis, found a significant correlation between PSMD14 expression and recurrence in HCC patients. Subsequently, we analyzed the PSMD14 mutations and found that the PSMD14 gene mutations can lead to a shorter disease-free survival time for HCC patients.

Results

The results of enrichment analysis indicated that the differentially expressed genes related to PSMD14 are mainly enriched in the signal release pathway.

Conclusion

In conclusion, our research showed that PSMD14 might be related to recurrence in HCC patients, and the expression of PSMD14 in tumor tissue might be a potential prognostic biomarker after tumor resection in HCC patients.

The odyssey of cGAS: From cytosol to nucleus

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

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.

Cancer cell-specific cGAS/STING Signaling pathway in the era of advancing cancer cell biology

Pattern-recognition receptors (PRRs) are critical to recognizing endogenous and exogenous threats to mount a protective proinflammatory innate immune response. PRRs may be located on the outer cell membrane, cytosol, and nucleus. The cGAS/STING signaling pathway is a cytosolic PRR system. Notably, cGAS is also present in the nucleus. The cGAS-mediated recognition of cytosolic dsDNA and its cleavage into cGAMP activates STING. Furthermore, STING activation through its downstream signaling triggers different interferon-stimulating genes (ISGs), initiating the release of type 1 interferons (IFNs) and NF-κB-mediated release of proinflammatory cytokines and molecules. Activating cGAS/STING generates type 1 IFN, which may prevent cellular transformation and cancer development, growth, and metastasis. The current article delineates the impact of the cancer cell-specific cGAS/STING signaling pathway alteration in tumors and its impact on tumor growth and metastasis. This article further discusses different approaches to specifically target cGAS/STING signaling in cancer cells to inhibit tumor growth and metastasis in conjunction with existing anticancer therapies.

Regulation of cGAS and STING signaling during inflammation and infection

Stimulator of interferon genes (STING) is a sensor of cyclic dinucleotides including cyclic GMP-AMP, which is produced by cyclic GMP-AMP synthase (cGAS) in response to cytosolic DNA. The cGAS-STING signaling pathway regulates both innate and adaptive immune responses, as well as fundamental cellular functions such as autophagy, senescence, and apoptosis. Mutations leading to constitutive activation of STING cause devastating human diseases. Thus, the cGAS-STING pathway is of great interest because of its role in diverse cellular processes and because of the potential therapeutic implications of targeting cGAS and STING. Here, we review molecular and cellular mechanisms of STING signaling, and we propose a framework for understanding the immunological and other cellular functions of STING in the context of disease.

Development of a risk model to predict prognosis in breast cancer based on cGAS-STING-related genes

Background: Breast cancer (BRCA) is regarded as a lethal and aggressive cancer with increasing morbidity and mortality worldwide. cGAS-STING signaling regulates the crosstalk between tumor cells and immune cells in the tumor microenvironment (TME), emerging as an important DNA-damage mechanism. However, cGAS-STING-related genes (CSRGs) have rarely been investigated for their prognostic value in breast cancer patients.

Methods: Our study aimed to construct a risk model to predict the survival and prognosis of breast cancer patients. We obtained 1087 breast cancer samples and 179 normal breast tissue samples from the Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEX) database, 35 immune-related differentially expression genes (DEGs) from cGAS-STING-related genes were systematically assessed. The Cox regression was applied for further selection, and 11 prognostic-related DEGs were used to develop a machine learning-based risk assessment and prognostic model.

Results: We successfully developed a risk model to predict the prognostic value of breast cancer patients and its performance acquired effective validation. The results derived from Kaplan-Meier analysis revealed that the low-risk score patients had better overall survival (OS). The nomogram that integrated the risk score and clinical information was established and had good validity in predicting the overall survival of breast cancer patients. Significant correlations were observed between the risk score and tumor-infiltrating immune cells, immune checkpoints and the response to immunotherapy. The cGAS-STING-related genes risk score was also relevant to a series of clinic prognostic indicators such as tumor staging, molecular subtype, tumor recurrence, and drug therapeutic sensibility in breast cancer patients.

Conclusion: cGAS-STING-related genes risk model provides a new credible risk stratification method to improve the clinical prognostic assessment for breast cancer.

Oxidized mitochondrial DNA: a protective signal gone awry

Despite the emergence of mitochondria as key regulators of innate immunity, the mechanisms underlying the generation and release of immunostimulatory alarmins by stressed mitochondria remains nebulous. We propose that the major mitochondrial alarmin in myeloid cells is oxidized mitochondrial DNA (Ox-mtDNA). Fragmented Ox-mtDNA enters the cytosol where it activates the NLRP3 inflammasome and generates IL-1β, IL-18, and cGAS-STING to induce type I interferons and interferon-stimulated genes. Inflammasome activation further enables the circulatory release of Ox-mtDNA by opening gasdermin D pores. We summarize new data showing that, in addition to being an autoimmune disease biomarker, Ox-mtDNA converts beneficial transient inflammation into long-lasting immunopathology. We discuss how Ox-mtDNA induces short- and long-term immune activation, and highlight its homeostatic and immunopathogenic functions.

African Swine Fever Virus L83L Negatively Regulates the cGAS-STING-Mediated IFN-I Pathway by Recruiting Tollip To Promote STING Autophagic Degradation

African swine fever (ASF) is a devastating infectious disease of pigs caused by the African swine fever virus (ASFV), which poses a great danger to the global pig industry. Many viral proteins can suppress with interferon signaling to evade the host's innate immune responses. Therefore, the development of an effective vaccine against ASFV has been dampened. Recent studies have suggested that the L83L gene may be integrated into the host genome, weakening the host immune system, but the underlying mechanism is unknown. Our study found that L83L negatively regulates the cGAS-STING-mediated type I interferon (IFN-I) signaling pathway. Overexpression of L83L inhibited IFN-β promoter and ISRE activity, and knockdown of L83L induced higher transcriptional levels of interferon-stimulated genes (ISGs) and phosphorylation levels of IRF3 in primary porcine alveolar macrophages. Mechanistically, L83L interacted with cGAS and STING to promote autophagy-lysosomal degradation of STING by recruiting Tollip, thereby blocking the phosphorylation of the downstream signaling molecules TBK1, IRF3, and IκBα and reducing IFN-I production. Altogether, our study reveals a negative regulatory mechanism involving the L83L-cGAS-STING-IFN-I axis and provides insights into an evasion strategy involving autophagy and innate signaling pathways employed by ASFV. IMPORTANCE African swine fever virus (ASFV) is a large double-stranded DNA virus that primarily infects porcine macrophages. The ASFV genome encodes a large number of immunosuppressive proteins. Current options for the prevention and control of this pathogen remain pretty limited. Our study showed that overexpression of L83L inhibited the cGAS-STING-mediated type I interferon (IFN-I) signaling pathway. In contrast, the knockdown of L83L during ASFV infection enhanced IFN-I production in porcine alveolar macrophages. Additional analysis revealed that L83L protein downregulated IFN-I signaling by recruiting Tollip to promote STING autophagic degradation. Although L83L deletion has been reported to have little effect on viral replication, its immune evade mechanism has not been elucidated. The present study extends our understanding of the functions of ASFV-encoded pL83L and its immune evasion strategy, which may provide a new basis for developing a live attenuated vaccine for ASF.