Zinc homeostasis regulates caspase activity and inflammasome activation.

Inflammasome activation drives pyroptotic cell death and the release of inflammatory cytokines, and many diseases involve its overactivation. Zinc is essential for all organisms as a trace element, but its functions in innate immunity remain undefined. Here, we reported that Zn2+ inhibits caspase-1 to hinder inflammasome activation.

γδ T Cell-mediated Tumor Immunity is Tightly Regulated by STING and TGF-β Signaling Pathways.

The STING pathway plays a critical role in tumor immunosurveillance. However, the precise mechanisms by which STING regulates gamma delta (γδ) T cell function during tumor progression remain unclear. Herein, we find that tumor-derived cyclic GMP-AMP (cGAMP) activates a distinct STING pathway by inducing TBK1-mediated phosphorylation of Eomes in γδ T cells during the early stage of tumor development is demonstrated.

ARMH3-mediated recruitment of PI4KB directs Golgi-to-endosome trafficking and activation of the antiviral effector STING.

The cGAS-STING pathway mediates cytoplasmic DNA-triggered innate immunity. STING activation is initiated by cyclic-GMP-AMP (cGAMP)-induced translocation from the endoplasmic reticulum and sulfated glycosaminoglycans-induced polymerization at the Golgi. Here, we examine the mechanisms underlying STING transport and activation beyond the Golgi.

Manganese potentiates lipopolysaccharide-induced innate immune responses and septic shock.

Divalent metal ions such as magnesium (Mg), manganese (Mn), and zinc (Zn) play important roles in regulating innate immune responses. Lipopolysaccharide stimulation led to increased intracellular Mn and Zn in macrophages. However, the effect of those metal ions in regulating lipopolysaccharide-induced innate immune responses remains unclear.

Recent advances in the activation and regulation of the cGAS-STING pathway.

The cGAS-STING pathway is responsible for cytoplasmic double-stranded DNA (dsDNA) -triggered innate immunity and involved in the pathology of various diseases including infection, autoimmune diseases, neurodegeneration and cancer. Understanding the activation and regulatory mechanisms of this pathway is critical to develop therapeutic strategies toward these diseases. Here, we review the signal transduction, cellular functions and regulations of cGAS and STING, particularly highlighting the latest understandings on the activation of cGAS by dsDNA and/or Manganese (Mn), STING trafficking, sulfated glycosaminoglycans (sGAGs)-induced STING polymerization and activation, and also regulation of the cGAS-STING pathway by different biocondensates formed via phase separation of proteins from host cells and viruses.

Dusp6 deficiency attenuates neutrophil-mediated cardiac damage in the acute inflammatory phase of myocardial infarction.

Dual-specificity phosphatase 6 (DUSP6) serves a specific and conserved function on the dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). We previously identified Dusp6 as a regenerative repressor during zebrafish heart regeneration, therefore we propose to investigate the role of this repressor in mammalian cardiac repair. Utilizing a rat strain harboring Dusp6 nonsense mutation, rat neutrophil-cardiomyocyte co-culture, bone marrow transplanted rats and neutrophil-specific Dusp6 knockout mice, we find that Dusp6 deficiency improves cardiac outcomes by predominantly attenuating neutrophil-mediated myocardial damage in acute inflammatory phase after myocardial infarction.

Intercellular transfer of activated STING triggered by RAB22A-mediated non-canonical autophagy promotes antitumor immunity.

STING, an endoplasmic reticulum (ER) transmembrane protein, mediates innate immune activation upon cGAMP stimulation and is degraded through autophagy. Here, we report that activated STING could be transferred between cells to promote antitumor immunity, a process triggered by RAB22A-mediated non-canonical autophagy. Mechanistically, RAB22A engages PI4K2A to generate PI4P that recruits the Atg12-Atg5-Atg16L1 complex, inducing the formation of ER-derived RAB22A-mediated non-canonical autophagosome, in which STING activated by agonists or chemoradiotherapy is packaged.

Recent progress on the activation of the cGAS-STING pathway and its regulation by biomolecular condensation.

The cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthetase (cGAS)-stimulator of interferon genes (STING) pathway, comprising the DNA sensor cGAS, the second messenger cyclic GMP-AMP (cGAMP), and the endoplasmic reticulum (ER) adaptor protein STING, detects cytoplasmic double-stranded DNA (dsDNA) to trigger type I-interferon responses for host defense against pathogens. Previous studies defined a model for the allosteric activation of cGAS by DNA-binding, but recent work reveals other layers of mechanisms to regulate cGAS activation such as the phase condensation and metal ions, especially the discovery of Mn2+ as a cGAS activator. Activation of the 2'3'-cGAMP sensor STING requires translocating from the ER to the Golgi apparatus.

Sensing of cytoplasmic chromatin by cGAS activates innate immune response in SARS-CoV-2 infection.

The global coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense RNA virus. How the host immune system senses and responds to SARS-CoV-2 infection remain largely unresolved. Here, we report that SARS-CoV-2 infection activates the innate immune response through the cytosolic DNA sensing cGAS-STING pathway.

T6SS translocates a micropeptide to suppress STING-mediated innate immunity by sequestering manganese.

Cellular ionic concentrations are a central factor orchestrating host innate immunity, but no pathogenic mechanism that perturbs host innate immunity by directly targeting metal ions has yet been described. Here, we report a unique virulence strategy of () involving modulation of the availability of Mn, an immunostimulatory metal ion in host cells. We showed that the type VI secretion system (T6SS) delivered a micropeptide, TssS, into host cells to enhance its virulence.

A human cell-based SARS-CoV-2 vaccine elicits potent neutralizing antibody responses and protects mice from SARS-CoV-2 challenge.

To curb the pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), multiple platforms have been employed toward a safe and highly effective vaccine. Here, we develop a novel cell-based vaccine candidate, namely K562-S, by utilizing human cell K562 as a cellular carrier to display Spike (S) protein of SARS-CoV-2 on the membrane. Analogous to the traditional inactivated vaccine, K562-S cells can be propagated to a large scale by culturing and completely lose their viability after exposure to X-ray irradiation or formalin.

Golgi apparatus-synthesized sulfated glycosaminoglycans mediate polymerization and activation of the cGAMP sensor STING.

Activation of the cyclic guanosine monophosphate (GMP)-AMP (cGAMP) sensor STING requires its translocation from the endoplasmic reticulum to the Golgi apparatus and subsequent polymerization. Using a genome-wide CRISPR-Cas9 screen to define factors critical for STING activation in cells, we identified proteins critical for biosynthesis of sulfated glycosaminoglycans (sGAGs) in the Golgi apparatus. Binding of sGAGs promoted STING polymerization through luminal, positively charged, polar residues.

The STING phase-separator suppresses innate immune signalling.

Biomolecular condensates (biocondensates) formed via liquid-liquid phase-separation of soluble proteins have been studied extensively. However, neither the phase-separation of endoplasmic reticulum (ER) transmembrane protein nor a biocondensate with organized membranous structures has been reported. Here, we have discovered a spherical ER membranous biocondensate with puzzle-like structures caused by condensation of the ER-resident stimulator of interferon genes (STING) in DNA virus-infected or 2'3'-cGAMP (cyclic GMP-AMP)-treated cells, which required STING transmembrane domains, an intrinsically disordered region (IDR) and a dimerization domain.

Manganese salts function as potent adjuvants.

Aluminum-containing adjuvants have been used for nearly 100 years to enhance immune responses in billions of doses of vaccines. To date, only a few adjuvants have been approved for use in humans, among which aluminum-containing adjuvants are the only ones widely used. However, the medical need for potent and safe adjuvants is currently continuously increasing, especially those triggering cellular immune responses for cytotoxic T lymphocyte activation, which are urgently needed for the development of efficient virus and cancer vaccines.

TBK1-Mediated DRP1 Targeting Confers Nucleic Acid Sensing to Reprogram Mitochondrial Dynamics and Physiology.

Mitochondrial morphology shifts rapidly to manage cellular metabolism, organelle integrity, and cell fate. It remains unknown whether innate nucleic acid sensing, the central and general mechanisms of monitoring both microbial invasion and cellular damage, can reprogram and govern mitochondrial dynamics and function. Here, we unexpectedly observed that upon activation of RIG-I-like receptor (RLR)-MAVS signaling, TBK1 directly phosphorylated DRP1/DNM1L, which disabled DRP1, preventing its high-order oligomerization and mitochondrial fragmentation function.

Manganese is critical for antitumor immune responses via cGAS-STING and improves the efficacy of clinical immunotherapy.

CD8 T cell-mediated cancer clearance is often suppressed by the interaction between inhibitory molecules like PD-1 and PD-L1, an interaction acts like brakes to prevent T cell overreaction under normal conditions but is exploited by tumor cells to escape the immune surveillance. Immune checkpoint inhibitors have revolutionized cancer therapeutics by removing such brakes. Unfortunately, only a minority of cancer patients respond to immunotherapies presumably due to inadequate immunity.

Mn Directly Activates cGAS and Structural Analysis Suggests Mn Induces a Noncanonical Catalytic Synthesis of 2'3'-cGAMP.

DNA binding allosterically activates the cytosolic DNA sensor cGAS (cyclic GMP-AMP [cGAMP] synthase) to synthesize 2'3'-cGAMP, using Mg as the metal cofactor that catalyzes two nucleotidyl-transferring reactions. We previously found that Mn potentiates cGAS activation, but the underlying mechanism remains unclear. Here, we report that Mn directly activates cGAS.

Transfer of cGAMP into Bystander Cells via LRRC8 Volume-Regulated Anion Channels Augments STING-Mediated Interferon Responses and Anti-viral Immunity.

The enzyme cyclic GMP-AMP synthase (cGAS) senses cytosolic DNA in infected and malignant cells and catalyzes the formation of 2'3'cGMP-AMP (cGAMP), which in turn triggers interferon (IFN) production via the STING pathway. Here, we examined the contribution of anion channels to cGAMP transfer and anti-viral defense. A candidate screen revealed that inhibition of volume-regulated anion channels (VRACs) increased propagation of the DNA virus HSV-1 but not the RNA virus VSV.

Metalloimmunology: The metal ion-controlled immunity.

Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation.

NLRP6 self-assembles into a linear molecular platform following LPS binding and ATP stimulation.

NOD-like receptors (NLRs) localize in the cytosol to recognize intracellular pathogen products and initialize the innate immune response. However, the ligands and ligand specificity of many NLRs remain unclear. One such NLR, NLRP6, plays an important role in maintaining intestinal homeostasis and protecting against various intestinal diseases such as colitis and intestinal tumorigenesis.

NLRP3 inflammasome activation by Foot-and-mouth disease virus infection mainly induced by viral RNA and non-structural protein 2B.

Foot-and-mouth disease virus (FMDV) is a positive-strand RNA virus of the family . Early studies show that some viruses of , such as EMCV and EV71, induce NLRP3 inflammasome activation. Our current study demonstrates that FMDV induces the secretion of caspase-1 and interleukin 1 beta (IL-1β), as well as activates the NLRP3 inflammasome in a dose- and time-dependent manner.

Non-hematopoietic STAT6 induces epithelial tight junction dysfunction and promotes intestinal inflammation and tumorigenesis.

Enhanced gut permeability due to dysregulated epithelial tight junction is often associated with inflammatory bowel diseases (IBD), which have a greater risk for developing colorectal cancer. STAT6 activation was detected in inflamed colonic epithelium of active IBD patients, suggesting a role of epithelial STAT6 in colitis development. Here, we demonstrated that non-hematopoietic STAT6, but not hematopoietic STAT6, triggered DSS-induced colitis and subsequent tumorigenesis.

Apoptotic Caspases Suppress Type I Interferon Production via the Cleavage of cGAS, MAVS, and IRF3.

Viral infection triggers host defenses through pattern-recognition receptor-mediated cytokine production, inflammasome activation, and apoptosis of the infected cells. Inflammasome-activated caspases are known to cleave cyclic GMP-AMP synthase (cGAS). Here, we found that apoptotic caspases are critically involved in regulating both DNA and RNA virus-triggered host defenses, in which activated caspase-3 cleaved cGAS, MAVS, and IRF3 to prevent cytokine overproduction.