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Frontiers in Immunology 2022The cGAS-cGAMP-STING pathway is an important innate immune signaling cascade responsible for the sensing of abnormal cytosolic double-stranded DNA (dsDNA), which is a... (Review)
Review
The cGAS-cGAMP-STING pathway is an important innate immune signaling cascade responsible for the sensing of abnormal cytosolic double-stranded DNA (dsDNA), which is a hallmark of infection or cancers. Recently, tremendous progress has been made in the understanding of the STING activation mechanism from various aspects. In this review, the molecular mechanism of activation of STING protein based on its structural features is briefly discussed. The underlying molecular mechanism of STING activation will enable us to develop novel therapeutics to treat STING-associated diseases and understand how STING has evolved to eliminate infection and maintain immune homeostasis in innate immunity.
Topics: Cytosol; DNA; Immunity, Innate; Membrane Proteins; Signal Transduction
PubMed: 35928815
DOI: 10.3389/fimmu.2022.808607 -
European Journal of Immunology Mar 2014The presence of DNA in the cytoplasm of mammalian cells is perceived as a danger signal, alerting the host to the presence of microbial infection. In response to the... (Review)
Review
The presence of DNA in the cytoplasm of mammalian cells is perceived as a danger signal, alerting the host to the presence of microbial infection. In response to the detection of cytoplasmic DNA, the immune system mounts a programed response that involves the transcription of anti-viral genes such as type I interferons and production of inflammatory cytokines such as IL-1β. The recent discovery of the cGAS-cGAMP second messenger pathway as well as IFI16 and additional sensors collectively provide critical insights into the molecular basis behind the sensing of cytoplasmic DNA. The insights obtained from these important discoveries could unveil new avenues to understand host-immunity, improve vaccine adjuvancy, and allow development of new treatments for inflammatory diseases associated with abberrant sensing of DNA.
Topics: Animals; Cytosol; DEAD-box RNA Helicases; DNA; Humans; Membrane Proteins; Mice; Nuclear Proteins; Nucleotidyltransferases; Protein Binding; Protein Transport
PubMed: 24356864
DOI: 10.1002/eji.201344127 -
Journal of Leukocyte Biology Jul 2019Proinflammatory immune responses to Gram-negative bacterial lipopolysaccharides (LPS) are crucial to innate host defenses but can also contribute to pathology. How host... (Review)
Review
Proinflammatory immune responses to Gram-negative bacterial lipopolysaccharides (LPS) are crucial to innate host defenses but can also contribute to pathology. How host cells sensitively detect structural features of LPS was a mystery for years, especially given that a portion of the molecule essential for its potent proinflammatory properties-lipid A-is buried in the bacterial membrane. Studies of responses to extracellular and vacuolar LPS revealed a crucial role for accessory proteins that specifically bind LPS-rich membranes and extract LPS monomers to generate a complex of LPS, MD-2, and TLR4. These insights provided means to understand better both the remarkable host sensitivity to LPS and the means whereby specific LPS structural features are discerned. More recently, the noncanonical inflammasome, consisting of caspases-4/5 in humans and caspase-11 in mice, has been demonstrated to mediate responses to LPS that has reached the host cytosol. Precisely how LPS gains access to cytosolic caspases-and in what form-is not well characterized, and understanding this process will provide crucial insights into how the noncanonical inflammasome is regulated during infection. Herein, we briefly review what is known about LPS detection by cytosolic caspases-4/5/11, focusing on lessons derived from studies of the better-characterized TLR4 system that might direct future mechanistic questions.
Topics: Animals; Caspases; Cytosol; Humans; Inflammasomes; Lipopolysaccharides; Lymphocyte Antigen 96; Toll-Like Receptor 4
PubMed: 30694581
DOI: 10.1002/JLB.3MIR1118-434R -
Frontiers in Immunology 2021The maintenance of genomic stability in multicellular organisms relies on the DNA damage response (DDR). The DDR encompasses several interconnected pathways that... (Review)
Review
The maintenance of genomic stability in multicellular organisms relies on the DNA damage response (DDR). The DDR encompasses several interconnected pathways that cooperate to ensure the repair of genomic lesions. Besides their repair functions, several DDR proteins have emerged as involved in the onset of inflammatory responses. In particular, several actors of the DDR have been reported to elicit innate immune activation upon detection of cytosolic pathological nucleic acids. Conversely, pattern recognition receptors (PRRs), initially described as dedicated to the detection of cytosolic immune-stimulatory nucleic acids, have been found to regulate DDR. Thus, although initially described as operating in specific subcellular localizations, actors of the DDR and nucleic acid immune sensors may be involved in interconnected pathways, likely influencing the efficiency of one another. Within this mini review, we discuss evidences for the crosstalk between PRRs and actors of the DDR. For this purpose, we mainly focus on cyclic GMP-AMP (cGAMP) synthetase (cGAS) and Interferon Gamma Inducible Protein 16 (IFI16), as major PRRs involved in the detection of aberrant nucleic acid species, and components of the DNA-dependent protein kinase (DNA-PK) complex, involved in the repair of double strand breaks that were recently described to qualify as potential PRRs. Finally, we discuss how the crosstalk between DDR and nucleic acid-associated Interferon responses cooperate for the fine-tuning of innate immune activation, and therefore dictate pathological outcomes. Understanding the molecular determinants of such cooperation will be paramount to the design of future therapeutic approaches.
Topics: Cytosol; DNA Damage; Humans; Immunity, Innate; Membrane Proteins; Nucleic Acids; Receptors, Pattern Recognition; Signal Transduction
PubMed: 33981307
DOI: 10.3389/fimmu.2021.660560 -
Frontiers in Cellular and Infection... 2012Some bacterial toxins and viruses have evolved the capacity to bind mammalian glycosphingolipids to gain access to the cell interior, where they can co-opt the... (Review)
Review
Some bacterial toxins and viruses have evolved the capacity to bind mammalian glycosphingolipids to gain access to the cell interior, where they can co-opt the endogenous mechanisms of cellular trafficking and protein translocation machinery to cause toxicity. Cholera toxin (CT) is one of the best-studied examples, and is the virulence factor responsible for massive secretory diarrhea seen in cholera. CT enters host cells by binding to monosialotetrahexosylganglioside (GM1 gangliosides) at the plasma membrane where it is transported retrograde through the trans-Golgi network (TGN) into the endoplasmic reticulum (ER). In the ER, a portion of CT, the CT-A1 polypeptide, is unfolded and then "retro-translocated" to the cytosol by hijacking components of the ER associated degradation pathway (ERAD) for misfolded proteins. CT-A1 rapidly refolds in the cytosol, thus avoiding degradation by the proteasome and inducing toxicity. Here, we highlight recent advances in our understanding of how the bacterial AB(5) toxins induce disease. We highlight the molecular mechanisms by which these toxins use glycosphingolipid to traffic within cells, with special attention to how the cell senses and sorts the lipid receptors. We also discuss several new studies that address the mechanisms of toxin unfolding in the ER and the mechanisms of CT A1-chain retro-translocation to the cytosol.
Topics: Animals; Bacterial Toxins; Cell Membrane; Cytosol; Endoplasmic Reticulum; Eukaryotic Cells; Glycosphingolipids; Golgi Apparatus; Humans; Mammals; Protein Binding; Protein Transport
PubMed: 22919642
DOI: 10.3389/fcimb.2012.00051 -
Biological Chemistry May 2015Cytosolic glyceraldehyde 3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.12) is present in all organisms and catalyzes the oxidation of triose phosphate during glycolysis.... (Review)
Review
Cytosolic glyceraldehyde 3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.12) is present in all organisms and catalyzes the oxidation of triose phosphate during glycolysis. GAPDH is one of the most prominent cellular targets of oxidative modifications when reactive oxygen and nitrogen species are formed during metabolism and under stress conditions. GAPDH harbors a strictly conserved catalytic cysteine, which is susceptible to a variety of thiol modifications, including S-sulfenylation, S-glutathionylation, S-nitrosylation, and S-sulfhydration. Upon reversible oxidative thiol modification of GAPDH, glycolysis is inhibited leading to a diversion of metabolic flux through the pentose-phosphate cycle to increase NADPH production. Furthermore, oxidized GAPDH may adopt new functions in different cellular compartments including the nucleus, as well as in new microcompartments associated with the cytoskeleton, mitochondria and plasma membrane. This review focuses on the recently discovered mechanism underlying the eminent reactivity between GAPDH and hydrogen peroxide and the subsequent redox-dependent moonlighting functions discriminating between the induction either of adaptive responses and adjustment of metabolism or of cell death in yeast, plants, and mammals. In light of the summarized results, cytosolic GAPDH might function as a sensor for redox signals and an information hub to transduce these signals for appropriate responses.
Topics: Cytosol; Glyceraldehyde-3-Phosphate Dehydrogenases; Oxidation-Reduction
PubMed: 25581756
DOI: 10.1515/hsz-2014-0295 -
Cell Stress & Chaperones Jul 2017Small heat shock proteins (sHsps) exhibit an ATP-independent chaperone activity to prevent the aggregation of misfolded proteins in vitro. The seemingly conflicting... (Review)
Review
Small heat shock proteins (sHsps) exhibit an ATP-independent chaperone activity to prevent the aggregation of misfolded proteins in vitro. The seemingly conflicting presence of sHsps in insoluble protein aggregates in cells obstructs a precise definition of sHsp function in proteostasis networks. Recent findings specify sHsp activities in protein quality control systems. The sHsps of yeast, Hsp42 and Hsp26, interact with early unfolding intermediates of substrates, keeping them in a ready-to-refold conformation close to the native state. This activity facilitates substrate refolding by ATP-dependent Hsp70-Hsp100 disaggregating chaperones. Hsp42 can actively sequester misfolded proteins and promote their deposition at specific cellular sites. This aggregase activity represents a cytoprotective protein quality control strategy. The aggregase function of Hsp42 controls the formation of cytosolic aggregates (CytoQs) under diverse stress regimes and can be reconstituted in vitro, demonstrating that Hsp42 is necessary and sufficient to promote protein aggregation. Substrates sequestered at CytoQs can be dissociated by Hsp70-Hsp100 disaggregases for subsequent triage between refolding and degradation pathways or are targeted for destruction by selective autophagy termed proteophagy.
Topics: Animals; Cytosol; Heat-Shock Proteins, Small; Humans; Models, Molecular; Protein Aggregates; Protein Folding
PubMed: 28120291
DOI: 10.1007/s12192-017-0762-4 -
ACS Chemical Biology Apr 2023A key limitation for the development of peptides as therapeutics is their lack of cell permeability. Recent work has shown that short, arginine-rich macrocyclic peptides...
A key limitation for the development of peptides as therapeutics is their lack of cell permeability. Recent work has shown that short, arginine-rich macrocyclic peptides containing hydrophobic amino acids are able to penetrate cells and reach the cytosol. Here, we have developed a new strategy for developing cyclic cell penetrating peptides (CPPs) that shifts some of the hydrophobic character to the peptide cyclization linker, allowing us to do a linker screen to find cyclic CPPs with improved cellular uptake. We demonstrate that both hydrophobicity and position of the alkylation points on the linker affect uptake of macrocyclic cell penetrating peptides (CPPs). Our best peptide, , is on par with or better than prototypical CPPs Arg () and under assays measuring total cellular uptake and cytosolic delivery. was also able to carry a peptide previously discovered from an selection, , and a cytotoxic peptide into the cytosol. A bicyclic variant of showed even better cytosolic entry than , highlighting the plasticity of this class of peptides toward modifications. Since our CPPs are cyclized via their side chains (as opposed to head-to-tail cyclization), they are compatible with powerful technologies for peptide ligand discovery including phage display and mRNA display. Access to diverse libraries with inherent cell permeability will afford the ability to find cell permeable hits to many challenging intracellular targets.
Topics: Biological Transport; Cell-Penetrating Peptides; Cytosol
PubMed: 36920103
DOI: 10.1021/acschembio.2c00680 -
Cell Reports Apr 2023Cyclic GMP-AMP synthase (cGAS), as the major DNA sensor, initiates DNA-stimulated innate immune responses and is essential for a healthy immune system. Although some...
Cyclic GMP-AMP synthase (cGAS), as the major DNA sensor, initiates DNA-stimulated innate immune responses and is essential for a healthy immune system. Although some regulators of cGAS have been reported, it still remains largely unclear how cGAS is precisely and dynamically regulated and how many potential regulators govern cGAS. Here we carry out proximity labeling of cGAS with TurboID in cells and identify a number of potential cGAS-interacting or -adjacent proteins. Deubiquitinase OTUD3, one candidate identified in cytosolic cGAS-DNA complex, is further validated to not only stabilize cGAS but also enhance cGAS enzymatic activity, which eventually promotes anti-DNA virus immune response. We show that OTUD3 can directly bind DNA and is recruited to the cytosolic DNA complex, increasing its association with cGAS. Our findings reveal OTUD3 as a versatile cGAS regulator and find one more layer of regulatory mechanism in DNA-stimulated innate immune responses.
Topics: Nucleotidyltransferases; Immunity, Innate; DNA; Cytosol; Deubiquitinating Enzymes
PubMed: 36966392
DOI: 10.1016/j.celrep.2023.112309 -
Biochimica Et Biophysica Acta Apr 2008The eukaryotic cytoplasm has long been regarded as a cellular compartment in which the reduced state of protein cysteines is largely favored. Under normal conditions,... (Review)
Review
The eukaryotic cytoplasm has long been regarded as a cellular compartment in which the reduced state of protein cysteines is largely favored. Under normal conditions, the cytosolic low-molecular weight redox buffer, comprising primarily of glutathione, is highly reducing and reactive oxygen species (ROS) and glutathionylated proteins are maintained at very low levels. In the present review, recent progress in the understanding of the cytosolic thiol-disulfide redox metabolism and novel analytical approaches to studying cytosolic redox properties are discussed. We will focus on the yeast model organism, Saccharomyces cerevisiae, where the combination of genetic and biochemical approaches has brought us furthest in understanding the mechanisms underlying cellular redox regulation. It has been shown in yeast that, in addition to the enzyme glutathione reductase, other mechanisms may exist for restricting the cytosolic glutathione redox potential to a relatively narrow interval. Several mutations in genes involved in cellular redox regulation cause ROS accumulation but only moderate decreases in the cytosolic glutathione reducing power. The redox regulation in the cytosol depends not only on multiple cytosolic factors but also on the redox homeostasis of other compartments like the secretory pathway and the mitochondria. Possibly, the cytosol is not just a reducing compartment surrounding organelles with high oxidative activity but also a milieu for regulation of the redox status of more than one compartment. Although much has been learned about redox homeostasis and oxidative stress response several important aspects of the redox regulation in the yeast cytosol are still unexplained.
Topics: Cytosol; Eukaryotic Cells; Oxidation-Reduction; Oxidative Stress; Reactive Oxygen Species
PubMed: 18039473
DOI: 10.1016/j.bbamcr.2007.10.013