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Plasma membrane rupture (PMR) in dying cells undergoing pyroptosis or apoptosis requires the cell-surface protein NINJ11. PMR releases pro-inflammatory cytoplasmic molecules, collectively called damage-associated molecular patterns (DAMPs), that activate immune cells. Therefore, inhibiting NINJ1 and PMR may limit the inflammation that is associated with excessive cell death. Here we describe an anti-NINJ1 monoclonal antibody that specifically targets mouse NINJ1 and blocks oligomerization of NINJ1, preventing PMR. Electron microscopy studies showed that this antibody prevents NINJ1 from forming oligomeric filaments. In mice, inhibition of NINJ1 or Ninj1 deficiency ameliorated hepatocellular PMR induced with TNF plus d-galactosamine, concanavalin A, Jo2 anti-Fas agonist antibody or ischaemia–reperfusion injury. Accordingly, serum levels of lactate dehydrogenase, the liver enzymes alanine aminotransaminase and aspartate aminotransferase, and the DAMPs interleukin 18 and HMGB1 were reduced. Moreover, in the liver ischaemia–reperfusion injury model, there was an attendant reduction in neutrophil infiltration. These data indicate that NINJ1 mediates PMR and inflammation in diseases driven by aberrant hepatocellular death.A monoclonal antibody that binds NINJ1 and inhibits NINJ1 oligomerization prevents plasma membrane rupture in dying cells, resulting in decreased inflammation of surrounding tissue in mice. [ABSTRACT FROM AUTHOR]

Plasma membrane rupture (PMR) is the final cataclysmic event in lytic cell death. PMR releases intracellular molecules known as damage-associated molecular patterns (DAMPs) that propagate the inflammatory response1–3. The underlying mechanism of PMR, however, is unknown. Here we show that the cell-surface NINJ1 protein4–8, which contains two transmembrane regions, has an essential role in the induction of PMR. A forward-genetic screen of randomly mutagenized mice linked NINJ1 to PMR. Ninj1−/− macrophages exhibited impaired PMR in response to diverse inducers of pyroptotic, necrotic and apoptotic cell death, and were unable to release numerous intracellular proteins including HMGB1 (a known DAMP) and LDH (a standard measure of PMR). Ninj1–/– macrophages died, but with a distinctive and persistent ballooned morphology, attributable to defective disintegration of bubble-like herniations. Ninj1–/– mice were more susceptible than wild-type mice to infection with Citrobacter rodentium, which suggests a role for PMR in anti-bacterial host defence. Mechanistically, NINJ1 used an evolutionarily conserved extracellular domain for oligomerization and subsequent PMR. The discovery of NINJ1 as a mediator of PMR overturns the long-held idea that cell death-related PMR is a passive event.The small transmembrane protein NINJ1 promotes plasma membrane rupture in lytic cell death associated with pyroptosis, necrosis and apoptosis. [ABSTRACT FROM AUTHOR]

The nucleotide-binding-domain (NBD)–and leucine-rich-repeat (LRR)–containing (NLR) family, pyrin-domain–containing 3 (NLRP3) inflammasome drives pathological inflammation in a suite of autoimmune, metabolic, malignant, and neurodegenerative diseases. Additionally, NLRP3 gain-of-function point mutations cause systemic periodic fever syndromes that are collectively known as cryopyrin-associated periodic syndrome (CAPS). There is significant interest in the discovery and development of diarylsulfonylurea Cytokine Release Inhibitory Drugs (CRIDs) such as MCC950/CRID3, a potent and selective inhibitor of the NLRP3 inflammasome pathway, for the treatment of CAPS and other diseases. However, drug discovery efforts have been constrained by the lack of insight into the molecular target and mechanism by which these CRIDs inhibit the NLRP3 inflammasome pathway. Here, we show that the domain conserved in NAIP, CIITA, HET-E, and TP1 (NACHT) domain of NLRP3 is the molecular target of diarylsulfonylurea inhibitors. Interestingly, we find photoaffinity labeling (PAL) of the NACHT domain requires an intact (d)ATP-binding pocket and is substantially reduced for most CAPS-associated NLRP3 mutants. In concordance with this finding, MCC950/CRID3 failed to inhibit NLRP3-driven inflammatory pathology in two mouse models of CAPS. Moreover, it abolished circulating levels of interleukin (IL)-1β and IL-18 in lipopolysaccharide (LPS)-challenged wild-type mice but not in Nlrp3L351P knock-in mice and ex vivo-stimulated mutant macrophages. These results identify wild-type NLRP3 as the molecular target of MCC950/CRID3 and show that CAPS-related NLRP3 mutants escape efficient MCC950/CRID3 inhibition. Collectively, this work suggests that MCC950/CRID3-based therapies may effectively treat inflammation driven by wild-type NLRP3 but not CAPS-associated mutants. [ABSTRACT FROM AUTHOR]

Type III secretion systems (T3SS) are central virulence factors for many pathogenic Gram-negative bacteria, and secreted T3SS effectors can block key aspects of host cell signaling. To counter this, innate immune responses can also sense some T3SS components to initiate anti-bacterial mechanisms. The Yersinia pestis T3SS is particularly effective and sophisticated in manipulating the production of pro-inflammatory cytokines IL-1β and IL-18, which are typically processed into their mature forms by active caspase-1 following inflammasome formation. Some effectors, like Y. pestis YopM, may block inflammasome activation. Here we show that YopM prevents Y. pestis induced activation of the Pyrin inflammasome induced by the RhoA-inhibiting effector YopE, which is a GTPase activating protein. YopM blocks YopE-induced Pyrin-mediated caspase-1 dependent IL-1β/IL-18 production and cell death. We also detected YopM in a complex with Pyrin and kinases RSK1 and PKN1, putative negative regulators of Pyrin. In contrast to wild-type mice, Pyrin deficient mice were also highly susceptible to an attenuated Y. pestis strain lacking YopM, emphasizing the importance of inhibition of Pyrin in vivo. A complex interplay between the Y. pestis T3SS and IL-1β/IL-18 production is evident, involving at least four inflammasome pathways. The secreted effector YopJ triggers caspase-8- dependent IL-1β activation, even when YopM is present. Additionally, the presence of the T3SS needle/translocon activates NLRP3 and NLRC4-dependent IL-1β generation, which is blocked by YopK, but not by YopM. Taken together, the data suggest YopM specificity for obstructing the Pyrin pathway, as the effector does not appear to block Y. pestis-induced NLRP3, NLRC4 or caspase-8 dependent caspase-1 processing. Thus, we identify Y. pestis YopM as a microbial inhibitor of the Pyrin inflammasome. The fact that so many of the Y. pestis T3SS components are participating in regulation of IL-1β/IL-18 release suggests that these effects are essential for maximal control of innate immunity during plague. [ABSTRACT FROM AUTHOR]

Gasdermin-D (GsdmD) is a critical mediator of innate immune defense because its cleavage by the inflammatory caspases 1, 4, 5, and 11 yields an N-terminal p30 fragment that induces pyroptosis, a death program important for the elimination of intracellular bacteria. Precisely how GsdmD p30 triggers pyroptosis has not been established. Here we show that human GsdmD p30 forms functional pores within membranes. When liberated from the corresponding C-terminal GsdmD p20 fragment in the presence of liposomes, GsdmD p30 localized to the lipid bilayer, whereas p20 remained in the aqueous environment. Within liposomes, p30 existed as higher-order oligomers and formed ring-like structures that were visualized by negative stain electron microscopy. These structures appeared withinminutes of GsdmD cleavage and released Ca2+ from preloaded liposomes. Consistent with GsdmD p30 favoring association with membranes, p30 was only detected in the membrane-containing fraction of immortalized macrophages after caspase-11 activation by lipopolysaccharide. We found that the mouse I105N/human I104N mutation, which has been shown to prevent macrophage pyroptosis, attenuated both cell killing by p30 in a 293T transient overexpression system and membrane permeabilization in vitro, suggesting that the mutants are actually hypomorphs, but must be above certain concentration to exhibit activity. Collectively, our data suggest that GsdmD p30 kills cells by forming pores that compromise the integrity of the cell membrane. [ABSTRACT FROM AUTHOR]

Intracellular lipopolysaccharide from Gram-negative bacteria including Escherichia coli, Salmonella typhimurium, Shigella flexneri, and Burkholderia thailandensis activates mouse caspase-11, causing pyroptotic cell death, interleukin-1β processing, and lethal septic shock. How caspase-11 executes these downstream signalling events is largely unknown. Here we show that gasdermin D is essential for caspase-11-dependent pyroptosis and interleukin-1β maturation. A forward genetic screen with ethyl-N-nitrosourea-mutagenized mice links Gsdmd to the intracellular lipopolysaccharide response. Macrophages from Gsdmd−/− mice generated by gene targeting also exhibit defective pyroptosis and interleukin-1β secretion induced by cytoplasmic lipopolysaccharide or Gram-negative bacteria. In addition, Gsdmd−/− mice are protected from a lethal dose of lipopolysaccharide. Mechanistically, caspase-11 cleaves gasdermin D, and the resulting amino-terminal fragment promotes both pyroptosis and NLRP3-dependent activation of caspase-1 in a cell-intrinsic manner. Our data identify gasdermin D as a critical target of caspase-11 and a key mediator of the host response against Gram-negative bacteria. [ABSTRACT FROM AUTHOR]

As a front line of defense against pathogenic microbes, our body employs a primitive, yet highly sophisticated and potent innate immune response pathway collectively referred to as the inflammasome. Innate immune cells, epithelial cells, and many other cell types are capable of detecting infection or tissue injury and mounting a coordinated molecular defense. For example, Gram-negative bacteria are specifically detected via a surveillance mechanism that involves activation of extracellular receptors such as Toll-like receptors ( TLRs) followed by intracellular recognition and activation of pathways such as caspase-11 (caspase-4/5 in humans). Importantly, lipopolysaccharide ( LPS), the major component of the outer membrane of Gram-negative bacteria, is a strong trigger of these pathways. Extracellular LPS primarily stimulates TLR4, which can serve as a priming signal for expression of inflammasome components. Intracellular LPS can then trigger caspase-11-dependent inflammasome activation in the cytoplasm. Here, we briefly review the burgeoning caspase-11-dependent non-canonical inflammasome field, focusing mainly on the innate sensing of LPS. [ABSTRACT FROM AUTHOR]

T-helper type 17 (TH17) cells that produce the cytokines interleukin-17A (IL-17A) and IL-17F are implicated in the pathogenesis of several autoimmune diseases. The differentiation of TH17 cells is regulated by transcription factors such as RORγt, but post-translational mechanisms preventing the rampant production of pro-inflammatory IL-17A have received less attention. Here we show that the deubiquitylating enzyme DUBA is a negative regulator of IL-17A production in T cells. Mice with DUBA-deficient T cells developed exacerbated inflammation in the small intestine after challenge with anti-CD3 antibodies. DUBA interacted with the ubiquitin ligase UBR5, which suppressed DUBA abundance in naive T cells. DUBA accumulated in activated T cells and stabilized UBR5, which then ubiquitylated RORγt in response to TGF-β signalling. Our data identify DUBA as a cell-intrinsic suppressor of IL-17 production. [ABSTRACT FROM AUTHOR]

Lipopolysaccharide from Gram-negative bacteria is sensed in the host cell cytoplasm by a non-canonical inflammasome pathway that ultimately results in caspase-11 activation and cell death. In mouse macrophages, activation of this pathway requires the production of type-I interferons, indicating that interferon-induced genes have a critical role in initiating this pathway. Here we report that a cluster of small interferon-inducible GTPases, the so-called guanylate-binding proteins, is required for the full activity of the non-canonical caspase-11 inflammasome during infections with vacuolar Gram-negative bacteria. We show that guanylate-binding proteins are recruited to intracellular bacterial pathogens and are necessary to induce the lysis of the pathogen-containing vacuole. Lysis of the vacuole releases bacteria into the cytosol, thus allowing the detection of their lipopolysaccharide by a yet unknown lipopolysaccharide sensor. Moreover, recognition of the lysed vacuole by the danger sensor galectin-8 initiates the uptake of bacteria into autophagosomes, which results in a reduction of caspase-11 activation. These results indicate that host-mediated lysis of pathogen-containing vacuoles is an essential immune function and is necessary for efficient recognition of pathogens by inflammasome complexes in the cytosol. [ABSTRACT FROM AUTHOR]

NLRC4 is a cytosolic member of the NOD-like receptor family that is expressed in innate immune cells. It senses indirectly bacterial flagellin and type III secretion systems, and responds by assembling an inflammasome complex that promotes caspase-1 activation and pyroptosis. Here we use knock-in mice expressing NLRC4 with a carboxy-terminal 3×Flag tag to identify phosphorylation of NLRC4 on a single, evolutionarily conserved residue, Ser?533, following infection of macrophages with Salmonella enterica serovar Typhimurium (also known as Salmonella typhimurium). Western blotting with a NLRC4 phospho-Ser?533 antibody confirmed that this post-translational modification occurs only in the presence of stimuli known to engage NLRC4 and not the related protein NLRP3 or AIM2. Nlrc4?/? macrophages reconstituted with NLRC4 mutant S533A, unlike those reconstituted with wild-type NLRC4, did not activate caspase-1 and pyroptosis in response to S. typhimurium, indicating that S533 phosphorylation is critical for NLRC4 inflammasome function. Conversely, phosphomimetic NLRC4 S533D caused rapid macrophage pyroptosis without infection. Biochemical purification of the NLRC4-phosphorylating activity and a screen of kinase inhibitors identified PRKCD (PKC?) as a candidate NLRC4 kinase. Recombinant PKC? phosphorylated NLRC4 S533 in vitro, immunodepletion of PKC? from macrophage lysates blocked NLRC4 S533 phosphorylation in vitro, and Prkcd?/? macrophages exhibited greatly attenuated caspase-1 activation and IL-1? secretion specifically in response to S. typhimurium. Phosphorylation-defective NLRC4 S533A failed to recruit procaspase-1 and did not assemble inflammasome specks during S. typhimurium infection, so phosphorylation of NLRC4 S533 probably drives conformational changes necessary for NLRC4 inflammasome activity and host innate immunity. [ABSTRACT FROM AUTHOR]

Inflammasomes are cytosolic multiprotein complexes assembled by intracellular nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and they initiate innate immune responses to invading pathogens and danger signals by activating caspase-1 (ref. 1). Caspase-1 activation leads to the maturation and release of the pro-inflammatory cytokines interleukin (IL)-1? and IL-18, as well as lytic inflammatory cell death known as pyroptosis. Recently, a new non-canonical inflammasome was described that activates caspase-11, a pro-inflammatory caspase required for lipopolysaccharide-induced lethality. This study also highlighted that previously generated caspase-1 knockout mice lack a functional allele of Casp11 (also known as Casp4), making them functionally Casp1?Casp11 double knockouts. Previous studies have shown that these mice are more susceptible to infections with microbial pathogens, including the bacterial pathogen Salmonella enterica serovar Typhimurium (S. typhimurium), but the individual contributions of caspase-1 and caspase-11 to this phenotype are not known. Here we show that non-canonical caspase-11 activation contributes to macrophage death during S. typhimurium infection. Toll-like receptor 4 (TLR4)-dependent and TIR-domain-containing adaptor-inducing interferon-? (TRIF)-dependent interferon-? production is crucial for caspase-11 activation in macrophages, but is only partially required for pro-caspase-11 expression, consistent with the existence of an interferon-inducible activator of caspase-11. Furthermore, Casp1?/? mice were significantly more susceptible to infection with S. typhimurium than mice lacking both pro-inflammatory caspases (Casp1?/??Casp11?/?). This phenotype was accompanied by higher bacterial counts, the formation of extracellular bacterial microcolonies in the infected tissue and a defect in neutrophil-mediated clearance. These results indicate that caspase-11-dependent cell death is detrimental to the host in the absence of caspase-1-mediated innate immunity, resulting in extracellular replication of a facultative intracellular bacterial pathogen. [ABSTRACT FROM AUTHOR]

Addition and removal of ubiquitin or ubiquitin chains to and from proteins is a tightly regulated process that contributes to cellular signaling and protein stability. Here we show that phosphorylation of the human deubiquitinase DUBA (OTUD5) at a single residue, Ser177, is both necessary and sufficient to activate the enzyme. The crystal structure of the ubiquitin aldehyde adduct of active DUBA reveals a marked cooperation between phosphorylation and substrate binding. An intricate web of interactions involving the phosphate and the C-terminal tail of ubiquitin cause DUBA to fold around its substrate, revealing why phosphorylation is essential for deubiquitinase activity. Phosphoactivation of DUBA represents an unprecedented mode of protease regulation and a clear link between two major cellular signal transduction systems: phosphorylation and ubiquitin modification. [ABSTRACT FROM AUTHOR]

Caspase-1 activation by inflammasome scaffolds comprised of intracellular nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and the adaptor ASC is believed to be essential for production of the pro-inflammatory cytokines interleukin (IL)-1? and IL-18 during the innate immune response. Here we show, with C57BL/6 Casp11 gene-targeted mice, that caspase-11 (also known as caspase-4) is critical for caspase-1 activation and IL-1? production in macrophages infected with Escherichia coli, Citrobacter rodentium or Vibrio cholerae. Strain 129 mice, like Casp11?/? mice, exhibited defects in IL-1? production and harboured a mutation in the Casp11 locus that attenuated caspase-11 expression. This finding is important because published targeting of the Casp1 gene was done using strain 129 embryonic stem cells. Casp1 and Casp11 are too close in the genome to be segregated by recombination; consequently, the published Casp1-/- mice lack both caspase-11 and caspase-1. Interestingly, Casp11-/- macrophages secreted IL-1? normally in response to ATP and monosodium urate, indicating that caspase-11 is engaged by a non-canonical inflammasome. Casp1-/-Casp11129mt/129mt macrophages expressing caspase-11 from a C57BL/6 bacterial artificial chromosome transgene failed to secrete IL-1? regardless of stimulus, confirming an essential role for caspase-1 in IL-1? production. Caspase-11 rather than caspase-1, however, was required for non-canonical inflammasome-triggered macrophage cell death, indicating that caspase-11 orchestrates both caspase-1-dependent and -independent outputs. Caspase-1 activation by non-canonical stimuli required NLRP3 and ASC, but caspase-11 processing and cell death did not, implying that there is a distinct activator of caspase-11. Lastly, loss of caspase-11 rather than caspase-1 protected mice from a lethal dose of lipopolysaccharide. These data highlight a unique pro-inflammatory role for caspase-11 in the innate immune response to clinically significant bacterial infections. [ABSTRACT FROM AUTHOR]

Macrophages respond to cytosolic nucleic acids by activating cysteine protease caspase-1 within a complex called the inflammasome. Subsequent cleavage and secretion of proinflammatory cytokines lL-1β and 11-18 are critical for innate immunity. Here, we show that macrophages from mice lacking absent in melanoma 2 (AIM2) cannot sense cytosolic double-stranded DNA and fail to trigger inflammasome assembly. Caspase-1 activation in response to intracellular pathogen Francisella tularensis also required AIM2. Immunofluorescence microscopy of macrophages infected with F. tularensis revealed striking colocalization of bacterial DNA with endogenous AIM2 and inflammasome adaptor ASC. By contrast, type I IFN (IFN-α and -β) secretion in response to F. tularensis did not require AIM2. IFN-l did, however, boost AIM2-dependent caspase-1 activation by increasing AIM2 protein levels. Thus, inflammasome activation was reduced in infected macrophages lacking either the IFN-I receptor or stimulator of interferon genes (STING). Finally. AIM2-deficient mice displayed increased susceptibility to F. tularensis infection compared with wild-type mice. Their increased bacterial burden in vivo confirmed that AIM2 is essential for an effective innate immune response. [ABSTRACT FROM AUTHOR]

Studies have suggested that endogenous TNF-related apoptosis-inducing ligand (TRAIL)/Apo2L may suppress the induction of some autoimmune diseases in mice. Here, we show that TRAIL/Apo2L suppresses autoimmune damage in relapsing-remitting, and non-remitting models of experimental autoimmune encephalomyelitis (EAE). TRAIL/Apo2L-deficient mice and wild-type mice treated with neutralizing anti-TRAIL/Apo2L antibody displayed enhanced clinical score, increased T-cell proliferative responses to myelin oligodendrocyte glycoprotein (MOG), and increased numbers of inflammatory lesions in the spinal cord and central nervous system. TRAIL neutralization immediately before disease onset was most effective at exacerbating disease score. More importantly, therapeutic intervention with recombinant soluble TRAIL/Apo2L delayed the onset and reduced the severity of MOG-induced EAE. These data are the first to illustrate the potential therapeutic value of recombinant TRAIL/Apo2L in suppressing T-cell-mediated autoimmune diseases. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various tumor cells in vitro, but its physiological role in tumor surveillance remains unknown. Here, we report that TRAIL is constitutively expressed on murine natural killer (NK) cells in the liver and plays a substantial role in suppressing tumor metastasis. Freshly isolated NK cells, but not natural killer T cells or ordinary T cells, from the liver expressed cell surface TRAIL, which was responsible for spontaneous cytotoxicity against TRAIL-sensitive tumor cells in vitro along with perforin and Fas ligand (FasL). Administration of neutralizing monoclonal antibody against TRAIL significantly increased experimental liver metastases of several TRAIL-sensitive tumor cell lines. Such an anti-metastatic effect of TRAIL was not observed in NK cell-depleted mice or interferon-?-deficient mice, the latter of which lacked TRAIL on liver NK cells. These findings provide the first evidence for the physiological function of TRAIL as a tumor suppressor. [ABSTRACT FROM AUTHOR]

Zoonotic pathogens, such as COVID-19, reside in animal hosts before jumping species to infect humans. The Carnivora, like mink, carry many zoonoses, yet how diversity in host immune genes across species affect pathogen carriage is poorly understood. Here, we describe a progressive evolutionary downregulation of pathogen-sensing inflammasome pathways in Carnivora. This includes the loss of nucleotide-oligomerization domain leucine-rich repeat receptors (NLRs), acquisition of a unique caspase-1/-4 effector fusion protein that processes gasdermin D pore formation without inducing rapid lytic cell death, and the formation of a caspase-8 containing inflammasome that inefficiently processes interleukin-1β. Inflammasomes regulate gut immunity, but the carnivorous diet has antimicrobial properties that could compensate for the loss of these immune pathways. We speculate that the consequences of systemic inflammasome downregulation, however, can impair host sensing of specific pathogens such that they can reside undetected in the Carnivora. [Display omitted] • Carnivorans lack key NLRs and express a unique caspase-1/-4 hybrid protein • This protein is defective in mediating activation of common inflammasome pathways • What little activity occurs is driven by caspase-8, rather than caspase-1/-4 Species of the order Carnivora have evolutionarily acquired the expression of a unique caspase-1/-4 hybrid protein. Digby et al. show that this protein is a poor mediator of NLRP3- and caspase-4-dependent inflammasome activation. This downregulation in inflammasome pathways could impair pathogen detection and facilitate transmission of zoonotic infections. [ABSTRACT FROM AUTHOR]

We examined the effect of a hydroxamic acid-based matrix metalloproteinase inhibitor (KB-R7785), which we previously demonstrated to have a potent ameliorating effect on acute graft-versus-host disease (GVHD), and on the graft-versus-leukaemia (GVL) effect of allogeneic bone marrow transplantation (BMT). KB-R7785 was administered to (C57BL/6 × BALB/c) F1 (CBF1) mice that had been inoculated with IgE-producing B53 hybridoma cells of BALB/c origin as a model tumour, along with or without transplantation of C57BL/6 (B6) bone marrow cells and spleen cells (BMS). Administration of KB-R7785 without BMS significantly prolonged the survival of B53-inoculated CBF1 mice by inhibiting the infiltration of B53 cells into the liver and spleen. Transplantation of B6 BMS without KB-R7785 resulted in the death of most recipients due to acute GVHD while efficiently eliminating B53 cells. Administration of KB-R7785 along with B6 BMS resulted in a 50% survival of B53-inoculated CBF1 mice over 50 d without histological manifestations of acute GVHD or residual B53 cells. These results indicate the beneficial effects of KB-R7785 that inhibit tumour infiltration and prevent acute GVHD while preserving the GVL effect of allogeneic BMT. [ABSTRACT FROM AUTHOR]

Characterizes the functional properties of generated mAbs that react with mouse Fas ligand (mFasL). Extracellular domains of human CD8alpha and mFasL; Flow cytometry analysis results; Blocking of bystander cytotoxic activity of cytotoxic T lymphocyte clones.

The correct name is: Vladimír Subr. 1 Vande Walle L, Stowe IB, Sácha P, Lee BL, Demon D, Fossoul A, et al. (2019) MCC950/CRID3 potently targets the NACHT domain of wild-type NLRP3 but not disease-associated mutants for inflammasome inhibition. [Extracted from the article]

Pyroptosis requires the induction of gasdermin D expression by the transcription factor IRF2. IRF2 induces gasdermin D: In response to activation of canonical and noncanonical inflammasomes, a subset of caspases processes the protein gasdermin D (GSDMD) to release N-terminal fragments that oligomerize and form pores in the plasma membrane. Assembly of the GSDMD pore leads to release of the inflammatory cytokine IL-1β and causes cell death by pyroptosis. Kayagaki et al. found that loss of the transcriptional regulator IRF2 reduced GSDMD mRNA and protein abundance in mice and in human cells, resulting in decreased IL-1β secretion and reduced pyroptosis in response to inflammasome activation. Given that loss of GSDMD in mice results in ameliorated disease in models of inflammasome-driven pathologies, these findings suggest that IRF2 might be a therapeutic target for the treatment of sepsis and other inflammasome-mediated diseases. Gasdermin-D (GSDMD) is cleaved by caspase-1, caspase-4, and caspase-11 in response to canonical and noncanonical inflammasome activation. Upon cleavage, GSDMD oligomerizes and forms plasma membrane pores, resulting in interleukin-1β (IL-1β) secretion, pyroptotic cell death, and inflammatory pathologies, including periodic fever syndromes and septic shock—a plague on modern medicine. Here, we showed that IRF2, a member of the interferon regulatory factor (IRF) family of transcription factors, was essential for the transcriptional activation of GSDMD. A forward genetic screen with N-ethyl-N-nitrosourea (ENU)–mutagenized mice linked IRF2 to inflammasome signaling. GSDMD expression was substantially attenuated in IRF2-deficient macrophages, endothelial cells, and multiple tissues, which corresponded with reduced IL-1β secretion and inhibited pyroptosis. Mechanistically, IRF2 bound to a previously uncharacterized but unique site within the GSDMD promoter to directly drive GSDMD transcription for the execution of pyroptosis. Disruption of this single IRF2-binding site abolished signaling by both the canonical and noncanonical inflammasomes. Together, our data illuminate a key transcriptional mechanism for expression of the gene encoding GSDMD, a critical mediator of inflammatory pathologies. [ABSTRACT FROM AUTHOR]