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unexpected contributor to canonical inflammasome activation for the generation of caspase-1 and active IL-1beta. Hemizygotic deletion of c-FLIP impaired ATP- and monosodium uric acid (MSU)-induced IL-1beta production in macrophages primed through Toll-like receptors (TLRs). Decreased IL-1beta expression was attributed to a reduced activation of caspase-1 in c-FLIP hemizygotic cells. In contrast, the production of TNF-alpha was not affected by downregulation in c-FLIP. c-FLIP(L) interacted with NLRP3 or procaspase-1. c-FLIP is required for the full NLRP3 inflammasome assembly and NLRP3 mitochondrial localization, and c-FLIP is associated with NLRP3 inflammasome. c-FLIP downregulation also reduced AIM2 inflammasome activation. In contrast, c-FLIP inhibited SMAC mimetic-, FasL-, or Dectin-1-induced IL-1beta generation that is caspase-8-mediated. Our results demonstrate a prominent role of c-FLIP(L) in the optimal activation of the NLRP3 and AIM2 inflammasomes, and suggest that c-FLIP could be a valid target for treatment of inflammatory diseases caused by over-activation of inflammasomes.

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hese mice, the contribution of the inflammasome pathway has not been explored. To this end, we studied the role of the DNA-sensing inflammasome receptor AIM2 in this self-DNA driven disease model. Arthritis-prone mice lacking AIM2 displayed strongly decreased signs of joint inflammation and associated histopathological findings. This was paralleled with a reduction of caspase-1 activation and pro-inflammatory cytokine production in diseased joints. Interestingly, systemic signs of inflammation that are associated with the lack of DNase II were not dependent on AIM2. Taken together, these data suggest a tissue-specific role for the AIM2 inflammasome as a sensor for endogenous DNA species in the course of a ligand-dependent autoinflammatory condition.

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. Whether the ALRs are essential for activation of this pathway remains unknown. To rigorously explore the function of ALRs, we generated mice lacking all 13 ALR genes. We found that ALRs are dispensable for the type I interferon (IFN) response to transfected DNA ligands, DNA virus infection, and lentivirus infection. We also found that ALRs do not contribute to autoimmune disease in the Trex1(-/-) mouse model of Aicardi-Goutieres Syndrome. Finally, CRISPR-mediated disruption of the human AIM2-like receptor IFI16 in primary fibroblasts revealed that IFI16 is not essential for the IFN response to human cytomegalovirus infection. Our findings indicate that ALRs are dispensable for the ISD response and suggest that alternative functions for these receptors should be explored.

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aspartyl protease, Nelfinavir, triggers inflammasome formation and elicits an IL-1R-dependent inflammation in mice. We found that Nelfinavir impaired the maturation of lamin A, a structural component of the nuclear envelope, thereby promoting the release of DNA in the cytosol. Moreover, deficiency of the cytosolic DNA-sensor AIM2 impaired Nelfinavir-mediated inflammasome activation. These findings identify a pharmacologic activator of inflammasome and demonstrate the role of AIM2 in detecting endogenous DNA release upon perturbation of nuclear envelope integrity.

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(AIM2) inflammasome, on the functional output from the stimulator of IFN genes (STING) pathway is poorly understood. We found that dendritic cells and macrophages deficient in AIM2, apoptosis-associated specklike protein, or caspase-1 produced markedly higher IFN-beta in response to DNA. Biochemical analyses showed enhanced generation of cyclic GMP-AMP, STING aggregation, and TANK-binding kinase 1 and IFN regulatory factor 3 phosphorylation in inflammasome-deficient cells. Induction of pyroptosis by the AIM2 inflammasome was a major component of this effect, and inhibition of caspase-1 reduced cell death, augmenting phosphorylation of TANK-binding kinase 1/IFN regulatory factor 3 and production of IFN-beta. Our data suggest that in vitro activation of the AIM2 inflammasome in murine macrophages and dendritic cells leads to reduced activation of the STING pathway, in part through promoting caspase-1-dependent cell death.

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ntribute to steatohepatitis. Here, we investigated the inter-relationship between TLR signalling and inflammasome activation in dietary steatohepatitis.
METHODS: Wild type (WT), TLR4- and MyD88-deficient (KO) mice received methionine-choline-deficient (MCD) or -supplemented (MCS) diets for 5 weeks and a subset was challenged with TLR9 ligand CpG-DNA.
RESULTS: TLR4, TLR9, AIM2 (absent in melanoma 2) and NLRP3 (NLR family pyrin domain containing 3) inflammasome mRNA, and mature IL-1β protein levels were increased in MCD diet-induced steatohepatitis compared to MCS controls. TLR9 stimulation resulted in greater up-regulation of the DNA-sensing AIM2 expression and IL-1β production in livers of MCD compared to MCS diet-fed mice. High mobility group box 1 (HMGB1), a TLR9-activating danger molecule and phospho-HMGB1 protein levels were also increased in livers of MCD diet-fed mice. MyD88- but not TLR4-deficiency prevented up-regulation of AIM2, NLRP3 mRNA and IL-1β protein production in dietary steatohepatitis. Selective MyD88 deficiency either in bone marrow (BM)-derived or non-BM-derived cells attenuated hepatic up-regulation of inflammasome mRNA, caspase-1 activation and IL-1β protein production, but only BM-derived cell-specific MyD88-deficiency attenuated liver injury.
CONCLUSIONS: Our data demonstrate that both bone marrow-derived and non-BM-derived cells contribute to inflammasome activation in a MyD88-dependent manner in dietary steatohepatitis. We show that AIM2 inflammasome expression and activation are further augmented by TLR9 ligands in dietary steatohepatitis.

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ing complex called the inflammasome. Other NLRs regulate key signaling pathways such as NF-kB and MAPK. Since inflammation is a central component of colorectal cancer (CRC), this work was undertaken to analyze NLR and AIM2 expression in human CRC by combining bioinformatics analysis and experimental verification using clinical tissue samples. Additional experiments analyzed the association of (i) gene expression and cancer staging, and (ii) gene expression among inflammasome components.Ten public CRC datasets from the Oncomine(R) Platform were analyzed. Genes analyzed include NLRP1, NLRP3, NLRP6, NLRP12, NLRC3, NLRC4, NLRC5, NOD1, NOD2 and AIM2. Additionally, forty case-matched cancer samples and adjacent healthy control tissues isolated from a cohort of Chinese CRC patients were profiled.Three patterns of gene expression in CRC are shown. The expression of NLRC3, a checkpoint of inflammation, and the inflammasome components NLRP1, NLRP3, NLRC4 and AIM2 were reduced in CRC. NOD1 and NOD2 expression was increased in CRC, while NLRC5, NLRP6 and NLRP12 showed little difference compared to controls. Reduced expression of NLRC3 in CRC was verified in all available databases analyzed and confirmed with our patient cohort. Furthermore, the extent of NLRC3 and AIM2 gene reduction was correlated with cancer progression. This report reveals the potential value of NLR and AIM2 genes as biomarkers of CRC and cancer progression.

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ndergoing thoracic surgery. Tumor masses presented a higher percentage of pDCs than healthy tissues; pDCs were in the immunosuppressive phenotype, as determined by higher levels of CD33 and PD-L1. Despite higher HLA-A and HLA-D expression, cancerous pDCs did not exert cytotoxic activity against tumor cells but instead promoted their proliferation. In this scenario, cancerous pDCs were able to produce high levels of IL-1alpha. This effect was observed on the specific activation of the inflammasome absent in melanoma 2 (AIM2), which led to higher cytoplasmic calcium release responsible for calpain activation underlying IL-1alpha release. The blockade of type I interferon receptor and of AIM2 via the addition of LL-37 significantly reduced the release of IL-1alpha, which was still high after Nod-like receptor P3 inhibition via glibenclamide. More important, mitochondrial-derived reactive oxygen species sequester diminished AIM2-dependent IL-1alpha release. Our data demonstrate that lung tumor-associated pDCs are responsive to the activation of AIM2 that promotes calcium efflux and reactive oxygen species from mitochondria, leading to calpain activation and high levels of IL-1alpha, which facilitate tumor cell proliferation in the lung.

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f genes encoding inflammasome sensor subunits was investigated in colonic mucosal biopsies from 2 cohorts of patients with IBD and controls. RESULTS: A significant upregulation (>2-fold change in expression, false discovery rate <0.05) of the PYHIN inflammasomes AIM2 and IFI16 in active IBD versus controls was found. Also IFI16 was significantly increased in inactive IBD versus controls. Moreover, responders to anti-tumor necrosis factor therapy showed decreased expression of these inflammasomes although IFI16 remained significantly increased in responders showing endoscopic healing versus controls. AIM2 was mainly expressed in epithelial cells, whereas IFI16 was expressed in both lymphocytes and epithelial cells. Functional activation of predominant AIM2/IFI16-mediated inflammasomes in active IBD colon was shown by the presence of the downstream effectors CASP1 and HMGB-1 in inflamed mucosa. CONCLUSIONS: Our results highlight the importance of PYHIN inflammasome signaling in IBD and also link anti-tumor necrosis factor responsiveness to inflammasome signaling. Together, this points to the potential value of the inflammasome pathway as a new therapeutic target for IBD treatment.