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Caspase-1 activation in GSDMD-deficient cells induces a rapid form of caspase-3–dependent secondary necrosis that is licenced by caspase-1–induced Bid cleavage and the release of mitochondrial SMAC., Caspase-1 drives a lytic inflammatory cell death named pyroptosis by cleaving the pore-forming cell death executor gasdermin-D (GSDMD). Gsdmd deficiency, however, only delays cell lysis, indicating that caspase-1 controls alternative cell death pathways. Here, we show that in the absence of GSDMD, caspase-1 activates apoptotic initiator and executioner caspases and triggers a rapid progression into secondary necrosis. GSDMD-independent cell death required direct caspase-1–driven truncation of Bid and generation of caspase-3 p19/p12 by either caspase-8 or caspase-9. tBid-induced mitochondrial outer membrane permeabilization was also required to drive SMAC release and relieve inhibitor of apoptosis protein inhibition of caspase-3, thereby allowing caspase-3 auto-processing to the fully active p17/p12 form. Our data reveal that cell lysis in inflammasome-activated Gsdmd-deficient cells is caused by a synergistic effect of rapid caspase-1–driven activation of initiator caspases-8/-9 and Bid cleavage, resulting in an unusually fast activation of caspase-3 and immediate transition into secondary necrosis. This pathway might be advantageous for the host in counteracting pathogen-induced inhibition of GSDMD but also has implications for the use of GSDMD inhibitors in immune therapies for caspase-1–dependent inflammatory disease.

DNA sequences of mono-, di-, and trinucleotide repeats are prone to replication errors and thus constitute mutational hot spots. This is well illustrated by the occurrence of DNA microsatellite instability in tumors from patients affected by hereditary nonpolyposis colorectal cancer (HNPCC) resulting from a defect in a gene that participates in postreplicative DNA mismatch repair (MMR). We selected repeat sequences present within coding regions of four genes involved in either cell proliferation or promotion of apoptosis. These repeats consisted of (A)10 in the TGF beta RII, (G)8 in the BAX, (A)8 in the CASP1, and (CCA)7 in the APP genes. These repeats were analyzed in ten tumors from HNPCC patients carrying a germline pathogenic mutation in the MMR gene MLH1. For each tumor the rate of somatic replication errors was measured by sequencing 20-50 cloned PCR-amplified fragments. Substantial intertumor variations were observed in the pattern of repeat alterations, with error rates varying between 12% and 80% for TGF beta RII, 2% and 84% for BAX, 0% and 30% for CASP1, and 0% to 18% for APP. The BAX repeat error rate did not exceed 20% in nine of the ten tumors, in contrast to results from previous studies. High error rates in more than one gene in a same tumor suggested additive selective effects from inactivation of different pathways influencing tumorigenesis. Our methodology can contribute to define tumor characteristics and may, if applied to genes strongly involved in tumorigenesis, improve tumor classification and outcome prediction.

c-Jun N-terminal kinases (SAPK/JNKs) are activated by inflammatory cytokines, and JNK signaling is involved in insulin resistance and beta-cell secretory function and survival. Chronic high glucose concentrations and leptin induce interleukin-1beta (IL-1beta) secretion from pancreatic islets, an event that is possibly causal in promoting beta-cell dysfunction and death. The present study provides evidence that chronically elevated concentrations of leptin and glucose induce beta-cell apoptosis through activation of the JNK pathway in human islets and in insulinoma (INS 832/13) cells. JNK inhibition by the dominant inhibitor JNK-binding domain of IB1/JIP-1 (JNKi) reduced JNK activity and apoptosis induced by leptin and glucose. Exposure of human islets to leptin and high glucose concentrations leads to a decrease of glucose-induced insulin secretion, which was partly restored by JNKi. We detected an interplay between the JNK cascade and the caspase 1/IL-1beta-converting enzyme in human islets. The caspase 1 gene, which contains a potential activating protein-1 binding site, was up-regulated in pancreatic sections and in isolated islets from type 2 diabetic patients. Similarly, cultured human islets exposed to high glucose- and leptin-induced caspase 1 and JNK inhibition prevented this up-regulation. Therefore, JNK inhibition may protect beta-cells from the deleterious effects of high glucose and leptin in diabetes.

Neuroinflammation is the local reaction of the brain to infection, trauma, toxic molecules or protein aggregates. The brain resident macrophages, microglia, are able to trigger an appropriate response involving secretion of cytokines and chemokines, resulting in the activation of astrocytes and recruitment of peripheral immune cells. IL-1β plays an important role in this response; yet its production and mode of action in the brain are not fully understood and its precise implication in neurodegenerative diseases needs further characterization. Our results indicate that the capacity to form a functional NLRP3 inflammasome and secretion of IL-1β is limited to the microglial compartment in the mouse brain. We were not able to observe IL-1β secretion from astrocytes, nor do they express all NLRP3 inflammasome components. Microglia were able to produce IL-1β in response to different classical inflammasome activators, such as ATP, Nigericin or Alum. Similarly, microglia secreted IL-18 and IL-1α, two other inflammasome-linked pro-inflammatory factors. Cell stimulation with α-synuclein, a neurodegenerative disease-related peptide, did not result in the release of active IL-1β by microglia, despite a weak pro-inflammatory effect. Amyloid-β peptides were able to activate the NLRP3 inflammasome in microglia and IL-1β secretion occurred in a P2X7 receptor-independent manner. Thus microglia-dependent inflammasome activation can play an important role in the brain and especially in neuroinflammatory conditions.