Resistance to cell death is a hallmark of cancer. Immunotherapy, particularly immune checkpoint blockade therapy, drives immunemediated cell death and has greatly improved treatment outcomes for some patients with cancer, but it often fails clinically. Its success relies on the cytokines and cytotoxic functions of effector immune cells to bypass the resistance to cell death and eliminate cancer cells. However, the specific cytokines capable of inducing cell death in tumors and the mechanisms that connect cytokines to cell death across cancer cell types remain unknown. In this study, we analyzed expression of several cytokines that are modulated in tumors and found correlations between cytokine expression and mortality. Of several cytokines tested for their ability to kill cancer cells, only TNF-a and IFN-g together were able to induce cell death in 13 distinct human cancer cell lines derived from colon and lung cancer, melanoma, and leukemia. Further evaluation of the specific programmed cell death pathways activated by TNF-a and IFN-g in these cancer lines identified PANoptosis, a form of inflammatory cell death that was previously shown to be activated by contemporaneous engagement of components from pyroptosis, apoptosis, and/or necroptosis. Specifically, TNF-a and IFN-g triggered activation of gasdermin D, gasdermin E, caspase-8, caspase-3, caspase-7, and MLKL. Furthermore, the intratumoral administration of TNF-a and IFN-g suppressed the growth of transplanted xenograft tumors in an NSG mouse model. Overall, this study shows that PANoptosis, induced by synergism of TNF-a and IFN-g, is an important mechanism to kill cancer cells and suppress tumor growth that could be therapeutically targeted.

Bacterial pathogens from the genus Yersinia cause fatal sepsis and gastritis in humans. Innate immune signaling and inflammatory cell death (pyroptosis, apoptosis, and necroptosis [PANoptosis]) serve as a first line of antimicrobial host defense. The receptor-interacting protein kinase 1 (RIPK1) is essential for Yersinia-induced pyroptosis and apoptosis and an effective host response. However, it is not clear whether RIPK1 assembles a multifaceted cell death complex capable of regulating caspase-dependent pyroptosis and apoptosis or whether there is cross-talk with necroptosis under these conditions. In this study, we report that Yersinia activates PANoptosis, as evidenced by the concerted activation of proteins involved in PANoptosis. Genetic deletion of RIPK1 abrogated the Yersinia-induced activation of the inflammasome/pyroptosis and apoptosis but enhanced necroptosis. We also found that Yersinia induced assembly of a RIPK1 PANoptosome complex capable of regulating all three branches of PANoptosis. Overall, our results demonstrate a role for the RIPK1 PANoptosome in Yersinia-induced inflammatory cell death and host defense.

The innate immune system acts as the first line of defense against infection. One key component of the innate immune response to gram-negative bacterial infections is inflammasome activation. The caspase-11 (CASP11)-nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome is activated by cytosolic lipopolysaccharide, a gram-negative bacterial cell wall component, to trigger pyroptosis and host defense during infection. Although several cellular signaling pathways have been shown to regulate CASP11-NLRP3 inflammasome activation in response to lipopolysaccharide, the upstream molecules regulating CASP11 activation during infection with live pathogens remain unclear. Here, we report that the understudied caspase-6 (CASP6) contributes to the activation of the CASP11-NLRP3 inflammasome in response to infections with gram-negative bacteria. Using in vitro cellular systems with bone marrow-derived macrophages and 293T cells, we found that CASP6 can directly process CASP11 by cleaving at Asp59 and Asp285, the CASP11 auto-cleavage sites, which could contribute to the activation of CASP11 during gram-negative bacterial infection. Thus, the loss of CASP6 led to impaired CASP11-NLRP3 inflammasome activation in response to gram-negative bacteria. These results demonstrate that CASP6 potentiates activation of the CASP11-NLRP3 inflammasome to produce inflammatory cytokines during gram-negative bacterial infections.

Programmed cell death (PCD) is essential for the innate immune response, which serves as the first line of defense against pathogens. Caspases regulate PCD, immune responses, and homeostasis. Caspase-8 specifically plays multifaceted roles in PCD pathways including pyroptosis, apoptosis, and necroptosis. However, because caspase-8–deficient mice are embryonically lethal, little is known about how caspase-8 coordinates different PCD pathways under physiological conditions. Here, we report an anti-inflammatory role of caspase-8 during influenza A virus infection. We generated viable mice carrying an uncleavable version of caspase-8 (Casp8DA/DA). We demonstrated that caspase-8 autoprocessing was responsible for activating caspase-3, thereby suppressing gasdermin D–mediated pyroptosis and inflammatory cytokine release. We also found that apoptotic and pyroptotic pathways were activated at the same time during influenza A virus infection, which enabled the cell-intrinsic anti-inflammatory function of the caspase-8–caspase-3 axis. Our findings provide new insight into the immunological consequences of caspase-8–coordinated PCD cross-talk under physiological conditions.

Isocitrate dehydrogenases (IDHs) are metabolic enzymes that are mutated in several cancers, resulting in overproduction of d‐2‐hydroxyglutarate (D‐2HG). However, the signalling pathways and factors that regulate mutant IDHs or their metabolites remain elusive. Here, we report that in synchronized cells and cells treated with anti‐mitotic agents, wild‐type and mutant IDH proteins are induced maximally in G2/M. Moreover, mutant IDH1‐expressing cells arrested in G2/M harbour high D2HG levels. Genetic or pharmacological perturbation of Forkhead box protein M1 (FOXM1) abrogates the levels of IDH1 mRNA, protein and D2HG in G2/M. Conversely, overexpression of FOXM1 or hyperactive FOXM1 activates the IDH1 promoter and increases the abundance of its protein levels. In summary, our results show that in G2/M, higher D2HG levels are dependent on FOXM1‐mediated transcription of IDH1.