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Cancer is a category of diseases involving abnormal cell growth with the potential to invade other parts of the body. Chemotherapy is the most widely used first-line treatment for multiple forms of cancer. Chemotherapeutic agents act via targeting the cellular apoptotic pathway. However, cancer cells usually acquire chemoresistance, leading to poor outcomes in cancer patients. For that reason, it is imperative to discover other cell death pathways for improved cancer intervention. Pyroptosis is a new form of programmed cell death that commonly occurs upon pathogen invasion. Pyroptosis is marked by cell swelling and plasma membrane rupture, which results in the release of cytosolic contents into the extracellular space. Currently, pyroptosis is proposed to be an alternative mode of cell death in cancer treatment. Accumulating evidence shows that the key components of pyroptotic cell death pathways, including inflammasomes, gasdermins and pro-inflammatory cytokines, are involved in the initiation and progression of cancer. Interfering with pyroptotic cell death pathways may represent a promising therapeutic option for cancer management. In this review, we describe the current knowledge regarding the biological significance of pyroptotic cell death pathways in cancer pathogenesis and also discuss their potential therapeutic utility. [ABSTRACT FROM AUTHOR]

Inflammasomes are cytosolic multiprotein complexes that regulate inflammatory responses to danger stimuli and infection, and their dysregulation is associated with an increasing number of autoinflammatory diseases. In recent years, zebrafish models of human pathologies to study inflammasome function in vivo have started to emerge. Here, we discuss inflammasome research in zebrafish in light of current knowledge about mammalian inflammasomes. We summarize the evolutionary conservation of inflammasome components between zebrafish and mammals, highlighting the similarities and possible divergence in functions of these components. We present new insights into the evolution of the caspase-1 family in the teleost lineage, and how its evolutionary origin may help contextualize its functions. We also review existing infectious and non-infectious models in zebrafish in which inflammasomes have been directly implicated. Finally, we discuss the advantages of zebrafish larvae for intravital imaging of inflammasome activation and summarize available tools that will help to advance inflammasome research. [ABSTRACT FROM AUTHOR]

Pyroptosis is a form of lytic inflammatory cell death driven by inflammatory caspase‐1, caspase‐4, caspase‐5 and caspase‐11. These caspases cleave and activate the pore‐forming protein gasdermin D (GSDMD) to induce membrane damage. By contrast, apoptosis is driven by apoptotic caspase‐8 or caspase‐9 and has traditionally been classified as an immunologically silent form of cell death. Emerging evidence suggests that therapeutics designed for cancer chemotherapy or inflammatory disorders such as SMAC mimetics, TAK1 inhibitors and BH3 mimetics promote caspase‐8 or caspase‐9‐dependent inflammatory cell death and NLRP3 inflammasome activation. However, the mechanism by which caspase‐8 or caspase‐9 triggers cell lysis and NLRP3 activation is still undefined. Here, we demonstrate that during extrinsic apoptosis, caspase‐1 and caspase‐8 cleave GSDMD to promote lytic cell death. By engineering a novel Gsdmd D88A knock‐in mouse, we further demonstrate that this proinflammatory function of caspase‐8 is counteracted by caspase‐3‐dependent cleavage and inactivation of GSDMD at aspartate 88, and is essential to suppress GSDMD‐dependent cell lysis during caspase‐8‐dependent apoptosis. Lastly, we provide evidence that channel‐forming glycoprotein pannexin‐1, but not GSDMD or GSDME promotes NLRP3 inflammasome activation during caspase‐8 or caspase‐9‐dependent apoptosis. Synopsis: The apoptotic signalling cascade promotes NLRP3 inflammasome assembly by activating the channel‐forming glycoprotein, pannexin‐1. Extrinsic apoptosis promotes caspase‐1 and ‐8‐dependent GSDMD activation in parallel with caspase‐3/7‐dependent secondary necrosis.Caspase‐3 suppresses GSDMD‐dependent cell lysis during extrinsic apoptosis.GSDME is activated during extrinsic and intrinsic apoptosis, but it does not contribute to cell lysis in macrophages.NLRP3 assembly during extrinsic and intrinsic apoptosis is dependent on pannexin‐1 but not gasdermin D or E pores. [ABSTRACT FROM AUTHOR]

Caspases are an evolutionary conserved family of cysteine proteases that are centrally involved in cell death and inflammation responses. A wealth of foundational insight into the molecular mechanisms that control caspase activation has emerged in recent years. Important advancements include the identification of additional inflammasome platforms and pathways that regulate activation of inflammatory caspases; the discovery of gasdermin D as the effector of pyroptosis and interleukin (IL)-1 and IL-18 secretion; and the existence of substantial crosstalk between inflammatory and apoptotic initiator caspases. A better understanding of the mechanisms regulating caspase activation has supported initial efforts to modulate dysfunctional cell death and inflammation pathways in a suite of communicable, inflammatory, malignant, metabolic, and neurodegenerative diseases. Here, we review current understanding of caspase biology with a prime focus on the inflammatory caspases and outline important topics for future experimentation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Neutrophil granule serine proteases contribute to immune responses through cleavage of microbial toxins and structural proteins. They induce tissue damage and modulate inflammation if levels exceed their inhibitors. Here, we show that the intracellular protease inhibitors Serpinb1a and Serpinb6a contribute to monocyte and neutrophil survival in steady-state and inflammatory settings by inhibiting cathepsin G (CatG). Importantly, we found that CatG efficiently cleaved gasdermin D (GSDMD) to generate the signature N-terminal domain GSDMD-p30 known to induce pyroptosis. Yet GSDMD deletion did not rescue neutrophil survival in Sb1a.Sb6a -/- mice. Furthermore, Sb1a.Sb6a -/- mice released high levels of pro-inflammatory cytokines upon endotoxin challenge in vivo in a CatG-dependent manner. Canonical inflammasome activation in Sb1a.Sb6a -/- macrophages showed increased IL-1β release that was dependent on CatG and GSDMD. Together, our findings demonstrate that cytosolic serpins expressed in myeloid cells prevent cell death and regulate inflammatory responses by inhibiting CatG and alternative activation of GSDMD., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

The cholesterol-dependent cytolysin (CDC) genes are present in bacterial species that span terrestrial, vertebrate, and invertebrate niches, which suggests that they have evolved to function under widely different environmental conditions. Using a combination of biophysical and crystallographic approaches, we reveal that the relative stability of an intramolecular interface in the archetype CDC perfringolysin O (PFO) plays a central role in regulating its pore-forming properties. The disruption of this interface allows the formation of the membrane spanning β-barrel pore in all CDCs. We show here that the relative strength of the stabilizing forces at this interface directly impacts the energy barrier posed by the transition state for pore formation, as reflected in the Arrhenius activation energy (E a ) for pore formation. This change directly impacts the kinetics and temperature dependence of pore formation. We further show that the interface structure in a CDC from a terrestrial species enables it to function efficiently across a wide range of temperatures by minimizing changes in the strength of the transition state barrier to pore formation. These studies establish a paradigm that CDCs, and possibly other β-barrel pore-forming proteins/toxins, can evolve significantly different pore-forming properties by altering the stability of this transitional interface, which impacts the kinetic parameters and temperature dependence of pore formation. IMPORTANCE The cholesterol-dependent cytolysins (CDCs) are the archetype for the superfamily of oligomeric pore-forming proteins that includes the membrane attack complex/perforin (MACPF) family of immune defense proteins and the stonefish venom toxins (SNTX). The CDC/MACPF/SNTX family exhibits a common protein fold, which forms a membrane-spanning β-barrel pore. We show that changing the relative stability of an extensive intramolecular interface within this fold, which is necessarily disrupted to form the large β-barrel pore, dramatically alters the kinetic and temperature-dependent properties of CDC pore formation. These studies show that the CDCs and other members of the CDC/MACPF/SNTX superfamily have the capacity to significantly alter their pore-forming properties to function under widely different environmental conditions encountered by these species., (Copyright © 2019 Wade et al.)

In this Annual Review Issue of The Journal of Pathology, we present 15 invited reviews on topical aspects of pathology, ranging from the impacts of the microbiome in human disease through mechanisms of cell death and autophagy to recent advances in immunity and the uses of genomics for understanding, classifying and treating human cancers. Each of the reviews is authored by experts in their fields and our intention is to provide comprehensive updates in specific areas of pathology in which there has been considerable recent progress. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

The gasdermin (GSDM) family consists of gasdermin A (GSDMA), B (GSDMB), C (GSDMC), D (GSDMD), E or DNFA5 (GSDME), and DFNB59 in human. Expressed in the skin, gastrointestinal tract, and various immune cells, GSDMs mediate homeostasis and inflammation upon activation by caspases and unknown proteases. In particular, GSDMD is activated by inflammasome-activated caspases-1/-4/-5/-11 as well as a caspase-8-mediated pathway during Yersinia infection. These caspases cleave GSDMD to release its functional N-terminal fragment (GSDMD-NT) from its auto-inhibitory C-terminal fragment (GSDMD-CT). GSDMD-NTs bind to acid lipids in mammalian cell membranes and bacterial membranes, oligomerize, and insert into the membranes to form large transmembrane pores. Consequently, cellular contents including inflammatory cytokines are released and cells can undergo pyroptosis, a highly inflammatory form of cell death. In this chapter, we summarize recent research findings and present experimental procedures to obtain pure recombinant GSDMs for biochemical studies. We highlight a liposome-based assay that yields robust fluorescence signals for characterizing GSDM activities in vitro and may be applicable to other pore-forming proteins and ion channels in general., (© 2019 Elsevier Inc. All rights reserved.)

During the progression of necroptosis and pyroptosis, the plasma membrane will become permeabilized through the activation of mixed lineage kinase domain like pseudokinase (MLKL) or gasdermin D (GSDMD), respectively. Recently, the progression of apoptotic cells into secondary necrotic cells following membrane lysis was shown to be regulated by gasdermin E (GSDME, or DFNA5), a process dependent on caspase 3-mediated cleavage of GSDME. Notably, GSDME was also proposed to negatively regulate the disassembly of apoptotic cells into smaller membrane-bound vesicles known as apoptotic bodies (ApoBDs) by promoting earlier onset of membrane permeabilisation. The presence of a process downstream of caspase 3 that would actively drive cell lysis and limit cell disassembly during apoptosis is somewhat surprising as this could favor the release of proinflammatory intracellular contents and hinder efficient clearance of apoptotic materials. In contrast to the latter studies, we present here that GSDME is not involved in regulating secondary necrosis in human T cells and monocytes, and also unlikely in epithelial cells. Furthermore, GSDME is evidently not a negative regulator of apoptotic cell disassembly in our cell models. Thus, the function of GSDME in regulating membrane permeabilization and cell disassembly during apoptosis may be more limited.

Intrinsic apoptosis resulting from BAX/BAK-mediated mitochondrial membrane damage is regarded as immunologically silent. We show here that in macrophages, BAX/BAK activation results in inhibitor of apoptosis (IAP) protein degradation to promote caspase-8-mediated activation of IL-1β. Furthermore, BAX/BAK signaling induces a parallel pathway to NLRP3 inflammasome-mediated caspase-1-dependent IL-1β maturation that requires potassium efflux. Remarkably, following BAX/BAK activation, the apoptotic executioner caspases, caspase-3 and -7, act upstream of both caspase-8 and NLRP3-induced IL-1β maturation and secretion. Conversely, the pyroptotic cell death effectors gasdermin D and gasdermin E are not essential for BAX/BAK-induced IL-1β release. These findings highlight that innate immune cells undergoing BAX/BAK-mediated apoptosis have the capacity to generate pro-inflammatory signals and provide an explanation as to why IL-1β activation is often associated with cellular stress, such as during chemotherapy., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Renal tubules represent an intercellular unit and function as a syncytium. When acute tubular necrosis was first visualized to occur through a process of synchronized regulated necrosis (SRN) in handpicked primary renal tubules, it became obvious that SRN actually promotes nephron loss. This realization adds to our current understanding of acute kidney injury (AKI)-chronic kidney disease (CKD) transition and argues for the prevention of AKI episodes to prevent CKD progression. Because SRN is triggered by necroptosis and executed by ferroptosis, 2 recently identified signaling pathways of regulated necrosis, a combination therapy employing necrostatins and ferrostatins may be beneficial for protection against nephron loss. Clinical trials in AKI and during the process of kidney transplantation are now required to prevent SRN. Additionally, necrotic cell death drives autoimmunity and necroinflammation and therefore represents a therapeutic target even for the prevention of antibody-mediated rejection of allografts years after the transplantation process., (© 2018 S. Karger AG, Basel.)

Inflammasomes activate the protease caspase-1, which cleaves interleukin-1β and interleukin-18 to generate the mature cytokines and controls their secretion and a form of inflammatory cell death called pyroptosis. By generating mice expressing enzymatically inactive caspase-1 C284A , we provide genetic evidence that caspase-1 protease activity is required for canonical IL-1 secretion, pyroptosis, and inflammasome-mediated immunity. In caspase-1-deficient cells, caspase-8 can be activated at the inflammasome. Using mice either lacking the pyroptosis effector gasdermin D (GSDMD) or expressing caspase-1 C284A , we found that GSDMD-dependent pyroptosis prevented caspase-8 activation at the inflammasome. In the absence of GSDMD-dependent pyroptosis, the inflammasome engaged a delayed, alternative form of lytic cell death that was accompanied by the release of large amounts of mature IL-1 and contributed to host protection. Features of this cell death modality distinguished it from apoptosis, suggesting it may represent a distinct form of pro-inflammatory regulated necrosis., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)

Pyroptosis is a lytic type of programmed cell death that was traditionally associated with the involvement of inflammatory caspases, such as caspase-1. These inflammatory caspases are activated within multi-protein complexes called inflammasomes that are assembled in response to invading pathogens and/or danger signals. Pyroptotic cell death was suggested to evolve via the formation of pores in the plasma membrane, but the exact mechanism underlying the formation of these pores remained unclear. Recently, gasdermin D, a member of the gasdermin protein family was identified as a caspase substrate and essential effector of pyroptosis, being identified as the protagonist of membrane pore formation. Gasdermins have emerged as a family of new class of cell death inducers, but many questions remain unanswered. Here, we present an overview of recent work being done in the area of programmed cell death and the latest evidence regarding the role and participation of gasdermin D as an effector of pyroptosis., (Copyright © 2017 Chang Gung University. Published by Elsevier B.V. All rights reserved.)

Immune cells and skin and mucosal epithelial cells recognize invasive microbes and other signs of danger to sound alarms that recruit responder cells and initiate an immediate "innate" immune response. An especially powerful alarm is triggered by cytosolic sensors of invasive infection that assemble into multimolecular complexes, called inflammasomes, that activate the inflammatory caspases, leading to maturation and secretion of proinflammatory cytokines and pyroptosis, an inflammatory death of the infected cell. Work in the past year has defined the molecular basis of pyroptosis. Activated inflammatory caspases cleave Gasdermin D (GSDMD), a cytosolic protein in immune antigen-presenting cells and epithelia. Cleavage separates the autoinhibitory C-terminal fragment from the active N-terminal fragment, which moves to the cell membrane, binds to lipids on the inside of the cell membrane, and oligomerizes to form membrane pores that disrupt cell membrane integrity, causing death and leakage of small molecules, including the proinflammatory cytokines and GSDMD itself. GSDMD also binds to cardiolipin on bacterial membranes and kills the very bacteria that activate the inflammasome. GSDMD belongs to a family of poorly studied gasdermins, expressed in the skin and mucosa, which can also form membrane pores. Spontaneous mutations that disrupt the binding of the N- and C-terminal domains of other gasdermins are associated with alopecia and asthma. Here, we review recent studies that identified the roles of the inflammasome, inflammatory caspases, and GSDMD in pyroptosis and highlight some of the outstanding questions about their roles in innate immunity, control of infection, and sepsis., (© 2017 Elsevier Inc. All rights reserved.)

In the previous issue of Biochemical Journal, Shi et al. [(2015) 468, 325-336] report that Gasdermin (Gsdm) family proteins regulate autophagy activity, which is counter-balanced by the opposite functions of well-conserved N- and C-terminal domains of the proteins. The Gsdm family was originally identified as the causative gene of dominant skin mutations exhibiting alopecia. Each member of the Gsdm gene family shows characteristic expression patterns in the epithelium, which is tissue and differentiation stage-specific. Previous phenotype analyses of mutant mice, biochemical analyses of proteins and genome-wide association studies showed that the Gsdm gene family might be involved in epithelial cell development, apoptosis, inflammation, carcinogenesis and immune-related diseases. To date, however, their molecular function(s) remain unclear. Shi et al. found that mutations in the C-terminal domain of Gsdma3, a member of the Gsdm family, induce autophagy. Further studies revealed that the wild-type N-terminal domain has pro-autophagic activity and that the C-terminal domain conversely inhibits this N-terminal function. These opposite functions of the two domains were also observed in other Gsdm family members. Thus, their study provides a new insight into the function of Gsdm genes in epithelial cell lineage, causality of cancers and immune-related diseases including childhood-onset asthma., (© 2015 Authors; published by Portland Press Limited.)