Impairment of DET1 causes neurological defects and lethality in mice and humans.

COP1 and DET1 are components of an E3 ubiquitin ligase that is conserved from plants to humans. Mammalian COP1 binds to DET1 and is a substrate adaptor for the CUL4A-DDB1-RBX1 RING E3 ligase. Transcription factor substrates, including c-Jun, ETV4, and ETV5, are targeted for proteasomal degradation to effect rapid transcriptional changes in response to cues such as growth factor deprivation.

Autoinhibition of dimeric NINJ1 prevents plasma membrane rupture.

Lytic cell death culminates in plasma membrane rupture, which releases large intracellular molecules to augment the inflammatory response. Plasma membrane rupture is mediated by the effector membrane protein ninjurin-1 (NINJ1), which polymerizes and ruptures the membrane via its hydrophilic face. How NINJ1 is restrained under steady-state conditions to ensure cell survival remains unknown.

N4BP1 coordinates ubiquitin-dependent crosstalk within the IκB kinase family to limit Toll-like receptor signaling and inflammation.

The ubiquitin-binding endoribonuclease N4BP1 potently suppresses cytokine production by Toll-like receptors (TLRs) that signal through the adaptor MyD88 but is inactivated via caspase-8-mediated cleavage downstream of death receptors, TLR3, or TLR4. Here, we examined the mechanism whereby N4BP1 limits inflammatory responses. In macrophages, deletion of N4BP1 prolonged activation of inflammatory gene transcription at late time points after TRIF-independent TLR activation.

Caspase cleavage of RIPK3 after Asp is dispensable for mouse embryogenesis.

The proteolytic activity of caspase-8 suppresses lethal RIPK1-, RIPK3- and MLKL-dependent necroptosis during mouse embryogenesis. Caspase-8 is reported to cleave RIPK3 in addition to the RIPK3-interacting kinase RIPK1, but whether cleavage of RIPK3 is crucial for necroptosis suppression is unclear. Here we show that caspase-8-driven cleavage of endogenous mouse RIPK3 after Asp is dependent on downstream caspase-3.

Inhibiting membrane rupture with NINJ1 antibodies limits tissue injury.

Plasma membrane rupture (PMR) in dying cells undergoing pyroptosis or apoptosis requires the cell-surface protein NINJ1. 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.

The road to death: Caspases, cleavage, and pores.

Vishva Dixit recounts his favorite discoveries after 30-plus years studying the proteins that allow infected, damaged, or obsolete cells to die.

Dying cells fan the flames of inflammation.

Inflammatory processes that recruit leukocytes to injured or infected tissues are crucial for tissue repair and the elimination of pathogens. However, excessive or chronic inflammation promotes tissue damage and disease, as in arthritis, atherosclerosis, inflammatory bowel disease, and COVID-19. Intracellular constituents released from dying cells are among the stimuli that trigger proinflammatory gene expression programs in innate immune cells.

Shigella ubiquitin ligase IpaH7.8 targets gasdermin D for degradation to prevent pyroptosis and enable infection.

The pore-forming protein gasdermin D (GSDMD) executes lytic cell death called pyroptosis to eliminate the replicative niche of intracellular pathogens. Evolution favors pathogens that circumvent this host defense mechanism. Here, we show that the Shigella ubiquitin ligase IpaH7.

Selective activation of PFKL suppresses the phagocytic oxidative burst.

In neutrophils, nicotinamide adenine dinucleotide phosphate (NADPH) generated via the pentose phosphate pathway fuels NADPH oxidase NOX2 to produce reactive oxygen species for killing invading pathogens. However, excessive NOX2 activity can exacerbate inflammation, as in acute respiratory distress syndrome (ARDS). Here, we use two unbiased chemical proteomic strategies to show that small-molecule LDC7559, or a more potent designed analog NA-11, inhibits the NOX2-dependent oxidative burst in neutrophils by activating the glycolytic enzyme phosphofructokinase-1 liver type (PFKL) and dampening flux through the pentose phosphate pathway.

NINJ1 mediates plasma membrane rupture during lytic cell death.

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 response. The underlying mechanism of PMR, however, is unknown.

Integration of innate immune signalling by caspase-8 cleavage of N4BP1.

Mutations in the death receptor FAS or its ligand FASL cause autoimmune lymphoproliferative syndrome, whereas mutations in caspase-8 or its adaptor FADD-which mediate cell death downstream of FAS and FASL-cause severe immunodeficiency in addition to autoimmune lymphoproliferative syndrome. Mouse models have corroborated a role for FADD-caspase-8 in promoting inflammatory responses, but the mechanisms that underlie immunodeficiency remain undefined. Here we identify NEDD4-binding protein 1 (N4BP1) as a suppressor of cytokine production that is cleaved and inactivated by caspase-8.

Ubiquitin Ligase COP1 Suppresses Neuroinflammation by Degrading c/EBPβ in Microglia.

Dysregulated microglia are intimately involved in neurodegeneration, including Alzheimer's disease (AD) pathogenesis, but the mechanisms controlling pathogenic microglial gene expression remain poorly understood. The transcription factor CCAAT/enhancer binding protein beta (c/EBPβ) regulates pro-inflammatory genes in microglia and is upregulated in AD. We show expression of c/EBPβ in microglia is regulated post-translationally by the ubiquitin ligase COP1 (also called RFWD2).

Classification and Nomenclature of Metacaspases and Paracaspases: No More Confusion with Caspases.

Metacaspases and paracaspases are proteases that were first identified as containing a caspase-like structural fold (Uren et al., 2000). Like caspases, meta- and paracaspases are multifunctional proteins regulating diverse biological phenomena, such as aging, immunity, proteostasis and programmed cell death.

Fiery Cell Death: Pyroptosis in the Central Nervous System.

Pyroptosis ('fiery death') is an inflammatory type of regulated cell death (RCD), which occurs downstream of inflammasome activation. Pyroptosis is mediated directly by the recently identified family of pore-forming proteins known as gasdermins, the best characterized of which is gasdermin D (GSDMD). Recent investigations implicate pyroptosis in the pathogenesis of multiple neurological diseases.

Activity of caspase-8 determines plasticity between cell death pathways.

Caspase-8 is a protease with both pro-death and pro-survival functions: it mediates apoptosis induced by death receptors such as TNFR1, and suppresses necroptosis mediated by the kinase RIPK3 and the pseudokinase MLKL. Mice that lack caspase-8 display MLKL-dependent embryonic lethality, as do mice that express catalytically inactive CASP8(C362A). Casp8Mlkl mice die during the perinatal period, whereas Casp8Mlkl mice are viable, which indicates that inactive caspase-8 also has a pro-death scaffolding function.

The RIPK4-IRF6 signalling axis safeguards epidermal differentiation and barrier function.

The integrity of the mammalian epidermis depends on a balance of proliferation and differentiation in the resident population of stem cells. The kinase RIPK4 and the transcription factor IRF6 are mutated in severe developmental syndromes in humans, and mice lacking these genes display epidermal hyperproliferation and soft-tissue fusions that result in neonatal lethality. Our understanding of how these genes control epidermal differentiation is incomplete.

Cleavage of RIPK1 by caspase-8 is crucial for limiting apoptosis and necroptosis.

The aspartate-specific cysteine protease caspase-8 suppresses necroptotic cell death mediated by RIPK3 and MLKL. Indeed, mice that lack caspase-8 die in a RIPK3- and MLKL-dependent manner during embryogenesis. In humans, caspase-8 deficiency is associated with immunodeficiency or very early onset inflammatory bowel disease.

Ubiquitin Ligases cIAP1 and cIAP2 Limit Cell Death to Prevent Inflammation.

Cellular inhibitor of apoptosis proteins cIAP1 and cIAP2 ubiquitinate nuclear factor κB (NF-κB)-inducing kinase (NIK) to suppress non-canonical NF-κB signaling and substrates such as receptor interacting protein kinase 1 (RIPK1) to promote cell survival. We investigate how these functions contribute to homeostasis by eliminating cIap2 from adult cIap1-deficient mice. cIAP1 and cIAP2 (cIAP1/2) deficiency causes rapid weight loss and inflammation, with aberrant cell death, indicated by cleaved caspases-3 and -8, prevalent in intestine and liver.

IRF2 transcriptionally induces expression for pyroptosis.

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 A forward genetic screen with -ethyl--nitrosourea (ENU)-mutagenized mice linked IRF2 to inflammasome signaling.