Caspase-10 Negatively Regulates Caspase-8-Mediated Cell Death, Switching the Response to CD95L in Favor of NF-κB Activation and Cell Survival

Comprehensive molecular biology and metabolomics analysis reveal the changes on muscle quality of Megalobrama amblycephala exposure to ammonia nitrogen during transportation

This study comprehensively investigated the effects of different ammonia nitrogen models during transportation on the energy metabolism, redox system, apoptosis, and changes in muscle quality of fish using molecular biology and metabolomics. Exposure to ammonia nitrogen caused intensive stress response as evidenced by alteration on the levels of biochemical indicators (cortisol, glucose, urea nitrogen, alanine transaminase, lactic dehydrogenase, superoxide dismutase, and glutathione peroxidase) and structural disruption of organs (including gill, cephalic kidney, kidney, and liver). As a result of the ammonia nitrogen stress, the redox system became imbalance, leading to disturbance in energy metabolism primarily through the pathways of D-amino acid metabolism, alanine/aspartate/glutamate metabolism, and purine metabolism. Additionally, apoptosis occurred following stress, regulated by FoxO, mTOR, NF-κB, and PI3K/AKT signaling pathways. Besides redox system, energy metabolism, and apoptosis, the change of muscle quality were also influenced by ammonia nitrogen concentration and exposure duration. Drip loss increased with higher ammonia nitrogen concentrations and longer exposure time, while shear force value showed an inverse trend. Although no significant changes were observed in a* and b* values following ammonia nitrogen exposure, the highest W and L* values were found in the low-concentration groups. The correlation of spearman indicates the changes in muscle quality, including drip loss, shear force, and color, induced by ammonia nitrogen during transportation was attributed to the interplay of redox system, energy metabolism, and apoptosis.

Caspases: structural and molecular mechanisms and functions in cell death, innate immunity, and disease

Caspases are critical regulators of cell death, development, innate immunity, host defense, and disease. Upon detection of pathogens, damage-associated molecular patterns, cytokines, or other homeostatic disruptions, innate immune sensors, such as NLRs, activate caspases to initiate distinct regulated cell death pathways, including non-lytic (apoptosis) and innate immune lytic (pyroptosis and PANoptosis) pathways. These cell death pathways are driven by specific caspases and distinguished by their unique molecular mechanisms, supramolecular complexes, and enzymatic properties. Traditionally, caspases are classified as either apoptotic (caspase-2, -3, -6, -7, -8, -9, and -10) or inflammatory (caspase-1, -4, -5, and -11). However, extensive data from the past decades have shown that apoptotic caspases can also drive lytic inflammatory cell death downstream of innate immune sensing and inflammatory responses, such as in the case of caspase-3, -6, -7, and -8. Therefore, more inclusive classification systems based on function, substrate specificity, or the presence of pro-domains have been proposed to better reflect the multifaceted roles of caspases. In this review, we categorize caspases into CARD-, DED-, and short/no pro-domain-containing groups and examine their critical functions in innate immunity and cell death, along with their structural and molecular mechanisms, including active site/exosite properties and substrates. Additionally, we highlight the emerging roles of caspases in cellular homeostasis and therapeutic targeting. Given the clinical relevance of caspases across multiple diseases, improved understanding of these proteins and their structure-function relationships is critical for developing effective treatment strategies.

FAS mediates apoptosis, inflammation, and treatment of pathogen infection

The FAS cell surface death receptor, a member of the tumor necrosis factor receptor family, activates both apoptotic and non-apoptotic signaling upon interaction with its ligand FASL. It is critical in cell migration, invasion, immune responses, and carcinogenesis. Pathogen infection can influence host cells' behavior by modulating the FAS/FASL pathway, thereby influencing disease progression. Understanding the role of FAS signaling in the context of pathogen interactions is therefore crucial. This review examines FAS-mediated apoptotic and non-apoptotic signaling pathways, with particular emphasis on the mechanisms of apoptosis and inflammation induced by bacterial and viral infections. Additionally, it highlights therapeutic strategies, including drug, cytokine, antibody, and FASL recombinant protein therapies, providing new directions for treating pathogenic infections and cancers, as well as insights into developing novel therapeutic approaches.

An activation-based high throughput screen identifies caspase-10 inhibitors

Caspases are a family of highly homologous cysteine proteases that play critical roles in inflammation and apoptosis. Small molecule inhibitors are useful tools for studying caspase biology, complementary to genetic approaches. However, achieving inhibitor selectivity for individual members of this highly homologous enzyme family remains a major challenge in developing such tool compounds. Prior studies have revealed that one strategy to tackle this selectivity gap is to target the precursor or zymogen forms of individual caspases, which share reduced structural homology when compared to active proteases. To establish a screening assay that favors the discovery of zymogen-directed caspase-10 selective inhibitors, we engineered a low-background and high-activity tobacco etch virus (TEV)-activated caspase-10 protein. We then subjected this turn-on protease to a high-throughput screen of approximately 100 000 compounds, with an average Z' value of 0.58 across all plates analyzed. Counter screening, including against TEV protease, delineated bona fide procaspase-10 inhibitors. Confirmatory studies identified a class of thiadiazine-containing compounds that undergo isomerization and oxidation to generate cysteine-reactive compounds with caspase-10 inhibitory activity. In parallel, mode-of-action studies revealed that pifithrin-μ (PFTμ), a reported TP53 inhibitor, also functions as a promiscuous caspase inhibitor. Both inhibitor classes showed preferential zymogen inhibition. Given the generalized utility of activation assays, we expect our screening platform to have widespread applications in identifying state-specific protease inhibitors.

Porcine epidemic diarrhea coronavirus infection activates caspase-8 to enhance innate immunity by blocking CYLD-mediated deubiquitination of RIG-I

Caspase-8 is best known as an initiator caspase that induces apoptosis. However, recent studies suggest that caspase-8 can modulate innate antiviral immunity in a context-dependent manner. Porcine epidemic diarrhea virus (PEDV), a coronavirus that rapidly replicates in porcine intestinal epithelial cells, triggers apoptosis, in part through caspase-8 activation. In this study, we investigated the role of caspase-8 activation in regulating antiviral responses in IPEC-DQ cells, a porcine intestinal epithelial cell line. We found that inhibition of caspase-8 activity using Z-Vad (a pan-caspase inhibitor) and Z-IETD (a caspase-8-specific inhibitor) reduced PEDV-induced phosphorylation of TBK1, IRF3, and the p65 subunit of NF-κB, and inhibited the nuclear translocation of p65 and IRF3. Similarly, caspase-8 knockout inhibited PEDV-induced phosphorylation of p65, IRF3, and TBK1, as well as RIG-I expression and IRF3- and NF-κB-driven luciferase activity. Notably, inhibition of caspase-3 with Z-DEVD had no effect on PEDV-induced TBK1 and IRF3 phosphorylation. Mechanistically, caspase-8 cleaves and inactivates CYLD, a deubiquitinase that removes K63-linked ubiquitin from RIG-I. Caspase-8 knockout and Z-Vad blocked PEDV-induced RIG-I K63 ubiquitination. While Z-Vad inhibited cleavage of the viral N protein and promoted PEDV replication, neither Z-IETD nor caspase-8 knockout affected N protein cleavage or virus replication. Our results suggest that caspase-8 activation enhances innate antiviral immunity in PEDV-infected intestinal epithelial cells without affecting viral replication, likely due to viral manipulation of IFN signaling.

Comprehensive Pan-cancer Analysis Revealed CASP10 As a Promising Biomarker For Diverse Tumor Types

We aimed to explore the comprehensive cancer landscape of Caspase-10 (CASP10). CASP10, a member of the caspase family, is located at the human chromosome locus 2q33-34. Studies have suggested its potential role in the development of certain cancers. To evaluate CASP10 expression in normal and pan-cancer tissues, we integrated data from The Cancer Genome Atlas (TCGA), GEO, Human Protein Atlas (HPA), and UALCAN databases. The diagnostic and prognostic significance of CASP10 was analyzed using Receiver Operating Characteristic (ROC), Cox regression, and Kaplan-Meier analysis. Correlations of CASP10 with clinical parameters were assessed via the Wilcoxon test, Kruskal-Wallis test, and logistic regression analysis. Genomic variations were explored with cBioPortal, GSCALite database, and UALCAN databases. LinkedOmics database was used to detect the function of CASP10 in pan-cancer. Interactions between CASP10 and the Tumor Immune Microenvironment (TIME) were investigated using TISIDB, TIMER2, and TISCH databases. The GSCALite database was utilized to assess the sensitivity of CASP10 to small-molecule drugs. In addition, Western Blotting (WB) was employed to detect the expression of the CASP10 in our clinical Liver Hepatocellular Carcinoma (LIHC) and Stomach Adenocarcinoma (STAD) cohorts. The transcription and protein expression of CASP10 significantly differ across cancer types, marking it as a biomarker for diagnosis and prognosis. Its expression correlated with certain clinical characteristics such as histological types and Alpha-Fetoprotein (AFP) levels. CASP10 gene exhibited a 2% alteration frequency across pan-cancer patients, with significant SNV and CNV profiles, and decreased methylation levels. CASP10 was closely related to the Nuclear Factor-κappa B (NF-κB), TNF, cell cycle, and JAK-STAT signal pathways. CASP10 showed correlation with immune components in the tumor microenvironment, including lymphocytes, immune stimulators, immune inhibitors, MHC molecules, chemokines, receptors, and Cancer-Associated Fibroblasts (CAFs). Importantly, CASP10 could predict the sensitivity of diverse anti-cancer drugs. Finally, WB analysis validated the overexpression of CASP10 in LIHC and STAD tissues. Our comprehensive bioinformatic analysis reveal the function of CASP10 on the diagnosis, prognosis, and progression of diverse cancer types.

Targeting caspase-8: a new strategy for combating hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents the most prevalent form of primary liver cancer and has a high mortality rate. Caspase-8 plays a pivotal role in an array of cellular signaling pathways and is essential for the governance of programmed cell death mechanisms, inflammatory responses, and the dynamics of the tumor microenvironment. Dysregulation of caspase-8 is intricately linked to the complex biological underpinnings of HCC. In this manuscript, we provide a comprehensive review of the regulatory roles of caspase-8 in apoptosis, necroptosis, pyroptosis, and PANoptosis, as well as its impact on inflammatory reactions and the intricate interplay with critical immune cells within the tumor microenvironment, such as tumor-associated macrophages, T cells, natural killer cells, and dendritic cells. Furthermore, we emphasize how caspase-8 plays pivotal roles in the development, progression, and drug resistance observed in HCC, and explore the potential of targeting caspase-8 as a promising strategy for HCC treatment.

Comprehensive Analysis of Immune Infiltration and Key Genes in Peri-Implantitis Using Bioinformatics and Molecular Biology Approaches

BACKGROUND Peri-implantitis is the main cause of failure of implant treatment, and there is little research on its molecular mechanism. This study aimed to identify key biomarkers and immune infiltration of peri-implantitis using a bioinformatics method. MATERIAL AND METHODS Three Gene Ontology (GO) gene expression profiles were selected from the Gene Expression Omnibus. Differentially expressed genes (DEGs) were identified by the LIMMA package, and functional correlations of DEGs were analyzed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. Information on immune-related genes was obtained from ImmPort (https://www.immport.org) and InnateDB (http://www.innatedb.com). Immune-related DEGs were screened by least absolute shrinkage and selection operator (LASSO) and support vector machine-recursive feature elimination (SVM-RFE). The single-sample Gene Set Enrichment Analysis algorithm was used to analyze immune cell infiltration in gingival tissue between peri-implantitis and normal controls. Finally, results of bioinformatics analysis were verified by qPCR. RESULTS A total of 398 DEGs were identified, of which 96 were immune-related. Enrichment analysis showed these genes were enriched in inflammatory response, leucocyte chemotaxis, immune response-regulating signaling pathway, and cell activation. Seven key genes were selected by LASSO and SVM-RFE. Receiver operating characteristic curve results showed these genes had excellent diagnostic efficacy. Results of qPCR showed significant differences in the expression of these genes. CONCLUSIONS Differences in key genes and immune infiltration between peri-implantitis and gingival tissues of normal controls may provide new insights into the development of peri-implantitis. Elucidating the difference in immune infiltration between peri-implantitis tissues and normal tissues will help to understand the development of peri-implantitis.

The Crosstalk of Apoptotic and Non-Apoptotic Signaling in CD95 System

The mechanisms of CD95 (Fas/APO-1)-mediated extrinsic apoptotic pathway in cancer cells have been extensively studied. The majority of human cells express CD95, but not all these cells can induce extrinsic apoptosis. Accumulating evidence has shown that CD95 is a multifunctional protein, and its stimulation can also elicit non-apoptotic or even survival signals. It has become clear that under certain cellular contexts, due to the various checkpoints, CD95 activation can trigger both apoptotic and non-apoptotic signals. The crosstalk of death and survival signals may occur at different levels of signal transduction. The strength of the CD95 stimulation, initial levels of anti-apoptotic proteins, and posttranslational modifications of the core DISC components have been proposed to be the most important factors in the life/death decisions at CD95. Successful therapeutic targeting of CD95 signaling pathways will require a better understanding of the crosstalk between CD95-induced apoptotic and cell survival pathways. In this review, in order to gain a systematic understanding of the crosstalk between CD95-mediated apoptosis and non-apoptotic signaling, we will discuss these issues in a step-by-step way.

Strong activation of p53 by actinomycin D and nutlin-3a overcomes the resistance of cancer cells to the pro-apoptotic activity of the FAS ligand

The FAS ligand (FASLG) is expressed on lymphocytes, which employ it to activate death receptors on target cells. Cancer cells are generally resistant to apoptosis triggered by FASLG. In this work, we found a way to circumvent this resistance by treatment with actinomycin D (ActD) and nutlin-3a (Nut3a). We selected this drug combination based on our transcriptomic data showing strong activation of proapoptotic genes, including those for receptor-mediated apoptosis, in cells exposed to actinomycin D and nutlin-3a. To test our hypothesis, we pre-exposed cancer cell lines to this drug combination for 45 h and then treated them with recombinant FASLG. This almost instantaneously killed most cells. Actinomycin D and nutlin-3a strongly cooperated in the sensitization because the effect of the drugs acting solo was not as spectacular as the drug combination, which together with FASLG killed more than 99% of cells. Based on the caspase activation pattern (caspase-8, caspase-9, caspase-10), we conclude that both extrinsic and intrinsic pro-apoptotic pathways were engaged. In engineered p53-deficient cells, this pro-apoptotic effect was completely abrogated. Therefore, the combination of ActD + Nut3a activates p53 in an extraordinary way, which overcomes the resistance of cancer cells to apoptosis triggered by FASLG. Interestingly, other combinations of drugs, e.g., etoposide + nutlin-3a, actinomycin D + RG7112, and actinomycin D + idasanutlin had a similar effect. Moreover, normal human fibroblasts are less sensitive to death induced by ActD + Nut3a + FASLG. Our findings create the opportunity to revive the abandoned attempts of cancer immunotherapy employing the recombinant FAS ligand.

Novel strategy for activating gene expression through triplex DNA formation targeting epigenetically suppressed genes

Triplex DNA formation is a useful genomic targeting tool that is expected to have a wide range of applications, including the antigene method; however, there are fundamental limitations in its forming sequence. We recently extended the triplex DNA-forming sequence to methylated DNA sequences containing 5mCG base pairs by developing guanidino-dN, which is capable of recognizing a 5mCG base pair with high affinity. We herein investigated the effect of triplex DNA formation using TFOs with guanidino-dN on methylated DNA sequences at the promoter of the RASSF1A gene, whose expression is epigenetically suppressed by DNA methylation in MCF-7 cells, on gene expression. Interestingly, triplex DNA formation increased the expression of the RASSF1A gene at the transcript and protein levels. Furthermore, RASSF1A-activated MCF-7 cells exhibited cell growth suppressing activity. Changes in the expression of various genes associated with the promotion of apoptosis and breast cancer survival accompanied the activation of RASSF1A in cells exhibited antiproliferative activity. These results suggest the potential of increases in gene expression through triplex DNA formation as a new genomic targeting tool.

Influenza A virus infection activates caspase-8 to enhance innate antiviral immunity by cleaving CYLD and blocking TAK1 and RIG-I deubiquitination

Caspase-8, an aspartate-specific cysteine protease that primarily functions as an initiator caspase to induce apoptosis, can downregulate innate immunity in part by cleaving RIPK1 and IRF3. However, patients with caspase-8 mutations or deficiency develop immunodeficiency and are prone to viral infections. The molecular mechanism underlying this controversy remains unknown. Whether caspase-8 enhances or suppresses antiviral responses against influenza A virus (IAV) infection remains to be determined. Here, we report that caspase-8 is readily activated in A549 and NL20 cells infected with the H5N1, H5N6, and H1N1 subtypes of IAV. Surprisingly, caspase-8 deficiency and two caspase-8 inhibitors, Z-VAD and Z-IETD, do not enhance but rather downregulate antiviral innate immunity, as evidenced by decreased TBK1, IRF3, IκBα, and p65 phosphorylation, decreased IL-6, IFN-β, MX1, and ISG15 gene expression; and decreased IFN-β production but increased virus replication. Mechanistically, caspase-8 cleaves and inactivates CYLD, a tumor suppressor that functions as a deubiquitinase. Caspase-8 inhibition suppresses CYLD cleavage, RIG-I and TAK1 ubiquitination, and innate immune signaling. In contrast, CYLD deficiency enhances IAV-induced RIG-I and TAK1 ubiquitination and innate antiviral immunity. Neither caspase-3 deficiency nor treatment with its inhibitor Z-DEVD affects CYLD cleavage or antiviral innate immunity. Our study provides evidence that caspase-8 activation in two human airway epithelial cell lines does not silence but rather enhances innate immunity by inactivating CYLD.

Effects of the nerve agent VX on hiPSC-derived motor neurons

Poisoning with the organophosphorus nerve agent VX can be life-threatening due to limitations of the standard therapy with atropine and oximes. To date, the underlying pathomechanism of VX affecting the neuromuscular junction has not been fully elucidated structurally. Results of recent studies investigating the effects of VX were obtained from cells of animal origin or immortalized cell lines limiting their translation to humans. To overcome this limitation, motor neurons (MN) of this study were differentiated from in-house feeder- and integration-free-derived human-induced pluripotent stem cells (hiPSC) by application of standardized and antibiotic-free differentiation media with the aim to mimic human embryogenesis as closely as possible. For testing VX sensitivity, MN were initially exposed once to 400 µM, 600 µM, 800 µM, or 1000 µM VX and cultured for 5 days followed by analysis of changes in viability and neurite outgrowth as well as at the gene and protein level using µLC-ESI MS/HR MS, XTT, IncuCyte, qRT-PCR, and Western Blot. For the first time, VX was shown to trigger neuronal cell death and decline in neurite outgrowth in hiPSC-derived MN in a time- and concentration-dependent manner involving the activation of the intrinsic as well as the extrinsic pathway of apoptosis. Consistent with this, MN morphology and neurite network were altered time and concentration-dependently. Thus, MN represent a valuable tool for further investigation of the pathomechanism after VX exposure. These findings might set the course for the development of a promising human neuromuscular test model and patient-specific therapies in the future.

Crosstalk between purinergic receptor P2Y11 and chemokine receptor CXCR7 is regulated by CXCR4 in human macrophages

P2Y11 is a G protein-coupled ATP receptor that activates IL-1 receptor (IL-1R) in a cyclic AMP dependent manner. In human macrophages, P2Y11/IL-1R crosstalk with CCL20 as a prime target is controlled by phosphodiesterase 4 (PDE4), which mediates breakdown of cyclic AMP. Here, we used gene expression analysis to identify activation of CXCR4 and CXCR7 as a hallmark of P2Y11 signaling. We found that PDE4 inhibition with rolipram boosts P2Y11/IL-1R-induced upregulation of CXCR7 expression and CCL20 production in an epidermal growth factor receptor dependent manner. Using an astrocytoma cell line, naturally expressing CXCR7 but lacking CXCR4, P2Y11/IL-1R activation effectively induced and CXCR7 agonist TC14012 enhanced CCL20 production even in the absence of PDE4 inhibition. Moreover, CXCR7 depletion by RNA interference suppressed CCL20 production. In macrophages, the simultaneous activation of P2Y11 and CXCR7 by their respective agonists was sufficient to induce CCL20 production with no need of PDE4 inhibition, as CXCR7 activation increased its own and eliminated CXCR4 expression. Finally, analysis of multiple CCL chemokines in the macrophage secretome revealed that CXCR4 inactivation and CXCR7 activation selectively enhanced P2Y11/IL-1R-mediated secretion of CCL20. Altogether, our data establish CXCR7 as an integral component of the P2Y11/IL-1R-initiated signaling cascade and CXCR4-associated PDE4 as a regulatory checkpoint.

Significance of TRAIL/Apo-2 ligand and its death receptors in apoptosis and necroptosis signalling: Implications for cancer-targeted therapeutics

The human immune defensesystem routinely expresses the tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), which is the most prevalent element for antitumor immunity. TRAIL associates with its death receptors (DRs), DR4 (TRAIL-R1), and DR5 (TRAIL-R2), in cancer cells to initiate the intracellular apoptosis cascade. Accordingly, numerous academic institutions and pharmaceutical companies havetried to exploreTRAIL's capacity to kill tumourcells by producing recombinant versions of it (rhTRAIL) or TRAIL receptor agonists (TRAs) [monoclonal antibody (mAb), synthetic and natural compounds, etc.] and molecules that sensitize TRAIL signalling pathway for therapeutic applications. Recently, several microRNAs (miRs) have been found to activate or inhibit death receptor signalling. Therefore, pharmacological regulation of these miRs may activate or resensitize the TRAIL DRs signal, and this is a novel approach for developing anticancer therapeutics. In this article, we will discuss TRAIL and its receptors and molecular pathways by which it induces various cell death events. We will unravel potential innovative applications of TRAIL-based therapeutics, and other investigated therapeutics targeting TRAIL-DRs and summarize the current preclinical pharmacological studies and clinical trials. Moreover, we will also emphasizea few situations where future efforts may be addressed to modulate the TRAIL signalling pathway.

Control of Cell Death in Health and Disease

Apoptosis, necroptosis, and pyroptosis are genetically programmed cell death mechanisms that eliminate obsolete, damaged, infected, and self-reactive cells. Apoptosis fragments cells in a manner that limits immune cell activation, whereas the lytic death programs of necroptosis and pyroptosis release proinflammatory intracellular contents. Apoptosis fine-tunes tissue architecture during mammalian development, promotes tissue homeostasis, and is crucial for averting cancer and autoimmunity. All three cell death mechanisms are deployed to thwart the spread of pathogens. Disabling regulators of cell death signaling in mice has revealed how excessive cell death can fuel acute or chronic inflammation. Here we review strategies for modulating cell death in the context of disease. For example, BCL-2 inhibitor venetoclax, an inducer of apoptosis, is approved for the treatment of certain hematologic malignancies. By contrast, inhibition of RIPK1, NLRP3, GSDMD, or NINJ1 to limit proinflammatory cell death and/or the release of large proinflammatory molecules from dying cells may benefit patients with inflammatory diseases.

cFLIPL acts as a suppressor of TRAIL- and Fas-initiated inflammation by inhibiting assembly of caspase-8/FADD/RIPK1 NF-κB-activating complexes

TRAIL and FasL are potent inducers of apoptosis but can also promote inflammation through assembly of cytoplasmic caspase-8/FADD/RIPK1 (FADDosome) complexes, wherein caspase-8 acts as a scaffold to drive FADD/RIPK1-mediated nuclear factor κB (NF-κB) activation. cFLIP is also recruited to FADDosomes and restricts caspase-8 activity and apoptosis, but whether cFLIP also regulates death receptor-initiated inflammation is unclear. Here, we show that silencing or deletion of cFLIP leads to robustly enhanced Fas-, TRAIL-, or TLR3-induced inflammatory cytokine production, which can be uncoupled from the effects of cFLIP on caspase-8 activation and apoptosis. Mechanistically, cFLIPL suppresses Fas- or TRAIL-initiated NF-κB activation through inhibiting the assembly of caspase-8/FADD/RIPK1 FADDosome complexes, due to the low affinity of cFLIPL for FADD. Consequently, increased cFLIPL occupancy of FADDosomes diminishes recruitment of FADD/RIPK1 to caspase-8, thereby suppressing NF-κB activation and inflammatory cytokine production downstream. Thus, cFLIP acts as a dual suppressor of apoptosis and inflammation via distinct modes of action.

Regulation of apoptosis by ubiquitination in liver cancer

Apoptosis is a programmed cell death process critical to cell development and tissue homeostasis in multicellular organisms. Defective apoptosis is a crucial step in the malignant transformation of cells, including hepatocellular carcinoma (HCC), where the apoptosis rate is higher than in normal liver tissues. Ubiquitination, a post-translational modification process, plays a precise role in regulating the formation and function of different death-signaling complexes, including those involved in apoptosis. Aberrant expression of E3 ubiquitin ligases (E3s) in liver cancer (LC), such as cellular inhibitors of apoptosis proteins (cIAPs), X chromosome-linked IAP (XIAP), and linear ubiquitin chain assembly complex (LUBAC), can contribute to HCC development by promoting cell survival and inhibiting apoptosis. Therefore, the review introduces the main apoptosis pathways and the regulation of proteins in these pathways by E3s and deubiquitinating enzymes (DUBs). It summarizes the abnormal expression of these regulators in HCC and their effects on cancer inhibition or promotion. Understanding the role of ubiquitination in apoptosis and LC can provide insights into potential targets for therapeutic intervention.

Harnessing TRAIL-induced cell death for cancer therapy: a long walk with thrilling discoveries

Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) can induce apoptosis in a wide variety of cancer cells, both in vitro and in vivo, importantly without killing any essential normal cells. These findings formed the basis for the development of TRAIL-receptor agonists (TRAs) for cancer therapy. However, clinical trials conducted with different types of TRAs have, thus far, afforded only limited therapeutic benefit, as either the respectively chosen agonist showed insufficient anticancer activity or signs of toxicity, or the right TRAIL-comprising combination therapy was not employed. Therefore, in this review we will discuss molecular determinants of TRAIL resistance, the most promising TRAIL-sensitizing agents discovered to date and, importantly, whether any of these could also prove therapeutically efficacious upon cancer relapse following conventional first-line therapies. We will also discuss the more recent progress made with regards to the clinical development of highly active non-immunogenic next generation TRAs. Based thereupon, we next propose how TRAIL resistance might be successfully overcome, leading to the possible future development of highly potent, cancer-selective combination therapies that are based on our current understanding of biology TRAIL-induced cell death. It is possible that such therapies may offer the opportunity to tackle one of the major current obstacles to effective cancer therapy, namely overcoming chemo- and/or targeted-therapy resistance. Even if this were achievable only for certain types of therapy resistance and only for particular types of cancer, this would be a significant and meaningful achievement.

Role of Caspase-10-P13tBID axis in erythropoiesis regulation

Red blood cell production is negatively controlled by the rate of apoptosis at the stage of CFU-E/pro-erythroblast differentiation, depending on the balance between erythropoietin (EPO) levels and activation of the Fas/FasL pathway. At this stage, activation of transient caspases through depolarization via mitochondrial outer membrane permeabilization (MOMP) is also required for terminal erythroid differentiation. Molecular mechanisms regulating the differential levels of MOMP during differentiation and apoptosis, however, remain poorly understood. Here we show a novel and essential role for the caspase-10-P13-tBID axis in erythroid terminal differentiation. Caspase-10 (but not caspase-8, which is activated during apoptosis) is activated at the early stages of erythroid terminal differentiation leading to the cleavage of P22-BID into P18-tBID, and later into P13-tBID. Erythropoietin (EPO) by inducing casein kinase I alpha (CKIα) expression, which in turn phosphorylates P18-tBID, prevents the generation of MYR-P15-tBID (leading to apoptosis) and allows the generation of P13-tBID by caspase-10. Unlike P15-tBID, P13-tBID is not myristoylated and as such, does not irreversibly anchor the mitochondrial membrane resulting in a transient MOMP. Likewise, transduction of a P13-tBID fragment induces rapid and strong erythroid terminal differentiation. Thus, EPO modulates the pattern of BID cleavage to control the level of MOMP and determines the fate of erythroblasts between apoptosis and differentiation. This pathway is impaired in 5q- myelodysplastic syndromes because of CK1α haplo-insufficiency and may contribute to erythroid differentiation arrest and high sensitivity of this disease to lenalidomide (LEN).

The dual role of the CD95 and CD95L signaling pathway in glioblastoma

Binding of CD95, a cell surface death receptor, to its homologous ligand CD95L, transduces a cascade of downstream signals leading to apoptosis crucial for immune homeostasis and immune surveillance. Although CD95 and CD95L binding classically induces programmed cell death, most tumor cells show resistance to CD95L-induced apoptosis. In some cancers, such as glioblastoma, CD95-CD95L binding can exhibit paradoxical functions that promote tumor growth by inducing inflammation, regulating immune cell homeostasis, and/or promoting cell survival, proliferation, migration, and maintenance of the stemness of cancer cells. In this review, potential mechanisms such as the expression of apoptotic inhibitor proteins, decreased activity of downstream elements, production of nonapoptotic soluble CD95L, and non-apoptotic signals that replace apoptotic signals in cancer cells are summarized. CD95L is also expressed by other types of cells, such as endothelial cells, polymorphonuclear myeloid-derived suppressor cells, cancer-associated fibroblasts, and tumor-associated microglia, and macrophages, which are educated by the tumor microenvironment and can induce apoptosis of tumor-infiltrating lymphocytes, which recognize and kill cancer cells. The dual role of the CD95-CD95L system makes targeted therapy strategies against CD95 or CD95L in glioblastoma difficult and controversial. In this review, we also discuss the current status and perspective of clinical trials on glioblastoma based on the CD95-CD95L signaling pathway.

PANoptosis: A Unique Innate Immune Inflammatory Cell Death Modality

Innate immunity is the first response to protect against pathogens and cellular insults. Pattern recognition receptors sense pathogen- and damage-associated molecular patterns and induce an innate immune response characterized by inflammation and programmed cell death (PCD). In-depth characterization of innate immune PCD pathways has highlighted significant cross-talk. Recent advances led to the identification of a unique inflammatory PCD modality called PANoptosis, which is regulated by multifaceted PANoptosome complexes that are assembled by integrating components from other PCD pathways. The totality of biological effects observed in PANoptosis cannot be accounted for by any other PCD pathway alone. In this review, we briefly describe mechanisms of innate immune cell death, including molecular mechanisms of PANoptosis activation and regulation. We also highlight the PANoptosomes identified to date and provide an overview of the implications of PANoptosis in disease and therapeutic targeting. Improved understanding of innate immune-mediated cell death, PANoptosis, is critical to inform the next generation of treatment strategies.

Dietary N-carbamylglutamate and L-arginine supplementation improves redox status and suppresses apoptosis in the colon of intrauterine growth-retarded suckling lambs

Previous studies have revealed that dietary N-carbamylglutamate (NCG) or L-arginine (Arg) improves small intestinal integrity and immune function in suckling Hu lambs that have experienced intrauterine growth retardation (IUGR). Whether these nutrients alter redox status and apoptosis in the colon of IUGR lambs is still unknown. This study, therefore, aimed at investigating whether dietary supplementation of Arg or NCG alters colonic redox status, apoptosis and endoplasmic reticulum (ER) stress and the underlying mechanism of these alterations in IUGR suckling Hu lambs. Forty-eight 7-d old Hu lambs, including 12 with normal birth weight (4.25 ± 0.14 kg) and 36 with IUGR (3.01 ± 0.12 kg), were assigned to 4 treatment groups (n = 12 each; 6 males and 6 females) for 3 weeks. The treatment groups were control (CON), IUGR, IUGR + Arg and IUGR + NCG. Relative to IUGR lambs, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) content, as well as proliferation index, were higher (P < 0.05) whereas reactive oxygen species (ROS), malondialdehyde (MDA) levels and apoptotic cell numbers were lower (P < 0.05) in colonic tissue for both IUGR + Arg and NCG lambs. Both mRNA and protein levels of C/EBP homologous protein 10 (CHOP10), B-cell lymphoma/leukaemia 2 (Bcl-2) -associated X protein (Bax), apoptosis antigen 1 (Fas), activating transcription factor 6 (ATF6), caspase 3, and glucose-regulated protein 78 (GRP78) were lower (P < 0.05) while glutathione peroxidase 1 (GPx1), Bcl-2 and catalase (CAT) levels were higher (P < 0.05) in colonic tissue for IUGR + Arg and IUGR + NCG lambs compared with IUGR lambs. Based on our results, dietary NCG or Arg supplementation can improve colonic redox status and suppress apoptosis via death receptor-dependent, mitochondrial and ER stress pathways in IUGR suckling lambs.

Clusters of apoptotic signaling molecule-enriched rafts, CASMERs: membrane platforms for protein assembly in Fas/CD95 signaling and targets in cancer therapy

Mammalian cells show the ability to commit suicide through the activation of death receptors at the cell surface. Death receptors, among which Fas/CD95 is one of their most representative members, lack enzymatic activity, and depend on protein-protein interactions to signal apoptosis. Fas/CD95 death receptor-mediated apoptosis requires the formation of the so-called death-inducing signaling complex (DISC), bringing together Fas/CD95, Fas-associated death domain-containing protein and procaspase-8. In the last two decades, cholesterol-rich lipid raft platforms have emerged as scaffolds where Fas/CD95 can be recruited and clustered. The co-clustering of Fas/CD95 and rafts facilitates DISC formation, bringing procaspase-8 molecules to be bunched together in a limited membrane region, and leading to their autoproteolytic activation by oligomerization. Lipid raft platforms serve as a specific region for the clustering of Fas/CD95 and DISC, as well as for the recruitment of additional downstream signaling molecules, thus forming the so-called cluster of apoptotic signaling molecule-enriched rafts, or CASMER. These raft/CASMER structures float in the membrane like icebergs, in which the larger portion lies inside the cell and communicates with other subcellular structures to facilitate apoptotic signal transmission. This allows an efficient spatiotemporal compartmentalization of apoptosis signaling machinery during the triggering of cell death. This concept of proapoptotic raft platforms as a basic chemical-biological structure in the regulation of cell death has wide-ranging implications in human biology and disease, as well as in cancer therapy. Here, we discuss how these raft-centered proapoptotic hubs operate as a major linchpin for apoptosis signaling and as a promising target in cancer therapy.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

Ars moriendi: Proteases as sculptors of cellular suicide

The Ars moriendi, which translates to "The Art of Dying," encompasses two Latin texts that gave advice on how to die well and without fear according to the Christian precepts of the late Middle Ages. Given that ten to hundred billion cells die in our bodies every day, it is obvious that the concept of a well and orderly ("regulated") death is also paramount at the cellular level. In apoptosis, as the most well-studied form of regulated cell death, proteases of the caspase family are the central mediators. However, caspases are not the only proteases that act as sculptors of cellular suicide, and therefore, we here provide an overview of the impact of proteases in apoptosis and other forms of regulated cell death.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

The concept of intrinsic versus extrinsic apoptosis

Regulated cell death is a vital and dynamic process in multicellular organisms that maintains tissue homeostasis and eliminates potentially dangerous cells. Apoptosis, one of the better-known forms of regulated cell death, is activated when cell-surface death receptors like Fas are engaged by their ligands (the extrinsic pathway) or when BCL-2-family pro-apoptotic proteins cause the permeabilization of the mitochondrial outer membrane (the intrinsic pathway). Both the intrinsic and extrinsic pathways of apoptosis lead to the activation of a family of proteases, the caspases, which are responsible for the final cell demise in the so-called execution phase of apoptosis. In this review, I will first discuss the most common types of regulated cell death on a morphological basis. I will then consider in detail the molecular pathways of intrinsic and extrinsic apoptosis, discussing how they are activated in response to specific stimuli and are sometimes overlapping. In-depth knowledge of the cellular mechanisms of apoptosis is becoming more and more important not only in the field of cellular and molecular biology but also for its translational potential in several pathologies, including neurodegeneration and cancer.

The apoptosis of grass carp (Ctenopharyngodon idella) muscle during postmortem condition regulated by the cytokines via TOR and NF-κB signaling pathways

Postmortem alteration by apoptosis has significant effects on flesh quality. Currently, the information necessary to understand the apoptotic behavior and the molecular mechanisms during postmortem alteration in fish muscle is still lacking. Activation of apoptosis and the cytokines involved in regulating apoptosis in fish muscle were evaluated during postmortem condition at 4 °C for 5 days in terms of apoptotic morphology changes, nucleus DNA fragmentation, caspases activation and related gene expressions. The triggering apoptotic mechanisms associated with multiple cytokines transcriptional levels showed that the up-regulated pro-apoptotic mediators [IFN-γ2, TNF-α, IL-6, IL-1β, IL-17D, IL-12p35 and IL-10 (except IL-15)] and the down-regulated anti-apoptotic mediators of [IL-8 and IL-11 (except TGF-β and IL-4)] both regulated apoptosis at early stage, which were regulated by NF-κB and TOR, respectively. Results suggested that transcriptional regulation of multiple cytokines produce a positive outcome on triggering apoptosis.

Function of BCLAF1 in human disease

Originally identified as a regulator of apoptosis and transcription, B-cell lymphoma-2-associated transcription factor 1 (BCLAF1) has since been shown to be associated with a multitude of biological processes, such as DNA damage response, splicing and processing of pre-mRNA, T-cell activation, lung development, muscle cell proliferation and differentiation, autophagy, ischemia-reperfusion injury, and viral infection. In recent years, an increasing amount of evidence has shown that BCLAF1 acts as either a tumor promoter or tumor suppressor in tumorigenesis depending on the cellular context and the type of cancer. Even in the same tumor type, BCLAF1 may have opposite effects. In the present review, the subcellular localization, structural features, mutations within BCLAF1 will be described, then the regulation of BCLAF1 and its downstream targets will be analyzed. Furthermore, the different roles and possible mechanisms of BCLAF1 in tumorigenesis will also be highlighted and discussed. Finally, BCLAF1 may be considered as a potential target for cancer therapy in the future.

The roles of cellular protease interactions in viral infections and programmed cell death: a lesson learned from the SARS-CoV-2 outbreak and COVID-19 pandemic

The unprecedented pandemic of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), which leads to COVID-19, is threatening global health. Over the last 2 years, we have witnessed rapid progress in research focusing on developing new antiviral vaccines and drugs, as well as in academic and clinical efforts to understand the biology and pathology of COVID-19. The roles of proteases among master regulators of SARS-CoV-2 invasion and replication and their pivotal roles in host defence against this pathogen, including programmed cell death, have not been well established. Our understanding of protease function in health and disease has increased considerably over the last two decades, with caspases, matrix metalloproteases, and transmembrane serine proteases representing the most prominent examples. Therefore, during the COVID-19 pandemic, these enzymes have been investigated as potential molecular targets for therapeutic interventions. Proteases that are responsible for SARS-CoV-2 cell entry and replication, such as TMPRSS2, ACE2 or cathepsins, are screened with inhibitor libraries to discover lead structures for further drug design that would prevent virus multiplication. On the other hand, proteases that orchestrate programmed cell death can also be harnessed to enhance the desired demise of infected cells through apoptosis or to attenuate highly inflammatory lytic cell death that leads to undesired cytokine storms, a major hallmark of severe COVID-19. Given the prominent role of proteases in SARS-CoV-2-induced cell death, we discuss the individual roles of these enzymes and their catalytic interactions in the pathology of COVID-19 in this article. We provide a rationale for targeting proteases participating in cell death as potential COVID-19 treatments and identify knowledge gaps that might be investigated to better understand the mechanism underlying SARS-CoV-2-induced cell death.

Anticancer Activity and Molecular Mechanism of Momordica cochinchinensis Seed Extract in Chronic Myeloid Leukemia Cells

Targeting Bcr-Abl is the key to the treatment of chronic myeloid leukemia. Despite great progress in the treatment of patients with chronic CML, advanced CML patients are still unable to obtain effective and safe drugs. Momordica cochinchinensis seed is the dried ripe seed of Momordica cochinchinensis, which is a kind of fruit and consumed for dietary as well as medicinal uses. This study aimed to investigate the anticancer activity of Momordica cochinchinensis seed extract (MCSE) in CML cells. CML cells (KBM5 and KBM5-T315I) were treated with MCSE and analyzed for growth, apoptosis, and signal transduction. Nude mouse xenograft model was used to evaluate the antitumor activity of MCSE In Vivo. MCSE significantly reduced the cell viability of CML cells, triggered G0/G1 phase arrest in KBM5 cells and S phase arrest in KBM5-T315I cells. Concurrently, MCSE caused the activation of caspase-3, -8, -9, PARP and the degradation of Mcl-1, ultimately triggering endogenous and exogenous cell apoptosis. Meanwhile, MCSE downregulated Bcr-Abl levels and its downstream signaling pathways. Additionally, MCSE inhibited the growth of CML cells in nude mouse xenografts. Taken together, this study demonstrated the anticancer mechanism of MCSE, namely blocking Bcr-Abl and downregulating Mcl-1, and finally induced apoptosis of CML cells.

Two-level modeling approach to identify the regulatory dynamics capturing drug response heterogeneity in single-cells

Single-cell multimodal technologies reveal the scales of cellular heterogeneity impairing cancer treatment, yet cell response dynamics remain largely underused to decipher the mechanisms of drug resistance they take part in. As the phenotypic heterogeneity of a clonal cell population informs on the capacity of each single-cell to recapitulate the whole range of observed behaviors, we developed a modeling approach utilizing single-cell response data to identify regulatory reactions driving population heterogeneity in drug response. Dynamic data of hundreds of HeLa cells treated with TNF-related apoptosis-inducing ligand (TRAIL) were used to characterize the fate-determining kinetic parameters of an apoptosis receptor reaction model. Selected reactions sets were augmented to incorporate a mechanism that leads to the separation of the opposing response phenotypes. Using a positive feedback loop motif to identify the reaction set, we show that caspase-8 is able to encapsulate high levels of heterogeneity by introducing a response delay and amplifying the initial differences arising from natural protein expression variability. Our approach enables the identification of fate-determining reactions that drive the population response heterogeneity, providing regulatory targets to curb the cell dynamics of drug resistance.

TNF-α synergises with IFN-γ to induce caspase-8-JAK1/2-STAT1-dependent death of intestinal epithelial cells

Rewiring of host cytokine networks is a key feature of inflammatory bowel diseases (IBD) such as Crohn's disease (CD). Th1-type cytokines-IFN-γ and TNF-α-occupy critical nodes within these networks and both are associated with disruption of gut epithelial barrier function. This may be due to their ability to synergistically trigger the death of intestinal epithelial cells (IECs) via largely unknown mechanisms. In this study, through unbiased kinome RNAi and drug repurposing screens we identified JAK1/2 kinases as the principal and nonredundant drivers of the synergistic killing of human IECs by IFN-γ/TNF-α. Sensitivity to IFN-γ/TNF-α-mediated synergistic IEC death was retained in primary patient-derived intestinal organoids. Dependence on JAK1/2 was confirmed using genetic loss-of-function studies and JAK inhibitors (JAKinibs). Despite the presence of biochemical features consistent with canonical TNFR1-mediated apoptosis and necroptosis, IFN-γ/TNF-α-induced IEC death was independent of RIPK1/3, ZBP1, MLKL or caspase activity. Instead, it involved sustained activation of JAK1/2-STAT1 signalling, which required a nonenzymatic scaffold function of caspase-8 (CASP8). Further modelling in gut mucosal biopsies revealed an intercorrelated induction of the lethal CASP8-JAK1/2-STAT1 module during ex vivo stimulation of T cells. Functional studies in CD-derived organoids using inhibitors of apoptosis, necroptosis and JAKinibs confirmed the causative role of JAK1/2-STAT1 in cytokine-induced death of primary IECs. Collectively, we demonstrate that TNF-α synergises with IFN-γ to kill IECs via the CASP8-JAK1/2-STAT1 module independently of canonical TNFR1 and cell death signalling. This non-canonical cell death pathway may underpin immunopathology driven by IFN-γ/TNF-α in diverse autoinflammatory diseases such as IBD, and its inhibition may contribute to the therapeutic efficacy of anti-TNFs and JAKinibs.

Induction of apoptosis on ovarian adenocarcinoma cells, A2780 by tricyclohexylphosphanegold (I) mercaptobenzoate derivatives via intrinsic and extrinsic pathways

Tricyclohexylphosphanegold(I) n-mercaptobenzoate (n = 2, 3, 4) labelled as 1-3 were previously reported to significantly suppress thioredoxin reductase (TrxR) activities towards ovarian cancer cells, A2780, in vitro. Herein, we explored the role of 1-3 for their apoptosis inducing ability against A2780 cells. 1-3 exhibited IC₅₀ values at 1.19 ± 0.03 µM, 2.28 ± 0.04 μM and 0.78 ± 0.01 μM, respectively, compared to cisplatin at 26.8 ± 0.15 µM. The compounds induced A2780 apoptosis via a caspase-dependent mitochondrion pathway as evidenced by ROS production, cytochrome c release, caspases-3/7, -8, -9 and -10 activation, APAF1 and BAX upregulation as well as BCL2A1 and BCL2 genes' downregulation. In addition, the death mode of 1-3 was also mediated via death receptor extrinsic pathway manifested by FAS, FASL, FADD, and TNFR1 genes' upregulation via Human Rt PCR analysis. In addition, 1-3 significantly caused A2780 arrest at S phase, which was associated with the upregulation of TP53, E2F1, RB1 and CDKN1A upregulation and downregulation of CDK1, CDK4, CDC25A and CDC25C genes. Based on these promising results, these phosphanegold(I) thiolate derivatives could act as feasible candidates for further advanced in vivo ovarian cancer studies to develop novel chemotherapeutic agents derived from metal-based agents.

Clinical Positioning of the IAP Antagonist Tolinapant (ASTX660) in Colorectal Cancer

Inhibitors of apoptosis proteins (IAPs) are intracellular proteins, with important roles in regulating cell death, inflammation, and immunity. Here, we examined the clinical and therapeutic relevance of IAPs in colorectal cancer. We found that elevated expression of cIAP1 and cIAP2 (but not XIAP) significantly correlated with poor prognosis in patients with microsatellite stable (MSS) stage III colorectal cancer treated with 5-fluorouracil (5FU)-based adjuvant chemotherapy, suggesting their involvement in promoting chemoresistance. A novel IAP antagonist tolinapant (ASTX660) potently and rapidly downregulated cIAP1 in colorectal cancer models, demonstrating its robust on-target efficacy. In cells co-cultured with TNFα to mimic an inflammatory tumor microenvironment, tolinapant induced caspase-8-dependent apoptosis in colorectal cancer cell line models; however, the extent of apoptosis was limited because of inhibition by the caspase-8 paralogs FLIP and, unexpectedly, caspase-10. Importantly, tolinapant-induced apoptosis was augmented by FOLFOX in human colorectal cancer and murine organoid models in vitro and in vivo, due (at least in part) to FOLFOX-induced downregulation of class I histone deacetylases (HDAC), leading to acetylation of the FLIP-binding partner Ku70 and downregulation of FLIP. Moreover, the effects of FOLFOX could be phenocopied using the clinically relevant class I HDAC inhibitor, entinostat, which also induced acetylation of Ku70 and FLIP downregulation. Further analyses revealed that caspase-8 knockout RIPK3-positive colorectal cancer models were sensitive to tolinapant-induced necroptosis, an effect that could be exploited in caspase-8-proficient models using the clinically relevant caspase inhibitor emricasan. Our study provides evidence for immediate clinical exploration of tolinapant in combination with FOLFOX in poor prognosis MSS colorectal cancer with elevated cIAP1/2 expression.

Relationship Between CASP9 and CASP10 Gene Polymorphisms and Cancer Susceptibility: Evidence from an Updated Meta-analysis

Caspase-9 (CASP9) and caspase-10 (CASP10) polymorphisms were associated with human cancers; however, the results remain controversial. In this meta-analysis, we aimed to estimate the relationship among CASP9 (rs1052576, rs1052571, rs4645978, rs4645981, rs4645982, rs2308950) and CASP10 (rs13006529, rs13010627, rs3900115) polymorphisms and the overall risk of cancers. Relevant studies were obtained from Web of Science, MEDLINE, PubMed, Scopus, and Google scholar databases (updated January 1, 2021). Odds ratio (OR) and 95% confidence intervals (CIs) were measured to estimate the strength of association. Our meta-analysis included 40 studies. The rs4645981 significantly enhanced the risk of cancer under TT vs. CC (OR = 2.42), TC vs. CC (OR = 1.55), TT+ TC vs. CC (OR = 1.66), TT vs. TC + CC (OR = 1.91), and T vs. C (OR = 1.57) inheritance models. As for the rs1052571 variant, increased risk of cancer was observed under TT vs. CC (OR =1.22), TC vs. CC (OR = 1.17), and TT+ TC vs. CC (OR = 1.18) models. The stratified analysis showed a significant correlation between rs4645978 or rs4645981 polymorphisms and cancer risk, while in Asians rs4645978 conferred an increased risk of colorectal, lung, and prostate cancer. Both rs4645981 and rs1052576 polymorphisms were correlated with an enhanced risk of lung cancer. In conclusion, our meta-analysis suggested that CASP9 rs4645981 and rs1052571 polymorphisms are associated with overall cancer risk. More studies on larger populations are warranted to validate these associations.

A unique death pathway keeps RIPK1 D325A mutant mice in check at embryonic day 10.5

Tumor necrosis factor receptor-1 (TNFR1) signaling, apart from its pleiotropic functions in inflammation, plays a role in embryogenesis as deficiency of varieties of its downstream molecules leads to embryonic lethality in mice. Caspase-8 noncleavable receptor interacting serine/threonine kinase 1 (RIPK1) mutations occur naturally in humans, and the corresponding D325A mutation in murine RIPK1 leads to death at early midgestation. It is known that both the demise of Ripk1D325A/D325A embryos and the death of Casp8-/- mice are initiated by TNFR1, but they are mediated by apoptosis and necroptosis, respectively. Here, we show that the defects in Ripk1D325A/D325A embryos occur at embryonic day 10.5 (E10.5), earlier than that caused by Casp8 knockout. By analyzing a series of genetically mutated mice, we elucidated a mechanism that leads to the lethality of Ripk1D325A/D325A embryos and compared it with that underlies Casp8 deletion-mediated lethality. We revealed that the apoptosis in Ripk1D325A/D325A embryos requires a scaffold function of RIPK3 and enzymatically active caspase-8. Unexpectedly, caspase-1 and caspase-11 are downstream of activated caspase-8, and concurrent depletion of Casp1 and Casp11 postpones the E10.5 lethality to embryonic day 13.5 (E13.5). Moreover, caspase-3 is an executioner of apoptosis at E10.5 in Ripk1D325A/D325A mice as its deletion extends life of Ripk1D325A/D325A mice to embryonic day 11.5 (E11.5). Hence, an unexpected death pathway of TNFR1 controls RIPK1 D325A mutation-induced lethality at E10.5.

Oxaliplatin resistance in colorectal cancer enhances TRAIL sensitivity via death receptor 4 upregulation and lipid raft localization

Colorectal cancer (CRC) remains a leading cause of cancer death, and its mortality is associated with metastasis and chemoresistance. We demonstrate that oxaliplatin-resistant CRC cells are sensitized to TRAIL-mediated apoptosis. Oxaliplatin-resistant cells exhibited transcriptional downregulation of caspase-10, but this had minimal effects on TRAIL sensitivity following CRISPR-Cas9 deletion of caspase-10 in parental cells. Sensitization effects in oxaliplatin-resistant cells were found to be a result of increased DR4, as well as significantly enhanced DR4 palmitoylation and translocation into lipid rafts. Raft perturbation via nystatin and resveratrol significantly altered DR4/raft colocalization and TRAIL sensitivity. Blood samples from metastatic CRC patients were treated with TRAIL liposomes, and a 57% reduction of viable circulating tumor cells (CTCs) was observed. Increased DR4/lipid raft colocalization in CTCs was found to correspond with increased oxaliplatin resistance and increased efficacy of TRAIL liposomes. To our knowledge, this is the first study to investigate the role of lipid rafts in primary CTCs.

Identification and characterization of caspases genes in rainbow trout (Oncorhynchus mykiss) and their expression profiles after Aeromonas salmonicida and Vibrio anguillarum infection

Caspases are highly conserved cysteine-dependent aspartyl-specific proteases that play an important role in regulating cell death and inflammation. However, the caspase genes have not been systematically studied in rainbow trout (Oncorhynchus mykiss). Rainbow trout experienced 4 rounds (4R) of genome duplication in the evolutionary history. Thereby an increased numbers of paralogs are observed in trout, probably with more complicated gene functions. We identified 18 caspase genes in rainbow trout, including two inflammatory caspases (casp1a, casp1b), six apoptosis executioner caspases (casp3, casp3a1, casp3a2, casp3b, casp6, and casp7), nine apoptosis initiator caspases (casp2a, casp2b, casp8, casp9a, casp9b, casp10a, casp10b, casp20a, and casp20b) and one uncategorized caspase gene (casp17). To investigate the potentially physiological functions of caspase genes, we challenged the rainbow trout with Aeromonas salmonicida (A. salmonicida) and Vibrio anguillarum (V. anguillarum). Results showed that the CASP3-regulated intrinsic apoptosis was activated after A. salmonicida infection, while the CASP8 and CASP6-regulated extrinsic apoptosis exerted the greatest effect on trout challenged with V. anguillarum. In response to V. anguillarum infection, the data of RNA-Seq further showed the casp8 was tightly integrated with the significantly enriched Gene Ontology terms and functional pathways, including apoptosis regulation, pathogen detection and immunomodulation. Our study provides a foundation for the physiological functions and regulatory network of the caspase genes in teleosts.

H2O2 mediated FLIP and XIAP down-regulation involves increased ITCH expression and ERK-Akt crosstalk in imatinib resistant Chronic Myeloid Leukemia cell line K562

Regulation of anti-apoptotic protein FLICE-like inhibitory protein (FLIP) and X-linked inhibitor of apoptosis protein (XIAP) remains a crucial step in the cell fate determination and thus targeting these anti-apoptotic proteins could be a viable strategy for the treatment of cancer. However the regulation of FLIP and XIAP is not very well established till date. Here we have shown that ROS decreased XIAP and FLIP by activation of ubiquitin-proteasomal pathway in imatinib resistant K562 cells. Activation of the components of MAPK pathway, ERK and JNK, played a crucial role in XIAP and FLIP degradation because ectopic expression or knock down of ERK and JNK changed the pattern of ROS mediated down-regulation of these two proteins. We have also found that JNK and ERK differentially regulates FLIP and XIAP, respectively. Moreover, our data suggests that activated ERK decreased Akt phosphorylation and thus its binding to and stabilization of XIAP. On the other hand, JNK activation increased E3 ubiquitin ligase ITCH expression and its binding to FLIP which leads to its degradation. Thus, we have, for the first time elucidated that ROS mediated ERK-Akt crosstalk regulates XIAP. We have also shown for the first time that ROS regulates ITCH expression which controls FLIP degradation.

Induction of interferon-β and interferon signaling by TRAIL and Smac mimetics via caspase-8 in breast cancer cells

Breast cancer prognosis is frequently good but a substantial number of patients suffer from relapse. The death receptor ligand TRAIL can in combination with Smac mimetics induce apoptosis in some luminal-like ER-positive breast cancer cell lines, such as CAMA-1, but not in MCF-7 cells. Here we show that TRAIL and the Smac mimetic LCL161 induce non-canonical NF-κB and IFN signaling in ER-positive MCF-7 cells and in CAMA-1 breast cancer cells when apoptosis is blocked by caspase inhibition. Levels of p52 are increased and STAT1 gets phosphorylated. STAT1 phosphorylation is induced by TRAIL alone in MCF-7 cells and is independent of non-canonical NF-κB since downregulation of NIK has no effect. The phosphorylation of STAT1 is a rather late event, appearing after 24 hours of TRAIL stimulation. It is preceded by an increase in IFNB1 mRNA levels and can be blocked by siRNA targeting the type I IFN receptor IFNAR1 and by inhibition of Janus kinases by Ruxolitinib. Moreover, downregulation of caspase-8, but not inhibition of caspase activity, blocks TRAIL-mediated STAT1 phosphorylation and induction of IFN-related genes. The data suggest that TRAIL-induced IFNB1 expression in MCF-7 cells is dependent on a non-apoptotic role of caspase-8 and leads to autocrine interferon-β signaling.

Cryo-EM structural analysis of FADD:Caspase-8 complexes defines the catalytic dimer architecture for co-ordinated control of cell fate

Regulated cell death is essential in development and cellular homeostasis. Multi-protein platforms, including the Death-Inducing Signaling Complex (DISC), co-ordinate cell fate via a core FADD:Caspase-8 complex and its regulatory partners, such as the cell death inhibitor c-FLIP. Here, using electron microscopy, we visualize full-length procaspase-8 in complex with FADD. Our structural analysis now reveals how the FADD-nucleated tandem death effector domain (tDED) helical filament is required to orientate the procaspase-8 catalytic domains, enabling their activation via anti-parallel dimerization. Strikingly, recruitment of c-FLIP_S into this complex inhibits Caspase-8 activity by altering tDED triple helix architecture, resulting in steric hindrance of the canonical tDED Type I binding site. This prevents both Caspase-8 catalytic domain assembly and tDED helical filament elongation. Our findings reveal how the plasticity, composition and architecture of the core FADD:Caspase-8 complex critically defines life/death decisions not only via the DISC, but across multiple key signaling platforms including TNF complex II, the ripoptosome, and RIPK1/RIPK3 necrosome.

The core FADD:Caspase-8 complex and its regulatory partners, such as the cell death inhibitor c-FLIP, coordinate cell fate. Here authors present the structure of full-length procaspase-8 in a complex with FADD and reveal how recruitment of c-FLIP_S into this complex inhibits Caspase-8 activity.

Location, location, location: A compartmentalized view of TNF-induced necroptotic signaling

Necroptosis is a lytic, proinflammatory cell death pathway, which has been implicated in host defense and, when dysregulated, the pathology of many human diseases. The central mediators of this pathway are the receptor-interacting serine/threonine protein kinases RIPK1 and RIPK3 and the terminal executioner, the pseudokinase mixed lineage kinase domain-like (MLKL). Here, we review the chronology of signaling along the RIPK1-RIPK3-MLKL axis and highlight how the subcellular compartmentalization of signaling events controls the initiation and execution of necroptosis. We propose that a network of modulators surrounds the necroptotic signaling core and that this network, rather than acting universally, tunes necroptosis in a context-, cell type-, and species-dependent manner. Such a high degree of mechanistic flexibility is likely an important property that helps necroptosis operate as a robust, emergency form of cell death.

Protein Kinases Signaling in Pancreatic Beta-cells Death and Type 2 Diabetes

Type 2 diabetes (T2D) is a worldwide serious public health problem. Insulin resistance and β-cell failure are the two major components of T2D pathology. In addition to defective endoplasmic reticulum (ER) stress signaling due to glucolipotoxicity, β-cell dysfunction or β-cell death initiates the deleterious vicious cycle observed in T2D. Although the primary cause is still unknown, overnutrition that contributes to the induction of the state of low-grade inflammation, and the activation of various protein kinases-related metabolic pathways are main factors leading to T2D. In this chapter following subjects, which have critical checkpoints regarding β-cell fate and protein kinases pathways are discussed; hyperglycemia-induced β-cell failure, chronic accumulation of unfolded protein in β-cells, the effect of intracellular reactive oxygen species (ROS) signaling to insulin secretion, excessive saturated free fatty acid-induced β-cell apoptosis, mitophagy dysfunction, proinflammatory responses and insulin resistance, and the reprogramming of β-cell for differentiation or dedifferentiation in T2D. There is much debate about selecting proposed therapeutic strategies to maintain or enhance optimal β-cell viability for adequate insulin secretion in T2D. However, in order to achieve an effective solution in the treatment of T2D, more intensive clinical trials are required on newer therapeutic options based on protein kinases signaling pathways.

Protein Kinase-Mediated Decision Between the Life and Death

Protein kinases are intracellular signaling enzymes that catalyze the phosphorylation of specific residues in their target substrate proteins. They play important role for regulation of life and death decisions. The complexity of the relationship between death receptors and protein kinases' cell death decision-making mechanisms create many difficulties in the treatment of various diseases. The most of fifteen different cell death pathways, which are reported by Nomenclature Committee on Cell Death (NCCD) are protein kinase signal transduction-mediated negative or positive selections. Tumor necrosis factor (TNF) as a main player of death pathways is a dual-functioning molecule in that it can promote both cell survival or cell death. All apoptotic and necrotic signal transductions are conveyed through death domain-containing death receptors, which are expressed on the surface of nearly all human cells. In humans, eight members of the death receptor family have been identified. While the interaction of TNF with TNF Receptor 1 (TNFR1) activates various signal transduction pathways, different death receptors activate three main signal transduction pathways: nuclear factor kappa B (NF-ĸB)-mediated differentiation or pro-inflammatory cytokine synthesis, mitogen-activated protein kinase (MAPK)-mediated stress response and caspase-mediated apoptosis. The link between the NF-ĸB and the c-Jun NH₂-terminal kinase (JNK) pathways comprise another check-point to regulate cell death. TNF-α also promotes the "receptor-interacting serine/threonine protein kinase 1" (RIPK1)/RIPK3/ mixed lineage kinase domain-like pseudokinase (MLKL)-dependent necrosis. Thus, necrosome is mainly comprised of MLKL, RIPK3 and, in some cases, RIPK1. In fact, RIPK1 is at the crossroad between life and death, downstream of various receptors as a regulator of endoplasmic reticulum stress-induced death. TNFR1 signaling complex (TNF-RSC), which contains multiple kinase activities, promotes phosphorylation of transforming growth factor β-activated kinase 1 (TAK1), inhibitor of nuclear transcription factor κB (IκB) kinase (IKK) α/IKKβ, IκBα, and NF-κB. IKKs affect cell-survival pathways in NF-κB-independent manner. Toll-like receptor (TLR) stimulation triggers various signaling pathways dependent on myeloid differentiation factor-88 (MyD88), Interleukin-1 receptor (IL-1R)-associated kinase (IRAK1), IRAK2 and IRAK4, lead to post-translational activation of nucleotide and oligomerization domain (NLRP3). Thereby, cell fate decisions following TLR signaling is parallel with death receptor signaling. Inhibition of IKKα/IKKβ or its upstream activators sensitize cells to death by inducing RIPK1-dependent apoptosis or necroptosis. During apoptosis, several kinases of the NF-κB pathway, including IKK1 and NF-κB essential modulator (NEMO), are cleaved by cellular caspases. This event can terminate the NF-κB-derived survival signals. In both canonical and non-canonical pathways, IKK is key to NF-κB activation. Whereas, the activation process of IKK, the functions of NEMO ubiquitination, IKK-related non-canonical pathway and the nuclear transportation of NEMO and functions of IKKα are still debated in cell death. In addition, cluster of differentiation 95 (CD95)-mediated non-apoptotic signaling and CD95- death-inducing signaling complex (DISC) interactions are waiting for clarification.

Effect of Bitis gabonica and Dendroaspis angusticeps snake venoms on apoptosis-related genes in human thymic epithelial cells

Background:

Certain environmental toxins permanently damage the thymic epithelium, accelerate immune senescence and trigger secondary immune pathologies. However, the exact underlying cellular mechanisms and pathways of permanent immune intoxication remain unknown. The aim of the present study was to demonstrate gene expressional changes of apoptosis-related cellular pathways in human thymic epithelial cells following exposure to snake venom from Bitis gabonica and Dendroaspis angusticeps.

Methods:

Snake venoms were characterized by analytical methods including reversed phase high-performance liquid chromatography and sodium dodecyl sulphate-polyacrylamide gel electrophoresis, then applied on human thymic epithelial cells (1889c) for 24 h at 10 μg/mL (as used in previous TaqMan Array study). Gene expressional changes restricted to apoptosis were assayed by TaqMan Array (Human Apoptosis Plate).

Results:

The most prominent gene expressional changes were shown by CASP5 (≈ 2.5 million-fold, confirmed by dedicated quantitative polymerase chain reaction) and CARD9 (0.016-fold) for B. gabonica, and BIRC7 (6.46-fold) and CASP1 (0.30-fold) for D. angusticeps.

Conclusion:

The observed apoptotic environment suggests that pyroptosis may be the dominant pathway through which B. gabonica and D. angusticeps snake venoms trigger thymic epithelial apoptosis following envenomation.