The Jekyll and Hyde functions of caspases

Death fuels growth: Emerging players bridging apoptosis and cell proliferation in Drosophila and beyond

Tissue homeostasis relies on a delicate balance between cell death and proliferation. Apoptosis plays a key role not only in removing damaged cells but also in promoting tissue recovery through a process known as apoptosis-induced proliferation (AiP). This review highlights how caspases, c-Jun N-terminal Kinase (JNK), and Reactive Oxygen Species (ROS) bridge cell death and proliferation, as revealed through studies using Drosophila as a model organism. We also compare these findings with advances in other model systems and discuss their broader implications for tissue regeneration and tumorigenesis.

Study on low concentration deltamethrin toxicity mediated by phospholipase D in Chinese mitten crab (Eriocheir sinensis) ovary

This study evaluates the impact of environmentally relevant, low-concentration deltamethrin exposure to Eriocheir sinensis ovaries. Our findings revealed that even at a concentration of 0.05 µg/L, deltamethrin exposure can induce significant ovarian toxicity through a 5-day exposure, with gradual amplification detected with time, demonstrating the toxicity amplification effect. Hematoxylin and Eosin staining revealed that low-concentration deltamethrin exposure produces pathological damage consistent with acute toxicity-yolk granules were dissolved and oocyte membranes were ruptured. High-throughput RNA-sequencing data indicated that the acute and low-concentration exposure groups involved completely different pathways and molecular functions, suggesting distinct mechanisms for their toxic effects. Following the identification of phospholipase D (PLD) as a potential core factor regulating the toxicity amplification effect of low concentration deltamethrin, we delved into subsequent mechanism studies using quantitative real-time PCR, immunofluorescence and enzyme-linked immunosorbent assay. Through the GnRH signaling pathway, increased PLD indirectly stimulates augmented estradiol secretion, subsequently inducing apoptosis by upregulating Cathepsin D, which can activate the key executioners of apoptosis-caspases (CASP3 and CASP7). In conclusion, low-concentration deltamethrin exposures can induce significant ovarian damage through apoptosis mediated by the upregulation of PLD in the ovaries of Eriocheir sinensis at environmentally relevant concentrations, which lays the preliminary theoretical groundwork for further elucidating the mechanism of toxicity amplification effect of pesticide exposure at low concentrations.

Diabetic peripheral neuropathy based on Schwann cell injury: mechanisms of cell death regulation and therapeutic perspectives

Diabetic peripheral neuropathy (DPN) is a complication of diabetes mellitus that lacks specific treatment, its high prevalence and disabling neuropathic pain greatly affects patients' physical and mental health. Schwann cells (SCs) are the major glial cells of the peripheral nervous system, which play an important role in various inflammatory and metabolic neuropathies by providing nutritional support, wrapping axons and promoting repair and regeneration. Increasingly, high glucose (HG) has been found to promote the progression of DPN pathogenesis by targeting SCs death regulation, thus revealing the specific molecular process of programmed cell death (PCD) in which SCs are disrupted is an important link to gain insight into the pathogenesis of DPN. This paper is the first to review the recent progress of HG studies on apoptosis, autophagy, pyroptosis, ferroptosis and necroptosis pathways in SCs, and points out the crosstalk between various PCDs and the related therapeutic perspectives, with the aim of providing new perspectives for a deeper understanding of the mechanisms of DPN and the exploration of effective therapeutic targets.

Caspase-mediated regulation of the distinct signaling pathways and mechanisms in neuronal survival

Caspases are intimately associated with altering various signaling pathways, resulting in programmed cell death or apoptosis. Apoptosis is necessary for the normal homeostasis of cells and their development. The untoward activation of apoptotic pathways indirectly or directly results in pathologies of various diseases. Identifying different caspases in apoptotic pathways directed the research to develop caspase inhibitors as therapeutic agents. However, no drug is available in the market that targets caspase inhibition and produces a therapeutic effect. Here, we will shed light on the role of caspases in the number of neuronal disorders and neurodegenerative diseases. The article reviews the findings about the activation of various upstream mechanisms associated with caspases in neurodegenerative disorders along with the recent progress in the generation of caspase inhibitors and the challenge faced in their development as therapeutic agents for neurological indications.

Triclosan (TCS) affects the level of DNA methylation in the human oral squamous cell carcinoma (SCC-15) cell line in a nontoxic concentration

The oral cancer is presumably caused by genetic factors and exposure to substances derived from cosmetics and disinfectants. Triclosan (TCS) is widely spread in many consumer products and oral care products. Since TCS can affect DNA methylation, which is one of the key mechanisms of gene expression that may lead to cancerogenesis, it is necessary to study this mechanism in oral cell carcinoma. The aim of the present study was to evaluate the impact of TCS on metabolic parameters, oxidative stress, gene expression, and DNA methylation and hydroxymethylation in the SCC-15 cell line. The experiments have shown TCS toxicity to SCC-15 cells only in the highest concentrations of 50 and 100 µM. TCS in a wide range of concentrations increases ROS production and caspase-3 activity. Our experiments have shown that TCS in the nontoxic concentrations of 10 µM exerts an impact on SOD2 mRNA expression and SOD activity in the SCC-15 cell line. Finally, our experiments have demonstrated that 6-h treatment with TCS decreases the mRNA expression of DNMT3A and DNMT3B. After 72-h exposure to TCS, an increased level of 5-methylcytosine and 5-hydroxymethylcytosine was observed in the SCC-15 cell line, but it was abolished by the NAC treatment. However, it is very likely that these results can be an effect of TET enzyme activity, especially in the case of the decrease in 5mC and the increase in 5hmC after the 48-h exposure to TCS, which was accompanied with a decrease in the mRNA expression of DNMT3A and DNMT3B.

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.

Rational deuteration of dronedarone attenuates its toxicity in human hepatic HepG2 cells

Deuteration is a chemical modification strategy that has recently gained traction in drug development. The replacement of one or more hydrogen atom(s) in a drug molecule with its heavier stable isotope deuterium can enhance its metabolic stability and pharmacokinetic properties. However, it remains uninterrogated if rational deuteration at bioactivation "hot-spots" could attenuate its associated toxicological consequences. Here, our preliminary screening with benzofuran antiarrhythmic agents first revealed that dronedarone and its major metabolite N-desbutyldronedarone elicited a greater loss of viability and cytotoxicity in human hepatoma G2 (HepG2) cells as compared with amiodarone and its corresponding metabolite N-desethylamiodarone. A comparison of dronedarone and its in-house synthesized deuterated analogue (termed poyendarone) demonstrated that deuteration could attenuate its in vitro toxicity in HepG2 cells by modulating the extent of mitochondrial dysfunction, reducing the dissipation of mitochondrial membrane potential, and evoking a distinct apoptotic kinetic signature. Furthermore, although pretreatment with the CYP3A inducer rifampicin or the substitution of glucose with galactose in the growth media significantly augmented the loss of cell viability elicited by dronedarone and poyendarone, a lower loss of cell viability was consistently observed in poyendarone across all concentrations. Taken together, our preliminary investigations suggested that the rational deuteration of dronedarone at its benzofuran ring reduces aberrant cytochrome P450 3A4/5-mediated bioactivation, which attenuated its mitochondrial toxicity in human hepatic HepG2 cells.

A long way to go: caspase inhibitors in clinical use

Caspases are an evolutionary conserved family of cysteine-dependent proteases that are involved in many vital cellular processes including apoptosis, proliferation, differentiation and inflammatory response. Dysregulation of caspase-mediated apoptosis and inflammation has been linked to the pathogenesis of various diseases such as inflammatory diseases, neurological disorders, metabolic diseases, and cancer. Multiple caspase inhibitors have been designed and synthesized as a potential therapeutic tool for the treatment of cell death-related pathologies. However, only a few have progressed to clinical trials because of the consistent challenges faced amongst the different types of caspase inhibitors used for the treatment of the various pathologies, namely an inadequate efficacy, poor target specificity, or adverse side effects. Importantly, a large proportion of this failure lies in the lack of understanding various caspase functions. To overcome the current challenges, further studies on understanding caspase function in a disease model is a fundamental requirement to effectively develop their inhibitors as a treatment for the different pathologies. Therefore, the present review focuses on the descriptive properties and characteristics of caspase inhibitors known to date, and their therapeutic application in animal and clinical studies. In addition, a brief discussion on the achievements, and current challenges faced, are presented in support to providing more perspectives for further development of successful therapeutic caspase inhibitors for various diseases.

Histone H2A.X phosphorylation and Caspase-Initiated Chromatin Condensation in late-stage erythropoiesis

Background

Condensation of chromatin prior to enucleation is an essential component of terminal erythroid maturation, and defects in this process are associated with inefficient erythropoiesis and anemia. However, the mechanisms involved in this phenomenon are not well understood. Here, we describe a potential role for the histone variant H2A.X in erythropoiesis.

Results

We find in multiple model systems that this histone is essential for normal maturation, and that the loss of H2A.X in erythroid cells results in dysregulation in expression of erythroid-specific genes as well as a nuclear condensation defect. In addition, we demonstrate that erythroid maturation is characterized by phosphorylation at both S139 and Y142 on the C-terminal tail of H2A.X during late-stage erythropoiesis. Knockout of the kinase BAZ1B/WSTF results in loss of Y142 phosphorylation and a defect in nuclear condensation, but does not replicate extensive transcriptional changes to erythroid-specific genes observed in the absence of H2A.X.

Conclusions

We relate these findings to Caspase-Initiated Chromatin Condensation (CICC) in terminal erythroid maturation, where aspects of the apoptotic pathway are invoked while apoptosis is specifically suppressed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-021-00408-5.

Expression of Caspases in the Pig Endometrium Throughout the Estrous Cycle and at the Maternal-Conceptus Interface During Pregnancy and Regulation by Steroid Hormones and Cytokines

Caspases, a family of cysteine protease enzymes, are a critical component of apoptotic cell death, but they are also involved in cellular differentiation. The expression of caspases during apoptotic processes in reproductive tissues has been shown in some species; however, the expression and regulation of caspases in the endometrium and placental tissues of pigs has not been fully understood. Therefore, we determined the expression of caspases CASP3, CASP6, CASP7, CASP8, CASP9, and CASP10 in the endometrium throughout the estrous cycle and pregnancy. During the estrous cycle, the expression of all caspases and during pregnancy, the expression of CASP3, CASP6, and CASP7 in the endometrium changed in a stage-specific manner. Conceptus and chorioallantoic tissues also expressed caspases during pregnancy. CASP3, cleaved-CASP3, and CASP7 proteins were localized to endometrial cells, with increased levels in luminal and glandular epithelial cells during early pregnancy, whereas apoptotic cells in the endometrium were limited to some scattered stromal cells with increased numbers on Day 15 of pregnancy. In endometrial explant cultures, the expression of some caspases was affected by steroid hormones (estradiol-17β and/or progesterone), and the cytokines interleukin-1β and interferon-γ induced the expression of CASP3 and CASP7, respectively. These results indicate that caspases are dynamically expressed in the endometrium throughout the estrous cycle and at the maternal-conceptus interface during pregnancy in response to steroid hormones and conceptus signals. Thus, caspase action could be important in regulating endometrial and placental function and epithelial cell function during the implantation period in pigs.

Disulfiram Chelated With Copper Inhibits the Growth of Gastric Cancer Cells by Modulating Stress Response and Wnt/β-catenin Signaling

Disulfiram (DSF) is a well-known drug for alcohol abuse. In recent decades, DSF has been demonstrated to exhibit anti-tumor activity; DSF chelated with copper shows enhanced anti-tumor effect. Our goal was to explore the effect of DSF/Cu complex on the growth and metastasis of gastric cancer (GC) in vitro and in vivo. DSF/Cu complex suppressed the proliferation, migration of MKN-45 and BGC-823 GC cells. Furthermore, DSF/Cu treatment reduced the tumor volume in GC mouse models with a tumor suppression rate of 48.24%. Additionally, DSF/Cu induced apoptosis in vitro in MKN-45 and BGC-823 GC cells in a dose- and time-dependent manner as well as in vivo in the xenograft tumor mouse model. Furthermore, DSF/Cu induced autophagy and autophagic flux in MKN-45 and BGC-823 cells, increased the expression of autophagy-related Beclin-1 and LC3 proteins in vivo. Additionally, DSF/Cu suppressed aerobic glycolysis and oxidative phosphorylation by reducing oxygen consumption rate and extracellular acidification rate, respectively, in MKN-45 and BGC-823 cells. Treatment with DSF/Cu induced oxidative stress and DNA damage response by elevating the reactive oxygen species levels; increasing the expression of P53, P21, and γ-H2AX proteins; and inhibiting Wnt/β-catenin signaling in vitro and in vivo. Thus, DSF/Cu suppressed the growth and metastasis of GC cells via modulating the stress response and Wnt/β-catenin signaling. Hence, DSF may be used as a potential therapeutic agent for the treatment of GC.

Occurrence of Retinal Ganglion Cell Loss via Autophagy and Apoptotic Pathways in an Autoimmune Glaucoma Model

PURPOSE

In glaucoma, an apoptotic death of retinal ganglion cells (RGCs) has been shown. However, little is known about other cell death mechanisms, like autophagy or necrosis. Therefore, we investigated these mechanisms in addition to antibody deposits in an experimental autoimmune glaucoma model.

METHODS

Rats were immunized with a retinal ganglion cell-layer homogenate (RGA), while controls received sodium chloride. Untreated rats served as natїve group. After seven weeks, retinal cross-sections were stained with antibodies against RGCs (Brn-3a), apoptosis (cleaved caspase 2, cleaved caspase 3 as well as caspase 3, 8, and 9), autophagy (LC3BII and LAMP1), and necrosis (RIPK3) followed by cell counts. Autophagy was additionally visualized via transmission electron microscopy on retinal sections. Antibody deposits were also analyzed.

RESULTS

We noted a RGC loss after RGA immunization compared to both control groups. Also, significantly more cleaved caspase 2+ RGCs were observed in RGA animals. More caspase 3 and 8 signals were noted in RGA retinas compared to both controls, while no changes were seen in regard to caspase 9. Furthermore, significantly more cleaved caspase 3+ cells were detected in RGA animals. We noted an increase of LC3BII+ and LAMP1+ autophagic cells in the RGA group, while no alterations were seen regarding necrotic RIPK3+ cells. Autophagic vesicles were observed via transmission electron microscopy. IgG staining revealed significant differences between the RGA group and controls concerning IgG deposits in the ganglion cell layer.

CONCLUSIONS

Due to the novel results from this study, we conclude that IgG antibodies are involved in RGC loss in this model leading to apoptotic and autophagic cell loss. These results could help to develop new therapy strategies for glaucoma patients.

Cerebral Blood Flow-Guided Manipulation of Arterial Blood Pressure Attenuates Hippocampal Apoptosis After Asphyxia-Induced Cardiac Arrest in Rats

Background In most post-cardiac arrest patients, the autoregulation mechanism of cerebral blood flow (CBF) is dysregulated. We examined whether recovery of CBF by adjusting mean arterial pressure mitigates post-cardiac arrest neuronal damage. Methods and Results Wistar rats that underwent 8-minute asphyxia-induced cardiac arrest and resuscitation were computer-randomized to norepinephrine or control groups. The CBF was measured at the dorsal hippocampal CA1 region of the left hemisphere. In the norepinephrine group, the mean arterial pressure was adjusted to recover CBF to 80% to 100% of baseline. Twenty-four hours following resuscitation, neurological outcomes were assessed, and brain tissues and blood samples were harvested for neuronal apoptosis and injury assessment. Thirty resuscitated rats were randomized into 2 groups, each containing 12 rats that completed the experiments. Norepinephrine infusion effectively prevented posthyperemia hypoperfusion and recovered CBF to pre-arrest baseline levels; a moderate positive linear correlation between mean arterial pressure and CBF during this period was also observed (P<0.001). There were no significant between-group differences in neurological recovery. In the norepinephrine group compared with the control group, upregulated cleaved caspase-3 protein expression in brain tissue determined by Western blot was reduced (P=0.02) and the densities of apoptotic cells in hippocampal CA1 and CA3 regions determined by terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labeling were decreased (P<0.001). No significant differences in serum neuron-specific enolase or S100β levels were detected between the 2 groups. Conclusions CBF recovery demonstrated neuroprotective effects by reducing activation of cerebral apoptosis and number of apoptotic neurons. However, these effects did not significantly improve clinical neurological function, necessitating further investigation.

Involvement of CASP9 (caspase 9) in IGF2R/CI-MPR endosomal transport

Recently, we reported that increased expression of CASP9 pro-domain, at the endosomal membrane in response to HSP90 inhibition, mediates a cell-protective effect that does not involve CASP9 apoptotic activity. We report here that a non-apoptotic activity of endosomal membrane CASP9 facilitates the retrograde transport of IGF2R/CI-MPR from the endosomes to the trans-Golgi network, indicating the involvement of CASP9 in endosomal sorting and lysosomal biogenesis. CASP9-deficient cells demonstrate the missorting of CTSD (cathepsin D) and other acid hydrolases, accumulation of late endosomes, and reduced degradation of bafilomycin A₁-sensitive proteins. In the absence of CASP9, IGF2R undergoes significant degradation, and its rescue is achieved by the re-expression of a non-catalytic CASP9 mutant. This endosomal activity of CASP9 is potentially mediated by herein newly identified interactions of CASP9 with the components of the endosomal membrane transport complexes. These endosomal complexes include the retromer VPS35 and the SNX dimers, SNX1-SNX5 and SNX2-SNX6, which are involved in the IGF2R retrieval mechanism. Additionally, CASP9 interacts with HGS/HRS/ESCRT-0 and the CLTC (clathrin heavy chain) that participate in the initiation of the endosomal ESCRT degradation pathway. We propose that endosomal CASP9 inhibits the endosomal membrane degradative subdomain(s) from initiating the ESCRT-mediated degradation of IGF2R, allowing its retrieval to transport-designated endosomal membrane subdomain(s). These findings are the first to identify a cell survival, non-apoptotic function for CASP9 at the endosomal membrane, a site distinctly removed from the cytoplasmic apoptosome. Via its non-apoptotic endosomal function, CASP9 impacts the retrograde transport of IGF2R and, consequently, lysosomal biogenesis.Abbreviations: ACTB: actin beta; ATG7: autophagy related 7; BafA1: bafilomycin A₁; CASP: caspase; CLTC/CHC: clathrin, heavy chain; CTSD: cathepsin D; ESCRT: endosomal sorting complexes required for transport; HEXB: hexosaminidase subunit beta; HGS/HRS/ESCRT-0: hepatocyte growth factor-regulated tyrosine kinase substrate; IGF2R/CI-MPR: insulin like growth factor 2 receptor; ILV: intraluminal vesicles; KD: knockdown; KO: knockout; M6PR/CD-MPR: mannose-6-phosphate receptor, cation dependent; MEF: murine embryonic fibroblasts; MWU: Mann-Whitney U test; PepA: pepstatin A; RAB7A: RAB7, member RAS oncogene family; SNX-BAR: sorting nexin dimers with a Bin/Amphiphysin/Rvs (BAR) domain each; TGN: trans-Golgi network; TUBB: tubulin beta; VPS26: VPS26 retromer complex component; VPS29: VPS29 retromer complex component; VPS35: VPS35 retromer complex component.

Mcl1 protein levels and Caspase-7 executioner protease control axial organizer cells survival

BACKGROUND

Organizing centers are groups of specialized cells that secrete morphogens, thereby influencing development of their neighboring territories. Apoptosis is a form of programmed cell death reported to limit the size of organizers. Little is known about the identity of intracellular signals driving organizer cell death. Here we investigated in Xenopus the role of both the anti-apoptotic protein Myeloid-cell-leukemia 1 (Mcl1) and the cysteine proteases Caspase-3 and Caspase-7 in formation of the axial organizing center-the notochord-that derives from the Spemann organizer, and participates in the induction and patterning of the neuroepithelium.

RESULTS

We confirm a role for apoptosis in establishing the axial organizer in early neurula. We show that the expression pattern of mcl1 is coherent with a role for this gene in early notochord development. Using loss of function approaches, we demonstrate that Mcl1 depletion decreases neuroepithelium width and increases notochord cells apoptosis, a process that relies on Caspase-7, and not on Caspase-3, activity. Our data provide evidence that Mcl1 protein levels physiologically control notochord cells' survival and that Caspase-7 is the executioner protease in this developmental process.

CONCLUSIONS

Our study reveals new functions for Mcl1 and Caspase-7 in formation of the axial signalling center.

Deletion of hypoxia-responsive microRNA-210 results in a sex-specific decrease in nephron number

Low nephron number results in an increased risk of developing hypertension and chronic kidney disease. Intrauterine growth restriction is associated with a nephron deficit in humans, and is commonly caused by placental insufficiency, which results in fetal hypoxia. The underlying mechanisms by which hypoxia impacts kidney development are poorly understood. microRNA-210 is the most consistently induced microRNA in hypoxia and is known to promote cell survival in a hypoxic environment. In this study, the role of microRNA-210 in kidney development was evaluated using a global microRNA-210 knockout mouse. A male-specific 35% nephron deficit in microRNA-210 knockout mice was observed. Wnt/β-catenin signaling, a pathway crucial for nephron differentiation, was misregulated in male kidneys with increased expression of the canonical Wnt target lymphoid enhancer binding factor 1. This coincided with increased expression of caspase-8-associated protein 2, a known microRNA-210 target and apoptosis signal transducer. Together, these data are consistent with a sex-specific requirement for microRNA-210 in kidney development.

Treatment of Hominis placenta pharmacopuncture for a patient with mild neurocognitive disorder: Case report

Hominis placenta pharmacopuncture, a treatment that injects Hominis placenta extract into acupoints, has been suggested in the literature and researches that it could be used for cognitive decline. We experienced a case of mild neurocognitive disorder treated with Hominis placenta pharmacopuncture. Hominis placenta pharmacopuncture could be a possible treatment modality producing substantial clinical result in cognitive function which is assessed with Mini-Mental State Examination-Dementia Screening (MMSE-DS), Korean Version of Montreal Cognitive Assessment (MoCA-K), and Korean-Dementia Rating Scale (K-DRS). A 84-year-old man with mild neurocognitive disorder received Hominis placenta pharmacopuncture on GV20, CV12, and bilateral ST36 for a month. The results of neuropsychological examination showed increase in scores after treatment of Hominis placenta pharmacopuncture. Before treatment, they were 15 points for MoCA-K, and 120 points for K-DRS (7.6%), but after treatment, they elevated by 21 points for MoCA-K and 137 points for K-DRS (100%). MMSE-DS score was 28 points, unchanged before and after treatment. It did not cause any side-effect. Hominis placenta pharmacopuncture could be a safe option for treating mild neurocognitive disorder.

Naesohwangryeon-tang Induced Apoptosis and Autophagy in A549 Human Lung Cancer Cells

Objectives

Naesohwangryeon-tang (NHT) is a type of traditional herbal formula, however, little is known about its antitumor activity. In this study, the antitumor properties of NHT was evaluated in human lung adenocarcinoma cells.

Methods

To check the inhibitory effect of NHT, MTT assay was performed. Cell cycle analysis and detection of ROS production were conducted by flow cytometry. To evaluate the signaling pathway, Western blotting was conducted.

Results

Our results showed that the decrease of cell proliferation by NHT stimulation occurred more significantly in A549 cells than in NCI-H460 cells. In addition, NHT-induced apoptosis was associated with the activation of caspases and production of reactive oxygen species (ROS). NHT-induced apoptosis was attenuated after pretreatments with z-VAD-fmk or N-acetylcysteine, suggesting that NHT-induced apoptosis was caspase- and ROS-dependent. Interestingly, NHT treatment led to the development of autophagic vesicular organelles and upregulation of several autophagy-related genes. The pretreatment of bafilomycin A1 decreased apoptosis slightly but increased cell viability in the presence of NHT.

Conclusion

These findings indicated that NHT induces both apoptosis and cell-protective autophagy in human lung cancer cells. This data suggests that NHT might be a novel herbal drug for lung cancer.

Cellular demolition: Proteins as molecular players of programmed cell death

Apoptosis, a well-characterized and regulated cell death programme in eukaryotes plays a fundamental role in developing or later-life periods to dispose of unwanted cells to maintain typical tissue architecture, homeostasis in a spatiotemporal manner. This silent cellular death occurs without affecting any neighboring cells/tissue and avoids triggering of immunological response. Furthermore, diminished forms of apoptosis result in cancer and autoimmune diseases, whereas unregulated apoptosis may also lead to the development of a myriad of neurodegenerative diseases. Unraveling the mechanistic events in depth will provide new insights into understanding physiological control of apoptosis, pathological consequences of abnormal apoptosis and development of novel therapeutics for diseases. Here we provide a brief overview of molecular players of programmed cell death with discussion on the role of caspases, modifications, ubiquitylation in apoptosis, removal of the apoptotic body and its relevance to diseases.

Neuronally Enriched RUFY3 Is Required for Caspase-Mediated Axon Degeneration

Selective synaptic and axonal degeneration are critical aspects of both brain development and neurodegenerative disease. Inhibition of caspase signaling in neurons is a potential therapeutic strategy for neurodegenerative disease, but no neuron-specific modulators of caspase signaling have been described. Using a mass spectrometry approach, we discovered that RUFY3, a neuronally enriched protein, is essential for caspase-mediated degeneration of TRKA+ sensory axons in vitro and in vivo. Deletion of Rufy3 protects axons from degeneration, even in the presence of activated CASP3 that is competent to cleave endogenous substrates. Dephosphorylation of RUFY3 at residue S34 appears required for axon degeneration, providing a potential mechanism for neurons to locally control caspase-driven degeneration. Neuronally enriched RUFY3 thus provides an entry point for understanding non-apoptotic functions of CASP3 and a potential target to modulate caspase signaling specifically in neurons for neurodegenerative disease.

Combined Fluorimetric Caspase-3/7 Assay and Bradford Protein Determination for Assessment of Polycation-Mediated Cytotoxicity

Cationic polyplexes and lipoplexes are widely used as artificial systems for nucleic acid delivery into the cells, but they can also induce cell death. Mechanistic understanding of cell toxicity and biological side effects of these cationic entities is essential for optimization strategies and design of safe and efficient nucleic acid delivery systems. Numerous methods are presently available to detect and delineate cytotoxicity and cell death-mediated signals in cell cultures. Activation of caspases is part of the classical apoptosis program and increased caspase activity is therefore a well-established hallmark of programmed cell death. Additional methods to monitor cell-death related signals must, however, also be carried out to fully define the type of cell toxicity in play. These may include methods that detect plasma membrane damage, loss of mitochondrial membrane potential, phosphatidylserine exposure, and cell morphological changes (e.g., membrane blebbing, nuclear changes, cytoplasmic swelling, cell rounding). Here we describe a 96-well format protocol for detection of caspase-3/7 activity in cell lysates, based on a fluorescent caspase-3 assay, combined with a method to simultaneously determine relative protein contents in the individual wells.

The prodomain of caspase-3 regulates its own removal and caspase activation

Caspase-3 is a cysteine–aspartic acid protease that cleaves cellular targets and executes cell death. Our current understanding is caspase-3 is activated by the cleavage of the interdomain linker and then subsequent cleavage of the N-terminal prodomain. However, previous reports have suggested that removal of the prodomain can result in the constitutive activation of caspase-3, although other studies have not observed this. To address this question in a more physiological setting, we developed an inducible doxycycline system to express a mutant form of caspase-3 that lacks the prodomain (∆28). We found that the removal of the prodomain renders the cells more susceptible to death signals, but the caspase is not constitutively active. To elucidate the regions of the prodomain that regulate activity, we created deletion constructs that remove 10 and 19 N-terminal amino acids. Surprisingly, removal of the first 10 amino acids renders caspase-3 inactive. Following serum withdrawal, the interdomain linker is cleaved, however, the remaining prodomain is not removed. Therefore, there is a specific amino acid or stretch of amino acids within the first 10 that are important for prodomain removal and caspase-3 function. We created different point mutations within the prodomain and found amino acid D9 is vital for caspase-3 function. We hypothesize that an initial cleavage event at D9 is required to allow cleavage at D28 that causes the complete removal of the prodomain allowing for full caspase activation. Together these findings demonstrate a previously unknown role of the prodomain in caspase activation.

Two Sides of the Same Coin - Compensatory Proliferation in Regeneration and Cancer

Apoptosis has long been regarded as a tumor suppressor mechanism and evasion from apoptosis is considered to be one hallmark of cancer. However, this principle is not always consistent with clinical data which often illustrate a correlation between apoptosis and poor prognosis. Work in the last 15 years has provided an explanation for this apparent paradox. Apoptotic cells communicate with their environment and can produce signals which promote compensatory proliferation of surviving cells. This behavior of apoptotic cells is important for tissue regeneration in several model organisms, ranging from hydra to mammals. However, it may also play an important feature for tumorigenesis and tumor relapse. Several distinct forms of apoptosis-induced compensatory proliferation (AiP) have been identified, many of which involve reactive oxygen species (ROS) and immune cells. One type of AiP, "undead" AiP, in which apoptotic cells are kept in an immortalized state and continuously divide, may have particular relevance for tumorigenesis. Furthermore, given that chemo- and radiotherapy often aim to kill tumor cells, an improved understanding of the effects of apoptotic cells on the tumor and the tumor environment is of critical importance for the well-being of the patient. In this review, we summarize the current knowledge of AiP and focus our attention on recent findings obtained in Drosophila and other model organisms, and relate them to tumorigenesis.

Proteinase 3 Limits the Number of Hematopoietic Stem and Progenitor Cells in Murine Bone Marrow

Hematopoietic stem and progenitor cells (HSPCs) undergo self-renewal and differentiation to guarantee a constant supply of short-lived blood cells. Both intrinsic and extrinsic factors determine HSPC fate, but the underlying mechanisms remain elusive. Here, we report that Proteinase 3 (PR3), a serine protease mainly confined to granulocytes, is also expressed in HSPCs. PR3 deficiency intrinsically suppressed cleavage and activation of caspase-3, leading to expansion of the bone marrow (BM) HSPC population due to decreased apoptosis. PR3-deficient HSPCs outcompete the long-term reconstitution potential of wild-type counterparts. Collectively, our results establish PR3 as a physiological regulator of HSPC numbers. PR3 inhibition is a potential therapeutic target to accelerate and increase the efficiency of BM reconstitution during transplantation.

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Proteinase 3 (PR3) is expressed in hematopoietic stem and progenitor cells (HSPCs)

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Deficiency of PR3 leads to expansion of HSPCs in murine bone marrow

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PR3 regulates spontaneous HSPC apoptosis by cleaving and activating caspase-3

Non-apoptotic Caspase regulation of stem cell properties

The evolutionarily conserved family of proteins called caspases are the main factors mediating the orchestrated programme of cell suicide known as apoptosis. Since this protein family was associated with this essential biological function, the majority of scientific efforts were focused towards understanding their molecular activation and function during cell death. However, an emerging body of evidence has highlighted a repertoire of non-lethal roles within a large variety of cell types, including stem cells. Here we intend to provide a comprehensive overview of the key role of caspases as regulators of stem cell properties. Finally, we briefly discuss the possible pathological consequences of caspase malfunction in stem cells, and the therapeutic potential of caspase regulation applied to this context.

Wentilactone A induces cell apoptosis by targeting AKR1C1 gene via the IGF-1R/IRS1/PI3K/AKT/Nrf2/FLIP/Caspase-3 signaling pathway in small cell lung cancer

Wentilactone A (WA), a marine-derived compound, inhibits proliferation of NCI-H446, as demonstrated by previous research; however, the anti-SCLC mechanism underlying WA was not fully investigated. The present study aimed to investigate the anti-SCLC mechanism underlying WA in vitro and in vivo. Cell Counting Kit-8 was used to assay cell growth, flow cytometry was conducted to analyze cell apoptosis and nude mice xenografts were used to examine SCLC growth following WA treatment. Bioinformatics was used for verification of the target gene of WA. Reverse transcription-quantitative polymerase chain reaction and western blot were used to examine aldo-keto reductase family 1 member C1 (AKR1C1) mRNA and protein levels, and AKR1C1-associated proteins prior to and following WA treatment. Cell growth, apoptosis and growth of nude mice xenografts were assayed prior to and following transfection with AKR1C1 knockdown or overexpression carriers, respectively. It was determined that AKR1C1 was a target gene of WA. Decreased AKR1C1 expression and WA treatment promoted apoptosis in SCLC via the insulin like growth factor-1 receptor/insulin receptor substrate 1/phosphoinositide 3-kinase/AKT/nuclear factor-erythroid 2-associated factor 2/Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein/Caspase-3 pathway. WA attenuated the proliferation and induced the apoptosis of SCLC cells in vitro and in vivo by targeting the AKR1C1 gene. WA may be a novel AKR1C1-targeted drug candidate for the treatment of SCLC in the future.

Pachymic Acid Sensitizes Gastric Cancer Cells to Radiation Therapy by Upregulating Bax through Hypoxia

We have previously shown that pachymic acid (PA) inhibited tumorigenesis of gastric cancer (GC) cells. However, the exact mechanism underlying the radiation response of GC was still elusive. To evaluate the effects of PA treatment on radiation response of GC cell lines both in vitro and in vivo, a colony formation assay and xenograft mouse model were employed. Changes in Bax and HIF1[Formula: see text] expressions were assessed in GC cells following PA treatment. Luciferase reporter and chromatin immune-precipitation assays were carried out to investigate the regulation of Bax through HIF1[Formula: see text]. Stable HIF1[Formula: see text] knockdown was introduced into GC cells to further study the mechanism underlying PA-enhanced response to radiation both in vitro and in vivo. PA greatly enhanced the sensitivity of GC cells to radiation in vitro and in vivo, upregulated Bax expression and inhibited hypoxia. Bax expression was under hypoxia inhibition, and PA increased Bax expression through repressing HIF1[Formula: see text]. Stable HIF1[Formula: see text] overexpression in GC cells abolished the sensitizing effect of PA on GC cells to radiation both in vitro and in vivo. PA functions as a radiation sensitizing compound in GC. PA treatment induces the expression of pro-apoptotic factor Bax by inhibiting hypoxia/HIF1[Formula: see text], supporting the therapeutic potential of PA in radiation therapy against GC.

Immunohistochemical expression of apoptosis-related biomarkers in normal tissues of camel (Camelus dromedarius): A survey in a desert-dwelling mammalian model

Programmed cell death is a fundamental event that takes place during organ development and plays an important role in cellular homeostasis. Since various body organs of the camel are under high ecological and physiological stress during food and water deprivation, desiccation, and the long exposure to solar radiation in these desert nomads, we aimed to examine the immunohistochemical expression of apoptosis-related biomarkers in some of its normal body organs to illustrate a basic track for further pathological investigation. Regarding apoptosis, the present study has revealed that the higher expression of cleaved caspase-9 (CC9) [initiator of the intrinsic pathway] and CC3 (effector caspase), and the scanty expression of CC8 (initiator of the extrinsic pathway), highlight the role of the caspase-dependent, intrinsic apoptotic pathway particularly in the intestines and lymphoid organs. The apoptosis- inducing factor (AIF)-immunoexpression was completely missing in the cell nuclei of the examined tissues, indicating the absence of the caspase-independent pathway. The nuclear overexpression of the phospho-histone H2AX (γ H2AX) and the occasional expression of single-stranded DNA, particularly among the CNS neurons, suggest an efficient, protective DNA-repair mechanism in such cells. Thus, despite efficient anti-apoptotic mechanisms intrinsic apoptotic pathways exists in brain, intestine and lymph organs of adult desert camels.

Changes in Plasma β-NGF and Its Receptors Expression on Peripheral Blood Monocytes During Alzheimer's Disease Progression

Alzheimer's disease (AD), the most common cause of dementia, is characterized by the deposition of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles, and by neuroinflammation. During the pathogenesis of AD, monocyte-macrophage lineage cells become increasingly ineffective in clearing Aβ deposits, less able to differentiate, and shift toward pro-inflammatory processes. Beta-nerve growth factor (β-NGF) and its receptors, TrKA and p75NTR, produce several biological responses, including cell apoptosis and survival, and inflammation. In the central nervous system, the involvement of these receptors in several critical hallmarks of AD is well known, but their role in circulating monocytes during the progression of dementia is unclear. We investigated the relationship between plasma β-NGF concentration and TrkA/p75NTR receptor expression in monocytes of patients with mild cognitive impairment (MCI), mild AD, and severe AD. We observed that plasma β-NGF concentration was increased with a higher expression of TrKA, but not of p75NTR, in monocytes from patients with MCI and mild AD, whereas β-NGF concentration and TrKA expression were decreased and p75NTR expression was increased, associated with caspase 3-mediated apoptosis, in patients with severe AD. In our study, we show evidence of variation in plasmatic β-NGF and monocytic TrkA/p75NTR receptor expression during the progression of dementia. These novel findings add evidence to support the hypothesis for the involvement of β-NGF and its receptors on monocytes during AD progression.

ABIN-1 regulates RIPK1 activation by linking Met1 ubiquitylation with Lys63 deubiquitylation in TNF-RSC

Ubiquitination of TNFR1-signaling-complex (TNF-RSC) controls the activation of RIPK1, a kinase critically involved in mediating multiple TNFα activated deleterious events. However, the molecular mechanism that coordinates different types of ubiquitination modifications to regulate the activation of RIPK1 kinase remains unclear. Here, we show that ABIN-1/NAF-1, a ubiquitin-binding protein, is recruited rapidly into TNF-RSC in a manner dependent upon M1 ubiquitinating complex LUBAC to regulate the recruitment of A20 to control K63 deubiquitination of RIPK1. ABIN-1 deficiency reduces the recruitment of A20 and licenses cells to die through necroptosis by promoting K63 ubiquitination and activation of RIPK1 with TNFα stimulation under conditions that would otherwise exclusively activate apoptosis in wild-type cells. Inhibition of RIPK1 kinase and RIPK3 deficiency block the embryonic lethality of Abin-1^−/− mice. We propose that ABIN-1 provides a critical link between M1 ubiquitination mediated by LUBAC complex and K63 deubiquitination by phospho-A20 to modulate the activation of RIPK1.

Pachymic acid inhibits the tumorigenicity of gastric cancer cells by the mitochondrial pathway

Pachymic acid (PA), a lanostane-type triterpenoid derived from traditional Chinese herbals, has been reported to have antitumor activity in versatile cancer cells. However, the antitumor effect of PA in gastric cancer (GC) cells remains unclear. In this study, we aimed to explore the efficacy and mechanisms of PA in GC. The antiproliferative effect of PA was assessed by a growth assay and a colony formation assay. Flow cytometry was used to detect changes in cell cycle distribution. Apoptosis was assessed by an annexin V/propidium iodide double-staining assay. The expressions of the apoptosis-related proteins were measured by western blot. The mitochondrial capacity was observed by immunostaining of Mito Tracker Red and mitochondrial function protein MT. Xenograft models of GC were constructed by a subcutaneous injection of SGC-7901 and MKN-49P cells pretreated with PA. PA could potently inhibit GC cell growth and colony formation. PA significantly induced G1, G2/M, and inhibited G0 phase arrest in GC cell lines SGC-7901 and MKN-49P. PA induced cell apoptosis by regulating the expressions of apoptosis-related proteins (caspase-3, PARP, Bcl-2, and Bax) and suppressing the mitochondrial capacity of GC cell lines in vitro in a dose-dependent manner. In addition, PA suppressed the tumor growth of xenograft models of GC and prolonged the survival of animals markedly. In brief, the present study shows that PA induces apoptosis through inhibition of mitochondrial capacity in human GC cells. Our findings suggest that PA may have therapeutic potential in GC.

Proteomic identification of synaptic caspase substrates

The dismantling and elimination of excess neurons and their connections (pruning) is essential for brain development and may be aberrantly reactivated in some neurodegenerative diseases. Growing evidence implicates caspase-mediated apoptotic and nonapoptotic cascades in the dysfunction and death of neurons in neurodegenerative disorders such as Alzheimer's, Parkinson, and Huntington's diseases. It is the cleaved caspase substrates that are the effectors of synapse elimination. However, their identities, specific cleavage sites, and functional consequences of cleavage are largely unknown. An important gap in our knowledge is a comprehensive catalog of synapse-specific or synapse-enriched caspase targets. Traditional biochemical approaches have revealed only a small number of neuronal caspase targets. Instead, we utilized a gel-based proteomics approach to enable the first global analysis of caspase-mediated cleavage events in mammalian brain synapses, employing both an in vitro system with recombinant activated caspases and an in vivo model of ethanol-induced neuronal apoptosis. Of the more than 70 putative cleavage substrates that were identified, 22 were previously known caspase substrates. Among the novel targets identified and validated by Western blot were the proton pump ATPase subunit ATP6V1B2 and the N-ethylmaleimide-sensitive fusion protein (NSF). Our work represents the first comprehensive, proteome-wide screen for proteolytic targets of caspases in neuronal synapses. Our discoveries will have significance for both furthering basic understanding of roles of caspases in synaptic plasticity and synaptic loss in neurodegeneration, and on a more immediately practical level, may provide candidate biomarkers for measuring synapse loss in human disease states.

Paths from DNA damage and signaling to genome rearrangements via homologous recombination

DNA damage is a constant threat to genome integrity. DNA repair and damage signaling networks play a central role maintaining genome stability, suppressing tumorigenesis, and determining tumor response to common cancer chemotherapeutic agents and radiotherapy. DNA double-strand breaks (DSBs) are critical lesions induced by ionizing radiation and when replication forks encounter damage. DSBs can result in mutations and large-scale genome rearrangements reflecting mis-repair by non-homologous end joining or homologous recombination. Ionizing radiation induces genetic change immediately, and it also triggers delayed events weeks or even years after exposure, long after the initial damage has been repaired or diluted through cell division. This review covers DNA damage signaling and repair pathways and cell fate following genotoxic insult, including immediate and delayed genome instability and cell survival/cell death pathways.

Exosomes derived from bone marrow stromal cells decrease the sensitivity of leukemic cells to etoposide

The aim of the study was to investigate the effect of exosomes derived from bone marrow stromal cells (BM-SCs) on the chemoresistant characteristics of nalm-6 cells treated with etoposide (VP16). The present study isolated exosomes from BM-SC-conditioned medium by using standard differential centrifugation steps and detected the expression of 70 kilodalton heat shock proteins (HSP70) and lysosomal-associated membrane protein 3 (CD63) in exosomes by western blot analysis. Nalm-6 cells were co-cultured with exosomes in the presence of VP16. Cell viability and apoptosis were then detected using the Cell Counting Kit-8 method and Annexin-V/propidium iodide, respectively. Finally, protein levels of B-cell lymphoma 2 (BCL-2), BCL-2-like protein 4 (BAX), caspase-3, and poly ADP-ribose polymerase (PARP) were examined by western blot analysis. Exosomes were successfully isolated from the conditioned medium and confirmed by the expression of HSP70 and CD63. BM-SC-derived exosomes increased the viability of nalm-6 cells in the presence of VP16 and inhibited the apoptosis induced by VP16. Western blot analysis results showed that exosomes can block the significant reduction of BCL-2, full-length caspase-3 and full-length PARP, while preventing the increase of BAX, cleaved caspase-3 and cleaved PARP induced by VP16. Exosomes derived from BM-SCs can protect nalm-6 cells from VP16-induced apoptosis to maintain their survival and induce resistance to VP16. In addition, BCL-2/BAX, caspase-3, and PARP may be involved in the mechanism of exosome-induced drug resistance.

Bright Bioluminescent BRET Sensor Proteins for Measuring Intracellular Caspase Activity

FRET-based caspase activity probes have become important tools to monitor apoptotic cell signaling. However, their dependence on external illumination is incompatible with light sensitive cells and hampers applications that suffer from autofluorescence and light scattering. Here we report the development of three caspase sensor proteins based on Bioluminescence Resonance Energy Transfer (BRET) that retain the advantages of genetically encoded, ratiometric optical probes but do not require external illumination. These sensors consist of the bright and stable luciferase NanoLuc and the fluorescent protein mNeonGreen, fused together via a linker containing a recognition site for caspase-3, -8, or -9. In vitro characterization showed that each caspase sensor displayed a robust 10-fold decrease in BRET ratio upon linker cleavage, with modest caspase specificity. Importantly, whereas scattering and background fluorescence precluded FRET-based detection of intracellular caspase activity in plate-reader assays, such measurements could be easily performed using our caspase BRET sensors in a high throughput format. The brightness of the BRET sensors also enabled long-term single-cell imaging, allowing BRET-based recording of cell heterogeneity in caspase activity in a heterogenic cell population.

Caspase-dependent non-apoptotic processes in development

Caspases are at the core of executing apoptosis by orchestrating cellular destruction with proteolytic cascades. Caspase-mediated proteolysis also controls diverse nonlethal cellular activities such as proliferation, differentiation, cell fate decision, and cytoskeletal reorganization. During the last decade or so, genetic studies of Drosophila have contributed to our understanding of the in vivo mechanism of the non-apoptotic cellular responses in developmental contexts. Furthermore, recent studies using C. elegans suggest that apoptotic signaling may play unexpected roles, which influence ageing and normal development at the organism level. In this review, we describe how the caspase activity is elaborately controlled during vital cellular processes at the level of subcellular localization, the duration and timing to avoid full apoptotic consequences, and also discuss the novel roles of non-apoptotic caspase signaling in adult homeostasis and physiology.

Maspin suppresses growth, proliferation and invasion in cutaneous squamous cell carcinoma cells

Cutaneous squamous cell carcinoma (cSCC) is a common malignant tumor. Mammary serine protease inhibitor (Maspin), a member of serpin family, has been reported as a tumor suppressor in various carcinomas. In this study, we detected the expression level of Maspin in cSCC tissues by real-time PCR and western blotting, and found that Maspin was downregulated in the cSCC tissues compared with the adjacent normal tissues. Moreover, Maspin was stably overexpressed in A431 cells, and CCK-8 assay, colony formation assay, Transwell assay, Hoechst staining and western blotting were carried out to detect the growth, proliferation, invasion, cell cycle and apoptosis of A431 cells. The results revealed that overexpression of Maspin inhibited growth, proliferation, invasion and cell cycle G1/S/G2 transition and enhanced apoptosis of A431 cells. The pro-apoptotic protein cleaved caspase-3, poly(ADP-ribose) polymerase (PARP) and Bax increased, and the anti-apoptotic protein Bcl-2 decreased after Maspin overexpression. Therefore, we demonstrated that Maspin suppressed growth, proliferation and invasion by delaying cell cycle transition and promoting apoptosis in cSCC cells, which may provide new insights for the clinical diagnosis and therapy of cSCC.

Oxidative stress and apoptosis after acute respiratory hypoxia and reoxygenation in rat brain

Acute hypoxia increases the formation of reactive oxygen species (ROS) in the brain. However, the effect of reoxygenation, unavoidable to achieve full recovery of the hypoxic organ, has not been clearly established. The aim of the present study was to evaluate the effects of exposition to acute severe respiratory hypoxia followed by reoxygenation on the evolution of oxidative stress and apoptosis in the brain. We investigated the effect of in vivo acute severe normobaric hypoxia (rats exposed to 7% O₂ for 6 h) and reoxygenation in normoxia (21% O₂ for 24 h or 48 h) on oxidative stress markers, the antioxidant system and apoptosis in the brain. After respiratory hypoxia we found increased levels of HIF-1α expression, lipid peroxidation, protein oxidation and nitric oxide in brain extracts. Antioxidant defence systems such as superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPx) and the reduced/oxidized glutathione (GSH/GSSG) ratio were significantly decreased in the brain. After 24 h of reoxygenation, oxidative stress parameters and the anti-oxidant system returned to control values. Regarding the apoptosis parameters, acute hypoxia increased cytochrome c, AIF and caspase 3 activity in the brain. The apoptotic effect is greatest after 24 h of reoxygenation. Immunohistochemistry suggests that CA3 and dentate gyrus in the hippocampus seem more susceptible to hypoxia than the cortex. Severe acute hypoxia increases oxidative damage, which in turn could activate apoptotic mechanisms. Our work is the first to demonstrate that after 24 h of reoxygenation oxidative stress is attenuated, while apoptosis is maintained mainly in the hippocampus, which may, in fact, be the cause of impaired brain function.

Metacaspases versus caspases in development and cell fate regulation

Initially found to be critically involved in inflammation and apoptosis, caspases have since then been implicated in the regulation of various signaling pathways in animals. How caspases and caspase-mediated processes evolved is a topic of great interest and hot debate. In fact, caspases are just the tip of the iceberg, representing a relatively small group of mostly animal-specific enzymes within a broad family of structurally related cysteine proteases (family C14 of CD clan) found in all kingdoms of life. Apart from caspases, this family encompasses para- and metacaspases, and all three groups of proteases exhibit significant variation in biochemistry and function in vivo. Notably, metacaspases are present in all eukaryotic lineages with a remarkable absence in animals. Thus, metacaspases and caspases must have adapted to operate under distinct cellular and physiological settings. Here we discuss biochemical properties and biological functions of metacaspases in comparison to caspases, with a major focus on the regulation of developmental aspects in plants versus animals.

In Vitro Cell Death Determination for Drug Discovery: A Landscape Review of Real Issues

Cell death plays a crucial role for a myriad of physiological processes, and several human diseases such as cancer are characterized by its deregulation. There are many methods available for both quantifying and qualifying the accurate process of cell death which occurs. Choosing the right assay tool is essential to generate meaningful data, provide sufficient information for clinical applications, and understand cell death processes. In vitro cell death assays are important steps in the search for new therapies against cancer as the ultimate goal remains the elaboration of drugs that interfere with specific cell death mechanisms. However, choosing a cell viability or cytotoxicity assay among the many available options is a daunting task. Indeed, cell death can be approached by several viewpoints and require a more holistic approach. This review provides an overview of cell death assays usually used in vitro for assessing cell death so as to elaborate new potential chemotherapeutics and discusses considerations for using each assay.

DNA damage signalling in D. melanogaster requires non-apoptotic function of initiator caspase Dronc

ϒH2Av response constitutes an important signalling event in DNA damage sensing ensuring effective repair by recruiting DNA repair machinery. In contrast, the occurrence of ϒH2Av response has also been reported in dying cells where it is shown to require activation of CAD (caspase activated DNase). Moreover, caspases are known to be required downstream of DNA damage for cell death execution. We show, for the first time, that initiator caspase Dronc, independent of executioner caspases, acts as an upstream regulator of DNA Damage Response (DDR) by facilitating ϒH2Av signalling perhaps involving non-apoptotic function. Such ϒH2Av response is mediated by ATM rather than ATR, suggesting that Dronc function is required upstream of ATM. In contrast, ϒH2Av appearance during cell death requires effector caspase and is associated with fragmented nuclei. Our study uncovers a novel function of Dronc in response to DNA damage aimed at promoting DDR via ϒH2Av signalling in intact nuclei. We propose that Dronc plays a dual role that can either initiate DDR or apoptosis depending upon the level and the required threshold of its activation in damaged cells.

MST1/MST2 Protein Kinases: Regulation and Physiologic Roles

The MST1 and MST2 protein kinases comprise the GCK-II subfamily of protein kinases. In addition to their amino-terminal kinase catalytic domain, related to that of the Saccharomyces cerevisiae protein kinase Ste20, their most characteristic feature is the presence near the carboxy terminus of a unique helical structure called a SARAH domain; this segment allows MST1/MST2 to homodimerize and to heterodimerize with the other polypeptides that contain SARAH domains, the noncatalytic polypeptides RASSF1-6 and Sav1/WW45. Early studies emphasized the potent ability of MST1/MST2 to induce apoptosis upon being overexpressed, as well as the conversion of the endogenous MST1/MST2 polypeptides to constitutively active, caspase-cleaved catalytic fragments during apoptosis initiated by any stimulus. Later, the cleaved, constitutively active form of MST1 was identified in nonapoptotic, quiescent adult hepatocytes as well as in cells undergoing terminal differentiation, where its presence is necessary to maintain those cellular states. The physiologic regulation of full length MST1/MST2 is controlled by the availability of its noncatalytic SARAH domain partners. Interaction with Sav1/WW45 recruits MST1/MST2 into a tumor suppressor pathway, wherein it phosphorylates and activates the Sav1-bound protein kinases Lats1/Lats2, potent inhibitors of the Yap1 and TAZ oncogenic transcriptional regulators. A constitutive interaction with the Rap1-GTP binding protein RASSF5B (Nore1B/RAPL) in T cells recruits MST1 (especially) and MST2 as an effector of Rap1's control of T cell adhesion and migration, a program crucial to immune surveillance and response; loss of function mutation in human MST1 results in profound immunodeficiency. MST1 and MST2 are also regulated by other protein kinases, positively by TAO1 and negatively by Par1, SIK2/3, Akt, and cRaf1. The growing list of candidate MST1/MST2 substrates suggests that the full range of MST1/MST2's physiologic programs and contributions to pathophysiology remains to be elucidated.

Dysregulation of a potassium channel, THIK-1, targeted by caspase-8 accelerates cell shrinkage

Activation of caspases is crucial for the execution of apoptosis. Although the caspase cascade associated with activation of the initiator caspase-8 (CASP8) has been investigated in molecular and biochemical detail, the physiological role of CASP8 is not fully understood. Here, we identified a two-pore domain potassium channel, tandem-pore domain halothane-inhibited K⁺ channel 1 (THIK-1), as a novel CASP8 substrate. The intracellular region of THIK-1 was cleaved by CASP8 in apoptotic cells. Overexpression of THIK-1, but not its mutant lacking the CASP8-target sequence in the intracellular portion, accelerated cell shrinkage in response to apoptotic stimuli. In contrast, knockdown of endogenous THIK-1 by RNA interference resulted in delayed shrinkage and potassium efflux. Furthermore, a truncated THIK-1 mutant lacking the intracellular region, which mimics the form cleaved by CASP8, led to a decrease of cell volume of cultured cells without apoptotic stimulation and excessively promoted irregular development of Xenopus embryos. Taken together, these results indicate that THIK-1 is involved in the acceleration of cell shrinkage. Thus, we have demonstrated a novel physiological role of CASP8: creating a cascade that advances the cell to the next stage in the apoptotic process.

Krebs Cycle Moonlights in Caspase Regulation

In this issue of Developmental Cell, Aram et al. (2016) identify a mechanism that uses a Krebs cycle protein to control local activation of a ubiquitin ligase complex at the mitochondrial outer membrane for temporally and spatially restricted caspase activation during Drosophila sperm differentiation.

The de-ubiquitylating enzyme DUBA is essential for spermatogenesis in Drosophila

De-ubiquitylating enzymes (DUBs) reverse protein ubiquitylation and thereby control essential cellular functions. Screening for a DUB that counteracts caspase ubiquitylation to regulate cell survival, we identified the Drosophila ovarian tumour-type DUB DUBA (CG6091). DUBA physically interacts with the initiator caspase death regulator Nedd2-like caspase (Dronc) and de-ubiquitylates it, thereby contributing to efficient inhibitor of apoptosis-antagonist-induced apoptosis in the fly eye. Searching also for non-apoptotic functions of DUBA, we found that Duba-null mutants are male sterile and display defects in spermatid individualisation, a process that depends on non-apoptotic caspase activity. Spermatids of DUBA-deficient flies showed reduced caspase activity and lack critical structures of the individualisation process. Biochemical characterisation revealed an obligate activation step of DUBA by phosphorylation. With genetic rescue experiments we demonstrate that DUBA phosphorylation and catalytic activity are crucial in vivo for DUBA function in spermatogenesis. Our results demonstrate for the first time the importance of de-ubiquitylation for fly spermatogenesis.

Chromatin Condensation and Enucleation in Red Blood Cells: An Open Question

Differentiating erythroid cells undergo dramatic changes in morphology, with reduction in cell size, chromatin and nuclear condensation, and enucleation. In this issue of Developmental Cell, Zhao et al. (2016) show that these events are associated with the formation of transient, recurring nuclear openings and selective histone release mediated by caspase-3.

The fibronectin III-1 domain activates a PI3-Kinase/Akt signaling pathway leading to αvβ5 integrin activation and TRAIL resistance in human lung cancer cells

Background

Fibronectin is a mechanically sensitive protein which is organized in the extracellular matrix as a network of interacting fibrils. The lung tumor stroma is enriched for fibronectin which is thought to contribute to metastasis and drug resistance. Fibronectin is an elastic, multi-modular protein made up of individually folded domains, some of which can stretch in response to increased mechanical tension. Very little is known about the relationship of fibronectin’s unfolded domains to lung cancer resistance to chemotherapy. In the present study, we evaluated the impact of unfolding the first Type III domain of fibronectin (FnIII-1c) on TNF-related apoptosis inducing ligand (TRAIL) resistance.

Methods

NCI-H460 non-small cell lung cancer cells were treated with FnIII-1c then assessed for TRAIL-induced apoptosis. Subsequent analysis of FnIII-1c-mediated signaling pathways was also completed. Human non-small cell lung cancer tissue sections were assessed for the expression of vitronectin by immunohistochemistry.

Results

FnIII-1c inhibited TRAIL-induced activation of caspase 8 and subsequent apoptosis in NCI-H460 lung cancer cells. FnIII-1c treatment was associated with the activation of the phosphatidylinositol-3-kinase/alpha serine/threonine kinase (PI3K/Akt) pathway and the αvβ5 integrin receptor for vitronectin, both of which were required for TRAIL resistance. Immunohistochemical staining of sections from non-small cell lung cancers showed that vitronectin was localized around blood vessels and in the tumor-stroma interface.

Conclusions

Unfolding of Type III domains within the fibronectin matrix may promote TRAIL resistance through the activation of a PI3K/Akt/αvβ5 signaling axis and point to a novel mechanism by which changes in secondary structure of fibronectin contribute to cancer cell resistance to apoptosis.

Multi-level structure-based pharmacophore modelling of caspase-3-non-peptide complexes: Extracting essential pharmacophore features and its application to virtual screening

Enormous caspase-3-non-peptide crystal structures have been developed to study the structural basis of caspase-3 enzyme inhibition using active site directed small molecular design. These complexes have not been explored thoroughly to decipher the essential non-covalent interactions made by crystal ligands. We present here a multi-level analysis of these caspase-3 complexes using structure-based pharmacophore approach wherein numerous candidate pharmacophore hypotheses were assessed for its ability to cover available caspase-3 small molecular inhibitor dataset. The reliability of the resultant pharmacophores was evaluated using three different validation sets comprising focussed caspase-3 inhibitors, focussed + random decoys, and focussed + structurally similar random decoys and its performance was measured by the Güner-Henry (GH) scoring and enrichment statistics. Furthermore, the effect on excluded volumes toward caspase-3 inhibitors mapping was investigated by an iterative deletion in the structure-based models and created optimal structure-based pharmacophore models to enable effective design of caspase-3 small molecular inhibitor design.