The iron chelator and OXPHOS inhibitor VLX600 induces mitophagy and an autophagy-dependent type of cell death in glioblastoma cells

Induction of alternative, non-apoptotic cell death programs such as cell-lethal autophagy and mitophagy represent possible strategies to combat glioblastoma (GBM). Here we report that VLX600, a novel iron chelator and oxidative phosphorylation (OXPHOS) inhibitor, induces a caspase-independent type of cell death that is partially rescued in adherent U251 ATG5/7 (autophagy related 5/7) knockout (KO) GBM cells and NCH644 ATG5/7 knockdown (KD) glioma stem-like cells (GSCs), suggesting that VLX600 induces an autophagy-dependent cell death (ADCD) in GBM. This ADCD is accompanied by decreased oxygen consumption, increased expression/mitochondrial localization of BNIP3 (BCL2 interacting protein 3) and BNIP3L (BCL2 interacting protein 3 like), the induction of mitophagy as demonstrated by diminished levels of mitochondrial marker proteins [e.g., COX4I1 (cytochrome c oxidase subunit 4I1)] and the mitoKeima assay as well as increased histone H3 and H4 lysine tri-methylation. Furthermore, the extracellular addition of iron is able to significantly rescue VLX600-induced cell death and mitophagy, pointing out an important role of iron metabolism for GBM cell homeostasis. Interestingly, VLX600 is also able to completely eliminate NCH644 GSC tumors in an organotypic brain slice transplantation model. Our data support the therapeutic concept of ADCD induction in GBM and suggest that VLX600 may be an interesting novel drug candidate for the treatment of this tumor.NEW & NOTEWORTHY Induction of cell-lethal autophagy represents a possible strategy to combat glioblastoma (GBM). Here, we demonstrate that the novel iron chelator and OXPHOS inhibitor VLX600 exerts pronounced tumor cell-killing effects in adherently cultured GBM cells and glioblastoma stem-like cell (GSC) spheroid cultures that depend on the iron-chelating function of VLX600 and on autophagy activation, underscoring the context-dependent role of autophagy in therapy responses. VLX600 represents an interesting novel drug candidate for the treatment of this tumor.

Recent advances in natural compounds inducing non-apoptotic cell death for anticancer drug resistance

The induction of cell death is recognized as a potent strategy for cancer treatment. Apoptosis is an extensively studied form of cell death, and multiple anticancer drugs exert their therapeutic effects by inducing it. Nonetheless, apoptosis evasion is a hallmark of cancer, rendering cancer cells resistant to chemotherapy drugs. Consequently, there is a growing interest in exploring novel non-apoptotic forms of cell death, such as ferroptosis, necroptosis, pyroptosis, and paraptosis. Natural compounds with anticancer properties have garnered significant attention due to their advantages, including a reduced risk of drug resistance. Over the past two decades, numerous natural compounds have been discovered to exert anticancer and anti-resistance effects by triggering these four non-apoptotic cell death mechanisms. This review primarily focuses on these four non-apoptotic cell death mechanisms and their recent advancements in overcoming drug resistance in cancer treatment. Meanwhile, it highlights the role of natural compounds in effectively addressing cancer drug resistance through the induction of these forms of non-apoptotic cell death.

GPX8 regulates pan-apoptosis in gliomas to promote microglial migration and mediate immunotherapy responses

Introduction

Gliomas have emerged as the predominant brain tumor type in recent decades, yet the exploration of non-apoptotic cell death regulated by the pan-optosome complex, known as pan-apoptosis, remains largely unexplored in this context. This study aims to illuminate the molecular properties of pan-apoptosis-related genes in glioma patients, classifying them and developing a signature using machine learning techniques.

Methods

The prognostic significance, mutation features, immunological characteristics, and pharmaceutical prediction performance of this signature were comprehensively investigated. Furthermore, GPX8, a gene of interest, was extensively examined for its prognostic value, immunological characteristics, medication prediction performance, and immunotherapy prediction potential.

Results

Experimental techniques such as CCK-8, Transwell, and EdU investigations revealed that GPX8 acts as a tumor accelerator in gliomas. At the single-cell RNA sequencing level, GPX8 appeared to facilitate cell contact between tumor cells and macrophages, potentially enhancing microglial migration.

Conclusions

The incorporation of pan-apoptosis-related features shows promising potential for clinical applications in predicting tumor progression and advancing immunotherapeutic strategies. However, further in vitro and in vivo investigations are necessary to validate the tumorigenic and immunogenic processes associated with GPX8 in gliomas.

Pyroptosis Modulators: New Insights of Gasdermins in Health and Disease

Pyroptosis is an inflammation-dependent type of cell death that has been in the spotlight for the scientific community in the last few years. Crucial players in the process of pyroptosis are the members of the gasdermin family of proteins, which have been parallelly studied. Upon induction of pyroptosis, gasdermins suffer from structural changes leading to the formation of pores in the membrane that subsequently cause the release of pro-inflammatory contents. Recently, it has been discovered that oxidation plays a key role in the activation of certain gasdermins. Here, we review the current knowledge on pyroptosis and human gasdermins, focusing on the description of the different members of the family, their molecular structures, and their influence on health and disease directly or non-directly related to inflammation. Noteworthy, we have focused on the existing understanding of the role of this family of proteins in cancer, which could translate into novel promising strategies aimed at benefiting human health. In conclusion, the modulation of pyroptosis and gasdermins by natural and synthetic compounds through different mechanisms, including modification of the redox state of cells, has been proven effective and sets precedents for future therapeutic strategies.

Harnessing the Potential of Non-Apoptotic Cell Death Processes in the Treatment of Drug-Resistant Melanoma

Melanoma is a highly malignant skin cancer that is known for its resistance to treatments. In recent years, there has been significant progress in the study of non-apoptotic cell death, such as pyroptosis, ferroptosis, necroptosis, and cuproptosis. This review provides an overview of the mechanisms and signaling pathways involved in non-apoptotic cell death in melanoma. This article explores the interplay between various forms of cell death, including pyroptosis, necroptosis, ferroptosis, and cuproptosis, as well as apoptosis and autophagy. Importantly, we discuss how these non-apoptotic cell deaths could be targeted as a promising therapeutic strategy for the treatment of drug-resistant melanoma. This review provides a comprehensive overview of non-apoptotic processes and gathers recent experimental evidence that will guide future research and eventually the creation of treatment strategies to combat drug resistance in melanoma.

Acute generation of reactive oxygen species that induced by doxycycline pretreatment results in rapid cell death in polyphyllin G-treated osteosarcoma cell lines

Polyphyllin G, a pennogenyl saponin extracted from Paris polyphylla, has been shown to possess antitumor effects. In this study, we demonstrated that doxycycline, an antibiotic medicine, could significantly enhance the sensitivities of osteosarcoma cell lines to polyphyllin G. As the cells were pretreated with doxycycline at non-toxic concentrations and then co-exposed to polyphyllin G, this combination could induce a rapid cell death distinct from apoptosis. The non-apoptotic cell death was characterized by a loss of integrity of plasma membrane without externalization of phosphatidyl serine. Furthermore, this combined treatment resulted in suppression of cell viability and colony-forming ability, and increased the level of γ-H2A.X, a critical marker for DNA damage, in osteosarcoma cell lines. When examining the underlying mechanism, it was revealed combination of polyphyllin G and doxycycline triggered an enhanced generation of reactive oxygen species (ROS), and up-regulated mitochondrial oxidative stress within 0.5 h. Co-administration of the ROS inhibitor NAC reversed the suppressed cell viability and colony-forming ability, and abolished the increased level of γ-H2A.X in the cells with the combined treatment, indicating that the enhanced ROS was involved in the anti-proliferative effect of the combined treatment. Overall, the results demonstrated that doxycycline may function as chemosensitizers by inducing an acute and lethal ROS production to enhance cytotoxic of polyphyllin G in osteosarcoma cell lines, and the combined use of drugs may provide an alternative thinking for the development of new therapeutic agents.

Apoptotic and Non-Apoptotic Modalities of Thymoquinone-Induced Lymphoma Cell Death: Highlight of the Role of Cytosolic Calcium and Necroptosis

Simple Summary

Diffuse large B cell lymphoma (DLBCL) represents the most common type of non-Hodgkin lymphoma with a high curability rate. However, 40% of patients will relapse or exhibit refractory disease, and compromised apoptotic pathways is among the prognosis-worsening factors. Therefore, drugging non-apoptotic modalities might be therapeutically promising. Thymoquinone (TQ) has been reported to promote apoptosis in cancer cells. Herein, we show that TQ selectively kills DLBCL cells, either cell lines or primary lymphoma cells bearing resistance features to standard treatment. Investigations show that, although TQ induced apoptotic markers, non-apoptotic death was the major mechanism responsible for TQ-induced cellular demise. We demonstrate critical and selective roles of cytosolic calcium and necroptosis in TQ-induced non-apoptotic cell death. Finally, TQ exhibits an improved selectivity profile over conventional chemotherapy. Collectively, this work provides new insights into the mode of action of TQ and points to the therapeutic relevance of non-apoptotic modalities as a fail-safe mechanism for pro-apoptotic DLBCL therapies.

Abstract

Targeting non-apoptotic modalities might be therapeutically promising in diffuse large B cell lymphoma (DLBCL) patients with compromised apoptotic pathways. Thymoquinone (TQ) has been reported to promote apoptosis in cancer cells, but little is known about its effect on non-apoptotic pathways. This work investigates TQ selectivity against DLBCL cell lines and the cell death mechanisms. TQ reduces cell viability and kills cell lines with minimal toxicity on normal hematological cells. Mechanistically, TQ promotes the mitochondrial caspase pathway and increases genotoxicity. However, insensitivity of most cell lines to caspase inhibition by z-VAD-fmk (benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone) pointed to a critical role of non-apoptotic signaling. In cells dying through non-apoptotic death, TQ increases endoplasmic reticulum (ER) stress markers and substantially increases cytosolic calcium ([Ca²⁺]_c) through ER calcium depletion and activation of store-operated calcium entry (SOCE). Chelation of [Ca²⁺]_c, but not SOCE inhibitors, reduces TQ-induced non-apoptotic cell death, highlighting the critical role of calcium in a non-apoptotic effect of TQ. Investigations showed that TQ-induced [Ca²⁺]_c signaling is primarily initiated by necroptosis upstream to SOCE, and inhibition necroptosis by necrostatin-1 alone or with z-VAD-fmk blocks the cell death. Finally, TQ exhibits an improved selectivity profile over standard chemotherapy agents, suggesting a therapeutic relevance of the pro-necroptotic effect of TQ as a fail-safe mechanism for DLBCL therapies targeting apoptosis.

Cell Death via Lipid Peroxidation and Protein Aggregation Diseases

Lipid peroxidation of cellular membranes is a complicated cellular event, and it is both the cause and result of various diseases, such as ischemia-reperfusion injury, neurodegenerative diseases, and atherosclerosis. Lipid peroxidation causes non-apoptotic cell death, which is associated with cell fate determination: survival or cell death. During the radical chain reaction of lipid peroxidation, various oxidized lipid products accumulate in cells, followed by organelle dysfunction and the induction of non-apoptotic cell death. Highly reactive oxidized products from unsaturated fatty acids are detected under pathological conditions. Pathological protein aggregation is the general cause of these diseases. The cellular response to misfolded proteins is well-known as the unfolded protein response (UPR) and it is partially concomitant with the response to lipid peroxidation. Moreover, the association between protein aggregation and non-apoptotic cell death by lipid peroxidation is attracting attention. The link between lipid peroxidation and protein aggregation is a matter of concern in biomedical fields. Here, we focus on lethal protein aggregation in non-apoptotic cell death via lipid peroxidation. We reviewed the roles of protein aggregation in the initiation and execution of non-apoptotic cell death. We also considered the relationship between protein aggregation and oxidized lipid production. We provide an overview of non-apoptotic cell death with a focus on lipid peroxidation for therapeutic targeting during protein aggregation diseases.

A Novel Thienopyrimidine Analog, TPH104, Mediates Immunogenic Cell Death in Triple-Negative Breast Cancer Cells

Simple Summary

Triple-negative breast cancer (TNBC) is the most lethal and aggressive subtype of breast cancer that lacks an estrogen receptor, the progesterone receptor and the human epidermal growth factor receptor 2 (HER2), making it unsuitable for hormonal- or HER2-based therapy. TNBC is known for its higher relapse rate, poorer prognosis and higher rate of metastasis compared to non-TNBC because although patients initially respond to chemotherapy that kills cancer cells through a form of programmed cell death called apoptosis, they later develop chemoresistance and stop responding to the treatment, accounting for one fourth of all breast cancer deaths. In this study, we report a novel compound, TPH104, that elicits a unique, non-apoptotic cell death in TNBC cells. Upon treatment with TPH104, TNBC cells swell and burst, releasing immunogenic markers that alert and activate the immune system to further recognize and attack the neighboring breast cancer cells.

Abstract

Enhancing the tumor immunogenic microenvironment has been suggested to circumvent triple-negative breast cancer (TNBC) resistance and increase the efficacy of conventional chemotherapy. Here, we report a novel chemotherapeutic compound, TPH104, which induces immunogenic cell death in the TNBC cell line MDA-MB-231, by increasing the stimulatory capacity of dendritic cells (DCs), with an IC₅₀ value of 140 nM. TPH104 (5 µM) significantly increased ATP levels in the supernatant and mobilized intracellular calreticulin to the plasma membrane in MDA-MB-231 cells, compared to cells incubated with the vehicle. Incubating MDA-MB-231 cells for 12 h with TPH104 (1–5 µM) significantly increased TNF-α mRNA levels. The supernatants of dying MDAMB-231 cells incubated with TPH104 increased mouse bone marrow-derived DC maturation, the expression of MHC-II and CD86 and the mRNA expression of TNF-α, IL-6 and IL-12. Overall, these results indicate that TPH104 induces immunogenic cell death in TNBC cells, in part, by activating DCs.

Induction of Lysosomal Membrane Permeabilization Is a Major Event of FTY720-Mediated Non-Apoptotic Cell Death in Human Glioma Cells

Simple Summary

FTY720, a sphingosine-1-phosphate (S1P) analog, is a potent immunosuppressant for the treatment of multiple sclerosis. In addition to being an immune modulator, FTY720 also features antitumor activity in several cancer models, but the molecular mechanisms are unclear. Here, we extended our research to analyze the signaling pathways mediating FTY720-induced cell death. FTY720 did not induce apoptotic cell death, autophagy, paraptosis, or necroptosis in glioma cells. Interestingly, FTY720 accumulated in lysosomes, resulting in the induction of lysosomal membrane permeabilization (LMP). Inhibition of LMP by overexpression of HSP70 and cathepsin inhibitors blocked FTY720-induced cell death. These data suggest that FTY720 induces cell death induced by LMP in glioma cells.

Abstract

FTY720, a sphingosine-1-phosphate (S1P) receptor modulator, is a synthetic compound produced by the modification of a metabolite from I. sinclairii. Here, we found that FTY720 induced non-apoptotic cell death in human glioma cells (U251MG, U87MG, and U118MG). FTY720 (10 µM) dramatically induced cytoplasmic vacuolation in glioma cells. However, FTY720-mediated vacuolation and cell death are not associated with autophagy. Genetic or pharmacological inhibition of autophagy did not inhibit FTY720-induced cell death. Herein, we detected that FTY720-induced cytoplasmic vacuoles were stained with lysotracker red, and FTY720 induced lysosomal membrane permeabilization (LMP). Interestingly, cathepsin inhibitors (E64D and pepstatin A) and ectopic expression of heat shock protein 70 (HSP70), which is an endogenous inhibitor of LMP, markedly inhibited FTY720-induced cell death. Our results demonstrated that FTY720 induced non-apoptotic cell death via the induction of LMP in human glioma cells.

A New Inhibitor of Tubulin Polymerization Kills Multiple Cancer Cell Types and Reveals p21-Mediated Mechanism Determining Cell Death after Mitotic Catastrophe

Induction of mitotic catastrophe through the disruption of microtubules is an established target in cancer therapy. However, the molecular mechanisms determining the mitotic catastrophe and the following apoptotic or non-apoptotic cell death remain poorly understood. Moreover, many existing drugs targeting tubulin, such as vincristine, have reduced efficacy, resulting from poor solubility in physiological conditions. Here, we introduce a novel small molecule 2-aminoimidazoline derivative—OAT-449, a synthetic water-soluble tubulin inhibitor. OAT-449 in a concentration range from 6 to 30 nM causes cell death of eight different cancer cell lines in vitro, and significantly inhibits tumor development in such xenograft models as HT-29 (colorectal adenocarcinoma) and SK-N-MC (neuroepithelioma) in vivo. Mechanistic studies showed that OAT-449, like vincristine, inhibited tubulin polymerization and induced profound multi-nucleation and mitotic catastrophe in cancer cells. HeLa and HT-29 cells within 24 h of treatment arrested in G2/M cell cycle phase, presenting mitotic catastrophe features, and 24 h later died by non-apoptotic cell death. In HT-29 cells, both agents altered phosphorylation status of Cdk1 and of spindle assembly checkpoint proteins NuMa and Aurora B, while G2/M arrest and apoptosis blocking was consistent with p53-independent accumulation in the nucleus and largely in the cytoplasm of p21/waf1/cip1, a key determinant of cell fate programs. This is the first common mechanism for the two microtubule-dissociating agents, vincristine and OAT-449, determining the cell death pathway following mitotic catastrophe demonstrated in HT-29 cells.

Autophagy Promotes Porcine Parvovirus Replication and Induces Non-Apoptotic Cell Death in Porcine Placental Trophoblasts

Autophagy plays important roles in the infection and pathogenesis of many viruses, yet the regulatory roles of autophagy in the process of porcine parvovirus (PPV) infection remain unclear. Herein, we show that PPV infection induces autophagy in porcine placental trophoblasts (PTCs). Induction of autophagy by rapamycin (RAPA) inhibited the occurrence of apoptotic cell death, yet promoted viral replication in PPV-infected cells; inhibition of autophagy by 3-MA or ATG5 knockdown increased cellular apoptosis and reduced PPV replication. Interestingly, we found that in the presence of caspase-inhibitor zVAD-fmk, PPV induces non-apoptotic cell death that was characterized by lysosomal damage and associated with autophagy. Induction of complete autophagy flux by RAPA markedly promoted PPV replication compared with incomplete autophagy induced by RAPA plus bafilomycin (RAPA/BAF) in the early phase of PPV infection (24 h.p.i.). Meanwhile, induction of complete autophagy with RAPA increased lysosomal damage and non-apoptotic cell death in the later phase of PPV infection. Therefore, our data suggest that autophagy can enhance PPV replication and promote the occurrence of lysosomal-damage-associated non-apoptotic cell death in PPV-infected porcine placental trophoblasts.

I Spy in the Developing Fly a Multitude of Ways to Die

Cell proliferation and cell death are two opposing, yet complementary fundamental processes in development. Cell proliferation provides new cells, while developmental programmed cell death adjusts cell numbers and refines structures as an organism grows. Apoptosis is the best-characterized form of programmed cell death; however, there are many other non-apoptotic forms of cell death that occur throughout development. Drosophila is an excellent model for studying these varied forms of cell death given the array of cellular, molecular, and genetic techniques available. In this review, we discuss select examples of apoptotic and non-apoptotic cell death that occur in different tissues and at different stages of Drosophila development. For example, apoptosis occurs throughout the nervous system to achieve an appropriate number of neurons. Elsewhere in the fly, non-apoptotic modes of developmental cell death are employed, such as in the elimination of larval salivary glands and midgut during metamorphosis. These and other examples discussed here demonstrate the versatility of Drosophila as a model organism for elucidating the diverse modes of programmed cell death.

Corosolic Acid Induces Non-Apoptotic Cell Death through Generation of Lipid Reactive Oxygen Species Production in Human Renal Carcinoma Caki Cells

Corosolic acid is one of the pentacyclic triterpenoids isolated from Lagerstroemia speciose and has been reported to exhibit anti-cancer and anti-proliferative activities in various cancer cells. In the present study, we investigated the molecular mechanisms of corosolic acid in cancer cell death. Corosolic acid induces a decrease of cell viability and an increase of cell cytotoxicity in human renal carcinoma Caki cells. Corosolic acid-induced cell death is not inhibited by apoptosis inhibitor (z-VAD-fmk, a pan-caspase inhibitor), necroptosis inhibitor (necrostatin-1), or ferroptosis inhibitors (ferrostatin-1 and deferoxamine (DFO)). Furthermore, corosolic acid significantly induces reactive oxygen species (ROS) levels, but antioxidants (N-acetyl-l-cysteine (NAC) and trolox) do not inhibit corosolic acid-induced cell death. Interestingly, corosolic acid induces lipid oxidation, and α-tocopherol markedly prevents corosolic acid-induced lipid peroxidation and cell death. Anti-chemotherapeutic effects of α-tocopherol are dependent on inhibition of lipid oxidation rather than inhibition of ROS production. In addition, corosolic acid induces non-apoptotic cell death in other renal cancer (ACHN and A498), breast cancer (MDA-MB231), and hepatocellular carcinoma (SK-Hep1 and Huh7) cells, and α-tocopherol markedly inhibits corosolic acid-induced cell death. Therefore, our results suggest that corosolic acid induces non-apoptotic cell death in cancer cells through the increase of lipid peroxidation.

Bacoside A Induces Tumor Cell Death in Human Glioblastoma Cell Lines through Catastrophic Macropinocytosis

Glioblastoma multiforme (GBM) is a highly aggressive type of brain tumor with an extremely poor prognosis. Recent evidences have shown that the "biomechanical imbalances" induced in GBM patient-derived glioblastoma cells (GC) and in vivo via the administration of synthetic small molecules, may effectively inhibit disease progression and prolong survival of GBM animal models. This novel concept associated with de novo anti-GBM drug development has however suffered obstacles in adequate clinical utility due to the appearance of unrelated toxicity in the prolonged therapeutic windows. Here, we took a "drug repurposing approach" to trigger similar physico-chemical disturbances in the GBM tumor cells, wherein, the candidate therapeutic agent has been previously well established for its neuro-protective roles, safety, efficacy, prolonged tolerance and excellent brain bioavailability in human subjects and mouse models. In this study, we show that the extracts of an Indian traditional medicinal plant Bacopa monnieri (BM) and its bioactive component Bacoside A can generate dosage associated tumor specific disturbances in the hydrostatic pressure balance of the cell via a mechanism involving excessive phosphorylation of calcium/calmodulin-dependent protein kinase IIA (CaMKIIA/CaMK2A) enzyme that is further involved in the release of calcium from the smooth endoplasmic reticular networks. High intracellular calcium stimulated massive macropinocytotic extracellular fluid intake causing cell hypertrophy in the initial stages, excessive macropinosome enlargement and fluid accumulation associated organellar congestion, cell swelling, cell rounding and membrane rupture of glioblastoma cells; with all these events culminating into a non-apoptotic, physical non-homeostasis associated glioblastoma tumor cell death. These results identify glioblastoma tumor cells to be a specific target of the tested herbal medicine and therefore can be exploited as a safe anti-GBM therapeutic.

Systematic Quantification of Population Cell Death Kinetics in Mammalian Cells

Cytotoxic compounds are important drugs and research tools. Here, we introduce a method, scalable time-lapse analysis of cell death kinetics (STACK), to quantify the kinetics of compound-induced cell death in mammalian cells at the population level. STACK uses live and dead cell markers, high-throughput time-lapse imaging, and mathematical modeling to determine the kinetics of population cell death over time. We used STACK to profile the effects of over 1,800 bioactive compounds on cell death in two human cancer cell lines, resulting in a large and freely available dataset. 79 potent lethal compounds common to both cell lines caused cell death with widely divergent kinetics. 13 compounds triggered cell death within hours, including the metallophore zinc pyrithione. Mechanistic studies demonstrated that this rapid onset lethal phenotype was caused in human cancer cells by metabolic disruption and ATP depletion. These results provide the first comprehensive survey of cell death kinetics and analysis of rapid-onset lethal compounds.

Adhesion-induced eosinophil cytolysis requires the receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase-like (MLKL) signaling pathway, which is counterregulated by autophagy

BACKGROUND

Eosinophils are a subset of granulocytes that can be involved in the pathogenesis of different diseases, including allergy. Their effector functions are closely linked to their cytotoxic granule proteins. Release takes place through several different mechanisms, one of which is cytolysis, which is associated with release of intact granules, so-called clusters of free eosinophil granules. The mechanism underlying this activation-induced form of cell death in eosinophils has remained unclear.

OBJECTIVE

We aimed to elucidate the molecular mechanism of eosinophil cytolysis.

METHODS

Isolated blood eosinophils were incubated on glass coverslips coated with intravenous immunoglobulin and inactive complement component 3b. A morphologic characterization of the distinct stages of the proposed cascade was addressed by means of time-lapse automated fluorescence microscopy, electron microscopy, and immunohistochemistry. Experiments with pharmacologic inhibitors were performed to elucidate the sequence of events within the cascade. Tissue samples of patients with eosinophilic skin diseases or eosinophilic esophagitis were used for in vivo analyses.

RESULTS

After eosinophil adhesion, we observed reactive oxygen species production, early degranulation, and granule fusion processes, leading to a distinct morphology exhibiting cytoplasmic vacuolization and, finally, cytolysis. Using a pharmacologic approach, we demonstrate the presence of a receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase-like (MLKL) signaling pathway in eosinophils, which, after its activation, leads to the production of high levels of reactive oxygen species in a p38 mitogen-activated protein kinase and phosphatidylinositol 3'-kinase-dependent manner. All these steps are required for cytoplasmic vacuolization and subsequent cytolysis to occur. Interestingly, triggering cytolysis is associated with an induction of autophagy in eosinophils, and additional stimulation of autophagy by means of pharmacologic inhibition of the mechanistic target of rapamycin counterregulates cell death. Moreover, MLKL phosphorylation, cytoplasmic vacuolization, and cytolysis were observed in eosinophils under in vivo inflammatory conditions.

CONCLUSION

We report that adhesion-induced eosinophil cytolysis takes place through RIPK3-MLKL-dependent necroptosis, which can be counterregulated by autophagy.

Ferroptosis: A missing puzzle piece in the p53 blueprint?

Recent evidence indicates that canonical functions of p53 (i.e., apoptosis and growth arrest) are dispensable for p53-mediated tumor suppression. We have uncovered a novel function of p53 that contributes to tumor suppression through regulation of cystine metabolism, reactive oxygen species responses, and ferroptosis. The p53-mediated ferroptotic response via SLC7A11 denotes an extra layer of defense against tumorigenesis in conjunction with other p53 functions.

Glutathione peroxidase 4 (Gpx4) and ferroptosis: what's so special about it?

The system X_C⁻/glutathione/glutathione peroxidase 4 (Gpx4) axis pivotally controls ferroptosis, a recently described form of regulated non-apoptotic cell death. Compelling evidence has established that this route of cell death is not only of high relevance for triggering cancer cell death, but also proves to be amenable for therapeutic intervention to halt ischemia/reperfusion-related diseases.

Nuclear importin α and its physiological importance

Importin α is recognized as a classical nuclear localization signal (cNLS) receptor which mediates nucleocytoplasmic transport. However, it rapidly accumulates in the nucleus in response to cellular stresses, including oxidative stress, causing a blockade of the classical nuclear import pathway. We set out to determine whether importin α performs roles in the nucleus after cellular exposure to stresses and discovered that it can act directly to modulate gene expression. With remarkable selectivity, importin α2 can access the promoter of Serine/threonine kinase 35 (STK35) and increase the levels of this transcript without requirement for importin β1. The nuclear accumulation of importin α occurred following exposure to stresses which decreased intracellular ATP levels and was followed by non-apoptotic cell death. Hence the gene regulatory function of nuclear importin α can direct cell fate. There are now several reports of nuclear-localized importin α proteins in diverse cellular states, including cancer. Here we discuss the physiological significance of this novel functional capacity of nuclear importin α relationship to a variety of cellular states and fates.