Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012

Programmed cell death: molecular mechanisms and implications for safety assessment of nanomaterials

Engineered nanomaterials offer numerous and tantalizing opportunities in many sectors of society, including medicine. Needless to say, attention should also be paid to the potential for unexpected hazardous effects of these novel materials. To date, much of the nanotoxicology literature has focused on the assessment of cell viability or cell death using primitive assays for the detection of plasma membrane integrity or mitochondrial function or assessment of cellular morphology. However, when assessing the cytotoxic effects of engineered nanomaterials, researchers need not only to consider whether cells are dead or alive but also to assess which of the numerous, highly specific pathways of cell death might be involved. Moreover, it is important to diagnose cell death based not only on morphological markers but on the assessment and quantification of biochemical alterations specific to each form of cell death. In this Account, we provide a description of the three major forms of programmed cell death in mammalian cells: apoptosis, autophagic cell death, and regulated necrosis, sometimes referred to as necroptosis. Apoptosis can be activated via the extrinsic (death receptor-dependent) or via the intrinsic (mitochondria-dependent) route. Apoptotic cell death may or may not require the activation of cytosolic proteases known as caspases. Autophagy (self-eating) has an important homeostatic role in the cell, mediating the removal of dysfunctional or damaged organelles thereby allowing the recycling of cellular building blocks. However, unrestrained autophagy can kill cells. Studies in recent years have revealed that necrosis that depends on activation of the kinases RIP1 and RIP3 is a major form of programmed cell death with roles in development and immunity. We also discuss recent examples of the impact of engineered nanoparticles on the three different pathways of programmed cell death. For example, acute exposure of cells to carbon nanotubes (CNTs) can induce apoptosis whereas chronic exposure to CNTs may yield an apoptosis-resistant and tumorigenic phenotype in lung epithelial cells. Several reports show that nanoparticles, including polystyrene particles, are routed to the lysosomal compartment and trigger cell death through the destabilization of lysosomal membranes with engagement of the intrinsic apoptosis pathway. In addition, a number of studies have demonstrated that nanomaterials such as CNTs, quantum dots, and gold nanoparticles can affect cellular autophagy. An improved understanding of the complexities of the nanomaterial-induced perturbation of different cell death pathways may allow for a better prediction of the consequences of human exposure.

An evidence-based review of obatoclax mesylate in the treatment of hematological malignancies

Obatoclax mesylate is an intravenously-administered drug under investigation in Phase I and II clinical trials as a novel anticancer therapeutic for hematological malignancies and solid tumors. Obatoclax was developed as a pan-inhibitor of antiapoptotic members of the B cell chronic lymphocytic leukemia/lymphoma 2 (BCL-2) family of proteins, which control the intrinsic or mitochondrial pathway of apoptosis. Resistance to apoptosis through dysregulation of BCL-2 family members is commonly observed in hematological malignancies, and can be linked to therapeutic resistance and poor clinical outcomes. By inhibiting pro-survival BCL-2 family proteins, including MCL-1, obatoclax is proposed to (1) trigger cell death as a single agent, and (2) potentiate the anticancer effects of other therapeutics. Preclinical investigations have supported these proposals and have provided evidence suggestive of a promising therapeutic index for this drug. Phase I trials of obatoclax mesylate in leukemia and lymphoma have defined well-tolerated regimens and have identified transient neurotoxicity as the most common adverse effect of this drug. In these studies, a limited number of objective responses were observed, along with hematological improvement in a larger proportion of treated patients. Published Phase II evaluations in lymphoma and myelofibrosis, however, have not reported robust single-agent activity. Emerging evidence from ongoing preclinical and clinical investigations suggests that the full potential of obatoclax mesylate as a novel anticancer agent may be realized (1) in rational combination treatments, and (2) when guided by molecular predictors of therapeutic response. By understanding the molecular underpinnings of obatoclax response, along with optimal therapeutic regimens and indications, the potential of obatoclax mesylate for the treatment of hematological malignancies may be further clarified.

Nilotinib induces apoptosis and autophagic cell death of activated hepatic stellate cells via inhibition of histone deacetylases

Increasing hepatic stellate cell (HSC) death is a very attractive approach for limiting liver fibrosis. Tyrosine kinase inhibitors have been shown to have anti-fibrotic properties, but the mechanisms are poorly understood. Here, we identified the mechanism of action of the second-generation tyrosine kinase inhibitor nilotinib in inducing HSC death. Human HSC line (LX-2) and rat HSCs were treated with nilotinib and its predecessor, imatinib, in the absence or presence of various blockers, known to interfere with death signaling pathways. Nilotinib, but not imatinib, induced progressive cell death of activated, but not quiescent, HSCs in a dose-dependent manner. Activated HSCs died through apoptosis, as denoted by increased DNA fragmentation and caspase activation, and through autophagy, as indicated by the accumulation of autophagic markers, light chain (LC)3A-II and LC3B-II. Although inhibition of caspases with Z-VAD-FMK suppressed nilotinib-induced HSCs' apoptosis, there was no increase in HSCs' survival, because autophagy was exacerbated. However, blocking the mitochondrial permeability transition pore (mPTP) opening with cyclosporin A completely abolished both apoptosis and autophagy due to nilotinib. Moreover, nilotinib treatment decreased the protein expression of histone deacetylases 1, 2 and 4. Interestingly, pretreament with C646, a selective p300/CBP histone acetyl transferase inhibitor, resulted in diverting nilotinib-induced apoptosis and autophagy towards necrosis. In conclusion, the identification of mPTP as a target of nilotinib in activated HSCs suggests coordination with histone deacetylases inhibition to induce apoptosis and autophagy. Thus, our study provides novel insights into the anti-fibrotic effects of nilotinib.

Lysosomal iron, iron chelation, and cell death

SIGNIFICANCE

Lysosomes are acidic organelles containing more than fifty hydrolases that provide for the degradation of intracellular and endocytosed materials by autophagy and heterophagy, respectively. They digest a variety of macromolecules, as well as all organelles, and their integrity is crucial. As a result of the degradation of iron-containing macromolecules (e.g., ferritin and mitochondrial components) or endocytosed erythrocytes (by macrophages), lysosomes can accumulate large amounts of iron. This iron occurs often as Fe(II) due to the acidic and reducing lysosomal environment. Fe(II) is known to catalyze Fenton reactions, yielding extremely reactive hydroxyl radicals that may jeopardize lysosomal membrane integrity during oxidative stress. This results in the release of hydrolases and redox-active iron into the cytosol with ensuing damage or cell death. Lysosomes play key roles not only in apoptosis and necrosis but also in neurodegeneration, aging, and atherosclerosis.

RECENT ADVANCES

The damaging effect of intralysosomal iron can be hampered by endogenous or exogenous iron chelators that enter the lysosomal compartment by membrane permeation, endocytosis, or autophagy.

CRITICAL ISSUES

Cellular sensitivity to oxidative stress is enhanced by lysosomal redox-active iron or by lysosomal-targeted copper chelators binding copper (from degradation of copper-containing macromolecules) in redox-active complexes. Probably due to higher copper levels, lysosomes of malignant cells may be specifically sensitized by such chelators.

FUTURE DIRECTIONS

By increasing lysosomal redox-active iron or exposing cells to lysosomal-targeted copper chelators, it should be possible to enhance the sensitivity of cancer cells to radiation-induced oxidative stress or treatment with cytostatics that induce such stress.

Determination of apoptotic and necrotic cell death in vitro and in vivo

Cell death research during the last decades has revealed many molecular signaling cascades, often leading to distinct cell death modalities followed by immune responses. For historical reasons, the prototypic and best characterized cell death modes are apoptosis and necrosis (dubbed necroptosis, to indicate that it is regulated). There is mounting evidence for the interplay between cell death modalities and their redundant action when one of them is interfered with. This increase in cell death research points to the need for characterizing cell death pathways by different approaches at the biochemical, cellular and if possible, physiological level. In this review we present a selection of techniques to detect cell death and to distinguish necrosis from apoptosis. The distinction should be based on pharmacologic and transgenic approaches in combination with several biochemical and morphological criteria. A particular problem in defining necrosis is that in the absence of phagocytosis, apoptotic cells become secondary necrotic and develop morphologic and biochemical features of primary necrosis.

Pro-autophagic polyphenols reduce the acetylation of cytoplasmic proteins

Resveratrol is a polyphenol contained in red wine that has been amply investigated for its beneficial effects on organismal metabolism, in particular in the context of the so-called "French paradox," i.e., the relatively low incidence of coronary heart disease exhibited by a population with a high dietary intake of cholesterol and saturated fats. At least part of the beneficial effect of resveratrol on human health stems from its capacity to promote autophagy by activating the NAD-dependent deacetylase sirtuin 1. However, the concentration of resveratrol found in red wine is excessively low to account alone for the French paradox. Here, we investigated the possibility that other mono- and polyphenols contained in red wine might induce autophagy while affecting the acetylation levels of cellular proteins. Phenolic compounds found in red wine, including anthocyanins (oenin), stilbenoids (piceatannol), monophenols (caffeic acid, gallic acid) glucosides (delphinidin, kuronamin, peonidin) and flavonoids (catechin, epicatechin, quercetin, myricetin), were all capable of stimulating autophagy, although with dissimilar potencies. Importantly, a robust negative correlation could be established between autophagy induction and the acetylation levels of cytoplasmic proteins, as determined by a novel immunofluorescence staining protocol that allows for the exclusion of nuclear components from the analysis. Inhibition of sirtuin 1 by both pharmacological and genetic means abolished protein deacetylation and autophagy as stimulated by resveratrol, but not by piceatannol, indicating that these compounds act through distinct molecular pathways. In support of this notion, resveratrol and piceatannol synergized in inducing autophagy as well as in promoting cytoplasmic protein deacetylation. Our results highlight a cause-effect relationship between the deacetylation of cytoplasmic proteins and autophagy induction by red wine components.

Autophagy in physiological and pathological processes – selected aspects

This paper describes a model of cell death, called autophagy, one among other typical and atypical processes of cell death. This phenomenon is present in the organism, from conception until death, and is conditioned by many genes of ATG family, or mTOR kinase and specific proteins, like BNIP3. This process plays a very important role not only in physiological functions of the organism but also in pathological, such as Alzheimer or Huntington disease, as well as diseases caused by viruses.

Mitochondrial dysfunction: a basic mechanism in inflammation-related non-communicable diseases and therapeutic opportunities

Obesity is not necessarily a predisposing factor for disease. It is the handling of fat and/or excessive energy intake that encompasses the linkage of inflammation, oxidation, and metabolism to the deleterious effects associated with the continuous excess of food ingestion. The roles of cytokines and insulin resistance in excessive energy intake have been studied extensively. Tobacco use and obesity accompanied by an unhealthy diet and physical inactivity are the main factors that underlie noncommunicable diseases. The implication is that the management of energy or food intake, which is the main role of mitochondria, is involved in the most common diseases. In this study, we highlight the importance of mitochondrial dysfunction in the mutual relationships between causative conditions. Mitochondria are highly dynamic organelles that fuse and divide in response to environmental stimuli, developmental status, and energy requirements. These organelles act to supply the cell with ATP and to synthesise key molecules in the processes of inflammation, oxidation, and metabolism. Therefore, energy sensors and management effectors are determinants in the course and development of diseases. Regulating mitochondrial function may require a multifaceted approach that includes drugs and plant-derived phenolic compounds with antioxidant and anti-inflammatory activities that improve mitochondrial biogenesis and act to modulate the AMPK/mTOR pathway.

Increased radiosensitivity and radiothermosensitivity of human pancreatic MIA PaCa-2 and U251 glioblastoma cell lines treated with the novel Hsp90 inhibitor NVP-HSP990

Background and purpose

Heat shock Protein 90 (Hsp90) is a molecular chaperone that folds, stabilizes, and functionally regulates many cellular proteins involved in oncogenic signaling and in the regulation of radiosensitivity. It is upregulated in response to stress such a heat. Hyperthermia is a potent radiosensitizer, but induction of Hsp90 may potentially limit its efficacy. Our aim was to investigate whether the new Hsp90 inhibitor NVP-HSP990 increases radiosensitivity, thermosensitivity and radiothermosensitivity of human tumor cell lines.

Material and methods

U251 glioblastoma and MIA PaCa-2 pancreatic carcinoma cells were used. To determine clonogenic survival, colony forming assays were performed. Cell viability and proliferation were assesed by Trypan blue staining. Cell cycle and apoptosis analyses were performed by flow cytometry. DAPI staining was used to detect mitotic catastrophe.

Results

NVP-HSP990 increased the thermosensitivity, radiosensitivity and radio-thermosensitivity of both cell lines in clonogenic assays. 72 hours after irradiation with 4 Gy, a significant reduction in cell number associated with considerable G2/M acumulation and mitotic catastrophe as well as cell death by apoptosis/necrosis was observed.

Conclusions

Treatment with NVP-HSP990 strongly sensitized U251 and MIA PaCa-2 cells to hyperthermia and ionizing radiation or combination thereof through augmentation of G2/M arrest, mitotic catastrophe and associated apoptosis.

Functions of BCL-X L at the Interface between Cell Death and Metabolism

The BCL-2 homolog BCL-XL, one of the two protein products of BCL2L1, has originally been characterized for its prominent prosurvival functions. Similar to BCL-2, BCL-XL binds to its multidomain proapoptotic counterparts BAX and BAK, hence preventing the formation of lethal pores in the mitochondrial outer membrane, as well as to multiple BH3-only proteins, thus interrupting apical proapoptotic signals. In addition, BCL-XL has been suggested to exert cytoprotective functions by sequestering a cytosolic pool of the pro-apoptotic transcription factor p53 and by binding to the voltage-dependent anion channel 1 (VDAC1), thereby inhibiting the so-called mitochondrial permeability transition (MPT). Thus, BCL-XL appears to play a prominent role in the regulation of multiple distinct types of cell death, including apoptosis and regulated necrosis. More recently, great attention has been given to the cell death-unrelated functions of BCL-2-like proteins. In particular, BCL-XL has been shown to modulate a number of pathophysiological processes, including-but not limited to-mitochondrial ATP synthesis, protein acetylation, autophagy and mitosis. In this short review article, we will discuss the functions of BCL-XL at the interface between cell death and metabolism.

Escherichia coli induces bovine neutrophil cell death independent from caspase-3/-7/-1, but with phosphatidylserine exposure prior to membrane rupture

Neutrophils are essential for the innate immune response against bacterial pathogens and play a key role during the early phases of infection, including mastitis and endometritis in cows. When directly challenged with bacteria, neutrophils undergo phagocytosis induced cell death (PICD). The molecular mechanisms of this cell death modality are poorly understood, especially for bovine neutrophils. Therefore, this study aimed to determine the mechanisms and hallmarks of PICD in bovine neutrophils after in vitro challenge with Escherichia coli (E. coli). Our data show that various apoptotic hallmarks such as blebbing, chromatin condensation and executioner caspase (C)-3/-7 activity are only observed during constitutive bovine neutrophil apoptosis. In contrast, bovine neutrophil PICD is characterized by production of reactive oxygen species (ROS), pro-inflammatory C-1 activation, nuclear factor (NF)-κB activation, and interleukin (IL)-1β and IL-6 secretion. Nevertheless, under both conditions these phagocytes undergo cell death with the exposure of phosphatidylserine (PS). Although PS exposure is generally attributed to the anti-inflammatory features of executioner caspase-dependent apoptosis, it surprisingly preceded plasma membrane rupture during bovine neutrophil PICD. Moreover, C-1 inhibition strongly affected IL-1β production but not the PICD kinetics. This indicates that the secretion of the latter pro-inflammatory cytokine is a bystander effect rather than a regulator of PICD in bovine neutrophils, in marked contrast to the IL-1β-dependent pyroptosis reported for macrophages.

Subamolide a induces mitotic catastrophe accompanied by apoptosis in human lung cancer cells

This study investigated the anticancer effects of subamolide A (Sub-A), isolated from Cinnamomum subavenium, on human nonsmall cell lung cancer cell lines A549 and NCI-H460. Treatment of cancer cells with Sub-A resulted in decreased cell viability of both lung cancer cell lines. Sub-A induced lung cancer cell death by triggering mitotic catastrophe with apoptosis. It triggered oxidant stress, indicated by increased cellular reactive oxygen species (ROS) production and decreased glutathione level. The elevated ROS triggered the activation of ataxia-telangiectasia mutation (ATM), which further enhanced the ATF3 upregulation and subsequently enhanced p53 function by phosphorylation at Serine 15 and Serine 392. The antioxidant, EUK8, significantly decreased mitotic catastrophe by inhibiting ATM activation, ATF3 expression, and p53 phosphorylation. The reduction of ATM and ATF3 expression by shRNA decreased Sub-A-mediated p53 phosphorylation and mitotic catastrophe. Sub-A also caused a dramatic 70% reduction in tumor size in an animal model. Taken together, cell death of lung cancer cells in response to Sub-A is dependent on ROS generation, which triggers mitotic catastrophe followed by apoptosis. Therefore, Sub-A may be a novel anticancer agent for the treatment of nonsmall cell lung cancer.

Synergistic interaction between cisplatin and PARP inhibitors in non-small cell lung cancer

The antineoplastic agent cis-diammineplatinum(II) dichloride (cisplatin, CDDP) is part of the poorly effective standard treatment of non-small cell lung carcinoma (NSCLC). Here, we report a novel strategy to improve the efficacy of CDDP. In conditions in which CDDP alone or either of two PARP inhibitors, PJ34 hydrochloride hydrate or CEP 8983, used as standalone treatments were inefficient in killing NSCLC cells, the combination of CDDP plus PJ34 or that of CDDP plus CEP 8983 were found to kill a substantial fraction of the cells. This cytotoxic synergy could be recapitulated by combining CDDP and the siRNA-mediated depletion of the principal PARP isoform, PARP1, indicating that it is mediated by on-target effects of PJ34 or CEP 8983. CDDP and PARP inhibitors synergized in inducing DNA damage foci, mitochondrial membrane permeabilization leading to cytochrome c release, and dissipation of the inner transmembrane potential, caspase activation, plasma membrane rupture and loss of clonogenic potential in NSCLC cells. Collectively, our results indicate that CDDP can be advantageously combined with PARP inhibitors to kill several NSCLC cell lines, independently from their p53 status. Combined treatment with CDDP and PARP inhibitors elicits the intrinsic pathway of apoptosis.

Regulation of cell death in cancer-possible implications for immunotherapy

Since most anticancer therapies including immunotherapy trigger programmed cell death in cancer cells, defective cell death programs can lead to treatment resistance and tumor immune escape. Therefore, evasion of programmed cell death may provide one possible explanation as to why cancer immunotherapy has so far only shown modest clinical benefits for children with cancer. A better understanding of the molecular mechanisms that regulate sensitivity and resistance to programmed cell death is expected to open new perspectives for the development of novel experimental treatment strategies to enhance the efficacy of cancer immunotherapy in the future.

Role of the c subunit of the FO ATP synthase in mitochondrial permeability transition

The term "mitochondrial permeability transition" (MPT) refers to an abrupt increase in the permeability of the inner mitochondrial membrane to low molecular weight solutes. Due to osmotic forces, MPT is paralleled by a massive influx of water into the mitochondrial matrix, eventually leading to the structural collapse of the organelle. Thus, MPT can initiate mitochondrial outer membrane permeabilization (MOMP), promoting the activation of the apoptotic caspase cascade as well as of caspase-independent cell death mechanisms. MPT appears to be mediated by the opening of the so-called "permeability transition pore complex" (PTPC), a poorly characterized and versatile supramolecular entity assembled at the junctions between the inner and outer mitochondrial membranes. In spite of considerable experimental efforts, the precise molecular composition of the PTPC remains obscure and only one of its constituents, cyclophilin D (CYPD), has been ascribed with a crucial role in the regulation of cell death. Conversely, the results of genetic experiments indicate that other major components of the PTPC, such as voltage-dependent anion channel (VDAC) and adenine nucleotide translocase (ANT), are dispensable for MPT-driven MOMP. Here, we demonstrate that the c subunit of the FO ATP synthase is required for MPT, mitochondrial fragmentation and cell death as induced by cytosolic calcium overload and oxidative stress in both glycolytic and respiratory cell models. Our results strongly suggest that, similar to CYPD, the c subunit of the FO ATP synthase constitutes a critical component of the PTPC.

Poly(ADP-ribose) signaling in cell death

Poly(ADP-ribosyl)ation (PARylation) is a reversible protein modification carried out by the concerted actions of poly(ADP-ribose) polymerase (PARP) enzymes and poly(ADP-ribose) (PAR) decomposing enzymes such as PAR glycohydrolase (PARG) and ADP-ribosyl hydrolase 3 (ARH3). Reversible PARylation is a pleiotropic regulator of various cellular functions but uncontrolled PARP activation may also lead to cell death. The cellular demise pathway mediated by PARylation in oxidatively stressed cells has been described almost thirty years ago. However, the underlying molecular mechanisms have only begun to emerge relatively recently. PARylation has been implicated in necroptosis, autophagic cell death but its role in extrinsic and intrinsic apoptosis appears to be less predominant and depends largely on the cellular model used. Currently, three major pathways have been made responsible for PARP-mediated necroptotic cell death: (1) compromised cellular energetics mainly due to depletion of NAD, the substrate of PARPs; (2) PAR mediated translocation of apoptosis inducing factor (AIF) from mitochondria to nucleus (parthanatos) and (3) a mostly elusive crosstalk between PARylation and cell death/survival kinases and phosphatases. Here we review how these PARP-mediated necroptotic pathways are intertwined, how PARylation may contribute to extrinsic and intrinsic apoptosis and discuss recent developments on the role of PARylation in autophagy and autophagic cell death.

Sustained tumour eradication after induced caspase-3 activation and synchronous tumour apoptosis requires an intact host immune response

Effective anticancer treatments often result in the induction of large amounts of tumour cell death. In vivo, such dying tumour cells are a potential source of antigens for T-cell stimulation. Although apoptosis is generally considered nonimmunogenic, recent evidence suggests that some anticancer therapies that induce apoptosis can elicit antitumour immune responses. Here, a doxycycline-inducible, constitutively active caspase-3 ('death switch') was constructed in a murine tumour model to explore the impact of the host immune response to rapid, synchronous and substantial tumour cell apoptosis. In vitro, up to 80% of tumour cells underwent apoptotic cell death within 24 h and death was accompanied by the release of potential 'danger signal' molecules HMGB1 and HSP90. In vivo, death switch induction provoked rapid, pronounced tumour regression in immune-competent and immune-deficient mice, but sustained tumour eradication was observed only in immune-competent mice. Moreover, the majority of mice that were tumour free after death switch induction were protected from further tumour rechallenge. In addition, long-term remission after induction of the death switch was completely abrogated following depletion of CD8 T cells. These data suggest that sustained tumour eradication after substantial tumour apoptosis requires an antitumour host immune response that prevents tumour relapse. In many patients, cancer therapies produce encouraging initial responses that are only short lived. These results provide new insights that may have important implications for further development of strategies that result in long-term tumour clearance after initially effective anticancer treatment.

Systematic review of central nervous system anomalies in incontinentia pigmenti

The objective of this study was to present a systematic review of the central nervous system (CNS) types of anomalies and to consider the possibility to include CNS anomalies in Incontinentia pigmenti (IP) criteria. The analyzed literature data from 1,393 IP cases were from the period 1993–2012. CNS anomalies were diagnosed for 30.44% of the investigated IP patients. The total number of CNS types of anomalies per patient was 1.62. In the present study there was no significantly higher number of anomalies per patient in females than males. The most frequent CNS types of anomalies were seizures, motor impairment, mental retardation, and microcephaly. The most frequently registered CNS lesions found using brain imaging methods were brain infarcts or necrosis, brain atrophies, and corpus callosum lesions. IKBKG exon 4–10 deletion was present in 86.00% of genetically confirmed IP patients. The frequency of CNS anomalies, similar to the frequency of retinal anomalies in IP patients, concurrent with their severity, supports their recognition in the list of IP minor criteria.

The emerging importance of autophagy in pulmonary diseases

Important cellular processes such as inflammation, apoptosis, differentiation, and proliferation confer critical roles in the pathogenesis of human diseases. In the past decade, an emerging process named "autophagy" has generated intense interest in both biomedical research and clinical medicine. Autophagy is a regulated cellular pathway for the turnover of organelles and proteins by lysosomal-dependent processing. Although autophagy was once considered a bulk degradation event, research shows that autophagy selectively degrades specific proteins, organelles, and invading bacteria, a process termed "selective autophagy." It is increasingly clear that autophagy is directly relevant to clinical disease, including pulmonary disease. This review outlines the principal components of the autophagic process and discusses the importance of autophagy and autophagic proteins in pulmonary diseases from COPD, α1-antitrypsin deficiency, pulmonary hypertension, acute lung injury, and cystic fibrosis to respiratory infection and sepsis. Finally, we examine the dual nature of autophagy in the lung, which has both protective and deleterious effects resulting from adaptive and maladaptive responses, and the challenge this duality poses for designing autophagy-based diagnostic and therapeutic targets in lung disease.

NLR activation takes a direct route

For the first time there is now clear biochemical and biophysical evidence indicating that members of the nucleotide-binding domain and leucine-rich repeat containing (NLR) family can be activated as a result of direct interaction between the receptor and ligand. NLRX1 leucine-rich repeats bind to RNA; murine NAIP (NLR family, apoptosis inhibitory protein) 5 binds flagellin directly; and NOD (nucleotide-binding oligomerization domain containing) 1 and NOD2 may interact directly with fragments of peptidoglycan. It remains to be seen if NLRP3 has a specific ligand, but progress has been made in addressing its mechanism of activation, with cellular imbalances and mitochondrial dysfunction being important. This review updates our understanding of NLR activation in light of these recent advances and their impact on the NLR research.

Protective role of autophagy in matrine‑induced gastric cancer cell death

Matrine has potent antitumor activity against a broad variety of cancer cells and our previous study showed that both autophagy and apoptosis were activated during matrine-induced gastric cancer cell death. The aim of the present study was to determine the significance of autophagy in antineoplastic effects of matrine and the molecular mechanism by which matrine induces autophagy in gastric cancer cells. Western blot analysis showed that exposure of gastric cancer cells to matrine resulted in the extent of autophagy increasing in a dose- and time-dependent manner by detecting micro-tubule-associated protein 1 light chain 3 (LC3). This induction was due to activation of autophagic flux, as supported using the lysosome inhibitor, bafilomycin A1, which produced an accumulation of LC3-II. Propidium iodide staining demonstrated that matrine induced cell death in a dose-dependent manner and the autophagy inhibitor 3-methyladenine (3-MA) or bafilomycin A1 enhanced lethality of matrine against gastric cancer cells. Moreover, after pretreatment with 3-MA, some of the gastric cancer cells treated with matrine exhibited prototypical characteristics of apoptosis by transmission electron microscopy. The ability of 3-MA to increase matrine-induced apoptosis was further confirmed by Annexin V-FITC/PI staining. Also, the combination of matrine and 3-MA was more potent than matrine alone in inhibiting the proliferation of SGC-7901 cells assessed by sulphorhodamine B assay. Furthermore, administration of the pan-caspase inhibitor zVAD-fmk or autophagy inducer rapamycin decreased the matrine-induced cell death. In addition, matrine treatment did not inhibit the phosphorylation of Akt and its downstream effectors mammalian target of rapamycin (mTOR) as well as p70 ribosomal protein S6 kinase (p70S6K), although the levels of the total Akt and mTOR were decreased. These results suggest that autophagy was activated as a protective mechanism against matrine-induced apoptosis and inhibition of autophagy may be an attractive strategy for enhancing the antitumor potential of matrine in gastric cancer.

Mitotic catastrophe triggered in human cancer cells by the viral protein apoptin

Mitotic catastrophe is an oncosuppressive mechanism that senses mitotic failure leading to cell death or senescence. As such, it protects against aneuploidy and genetic instability, and its induction in cancer cells by exogenous agents is currently seen as a promising therapeutic end point. Apoptin, a small protein from Chicken Anemia Virus (CAV), is known for its ability to selectively induce cell death in human tumor cells. Here, we show that apoptin triggers p53-independent abnormal spindle formation in osteosarcoma cells. Approximately 50% of apoptin-positive cells displayed non-bipolar spindles, a 10-fold increase as compared to control cells. Besides, tumor cells expressing apoptin are greatly limited in their progress through anaphase and telophase, and a significant drop in mitotic cells past the meta-to-anaphase transition is observed. Time-lapse microscopy showed that mitotic osteosarcoma cells expressing apoptin displayed aberrant mitotic figures and/or had a prolonged cycling time during mitosis. Importantly, all dividing cells expressing apoptin eventually underwent cell death either during mitosis or during the following interphase. We infer that apoptin can efficiently trigger cell death in dividing human tumor cells through induction of mitotic catastrophe. However, the killing activity of apoptin is not only confined to dividing cells, as the CAV-derived protein is also able to trigger caspase-3 activation and apoptosis in non-mitotic cancer cells.

Features of autophagic cell death in Plasmodium liver-stage parasites

Analyzing molecular determinants of Plasmodium parasite cell death is a promising approach for exploring new avenues in the fight against malaria. Three major forms of cell death (apoptosis, necrosis and autophagic cell death) have been described in multicellular organisms but which cell death processes exist in protozoa is still a matter of debate. Here we suggest that all three types of cell death occur in Plasmodium liver-stage parasites. Whereas typical molecular markers for apoptosis and necrosis have not been found in the genome of Plasmodium parasites, we identified genes coding for putative autophagy-marker proteins and thus concentrated on autophagic cell death. We characterized the Plasmodium berghei homolog of the prominent autophagy marker protein Atg8/LC3 and found that it localized to the apicoplast. A relocalization of PbAtg8 to autophagosome-like vesicles or vacuoles that appear in dying parasites was not, however, observed. This strongly suggests that the function of this protein in liver-stage parasites is restricted to apicoplast biology.

DAMPs and autophagy: cellular adaptation to injury and unscheduled cell death

Autophagy is a lysosome-mediated catabolic process involving the degradation of intracellular contents (e.g., proteins and organelles) as well as invading microbes (e.g., parasites, bacteria and viruses). Multiple forms of cellular stress can stimulate this pathway, including nutritional imbalances, oxygen deprivation, immunological response, genetic defects, chromosomal anomalies and cytotoxic stress. Damage-associated molecular pattern molecules (DAMPs) are released by stressed cells undergoing autophagy or injury, and act as endogenous danger signals to regulate the subsequent inflammatory and immune response. A complex relationship exists between DAMPs and autophagy in cellular adaption to injury and unscheduled cell death. Since both autophagy and DAMPs are important for pathogenesis of human disease, it is crucial to understand how they interplay to sustain homeostasis in stressful or dangerous environments.

NETosis

Neutrophils are the first line of defense of the immune system against infection. Among their weaponry, they have the ability to mix and extrude their DNA and bactericidal molecules creating NET-like structures in a unique type of cell death called NETosis. This process is important in order to control extracellular infections limiting collateral damage. Its aberrant function has been implicated in several human diseases including sepsis and autoimmune disease. The purpose of the present paper is to give a general introduction to this concept.

Caspase inhibitors protect neurons by enabling selective necroptosis of inflamed microglia

Microglia are resident brain macrophages, which can cause neuronal loss when activated in infectious, ischemic, traumatic, and neurodegenerative diseases. Caspase-8 has both prodeath and prosurvival roles, mediating apoptosis and/or preventing RIPK1-mediated necroptosis depending on cell type and stimulus. We found that inflammatory stimuli (LPS, lipoteichoic acid, or TNF-α) caused an increase in caspase-8 IETDase activity in primary rat microglia without inducing apoptosis. Inhibition of caspase-8 with either Z-VAD-fmk or IETD-fmk resulted in necrosis of activated microglia. Inhibition of caspases with Z-VAD-fmk did not kill non-activated microglia, or astrocytes and neurons in any condition. Necrostatin-1, a specific inhibitor of RIPK1, prevented microglial caspase inhibition-induced death, indicating death was by necroptosis. In mixed cerebellar cultures of primary neurons, astrocytes, and microglia, LPS induced neuronal loss that was prevented by inhibition of caspase-8 (resulting in microglial necroptosis), and neuronal death was restored by rescue of microglia with necrostatin-1. We conclude that the activation of caspase-8 in inflamed microglia prevents their death by necroptosis, and thus, caspase-8 inhibitors may protect neurons in the inflamed brain by selectively killing activated microglia.

Effect of repetitive daily ethanol intoxication on adult rat brain: significant changes in phospholipase A2 enzyme levels in association with increased PARP-1 indicate neuroinflammatory pathway activation

Collaborating on studies of subchronic daily intoxication in juvenile and adult rats, we examined whether the repetitive ethanol treatments at these two life stages altered levels of key neuroinflammation-associated proteins-aquaporin-4 (AQP4), certain phospholipase A2 (PLA2) enzymes, PARP-1 and caspase-3-in hippocampus (HC) and entorhinal cortex (EC). Significant changes in the proteins could implicate activation of specific neuroinflammatory signaling pathways in these rats as well as in severely binge-intoxicated adult animals that are reported to incur degeneration of vulnerable neurons in HC and EC. Male Wistar rats, ethanol-intoxicated (3 g/kg i.p.) once daily for 6 days over an 8-day interval beginning at 37 days old and repeated at age 68-75 days, were sacrificed 1 h after the day 75 dose (blood ethanol, 200- 230 mg/dl). Analysis of HC with an immunoblot technique showed that AQP4, Ca(+2)-dependent PLA2 (cPLA2 IVA), phosphorylated (activated) p-cPLA2, cleaved (89 kD) PARP (c-PARP), and caspase-3 levels were significantly elevated over controls, whereas Ca(+2)-independent PLA2 (iPLA2 VIA) was reduced ∼70%; however, cleaved caspase-3 was undetectable. In the EC, AQP4 was unchanged, but cPLA2 and p-cPLA2 were significantly increased while iPLA2 levels were diminished (∼40%) similar to HC, although just outside statistical significance (p = 0.06). In addition, EC levels of PARP-1 and c-PARP were significantly increased. The ethanol-induced activation of cPLA2 in association with reduced iPLA2 mirrors PLA2 changes in reports of neurotrauma and also of dietary omega-3 fatty acid depletion. Furthermore, the robust PARP-1 elevations accompanied by negligible caspase-3 activation indicate that repetitive ethanol intoxication may be potentiating non-apoptotic neurodegenerative processes such as parthanatos. Overall, the repetitive ethanol treatments appeared to instigate previously unappreciated neuroinflammatory pathways in vivo. The data provide insights into mechanisms of binge ethanol abuse that might suggest new therapeutic approaches to counter neurodegeneration and dementia.

Mechanisms regulating neutrophil survival and cell death

Neutrophils not only play a critical role as a first line of defense against bacteria and fungi infections but also contribute to tissue injury associated with autoimmune and inflammatory diseases. Neutrophils are rapidly and massively recruited from the circulation into injured tissues displaying an impressive arsenal of toxic weapons. Although effective in their ability to kill pathogens, these weapons were equally effective to induce tissue damage. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task mainly achieved through a complex network of mechanisms, which regulate neutrophil survival. Neutrophils have the shortest lifespan among leukocytes and usually die via apoptosis although new forms of cell death have been characterized over the last few years. The lifespan of neutrophils can be dramatically modulated by a large variety of agents such as cytokines, pathogens, danger-associated molecular patterns as well as by pharmacological manipulation. Recent findings shed light about the complex mechanisms responsible for the regulation of neutrophil survival in different physiological, pathological, and pharmacological scenarios. Here, we provide an updated review on the current knowledge and new findings in this field and discuss novel strategies that could be used to drive the resolution of neutrophil-mediated inflammatory diseases.

Sensing of cell death by myeloid C-type lectin receptors

Molecules associated with dead or dying cells can be detected by receptors on macrophages and dendritic cells. Signals from these receptors impact myeloid cell function and play a role in determining whether death is silent or proinflammatory, tolerogenic or immunogenic. Prominent among myeloid receptors detecting dead cells are C-type lectin receptors (CLRs). Signals from these receptors variably induce endocytosis of cell corpses, corpse degradation, retrieval of dead cell-associated antigens and/or modulation of immune responses. The sensing of tissue damage by myeloid CLRs complements detection of pathogens in immunity and represents an ancient response aimed at restoring tissue homeostasis.

Physiological roles of the permeability transition pore

Mitochondria are implicated in many important cellular functions covering the whole life cycle from mitochondrial biogenesis to cell death. Mitochondrial homeostasis is tightly regulated, and mitochondrial dysfunction is frequently associated with severe human pathologies (eg, cardiovascular diseases, cancer, and neurodegeneration). The permeability transition pore (PTP) is an unselective voltage-dependent mitochondrial channel. Despite the extensive use of electrophysiology, biochemistry, pharmacology, and genetic invalidation in mice, the molecular identity of PTP is still unknown. Nevertheless, PTP is central to mitochondrial vital functions and can play a lethal role in many pathophysiological conditions. This review recapitulates the current knowledge of the various modes of conductance of the PTP channel and discusses their implication in the physiological roles of PTP and their regulation. Based on its involvement in normal physiology and human pathology, a better understanding of this channel and its roles remains a major goal for basic scientists and clinicians.

Cysteine proteases: mode of action and role in epidermal differentiation

Desquamation or cell shedding in mammalian skin is known to involve serine proteases, aspartic proteases and glycosidases. In addition, evidence continues to accumulate that papain-like cysteine proteases and an inhibitor cystatin M/E largely confined to the cutaneous epithelia also play key roles in the process. This involves the complete proteolysis of cell adhesive structures of the stratum corneum, the corneodesmosomes and notably of the desmogleins. Continual cell replacement in the epidermis is the result of the balance between the loss of the outer squames and mitosis of the cells in the basal cell layer. This article provides a brief account of the salient features of the characteristics and catalytic mechanism of cysteine proteases, followed by a discussion of the relevant epidermal biology. The proteases include the asparaginyl endopeptidase legumain, which exerts a strict specificity for the hydrolysis of asparaginyl bonds, cathepsin-V and cathepsin-L. The control of these enzymes by cystatin M/E regulates the processing of transglutaminases and is crucial in the biochemical pathway responsible for regulating the cross-linking and desquamation of the stratum corneum. In addition, caspase-14 has now been shown to play a major part in epidermal maturation. Uncontrolled proteolytic activity leads to abnormal hair follicle formation and deleterious effects on the skin barrier function.

Sequential Cdk1 and Plk1 phosphorylation of protein tyrosine phosphatase 1B promotes mitotic cell death

Mitotic cell death following prolonged arrest is an important death mechanism that is not completely understood. This study shows that Protein Tyrosine Phosphatase 1B (PTP1B) undergoes phosphorylation during mitotic arrest induced by microtubule-targeting agents (MTAs) in chronic myeloid leukaemia cells. Inhibition of cyclin-dependent kinase 1 (Cdk1) or polo-like kinase 1 (Plk1) during mitosis prevents PTP1B phosphorylation, implicating these kinases in PTP1B phosphorylation. In support of this, Cdk1 and Plk1 co-immunoprecipitate with endogenous PTP1B from mitotic cells. In addition, active recombinant Cdk1-cyclin B1 directly phosphorylates PTP1B at serine 386 in a kinase assay. Recombinant Plk1 phosphorylates PTP1B on serine 286 and 393 in vitro, however, it requires a priming phosphorylation by Cdk1 at serine 386 highlighting a novel co-operation between Cdk1 and Plk1 in the regulation of PTP1B. Furthermore, overexpression of wild-type PTP1B induced mitotic cell death, which is potentiated by MTAs. Moreover, mutation of serine 286 abrogates the cell death induced by PTP1B, whereas mutation of serine 393 does not, highlighting the importance of serine 286 phosphorylation in the execution of mitotic cell death. Finally, phosphorylation on serine 286 enhanced PTP1B phosphatase activity. Collectively, these data reveal that PTP1B activity promotes mitotic cell death and is regulated by the co-operative action of Cdk1 and Plk1 during mitotic arrest.

Prognostic value of LIPC in non-small cell lung carcinoma

Non-small cell lung carcinoma (NSCLC) is the most common form of lung cancer and is associated with a high mortality rate worldwide. The majority of individuals bearing NSCLC are treated with surgery plus adjuvant cisplatin, an initially effective therapeutic regimen that, however, is unable to prevent relapse within 5 years after tumor resection in an elevated proportion of patients. The factors that predict the clinical course of NSCLC and its sensitivity to therapy remain largely obscure. One notable exception is provided by pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. PDXK has recently been shown to be required for optimal cisplatin responses in vitro and in vivo and to constitute a bona fide prognostic marker in the NSCLC setting. Together with PDXK, 84 additional factors were identified that influence the response of NSCLC cells to cisplatin, in vitro including the hepatic lipase LIPC. Here, we report that the intratumoral levels of LIPC, as assessed by immunohistochemistry in two independent cohorts of NSCLC patients, positively correlate with disease outcome. In one out of two cohorts studied, the overall survival of NSCLC patients bearing LIPChigh lesions was unaffected, if not slightly worsened, by cisplatin-based adjuvant therapy. Conversely, the overall survival of patients with LIPClow lesions was prolonged by post-operative cisplatin. Pending validation in appropriate clinical series, these results suggest that LIPClow NSCLC patients would be those who mainly benefit from adjuvant cisplatin therapy. Thus, the expression levels of LIPC appear to have an independent prognostic value (and perhaps a predictive potential) in the setting of NSCLC. If these findings were confirmed by additional studies, LIPC expression levels might allow not only for NSCLC patient stratification, but also for the implementation of personalized therapeutic approaches.

Houttuynia cordata Thunb fraction induces human leukemic Molt-4 cell apoptosis through the endoplasmic reticulum stress pathway

Houttuynia cordata Thunb (HCT) is a native herb found in Southeast Asia which features various pharmacological activities against allergy, inflammation, viral and bacterial infection, and cancer. The aims of this study were to determine the cytotoxic effect of 6 fractions obtained from silica gel column chromatography of alcoholic HCT extract on human leukemic Molt-4 cells and demonstrate mechanisms of cell death. Six HCT fractions were cytotoxic to human lymphoblastic leukemic Molt-4 cells in a dose-dependent manner by MTT assay, fraction 4 exerting the greatest effects. Treatment with IC50 of HCT fraction 4 significantly induced Molt-4 apoptosis detected by annexinV-FITC/propidium iodide for externalization of phosphatidylserine to the outer layer of cell membrane. The mitochondrial transmembrane potential was reduced in HCT fraction 4-treated Molt-4 cells. Moreover, decreased expression of Bcl-xl and increased levels of Smac/Diablo, Bax and GRP78 proteins were noted on immunoblotting. In conclusion, HCT fraction 4 induces Molt-4 apoptosis cell through an endoplasmic reticulum stress pathway.

Alternative cell death pathways and cell metabolism

While necroptosis has for long been viewed as an accidental mode of cell death triggered by physical or chemical damage, it has become clear over the last years that necroptosis can also represent a programmed form of cell death in mammalian cells. Key discoveries in the field of cell death research, including the identification of critical components of the necroptotic machinery, led to a revised concept of cell death signaling programs. Several regulatory check and balances are in place in order to ensure that necroptosis is tightly controlled according to environmental cues and cellular needs. This network of regulatory mechanisms includes metabolic pathways, especially those linked to mitochondrial signaling events. A better understanding of these signal transduction mechanisms will likely contribute to open new avenues to exploit our knowledge on the regulation of necroptosis signaling for therapeutic application in the treatment of human diseases.

Aneuploid cells are differentially susceptible to caspase-mediated death during embryonic cerebral cortical development

Neural progenitor cells, neurons, and glia of the normal vertebrate brain are diversely aneuploid, forming mosaics of intermixed aneuploid and euploid cells. The functional significance of neural mosaic aneuploidy is not known; however, the generation of aneuploidy during embryonic neurogenesis, coincident with caspase-dependent programmed cell death (PCD), suggests that a cell's karyotype could influence its survival within the CNS. To address this hypothesis, PCD in the mouse embryonic cerebral cortex was attenuated by global pharmacological inhibition of caspases or genetic removal of caspase-3 or caspase-9. The chromosomal repertoire of individual brain cells was then assessed by chromosome counting, spectral karyotyping, fluorescence in situ hybridization, and DNA content flow cytometry. Reducing PCD resulted in markedly enhanced mosaicism that was comprised of increased numbers of cells with the following: (1) numerical aneuploidy (chromosome losses or gains); (2) extreme forms of numerical aneuploidy (>5 chromosomes lost or gained); and (3) rare karyotypes, including those with coincident chromosome loss and gain, or absence of both members of a chromosome pair (nullisomy). Interestingly, mildly aneuploid (<5 chromosomes lost or gained) populations remained comparatively unchanged. These data demonstrate functional non-equivalence of distinguishable aneuploidies on neural cell survival, providing evidence that somatically generated, cell-autonomous genomic alterations have consequences for neural development and possibly other brain functions.

NETs: the missing link between cell death and systemic autoimmune diseases?

For almost 20 years, apoptosis and secondary necrosis have been considered the major source of autoantigens and endogenous adjuvants in the pathogenic model of systemic autoimmune diseases. This focus is justified in part because initial evidence in systemic lupus erythematosus (SLE) guided investigators toward the study of apoptosis, but also because other forms of cell death were unknown. To date, it is known that many other forms of cell death occur, and that they vary in their capacity to stimulate as well as inhibit the immune system. Among these, NETosis (an antimicrobial form of death in neutrophils in which nuclear material is extruded from the cell forming extracellular traps), is gaining major interest as a process that may trigger some of the immune features found in SLE, granulomatosis with polyangiitis (formerly Wegener’s granulomatosis) and Felty’s syndrome. Although there have been volumes of very compelling studies published on the role of cell death in autoimmunity, no unifying theory has been adopted nor have any successful therapeutics been developed based on this important pathway. The recent inclusion of NETosis into the pathogenic model of autoimmune diseases certainly adds novel insights into this paradigm, but also reveals a previously unappreciated level of complexity and raises many new questions. This review discusses the role of cell death in systemic autoimmune diseases with a focus on apoptosis and NETosis, highlights the current short comings in our understanding of the vast complexity of cell death, and considers the potential shift in the cell death paradigm in autoimmunity. Understanding this complexity is critical in order to develop tools to clearly define the death pathways that are active in systemic autoimmune diseases, identify drivers of disease propagation, and develop novel therapeutics.

Immunosurveillance against tetraploidization-induced colon tumorigenesis

Circumstantial evidence suggests that colon carcinogenesis can ensue the transient tetraploidization of (pre-)malignant cells. In line with this notion, the tumor suppressors APC and TP53, both of which are frequently inactivated in colon cancer, inhibit tetraploidization in vitro and in vivo. Here, we show that-contrarily to their wild-type counterparts- Tp53 (-/-) colonocytes are susceptible to drug-induced or spontaneous tetraploidization in vitro. Colon organoids generated from tetraploid Tp53 (-/-) cells exhibit a close-to-normal morphology as compared to their diploid Tp53 (-/-) counterparts, yet the colonocytes constituting these organoids are characterized by an increased cell size and an elevated expression of the immunostimulatory protein calreticulin on the cell surface. The subcutaneous injection of tetraploid Tp53 (-/-) colon organoids led to the generation of proliferating tumors in immunodeficient, but not immunocompetent, mice. Thus, tetraploid Tp53 (-/-) colonocytes fail to survive in immunocompetent mice and develop neoplastic lesions in immunocompromised settings only. These results suggest that tetraploidy is particularly oncogenic in the context of deficient immunosurveillance.

Quantification of cell cycle-arresting proteins

Cellular senescence, which can be defined as a stress response preventing the propagation of cells that have accumulated potentially oncogenic alterations, is invariably associated with a permanent cell cycle arrest. Such an irreversible blockage is mainly mediated by the persistent upregulation of one or more cyclin-dependent kinase inhibitors (CKIs), including (though not limited to) p16( INK4A ) and p21( CIP1 ) and p27( KIP1 ). CKIs operate by binding to cyclin-dependent kinases (CDKs), de facto inhibiting their enzymatic activity. Here, we provide an immunoblotting-based method for the detection and quantification of CKIs in vitro and ex vivo, together with a set of guidelines for the interpretation of results.

Time-lapse imaging of necrosis

The processes of dying are as tightly regulated as those of growth and proliferation. Recent work into the molecular pathways that regulate and execute cell death have uncovered a plethora of signalling cascades that lead to distinct modes of cell death, including "apoptosis," "necrosis," "autophagic cell death," and "mitotic catastrophe." Given that cells can readily switch from one form of death to another, it is vital to carefully monitor the form of death under investigation. Particularly, end-point techniques are intrinsically unsuitable for assessing apoptosis versus necrosis, as they cannot reconstruct the sequence of events that have led to cell death. Since apoptotic cells frequently undergo secondary necrosis under in vitro culture conditions, novel methods relying on high-throughput time-lapse fluorescence video microscopy have been developed. Here we describe the use of this technique to reliably distinguish necrosis from apoptosis and secondary necrosis.

Hyperthermia induces cytoskeletal alterations and mitotic catastrophe in p53-deficient H1299 lung cancer cells

Hyperthermia is used in cancer therapy, however much remains to be discovered regarding its mechanisms of action at the cellular level. In this study, the effects of hyperthermia on cell death, survival, morphology and the cytoskeleton were investigated in a non-small cell lung cancer cell line, H1299. Despite the fact that this cell line is widely used in research, it has not yet been tested for heat shock sensitivity. Cells were given a 30-min heat shock at 43.5°C and 45°C and left to recover at 37°C for 24 and 48 h. 24 h after heat shock treatment, we monitored changes in the organization of the cytoskeleton using immunofluorescence microscopy. The number of actin stress fibers was significantly reduced, microtubules formed a looser meshwork, a portion of the cells possessed multipolar mitotic spindles, whereas vimentin filaments collapsed into perinuclear complexes. 48 h following heat stress, most of the cells showed recovery of the cytoskeleton, however we observed a considerable number of giant cells that were multinucleated or contained one enlarged nucleus. The data obtained by MTT assay showed a dose-dependent decrease of cell viability, while flow cytometric analysis revealed an increase in the number of cells with externalized phosphatidylserine. The results suggest that one of the modes of heat-induced cell death in H1299 cells is mitotic catastrophe, which probably ends in apoptosis.

Modes of Retinal Cell Death in Diabetic Retinopathy

Cell death seems to be a prominent feature in the progression of diabetic retinopathy. Several retinal cell types have been identified to undergo cell death in a diabetic environment. Most emphasis has been directed towards identifying apoptosis in the diabetic retina. However, new research has established that there are multiple forms of cell death. This review discusses the different modes of cell death and attempts to classify cell death of retinal cells known to die in diabetic retinopathy. Special emphasis is given to apoptosis, necrosis, autophagic cell death, and pyroptosis. It seems that different retinal cell types are dying by diverse types of cell death. Whereas endothelial cells predominantly undergo apoptosis, pericytes might die by apoptosis as well as necrosis. On the other hand, Müller cells are suggested to die by a pyroptotic mechanism. Diabetes leads to significant Müller cell loss at 7 months duration of diabetes in retinas of diabetic mice compared to non-diabetic, which is prevented by the inhibition of the caspase-1/IL-1β (interleukin-1beta) pathway using the IL-1 receptor knockout mouse. Since pyroptosis is characterized by the activation of the caspase-1/IL-1β pathway subsequently leading to cell death, Müller cells seem to be a prime candidate for this form of inflammation-driven cell death. Considering that diabetic retinopathy is now discussed to potentially be a chronic inflammatory disease, pyroptotic cell death might play an important role in disease progression. Understanding mechanisms of cell death will lead to a more targeted approach in the development of new therapies to treat diabetic retinopathy.

Fluorescent biosensors for the detection of HMGB1 release

During necrosis and following some instances of apoptosis (in particular in the absence of a proficient phagocytic system), the nonhistone chromatin component high-mobility group box 1 (HMGB1) is released in the extracellular space. In vivo, extracellular HMGB1 can bind Toll-like receptor 4 on the surface of dendritic cells, de facto operating as a danger-associated molecular pattern and alarming the organism to the presence of stressful conditions. Recent results indicate that the release of HMGB1 is one of the key features for cell death to be perceived as immunogenic, i.e., to be capable of triggering a cognate immune response in vivo. Thus, only anticancer agents that-among other features-allow for the release of HMGB1 as they induce cell death are expected to stimulate anticancer immune responses. To investigate the immunogenic potential of conventional anticancer agents and novel cell death inducers on a high-throughput scale, we engineered human osteosarcoma U2OS cells to express HMGB1 fused at the N-terminus of the green fluorescent protein (GFP). Coupled to fluorescence microscopy workstations for automated image acquisition and analysis, this HMGB1-GFP-based biosensor is amenable for the identification of potential inducers of immunogenic cell death among large chemical libraries.

Cytofluorometric assessment of cell cycle progression

One of the most prominent features of cellular senescence, a stress response that prevents the propagation of cells that have accumulated potentially oncogenic alterations, is a permanent loss of proliferative potential. Thus, at odds with quiescent cells, which resume proliferation when stimulated to do so, senescent cells cannot proceed through the cell cycle even in the presence of mitogenic factors. Here, we describe a set of cytofluorometric techniques for studying how chemical and/or physical stimuli alter the cell cycle in vitro, in both qualitative and quantitative terms. Taken together, these methods allow for the identification of bona fide cytostatic effects as well as for a refined characterization of cell cycle distributions, providing information on proliferation, DNA content as well as on the presence of cell cycle phase-specific markers. At the end of the chapter, a set of guidelines is offered to assist researchers that approach the study of the cell cycle with the interpretation of results.