Epidermal growth factor triggers an original, caspase-independent pituitary cell death with heterogeneous phenotype

Programmed cell death (PCD) is physiologically involved in the regulation of cell division and differentiation. It encompasses caspase-dependent mitochondrial and nonmitochondrial pathways. Additional caspase-independent pathways have been characterized in mitochondrial PCDs but remain hypothetical in nonmitochondrial PCDs. Epidermal growth factor (EGF) has been shown to inhibit division of pituitary somato-lactotrope cells occurring in parallel with EGF-mediated differentiation of these precursors into lactotrope cells. We show here that in somato-lactotrope pituitary cell line GH4C1, EGF triggers a PCD characterized by an apoptosis-like DNA fragmentation, insensitivity to broad-range caspase inhibitors, and absence of either cytochrome c or apoptosis-inducing factor release from mitochondria. Dying cells display loose chromatin clustering and numerous cytoplasmic vacuoles, a fraction of which are autophagic, thus conferring a heterogeneous phenotype to this PCD. Moreover, overexpression of cell death inhibitor Bcl-2 prevented not only the EGF-induced PCD but also its prodifferentiation effects, thus pointing to a mechanistic relationship existing between these two phenomena. Overall, the characterized differentiation-linked cell death represents an original form of caspase-independent PCD. The mechanisms underlying this PCD involve combinatorial engagement of discrete death effectors leading to a heterogeneous death phenotype that might be evolutionary related to PCD seen during the differentiation of some unicellular organisms.     

Protozoan programmed cell death--insights from Blastocystis deathstyles

Programmed cell death (PCD) is an essential process in the growth and development of multicellular organisms. However, accumulating evidence indicates that unicellular eukaryotes can also undergo PCD with apoptosis-like features. The protozoan parasite Blastocystis hominis has been reported to exhibit both apoptotic and non-apoptotic features of PCD when exposed to a variety of stimuli. Recent observations of PCD pathways in Blastocystis suggest that this protozoan, as is the case with its multicellular counterparts, possesses complex cell-death mechanisms.     

The apoptosis inhibitory domain of FE65-like protein 1 regulates both apoptotic and caspase-independent programmed cell death mediated by tumor necrosis factor

Tumor necrosis factor (TNF) can induce caspase-dependent (apoptotic) and caspase-independent pathways to programmed cell death (PCD). Here, we demonstrate that stable transfection of a cDNA encompassing the C-terminal apoptosis inhibitory domain (AID) of FE65-like protein 1 into mouse L929 fibrosarcoma cells protects from caspase-independent as well as from apoptotic PCD induced by TNF. We show that the AID does not protect from caspase-independent PCD elicited by 1-methyl-3-nitro-1-nitrosoguanidine, suggesting that the AID might prevent cell death by affecting assembly of the death inducing signaling complex of the 55 kDa TNF receptor or clustering of the receptor itself. Interference with caspase-independent PCD mediated by the sphingolipid ceramide further increases protection conferred by the AID, as does the antioxidant butylated hydroxyanisole, implicating ceramide and reactive oxygen species as potential factors interacting with caspase-independent PCD regulated by the AID.     

Developmental programmed cell death in plants

Mechanisms of plant developmental programmed cell death (PCD) have been intensively studied in recent years. Most plant developmental PCD is triggered by plant hormones, and the 'death signal' may be transduced by hormonal signaling pathways. Although there are some fundamental differences in the regulation of developmental PCD in various eukaryotes of different kingdoms, hormonal control and death signal transduction via pleiotropic signaling pathways constitute a common framework. However, plants possess a unique process of PCD execution that depends on vacuolar lytic function. Comparisons of the developmental PCD mechanisms of plants and other organisms are providing important insights into the detailed characteristics of developmental PCD in plants.     

Polygonatum cyrtonema lectin, a potential antineoplastic drug targeting programmed cell death pathways

Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding plant lectin, has recently drawn a rising attention for cancer biologists because PCL bears remarkable anti-tumor activities and thus inducing programmed cell death (PCD) including apoptosis and autophagy in cancer cells. In this review, we focus on exploring the precise molecular mechanisms by which PCL induces cancer cell apoptotic death such as the caspase-dependent pathway, mitochondria-mediated ROS–p38–p53 pathway, Ras–Raf and PI3K–Akt pathways. In addition, we further elucidate that PCL induces cancer cell autophagic death via activating mitochondrial ROS–p38–p53 pathway, as well as via blocking Ras–Raf and PI3K–Akt pathways, suggesting an intricate relationship between autophagic and apoptotic death in PCL-induced cancer cells. In conclusion, these findings may provide a new perspective of Polygonatum cyrtonema lectin (PCL) as a potential anti-tumor drug targeting PCD pathways for future cancer therapeutics.     

Apoptotic-like programmed cell death in plants

Programmed cell death (PCD) is now accepted as a fundamental cellular process in plants. It is involved in defence, development and response to stress, and our understanding of these processes would be greatly improved through a greater knowledge of the regulation of plant PCD. However, there may be several types of PCD that operate in plants, and PCD research findings can be confusing if they are not assigned to a specific type of PCD. The various cell-death mechanisms need therefore to be carefully described and defined. This review describes one of these plant cell death processes, namely the apoptotic-like PCD (AL-PCD). We begin by examining the hallmark 'apoptotic-like' features (protoplast condensation, DNA degradation) of the cell's destruction that are characteristic of AL-PCD, and include examples of AL-PCD during the plant life cycle. The review explores the possible cellular 'executioners' (caspase-like molecules; mitochondria; de novo protein synthesis) that are responsible for the hallmark features of the cellular destruction. Finally, senescence is used as a case study to show that a rigorous definition of cell-death processes in plant cells can help to resolve arguments that occur in the scientific literature regarding the timing and control of plant cell death.     

The serine protease inhibitor TLCK attenuates intrinsic death pathways in neurons upstream of mitochondrial demise

It is well-established that activation of proteases, such as caspases, calpains and cathepsins are essential components in signaling pathways of programmed cell death (PCD). Although these proteases have also been linked to mechanisms of neuronal cell death, they are dispensable in paradigms of intrinsic death pathways, e.g. induced by oxidative stress. However, emerging evidence implicated a particular role for serine proteases in mechanisms of PCD in neurons. Here, we investigated the role of trypsin-like serine proteases in a model of glutamate toxicity in HT-22 cells. In these cells glutamate induces oxytosis, a form of caspase-independent cell death that involves activation of the pro-apoptotic protein BH3 interacting-domain death agonist (Bid), leading to mitochondrial demise and ensuing cell death. In this model system, the trypsin-like serine protease inhibitor Nα-tosyl-l-lysine chloromethyl ketone hydrochloride (TLCK) inhibited mitochondrial damage and cell death. Mitochondrial morphology alterations, the impairment of the mitochondrial membrane potential and ATP depletion were prevented and, moreover, lipid peroxidation induced by glutamate was completely abolished. Strikingly, truncated Bid-induced cell death was not affected by TLCK, suggesting a detrimental activity of serine proteases upstream of Bid activation and mitochondrial demise. In summary, this study demonstrates the protective effect of serine protease inhibition by TLCK against oxytosis-induced mitochondrial damage and cell death. These findings indicate that TLCK-sensitive serine proteases play a crucial role in cell death mechanisms upstream of mitochondrial demise and thus, may serve as therapeutic targets in diseases, where oxidative stress and intrinsic pathways of PCD mediate neuronal cell death.     

Lesion mimic mutants: keys for deciphering cell death and defense pathways in plants?

The identification of several lesion mimic mutants (LMM) that misregulate cell death constitutes a powerful tool to unravel programmed cell death (PCD) pathways in plants, particularly the hypersensitive response (HR), a form of PCD associated with resistance to pathogens. Recently, the characterization of novel LMM has enabled genes that might regulate cell death programmes to be identified as well as the dissection of defense signaling pathways and of crosstalk between multiple pathways in ways that might not be possible by studying the responses of wild-type plants to pathogens.     

mTOR in programmed cell death and its therapeutic implications

Mechanistic target of rapamycin (mTOR), a highly conserved serine/threonine kinase, is involved in cellular metabolism, protein synthesis, and cell death. Programmed cell death (PCD) assists in eliminating aging, damaged, or neoplastic cells, and is indispensable for sustaining normal growth, fighting pathogenic microorganisms, and maintaining body homeostasis. mTOR has crucial functions in the intricate signaling pathway network of multiple forms of PCD. mTOR can inhibit autophagy, which is part of PCD regulation. Cell survival is affected by mTOR through autophagy to control reactive oxygen species production and the degradation of pertinent proteins. Additionally, mTOR can regulate PCD in an autophagy-independent manner by affecting the expression levels of related genes and phosphorylating proteins. Therefore, mTOR acts through both autophagy-dependent and -independent pathways to regulate PCD. It is conceivable that mTOR exerts bidirectional regulation of PCD, such as ferroptosis, according to the complexity of signaling pathway networks, but the underlying mechanisms have not been fully explained. This review summarizes the recent advances in understanding mTOR-mediated regulatory mechanisms in PCD. Rigorous investigations into PCD-related signaling pathways have provided prospective therapeutic targets that may be clinically beneficial for treating various diseases.     

Involvement of de novo ceramide biosynthesis in macrophage death induced by activation of ATP-sensitive P2X7 receptor

Macrophage ionotropic P2X7 receptors regulate cell-death through ill-defined signaling pathways. Here, we investigated the role of ceramide, an apoptogenic sphingolipid and showed that ATP stimulated ceramide accumulation in macrophages. Benzoylbenzoyl-ATP, a potent P2X7 agonist, was able to mimic the effects of ATP on ceramide accumulation while oxidized ATP had the opposite effect. Ceramide accumulation was blocked by de novo ceramide biosynthesis inhibitors. Interestingly, ATP-induced caspase-3/7 activation was dependent on ceramide generation. Finally, we showed that de novo ceramide biosynthesis is involved in ATP-induced macrophage death in a caspase-dependent manner. Our results indicate a novel role of ceramide in P2X7-regulated cell-death.     

中国科学家在植物程序性细胞死亡领域取得重要成果

程序性细胞死亡不仅在植物生长发育中起重要作用, 而且与植物适应逆境密切相关。近日, 中国科学家在解析植物程序性细胞死亡(PCD)信号通路的研究中取得了突破性进展。     

Insect muscle as a model for programmed cell death.

Programmed cell death (PCD) is a fundamental component of development in virtually all animals. Despite the ubiquity of this phenomenon, little is known about what tells a cell to die, and less still about the physiological and molecular mechanisms that bring about death. One system that has proven to be very amenable for the study of PCD is the intersegmental muscle (ISM) of the tobacco hawkmoth Manduca sexta. These giant muscle cells are used during the eclosion (emergence) behavior of the adult moth, and then die during the subsequent 30 h. This review uses the ISMs as a model system to address questions that are basic to any cell death system, including the following: (1) how do cells know when to die; (2) what physiological changes accompany death; (3) what are the molecular mechanisms that mediate death; and (4) do all cells die by the same process? For the ISMs, the trigger for PCD is a decline in the circulating titer of the insect molting hormone, 20-hydroxyecdysone (20-HE). During cell death there are rapid decreases in both the myofibrillar sensitivity to intracellular calcium and the resulting force of fiber contraction. The ability of the ISMs to undergo PCD requires the repression and activation of specific genes. Two of the repressed genes encode actin and myosin. One of the upregulated presumptive cell-death genes encodes polyubiquitin, which appears to play a critical role in the rapid proteolysis that accompanies ISM death.(ABSTRACT TRUNCATED AT 250 WORDS)     

The murine TRAIL receptor signals caspase-independent cell death through ceramide

Death receptors such as the 55 kDa tumor necrosis factor (TNF) receptor (TNF-R55) or Fas can initiate both apoptotic (caspase-dependent) and caspase-independent routes to programmed cell death (PCD). Here, we demonstrate for the first time that the single murine receptor for (TNF)-related apoptosis-inducing ligand (mTRAIL-R2) can induce a caspase-independent form of PCD with necrosis-like features in addition to apoptosis. Analysis of morphological and cellular features of caspase-independent PCD in response to TRAIL and TNF suggests that mTRAIL-R2 and TNF-R55 elicit caspase-independent PCD through similar pathways, although without participation of cathepsins. Cells overexpressing acid ceramidase (AC), an enzyme that metabolizes the sphingolipid ceramide, show enhanced survival from TRAIL-induced caspase-independent PCD but not from apoptosis, implicating a function of ceramide as a key mediator in caspase-independent PCD (but not apoptosis) induced by mTRAIL-R2. In concert with the enhanced resistance of AC-overexpressing cells against caspase-independent PCD induced by TNF, our results suggest that ceramide acts as a common mediator of caspase-independent PCD caused by death receptors such as mTRAIL-R2 and TNF-R55.     

AIF-mediated caspase-independent necroptosis: a new chance for targeted therapeutics

Cell death has been initially divided into apoptosis, in which the cell plays an active role, and necrosis, which is considered a passive cell death program. Intense research performed in the last decades has concluded that "programmed" cell death (PCD) is a more complex physiological process than initially thought. Indeed, although in most cases the PCD process is achieved via a family of Cys proteases known as caspases, an important number of regulated PCD pathways do not involve this family of proteases. As a consequence, active forms of PCD are initially referred to as caspase-dependent and caspase-independent. More recent data has revealed that there are also active caspase-independent necrotic pathways defined as necroptosis (programmed necrosis). The existence of necroptotic forms of death was corroborated by the discovery of key executioners such as the kinase RIP1 or the mitochondrial protein apoptosis-inducing factor (AIF). AIF is a Janus protein with a redox activity in the mitochondria and a pro-apoptotic function in the nucleus. We have recently described a particular form of AIF-mediated caspase-independent necroptosis that also implicates other molecules such as PARP-1, calpains, Bax, Bcl-2, histone H2AX, and cyclophilin A. From a therapeutic point of view, the unraveling of this new form of PCD poses a question: is it possible to modulate this necroptotic pathway independently of the classical apoptotic paths? Because the answer is yes, a wider understanding of AIF-mediated necroptosis could theoretically pave the way for the development of new drugs that modulate PCD. To this end, we present here an overview of the current knowledge of AIF and AIF-mediated necroptosis. We also summarize the state of the art in some of the most interesting therapeutic strategies that could target AIF or the AIF-mediated necroptotic pathway.     

Control of mitochondrial integrity by Bcl-2 family members and caspase-independent cell death

Programmed cell death (PCD) is essential for normal development and maintenance of tissue homeostasis in multicellular organisms. While it is now evident that PCD can take many different forms, apoptosis is probably the most well-defined cell death programme. The characteristic morphological and biochemical features associated with this highly regulated form of cell death have until recently been exclusively attributed to the caspase family of cysteine proteases. As a result, many investigators affiliate apoptosis with its pivotal execution system, i.e. caspase activation. However, it is becoming increasingly clear that PCD or apoptosis can also proceed in a caspase-independent manner and maintain key characteristics of apoptosis. Mitochondrial integrity is central to both caspase-dependent and-independent cell death. The release of pro-apoptotic factors from the mitochondrial intermembrane space is a key event in a cell's commitment to die and is under the tight regulation of the Bcl-2 family. However, the underlying mechanisms governing the efflux of these pro-death molecules are largely unknown. This review will focus on the regulation of mitochondrial integrity by Bcl-2 family members with particular attention to the controlled release of factors involved in caspase-independent cell death.     

Autophagy promotes caspase-dependent cell death during Drosophila development

The relationship between autophagic cell death and apoptosis is a poorly understood aspect of programmed cell death (PCD). We have examined this relationship by studying the elimination of an extra-embryonic tissue, known as the amnioserosa (AS), during Drosophila development. The AS becomes autophagic during the final stages of embryogenesis; ultimately, however, the elimination of the AS involves caspase-dependent nuclear fragmentation, tissue dissociation, and engulfment by phagocytic macrophages. Mutants that are defective in the activation or execution of caspase-dependent PCD fail to degrade and eliminate the AS but show no abatement in AS autophagy. Sustained autophagy does not, therefore, necessarily result in cell death. Surprisingly, the down-regulation of autophagy also results in a persistent AS phenotype and reduced cell death. Conversely, up-regulation of autophagy results in caspase-dependent premature AS dissociation. These observations are consistent with the interpretation that autophagy is a prerequisite for caspase-dependent cell death in the AS.     

Another way to die: autophagic programmed cell death

Programmed cell death (PCD) is one of the important terminal paths for the cells of metazoans, and is involved in a variety of biological events that include morphogenesis, maintenance of tissue homeostasis, and elimination of harmful cells. Dysfunction of PCD leads to various diseases in humans, including cancer and several degenerative diseases. Apoptosis is not the only form of PCD. Recent studies have provided evidence that there is another mechanism of PCD, which is associated with the appearance of autophagosomes and depends on autophagy proteins. This form of cell death most likely corresponds to a process that has been morphologically defined as autophagic PCD. The present review summarizes recent experimental evidence about autophagic PCD and discusses some aspects of this form of cell death, including the mechanisms that may distinguish autophagic death from the process of autophagy involved in cell survival.     

AIF-Mediated Programmed Necrosis: A Highly Orchestrated Way to Die

Historically, two main forms of cell death have been distinguished: apoptosis and necrosis. Apoptosis was initially considered as the only physiological and programmed form of cell death. This type of death is recurrently associated with caspases, a family of cysteine proteases activated in apoptotic conditions. However, it is now widely recognized that programmed cell death (PCD) can also occur in the complete absence of caspase activation. The existence of non-caspase PCD pathways was corroborated by the discovery of caspase-independent executioners, such as the mitochondrial protein Apoptosis-Inducing Factor (AIF). Necrosis has often been viewed as an accidental and uncontrolled cell death process. Nevertheless, increasing evidence shows that, like apoptosis, necrosis could be a highly regulated type of PCD. Indeed, apoptosis and necrosis present more similarities than it has been originally thought. Here, we summarize the different classifications of PCD and the current knowledge of a necrotic PCD pathway mediated by AIF: alkylating DNA-damage mediated death. We also outline the molecular mechanisms controlling this form of PCD and discuss their potential relevance in physiological and pathological settings. These emerging data on the molecular mechanisms regulating programmed necrosis may certainly have potent therapeutic consequences in treating both apoptotic-resistant tumors and degenerating adult neurons.     

Systems biology of yeast cell death

Programmed cell death (PCD) (including apoptosis) is an essential process, and many human diseases of high prevalence such as neurodegenerative diseases and cancer are associated with deregulations in the cell death pathways. Yeast Saccharomyces cerevisiae, a unicellular eukaryotic organism, shares with multicellular organisms (including humans) key components and regulators of the PCD machinery. In this article, we review the current state of knowledge about cell death networks, including the modeling approaches and experimental strategies commonly used to study yeast cell death. We argue that the systems biology approach will bring valuable contributions to our understanding of regulations and mechanisms of the complex cell death pathways.