The phosphatidylserine receptor from <Emphasis Type="Italic">Hydra</Emphasis> is a nuclear protein with potential Fe(II) dependent oxygenase activity

Background  

Apoptotic cell death plays an essential part in embryogenesis, development and maintenance of tissue homeostasis in metazoan animals. The culmination of apoptosis in vivo is the phagocytosis of cellular corpses. One morphological characteristic of cells undergoing apoptosis is loss of plasma membrane phospholipid asymmetry and exposure of phosphatidylserine on the outer leaflet. Surface exposure of phosphatidylserine is recognised by a specific receptor (phosphatidylserine receptor, PSR) and is required for phagocytosis of apoptotic cells by macrophages and fibroblasts.     

Hydra and the evolution of apoptosis

Programmed cell death occurs in most, if not all life forms.It is used to sculpt tissue during embryogenesis, to removedamaged cells, to protect against pathogen infection and toregulate cell numbers and tissue homeostasis. In animals celldeath often occurs by a morphologically and biochemically conservedprocess called apoptosis. A novel group of cysteine proteases,referred to as caspases, constitute the central component ofthis process. Caspases are activated following the inductionof apoptosis and cleave a variety of cellular substrates, thusgiving rise to the characteristic morphological events of apoptosis.Apoptosis is rapid and cell corpses are removed by phagocytosis.Recent work has shown that apoptosis also occurs in Cnidariaand Porifera, thus extending the origin of this evolutionaryinnovation down to the first metazoan animal phyla. Here, wereview several examples of the role of apoptosis in cnidariansand then summarize new results on the subcellular localizationof caspases and the control of apoptosis in Hydra. We show byimmuncytochemistry that caspases in Hydra are localized in mitochondria.Following induction of apoptosis caspases are released frommitochondria as proenzymes and then activated by proteolyticcleavage in the cytoplasm. We also present evidence that apoptosisin Hydra is dramatically stimulated by inhibitors of PI3-kinase.Since PI3-kinase is a central component of growth factor signalingcascades in higher metazoans, this result suggests that controlof apoptosis by growth factors is also evolutionarily conserved.We speculate on the role of growth factors in the evolutionof apoptosis.     

The human homologue of Caenorhabditis elegans CED-6 specifically promotes phagocytosis of apoptotic cells

A key feature of the process of programmed cell death (apoptosis) is the efficiency with which the dying cells are recognized and engulfed by phagocytes [1]. Apoptotic cells are rapidly cleared either by neighbouring cells acting as semi-professional phagocytes or by experts of the macrophage line, so that an inflammatory response is avoided [2]. The Caenorhabditis elegans gene ced-6 is required for efficient engulfment of apoptotic cells [3] and is one of a group of genes that define two partially redundant parallel pathways for the engulfment process [4] [5]. These pathways may be conserved across evolution, as two other engulfment genes have human homologues. A CED-5 homologue is part of a human CrkII-DOCK180-Rac signaling pathway proposed to mediate cytoskeletal reorganization [6] [7] [8] and a CED-7 homologue is similar to the ABC transporters [9] [10]. Here, we report the cloning and characterization of human CED-6, a human homologue of C. elegans CED-6. The 34 kDa hCED-6 protein is expressed in most tissues, some human cancer cells, and in primary human macrophages. We developed an assay that quantitates the phagocytic activity of mammalian macrophages: the number of apoptotic cells that have been internalized is measured by the uptake of lacZ-positive apoptotic cells by adherent transgenic macrophages. The results of this assay demonstrate that overexpression of hCED-6 promotes phagocytosis only of apoptotic cells and suggest that hCED-6 is the mammalian orthologue of C. elegans CED-6 and is a part of a highly conserved pathway that specifically mediates the phagocytosis of apoptotic cells.     

Mitochondrial fission and apoptosis: an ongoing trial

Apoptosis is a form of programmed cell death that is essential for the development and tissue homeostasis in all metazoan animals. Mitochondria play a critical role during apoptosis, since the release of pro-apoptogenic proteins from the organelle is a pivotal event in cell death triggered by many cytotoxic stimuli. A striking morphological change occurring during apoptosis is the disintegration of the semi-reticular mitochondrial network into small punctiform organelles. It is only recently that this event has been shown to require the activity of proteins involved in the physiological processes of mitochondrial fission and fusion. Here, we discuss how this mitochondrial morphological transition occurs during cell death and the role that it may have in apoptosis.     

Apoptosis in yeast--a monocellular organism exhibits altruistic behaviour

Apoptosis is a highly regulated form of programmed cell death crucial for life and health in metazoan animals. Apoptosis is defined by a set of cytological alterations. The recent discovery of these markers in yeast indicates the presence of the basic mechanisms of apoptosis already in unicellular eukaryotes. Oxygen radicals regulate both mammalian and yeast apoptosis. We suggest that apoptosis originated in unicellular organisms as an altruistic response to severe oxidative damage. Later, cells developed mechanisms to purposely produce reactive oxygen species as a regulator of apoptosis. Yeast may become an important model to investigate the conserved steps of apoptosis.     

Apoptosis and catastrophic cell death in benzo[a]pyrene-transformed human breast epithelial cells

Apoptosis and mitotic death, bi- and multinucleation, giant cells and micronucleation were investigated in human breast epithelial cell lines transformed by benzo[a]pyrene (BP) (BP1, BP1-E and BP1-E1 cells) and in BP1 cells transfected with the c-Ha-ras oncogene (BP1-Tras cells). Since BP induces apoptosis and the abnormal expression of ras genes elicits catastrophic mitosis, both cell death phenomena were expected to occur in this system, especially in BP1-Tras cells. Regardless of the cell line considered, single-nucleate cells were found to be eliminated preferentially through apoptosis, while bi- and multinucleate cells were eliminated through catastrophic mitosis. Apoptosis and catastrophic mitosis were observed in all cell lines but were significantly more frequent in BP1-Tras cells. The abnormal expression of Ha-ras in the latter cells may enhance in this system the effects of the BP apoptosis path reported for BP-transformed Hepa 1c1c7 hepatoma cells. Transfection with the ras oncogene also enhanced the mitotic disturbances, which produced multi- and micronucleation and mitotic death, possibly because of the genomic instability promoted by this oncogene in the BP-transformed cell line.     

Programmed cell death

This paper reviews data on programmed cell death (apoptosis) in animals and plants. Necrosis is a pathological scenario of cell death, which entails an inflammatory response in animal tissues. Apoptosis results in the disintegration of animal/plant cells into membrane vesicles enclosing the intracellular content, which are thereupon engulfed by adjacent or specialized cells (phagocytes) in animals. Plants lack such specialized cells, and plant cell walls prevent phagocytosis. The paper considers the main molecular mechanisms of apoptosis in animals and the pathways of activation of caspases, evolutionarily conserved cysteine proteases. A self-contained section concerns itself with the process of programmed cell death (PCD) in microorganisms including: 1) cell death in the myxomycete Dictyostelium discoideum and the parasitic flagellate Trypanosoma cruzi; 2) PCD in genetically manipulated yeast expressing the proapoptotic Bax and Bak proteins; 3) the death of a part of a prokaryotic cell population upon the depletion of nutrient resources or under stress; 4) the elimination of cells after a loss of a plasmid encoding a stable cytotoxic agent in combination with an unstable antidote; and 5) PCD in phage-infected bacterial cells.     

Apoptosis in the pathogenesis of infectious diseases of the eastern oyster Crassostrea virginica

Apoptosis, or programmed cell death, has been reported as being pivotal in infectious diseases of different organisms. The effects of apoptosis on the progression and transmission of the protistan parasites Perkinsus marinus and Haplosporidium nelsoni in the eastern oyster Crassostrea virginica were studied. Oysters were diagnosed for their respective infections by standard methods, and apoptosis was detected using in situ hybridization to detect DNA fragments by end labeling on paraffin sections. A digoxigenin nucleotide probe was used to label the 200 bp fragment produced by apoptosis and detected immunohistochemically using an antidigoxigenin peroxidase conjugate. The probe/DNA fragment complex was stained with a peroxidase substrate and tissues were counterstained with methyl green. Uninfected oysters had large numbers of apoptotic hemocytes present in the connective tissue underlying the stomach, gill, and mantle epithelia, whereas oysters infected with P. marinus had a reduced number of apoptotic hemocytes. The parasite may prevent hemocyte apoptosis in order to yield a greater number of hemocytes in which to house itself. Large numbers of P. marinus cells in some infected oysters were eliminated via apoptosis in the stomach epithelia, disabling the spread of infectious particles through seawater. The oysters infected with H. nelsoni also had reduced numbers of apoptotic hemocytes, while part of the vesicular connective tissue cells were apoptotic. H. nelsoni plasmodia were eliminated via apoptosis in some oysters. Apoptosis may enhance progression and prevent transmission of infectious oyster diseases.     

Synthetic retinoids as inducers of apoptosis in ovarian carcinoma cell lines

Apoptosis is also known as programmed cell death. Apoptosis plays an essential role in maintaining normal tissue and cell physiology in multicellular organisms. Clearance of aberrant or pre-cancerous cells occurs through the induction of apoptosis. It has been reported that many tumors and tumor cell lines have dysfunctional apoptosis signaling, causing these tumors to escape immune monitoring and internal cellular control mechanisms. One potential cause of this dysfunctional apoptosis is the tumor suppressor p53, an important regulator of growth arrest and apoptosis that is mutated in over 50% of all cancers. Retinoids have great potential in the areas of cancer therapy and chemoprevention. While some tumor cells are sensitive to the growth inhibitory effects of natural retinoids such as all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-[3-(1-Admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and fenretinide N-[4-hydroxyphenyl] retinamide (4-HPR) are conformationally restricted synthetic retinoids that induce growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. Recently, we have identified the molecular pathways of apoptosis induced by treatment of ovarian carcinoma cells with mutated p53 by CD437 and 4-HPR.     

哺乳动物卵母细胞凋亡的研究进展

细胞凋亡是发育过程中的基本生命现象,除各种体细胞凋亡外,生殖细胞的发生过程中也发生细胞凋亡。就雌性生殖系而言,细胞凋亡是其发育过程中的一个重要组成部分。在哺乳动物中,超过99．9％的雌性生殖细胞都会在卵子发生的不同阶段发生凋亡。有三种学说解释这一现象：1)被忽视死亡;2)因缺陷死亡;3)自我牺牲死亡。本文主要综述了哺乳动物卵母细胞凋亡的现象、卵母细胞凋亡学说、线粒体遗传与卵母细胞凋亡的关系以及凋亡的分子机理,同时还探讨了卵母细胞凋亡的生物学意义。     

Apoptosis in procyclic Trypanosoma brucei rhodesiense in vitro

Apoptosis is a phenomenon previously associated exclusively with metazoan organisms. We show here that procyclic insect form Trypanosoma brucei rhodesiense, a protozoan parasite, when treated in vitro with concanavalin A displayed several features normally associated with apoptosis in metazoan cells. Lectin treatment induced cleavage of nuclear DNA into oligonucleosomal fragments, suggesting activation of an endogenous nuclease in the parasite. Treated trypanosomes, although agglutinated and non-motile, exhibited fluorescence after treatment with the vital stain fluorescein diacetate and retained (3)H-uridine indicating that their cell membranes remained intact during the period of DNA fragmentation. Electron micrographs showed characteristic morphology of cells undergoing apoptosis, including surface membrane vesiculation and migration of chromatin to the periphery of the nuclear membrane while mitochondria remained intact. These results suggest that treatment with concanavalin A triggers a cell death mechanism in T. b. rhodesiense similar to the process of apoptosis described in metazoa.     

Phosphatidylserine-mediated phagocytosis of anticancer drug-treated cells by macrophages

Apoptotic cells are rapidly phagocytosed and eliminated from the organism. Although cancer cells apoptose when treated with anticancer drugs, how those cells are recognized by phagocytic cells has remained unclear. The human leukemia cell line Jurkat was cultured with doxorubicin or bufalin and induced to undergo apoptosis accompanied by phosphatidylserine externalization. When apoptotic Jurkat cells were mixed with mouse peritoneal macrophages, efficient phagocytosis was observed. Apoptosis and phagocytosis of Jurkat cells were both inhibited by Z-VAD-FMK, and phagocytosis was significantly reduced in the presence of phosphatidylserine-containing liposomes. These results suggest that anticancer drugs induce apoptosis-dependent and phosphatidylserine-mediated phagocytosis in cancer cells.     

The role of apoptosis in the development and function of T lymphocytes

Apoptosis plays an essential role in T cell biology. Thymocytes expressing nonfunctional or autoreactive TCRs are eliminated by apoptosis during development. Apoptosis also leads to the deletion of expanded effector T cells during immune responses. The dysregulation of apoptosis in the immune system results in autoimmunity, tumorogenesis and immunodeficiency. Two major pathways lead to apoptosis： the intrinsic cell death pathway controlled by Bcl-2 family members and the extrinsic cell death pathway controlled by death receptor signaling. These two pathways work together to regulate T lymphocyte development and function.     

Interdigital cell death can occur through a necrotic and caspase-independent pathway.

Programmed cell death in animals is usually associated with apoptotic morphology and requires caspase activation. Necrosis and caspase-independent cell death have been reported, but mostly in experimental conditions that lead some to question their existence it in vivo. Loss of interdigital cells in the mouse embryo, a paradigm of cell death during development [1], is known to include an apoptotic [2] and caspase-dependent [3] [4] mechanism. Here, we report that, when caspase activity was inhibited using drugs or when apoptosis was prevented genetically (using Hammertoe mutant mice, or mice homozygous for a mutation in the gene encoding APAF-1, a caspase-activating adaptor protein), interdigital cell death still occurred. This cell death was negative for the terminal-deoxynucleotidyl-mediated dUTP nick end-labelling (TUNEL) assay and there was no overall cell condensation. At the electron microscopy level, peculiar 'mottled' chromatin alterations and marked mitochondrial and membrane lesions, suggestive of classical necrotic cell death, were observed with no detectable phagocytosis and no local inflammatory response. Thus, in this developmental context, although caspase activity confers cell death with an apoptotic morphotype, in the absence of caspase activity an underlying mechanism independent of known caspases can also confer cell death, but with a necrotic morphotype. This cell death can go undetected when using apoptosis-specific methodology, and cannot be blocked by agents that act on caspases.     

Synthesis,proapoptotic screening,and structure–activity relationships of novel aza-lupane triterpenoids

Apoptosis is a highly regulated process by which excessive cells are eliminated in order to maintain normal cell development and tissue homeostasis. Resistance to apoptosis often contributes to failure in cancer prevention and treatment. Apoptotic cell death regulators are considered important targets for discovery and development of new therapeutic agents in oncology research. A class of novel aza-lupane triterpenoids were designed, synthesized, and evaluated for antitumor activity against a panel of cancer cell lines of different histogenic origin and for ability to induce apoptosis. 3,30-Bis(aza) derivatives were identified not only to possess improved cytotoxicity compared to the natural product betulinic acid but also to affect cell death predominantly via apoptosis, whereas the mono(aza) derivatives apparently triggered cell death via different, non-apoptotic pathway(s).     

Apoptosis in yeast

Apoptosis is a highly regulated cellular suicide program crucial for metazoan development. However, dysfunction of apoptosis also leads to several diseases. Yeast undergoes apoptosis after application of acetic acid, sugar- or salt-stress, plant antifungal peptides, or hydrogen peroxide. Oxygen radicals seem to be key elements of apoptotic execution, conserved during evolution. Furthermore, several yeast orthologues of central metazoan apoptotic regulators have been identified, such as a caspase and a caspase-regulating serine protease. In addition, physiological occurrence of cell death has been detected during aging and mating in yeast. The finding of apoptosis in yeast, other fungi and parasites is not only of great medical relevance but will also help to understand some of the still unknown molecular mechanisms at the core of apoptotic execution.     

Human Bak induces cell death in Schizosaccharomyces pombe with morphological changes similar to those with apoptosis in mammalian cells.

Apoptosis as a form of programmed cell death (PCD) in multicellular organisms is a well-established genetically controlled process that leads to elimination of unnecessary or damaged cells. Recently, PCD has also been described for unicellular organisms as a process for the socially advantageous regulation of cell survival. The human Bcl-2 family member Bak induces apoptosis in mammalian cells which is counteracted by the Bcl-x(L) protein. We show that Bak also kills the unicellular fission yeast Schizosaccharomyces pombe and that this is inhibited by coexpression of human Bcl-x(L). Moreover, the same critical BH3 domain of Bak that is required for induction of apoptosis in mammalian cells is also required for inducing death in yeast. This suggests that Bak kills mammalian and yeast cells by similar mechanisms. The phenotype of the Bak-induced death in yeast involves condensation and fragmentation of the chromatin as well as dissolution of the nuclear envelope, all of which are features of mammalian apoptosis. These data suggest that the evolutionarily conserved metazoan PCD pathway is also present in unicellular yeast.     

Death by design: apoptosis, necrosis and autophagy

Apoptosis is the principal mechanism by which cells are physiologically eliminated in metazoan organisms. During apoptotic death, cells are neatly carved up by caspases and packaged into apoptotic bodies as a mechanism to avoid immune activation. Recently, necrosis, once thought of as simply a passive, unorganized way to die, has emerged as an alternate form of programmed cell death whose activation might have important biological consequences, including the induction of an inflammatory response. Autophagy has also been suggested as a possible mechanism for non-apoptotic death despite evidence from many species that autophagy represents a survival strategy in times of stress. Recent advances have helped to define the function of and mechanism for programmed necrosis and the role of autophagy in cell survival and suicide.     

Rapid induction of apoptosis mediated by peptides that bind initiation factor eIF4E

Overexpression of the translation initiation factor eIF4E leads to cell transformation and occurs in a number of human cancers [1]. mRNA translation and cell growth can be regulated through the availability of eIF4E to form initiation complexes by binding to eIF4G. The availability of eIF4E is blocked through the binding of members of a family of eIF4E-binding proteins (4E-BPs) [2] [3]. Indeed, cell transformation caused by the overexpression of eIF4E can be reversed by the overexpression of 4E-BPs [4] [5] [6] [7] [8]. To study the role of eIF4E in cell transformation, we developed a series of peptides based on the conserved eIF4E-binding motifs in 4E-BPs and eIF4G [9] linked to the penetratin peptide-carrier sequence, which mediates the rapid transport of peptides across cell membranes. Surprisingly, introduction of these eIF4E-binding peptides into MRC5 cells led to rapid, dose-dependent cell death, with characteristics of apoptosis. Single alanine substitutions at key positions in the peptides impair their binding to eIF4E and markedly reduce their ability to induce apoptosis. A triple alanine substitution, which abolishes binding to eIF4E, renders the peptide unable to induce apoptosis. Our data provide strong evidence that the peptides induce apoptosis through binding to eIF4E. They do not induce apoptosis through inhibition of protein synthesis, as chemical inhibitors of translation did not induce apoptosis or affect peptide-induced cell death. Thus these new data indicate that eIF4E has a direct role in controlling cell survival that is not linked to its known role in mRNA translation.