Showing papers on "Apoptosis published in 1999"
TL;DR: Caspase-3 is essential for certain processes associated with the dismantling of the cell and the formation of apoptotic bodies, but it may also function before or at the stage when commitment to loss of cell viability is made.
Abstract: Caspases are crucial mediators of programmed cell death (apoptosis). Among them, caspase-3 is a frequently activated death protease, catalyzing the specific cleavage of many key cellular proteins. However, the specific requirements of this (or any other) caspase in apoptosis have remained largely unknown until now. Pathways to caspase-3 activation have been identified that are either dependent on or independent of mitochondrial cytochrome c release and caspase-9 function. Caspase-3 is essential for normal brain development and is important or essential in other apoptotic scenarios in a remarkable tissue-, cell type- or death stimulus-specific manner. Caspase-3 is also required for some typical hallmarks of apoptosis, and is indispensable for apoptotic chromatin condensation and DNA fragmentation in all cell types examined. Thus, caspase-3 is essential for certain processes associated with the dismantling of the cell and the formation of apoptotic bodies, but it may also function before or at the stage when commitment to loss of cell viability is made.
3,259 citations
01 Jan 1999
TL;DR: Caspases, a family of cysteine-dependent aspartate-directed proteases, are prominent among the death proteases as discussed by the authors, and they play critical roles in initiation and execution of this process.
Abstract: ■ Abstract Apoptosis is a genetically programmed, morphologically distinct form of cell death that can be triggered by a variety of physiological and pathological stimuli. Studies performed over the past 10 years have demonstrated that proteases play critical roles in initiation and execution of this process. The caspases, a family of cysteine-dependent aspartate-directed proteases, are prominent among the death proteases. Caspases are synthesized as relatively inactive zymogens that become activated by scaffold-mediated transactivation or by cleavage via upstream proteases in an intracellular cascade. Regulation of caspase activation and activity occurs at several different levels: ( a) Zymogen gene transcription is regulated; ( b) antiapoptotic members of the Bcl-2 family and other cellular polypeptides block proximity-induced activation of certain procaspases; and ( c) certain cellular inhibitor of apoptosis proteins (cIAPs) can bind to and inhibit active caspases. Once activated, caspases cleave a variety of intracellular polypeptides, including major structural elements of the cytoplasm and nucleus, components of the DNA repair machinery, and a number of protein kinases. Collectively, these scissions disrupt survival pathways and disassemble important architectural components of the cell, contributing to the stereotypic morphological and biochemical changes that characterize apoptotic cell death.
2,685 citations
TL;DR: Although the mechanism used by the IAPs to suppress cell death remains debated, several studies have provided insights into the biochemical functions of these intriguing proteins and a variety of reports have suggested an important role for the I APs in some human diseases.
Abstract: Apoptosis is a physiological cell suicide program that is critical for the development and maintenance of healthy tissues. Dysregulation of cell death pathways occur in cancer, autoimmune and immunodeficiency diseases, reperfusion injury after ischemic episodes, and in neurodegenerative disorders. Thus, proteins involved in apoptosis regulation are of intense biological interest and many are attractive therapeutic targets. This review discusses the Inhibitor of Apoptosis (IAP) family of proteins. First discovered in baculoviruses, IAPs were shown to be involved in suppressing the host cell death response to viral infection. Interestingly, ectopic expression of some baculoviral IAPs blocks apoptosis in mammalian cells, suggesting conservation of the cell death program among diverse species and commonalities in the mechanism used by the IAPs to inhibit apoptosis. Although the mechanism used by the IAPs to suppress cell death remains debated, several studies have provided insights into the biochemical functions of these intriguing proteins. Moreover, a variety of reports have suggested an important role for the IAPs in some human diseases.
2,637 citations
TL;DR: This work has shown that apoptotic cell death is a genetically programmed, morphologically distinct form of cell death that can be triggered by a variety of physiological and pathological stimuli, and that proteases play critical roles in initiation and execution of this process.
Abstract: ▪ Abstract Apoptosis is a genetically programmed, morphologically distinct form of cell death that can be triggered by a variety of physiological and pathological stimuli. Studies performed over the past 10 years have demonstrated that proteases play critical roles in initiation and execution of this process. The caspases, a family of cysteine-dependent aspartate-directed proteases, are prominent among the death proteases. Caspases are synthesized as relatively inactive zymogens that become activated by scaffold-mediated transactivation or by cleavage via upstream proteases in an intracellular cascade. Regulation of caspase activation and activity occurs at several different levels: (a) Zymogen gene transcription is regulated; (b) antiapoptotic members of the Bcl-2 family and other cellular polypeptides block proximity-induced activation of certain procaspases; and (c) certain cellular inhibitor of apoptosis proteins (cIAPs) can bind to and inhibit active caspases. Once activated, caspases cleave a variet...
2,636 citations
TL;DR: This review focuses on the two most well-studied pathways of caspase activation: the cell surface death receptor pathway and the mitochondria-initiated pathway.
Abstract: ▪ Abstract Caspase activation plays a central role in the execution of apoptosis. The key components of the biochemical pathways of caspase activation have been recently elucidated. In this review, we focus on the two most well-studied pathways of caspase activation: the cell surface death receptor pathway and the mitochondria-initiated pathway. In the cell surface death receptor pathway, activation of caspase-8 following its recruitment to the death-inducing signaling complex (DISC) is the critical event that transmits the death signal. This event is regulated at several different levels by various viral and mammalian proteins. Activated caspase-8 can activate downstream caspases by direct cleavage or indirectly by cleaving Bid and inducing cytochrome c release from the mitochondria. In the mitochondrial-initiated pathway, caspase activation is triggered by the formation of a multimeric Apaf-1/cytochrome c complex that is fully functional in recruiting and activating procaspase-9. Activated caspase-9 wil...
2,579 citations
TL;DR: Recurrent treatments with LZ–huTRAIL actively suppressed growth of the TRAIL–sensitive human mammary adenocarcinoma cell line MDA–231 in CB.17 (SCID) mice, and histologic examination of tumors from SCID mice treated with Lz–hu TRAIL demonstrated clear areas of apoptotic necrosis within 9–12 hours of injection.
Abstract: To evaluate the utility of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as a cancer therapeutic, we created leucine zipper (LZ) forms of human (hu) and murine (mu) TRAIL to promote and stabilize the formation of trimers. Both were biologically active, inducing apoptosis of both human and murine target cells in vitro with similar specific activities. In contrast to the fulminant hepatotoxicity of LZ-huCD95L in vivo, administration of either LZ-huTRAIL or LZ-muTRAIL did not seem toxic to normal tissues of mice. Finally, repeated treatments with LZ-huTRAIL actively suppressed growth of the TRAIL-sensitive human mammary adenocarcinoma cell line MDA-231 in CB.17 (SCID) mice, and histologic examination of tumors from SCID mice treated with LZ-huTRAIL demonstrated clear areas of apoptotic necrosis within 9-12 hours of injection.
2,512 citations
TL;DR: Apo2L may have potent anticancer activity without significant toxicity toward normal tissues, and cooperated synergistically with the chemotherapeutic drugs 5-fluorouracil or CPT-11, causing substantial tumor regression or complete tumor ablation.
Abstract: TNF and Fas ligand induce apoptosis in tumor cells; however, their severe toxicity toward normal tissues hampers their application to cancer therapy. Apo2 ligand (Apo2L, or TRAIL) is a related molecule that triggers tumor cell apoptosis. Apo2L mRNA is expressed in many tissues, suggesting that the ligand may be nontoxic to normal cells. To investigate Apo2L’s therapeutic potential, we generated in bacteria a potently active soluble version of the native human protein. Several normal cell types were resistant in vitro to apoptosis induction by Apo2L. Repeated intravenous injections of Apo2L in nonhuman primates did not cause detectable toxicity to tissues and organs examined. Apo2L exerted cytostatic or cytotoxic effects in vitro on 32 of 39 cell lines from colon, lung, breast, kidney, brain, and skin cancer. Treatment of athymic mice with Apo2L shortly after tumor xenograft injection markedly reduced tumor incidence. Apo2L treatment of mice bearing solid tumors induced tumor cell apoptosis, suppressed tumor progression, and improved survival. Apo2L cooperated synergistically with the chemotherapeutic drugs 5-fluorouracil or CPT-11, causing substantial tumor regression or complete tumor ablation. Thus, Apo2L may have potent anticancer activity without significant toxicity toward normal tissues.
2,160 citations
TL;DR: Six additional caspases (caspases-2, -3, -6, -7, -8, and -10) are processed in cell-free extracts in response to cytochrome c, and that three others failed to be activated under the same conditions.
Abstract: Exit of cytochrome c from mitochondria into the cytosol has been implicated as an important step in apoptosis. In the cytosol, cytochrome c binds to the CED-4 homologue, Apaf-1, thereby triggering Apaf-1–mediated activation of caspase-9. Caspase-9 is thought to propagate the death signal by triggering other caspase activation events, the details of which remain obscure. Here, we report that six additional caspases (caspases-2, -3, -6, -7, -8, and -10) are processed in cell-free extracts in response to cytochrome c, and that three others (caspases-1, -4, and -5) failed to be activated under the same conditions. In vitro association assays confirmed that caspase-9 selectively bound to Apaf-1, whereas caspases-1, -2, -3, -6, -7, -8, and -10 did not. Depletion of caspase-9 from cell extracts abrogated cytochrome c–inducible activation of caspases-2, -3, -6, -7, -8, and -10, suggesting that caspase-9 is required for all of these downstream caspase activation events. Immunodepletion of caspases-3, -6, and -7 from cell extracts enabled us to order the sequence of caspase activation events downstream of caspase-9 and reveal the presence of a branched caspase cascade. Caspase-3 is required for the activation of four other caspases (-2, -6, -8, and -10) in this pathway and also participates in a feedback amplification loop involving caspase-9.
1,950 citations
TL;DR: The c-myc gene was discovered as the cellular homolog of the retroviral v- myc oncogene 20 years ago and found to be activated in various animal and human tumors, suggesting that it is critical for development.
Abstract: The c-myc gene was discovered as the cellular homolog of the retroviral v-myc oncogene 20 years ago (23, 25, 167). The c-myc proto-oncogene was subsequently found to be activated in various animal and human tumors (37, 39, 42). It belongs to the family of myc genes that includes B-myc, L-myc, N-myc, and s-myc; however, only c-myc, L-myc, and N-myc have neoplastic potential (54, 82, 102, 118, 178). Targeted homozygous deletion of the murine c-myc gene results in embryonic lethality, suggesting that it is critical for development (43). Homozygous inactivation of c-myc in rat fibroblasts caused a marked prolongation of cell doubling time, further suggesting a central role for c-myc in regulating cell proliferation (121).
The frequency of genetic alterations of c-myc in human cancers (42) has allowed an estimation that approximately 70,000 U.S. cancer deaths per year are associated with changes in the c-myc gene or its expression. Given that c-myc may contribute to one-seventh of U.S. cancer deaths, recent efforts have been directed toward understanding the function of the c-Myc protein in cancer biology with the hope that therapeutic insights will emerge. Past efforts, which have contributed significantly to our current understanding of c-myc, are discussed in a number of excellent reviews (23, 29, 37, 40, 44, 52, 66, 82, 94, 102, 118, 125, 132, 145, 178, 182, 186).
1,630 citations
TL;DR: These enzymes define a new class of cysteine proteases and comprise a multi-gene family with more than a dozen distinct mammalian family members that account for the majority of cellular and morphological events that occur during cell death.
Abstract: Caspases play an essential role during apoptotic cell death These enzymes define a new class of cysteine proteases and comprise a multi-gene family with more than a dozen distinct mammalian family members The discrete and highly limited subset of cellular polypeptides that are cleaved by these proteases is sufficient to account for the majority of cellular and morphological events that occur during cell death In some cases, caspases also play a contributory role in escalating the propensity for apoptosis, and in doing so may exacerbate disease pathogenesis
1,531 citations
Journal Article•
TL;DR: The data show that inhibition of this target site by PS-341 results in reduced tumor growth in murine tumor models and highlight that the proteasome is a novel biochemical target and that inhibitors such asPS-341 represent a unique class of antitumor agents.
Abstract: The ubiquitin-proteasome pathway plays a critical role in the regulated degradation of proteins involved in cell cycle control and tumor growth. Dysregulating the degradation of such proteins should have profound effects on tumor growth and cause cells to undergo apoptosis. To test this hypothesis, we developed a novel series of proteasome inhibitors, exemplified by PS-341, which we describe here. As determined by the National Cancer Institute in vitro screen, PS-341 has substantial cytotoxicity against a broad range of human tumor cells, including prostate cancer cell lines. The PC-3 prostate cell line was, therefore, chosen to further examine the antitumor activity of PS-341. In vitro, PS-341 elicits proteasome inhibition, leading to an increase in the intracellular levels of specific proteins, including the cyclin-dependent kinase inhibitor, p21. Moreover, exposure of such cells to PS-341 caused them to accumulate in the G2-M phase of the cell cycle and subsequently undergo apoptosis, as indicated by nuclear condensation and poly(ADP-ribose) polymerase cleavage. Following weekly i.v. treatment of PS-341 to mice bearing the PC-3 tumor, a significant decrease (60%) in tumor burden was observed in vivo. Direct injection of PS-341 into the tumor also caused a substantial (70%) decrease in tumor volume with 40% of the drug-treated mice having no detectable tumors at the end of the study. Studies also revealed that i.v. administration of PS-341 resulted in a rapid and widespread distribution of PS-341, with highest levels identified in the liver and gastrointestinal tract and lowest levels in the skin and muscle. Modest levels were found in the prostate, whereas there was no apparent penetration of the central nervous system. An assay to follow the biological activity of the PS-341 was established and used to determine temporal drug activity as well as its ability to penetrate tissues. As such, PS-341 was shown to penetrate PC-3 tumors and inhibit intracellular proteasome activity 1.0 h after i.v. dosing. These data illustrate that PS-341 not only reaches its biological target but has a direct effect on its biochemical target, the proteasome. Importantly, the data show that inhibition of this target site by PS-341 results in reduced tumor growth in murine tumor models. Together, the results highlight that the proteasome is a novel biochemical target and that inhibitors such as PS-341 represent a unique class of antitumor agents. PS-341 is currently under clinical evaluation for advanced cancers.
TL;DR: The results suggest that, during certain types of apoptosis, Bid translocates to mitochondria and binds to Bax, leading to a change in conformation of Bax and to cytochrome c release from mitochondria.
Abstract: Here we report that in staurosporine-induced apoptosis of HeLa cells, Bid, a BH3 domain containing protein, translocates from the cytosol to mitochondria. This event is associated with a change in conformation of Bax which leads to the unmasking of its NH2-terminal domain and is accompanied by the release of cytochrome c from mitochondria. A similar finding is reported for cerebellar granule cells undergoing apoptosis induced by serum and potassium deprivation. The Bax-conformational change is prevented by Bcl-2 and Bcl-xL but not by caspase inhibitors. Using isolated mitochondria and various BH3 mutants of Bid, we demonstrate that direct binding of Bid to Bax is a prerequisite for Bax structural change and cytochrome c release. Bcl-xL can inhibit the effect of Bid by interacting directly with Bax. Moreover, using mitochondria from Bax-deficient tumor cell lines, we show that Bid- induced release of cytochrome c is negligible when Bid is added alone, but dramatically increased when Bid and Bax are added together. Taken together, our results suggest that, during certain types of apoptosis, Bid translocates to mitochondria and binds to Bax, leading to a change in conformation of Bax and to cytochrome c release from mitochondria.
TL;DR: An understanding of the role of Rel/NF-κB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.
Abstract: Apoptosis is a physiological process critical for organ development, tissue homeostasis, and elimination of defective or potentially dangerous cells in complex organisms. Apoptosis can be initiated by a wide variety of stimuli, which activate a cell suicide program that is constitutively present in most vertebrate cells. In diverse cell types, Rel/NF-kappaB transcription factors have been shown to have a role in regulating the apoptotic program, either as essential for the induction of apoptosis or, perhaps more commonly, as blockers of apoptosis. Whether Rel/NF-kappaB promotes or inhibits apoptosis appears to depend on the specific cell type and the type of inducer. An understanding of the role of Rel/NF-kappaB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.
TL;DR: While BID appears to be required for the release of cytochrome c in the TNF death pathway, the release is likely not required for cell death, as other aspects of mitochondrial dysfunction still transpired and cells died nonetheless.
TL;DR: Immunological, cellular, and molecular evidence indicates that throughout the life of a T cell, apoptosis may be evoked in excessive, harmful, or useless clonotypes to preserve a healthy and balanced immune system.
Abstract: Apoptosis of mature T lymphocytes preserves peripheral homeostasis and tolerance by countering the profound changes in the number and types of T cells stimulated by diverse antigens. T cell apoptosis occurs in at least two major forms: antigen-driven and lymphokine withdrawal. These forms of death are controlled in response to local levels of IL-2 and antigen in a feedback mechanism termed propriocidal regulation. Active antigen-driven death is mediated by the expression of death cytokines such as FasL and TNF. These death cytokines engage specific receptors that assemble caspase-activating protein complexes. These signaling complexes tightly regulate cell death but are vulnerable to inherited defects. Passive lymphokine withdrawal death may result from the cytoplasmic activation of caspases that is regulated by mitochondria and the Bcl-2 protein. The human disease, Autoimmune Lymphoproliferative Syndrome (ALPS) is due to dominant-interfering mutations in the Fas/APO-1/CD95 receptor and other components of the death pathway. The study of ALPS patients reveals the necessity of apoptosis for preventing autoimmunity and allows the genetic investigation of apoptosis in humans. Immunological, cellular, and molecular evidence indicates that throughout the life of a T cell, apoptosis may be evoked in excessive, harmful, or useless clonotypes to preserve a healthy and balanced immune system.
TL;DR: This loss-of-function model indicates that Bid is a critical substrate in vivo for signalling by death-receptor agonists, which mediates a mitochondrial amplification loop that is essential for the apoptosis of selected cells.
Abstract: The protein Bid is a participant in the pathway that leads to cell death (apoptosis), mediating the release of cytochrome c from mitochondria in response to signals from 'death' receptors known as TNFR1/Fas on the cell surface It is a member of the proapoptotic Bcd-2 family and is activated as a result of its cleavage by caspase 8, one of a family of proteolytic cell-death proteins To investigate the role of Bid in vivo, we have generated mice deficient for Bid We find that when these mice are injected with an antibody directed against Fas, they nearly all survive, whereas wild-type mice die from hepatocellular apoptosis and haemorrhagic necrosis About half of the Bid-deficient animals had no apparent liver injury and showed no evidence of activation of the effector caspases 3 and 7, although the initiator caspase 8 had been activated Other Bid-deficient mice survived with only moderate damage: all three caspases (8 and 37) were activated but their cell nuclei were intact and no mitochondrial cytochrome c was released We also investigated the effects of Bid deficiency in cultured cells treated with anti-Fas antibody (hepatocytes and thymocytes) or with TNFalpha (fibroblasts) In these Bid-/- cells, mitochondrial dysfunction was delayed, cytochrome c was not released, effector caspase activity was reduced and the cleavage of apoptosis substrates was altered This loss-of-function model indicates that Bid is a critical substrate in vivo for signalling by death-receptor agonists, which mediates a mitochondrial amplification loop that is essential for the apoptosis of selected cells
TL;DR: It is found that apoptosis can be induced in the yeast Saccharomyces cerevisiae by depletion of glutathione or by low external doses of H2O2, and oxygen radicals to accumulate in the cell, whereas radical depletion or hypoxia prevents apoptosis.
Abstract: Oxygen radicals are important components of metazoan apoptosis. We have found that apoptosis can be induced in the yeast Saccharomyces cerevisiae by depletion of glutathione or by low external doses of H2O2. Cycloheximide prevents apoptotic death revealing active participation of the cell. Yeast can also be triggered into apoptosis by a mutation in CDC48 or by expression of mammalian bax. In both cases, we show oxygen radicals to accumulate in the cell, whereas radical depletion or hypoxia prevents apoptosis. These results suggest that the generation of oxygen radicals is a key event in the ancestral apoptotic pathway and offer an explanation for the mechanism of bax-induced apoptosis in the absence of any established apoptotic gene in yeast.
TL;DR: This work reviews caspase proteinases with an emphasis on their structure, activation, and critical role in the apoptotic mechanism.
TL;DR: Evidence for a hypothesis-the induced-proximity model-that describes how the first proteolytic signal is produced after adapter-mediated clustering of initiator caspase zymogens is reviewed.
Abstract: Members of the caspase family of proteases transmit the events that lead to apoptosis of animal cells. Distinct members of the family are involved in both the initiation and execution phases of cell death, with the initiator caspases being recruited to multicomponent signaling complexes. Initiation of apoptotic events depends on the ability of the signaling complexes to generate an active protease. The mechanism of activation of the caspases that constitute the different apoptosis-signaling complexes can be explained by an unusual property of the caspase zymogens to autoprocess to an active form. This autoprocessing depends on intrinsic activity that resides in the zymogens of the initiator caspases. We review evidence for a hypothesis-the induced-proximity model-that describes how the first proteolytic signal is produced after adapter-mediated clustering of initiator caspase zymogens.
TL;DR: The results indicate that c-Abl and p73 are components of a mismatch-repair-dependent apoptosis pathway which contributes to cisplatin-induced cytotoxicity.
Abstract: The tyrosine kinase c-Abl regulates p73 in apoptotic response to cisplatin-induced DNA damage
TL;DR: It is suggested that Jnk1 andJnk2 regulate region-specific apoptosis during early brain development by reducing cell death in the lateral edges of hindbrain prior to neural tube closure and increasing apoptosis and caspase activation in the mutant forebrain.
TL;DR: These findings, together with cell death patterns in PARP(-/-) animals receiving other types of insults, indicate that PARP activation is an active trigger of necrosis, whereas other mechanisms mediate apoptosis.
Abstract: Apoptotic and necrotic cell death are well characterized and are influenced by intracellular ATP levels. Poly(ADP-ribose) polymerase (PARP), a nuclear enzyme activated by DNA strand breaks, physiologically participates in DNA repair. Overactivation of PARP after cellular insults can lead to cell death caused by depletion of the enzyme’s substrate β-nicotinamide adenine dinucleotide and of ATP. In this study, we have differentially elicited apoptosis or necrosis in mouse fibroblasts. Fibroblasts from PARP-deficient (PARP−/−) mice are protected from necrotic cell death and ATP depletion but not from apoptotic death. These findings, together with cell death patterns in PARP−/− animals receiving other types of insults, indicate that PARP activation is an active trigger of necrosis, whereas other mechanisms mediate apoptosis.
TL;DR: The morphologic ritual cells go through when experiencing programmed cell death has been termed apoptosis and is executed by a family of intracellular proteases, called caspases as discussed by the authors.
Abstract: Each day, approximately 50 to 70 billion cells perish in the average adult because of programmed cell death (PCD). Cell death in self-renewing tissues, such as the skin, gut, and bone marrow, is necessary to make room for the billions of new cells produced daily. So massive is the flux of cells through our bodies that, in a typical year, each of us will produce and, in parallel, eradicate a mass of cells equal to almost our entire body weight. The morphologic ritual cells go through when experiencing PCD has been termed apoptosis and is executed by a family of intracellular proteases, called caspases. Unlike accidental cell deaths caused by infarction and trauma, these physiologic deaths culminate in fragmentation of cells into membrane-encased bodies which are cleared through phagocytosis by neighboring cells without inciting inflammatory reactions or tissue scarring. Defects in the processes controlling PCD can extend cell life span, contributing to neoplastic cell expansion independently of cell division. Moreover, failures in normal apoptosis pathways contribute to carcinogenesis by creating a permissive environment for genetic instability and accumulation of gene mutations, promoting resistance to immune-based destruction, allowing disobeyance of cell cycle checkpoints that would normally induce apoptosis, facilitating growth factor/hormone-independent cell survival, supporting anchorage-independent survival during metastasis, reducing dependence on oxygen and nutrients, and conferring resistance to cytotoxic anticancer drugs and radiation. Elucidation of the genes that constitute the core machinery of the cell death pathway has provided new insights into tumor biology, revealing novel strategies for combating cancer.
TL;DR: The distinguishing features of the various cell death pathways are reviewed: caspases (cysteine proteases cleaving after particular aspartate residues), mitochondria and/or reactive oxygen species are often, but not always, key components.
Abstract: Cell death is an essential phenomenon in normal development and homeostasis, but also plays a crucial role in various pathologies. Our understanding of the molecular mechanisms involved has increased exponentially, although it is still far from complete. The morphological features of a cell dying either by apoptosis or by necrosis are remarkably conserved for quite different cell types derived from lower or higher organisms. At the molecular level, several gene products play a similar, crucial role in a major cell death pathway in a worm and in man. However, one should not oversimplify. It is now evident that there are multiple pathways leading to cell death, and some cells may have the required components for one pathway, but not for another, or contain endogenous inhibitors which preclude a particular pathway. Furthermore, different pathways can co-exist in the same cell and are switched on by specific stimuli. Apoptotic cell death, reported to be non-inflammatory, and necrotic cell death, which may be inflammatory, are two extremes, while the real situation is usually more complex. We here review the distinguishing features of the various cell death pathways: caspases (cysteine proteases cleaving after particular aspartate residues), mitochondria and/or reactive oxygen species are often, but not always, key components. As these various caspase-dependent and caspase-independent cell death pathways are becoming better characterized, we may learn to differentiate them, fill in the many gaps in our understanding, and perhaps exploit the knowledge acquired for clinical benefit.
TL;DR: It is shown that c-FLIP is expressed in two isoforms, both of which, like FADD and caspase-8, are recruited to the CD95 DISC in a stimulation-dependent fashion and inhibits CD95-mediated apoptosis.
19 Feb 1999
TL;DR: It is demonstrated that both receptor-induced (CD95 and tumor necrosis factor) and chemical-induced apoptosis result in a similar time-dependent activation of caspases-3, -7, -8, and -9 in Jurkat T cells and human leukemic U937 cells.
Abstract: Release of cytochrome c is important in many forms of apoptosis. Recent studies of CD95 (Fas/APO-1)-induced apoptosis have implicated caspase-8 cleavage of Bid, a BH3 domain-containing proapoptotic member of the Bcl-2 family, in this release. We now demonstrate that both receptor-induced (CD95 and tumor necrosis factor) and chemical-induced apoptosis result in a similar time-dependent activation of caspases-3, -7, -8, and -9 in Jurkat T cells and human leukemic U937 cells. In receptor-mediated apoptosis, the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD.FMK), inhibits apoptosis prior to commitment to cell death by inhibiting the upstream activator caspase-8, cleavage of Bid, release of mitochondrial cytochrome c, processing of effector caspases, loss of mitochondrial membrane potential, and externalization of phosphatidylserine. However, Z-VAD.FMK inhibits chemical-induced apoptosis at a stage after commitment to cell death by inhibiting the initiator caspase-9 and the resultant postmitochondrial activation of effector caspases. Cleavage of Bid but not release of cytochromec is blocked by Z-VAD.FMK demonstrating that in chemical-induced apoptosis cytochrome c release is caspase-independent and is not mediated by activation of Bid. We propose that caspases form an integral part of the cell death-inducing mechanism in receptor-mediated apoptosis, whereas in chemical-induced apoptosis they act solely as executioners of apoptosis.
TL;DR: Investigating the role of PARP cleavage in apoptosis in human osteosarcoma cells and PARP −/− fibroblasts stably transfected with a vector encoding a caspase-3-resistant PARP mutant indicates that PARP activation and subsequent cleavage have active and complex roles in apoptotic process.
TL;DR: Loss-of-function mutations in the signaling molecules involved in apoptosis cause hyper-proliferation of cells in mouse and human and exaggeration of this death cascade causes the destruction of various tissues.
Abstract: The immune response is regulated not only by cell proliferation and differentiation, but also by programmed cell death, or apoptosis. In response to various stimuli, death factors bind to their respective receptors and activate the apoptotic death program in target cells. A cascade of specific proteases termed caspases mediates the apoptotic process. The activated caspases cleave various cellular components, a process that leads to morphological changes of the cells and nuclei, as well as to degradation of the chromosomal DNA. Loss-of-function mutations in the signaling molecules involved in apoptosis cause hyper-proliferation of cells in mouse and human. In contrast, exaggeration of this death cascade causes the destruction of various tissues.
TL;DR: This study reports that the death domain kinase RIP, a key component of the TNF signaling complex, was cleaved by Caspase-8 in TNF-induced apoptosis, and demonstrated that the cleavage of RIP resulted in the blockage of T NF-kappaB activation.
Abstract: Although the molecular mechanisms of TNF signaling have been largely elucidated, the principle that regulates the balance of life and death is still unknown. We report here that the death domain kinase RIP, a key component of the TNF signaling complex, was cleaved by Caspase-8 in TNF-induced apoptosis. The cleavage site was mapped to the aspartic acid at position 324 of RIP. We demonstrated that the cleavage of RIP resulted in the blockage of TNF-induced NF-κB activation. RIPc, one of the cleavage products, enhanced interaction between TRADD and FADD/MORT1 and increased cells' sensitivity to TNF. Most importantly, the Caspase-8 resistant RIP mutants protected cells against TNF-induced apopotosis. These results suggest that cleavage of RIP is an important process in TNF-induced apoptosis. Further more, RIP cleavage was also detected in other death receptor-mediated apoptosis. Therefore, our study provides a potential mechanism to convert cells from life to death in death receptor-mediated apoptosis.
TL;DR: The data indicate that induction of T-cell apoptosis and peripheral allograft tolerance is prevented by blocking both signal 1 and signal 2 ofT-cell activation.
Abstract: The alloimmune response against fully MHC-mismatched allografts, compared with immune responses to nominal antigens, entails an unusually large clonal size of alloreactive T cells. Thus, induction of peripheral allograft tolerance established in the absence of immune system ablation and reconstitution is a challenging task in transplantation. Here, we determined whether a reduction in the mass of alloreactive T cells due to apoptosis is an essential initial step for induction of stable allograft tolerance with non-lymphoablative therapy. Blocking both CD28-B7 and CD40-CD40 ligand interactions (co-stimulation blockade) inhibited proliferation of alloreactive T cells in vivo while allowing cell cycle-dependent T-cell apoptosis of proliferating T cells, with permanent engraftment of cardiac allografts but not skin allografts. Treatment with rapamycin plus co-stimulation blockade resulted in massive apoptosis of alloreactive T cells and produced stable skin allograft tolerance, a very stringent test of allograft tolerance. In contrast, treatment with cyclosporine A and co-stimulation blockade abolished T-cell proliferation and apoptosis, as well as the induction of stable allograft tolerance. Our data indicate that induction of T-cell apoptosis and peripheral allograft tolerance is prevented by blocking both signal 1 and signal 2 of T-cell activation.