Molecular ordering of apoptosis induced by anticancer drugs in neuroblastoma cells

Apoptosis mediated by anticancer drugs may involve activation of death-inducing ligand/receptor systems such as CD95 (APO-1/Fas), cleavage of caspases, and perturbance of mitochondrial functions. We investigated the sequence of these events in SHEP neuroblastoma cells transfected with Bcl-2 or Bcl-X(L) using two different drugs, namely, doxorubicin (Doxo), which activates the CD95/CD95 ligand (CD95-L) system, and betulinic acid (Bet A), which does not enhance the expression of CD95 or CD95-L and which, as shown here, directly targets mitochondria. Apoptosis induced by both drugs was inhibited by Bcl-2 or Bcl-X(L) overexpression or by bongkrekic acid, an agent that stabilizes mitochondrial membrane barrier function, suggesting a critical role for mitochondria. After Doxo treatment, enhanced CD95/CD95-L expression and caspase-8 activation were not blocked by Bcl-2 or Bcl-X(L) and were found in cells with a mitochondrial transmembrane potential (delta psi(m)) that was still normal (delta psi(m)high cells). In marked contrast, after Bet A treatment, caspase-8 activation occurred in a Bcl-2- or Bcl-X(L)-inhibitable fashion and was confined to cells that had lost their delta psi(m) (delta psi(m)low cells). Mitochondria from cells treated with either Doxo or Bet A induced cleavage of both caspase-8 and caspase-3 in cytosolic extracts. Thus, caspase-8 activation may occur upstream or downstream of mitochondria, depending on the apoptosis-initiating stimulus. In contrast to caspase-8, cleavage of caspase-3 or poly(ADP-ribose)polymerase was always restricted to delta psi(m)low cells, downstream of the Bcl-2- or Bcl-X(L)-controlled checkpoint of apoptosis. Cytochrome c, released from mitochondria undergoing permeability transition, activated caspase-3 but not caspase-8 in a cell-free system. However, both caspases were activated by apoptosis-inducing factor, indicating that the mechanism of caspase-8 activation differed from that of caspase-3 activation. Taken together, our findings demonstrate that perturbance of mitochondrial function constitutes a central coordinating event in drug-induced cell death.     

Bcl-2 and adenovirus E1B 19 kDA protein prevent E1A-induced processing of CPP32 and cleavage of poly(ADP-ribose) polymerase

The E1A oncoproteins of adenovirus type 5 are potent inducers of apoptotic cell death. To manifest growth promoting and transforming properties, therefore, E1A requires the co-expression of a suppressor of apoptosis. During normal viral infection, this function is provided by the E1B 19 kDa protein. However, the cellular suppressor Bcl-2 can substitute for 19K during infection, and both proteins can effectively cooperate with E1A to facilitate transformation of primary cells in culture. How E1A induces apoptosis and at what point(s) on this pathway Bcl-2 and E1B 19K act are not presently known. Here, we demonstrate that E1A-induced apoptosis is accompanied by specific endo-proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), an event that is linked to the Ced-3/ICE apoptotic pathway in other systems. PARP cleavage was also observed in p53-null cells infected with 19K- virus expressing 13S E1A. In addition to PARP cleavage, expression of E1A caused processing of the zymogen form of CPP32, a Ced-3/ICE protease that cleaves PARP and is required for apoptosis in mammalian cells. These events were prevented when E1A was co-expressed with E1B 19K or BCL-2, which places these suppressors of apoptosis either at or upstream of processing of pro-CPP32.     

Molecular ordering of the Fas-apoptotic pathway: the Fas/APO-1 protease Mch5 is a CrmA-inhibitable protease that activates multiple Ced-3/ICE-like cysteine proteases

The Fas/APO-1-receptor associated cysteine protease Mch5 (MACH/FLICE) is believed to be the enzyme responsible for activating a protease cascade after Fas-receptor ligation, leading to cell death. The Fas-apoptotic pathway is potently inhibited by the cowpox serpin CrmA, suggesting that Mch5 could be the target of this serpin. Bacterial expression of proMch5 generated a mature enzyme composed of two subunits, which are derived from the pre-cursor proenzyme by processing at Asp-227, Asp-233, Asp-391, and Asp-401. We demonstrate that recombinant Mch5 is able to process/activate all known ICE/Ced-3-like cysteine proteases and is potently inhibited by CrmA. This contrasts with the observation that Mch4, the second FADD-related cysteine protease that is also able to process/activate all known ICE/Ced-3-like cysteine proteases, is poorly inhibited by CrmA. These data suggest that Mch5 is the most upstream protease that receives the activation signal from the Fas-receptor to initiate the apoptotic protease cascade that leads to activation of ICE-like proteases (TX, ICE, and ICE-relIII), Ced-3-like proteases (CPP32, Mch2, Mch3, Mch4, and Mch6), and the ICH-1 protease. On the other hand, Mch4 could be a second upstream protease that is responsible for activation of the same protease cascade in CrmA-insensitive apoptotic pathways.     

Investigation of glucocorticoid-induced apoptotic pathway: processing of caspase-6 but not caspase-3

Glucocorticoids (GCs) are essential therapeutic reagents for the treatment of lymphomas and leukemias. GCs cause cell death in certain types of lymphoid cells mediated by the process known as apoptosis. This cell death is completely inhibited by Bcl-2. Here we report that Bcl-2 and benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk), a broad spectrum caspase inhibitor, prevent loss of mitochondrial membrane potential (delta psi m) and the production of reactive oxygen species (ROS) caused by GC, while acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), an inhibitor of the caspase-3 family proteases, does not. This suggests that the inhibition by Bcl-2 and activation of some initiator caspases are upstream events of mitochondrial damage, whereas the activation of caspase-3 family proteases occurs downstream of mitochondrial changes. We also demonstrate that caspase-6 but not caspase-3 is cleaved and activated during GC-mediated apoptosis and that poly(ADP-ribose) polymerase (PARP), a substrate of caspases, also undergoes proteolysis. In addition, we provide the evidence that DNA fragmentation is markedly inhibited by Ac-DEVD-CHO, while cell death, assessed by the damage of the plasma membrane, is marginally inhibited or merely delayed.     

Ceramide induces apoptosis via CPP32 activation

Although both ceramide and interleukin-1beta converting enzyme (ICE) family proteases are key molecules during apoptosis, their relationship remains to be elucidated. We report here that cell-permeable ceramide induced cleavage and activation of CPP32, a Ced-3/ICE-like protease, but not ICE. Ceramide-induced apoptosis of Jurkat cells was blocked by the CPP32-specific tetrapeptide inhibitor DEVD-CHO, but not by the ICE inhibitor YVAD-CHO. Furthermore, variant Jurkat cells with defective CPP32 activation were resistant to both anti-Fas- and ceramide-induced apoptosis. These results indicate that CPP32 activation is required for ceramide-induced apoptosis, and suggest sphingomyelin-ceramide pathway functions upstream of CPP32.     

The prevention of adhesions in surgery. A clinical review and experimental contribution

Induction of apoptosis in human monocytic THP.1 cells by etoposide or N-tosyl-L-phenylalanyl chloromethyl ketone resulted in release of mitochondrial cytochrome c, formation of ultracondensed mitochondria, development of outer mitochondrial membrane discontinuities and a reduction in mitochondrial membrane potential (delta psi m), as well as externalisation of phosphatidylserine, caspase-3 and -7 activation, proteolysis of poly(ADP-ribose) polymerase and lamin B1. The caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone inhibited all these ultrastructural and biochemical characteristics of apoptosis except for the release of cytochrome c. Release of mitochondrial cytochrome c was a late event in non-apoptotic cell death occurring after commitment to cell death and without caspase activation. Thus apoptosis is characterised by release of mitochondrial cytochrome c prior to formation of ultracondensed mitochondria and a reduction in delta psi m and by a mechanism independent of rupture of the outer mitochondrial membrane.     

Oral Neospora caninum inoculation of neonatal calves

The bcl-2 protein plays an essential role in preventing cell death. Its activity is regulated through association with bcl-2 homologous and nonhomologous proteins and also by serine phosphorylation. We now report that bcl-2 can be proteolytically cleaved towards its N-terminus by a cysteine proteinase present in RL-7 lymphoma cell lysates, yielding a major product of apparent MW 20 kDa, different from the products of bcl-2 cleavage by HIV protease. Moreover, bcl-2 proteins mutated for Asp residues at positions 31 and 34 were efficiently cleaved by RL-7 cell lysates, indicating that this proteolytic activity is distinct from the caspase-3 that cleaves bcl-2 at Asp 34. This bcl-2 cleaving activity is inhibited by E-64 and is therefore distinct from the proteinases of the ICE/Ced-3 family (caspases), whereas reciprocally, ICE (caspase-1) is unable to cleave bcl-2. It is optimally active at pH 5, a feature distinguishing it from calpain, another non-ICE cysteine proteinase which has been associated with apoptosis. This novel bcl-2 cleaving protease, although constitutively present in RL-7 cells and resting peripheral blood lymphocytes (PBL) was upregulated following induction of apoptosis in RL-7 cells or mitogen activation in PBL. The N-terminus of bcl-2 which contains the BH4 domain that binds the kinase Raf-1 and the phosphatase calcineurin is essential for anti-apoptotic activity. Its cleavage might provide a novel post-translational mechanism for regulating bcl-2 function and could amplify ongoing programmed cell death.     

The overexpression of Bax produces cell death upon induction of the mitochondrial permeability transition

Stably transfected Jurkat T cells were produced in which Bax expression is inducible by muristerone A. The cell death resulting from induction of the overexpression of Bax was prevented by inhibition of the mitochondrial permeability transition (MPT) with cyclosporin A (CyA) in combination with the phospholipase A2 inhibitor aristolochic acid (ArA). The caspase-3 inhibitor Z-Asp-Glu-Val aspartic acid fluoromethylketone (Z-DEVD-FMK) had no effect on the loss of viability. The MPT was measured as the CyA plus ArA-preventable loss of the mitochondrial membrane potential (DeltaPsim). The MPT was accompanied by the release of cytochrome c from the mitochondria, caspase-3 activation in the cytosol, cleavage of the nuclear enzyme poly(ADP-ribose)polymerase (PARP), and DNA fragmentation, all of which were inhibited by CyA plus ArA. Z-DEVD-FMK had no effect on the loss of DeltaPsim and the redistribution of cytochrome c but did prevent caspase-3 activation, PARP cleavage, and DNA fragmentation. It is concluded that Bax induces the MPT, a critical event in the loss of cell viability. In addition to the cell death, the MPT mediates other typical manifestations of apoptosis in this model, namely release of cytochrome c, caspase activation with PARP cleavage, and DNA fragmentation.     

Eukaryotic mRNAs encoding abundant and scarce proteins are statistically dissimilar in many structural features

The ability of H2O2 and tributyltin (TBT) to trigger pro-caspase activation via export of cytochrome c from mitochondria to the cytoplasm was investigated. Treatment of Jurkat T lymphocytes with H2O2 resulted in the appearance of cytochrome c in the cytosol within 2 h. This was at least 1 h before caspase activation was observed. TBT caused cytochrome c release already after 5 min, followed by caspase activation within 1 h. Measurement of mitochondrial membrane potential (delta psi(m)) showed that both H2O2 and TBT dissipated delta psi(m), but with different time courses. TBT caused a concomitant loss of delta psi(m) and release of cytochrome c, whereas cytochrome c release and caspase activation preceded any apparent delta psi(m) loss in H2O2-treated cells. Thus, our results suggest that different mechanisms are involved in triggering cytochrome c release with these apoptosis-inducing agents.     

Caspase-independent cell death induced by anti-CD2 or staurosporine in activated human peripheral T lymphocytes

We examined the effects of the cell-permeable, broad spectrum peptide caspase inhibitors, benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethyl ketone (Z-VAD.fmk), and BOC-Asp(OMe)-fluoromethyl ketone (BOC-D.fmk), on apoptosis induced by anti-CD2, anti-Fas, and the protein kinase inhibitor staurosporine in activated human peripheral T lymphocytes. We monitored ultrastructural, flow cytometric, and biochemical apoptotic changes, including externalization of phosphatidylserine, cleavage of poly(ADP-ribose) polymerase (PARP) and lamins, activation of caspase-3 and caspase-7, decrease in mitochondrial membrane potential, and DNA fragmentation. Z-VAD.fmk and BOC-D.fmk completely inhibited all the biochemical and ultrastructural changes of apoptosis in anti-Fas-treated cells. In marked contrast, neither Z-VAD.fmk nor BOC-D.fmk inhibited CD2- or staurosporine-mediated cell shrinkage, dilatation of the endoplasmic reticulum (seen in anti-CD2-treated cells), externalization of phosphatidylserine, and loss of mitochondrial membrane potential that accompanied cell death. However, these inhibitors did inhibit the cleavage of PARP and lamins and the formation of hypodiploid cells, and partially inhibited chromatin condensation. These results demonstrate that in activated T cells, anti-CD2 and staurosporine induce a caspase-independent cell death pathway that exhibits prominent cytoplasmic features of apoptosis. However, caspase activation is required for the proteolytic degradation of nuclear substrates such as PARP and lamins together with the DNA fragmentation and extreme chromatin condensation that occur in apoptotic cells.     

The thiol crosslinking agent diamide overcomes the apoptosis-inhibitory effect of Bcl-2 by enforcing mitochondrial permeability transition

In several different cell lines, Bcl-2 prevents the induction of apoptosis (DNA fragmentation, PARP cleavage, phosphatidylserine exposure) by the pro-oxidant ter-butylhydroperoxide (t-BHP) but has no cytoprotective effect when apoptosis is induced by the thiol crosslinking agent diazenedicarboxylic acid his 5N,N-dimethylamide (diamide). Both t-BHP and diamide cause a disruption of the mitochondrial transmembrane potential delta psi(m) that is not inhibited by the broad spectrum caspase inhibitor z-VAD.fmk, although z-VAD.fmk does prevent nuclear DNA fragmentation and poly(ADP-ribose) polymerase cleavage in these models. Bcl-2 stabilizes the delta psi(m) of t-BHP-treated cells but has no inhibitory effect on the delta psi(m) collapse induced by diamide. As compared to normal controls, isolated mitochondria from Bcl-2 overexpressing cells are relatively resistant to the induction of delta psi(m) disruption by t-BHP in vitro. Such Bcl-2 overexpressing mitochondria also fail to release apoptosis-inducing factor (AIF) and cytochrome c from the intermembrane space, whereas control mitochondria not overexpressing Bcl-2 do liberate AIF and cytochrome c in response to t-BHP. In contrast, Bcl-2 does not confer protection against diamide-triggered delta psi(m) collapse and the release of AIF and cytochrome c. This indicates that Bcl-2 suppresses the permeability transition (PT) and the associated release of intermembrane proteins induced by t-BHP but not by diamide. To further investigate the mode of action of Bcl-2, semi-purified PT pore complexes were reconstituted in liposomes in a cell-free, organelle-free system. Recombinant Bcl-2 or Bcl-X(L) proteins augment the resistance of reconstituted PT pore complexes to pore opening induced by t-BHP. In contrast, mutated Bcl-2 proteins which have lost their cytoprotective potential also lose their PT-modulatory capacity. Again, Bcl-2 fails to confer protection against diamide in this experimental system. The reconstituted PT pore complex itself cannot release cytochrome c encapsulated into liposomes. Altogether these data suggest that pro-oxidants, thiol-reactive agents, and Bcl-2 can regulate the PT pore complex in a direct fashion, independently from their effects on cytochrome c. Furthermore, our results suggest a strategy for inducing apoptosis in cells overexpressing apoptosis-inhibitory Bcl-2 analogs.     

Caspase activation in MCF7 cells responding to etoposide treatment

Studies of the biochemical mechanisms evoked by conventional treatments for neoplastic diseases point to apoptosis as a key process for elimination of unwanted cells. Although the pathways through which chemotherapeutics promote cell death remain largely unknown, caspase proteases play a central role in the induction of apoptosis in response to a variety of stimuli including tumor necrosis factor, fas ligand, and growth factor deprivation. In this article, we demonstrate the induction of caspase protease activity in MCF7 human breast carcinoma cells exposed to the topoisomerase inhibitor, etoposide. Caspase protease activity was assessed by incubating cell lysates with the known caspase substrates, acetyl-L-aspartic-L-glutamic-L-valyl-L-aspartic acid 4-methyl-7-aminocoumarin or acetyl-L-tyrosyl-L-valyl-L-aspartic acid 4-methyl-7-aminocoumarin. We observed maximal cleavage of acetyl-L-aspartic-L-glutamic-L-valyl-L-aspartic acid 4-methyl-7-aminocoumarin within 6 hr following etoposide addition, a time that precedes cell death. In contrast, acetyl-L-tyrosyl-L-valyl-L-aspartic acid 4-methyl-7-aminocoumarin was resistant to cleavage activity. This substrate cleavage specificity implies that a caspase-3-like protease is activated in response to DNA damage. Consistent with the lysate protease activity, an intracellular marker of caspase activation, poly-ADP ribose polymerase (PARP), was cleaved in a concentration- and time-dependent manner after etoposide-treatment. PARP cleavage followed caspase activation and reached maximum cleavage between 12 and 16 hr. Incubation of the cells with the peptidic caspase inhibitor z-valine-alanine-asparagine-CH2F prevented caspase activation, inhibited PARP cleavage, and inhibited cell death. Thus, etoposide killing of MCF7 cells requires a caspase-3-like protease.     

Role of Ced-3/ICE-family proteases in staurosporine-induced programmed cell death

In the accompanying paper by Weil et al. (1996) we show that staurosporine (STS), in the presence of cycloheximide (CHX) to inhibit protein synthesis, induces apoptotic cell death in a large variety of nucleated mammalian cell types, suggesting that all nucleated mammalian cells constitutively express all of the proteins required to undergo programmed cell death (PCD). The reliability of that conclusion depends on the evidence that STS-induced, and (STS + CHS)-induced, cell deaths are bona fide examples of PCD. There is rapidly accumulating evidence that some members of the Ced-3/Interleukin-1 beta converting enzyme (ICE) family of cysteine proteases are part of the basic machinery of PCD. Here we show that Z-Val-Ala-Asp-fluoromethylketone (zVAD-fmk), a cell-permeable, irreversible, tripeptide inhibitor of some of these proteases, suppresses STS-induced and (STS + CHX)-induced cell death in a wide variety of mammalian cell types, including anucleate cytoplasts, providing strong evidence that these are all bona fide examples of PCD. We show that the Ced-3/ICE family member CPP32 becomes activated in STS-induced PCD, and that Bcl-2 inhibits this activation. Most important, we show that, in some cells at least, one or more CPP32-family members, but not ICE itself, is required for STS-induced PCD. Finally, we show that zVAD-fmk suppresses PCD in the interdigital webs in developing mouse paws and blocks the removal of web tissue during digit development, suggesting that this inhibition will be a useful tool for investigating the roles of PCD in various developmental processes.     

Role of the C-terminal domain of Bax and Bcl-XL in their localization and function in yeast cells

It has been suggested that the C-terminal domain of Bcl-2 family members may contain a signal anchor sequence that targets these proteins to the mitochondrial outer membrane. We have investigated the consequence of deleting this domain upon cytochrome c release in yeast strains that coexpress truncated forms of Bax (i.e. BaxA) and Bcl-X(L) (i.e. Bcl-X(L)delta). We find that (i) Bax(delta) is as efficient as full-length Bax in promoting cytochrome c release, but Bcl-x(L)delta has remarkably reduced rescuing ability compared to full-length Bcl-x(L); (ii) full-length Bcl-X(L) protein acts by relocalizing Bax from the mitochondrial fraction to the soluble cytosolic fraction; (iii) Bax undergoes N-terminal cleavage when expressed in yeast, which is prevented by coexpression of Bcl-X(L), suggesting that Bcl-x(L) may mask the cleavage site of Bax through a direct physical interaction of the two proteins.     

Ethane dimethane sulfonate and NNN'N'-tetrakis-(2-pyridylmethyl)ethylenediamine inhibit steroidogenic acute regulatory (StAR) protein expression in MA-10 Leydig cells and rat Sertoli cells

Apoptosis inhibits steroid biosynthesis, but it is not clear how the Steroidogenic Acute Regulatory (StAR) protein, is affected. To characterize StAR expression during apoptosis, mouse MA-10 Leydig tumor cells were treated with ethane dimethane sulfonate (EDS), an inducer of apoptosis, and the metal ion chelator NNN'N'-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN), an inducer of cell death. Both chemicals induced cell death and similarly inhibited dbcAMP-stimulated steroidogenesis and accumulation of the 30 kDa form of StAR. Utilizing the dye JC-1, it was found that TPEN and EDS also impaired the mitochondrial electrochemical potential (delta psi). In Sertoli cells, which also express StAR, EDS induced cell death and attenuated StAR expression. We conclude 1) steroidogenesis and accumulation of mature StAR protein are inhibited as a consequence of the induction of apoptosis; 2) reduced levels of StAR may be partially attributed to inhibition of import because of the loss of delta psi; 3) loss of steroidogenesis is probably due to loss of StAR synthesis and disruption of delta psi.     

Role of the human heat shock protein hsp70 in protection against stress-induced apoptosis

Resistance to stress-induced apoptosis was examined in cells in which the expression of hsp70 was either constitutively elevated or inducible by a tetracycline-regulated transactivator. Heat-induced apoptosis was blocked in hsp70-expressing cells, and this was associated with reduced cleavage of the common death substrate protein poly(ADP-ribose) polymerase (PARP). Heat-induced cell death was correlated with the activation of the stress-activated protein kinase SAPK/JNK (c-Jun N-terminal kinase). Activation of SAPK/JNK was strongly inhibited in cells in which hsp70 was induced to a high level, indicating that hsp70 is able to block apoptosis by inhibiting signaling events upstream of SAPK/JNK activation. In contrast, SAPK/JNK activation was not inhibited by heat shock in cells with constitutively elevated levels of hsp70. Cells that constitutively overexpress hsp70 resist apoptosis induced by ceramide, a lipid signaling molecule that is generated by apoptosis-inducing treatments and is linked to SAPK/JNK activation. Similar to heat stress, resistance to ceramide-induced apoptosis occurs in spite of strong SAPK/JNK activation. Therefore, hsp70 is also able to inhibit apoptosis at some point downstream of SAPK/JNK activation. Since PARP cleavage is prevented in both cell lines, these results suggest that hsp70 is able to prevent the effector steps of apoptotic cell death. Processing of the CED-3-related protease caspase-3 (CPP32/Yama/apopain) is inhibited in hsp70-expressing cells; however, the activity of the mature enzyme is not affected by hsp70 in vitro. Caspase processing may represent a critical heat-sensitive target leading to cell death that is inhibited by the chaperoning function of hsp70. The inhibition of SAPK/JNK signaling and apoptotic protease effector steps by hsp70 likely contributes to the resistance to stress-induced apoptosis seen in transiently induced thermotolerance.     

Effects of Ca2+ deregulation on mitochondrial membrane potential and cell viability in nucleated cells following lytic complement attack

We have previously shown [Papadimitriou JC. Ramm LE. Drachenberg CB. Trump BF. Shin ML. (1991) J. Immunol., 147, 212-217] that formation of lytic C5b-9 channels on Ehrlich ascites tumor cells induced rapid depletion of adenine nucleotides associated with prelytic leakage preceding cell death. Extracellular Ca2+ concentration ([Ca2+]e) reduction by chelation markedly delayed the onset of cell death, although the adenine nucleotide leakage was enhanced. In the present study, we examined the temporal relationships between ionized cytosolic Ca2+ ([Ca2+]i), mitochondrial membrane potential (delta psi m) and cell death in individual cells by digital imaging fluorescence microscopy (DIFM), during the earliest phase of C5b-9 attack. The results showed an immediate, > 20-fold rise in [Ca2+]i, rapidly followed by dissipation of delta psi m and subsequent acute cell death. These events were markedly delayed by chelation of Ca2+e, but not by nominally Ca2+ free medium. Differing from previous reports indicating propidium iodide labeling of viable cells bearing C5b-9 channels, with DIFM we observed nuclear fluorescence with that marker only in association with cell death. These findings indicate that Ca2+ influx through lytic C5b-9 channels is responsible for the massive increase in [Ca2+]i, as well as for the rapid loss of delta psi m, followed by acute cell death. When this [Ca2+]i increase is prevented, the cell death is probably related to metabolic depletion.     

Unsymmetrically substituted polyamine analogue induces caspase-independent programmed cell death in Bcl-2-overexpressing cells

The polyamine analogue, N1-ethyl-N11-[(cycloheptyl)methyl]-4,8-diazaundecane (CHENSpm)-induced programmed cell death in NCI H157 cells is accompanied by cytochrome c release, the loss of mitochondrial membrane potential, activation of caspase-3, caspase-mediated poly(ADP-ribose) polymerase cleavage, G2-M arrest, and DNA and nuclear fragmentation. Overexpression of Bcl-2 completely inhibits CHENSpm-induced cytochrome c release, caspase-3 activation, and poly(ADP-ribose) polymerase cleavage. However, Bcl-2 does not abrogate CHENSpm-induced programmed cell death. These results suggest that although cytochrome c release and activation of the caspase-3 protease cascade contribute to the rapid and efficient execution of apoptosis, a caspase cascade-independent pathway also exists and can be activated by CHENSpm treatment.     

Requirement of an ICE/CED-3 protease for Fas/APO-1-mediated apoptosis

The Fas/APO-1 receptor is one of the major regulators of apoptosis. We report here that Fas/APO-1-mediated apoptosis requires the activation of a new class of cysteine proteases, including interleukin-1 beta-converting enzyme (ICE), which are homologous to the product of the Caenorhabditis elegans cell-death gene ced-3 (refs 11, 12). Triggering of Fas/APO-1 rapidly stimulated the proteolytic activity of ICE. Overexpression of ICE, achieved by electroporation and microinjection, strongly potentiated Fas/APO-1-mediated cell death. In addition, inhibition of ICE activity by protease inhibitors, as well as by transient expression of the pox virus-derived serpin inhibitor CrmA or an antisense ICE construct, substantially suppressed Fas/APO-1-triggered cell death. We conclude that activation of ICE or an ICE-related protease is a critical event in Fas/APO-1-mediated cell death.