Acinus is a caspase-3-activated protein required for apoptotic chromatin condensation

Modulation of caspase-3 activity by zinc ions and by the cell redox state

It is known that DNA fragmentation during apoptosis is controlled by a number of factors, a crucial step being the caspase-operated cleavage of ICAD, the DNase inhibitor. We have previously demonstrated that hydrogen peroxide-treated lymphocytes undergo apoptosis without formation of a DNA ladder; however, the use of micromolar amounts of a Zn(2+) chelator allowed DNA cleavage at internucleosomal sites. Such results were extended in the present work, thus allowing their framing into the events related to alterations in the redox state of the cell. Apoptosis in hydrogen peroxide-treated lymphocytes was found to occur with caspase-3 activation, but the enzyme activity was found to be impaired, thus affecting internucleosomal fragmentation as well as nuclear morphology. Caspase-3 activity was found to resume upon mild Zn(2+) chelation. These results provide as well an experimental model from which apoptotic events upstream and downstream of caspase-3 activity can be examined.

Caspase activity in newt spermatogonial apoptosis induced by prolactin and cycloheximide

We previously showed in vivo and in vitro, that among the spermatogenic stages of the newt, prolactin (PRL) induces apoptosis specifically in the penultimate stage of secondary spermatogonia. In the current report, we demonstrate in vitro that cycloheximide (CHX), an inhibitor of protein synthesis, induces morphological apoptotic changes similar to those caused by PRL, such as chromatin condensation and apoptotic body formation. Next, we found that Z-VAD-fmk, an inhibitor of various caspases, suppressed the apoptosis induced by PRL and CHX, but ICE inhibitor Ac-YVAD-CHO or caspase-3 inhibitor Ac-DEVD-CHO did not. As high caspase activity was present in extracts of testes treated with CHX, we suggest that an unidentified caspase induces the morphological changes of apoptosis in newt spermatogonia.

Apoptotic cell death in the hippocampus due to prolonged hypothermic circulatory arrest: comparison of cyclosporine A and cycloheximide on neuron survival

OBJECTIVE

To determine whether cyclosporine A (CsA) or cycloheximide (CHX) can reduce neuronal apoptosis in the hippocampus in a chronic animal model of hypothermic circulatory arrest (HCA).

METHODS

Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In a blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), or 1 mg/kg CHX (n=8). After elective sacrifice 7 days postoperatively, brains were perfusion-fixed and the left hippocampus was examined for evidence of neuronal cell death. An in situ double-labeling method was used on cryosections to unequivocally identify apoptotic nuclei by the simultaneous visualization of DNA fragmentation and apoptotic chromatin condensation. Sections were also examined by immunocytochemistry for upregulation of the pro-apoptotic proteins Bax, activated caspase 3, and glyceraldehyde-3-phosphate dehydrogenase.

RESULTS

Apoptotic nuclear degradation was clearly present in the CA1, CA2 and CA3 subregions of the hippocampus after HCA. However, there was also morphological evidence for an accompanying necrotic-like cell death. There was no significant difference between the number of apoptotic nuclei observed in CSA-treated animals, mean value 4.4+/-1.63 SEM or CHX-treated animals, mean value 4.0+/-1.92 SEM, and age-matched control HCA pigs, mean value 4.85+/-1.69 SEM, (P>0.10).

CONCLUSIONS

The data clearly demonstrate apoptotic cell death in pigs after HCA by simultaneously demonstrating in situ end labeling (TUNEL reaction) and apoptotic chromatin condensation using a nucleic acid-binding dye. Since CsA shows promising neuroprotective effects in behavioral studies, and since the peak of HCA-induced apoptosis occurs earlier than 7 days, further studies will be required to determine whether CsA can improve neuronal survival in the first few days after HCA. CHX was not effective in reducing apoptosis in this model.

Deafness Due to Degeneration of Cochlear Neurons in Caspase-3-Deficient Mice

Mice that lack caspase-3, which functions in apoptosis, were generated by gene targeting and shown to undergo hearing loss. The ABR threshold of the caspase-3(-/-) mice was significantly elevated compared to that of caspase-3(+/+) mice at 15 days of age and was progressively elevated further by 30 days. Distortion product otoacoustic emissions were not detectable in caspase-3(-/-) mice at 15 days of age. Caspase-3(-/-) mice exhibited marked degeneration of spiral ganglion neurons and a loss of inner and outer hair cells in the cochlea at 30 days of age, although no such changes were apparent at 15 days. The degenerating neurons manifested features, including cytoplasmic vacuolization, distinct from those characteristic of apoptosis. Spiral ganglion neurons and cochlear hair cells thus appear to require caspase-3 for survival but not for initial development. The mapping of both the human caspase-3 gene and the locus responsible for an autosomal dominant, nonsyndromic form of hearing loss (DFNA24) to chromosome 4q35 suggests that the caspase-3(-/-) mice may represent a model of this human condition.

Involvement of p38 in apoptosis-associated membrane blebbing and nuclear condensation

The stress-activated protein kinase p38 is often induced by cytotoxic agents, but its contribution to cell death is ill defined. In Rat-1 cells, we found a strong correlation between activation of p38 and induction of c-Myc-dependent apoptosis. In cells with deregulated c-Myc expression but not in control cells, cis-diamminedichloroplatinum induced p38 activity and typical features of apoptosis, including internucleosomal DNA degradation, induction of caspase activities, and both nuclear (nuclear condensation and fragmentation) and extranuclear (cell blebbing) morphological alterations. The pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone did not block p38 activation and the p38 inhibitor SB203580 had no detectable effect on the activation of caspases or the in vivo cleavage of several caspase substrates, suggesting that p38 and caspase activation can contribute distinct features of apoptosis. Accordingly, we found that cell blebbing was independent of caspase activity and, rather, depended on p38-sensitive changes in microfilament dynamics likely mediated by heat shock protein 27 phosphorylation. Furthermore, p38 activity contributed to both caspase-dependent and caspase-independent nuclear condensation and fragmentation, suggesting a role in an early event triggering both mechanisms of apoptosis or sensitizing the cells to the action of both types of apoptosis executioners. Inhibiting p38 also resulted in a significant enhancement in cell survival estimated by colony formation. This capacity to modulate the sensitivity to apoptosis in cells with deregulated c-Myc expression suggests an important role for p38 in tumor cell killing by chemotherapeutic agents.

MST1-JNK promotes apoptosis via caspase-dependent and independent pathways

BACKGROUND

MST1 is an upstream kinase of the JNK and p38 MAPK pathways whose expression induces apoptotic morphological changes such as nuclear condensation. During apoptosis, caspase cleavage of MST1 removes a C-terminal regulatory domain, increasing the kinase activity of the MST1 N-terminal domain. Downstream pathways of MST1 in the induction of apoptosis remain to be clarified.

RESULTS

In this study, we found that the expression of MST1 resulted in caspase-3 activation. Therefore, MST1 is not only a target of caspases but also an activator of caspases. This caspase activation and apoptotic changes occur through JNK, since the co-expression of a dominant-negative mutant of JNK inhibited MST1-induced morphological changes as well as caspase activation. In contrast, neither a dominant-negative p38 nor the p38 inhibitor SB203580 inhibited them. MST1 induced nucleosomal DNA fragmentation, which was suppressed by caspase inhibitors or ICAD (Inhibitor of Caspase-Activated DNase). Surprisingly, however, other changes such as membrane blebbing and chromatin condensation were not inhibited by caspase inhibitors.

CONCLUSION

These results suggest that MST1 most likely promotes two events through JNK activation; first, MST1 induces the activation of caspases, resulting in CAD-mediated DNA fragmentation, and second, MST1 induces chromatin condensation and membrane blebbing without utilizing downstream caspases.

An integrated approach in the discovery and characterization of a novel nuclear protein over-expressed in liver and pancreatic tumors

An integrated approach in protein discovery through the use of multidisciplinary tools was reported. A novel protein, Hcc-1, was identified by analysis of the hepatocellular carcinoma (HCC)-M cell proteome. The assembled EST sequence of the 210 amino acid novel protein was subsequently confirmed by rapid amplification of cDNA ends (RACE). A total of 687 bp at the 5' untranslated region of Hcc-1 was identified. Promoter activity and several upstream open reading frames (uORFs) were demonstrated at this region. Bioinformatics prediction showed that the first 42 amino acids of the protein is a SAP domain with sequence matches to hnRNP from various vertebrate species. The Hcc-1 protein was localized to the cell nucleus while the gene was localized to chromosome 7q22.1. Hcc-1 cDNA level was increased in pancreatic adenocarcinoma. The level was also increased in well-differentiated hepatocellular carcinoma but decreases as the carcinoma progressed to a poorly differentiated stage.

Caspases mediate nucleoporin cleavage, but not early redistribution of nuclear transport factors and modulation of nuclear permeability in apoptosis

In eukaryotic cells, both soluble transport factors and components of the nuclear pore complex mediate protein and RNA trafficking between the nucleus and the cytoplasm. Here, we investigated whether caspases, the major execution system in apoptosis, target the nuclear pore or components of the nuclear transport machinery. Four nucleoporins, Nup153, RanBP2, Nup214 and Tpr are cleaved by caspases during apoptosis. In contrast, the nuclear transport factors, Ran, importin alpha and importin beta are not proteolytically processed, but redistribute across the nuclear envelope independently and prior to caspase activation. Also, mRNA accumulates into the nucleus before caspases become active. Microinjection experiments further revealed that early in apoptosis, the nucleus becomes permeable to dextran molecules of 70 kD molecular weight. Redistribution of import factors and mRNA, as well as nuclear permeabilisation, occur prior to caspase-mediated nucleoporin cleavage. Our findings suggest that the apoptotic programme includes modifications in the machinery responsible for nucleocytoplasmic transport, which are independent from caspase-mediated degradation of nuclear proteins.

Both caspase-dependent and caspase-independent pathways may be involved in hippocampal CA1 neuronal death because of loss of cytochrome c From mitochondria in a rat forebrain ischemia model

In a rat forebrain ischemia model, the authors examined whether loss of cytochrome c from mitochondria correlates with ischemic hippocampal CA1 neuronal death and how cytochrome c release may shape neuronal death. Forebrain ischemia was induced by bilateral common carotid artery occlusion with simultaneous hypotension for 10 minutes. After reperfusion, an early rapid depletion of mitochondrial cytochrome c and a late phase of diffuse redistribution of cytochrome c occurred in the hippocampal CA1 region, but not in the dentate gyrus and CA3 regions. Intracerebroventricular administration of Z-DEVD-FMK, a relatively selective caspase-3 inhibitor, provided limited but significant protection against ischemic neuronal damage on day 7 after reperfusion. Treatment with 3 minutes of ischemia (ischemic preconditioning) 48 hours before the 10-minute ischemia attenuated both the early and late phases of cytochrome c redistribution. In another subset of animals treated with cycloheximide, a general protein synthesis inhibitor, the late phase of cytochrome c redistribution was inhibited, whereas most hippocampal CA1 neurons never regained mitochondrial cytochrome c. Examination of neuronal survival revealed that ischemic preconditioning prevents, whereas cycloheximide only delays, ischemic hippocampal CA1 neuronal death. DNA fragmentation detected by terminal deoxytransferase-mediated dUTP-nick end labeling (TUNEL) in situ was largely attenuated by ischemic preconditioning and moderately reduced by cycloheximide. These results indicate that the loss of cytochrome c from mitochondria correlates with hippocampal CA1 neuronal death after transient cerebral ischemia in relation to both caspase-dependent and -independent pathways. The amount of mitochondrial cytochrome c regained may determine whether ischemic hippocampal CA1 neurons survive or succumb to late-phase death.

The role of bim, a proapoptotic BH3-only member of the Bcl-2 family in cell-death control

Apoptosis is an evolutionarily conserved process for killing unwanted cells. Genetic and biochemical experiments have indicated that three groups of proteins are necessary for activation of the cell-death effector machinery: cysteine proteases, their adaptors, and proapoptotic Bcl-2 family members. Antiapoptotic Bcl-2 family members are needed for cell survival. We have cloned Bim, a proapoptotic Bcl-2 family member that shares with the family only a 9-16 aa region of homology [Bcl-3 homology region(BH3)], but is otherwise unique. Bim requires its BH3 region for binding to Bcl-2 and activation of apoptosis. Analysis of Bim-deficient mice has shown that Bim is essential for the execution of some but not all apoptotic stimuli that can be antagonized by Bcl-2. Bim-deficient mice have increased numbers of lymphocytes, plasma cells, and myeloid cells, and most develop fatal autoimmune glomerulonephritis. In healthy cells, Bim is bound to the microtubule-associated dynein motor complex, and is thereby sequestered from Bcl-2. Certain apoptotic signals unleash Bim and allow it to translocate to intracellular membranes, where it interacts with Bcl-2 or its homologues. These results indicate that BH3-only proteins are essential inducers of apoptosis that can be unleashed by certain death signals. Unleashed BH3-only proteins neutralize the prosurvival function of Bcl-2-like molecules, and this is thought to liberate Apaf-l-like adapters to activate caspase zymogens, which then initiate cell degradation.

Comprehensive studies on subcellular localizations and cell death-inducing activities of eight GFP-tagged apoptosis-related caspases

By using green fluorescent protein fusion, we investigated the subcellular localization of all the caspases that have been cloned from humans and implicated in the execution of apoptosis. We divided these caspases into three groups according to subcellular localization. The first group includes caspase-1, -3, -6, -7, and -9, which are expressed mainly in the cytoplasm with various levels of nuclear localization depending on the cell type. The second group has a single member, caspase-2, which is primarily localized in the nucleus. The nuclear localization was demonstrated to be mediated by a nuclear localization signal near the NH(2)-terminus of the prodomain. The third group includes caspase-8 and -10, which have a cytoplasmic distribution. These two members have potent, rapid cell death-inducing activity and are prone to make aggregates when overexpressed. Their prodomains formed marked fibrous structures in the cytoplasm whose localization seemed distinct from organelles or cytoskeletons. None of the GFP-caspases examined in this study showed a predominant mitochondrial localization as has been reported for some caspases.

Characterization of ultrastructure and its relation with DNA fragmentation in Fas-induced apoptosis of cultured cardiac myocytes

The purposes of the present study were to define precisely the ultrastructural features of apoptosis in cultured cardiomyocytes and to determine whether DNA fragmentation is essential for the apoptotic morphology. When cultured neonatal murine cardiomyocytes were incubated with an agonistic anti-Fas antibody in the presence of a non-toxic amount of actinomycin D or cycloheximide, approximately 70% of them had lost their viability after 24 h. The dead cardiomyocytes showed the typical ultrastructural changes of apoptosis on transmission and scanning electron microscopy, as well as by positive in situ nick end-labelling (TUNEL), positive Taq polymerase-based in situ ligation, a DNA ladder pattern on gel electrophoresis, and an increase in the active fragment of caspase-3. According to TUNEL at the electron microscopic level, apoptotic nuclear change, cytoplasmic shrinkage, and DNA fragmentation always occurred simultaneously in apoptotic cardiomyocytes. Other ultrastructural features of apoptosis were the appearance of abundant lipid-like structures in the cytoplasm of cardiomyocytes at the early phase, and a high incidence of plasma membrane rupture and formation of apoptotic bodies at the later phase. When zinc, an inhibitor of Ca2+/Mg2+-dependent endonuclease, was added to the present model, activation of caspase-3 and an apoptotic ultrastructure were still observed in spite of the lack of DNA fragmentation, indicating that this type of myocyte death is also apoptosis. In conclusion, the typical apoptotic ultrastructure and DNA fragmentation occur simultaneously in association with caspase-3 activation in Fas-stimulated cultured cardiomyocytes. Apoptotic morphology can, however, be observed even without DNA fragmentation.

Caspase activation as an apoptotic evidence in the gerbil hippocampal CA1 pyramidal cells following transient forebrain ischemia

To determine whether apoptotic process is involved in the delayed neuronal death in hippocampal CA1 region following forebrain ischemia in gerbils, time dependent activation of caspase and DNA fragmentation were evaluated by immuno-staining and terminal dUTP nick-end-labeling staining, respectively. After transient forebrain ischemia in gerbils, activation of apoptosis related caspase, including caspase-3, was apparent, and it preceded DNA fragmentation in CA1 region. These observations suggest that apoptotic process is involved in hippocampal delayed neuronal death.

CUG-initiated FGF-2 induces chromatin compaction in cultured cardiac myocytes and in vitro

Fibroblast growth factor-2 (FGF-2) is a mitogen found in CUG-initiated 21-25 kDa ("hi") or AUG-initiated 16-18 kDa ("lo") forms. Previously we demonstrated that "hi"-but not "lo"-FGF-2 caused a distinct nuclear phenotype characterized by apparently condensed chromatin present as separate clumps in the nucleus of cardiac myocytes. In this manuscript we investigated whether these effects were related to apoptosis or mitosis and whether they reflected a direct effect of "hi" FGF-2 on chromatin. Myocytes overexpressing "hi" FGF-2 and presenting the clumped chromatin phenotype: (i) were not labeled above background with antibodies to phosphorylated histones H1 and H3 used as indicators of mitotic chromatin condensation; (ii) did not stain positive for TUNEL; (iii) their nuclear lamina, visualized by anti-laminB immunofluorescence, appeared intact; (iv) neither caspase inhibitors, nor Bcl-2 or "lo" FGF-2 overexpression prevented the manifestation of the compacted nuclear phenotype. Purified recombinant "hi" FGF-2 was more potent than "lo" FGF-2 in promoting the condensation/aggregation of chick erythrocyte chromatin partially reconstituted with histone H1 in vitro. We conclude that the DNA phenotype induced by "hi" FGF-2 in cardiac myocytes likely reflects a direct effect on chromatin structure that does not require the engagement of mitosis or apoptosis. By affecting chromatin compaction "hi" FGF-2 may contribute to the regulation of gene expression.

Molecular basis of partial lipodystrophy and prospects for therapy

Lipodystrophy is characterized by altered partition of adipose tissue. Despite heterogeneous causes, which include genetic, autoimmune and drug-induced forms, lipodystrophy syndromes have similar metabolic attributes, including insulin resistance, hyperlipidemia and diabetes. The mechanisms underlying the insulin resistance are unknown. One form of lipodystrophy, namely Dunnigan-type familial partial lipodystrophy (FPLD) was shown to result from mutations in the LMNA gene, which encodes nuclear lamins A and C. Although the relationship between the mutations in the nuclear envelope and insulin resistance is unclear at present, these findings might eventually be shown to have relevance for the common insulin resistance syndrome and for drug-associated lipodystrophies.

A single cell analysis of apoptosis. Ordering the apoptotic phenotype

Microcinematography was applied to the analysis of the kinetics of apoptotic cell death. Apoptosis was found to be a process that proceeds in different cells at different times after an initial stress, and therefore kinetic studies of apoptotic events in bulk cultures can be problematic. Using single cell analysis we found that stronger apoptotic stimuli induce an earlier onset of apoptosis, but that there is no relationship between time of onset and duration of the apoptotic process. That is, cells that initiate apoptosis shortly after induction do not proceed more rapidly through the process. This suggests an all-or-non-mechanism that is supported by some models of the biochemical pathways of apoptosis.

Segregation of nucleolar components coincides with caspase-3 activation in cisplatin-treated HeLa cells

We studied morphological changes of the nucleoli in HeLa cells treated with cisplatin and compared them with induction of markers of programmed cell death and TUNEL staining. We used different light microscopic nucleolar staining methods allowing us to visualize not only nucleolar proteins but also nucleolar RNA. Our results show predominantly compact, centrally localized nucleoli in intact control HeLa cells. In cisplatin-treated HeLa cells, we found an early onset of nucleolar segregation of proteins detected by argyrophilic nucleolar organizer regions and anti-nucleolar monoclonal antibody as well as an increased immunoreactivity for activated caspase-3 after 6 hours. Staining with Toluidine Blue and Methyl-green Pyronine revealed segregated nucleoli 12 hours after the treatment with cisplatin. TUNEL positivity in cisplatin-treated HeLa cells was accompanied by the aggregation of the argyrophilic proteins in the central portion of nucleus, disappearance of nucleolar RNA and shrinkage of the nucleus after 24 hours. Monitoring of the biochemical changes by immunoblotting revealed that activation of distinct caspases and degradation of their downstream protein substrates is executed in two phases. During an early apoptotic stage beginning 4.5 hours post treatment an activation of caspase-9 and caspase-3 was observed. This was accompanied by proteolytic cleavage of poly(ADP-ribose) polymerase-1 (PARP-1). The caspase-9 activation seems to be mediated by recruitment by the activating factor Apaf-1 because the increased accumulation of Apaf-1 and cytochrome C in cytosol preceded the generation of mature caspase-9 form. A second phase of apoptosis occurring between 10 and 15 hours post treatment was characterized by degradation of other nucleolar and nuclear proteins such as nuclear lamins, topoisomerase I and B23. In conclusion, remarkable segregation of nucleolar argyrophilic proteins, nucleolar RNA and a simultaneous activation of the cascade of caspases markedly preceded the TUNEL positivity in cisplatin-treated HeLa cells thereby substantiating the hypothesis that the nucleolus is a preferred target for caspase-3-dependent proteolysis in cisplatin-treated HeLa cells.

Programmed cell death in cerebral ischemia

Programmed cell death (PCD) is an ordered and tightly controlled set of changes in gene expression and protein activity that results in neuronal cell death during brain development. This article reviews the molecular pathways by which PCD is executed in mammalian cells and the potential relation of these pathways to pathologic neuronal cell death. Whereas the classical patterns of apoptotic morphologic change often do not appear in the brain after ischemia, there is emerging biochemical and pharmacologic evidence suggesting a role for PCD in ischemic brain injury. The most convincing evidence for the induction of PCD after ischemia includes the altered expression and activity in the ischemic brain of deduced key death-regulatory genes. Furthermore, studies have shown that alterations in the activity of these gene products by peptide inhibitors, viral vector-mediated gene transfer, antisense oligonucleotides, or transgenic mouse techniques determine, at least in part, whether ischemic neurons live or die after stroke. These studies provide strong support for the hypothesis that PCD contributes to neuronal cell death caused by ischemic injury. However, many questions remain regarding the precise pathways that initiate, sense, and transmit cell death signals in ischemic neurons and the molecular mechanisms by which neuronal cell death is executed at different stages of ischemic injury. Elucidation of these pathways and mechanisms may lead to the development of novel therapeutic strategies for brain injury after stroke and related neurologic disorders.

Apoptosis and caspases

The expedition into the apoptosis signaling pathway, although it has just begun, has resulted in the discovery of a significant number of remarkable signaling molecules at all levels of this novel pathway After the pinnacle of this frenetic cloning effort has been reached, however, it is important to put this pathway and its constituents into a biological and pathophysiological context. It has become clear that cell death does not automatically mean activation of caspases. The recent discovery of a function of effector caspases of the apoptosis pathway outside of apoptosis is currently revolutionizing our view of these seemingly unrelated and rather counteracting processes, cell death and cell proliferation. It appears that caspases play a much more fundamental role in cells than originally expected.

Caspase activation is required for terminal erythroid differentiation

The cysteine proteases known as caspases play a central role in most apoptotic pathways. Here, we show that caspase inhibitors arrest the maturation of human erythroid progenitors at early stages of differentiation, before nucleus and chromatin condensation. Effector caspases such as caspase-3 are transiently activated through the mitochondrial pathway during erythroblast differentiation and cleave proteins involved in nucleus integrity (lamin B) and chromatin condensation (acinus)without inducing cell death and cleavage of GATA-1. These observations indicate a new function for caspases as key proteases in the process of erythroid differentiation.

The Rela(p65) subunit of NF-kappaB is essential for inhibiting double-stranded RNA-induced cytotoxicity

Double-stranded RNA (dsRNA) molecules generated during virus infection can initiate a host antiviral response to limit further infection. Such a response involves induction of antiviral gene expression by the dsRNA-activated protein kinase (PKR) and the NF-kappaB transcription factor. In addition, dsRNA can also induce apoptosis by an incompletely understood mechanism that may serve to further limit viral replication. Here we demonstrate a novel role for the RelA subunit of NF-kappaB in inhibiting dsRNA-induced cell death. dsRNA treatment resulted in caspase 3 activation and apoptotic morphological transformations in mouse embryonic fibroblasts (MEFs) derived from RelA-/- mice but not from RelA+/+ mice. Such dsRNA-induced killing could be inhibited by expression of either a dominant-negative mutant of PKR or wild-type RelA. Interestingly, caspase 3 activated following dsRNA treatment of RelA-/- MEFs was essential for apoptotic nuclear changes but dispensable for cytotoxicity. A broader specificity caspase inhibitor was also unable to inhibit dsRNA-induced cytotoxicity, suggesting that caspase activation is not essential for the induction of cell death by dsRNA in MEFs. However, combined inhibition of caspase 3 and reactive oxygen species production resulted in complete inhibition of dsRNA-induced cytotoxicity. These results demonstrate an essential role for NF-kappaB in protecting cells from dsRNA-induced apoptosis and suggest that NF-kappaB may inhibit both caspase-dependent and reactive oxygen species-dependent cytotoxic pathways.

Modulation of apoptosis by procaspase-2 short isoform: selective inhibition of chromatin condensation, apoptotic body formation and phosphatidylserine externalization

Procaspase-2 is one of the cysteine aspartate proteases involved in apoptotic cell death. Alternative splicing of CASP-2 messenger RNA generates a long isoform, procaspase-2L, whose overexpression induces cell death and a truncated isoform, procaspase-2S, whose function remains poorly defined. The present study explored the consequences of procaspase-2S overexpression in U937 human leukemic cells exposed to the topoisomerase II inhibitor etoposide as an apoptotic stimulus. Overexpression of procaspase-2S in U937 cells partially prevented nuclear changes associated with etoposide-induced cell death, as determined by Hoechst 33342 staining of nuclear chromatin and electron microscopy studies. Procaspase-2S also prevented the maturation of apoptotic bodies, delayed phosphatidylserine externalization on the plasma membrane and prevented the cleavage and activation of procaspase-2L. These effects were not observed when the cysteine 289 in the consensus QACRG motif was mutated into a serine. Wild-type procaspase-2S overexpression did not influence the cleavage of procaspase-3, procaspase-7 and poly(ADP-ribose)polymerase nor the fragmentation of nuclear DNA into nucleosome-sized fragments. Altogether, these results indicate that the short isoform of procaspase-2 negatively interferes with selective features of apoptosis, an activity that is suppressed by mutation of the cysteine 289.

SADS: A new component of Fas-DISC is the accelerator for cell death signaling and is downregulated in patients with colon carcinoma

Fas is the death receptor, transducing cell death signaling upon stimulation by Fas ligand. During Fas-initiated cell death signaling, the formation of Fas-death inducing signaling complex (Fas-DISC) is the first step. Here we have identified a new component of Fas-DISC which we call 'small-accelerator for death signaling' (SADS). SADS cDNA encodes a 150 amino acid polypeptide (Mr = 16,700). During Fas-mediated cell death, SADS enhances the interaction of Fas-death domain-interactive factors (FADD) and procaspase-8, and deletion mutant analysis has identified FADD- and caspase-8-interactive domains in SADS. Inhibition or removal of SADS delays Fas-mediated cell death. In addition, we demonstrate the deletion or mutation of SADS in patients with colon carcinoma and that exogenous SADS expression in human colon carcinoma SW480 cells that lack SADS leads to re-acquisition of Fas-mediated cell death. Here, we propose that SADS is one of the cell death-associated factors and enhances Fas-DISC formation, especially FADD and procaspase-8 recruitment.

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) induces apoptosis in rat splenocytes and thymocytes by different mechanisms

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is a potent carcinogen present in cooked meat. Although the target of this carcinogen is mainly in the liver, Trp-P-1 is distributed in the thymus and spleen as well as in the liver after administration. However, the cytotoxic effect of Trp-P-1 on lymphocytes has not been examined in detail. In the present study, we investigated the cytotoxicity of Trp-P-1 against rat splenocytes and thymocytes. Trp-P-1 reduced viability of both types of cells in the same manner, the LD(50) at 6h in culture was 15 microM, and the time for the 50% decrease in cell viability (t(1/2)) at 20 microM was 3h. In both types of cells, Trp-P-1 caused the activation of caspase-3-like proteases and the cleavage of poly(ADP-ribose) polymerase, both of which are biochemical markers of apoptosis. On the other hand, DNA fragmentation occurred in splenocytes, but not in thymocytes although Trp-P-1 activated 32-34kDa nucleases that may not be able to degrade DNA into nucleosomal units. These results indicated that Trp-P-1 induces apoptosis in both splenocytes and thymocytes by different mechanisms in which distinct apoptotic pathways may exist downstream of the caspase cascade.

Taube nuss is a novel gene essential for the survival of pluripotent cells of early mouse embryos

The cells of the inner cell mass constitute the pluripotent cell population of the early embryo. They have the potential to form all of the tissues of the embryo proper and some extra-embryonic tissues. They can be considered a transient stem cell population for the whole of the embryo, and stem cells maintaining the same capacity can be isolated from these cells. We have isolated, characterised and mutated a novel gene, taube nuss (Tbn), that is essential for the survival of this important cell population. The taube nuss protein sequence (TBN) was highly conserved between human, mouse, Xenopus laevis, Drosophila melanogaster, Caenorhabditis elegans and Arabidopsis thaliana, particularly in a domain that is not present in any published proteins, showing that TBN is the founding member of a completely new class of proteins with an important function in development. The Tbn gene was expressed ubiquitously as early as E2. 5 and throughout embryonic development. It was also expressed in adult brain with slightly higher levels in the hippocampus. The Tbn mutant embryos developed normally to the blastocyst stage and contained inner cell masses. They hatched from the zonae pellucidae, implanted and induced decidual reactions, but failed to develop beyond E4.0. At this time the trophoblast cells were viable, but inner cell masses were not detectable. At E3.75, massive TUNEL-positive DNA degradation and chromatin condensation were visible within the inner cell masses, whereas the cell membranes where intact. Caspase 3 was expressed in these cells. In vitro, the inner cell mass of mutant embryos failed to proliferate and died after a short period in culture. These results indicate that the novel protein, taube nuss, is necessary for the survival of the inner cell mass cells and that inner cell mass cells died of apoptosis in the absence of the taube nuss protein. As cell pruning by apoptosis is a recognised developmental process at this stage of development, the taube nuss protein may be one of the factors regulating the extent of programmed cell death at this time point.

Characterization of the rat DNA fragmentation factor 35/Inhibitor of caspase-activated DNase (Short form). The endogenous inhibitor of caspase-dependent DNA fragmentation in neuronal apoptosis

Nuclear changes, including internucleosomal DNA fragmentation, are classical manifestations of apoptosis for which the biochemical mechanisms have not been fully elucidated, particularly in neuronal cells. We have cloned the rat DNA fragmentation factor 35/inhibitor of caspase-activated DNase (short form) (DFF35/ICAD(S)) and found it to be the predominant form of ICAD present in rodent brain cells as well as in many other types of cells. DFF35/ICAD(S) forms a functional complex with DFF40/caspase-activated DNase (CAD) in the nucleus, and when its caspase-resistant mutant is over-expressed, it inhibits the nuclease activity, internucleosomal DNA fragmentation, and nuclear fragmentation but not the shrinkage and condensation of the nucleus, in neuron-differentiated PC12 cells in response to apoptosis inducers. DFF40/CAD is found to be localized mainly in the nucleus, and during neuronal apoptosis, there is no evidence of further nuclear translocation of this molecule. It is further suggested that inactivation of DFF40/CAD-bound DFF35 and subsequent activation of DFF40/CAD during apoptosis of neuronal cells may not occur in the cytosol but rather in the nucleus through a novel mechanism that requires nuclear translocation of caspases. These results establish that DFF35/ICAD(S) is the endogenous inhibitor of DFF40/CAD and caspase-dependent apoptotic DNA fragmentation in neurons.

Proteases for cell suicide: functions and regulation of caspases

Caspases are a large family of evolutionarily conserved proteases found from Caenorhabditis elegans to humans. Although the first caspase was identified as a processing enzyme for interleukin-1beta, genetic and biochemical data have converged to reveal that many caspases are key mediators of apoptosis, the intrinsic cell suicide program essential for development and tissue homeostasis. Each caspase is a cysteine aspartase; it employs a nucleophilic cysteine in its active site to cleave aspartic acid peptide bonds within proteins. Caspases are synthesized as inactive precursors termed procaspases; proteolytic processing of procaspase generates the tetrameric active caspase enzyme, composed of two repeating heterotypic subunits. Based on kinetic data, substrate specificity, and procaspase structure, caspases have been conceptually divided into initiators and effectors. Initiator caspases activate effector caspases in response to specific cell death signals, and effector caspases cleave various cellular proteins to trigger apoptosis. Adapter protein-mediated oligomerization of procaspases is now recognized as a universal mechanism of initiator caspase activation and underlies the control of both cell surface death receptor and mitochondrial cytochrome c-Apaf-1 apoptosis pathways. Caspase substrates have bene identified that induce each of the classic features of apoptosis, including membrane blebbing, cell body shrinkage, and DNA fragmentation. Mice deficient for caspase genes have highlighted tissue- and signal-specific pathways for apoptosis and demonstrated an independent function for caspase-1 and -11 in cytokine processing. Dysregulation of caspases features prominently in many human diseases, including cancer, autoimmunity, and neurodegenerative disorders, and increasing evidence shows that altering caspase activity can confer therapeutic benefits.

Caspase-3 activation and apoptosis induction coupled with the retrograde transport of shiga toxin: inhibition by brefeldin A

Caspase proteolytic activities, such as caspase-3, -2 and -6, of THP-1 human monocytic cells were markedly increased in a time- and dose-dependent manner by treatment with purified Shiga toxin 1 (Stx1) or Stx2. Caspase-3 activation was strictly correlated with internucleosomal DNA fragmentation and chromatin condensation of the cells. In addition, the specific caspase-3 inhibitor, Ac-DEVD-CHO, decreased the percentage of apoptotic cells. The purified B-subunit of Stx1 did not induce apoptosis in THP-1 cells. Caspase-3 activation, DNA fragmentation and chromatin condensation caused by Stx were completely blocked by pretreatment of cells with brefeldin A, an inhibitor of Golgi functions. The findings suggest that Stx1 as well as Stx2 activate caspase-3, which plays a critical role in apoptosis, and that the apoptotic signals rise after Stx is transported to the Golgi apparatus.

VDAC regulation by the Bcl-2 family of proteins

The Bcl-2 family of proteins consists of anti-apoptotic and pro-apoptotic members, which determine the life or death of cells by altering mitochondrial membrane permeability. Pro-apoptotic Bcl-2 family members increase mitochondrial membrane permeability, resulting in the release of mitochondrial apoptogenic factors such as cytochrome c that activates death proteases called caspases, whereas anti-apoptotic family members prevent this increase of mitochondrial membrane permeability. The release of cytochrome c is central to apoptotic signal transduction in mammals, and has been studied extensively, leading to the development of several models for cytochrome c release including rupture of the mitochondrial outer membrane and involvement of specific channels. This article describes the important role of a mitochondrial outer membrane channel, the voltage-dependent anion channel (VDAC), in apoptogenic cytochrome c release and its regulation by Bcl-2 family members, and also discusses the molecular architecture of the life - death switch in mammalian cells. Cell Death and Differentiation (2000) 7, 1174 - 1181

Caspases that are activated during generation of nuclear polyglutamine aggregates are necessary for DNA fragmentation but not sufficient for cell death

Truncated polypeptides containing expanded polyglutamine (polyQ) stretches tend to form cytoplasmic or nuclear aggregates in cultured cells, leading to cell death. Although it has been shown recently that caspase-8 coaggregates with polyQ and is activated during polyQ-mediated cell death, little is known of the location and timing of caspase-8 activation by nuclear polyQ aggregates. Also, the relationship between nuclear polyQ aggregate-mediated cell death and activation of other caspases is unclear. In P19 embryonal carcinoma (EC) cells, which can be made to differentiate into neuronal cells, polyQ72 repeats preferentially aggregate in the nucleus. Nuclear aggregates of polyQ72 induced P19 EC cell death, with a high frequency of cells exhibiting morphology characteristic of apoptosis (i.e., roundness, cell shrinkage, chromatin condensation) and DNA fragmentation. In the present study, we used antisera that specifically recognized the active forms of caspase-8, -3, and -9 but not their proforms, and showed that only caspase-8 and -3 were activated during the generation of polyQ72 aggregates in P19 EC cell nuclei. Furthermore, we showed that the caspase inhibitor z-VAD-fmk inhibited DNA fragmentation, but only partially inhibited the appearance of apoptotic morphology. Thus, caspase activation, including caspase-8 and -3, is necessary for polyQ-mediated DNA fragmentation but not sufficient for polyQ-mediated cell death in P19 EC cells.

Mechanism of nitric oxide-induced apoptosis in human neuroblastoma SH-SY5Y cells

We have attempted to elucidate the precise mechanism of nitric oxide (NO)-induced apoptotic neuronal cell death. Enzymatic cleavages of DEVD-AFC, VDVAD-AFC, and LEHD-AFC (specific substrates for caspase-3-like protease (caspase-3 and -7), caspase-2, and caspase-9, respectively) were observed by treatment with NO. Western blot analysis showed that pro-forms of caspase-2, -3, -6, and -7 are decreased during apoptosis. Interestingly, Ac-DEVD-CHO, a caspase-3-like protease inhibitor, blocked not only the decreases in caspase-2 and -7, but also the formation of p17 from p20 in caspase-3 induced by NO, suggesting that caspase-3 exists upstream of caspase-2 and -7. Bongkrekic acid, a potent inhibitor of mitochondrial permeability transition, specifically blocked both the loss of mitochondrial membrane potential and subsequent DNA fragmentation in response to NO. Thus, NO results in neuronal apoptosis through the sequential loss of mitochondrial membrane potential, caspase activation, and degradation of inhibitor of caspase-activated DNase (CAD) (CAD activation).

Cell death induction by CTL: perforin/granzyme B system dominantly acts for cell death induction in human hepatocellular carcinoma cells

Cell death induction by cytotoxic T lymphocytes (CTLs) is an important thesis for the understanding of tumor immunotherapy. In the current study we investigated the molecular machinery of CTL-induced cell death in human hepatocellular carcinoma cell lines (HCC lines). CTLs prepared from human peripheral blood induced cell death in all tested HCC lines. As the CTL-induced death system, the effectiveness of Fas ligand/Fas and/or Perforin/Granzyme B systems has been suggested, whereas cell death induction by CTLs was shown independently on Fas expression in the current study. Using various tetrapeptide inhibitors for caspase and its associated factor, we additionally demonstrated that inhibitors for caspase 3 (Ac-DEVD-CHO) and caspase 8/granzyme B (Ac-IETD-CHO) suppressed CTL-induced cell death, but an inhibitor for Fas-activated serine proteinase, which acts for the caspase 3 activator, did not, suggesting that CTL-induced cell death was initiated by the Perforin/Granzyme B system, rather than the Fas ligand/Fas system. On the basis of our current results, we report here that the Perforin/Granzyme B system acts dominantly for the cell death induction of HCC lines.

Perturbation of mitochondrial structure and function plays a central role in Actinobacillus actinomycetemcomitans leukotoxin-induced apoptosis

Certain pore-forming bacterial toxins, including the leukotoxin (Ltx) produced by Actinobacillus actinomycetemcomitans, induce apoptosis in susceptible target cells. Although binding to the target cell surface represents the first step in the initiation of this process, the downstream events leading to toxin-induced apoptotic cell death have not been identified. Perturbation of mitochondrial function has been shown to have a major role in regulating progression of apoptosis initiated by exposure to numerous stimuli. Using Ltx as a model, the aim of this study was to evaluate whether induction of apoptosis by pore-forming toxins follows a similar paradigm. After exposure to Ltx, Epstein-Barr virus transformed B cells (JY cell line) exhibited the classical morphological features of apoptosis including decreased cell size, plasma membrane blebbing, selective alterations in plasma membrane permeability and condensation of nuclear DNA. The morphologic changes were accompanied by swelling of the mitochondria, a decrease in mitochondrial transmembrane potential (Psi(m)), hyperproduction of reactive oxygen intermediates (ROIs) and release of cytochrome c from the intermembrane space. Subsequently, we detected activation of the c ysteine asp artate-specific prote ases (caspases)-3 and -9, cleavage of the nuclear DNA repair enzyme, poly(ADP-ribose)polymerase (PARP) and internucleosomal DNA fragmentation. These results indicate that perturbation of mitochondrial structure and function, in concert with activation of specific caspases, initiate the effector phase of Ltx-induced apoptosis.

Mitochondrial membrane potential differentiates cells resistant to apoptosis in hybridoma cultures

Previous research has implicated mitochondrial physiology and, by extension, respiratory capacity in the initiation and progress of apoptosis of cells in culture and tissue environments. This hypothesis was tested by separating a hybridoma cell population into subpopulations of varying mitochondrial membrane potential (MMP) using Rhodamine 123 stain and fluorescence-activated cell sorter analysis and subjecting them to two apoptosis inducers, rotenone and staurosporin. Apoptotic death was characterized morphologically through the determination of apoptosis-related chromatin condensation and biochemically through the measurement of caspase-3 enzymatic activity. We found dramatic differences in the apoptotic death kinetics for the subpopulations, with the high MMP cells showing higher resistance to apoptotic death. After incubation with 30 microM rotenone, the low MMP cells exhibited one-third of the viability of the high MMP cells and a three-fold increase in the capsase-3 enzymatic activity. No changes were observed in the DNA content or the cell cycle distributions of the two cell subpopulations, which maintained their mean MMP difference after 20 generations. These results suggest that heterogeneity exists in mammalian cell populations with respect to mitochondrial physiology, which correlates with resistance to apoptotic death.

Increased caspase 3 and Bax immunoreactivity accompany nuclear GAPDH translocation and neuronal apoptosis in Parkinson's disease

In situ end labeling combined with YOYO staining was used to mark apoptotic DNA fragmentation and chromatin condensation respectively in human postmortem brain sections. Increased numbers of apoptotic neuronal nuclei were identified in the Parkinson's disease (PD) nigra compared with age-matched controls. Caspase 3 and Bax showed increased immunoreactivity in melanized neurons of the PD nigra compared with controls. Importantly, GAPDH nuclear accumulation was also observed in the PD nigra, suggesting apoptotic rather than necrotic cell death. Interestingly, both Lewy bodies and the intranuclear Marinesco's bodies were GAPDH immunoreactive in the PD brain.

Induction of neuronal apoptosis by thiol oxidation: putative role of intracellular zinc release

The membrane-permeant oxidizing agent 2,2'-dithiodipyridine (DTDP) can induce Zn(2+) release from metalloproteins in cell-free systems. Here, we report that brief exposure to DTDP triggers apoptotic cell death in cultured neurons, detected by the presence of both DNA laddering and asymmetric chromatin formation. Neuronal death was blocked by increased extracellular potassium levels, by tetraethylammonium, and by the broad-spectrum cysteine protease inhibitor butoxy-carbonyl-aspartate-fluoromethylketone. N,N,N', N'-Tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN) and other cell-permeant metal chelators also effectively blocked DTDP-induced toxicity in neurons. Cell death, however, was not abolished by the NMDA receptor blocker MK-801, by the intracellular calcium release antagonist dantrolene, or by high concentrations of ryanodine. DTDP generated increases in fluorescence signals in cultured neurons loaded with the zinc-selective dye Newport Green. The fluorescence signals following DTDP treatment also increased in fura-2- and magfura-2-loaded neurons. These responses were completely reversed by TPEN, consistent with a DTDP-mediated increase in intracellular free Zn(2+) concentrations. Our studies suggest that under conditions of oxidative stress, Zn(2+) released from intracellular stores may contribute to the initiation of neuronal apoptosis.

Positive and negative regulation of apoptotic pathways by cytotoxic agents in hematological malignancies

Most chemotherapeutic drugs can induce tumor cell death by apoptosis. Analysis of the molecular mechanisms that regulate apoptosis has indicated that anticancer agents simultaneously activate several pathways that either positively or negatively regulate the death process. The main pathway from specific damage induced by the drug to apoptosis involves activation of caspases in the cytosol by pro-apoptotic molecules such as cytochrome c released from the mitochondrial intermembrane space. At least in some cell types, anticancer drugs also upregulate the expression of death receptors and sensitize tumor cells to their cognate ligands. The Fas-mediated pathway could contribute to the early steps of drug-induced apoptosis while sensitization to the cytokine TRAIL could be used to amplify the response to cytotoxic drugs. The Bcl-2 family of proteins, that includes anti- and pro-apoptotic molecules, regulates cell sensitivity mainly at the mitochondrial level. Anticancer drugs modulate their expression (eg through p53-dependent gene transcription), their activity (eg by phosphorylating Bcl-2) and their subcellular localization (eg by inducing the translocation of specific BH3-only pro-apoptotic proteins). Very early after interacting with tumor cells, anticancer drugs also activate lipid-dependent signaling pathways that either increase or decrease cell ability to die by apoptosis. In addition, cytotoxic agents can activate protective pathways that involve activation of NFkappaB transcription factor, accumulation of heat shock proteins such as Hsp27 and activation of proteins involved in cell cycle regulation. This review discusses how modulation of the balance between noxious and protective signals that regulate drug-induced apoptosis could be used to improve the efficacy of current therapeutic regimens in hematological malignancies.

Caspase-3 is activated following axotomy of neonatal facial motoneurons and caspase-3 gene deletion delays axotomy-induced cell death in rodents

In this report, we examined the possible functions of the cell death protease, caspase-3, in the axotomy-induced apoptosis of facial motoneurons in newborn rodents. Using in situ hybridization and Western blot, we found higher levels of caspase-3 mRNA and pro-caspase-3 protein expression in motoneurons of neonatal and 2-week-old rats than adult rats. Following facial motoneuron axotomy, caspase-3 mRNA and protein expression increased in motoneurons of both neonatal and adult rats. However, using an antibody directed to the activated form of the caspase-3 protease, we found that catalytically active caspase-3 was present only in axotomized neonatal motoneurons. As motoneurons in neonatal but not adult rodents are susceptible to axotomy-induced apoptosis, we hypothesized that caspase-3 may play a role in their demise. To determine the necessity of caspase-3 activation in axotomy-induced apoptosis, we counted the number of surviving motoneurons at 4 and 7 days following axotomy in wild type mice and caspase-3 gene-deleted mice. There were nearly three times more surviving motoneurons in caspase-3 gene-deleted mice than in wild type mice at both 4 days (mean 1074 vs. 464, P<0.005) and 7 days (mean 469 vs. 190, P<0.005) following injury, indicating a slower rate of death. Examination of the dying motoneurons using TUNEL staining (for fragmented DNA) and bisbenzimide staining (for nuclear morphology) revealed incomplete nuclear condensation in caspase-3-deficient motoneurons. These results demonstrate that caspase-3 activation plays important roles in the rapid demise of axotomized neonatal motoneurons.

Caspase pathways, neuronal apoptosis, and CNS injury

Caspases are a family of mammalian proteases related to the ced-3 gene of Caenorhabditis elegans. They mediate many of the morphological and biochemical features of apoptosis, including structural dismantling of cell bodies and nuclei, fragmentation of genomic DNA, destruction of regulatory proteins, and propagation of other pro-apoptotic molecules. Based on their substrate specificities and DNA sequence homologies, the 14 currently identified caspases may be divided into three groups: apoptotic initiators, apoptotic executioners, and inflammatory mediators. Caspases are activated through two principal pathways, known as the "extrinsic pathway," which is initiated by cell surface death receptor ligation, and the intrinsic pathway, which arises from mitochondria. Endogenous inhibitors, such as the inhibitors of apoptosis (IAP) family, modulate caspase activity at various points within these pathways. Upon activation, caspases appear to play an important role in sequelae of traumatic brain injury, spinal cord injury, and cerebral ischemia. In addition, they may also play a role in mediating cell death in chronic neurodegenerative conditions such as Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. This article reviews the current literature on the role of caspases in acute and chronic CNS injury, and provides evidence for the potential therapeutic use of caspase inhibitors in the setting of these conditions.

The effect of caffeine on p53-dependent radioresponses in undifferentiated mouse embryonal carcinoma cells after X-ray and UV-irradiations

The effect of caffeine was studied on the radioresponses of undifferentiated mouse embryonal carcinoma cells (EC cells) with or without the functional p53. The radioresponses studied included radiosensitivity, the activation of p53, apoptosis with characteristic DNA ladder formation and cell cycle progression. An undifferentiated mouse EC cell line, ECA2, and a newly established p53-deficient EC cell line, p53 delta, were used in the present study. The status of the p53 gene did not significantly affect the colony survivals of undifferentiated EC cells to X-rays and UV. Although a post-irradiation treatment with caffeine sensitized both lines to X-rays marginally, the sensitization was prominent for UV regardless of the p53 status of the cells. The activation of a p53 responsible lacZ reporter construct was observed in stably transfected ECA2 cells after X-ray and UV irradiations. Caffeine suppressed the X-ray induced activation of the lacZ reporter, while it drastically enhanced the activation after UV irradiation. X-rays and UV readily triggered the apoptosis of ECA2 cells with the characteristic DNA ladder. Although UV-induced DNA ladder formation was enhanced by caffeine, that induced by X-rays was unaffected. Therefore, the effects of caffeine on the p53-dependent radioresponses were found to be agent specific: suppression for the X-ray induced and augmentation for the UV induced. In contrast to p53-proficient ECA2 cells, smear-like DNA degradation was observed for irradiated p53 delta cells, suggesting the presence of a mode of cell death without DNA ladder formation. UV induction of the smear-like DNA degradation was enhanced in the presence of caffeine. Regardless of the state of the p53 gene, G1/S arrest was not observed in X-ray and UV irradiated EC cells. X-ray induced G2/M arrest in both lines, which was abrogated by caffeine, while G2/M arrest after UV was unaffected by a caffeine treatment. These results indicate that the radioresponses of undifferentiated EC cells differ considerably from those of somatic cells, and that these radioresponses were modulated by a post-irradiation treatment with caffeine.

UVC-induced apoptosis in human epithelial tumor A431 cells: sequence of apoptotic changes and involvement of caspase (-8 and -3) cascade

Human epidermoid tumor A431 cells underwent apoptosis following exposure to ultraviolet C (UVC). The apoptosis was of the interphase death type, and mostly occurred within one cell cycle, independent of the cell-cycle phases. We further examined the detailed sequential order of apoptotic changes in cells after UVC exposure and the involvement of caspases using six caspase inhibitors. The loss of mitochondrial transmembrane potential (delta psi m) appeared in the earliest phase; subsequently, the chromatin condensation and DNA-fragmentation occurred. Cell shrinkage and loss of the plasma-membrane integrity, judged by propidium iodide (PI) staining, were observed in the later phase. A broad-spectrum caspase inhibitor, z-VAD-fmk, completely prevented all apoptotic changes, except for the depletion of delta psi m. Both Ac-DEVD-CHO and Ac-IETD-CHO, inhibitors of caspase -3 and -8, respectively, effectively inhibited typical chromatin condensation to almost the same extent. However, the nuclei still showed partial condensation. A caspase -9 inhibitor, Ac-LEHD-CHO, did not prevent chromatin condensation, though it partially inhibited cell-size reduction and PI-stainability. None of the caspase inhibitors could inhibit the delta psi m reduction. These results strongly suggest that the collapse of delta psi m is not a part of the central apoptotic machinery, and that caspase cascade(s), especially caspase-8 to -3, play an important role in UVC-induced apoptosis in A431.

Two distinct pathways leading to nuclear apoptosis

Apaf-1(-/-) or caspase-3(-/-) cells treated with a variety of apoptosis inducers manifest apoptosis-associated alterations including the translocation of apoptosis-inducing factor (AIF) from mitochondria to nuclei, large scale DNA fragmentation, and initial chromatin condensation (stage I). However, when compared with normal control cells, Apaf-1(-/-) or caspase-3(-/-) cells fail to exhibit oligonucleosomal chromatin digestion and a more advanced pattern of chromatin condensation (stage II). Microinjection of such cells with recombinant AIF only causes peripheral chromatin condensation (stage I), whereas microinjection with activated caspase-3 or its downstream target caspase-activated DNAse (CAD) causes a more pronounced type of chromatin condensation (stage II). Similarly, when added to purified HeLa nuclei, AIF causes stage I chromatin condensation and large-scale DNA fragmentation, whereas CAD induces stage II chromatin condensation and oligonucleosomal DNA degradation. Furthermore, in a cell-free system, concomitant neutralization of AIF and CAD is required to suppress the nuclear DNA loss caused by cytoplasmic extracts from apoptotic wild-type cells. In contrast, AIF depletion alone suffices to suppress the nuclear DNA loss contained in extracts from apoptotic Apaf-1(-/-) or caspase-3(-/-) cells. As a result, at least two redundant parallel pathways may lead to chromatin processing during apoptosis. One of these pathways involves Apaf-1 and caspases, as well as CAD, and leads to oligonucleosomal DNA fragmentation and advanced chromatin condensation. The other pathway, which is caspase-independent, involves AIF and leads to large-scale DNA fragmentation and peripheral chromatin condensation.

Caspase-independent commitment phase to apoptosis in activated blood T lymphocytes: reversibility at low apoptotic insult

Little is known about the mechanisms of programmed death triggered in T lymphocytes by stimuli that can bypass caspase activation. Anti-CD2 monoclonal antibody and staurosporine are such apoptosis inducers because they operate in the presence of broad-spectrum caspase inhibitors BOC-D.fmk and Z-VAD.fmk. A system was devised, based on the isolation according to density of activated blood T cells progressively engaged in the apoptotic process. This allowed definition of a sequence of caspase-dependent and caspase-independent apoptogenic events that are triggered by anti-CD2 and staurosporine. Thus, a commitment phase to apoptosis was defined that is entirely caspase independent and that is characterized by cell volume loss, partial chromatin condensation, and release into the cytosol and the nucleus of mitochondrial “apoptosis-inducing factor ” (AIF). Committed cells were viable, displayed a high mitochondrial inner transmembrane potential (▵Ψm), and lacked large-scale and oligonucleosomal DNA fragmentation. Mitochondrial release of AIF was selective because cytochrome c was retained in mitochondria of the very same cells. Mitochondrial release of cytochrome c occurred later, at the onset of the execution phase of apoptosis, concurrently with ▵Ψm collapse, poly (ADP-ribose) polymerase cleavage, and DNA fragmentation. The apoptogenic events of this commitment phase are reversible if the strength of the stimulus is low and of short duration.

The most unkindest cut of all: on the multiple roles of mammalian caspases

The caspases, first discovered almost a decade ago, are intracellular cysteine proteases which have been shown to play an essential role in the initiation and execution phases of apoptotic cell death. Numerous strategies for the activation and inhibition of these 'killer' proteases have evolved, including the regulation of caspase expression and function at the transcriptional and post-translational level, as well as the expression of viral and cellular inhibitors of caspases. Emerging evidence in recent years has also implicated the caspases in various, nonapoptotic aspects of cellular physiology, such as cytokine processing during inflammation, differentiation of progenitor cells during erythropoiesis and lens fiber development, and proliferation of T lymphocytes, thus attesting to the pleiotropic functions of these proteases. The present review aims to discuss the multiple roles of the mammalian caspases with particular emphasis on their activation and regulation in cells of leukemic origin and the attendant possibilities of therapeutic intervention.

Caspase-independent commitment phase to apoptosis in activated blood T lymphocytes: reversibility at low apoptotic insult

Little is known about the mechanisms of programmed death triggered in T lymphocytes by stimuli that can bypass caspase activation. Anti-CD2 monoclonal antibody and staurosporine are such apoptosis inducers because they operate in the presence of broad-spectrum caspase inhibitors BOC-D.fmk and Z-VAD.fmk. A system was devised, based on the isolation according to density of activated blood T cells progressively engaged in the apoptotic process. This allowed definition of a sequence of caspase-dependent and caspase-independent apoptogenic events that are triggered by anti-CD2 and staurosporine. Thus, a commitment phase to apoptosis was defined that is entirely caspase independent and that is characterized by cell volume loss, partial chromatin condensation, and release into the cytosol and the nucleus of mitochondrial “apoptosis-inducing factor ” (AIF). Committed cells were viable, displayed a high mitochondrial inner transmembrane potential (▵Ψm), and lacked large-scale and oligonucleosomal DNA fragmentation. Mitochondrial release of AIF was selective because cytochrome c was retained in mitochondria of the very same cells. Mitochondrial release of cytochrome c occurred later, at the onset of the execution phase of apoptosis, concurrently with ▵Ψm collapse, poly (ADP-ribose) polymerase cleavage, and DNA fragmentation. The apoptogenic events of this commitment phase are reversible if the strength of the stimulus is low and of short duration.

DNA topoisomerase IIalpha interacts with CAD nuclease and is involved in chromatin condensation during apoptotic execution

Apoptotic execution is characterized by dramatic changes in nuclear structure accompanied by cleavage of nuclear proteins by caspases (reviewed in [1]). Cell-free extracts have proved useful for the identification and functional characterization of activities involved in apoptotic execution [2-4] and for the identification of proteins cleaved by caspases [5]. More recent studies have suggested that nuclear disassembly is driven largely by factors activated downstream of caspases [6]. One such factor, the caspase-activated DNase, CAD/CPAN/DFF40 [4,7,8] (CAD) can induce apoptotic chromatin condensation in isolated HeLa cell nuclei in the absence of other cytosolic factors [6,8]. As chromatin condensation occurs even when CAD activity is inhibited, however, CAD cannot be the sole morphogenetic factor triggered by caspases [6]. Here we show that DNA topoisomerase IIalpha (Topo IIalpha), which is essential for both condensation and segregation of daughter chromosomes in mitosis [9], also functions during apoptotic execution. Simultaneous inhibition of Topo IIalpha and caspases completely abolishes apoptotic chromatin condensation. In addition, we show that CAD binds to Topo IIalpha, and that their association enhances the decatenation activity of Topo IIalpha in vitro.