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Involvement of protein kinase C-regulated ceramide generation in inostamycin-induced apoptosis.

Activation of caspases is commonly involved in the apoptosis induced by various anticancer drugs. However, the upstream events leading to the activation of caspases seem to be specific to each anticancer drug. In the present study, we examined the possible involvement of protein kinase C (PKC) and ceramide generation in caspase-3(-like) protease activation induced by inostamycin, a phosphatidylinositol synthesis inhibitor. Treatment of cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA), an activator of PKC, suppressed the release of cytochrome c from mitochondria and the activation of caspase-3(-like) proteases in inostamycin-treated cells, but not in other anticancer drug-treated cells. Inostamycin induced the elevation of intracellular ceramide levels, and fumonisin B1, an inhibitor of ceramide synthase, inhibited inostamycin-induced cytochrome c release, caspase-3(-like) protease activation, and apoptosis. Moreover, TPA also inhibited inostamycin-induced ceramide synthesis. Taken together, our results suggest that inostamycin-induced apoptosis is mediated by PKC-regulated ceramide generation, leading to the activation of a caspase cascade.

Anti-Bacterial Agents↗

Primary pulmonary MALT lymphomas show frequent and heterogeneous cytogenetic abnormalities, including aneuploidy and translocations involving API2 and MALT1 and IGH and MALT1.

API2-MALT1 fusion and aneuploidy are common chromosomal abnormalities in MALT lymphoma. In studying their incidence and relationship in primary pulmonary MALT lymphomas, a translocation involving MALT1 and IGH was also identified. In all, 28 primary pulmonary MALT lymphomas were studied by fluorescence in situ hybridization using an API2-MALT1 probe and multiple centromeric probes, as well as IGH-BCL2, IGH-MALT1, and MALT1 breakapart probes in selected cases. Seven (25%) had API2-MALT1 fusion; all seven lacked aneuploidy except for two with trisomy 3 in a small clone. Three (11%) had IGH-MALT1 fusion; two also showed trisomy 3 and 12. A total of 11 (39%) had aneuploidy only, with trisomy 3 and 18 being the most common. Ectopic nuclear bcl-10 expression, which has been previously associated with API2-MALT1, was seen by immunohistochemistry in 86% of API2-MALT1 fusion-positive cases, one IGH-MALT1 fusion-positive case, two aneuploidy-only cases, and two normal cases. In primary pulmonary MALT lymphomas, cytogenetic abnormalities are common (75%) and heterogeneous, encompassing API2-MALT1 and IGH-MALT1, which are mutually exclusive, as well as aneuploidy, which may be present in the latter but is rare in the former. Ectopic nuclear bcl-10 expression is associated with API2-MALT1 but may also be seen in IGH-MALT1 fusion-positive, aneuploidy-only, and normal cases.

Adaptor Proteins, Signal Transducing↗

Cardiomyocyte apoptosis induced by Galphaq signaling is mediated by permeability transition pore formation and activation of the mitochondrial death pathway.

Expression of the wild-type alpha subunit of Gq stimulates phospholipase C and induces hypertrophy in cardiomyocytes. Addition of Gq-coupled receptor agonists additionally activates phospholipase C, as does expression of a constitutively active mutant form of Galphaq. Under these conditions, hypertrophy is rapidly succeeded by apoptotic cellular and molecular changes, including myofilament disorganization, loss of mitochondrial membrane potential, alterations in Bcl-2 family protein levels, DNA fragmentation, increased caspase activity ( approximately 4-fold), cytochrome c redistribution, and nuclear chromatin condensation in approximately 12% of the cells. We used various interventions to define the molecular relationships between these events and identify potential sites at which these features of apoptosis could be rescued. Treatment with caspase inhibitors prevented DNA fragmentation and promoted myocyte survival; however, cytochrome c release and loss of mitochondrial membrane potential still occurred. In contrast, treatment with bongkrekic acid, an inhibitor of the mitochondrial permeability transition pore, not only prevented DNA fragmentation and reduced nuclear chromatin condensation but also preserved mitochondrial membrane potential and limited cytochrome c redistribution to only approximately 2% of cells. These data demonstrate the central role of mitochondrial membrane potential in initiation of caspase activation and downstream apoptotic events and suggest that preservation of mitochondrial integrity is crucial for prolonging the life and function of cardiomyocytes exposed to pathological levels of stress.

Adenoviridae↗

Persistent infarct-related artery occlusion is associated with an increased myocardial apoptosis at postmortem examination in humans late after an acute myocardial infarction.

BACKGROUND: Myocardial apoptosis persists beyond the acute phases of acute myocardial infarction (AMI) and is associated with left ventricular (LV) remodeling. Infarct-related artery (IRA) patency is considered a favorable prognostic factor after AMI and may be associated with more favorable LV remodeling because of reduced apoptosis at the site of AMI. The aim of this study was to assess the influence of IRA status on apoptotic rate (AR) in the hearts of subjects dying late after AMI. METHODS AND RESULTS: We used colocalization for in situ end-labeling of DNA fragmentation and immunohistochemistry for caspase-3 to calculate the AR at time of death (12 to 62 days after AMI) in 16 hearts with persistently occluded IRAs and in 8 hearts with patent IRAs. No significant differences were found when comparing the clinical characteristics of the 2 groups. Occluded IRA was associated with significantly higher AR at site of infarction (25.8% [interquartile range 20.9% to 28.5%] versus 2.3% [interquartile range 0.6% to 5.0%], P<0.001). This strong correlation between IRA occlusion and AR remained statistically significant even after correction for clinical characteristics such as sex, age, history of previous additional AMI or heart failure, transmural AMI, anterior AMI, fibrinolytic treatment, time from AMI to death, trauma as cause of death, and multivessel coronary disease (P=0.003). CONCLUSIONS: A significantly higher AR was associated with persistent IRA occlusion late post-AMI. These data may suggest that the post-AMI benefits observed with a patent IRA (the "open-artery hypothesis") may in part be due to reduced myocardial apoptosis.

Acute Disease↗

IL-18 regulates IL-1beta-dependent hepatic melanoma metastasis via vascular cell adhesion molecule-1.

Proinflammatory cytokines, including IL-1beta and tumor necrosis factor-alpha (TNF-alpha), promote cancer cell adhesion and liver metastases by up-regulating the expression of vascular cell adhesion molecule-1 (VCAM-1) on hepatic sinusoidal endothelium (HSE). In this study, hepatic metastasis after intrasplenically injected mouse B16 melanoma (B16M) cells was reduced 84-95% in mice with null mutations for either IL-1beta or the IL-1beta-converting enzyme (ICE, caspase-1) compared with wild-type mice. On day 12, 47% of wild-type mice were dead compared with 19% of either IL-1beta or ICE-deficient mice. In vitro, conditioned medium from B16M cells (B16M-CM) induced the release of TNF-alpha and IL-1beta from cultures of primary murine HSE. The effect of B16M-CM on HSE resulted in increased numbers of B16M cells adhering to HSE, which was completely abrogated by a specific inhibitor of ICE, anti-IL-18 or IL-18-binding protein. Exogenous IL-18 added to HSE also increased the number of adhering melanoma cells; however, this was not affected by IL-1 receptor blockade or TNF neutralization but rather by anti-VCAM-1. These results demonstrate a role for IL-1beta and IL-18 in the development of hepatic metastases of B16M in vivo. In vitro, soluble products from B16M cells stimulate HSE to sequentially release TNF-alpha, IL-1beta, and IL-18. The IL-18 cytokine increases expression of VCAM-1 and the adherence of melanoma cells.

Animals↗

Hair cell death in the avian basilar papilla: characterization of the in vitro model and caspase activation.

Caspases are a family of proteases that have been implicated as key mediators of cell death. Although nonspecific inhibition of caspase activation has been reported to prevent mammalian sensory hair cell death, the exact roles of individual caspases during hair cell death are unclear. In other systems, the activation of initiator caspases, such as caspase-8 and caspase-9, can lead to the activation of the effector caspase-3. We have begun to systematically characterize hair cell death in an in vitro system by examining the activation of these specific caspases in degenerating hair cells after acutely damaging the whole avian basilar papilla with gentamicin. Basilar papillae (BP) displayed a dose-dependent hair cell loss after a 24-h treatment with gentamicin at concentrations of 0.1, 0.5, and 2.0 mM. When treated with 0.5 mM gentamicin for 6, 12, or 24 h, hair cells first began to degenerate in the basal third of the BP and damage progressed apically. Supplementation of z-VAD-fmk, a general caspase inhibitor, provided short-term protection against gentamicin-induced hair cell death. Treatment with gentamicin for 6 or 12 h promoted the expression of active caspase-3 and active caspase-9 in many hair cells along the BP as shown by immunohistochemistry. At these time-points, specific fluorescent-labeled peptide substrates detected more active caspase-3, caspase-8, and caspase-9 in gentamicin-treated hair cells relative to controls. Our data indicate that auditory hair cells degenerate as a result of gentamicin exposure in a caspase-dependent manner. Specifically, the upstream caspases, caspase-8 and caspase-9, and the downstream caspase-3 are activated in aminoglycoside-damaged hair cells.

Animals↗

TNF-alpha-induced impairment of mitochondrial integrity and apoptosis mediated by caspase-8 in adult ventricular myocytes.

Tumor necrosis factor (TNF)-alpha has been shown to induce apoptosis in a variety of cell types including cardiac myocytes. Sphingosine/ceramide and nitric oxide have been associated with apoptosis induced by TNF-alpha; however, signaling mechanisms of TNF-alpha-induced apoptosis in cardiac myocytes are not well defined. This study examined whether alterations in mitochondrial integrity are involved in TNF-alpha-induced apoptosis in adult ventricular myocytes (ARVM) and determined the roles of caspase-8 (an upstream mediator of TNF-alpha receptor-associated signaling) in this process. After incubation for 24-48 h in serum-free culture medium, ARVM underwent spontaneous apoptosis, which remained stable and was not affected by Z-IETD-FMK, a selective caspase-8 inhibitor. Meanwhile, exposure to TNF-alpha resulted in an increase in apoptosis that was detectable at 6 h and became significant after 12 h, when compared to time-controls. After 24-h exposure, TNF-alpha increased caspase-8 activities, mitochondrial cytochrome C (Cyt C) release to the cytosol, accompanied by loss of mitochondrial transmembrane potential (delta psi(m)). Inhibition of caspase-8 activation in the presence of Z-IETD-FMK abolished the TNF-alpha-induced increases in mitochondrial Cyt C release, loss of delta psi(m) and apoptosis. Therefore, these results suggest that TNF-alpha-induced increase in apoptosis in ARVM results from caspase-8-dependent impairment of mitochondrial integrity.

Animals↗

Assessment of caspase activity as a possible prognostic factor in acute myeloid leukaemia.

Caspases are one of the key effector molecules in apoptosis. Caspase-3 activity (identified by cleavage of the peptide DEVD) was analysed in bone marrow blasts (minimum 70%) from 45 acute myeloid leukaemia (AML) patients. 12 patients (25%) exhibited high levels of specific DEVDase activity. These blast cells, despite having activated caspase-3, displayed none of the classical caspase-dependent morphological characteristics of apoptosis, such as degradation of DNA fragmentation factor 45, DNA fragmentation, and appeared to be more resistant to drug-induced apoptosis. Our results suggest that in these AML cells, resistance to apoptosis occurred downstream of caspase-3 activation.

Acute Disease↗

Evaluation of oxidative stress based on lipid hydroperoxide, vitamin C and vitamin E during apoptosis and necrosis caused by thioacetamide in rat liver.

After 12 h of thioacetamide (500 mg/kg body weight) administration to rats, the activity of caspase-3-like protease in the liver increased significantly compared to that in the control group. In plasma, the activity of caspase-3 was barely detectable in the control rat, but had increased significantly after 24 h of drug administration along with a dramatic increase in GOT. These results indicate that thioacetamide causes apoptosis in the liver by activating caspase-3, which is released to plasma by successive necrosis. At 24 h, the concentration of liver lipid hydroperoxides, a mediator of radical reaction, was 2.2 times as high as that of control rats. After 12 and 24 h of thioacetamide administration, the liver concentrations of vitamins C and E decreased significantly. The decrease of antioxidants and formation of lipid hydroperoxides 24 h after thioacetamide administration support the view that extensive radical reactions occur in the liver during the necrotic process.

Animals↗

Environmental chemical-induced bone marrow B cell apoptosis: death receptor-independent activation of a caspase-3 to caspase-8 pathway.

Programmed cell death is a critical process in B lymphocyte development. Premature apoptosis in developing B cells could affect the repertoire and number of mature B cells produced. Of particular concern is the ability of environmentally ubiquitous polycyclic aromatic hydrocarbons (PAH) to induce B cell apoptosis within the bone marrow microenvironment in a clonally nonspecific way. Here, models of bone marrow B cell development were used to assess the role of the "extrinsic" apoptosis pathway in PAH-induced apoptosis and to compare PAH-induced apoptosis with that induced during clonal deletion. As demonstrated previously with a nontransformed pro-/pre-B cell line, primary pro-B cells cultured on bone marrow stromal cells underwent apoptosis after exposure to a prototypic PAH, 7,12-dimethylbenz[a]anthracene (DMBA). Apoptosis was preceded by cleavage of caspase-3 (4-6 h) and caspase-8 (6-8 h) and their respective substrates, alpha-fodrin and Bid. Inhibition of caspase-3 blocked caspase-8 activation and apoptosis. Furthermore, a pan-caspase inhibitor blocked apoptosis and activation of both caspases-3 and -8. Cells from mice defective in tumor necrosis factor (TNF)-alpha, TNF-beta, lymphotoxin-beta, or TNFR1, TNFR2, Fas, or death receptor 6 were as susceptible to apoptosis signaling as wild-type cells. These results suggest a complex death receptor-independent B cell apoptosis pathway in which caspase-8 is activated downstream of caspase-3.

Apoptosis↗

Antitumor effect of resveratrol oligomers against human cancer cell lines and the molecular mechanism of apoptosis induced by vaticanol C.

Twenty resveratrol (3,5,4'-trihydroxystilbene) (Res) derivatives, which were isolated from stem bark of Vatica rassak (Dipterocarpaceae), were evaluated for in vitro cytotoxicity against a panel of human tumor cell lines. Among them, seven compounds displayed marked cytotoxicity. Vaticanol C (Vat C) as a major component induced a considerable cytotoxicity in all cell lines tested and exhibited growth suppression in colon cancer cell lines at low dose. Vat C caused two cell lines (SW480 and HL60) to induce cell death at four to seven times lower concentrations, compared with Res. The growth suppression by Vat C was found to be due to apoptosis, which was assessed by morphological findings (nuclear condensation and fragmentation) and DNA ladder formation in the colon cancer cell lines. The apoptosis in SW480 colon cancer cells was executed by the activation of caspase-3, which was shown by western blot and apoptosis inhibition assay. Furthermore, the mitochondrial membrane potential of apoptotic SW480 cells after 12 h treatment with Vat C was significantly lost, and concurrently the cytochrome c release and activation of caspase-9 were also detected by western blot analysis. Over-expression of Bcl-2 protein in SW480 cells significantly prevented the cell death induced by Vat C. Taken together, the findings presented here indicate that Vat C induced marked apoptosis in malignant cells mainly by affecting mitochondrial membrane potential.

Antineoplastic Agents, Phytogenic↗

Roles of p53, c-Myc, Bcl-2, Bax and caspases in glutamate-induced neuronal apoptosis and the possible neuroprotective mechanism of basic fibroblast growth factor.

By using flow-cytometric analysis, we examined the involvement of p53, c-Myc, Bcl-2 and Bax in the glutamate-induced cell death in cultured cortical neurons. The activities of caspase-1-like and caspase-3-like proteases were also measured after the glutamate treatment. The apoptosis rate of the cells increased after 12 h and 24 h treatment with glutamate. The temporal profile of p53, c-Myc, Bcl-2, Bax expression and caspases activation after glutamate treatment suggest that Bcl-2, c-Myc and caspase-3 play important roles in the excitotoxic neuronal cell death. The down-regulation of Bcl-2 may be an important early stage event, which may cause the activation of caspase-3. c-Myc is also involved in the process of apoptosis though its precise role remains elusive. bFGF exhibited the capability to antagonize the neuronal apoptosis caused by glutamate. The antiapoptotic potential of bFGF may result from its attenuating effect on the down-regulation of Bcl-2 induced by glutamate and, subsequently, blockade of apoptosis cascade. This may provide a possible explanation for its neuroprotective effect against ischemic cell death.

Animals↗

Androgen regulation of FLICE-like inhibitory protein gene expression in the rat prostate.

In hope of eventually identifying defects in human prostatic neoplasias that render them insensitive to anti-androgen therapy, we have examined the regulation of components of ligand-induced cell death pathways during castration-induced regression of the prostate. Rat prostates were obtained after surgical castration with or without subsequent androgen replacement. The mRNA levels of genes encoding components of the apoptotic pathway were measured from individual prostates. Whole prostates 1-10 days after castration did not show a significant change in mRNA levels encoding either Fas or FasL, which some studies suggest are necessary for regression to occur. However, the mRNA encoding a catalytically inactive cysteinyl aspartate-specific protease (caspase) analog, FLICE-like inhibitor protein (FLIP), decreases during the first day following castration. In the most apoptotically responsive ventral lobe of the rat prostate, the reduction in FLIP mRNA levels is evident within 12 h of castration. The mRNA levels of the principal target of FLIP inhibition, caspase-8, do not change during the period preceding the onset of detectable DNA fragmentation. Androgen administration to castrated rats reverses prostate regression, and restores FLIP mRNA to normal levels. By acting as an inhibitor of caspase-8, FLIP may protect prostatic epithelium from apoptosis. Androgen withdrawal, by reducing FLIP mRNA levels, might leave the cells vulnerable to as yet unidentified cell death signals.

Androgens↗

Apoptosis and Bcl-2 expression in the livers of patients with steatohepatitis.

OBJECTIVES: Apoptosis may play a role in the pathogenesis of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH). In this study, we investigated the modulation of apoptosis-related liver proteins in steatohepatitis. METHODS: Hepatocyte apoptosis was evaluated by the TUNEL assay in liver tissue of 12 patients with NASH, 12 with ASH and in histologically normal controls. In addition, caspase-3 processing was evaluated by immunoblot analysis. Expression of death receptors, Bcl-2 family members, and NF-kappaB inhibitor (IkappaB) were determined by western blot. Liver biopsies were also graded for inflammation and fibrosis. RESULTS: Apoptotic hepatocytes were markedly increased in NASH (P<0.05) and ASH (P<0.001) as compared to controls. Active caspase-3 was also elevated in steatohepatitis (P<0.01), coinciding with upregulation of pro-apoptotic Bax (P<0.001). Further, production of tumour necrosis factor-receptor 1 was increased up to 4-fold (P<0.05). Degradation of IkappaB increased >70% in steatohepatitis (P<0.001). Notably, Bcl-2 was also strongly expressed (>100-fold; P<0.001). These data were significantly correlated with relative degrees of portal and lobular inflammation. CONCLUSION: The results show that liver injury in NASH and ASH is associated with apoptosis and NF-kappaB activation. Anti-apoptotic Bcl-2 is strongly expressed, probably reflecting an adaptive response to obesity or alcohol-related stress.

Adult↗

Antitumor activity of novel indirubin derivatives in rat tumor model.

PURPOSE: The novel indirubin derivatives 5'-nitro-indirubinoxime, 5'-fluoro-indirubinoxime, and 5'-trimethylacetamino-indirubinoxime were designed and tested for antitumor activity both in vitro and in vivo using rat tumor model. EXPERIMENTAL DESIGN: Three-week-old male Sprague-Dawley rats were inoculated s.c. on the left flank with 10(7) RK3E-ras rat kidney epithelial cells harboring k-ras gene. Alternatively, 5 x 10(6) RK3E-ras cells were injected into the oral mucosa. Indirubin derivative treatment began on the 3rd or 6th day after oral or s.c. cell injection, respectively. Indirubin derivatives were directly injected into the tumor every other day for a total of five times. Animals were monitored daily and tumor volume was measured by caliper. RESULTS: Indirubin derivatives showed potent antiproliferative activity on various human cancer cells and oncogenic RK3E-ras rat kidney cells, with IC(50) ranging from 1 to 12 mumol/L. Treatment with indirubin derivatives induced the activation of caspase-7 followed by apoptosis in RK3E-ras cells. Indirubin derivatives showed strong antitumor activity in rat solid and oral tumor models. Direct injection of indirubin derivatives every other day for 10 days induced significant inhibition of tumor growth in Sprague-Dawley rats bearing RK3E-ras-induced tumors. Histologically, treatment with indirubin derivatives caused significant inhibition of tumor formation with increased apoptosis and decreased tumor cell proliferation. CONCLUSIONS: Our data showed that novel indirubin derivatives 5'-nitro-indirubinoxime, 5'-fluoro-indirubinoxime, and 5'-trimethylacetamino-indirubinoxime effectively arrested the tumor growth by inhibiting cell proliferation and inducing apoptosis. These findings provide the potential value of indirubin derivatives as novel candidates for antitumor agents.

Animals↗

Glucagon-like peptide 1 inhibits cell apoptosis and improves glucose responsiveness of freshly isolated human islets.

The peptide hormone, glucagon-like peptide 1 (GLP-1), has been shown to increase glucose-dependent insulin secretion, enhance insulin gene transcription, expand islet cell mass, and inhibit beta-cell apoptosis in animal models of diabetes. The aim of the present study was to evaluate whether GLP-1 could improve function and inhibit apoptosis in freshly isolated human islets. Human islets were cultured for 5 d in the presence, or absence, of GLP-1 (10 nm, added every 12 h) and studied for viability and expression of proapoptotic (caspase-3) and antiapoptotic factors (bcl-2) as well as glucose-dependent insulin production. We observed better-preserved three-dimensional islet morphology in the GLP-1-treated islets, compared with controls. Nuclear condensation, a feature of cell apoptosis, was inhibited by GLP-1. The reduction in the number of apoptotic cells in GLP-1-treated islets was particularly evident at d 3 (6.1% apoptotic nuclei in treated cultures vs. 15.5% in controls; P < 0.01) and at d 5 (8.9 vs. 18.9%; P < 0.01). The antiapoptotic effect of GLP-1 was associated with the down-regulation of active caspase-3 (P < 0.001) and the up-regulation of bcl-2 (P < 0.01). The effect of GLP-1 on the intracellular levels of bcl-2 and caspase-3 was observed at the mRNA and protein levels. Intracellular insulin content was markedly enhanced in islets cultured with GLP-1 vs. control (P < 0.001, at d 5), and there was a parallel GLP-1-dependent potentiation of glucose-dependent insulin secretion (P < 0.01 at d 3; P < 0.05 at d 5). Our findings provide evidence that GLP-1 added to freshly isolated human islets preserves morphology and function and inhibits cell apoptosis.

Apoptosis↗

Induction mechanism of apoptosis by troglitazone through peroxisome proliferator-activated receptor-gamma in gastric carcinoma cells.

BACKGROUND: It has been reported recently that the antidiabetic thiazolidinediones not only induce fibroblast differentiation but also inhibit the growth of carcinoma cells. MATERIALS AND METHODS: In the present study, in order to elucidate the further mechanism of growth inhibition by troglitazone, the expression of cell cycle regulators and apoptotic regulators were examined by cDNA microarrays and Western blot analysis by gastric carcinoma cells. RESULTS: Six gastric carcinoma cell lines (TMK-1, MKN-1,7,28,45,74) were treated with 0.1, 1, 10, 100 microM of troglitazone in vitro. The growth of 5 cell lines were inhibited by troglitazone in a time- and dose-dependent manner. Interestingly, the expression of cyclin D mRNA and protein was decreased and that of p27 was increased in TMK-1 cells at 12 hours after troglitazone treatment, suggesting the induction of cell cycle arrest of the cells. On the other hand, DNA ladder formation was observed at 12 hours after treatment. Moreover, the expression of cytochrome C, caspases 3 and 8 and PARP genes was increased after treatment and the gradual reduction of Bcl-XL protein was observed, which indicate that the apoptotic signals were induced after treatment by troglitazone. CONCLUSION: These results suggest that the thiazolidinediones can be a new therapeutic tool for gastric carcinoma via cell cycle regulation and apoptosis.

Antineoplastic Agents↗

Staurosporine induces apoptosis through both caspase-dependent and caspase-independent mechanisms.

Sensitivity of tumor cells to anticancer therapy depends on the ability of the drug to induce apoptosis. However, multiple signaling pathways control this induction and thus determine this sensitivity. We report here that staurosporine, a well known inducer of apoptosis in a wide range of cell lines, displays distinct ability to trigger apoptosis in two different L1210 sublines (termed L1210/S and L1210/0). Staurosporine treatment resulted in an early cell death (within 3 h) in L1210/S cells, while in L1210/0 cells, death occurred only after 12 h. In both instances, death occurred by apoptosis. A broad spectrum caspase inhibitor, Z-VAD-fmk, blocked early apoptosis in L1210/S cells but did not confer any protection on late apoptosis in L1210/0 cells. Protection by Z-VAD-fmk observed in L1210/S cells was not lasting and unmasked a secondary process of cell death that also exhibited characteristics of apoptosis. Thus, staurosporine induces apoptotic cell death through at least two redundant parallel pathways. These two pathways normally coexist in L1210/S cells. However, the early cell death mechanism depending on caspase activation disguises the late caspase-independent apoptotic process. Staurosporine-induced apoptosis in L1210/0 cells develops only by the caspase-independent mechanism due to a general defect in caspase activation.

Amino Acid Chloromethyl Ketones↗