Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.22.62 (caspase-9)
 7,507 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent progress in studies on apoptosis has revealed that cytochrome c is a pro-apoptotic factor. It is released from its places on the outer surface of the inner mitochondrial membrane at early steps of apoptosis and, combining with some cytosolic proteins, activates conversion of the latent apoptosis-promoting protease pro-caspase-9 to its active form. Cytochrome c release can be initiated by the pro-apoptotic protein Bax. This process is blocked by the anti-apoptotic proteins Bcl-2 and Bcl-xL. The role of cytochrome c in apoptosis may be understood within the framework of the concept assuming that the evolutionary primary function of apoptosis was to purify tissues from ROS-overproducing cells. In this context, the pro-apoptosis activity of cytochrome c might represent one of the anti-oxidant functions inherent in this cytochrome. Among other cytochrome c-linked antioxidant mechanisms, the following systems can be indicated. (1) Cytochrome c released from the inner mitochondrial membrane to the intermembrane space can operate as an enzyme oxidizing O2.- back to O2. The reduced cytochrome c is oxidized by cytochrome oxidase (or in yeasts and bacteria, by cytochrome c peroxidase). (2) The intermembrane cytochrome c can activate the electron transport chain in the outer mitochondrial membrane. This bypasses the initial and middle parts of the main respiratory chain, which produce, as a rule, the major portion of ROS in the cell. (3) The main respiratory chain losing its cytochrome c is inhibited in such a fashion that antimycin-like agents fail to stimulate ROS production.
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PMID:Cytochrome c in the apoptotic and antioxidant cascades. 951 23

To identify human proteins that bind to the Smac and caspase-9 binding pocket on the baculoviral inhibitor of apoptosis protein (IAP) repeat 3 (BIR3) domain of human XIAP, we used BIR3 as an affinity reagent, followed by elution with the BIR3 binding peptide AVPIA, microsequencing, and mass spectrometry. The mature serine protease Omi (also known as HtrA2) was identified as a mitochondrial direct BIR3-binding protein and a caspase activator. Like mature Smac (also known as Diablo), mature Omi contains a conserved IAP-binding motif (AVPS) at its N terminus, which is exposed after processing of its N-terminal mitochondrial targeting sequence upon import into the mitochondria. Mature Omi is released together with mature Smac from the mitochondria into the cytosol upon disruption of the outer mitochondrial membrane during apoptosis. Finally, mature Omi can induce apoptosis in human cells in a caspase-independent manner through its protease activity and in a caspase-dependent manner via its ability to disrupt caspase-IAP interaction. Our results provide clear evidence for the involvement of a mitochondrial serine protease in the apoptotic pathway, emphasizing the critical role of the mitochondria in cell death.
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PMID:Identification of Omi/HtrA2 as a mitochondrial apoptotic serine protease that disrupts inhibitor of apoptosis protein-caspase interaction. 1160 97

The proto-oncogene Bcl-2 is expressed in membranes of mitochondria and endoplasmic reticulum and mediates resistance against a broad range of apoptotic stimuli. Although several mechanisms of Bcl-2 action have been proposed, its role in different cellular organelles remains elusive. Here, we analyzed the function of Bcl-2 targeted specifically to certain subcellular compartments in Jurkat cells. Bcl-2 expression was restricted to the outer mitochondrial membrane by replacing its membrane anchor with the mitochondrial insertion sequence of ActA (Bcl-2/MT) or the ER-specific sequence of cytochrome b5 (Bcl-2/ER). Additionally, cells expressing wild-type Bcl-2 (Bcl-2/WT) or a transmembrane domain-lacking mutant (Bcl-2/DeltaTM) were employed. Apoptosis induced by ionizing radiation or by the death receptors for CD95L or TRAIL was analyzed by determination of the mitochondrial membrane potential (DeltaPsi(m)) and activation of different caspases. Bcl-2/WT and Bcl-2/MT strongly inhibited radiation-induced apoptosis and caspase activation, whereas Bcl-2/DeltaTM had completely lost its anti-apoptotic effect. Interestingly, Bcl-2/ER conferred protection against radiation-induced mitochondrial damage and apoptosis similarly to Bcl-2/MT. The finding that ER-targeted Bcl-2 interfered with mitochondrial DeltaPsi(m) breakdown and caspase-9 activation indicates the presence of a crosstalk between both organelles in radiation-induced apoptosis. By contrast, Bcl-2 in either subcellular position did not influence CD95- or TRAIL-mediated apoptosis.
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PMID:Wild-type, mitochondrial and ER-restricted Bcl-2 inhibit DNA damage-induced apoptosis but do not affect death receptor-induced apoptosis. 1173 49

Methylglyoxal (MG) is an endogenous metabolite that increases in the blood and tissues of diabetic patients and is believed to be linked to the development of chronic complications of diabetes. We showed previously that Jurkat cells treated with MG rapidly undergo apoptosis via c-Jun N-terminal kinase (JNK) activation. In this study, we examined whether phorbol 12-myristate 13-acetate (PMA) can prevent MG-induced apoptosis in Jurkat cells. The results showed the following: 1) PMA can prevent MG-induced apoptosis; 2) triggering of this antiapoptotic signal depends on the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) pathway; 3) PMA inhibits MG-induced activation of caspase-3 and caspase-9, release of cytochrome c, and decline of mitochondrial membrane potential, but it does not affect MG-induced JNK activation; 4) the ERK pathway modulates outer mitochondrial membrane permeability and regulates the mitochondrial death machinery; and 5) activated ERK prevents JNK-induced leakage of cytochrome c from isolated mitochondria. Taken together, these results suggest that PMA-induced ERK activation can protect Jurkat cells from methylglyoxal-induced apoptosis and that activated ERK exerts its antiapoptotic effects on mitochondria by inhibiting activated JNK-induced permeabilization of the outer mitochondrial membrane.
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PMID:Phorbol 12-myristate 13-acetate protects Jurkat cells from methylglyoxal-induced apoptosis by preventing c-Jun N-terminal kinase-mediated leakage of cytochrome c in an extracellular signal-regulated kinase-dependent manner. 1497 57

During apoptosis, a key event is the release of Smac/DIABLO (an inhibitor of XIAP) and cytochrome c (Cyt-c, an activator of caspase-9) from mitochondria to cytosol. It was not clear, however, whether the releasing mechanisms of these two proteins are the same. Using a combination of single living-cell analysis and immunostaining techniques, we investigated the dynamic process of Smac and Cyt-c release during UV-induced apoptosis in HeLa cells. We found that YFP-labeled Smac and GFP-labeled Cyt-c were released from mitochondria in the same time window, which coincided with the mitochondrial membrane potential depolarization. Furthermore, using immunostaining, we found that the endogenous Smac and Cyt-c were always released together within an individual cell. Finally, when cells were pre-treated with caspase inhibitor (z-VAD-fmk) to block caspase activation, the process of Smac release, like that of Cyt-c, was not affected. This was true for both YFP-labeled Smac and endogenous Smac. These results suggest that in HeLa cells, both Smac and Cyt-c are released from mitochondria during UV-induced apoptosis through the same permeability transition mechanism, which we believe is triggered by the aggregation of Bax in the outer mitochondrial membrane to form lipid-protein complex.
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PMID:Smac/DIABLO and cytochrome c are released from mitochondria through a similar mechanism during UV-induced apoptosis. 1584 90

Mannheimia haemolytica is a key pathogen in the bovine respiratory disease complex. It produces a leukotoxin (LKT) that is an important virulence factor, causing cell death in bovine leukocytes. The LKT binds to the beta(2) integrin CD11a/CD18, which usually activates signaling pathways that facilitate cell survival. In this study, we investigated mechanisms by which LKT induces death in bovine lymphoblastoid cells (BL-3). Incubation of BL-3 cells with a low concentration of LKT results in the activation of caspase-3 and caspase-9 but not caspase-8. Similarly, the proapoptotic proteins Bax and BAD were significantly elevated, while the antiapoptotic proteins Bcl-2, Bcl(XL) and Akt-1 were downregulated. Following exposure to LKT, we also observed a reduction in mitochondrial cytochrome c and corresponding elevation of cytosolic cytochrome c, suggesting translocation from the mitochondrial compartment to the cytosol. Consistent with this observation, tetramethylrhodamine ethyl ester perchlorate staining revealed that mitochondrial membrane potential was significantly reduced. These data suggest that LKT induces apoptosis of BL-3 cells via a caspase-9-dependent mitochondrial pathway. Furthermore, scanning electron micrographs of mitochondria from LKT-treated BL-3 cells revealed lesions in the outer mitochondrial membrane, which are larger than previous reports of the permeability transition pore through which cytochrome c is usually released.
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PMID:Mannheimia haemolytica leukotoxin induces apoptosis of bovine lymphoblastoid cells (BL-3) via a caspase-9-dependent mitochondrial pathway. 1611 66

The role of the cyclin-dependent kinase (CDK) inhibitor p21 as a mediator of p53-induced growth arrest is well established. In addition, recent data provide strong evidence for new emerging functions of p21, including a role as a modulator of apoptosis. The mechanisms, however, by which p21 interferes with the death machinery, especially following ionizing radiation (IR), are largely unknown. Here, we report that IR induced caspase-9 and caspase-3 activation and subsequent apoptosis only in p21-deficient colon carcinoma cells, whereas similar treated wild-type cells were permanently arrested in the G(2)-M phase, correlating with the induction of cellular senescence. Interestingly, activation of the mitochondrial pathway, including caspase-2 processing, depolarization of the outer mitochondrial membrane, and cytochrome c release, was achieved by IR in both cell lines, indicating that p21 inhibits an event downstream of mitochondria but preceding caspase-9 activation. IR-induced p21 protein expression was restricted to the nucleus, and no evidence for a mitochondrial or cytoplasmic association was found. In addition, p21 did neither interact with caspase-3 or caspase-9, suggesting that these events are not required for the observed protection. Consistent with this assumption, we found that CDK inhibitors potently abrogated IR-induced caspase processing and activation without affecting mitochondrial events. In addition, in vitro caspase activation assays yielded higher caspase-3 activities in extracts of irradiated p21-deficient cells compared with extracts of similar treated wild-type cells. Thus, our results strongly indicate that p21 protects cells from IR-induced apoptosis by suppression of CDK activity that seems to be required for activation of the caspase cascade downstream of the mitochondria.
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PMID:p21 blocks irradiation-induced apoptosis downstream of mitochondria by inhibition of cyclin-dependent kinase-mediated caspase-9 activation. 1714 70

Apoptosis represents a physiological form of cell death, the perturbation of which may contribute to the development of several diseases connected with accumulation of unwanted cells or excessive cell loss. We have previously shown that the continuous presence of low concentrations of H2O2 (generated by the action of glucose oxidase) was able to inhibit caspase-mediated apoptosis in Jurkat cells. The main purpose of the present study was to elucidate the exact molecular mechanism(s) underlying this inhibitory action of H2O2. The results presented show that events like outer mitochondrial membrane permeabilization, release of cytochrome c from mitochondria, oligomerization of Apaf-1, and recruitment of procaspase-9 to apoptosomes were taking place normally, but further advancement toward activation of the execution caspases was interrupted when H2O2 was present during the apoptotic process. From the results presented in this work, it emerges that the inhibition of procaspase-9 autoactivation was probably due to the reversible oxidation of sensitive cysteine residues in this molecule. Remarkably, caspase-9 activation and the ensuing caspase cascade proceeded normally in the presence of H2O2 under conditions of iron deprivation, indicating that the inhibition of procaspase-9 activation was an iron-dependent process. Collectively, these results highlighted the potential role of available intracellular iron ions in signaling mechanisms related to apoptotic cell death.
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PMID:Hydrogen peroxide inhibits caspase-dependent apoptosis by inactivating procaspase-9 in an iron-dependent manner. 1793 82

Activation of Bax following diverse cytotoxic stress has been shown to be an essential gateway to mitochondrial dysfunction and activation of the intrinsic apoptotic pathway characterized by cytochrome c release with caspase-9/-3 activation. Interestingly, c-Myc has been reported to promote apoptosis by destabilizing mitochondrial integrity in a Bax-dependent manner. Stress-induced activation of caspase-2 may also induce permeabilization of mitochondria with activation of the intrinsic death pathway. To test whether c-Myc and caspase-2 cooperate to activate Bax and thereby mediate intrinsic apoptosis, small interfering RNA was used to efficiently knock down the expression of c-Myc, caspase-2, and Apaf-1, an activating component in the apoptosome, in two human cancer cell lines, lung adenocarcinoma A-549 and osteosarcoma U2-OS cells. Under conditions when the expression of endogenous c-Myc, caspase-2, or Apaf-1 is reduced 80-90%, cisplatin (or etoposide)-induced apoptosis is significantly decreased. Biochemical studies reveal that the expression of c-Myc and caspase-2 is crucial for cytochrome c release from mitochondria during cytotoxic stress and that Apaf-1 is only required following cytochrome c release to activate caspases-9/-3. Although knockdown of c-Myc or caspase-2 does not affect Bax expression, caspase-2 is important for cytosolic Bax to integrate into the outer mitochondrial membrane, and c-Myc is critical for oligomerization of Bax once integrated into the membrane.
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PMID:c-Myc and caspase-2 are involved in activating Bax during cytotoxic drug-induced apoptosis. 1837 82

2-Chloro-2'-deoxyadenosine (CdA; cladribine) is a chemotherapeutic agent used in the treatment of certain leukemias. However, the signalling events that govern CdA-mediated cytotoxicity in leukemia cells remain unclear. We show here that CdA treatment caused Jurkat human T leukemia cells to die via apoptosis in a dose- and time-dependent fashion. Bcl-2 overexpression protected Jurkat T leukemia cells from CdA-induced apoptosis and loss of mitochondrial transmembrane potential (Delta Psi m). Furthermore, mitochondria that were isolated from Jurkat T leukemia cells and then exposed to CdA showed a loss of Delta Psi m, indicating that CdA directly compromised outer mitochondrial membrane integrity. CdA treatment of Jurkat T leukemia cells resulted in the activation of caspase-3, -8, and -9, while inhibition of these caspases prevented the CdA-induced loss of Delta Psi m, as well as DNA fragmentation. In addition, caspase-3 inhibition prevented caspase-8 activation while caspase-8 inhibition prevented caspase-9 activation. Death receptor signalling was not involved in CdA-induced apoptosis since cytotoxicity was not affected by FADD-deficiency or antibody neutralization of either Fas ligand or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Taken together, these data suggested that CdA-induced apoptosis in Jurkat T leukemia cells was mediated via a caspase-3-dependent mitochondrial feedback amplification loop. CdA treatment also increased p38 mitogen-activated protein (MAPK) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation in Jurkat T leukemia cells. Although ERK1/2 inhibition did not affect CdA-mediated cytotoxicity, inhibition of p38 MAPK had an enhancing effect, which suggested a cytoprotective function for p38 MAPK. Agents that inhibit p38 MAPK might therefore increase the effectiveness of CdA-based chemotherapy.
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PMID:2-Chloro-2'-deoxyadenosine-induced apoptosis in T leukemia cells is mediated via a caspase-3-dependent mitochondrial feedback amplification loop. 1849 95


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