Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.22.61 (caspase-8)
 6,833 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Signaling through the CD95/Fas/APO-1 death receptor plays a critical role in the homeostasis of the immune system. RICK, a novel protein kinase that regulates CD95-mediated apoptosis was identified and characterized. RICK is composed of an N-terminal serine-threonine kinase catalytic domain and a C-terminal region containing a caspase-recruitment domain. RICK physically interacts with CLARP, a caspase-like molecule known to bind to Fas-associated protein with death domain (FADD) and caspase-8. Expression of RICK promoted the activation of caspase-8 and potentiated apoptosis induced by Fas ligand, FADD, CLARP, and caspase-8. Deletion mutant analysis revealed that both the kinase domain and caspase-recruitment domain were required for RICK to promote apoptosis. Significantly, expression of a RICK mutant in which the lysine of the putative ATP-binding site at position 38 was replaced by a methionine functioned as an inhibitor of CD95-mediated apoptosis. Thus, RICK represents a novel kinase that may regulate apoptosis induced by the CD95/Fas receptor pathway.
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PMID:RICK, a novel protein kinase containing a caspase recruitment domain, interacts with CLARP and regulates CD95-mediated apoptosis. 957 81

Cytolytic granule-mediated target cell killing is effected in part through synergistic action of the membrane-acting protein perforin and serine proteases such as granzymes A (GrA) or B (GrB). In the present study we examine GrA cellular entry and nuclear uptake in intact mouse myeloid FDC-P1 cells exposed to perforin using confocal laser scanning microscopy, as well as reconstitute GrA nuclear uptake in vitro. GrA alone was found to be able to enter the cytoplasm of intact cells but did not accumulate in nuclei. In the presence of perforin, it specifically accumulated in the cell nuclei, with maximal levels about 2.5 times those in the cytoplasm after 2. 5 hours. In vitro, GrA accumulated in the nucleus and nucleolus maximally to levels that were four- and sixfold, respectively, those in the cytoplasm. In contrast, the active form of the apoptotic cysteine protease CPP32 did not accumulate in nuclei in vitro. Nuclear/nucleolar import of GrA in vitro was independent of ATP and not inhibitable by the non-hydrolyzable GTP analog GTPgammaS, but was dependent on exogenously added cytosol. Importantly, GrA was found to be able to accumulate in the nucleus of semi-intact cells in the presence of the nuclear envelope-permeabilizing detergent CHAPS, implying that the mechanism of nuclear accumulation was through binding to insoluble factors in the nucleus. GrB was found for the first time to be similar in this regard. The results support the contention that GrA and GrB accumulate in the nucleus through a novel nuclear import pathway, and that this is integral to induction of the nuclear changes associated with cytolytic granule-mediated apoptosis.
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PMID:Nuclear targeting of the serine protease granzyme A (fragmentin-1). 970 63

Apoptosis is induced by different stimuli, among them triggering of the death receptor CD95, staurosporine, and chemotherapeutic drugs. In all cases, apoptosis is mediated by caspases, although it is unclear how these diverse apoptotic stimuli cause protease activation. Two regulatory pathways have been recently identified, but it remains unknown whether they are functionally independent or linked to each other. One is mediated by recruitment of the proximal regulator caspase-8 to the death receptor complex. The other pathway is controlled by the release of cytochrome c from mitochondria and the subsequent ATP-dependent activation of the death regulator apoptotic protease-activating factor 1 (Apaf-1). Here, we report that both pathways can be dissected by depletion of intracellular ATP. Prevention of ATP production completely inhibited caspase activation and apoptosis in response to chemotherapeutic drugs and staurosporine. Interestingly, caspase-8, whose function appeared to be restricted to death receptors, was also activated by these drugs under normal conditions, but not after ATP depletion. In contrast, inhibition of ATP production did not affect caspase activation after triggering of CD95. These results suggest that chemotherapeutic drug-induced caspase activation is entirely controlled by a receptor-independent mitochondrial pathway, whereas CD95-induced apoptosis can be regulated by a separate pathway not requiring Apaf-1 function.
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PMID:Differential regulation and ATP requirement for caspase-8 and caspase-3 activation during CD95- and anticancer drug-induced apoptosis. 973 Aug 99

Brief periods of in vitro hypoxia/ischemia induce apoptosis of cultured renal epithelial cells, but the underlying mechanisms remain unknown. We show that partial ATP depletion (approximately 10-65% of control) results in a duration-dependent induction of apoptosis in Madin-Darby canine kidney (MDCK) cells, as evidenced by internucleosomal DNA cleavage (DNA laddering and in situ nick end labeling), morphological changes (cell shrinkage), and plasma membrane alterations (externalization of phosphatidylserine). The ATP-depleted cells display a significant upregulation of Fas, Fas ligand, and the Fas-associating protein with death domain (FADD). Exogenous application of stimulatory Fas monoclonal antibodies also induces apoptosis in nonischemic MDCK cells, indicating that they retain Fas-dependent pathways of programmed cell death. Furthermore, cleavage of poly(ADP)ribose polymerase (PARP) is evident after ATP depletion, indicating activation of caspases. Indeed, the apoptotic cells display a significant increase in caspase-8 (FLICE) activity. Finally, apoptosis induced by ATP depletion is ameliorated by pretreatment with inhibitors of caspase-8 (IETD), caspase-1 (YVAD), or caspase-3 (DEVD) but is not affected by inhibitors of serine proteases (TPCK). Our results indicate that partial ATP depletion of MDCK cells results in apoptosis and that Fas- and caspase-mediated pathways may play a critical role.
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PMID:Partial ATP depletion induces Fas- and caspase-mediated apoptosis in MDCK cells. 1036 72

Caspase activation plays a central role in the execution of apoptosis. The key components of the biochemical pathways of caspase activation have been recently elucidated. In this review, we focus on the two most well-studied pathways of caspase activation: the cell surface death receptor pathway and the mitochondria-initiated pathway. In the cell surface death receptor pathway, activation of caspase-8 following its recruitment to the death-inducing signaling complex (DISC) is the critical event that transmits the death signal. This event is regulated at several different levels by various viral and mammalian proteins. Activated caspase-8 can activate downstream caspases by direct cleavage or indirectly by cleaving Bid and inducing cytochrome c release from the mitochondria. In the mitochondrial-initiated pathway, caspase activation is triggered by the formation of a multimeric Apaf-1/cytochrome c complex that is fully functional in recruiting and activating procaspase-9. Activated caspase-9 will then cleave and activate downstream caspases such as caspase-3, -6, and -7. This pathway is regulated at several steps, including the release of cytochrome c from the mitochondria, the binding and hydrolysis of dATP/ATP by Apaf-1, and the inhibition of caspase activation by the proteins that belong to the inhibitors of apoptosis (IAP).
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PMID:Biochemical pathways of caspase activation during apoptosis. 1061 63

Activation of initiator and effector caspases, mitochondrial changes involving a reduction in its membrane potential and release of cytochrome c (cyt c) into the cytosol, are characteristic features of apoptosis. These changes are associated with cell acidification in some models of apoptosis. The hierarchical relationship between these events has, however, not been deciphered. We have shown that somatostatin (SST), acting via the Src homology 2 bearing tyrosine phosphatase SHP-1, exerts cytotoxic action in MCF-7 cells, and triggers cell acidification and apoptosis. We investigated the temporal sequence of apoptotic events linking caspase activation, acidification, and mitochondrial dysfunction in this system and report here that (i) SHP-1-mediated caspase-8 activation is required for SST-induced decrease in pH(i). (ii) Effector caspases are induced only when there is concomitant acidification. (iii) Decrease in pH(i) is necessary to induce reduction in mitochondrial membrane potential, cyt c release and caspase-9 activation and (iv) depletion of ATP ablates SST-induced cyt c release and caspase-9 activation, but not its ability to induce effector caspases and apoptosis. These data reveal that SHP-1-/caspase-8-mediated acidification occurs at a site other than the mitochondrion and that SST-induced apoptosis is not dependent on disruption of mitochondrial function and caspase-9 activation.
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PMID:Caspase-8-mediated intracellular acidification precedes mitochondrial dysfunction in somatostatin-induced apoptosis. 1073 62

In cultured cerebrocortical neurons, mild excitotoxic insults or staurosporine result in apoptosis. We show here that N-methyl-d-aspartate (NMDA) receptor-mediated, but not staurosporine-mediated, apoptosis is preceded by depolarization of the mitochondrial membrane potential (Deltapsi(m)) and ATP loss. Both insults, however, release cytochrome c (Cyt c) into the cytoplasm. What prompts mitochondria to release Cyt c and the mechanism of release are as yet unknown. We examined the effect of inhibition of the adenine nucleotide translocator (ANT), a putative component of the mitochondrial permeability transition pore. Inhibition of the mitochondrial ANT with bongkrekic acid (BA) prevented NMDA receptor-mediated apoptosis of cerebrocortical neurons. Concomitantly, BA prevented Deltapsi(m) depolarization, promoted recovery of cellular ATP content, and blocked caspase-3 activation. However, in the presence of BA, Cyt c was still released. Because BA prevented NMDA-induced caspase-3 activation and apoptosis, the presence of Cyt c in the neuronal cytoplasm is not sufficient for the induction of caspase activity or apoptosis. In contrast to these findings, BA was ineffective in preventing staurosporine-induced activation of caspases or apoptosis. Additionally, staurosporine-induced, but not NMDA-induced, apoptosis was associated with activation of caspase-8. These results indicate that, in cerebrocortical cultures, excessive NMDA receptor activation precipitates neuronal apoptosis by means of mitochondrial dysfunction, whereas staurosporine utilizes a distinct pathway.
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PMID:Mitochondrial and extramitochondrial apoptotic signaling pathways in cerebrocortical neurons. 1081 98

We investigated the cytotoxic responsiveness of 40 cell lines derived from representatives of the Ewing's sarcoma family of tumours (ESFT), i.e., Ewing's sarcoma (ES), peripheral primitive neuroectodermal tumour (pPNET) and Askin tumour (AT), to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Incubation with TRAIL at 100 ng/ml induced cell death at 24 hr in 19 of 26 ES, 11 of 12 pPNET and 2 of 2 AT cell lines. Half-maximal cell death concentrations (IC(50) values) varied from 0.1 to 20 ng/ml. TRAIL displayed potent cytotoxic activity against freshly derived ESFT cell isolates. Cytotoxicity was associated with phosphatidylserine expression and internucleosomal DNA fragmentation, features characteristic of apoptosis. The apoptotic programme in the sensitive ESFT VH-64 cell line revealed TRAIL-induced activation of FLICE/MACH1 (caspase-8) and CPP32/Yama/apopain (caspase-3) and processing of the prototype caspase substrate poly(ADP-ribose) polymerase. In addition, TRAIL provoked a collapse of the mitochondrial transmembrane potential (DeltaPsi(m)), parallelled by a reduction in ATP levels and release of cytochrome c from mitochondria into the cytosol. Inhibition of caspase-8 and caspase-3 by zIETDfmk and zDEVDfmk, respectively, substantially prevented TRAIL-induced apoptosis. However, zIETDfmk, but not zDEVDfmk, reduced TRAIL-mediated DeltaPsi(m) dissipation, indicating that TRAIL causes mitochondrial dysfunction through caspase-8 acting upstream of mitochondria. While macromolecule synthesis inhibitors (actinomycin D, cycloheximide) augmented susceptibility to TRAIL in TRAIL-responsive cell lines, these agents did not render TRAIL-resistant cell lines susceptible to TRAIL. However, the proteasome inhibitor MG132 sensitised to TRAIL in resistant cell lines. Collectively, these results show that TRAIL initiates effective death in the vast majority (80%) of cell lines derived from ESFT. Since TRAIL provoked cell death in ESFT ex vivo, this cytokine may be a promising drug for the treatment of ESFT in vivo.
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PMID:Apoptotic responsiveness of the Ewing's sarcoma family of tumours to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). 1100 77

The recruitment and cleavage of pro-caspase-8 to produce the active form of caspase-8 is a critical biochemical event in death receptor-mediated apoptosis. However, the source of pro-caspase-8 available for activation by apoptotic triggers is unknown. In human fibroblasts and mouse clonal striatal cells, confocal microscopy revealed that pro-caspase-8 immunofluorescence was colocalized with cytochrome c in mitochondria and was also distributed diffusely in some nuclei. Biochemical analysis of subcellular fractions indicated that pro-caspase-8 was enriched in mitochondria and in nuclei. Pro-caspase-8 was found in the intermembrane space, inner membrane, and matrix of mitochondria after limited digestion of mitochondrial fractions, and this distribution was confirmed by immunogold electron microscopy. Pro-caspase-8 and cytochrome c were released from isolated mitochondria that were treated with an inhibitor of the ADP/ATP carrier atractyloside, which opens the mitochondria permeability transition pore. Release was blocked by the mitochondria permeability transition pore inhibitor cyclosporin A (CsA). After clonal striatal cells were exposed for 6 h to an apoptotic inducer tumor necrosis factor-alpha (TNF-alpha), mitochondria immunoreactive for cytochrome c and pro-caspase-8 became clustered at perinuclear sites. Pro-caspase-8 and cytochrome c levels decreased in mitochondrial fractions and increased, along with pro-caspase-8 cleavage products, in the cytoplasm of the TNF-alpha-treated striatal cells. CsA blocked the TNF-alpha-induced release of pro-caspase 8 but not cytochrome c. Internucleosomal DNA fragmentation started at 6 h and peaked 12 h after TNF-alpha treatment. These results suggest that pro-caspase-8 is predominantly localized in mitochondria and is released upon apoptotic stimulation through a CsA-sensitive mechanism.
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PMID:Pro-caspase-8 is predominantly localized in mitochondria and released into cytoplasm upon apoptotic stimulation. 1110 41

Caspase-8 is a proximal effector protein of the tumor necrosis factor receptor family death pathway. In the present human postmortem study, we observed a significantly higher percentage of dopaminergic (DA) substantia nigra pars compacta neurons that displayed caspase-8 activation in Parkinson's disease (PD) patients compared with controls. In an in vivo experimental PD model, namely subchronically 1,2,3,6-tetrahydropyridine-treated mice, we also show that caspase-8 is indeed activated after exposure to this toxin early in the course of cell demise, suggesting that caspase-8 activation precedes and is not the consequence of cell death. However, cotreatment of 1-methyl-4-phenylpyridinium-intoxicated primary DA cultures with broad-spectrum and specific caspase-8 inhibitors did not result in neuroprotection but seemed to trigger a switch from apoptosis to necrosis. We propose that this effect is related to ATP depletion and suggest that the use of caspase inhibitors in pathologies linked to intracellular energy depletion, such as PD, should be cautiously evaluated.
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PMID:Caspase-8 is an effector in apoptotic death of dopaminergic neurons in Parkinson's disease, but pathway inhibition results in neuronal necrosis. 1126


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