Biomedical subjects

E M Creagh

Publications and source records attributed to E M Creagh.

8 recordsLinked to original sources

PubMed2001

Apoptosis-associated release of Smac/DIABLO from mitochondria requires active caspases and is blocked by Bcl-2.

Smac/DIABLO is a mitochondrial protein that potentiates some forms of apoptosis, possibly by neutralizing one or more members of the IAP family of apoptosis inhibitory proteins. Smac has been shown to exit mitochondria and enter the cytosol during apoptosis triggered by UV- or gamma-irradiation. Here, we report that Smac/DIABLO export from mitochondria into the cytosol is provoked by cytotoxic drugs and DNA damage, as well as by ligation of the CD95 death receptor. Mitochondrial efflux of Smac/DIABLO, in response to a variety of pro-apoptotic agents, was profoundly inhibited in Bcl-2-overexpressing cells. Thus, in addition to modulating apoptosis-associated mitochondrial cytochrome c release, Bcl-2 also regulates Smac release, suggesting that both molecules may escape via the same route. However, whereas cell stress-associated mitochondrial cytochrome c release was largely caspase independent, release of Smac/DIABLO in response to the same stimuli was blocked by a broad-spectrum caspase inhibitor. This suggests that apoptosis-associated cytochrome c and Smac/DIABLO release from mitochondria do not occur via the same mechanism. Rather, Smac/DIABLO efflux from mitochondria is a caspase-catalysed event that occurs downstream of cytochrome c release.

Antibiotics, Antineoplastic↗

PubMed2001

CARDINAL, a novel caspase recruitment domain protein, is an inhibitor of multiple NF-kappa B activation pathways.

Proteins possessing the caspase recruitment domain (CARD) motif have been implicated in pathways leading to activation of caspases or NF-kappaB in the context of apoptosis or inflammation, respectively. Here we report the identification of a novel protein, CARDINAL, that contains a CARD motif and also exhibits a high degree of homology to the C terminus of DEFCAP/NAC, a recently described member of the Apaf-1/Nod-1 family. In contrast with the majority of CARD proteins described to date, CARDINAL failed to promote apoptosis or NF-kappaB activation. Rather, CARDINAL potently suppressed NF-kappaB activation associated with overexpression of TRAIL-R1, TRAIL-R2, RIP, RICK, Bcl10, and TRADD, or through ligand-induced stimulation of the interleukin-1 or tumor necrosis factor receptors. Co-immunoprecipitation experiments revealed that CARDINAL interacts with the regulatory subunit of the IkappaB kinase (IKK) complex, IKKgamma (NEMO), providing a molecular basis for CARDINAL function. Thus, CARDINAL is a novel regulator of NF-kappaB activation in the context of pro-inflammatory signals.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Caspases: cellular demolition experts.

Apoptosis is co-ordinated by a family of cysteine proteases, the caspases, that dismantle the cell by targeting a panoply of proteins for limited proteolysis. The mammalian caspase family contains 14 members, a subset of which participates in apoptosis, with the remainder likely to be involved in the processing of pro-inflammatory cytokines. Apical caspase activation events are typically initiated by adaptor molecules that promote caspase aggregation and facilitate caspase autoactivation. In contrast, distal caspase activation events are controlled by caspases activated earlier in the cascade. Many cellular stresses provoke apoptosis by damaging mitochondria which results in the release of factors [such as cytochrome c and SMAC (second mitochondrial-derived activator of caspase)/Diablo] that trigger caspase activation and cell death. Here, we discuss the hierarchical nature of the caspase cascade that is triggered upon the release of mitochondrial cytochrome c into the cytoplasm, and the role of specific caspases within this cascade in targeting proteins for degradation. Finally, feedback amplification loops and important control points within the caspase cascade will be discussed.

Animals↗

PubMed2000

Heat shock protein 70 inhibits caspase-dependent and -independent apoptosis in Jurkat T cells.

Heat shock protein 70 (hsp70) is a stress-inducible protein that prevents apoptosis induced by a wide range of cytotoxic agents by an as yet undefined mechanism. The caspase family of cysteine proteases have been attributed a central role in the execution of apoptosis. However, several cases of caspase-independent apoptosis have been recently reported, suggesting that caspases may not be necessary for apoptosis in all cells. This study examines the protective role of hsp70 in both caspase-dependent and -independent apoptosis. Hydrogen peroxide (H2O2) used at low and high concentrations in Jurkat T cells induces caspase-dependent and -independent apoptosis, respectively. A hsp70-transfected Jurkat clone was used to observe the protection mediated by hsp70 during these two forms of apoptosis. Results reveal that hsp70 inhibits both caspase-dependent and -independent apoptosis. Furthermore, measurement of caspase-3 activity during caspase-dependent apoptosis revealed that caspase activation was inhibited in hsp70 transfectants. Early apoptotic events, such as mitochondrial depolarization, cytochrome c release, and increased intracellular calcium, were demonstrated to be common to both caspase-dependent and -independent H2O2-induced apoptosis. The inhibition of these events by hsp70 suggests that hsp70 may be an important anti-apoptotic regulator, functioning at a very early stage in the apoptotic pathway.

Apoptosis↗

PubMed2000

Heat shock proteins--modulators of apoptosis in tumour cells.

Apoptosis is a genetically programmed, physiological method of cell destruction. A variety of genes are now recognised as positive or negative regulators of this process. Expression of inducible heat shock proteins (hsp) is known to correlate with increased resistance to apoptosis induced by a range of diverse cytotoxic agents and has been implicated in chemotherapeutic resistance of tumours and carcinogenesis. Intensive research on apoptosis over the past number of years has provided significant insights into the mechanisms and molecular events that occur during this process. The modulatory effects of hsps on apoptosis are well documented, however, the mechanisms of hsp-mediated protection against apoptosis remain to be fully defined, although several hypotheses have been proposed. Elucidation of these mechanisms should reveal novel targets for manipulating the sensitivity of leukaemic cells to therapy. This review aims to explain the currently understood process of apoptosis and the effects of hsps on this process. Several proposed mechanisms for hsp protection against apoptosis and the therapeutic implications of hsps in leukaemia are also discussed.

Animals↗

PubMed1999

The antioxidant 4b,5,9b,10-Tetrahydroindeno[1,2-b]indole inhibits apoptosis by preventing caspase activation following mitochondrial depolarization.

Oxidative stress appears to have a central role in the induction of apoptosis following the exposure of cells to a range of cytotoxic insults. The modulation of apoptosis by a diverse range of antioxidants has been reported in many systems. We demonstrate, for the first time, the anti-apoptotic properties of the antioxidant, 4b, 5,9b,10-tetrahydroindeno[1,2-b]indole (THII), in Jurkat T cells subjected to a number of cytotoxic insults. THII was found to inhibit the morphological features of apoptosis in cells treated with the cytotoxic agents camptothecin, actinomycin D and ultraviolet (UV) irradiation. However, THII was unable to inhibit apoptosis induced by anti-Fas IgM. Peroxide and superoxide anion production following UV treatment was monitored, and THII was found to only partially inhibit superoxide anion production. THII was unable to inhibit mitochondrial depolarization in UV, Camptothecin or anti-Fas-treated cells. Further downstream, THII exibited strong inhibition of caspase-3 activation in UV, but not in anti-Fas-treated cells. These results suggest that THII may exert its effects downstream of mitochondrial depolarization, but upstream of caspase-3 activation.

Antioxidants↗

PubMed1999

Selective protection by hsp 70 against cytotoxic drug-, but not Fas-induced T-cell apoptosis.

The phenomenon of heat-shock (HS) protection to many cytotoxic insults has previously been described; however, the specific molecular mechanism underlying this HS-mediated protection remains undefined. To gain insight into this protective mechanism, heat-shocked Jurkat T cells were treated with a range of cytotoxic agents. Those against which HS conferred protection (camptothecin and actinomycin D) were compared with agents against which HS showed no protective effect (anti-Fas monoclonal antibody (mAb)). Reactive oxygen species (ROS) production was found to be an event common to apoptosis induced by camptothecin and actinomycin D, whereas Fas-mediated apoptosis was shown to occur via a ROS-independent mechanism. The selective protection observed against these agents was found to be mimicked by pretreatment with antioxidant compounds. Furthermore, this antioxidant protection appears to be occurring downstream of ROS production. Experiments were extended using heat-shock protein (hsp) 70 gene-transfected Jurkat T cells to confirm that the protective effects observed were caused by hsp 70 synthesis rather than any other cellular response to HS. Bcl-2 expression levels were also examined to determine whether any correlation existed between Bcl-2- and hsp 70-mediated protection.

Antineoplastic Agents↗

PubMed1976

Effects of hypocapnia and hypocapnic alkalosis on cardiovascular function.

Cardiovascular effects of hypocapnia and hypocapnic alkalosis with and without a fluid load were studied in four groups of dogs (group I: fluid load control; group II: fluid load-isolated hypocapnia; group III: fluid load-hypocapnic alkalosis; group IV: no fluid load-hypocapnic alkalosis). Hypocapnic alkalosis was induced by mechanical hyperventilation, and isolated hypocapnia by the simultaneous administration of 0.1 N HCl. Respiratory alkalosis was also studied during administration of a saline fluid load. Cardiac output and stroke volume increased in all groups receiving a fluid load (including isolated hypocapnia and hypocapnic alkalosis groups), but both fell significantly during hypocapnic alkalosis without fluid load. Pulmonary artery wedge pressure rose in groups with hypocapnic alkalosis with fluid load and isolated hypocapnia with fluid load, but did not change significantly with hypocapnic alkalosis without fluid load or in the normocapnic group with fluid load. It is concluded that cardiac output and stroke volume fall in response to hypocapnic alkalosis but both are maintained with a fluid load at the expense of an increased left ventricular preload.

Alkalosis↗