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ABSTRACT: The intracellular ATP concentration decides on the onset of either apoptosis or necrosis in Jurkat cells exposed to death stimuli. Bcl-2 can block apoptotic demise, which occurs preferably under conditions of high cellular ATP levels. Here, we investigated the effects of Bcl-2 on the necrotic type of cell demise that prevails under conditions of energy loss. ATP levels were modulated by using mitochondrial inhibitors, such as rotenone or S-nitrosoglutathione, in medium either lacking glucose or supplemented with glucose to stimulate glycolytic ATP generation. Under conditions of ATP depletion, staurosporine (STS) induced >90% necrosis in vector control-transfected cells, whereas bcl-2-transfected cells were protected. Thus, the antiapoptotic protein Bcl-2 can reduce the overall amount of cell death in ATP-depleted cells regardless whether it occurs by apoptosis or necrosis. Cytochrome c release, normally preceding STS-induced necrosis, was also inhibited by Bcl-2. However, Bcl-2 did not prevent an initial STS-induced drop of the mitochondrial membrane potential (ΔΨm). Therefore, the mechanisms whereby Bcl-2 prevents cell death and favors retention of cytochrome c in the mitochondria require neither the maintenance of mitochondrial ΔΨ nor the maintenance of normal ATP levels.
Experimental Cell Research 01/2001; · 3.58 Impact Factor
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ABSTRACT: Under pathological conditions, the mode of cell death, apoptosis or necrosis, is relevant for the subsequent fate of the tissue. Cell demise may be shaped by endogenous mediators such as nitric oxide (NO) which interfere with subroutines of the death program. Here we show that apoptosis of Jurkat cells elicited by either staurosporine (STS) or anti-CD95 antibodies in glucose-free medium is converted to necrosis by NO donors. In the presence of NO, release of mitochondrial cytochrome c was delayed and activation of execution caspases was prevented. Stimulated cells died nonetheless. The switch in the mode of cell death was due to NO-dependent failure of mitochondrial energy production. Restoration of intracellular ATP by glucose supplementation recovered the cells' ability to activate caspases and undergo apoptosis. In this system, the apoptosis/necrosis conversion promoted by NO was not mediated by cyclic guanosine monophosphate-dependent mechanisms, poly-(ADP-ribose)-polymerase (PARP) activation, or inhibition of caspases due to S-nitrosylation and glutathione depletion. In contrast, depleting intracellular ATP with rotenone, an inhibitor of mitochondrial complex I mimicked the effect of NO. The findings presented here suggest that NO can decide the shape of cell death by lowering intracellular ATP below the level required to allow the coordinated execution of apoptosis.
Experimental Cell Research 07/1999; · 3.58 Impact Factor
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ABSTRACT: The endogenous mediator nitric oxide (NO) blocked apoptosis of Jurkat cells elicited by staurosporine, anti-CD95 or chemotherapeutics, and switched death to necrosis. The switch in the mode of cell death was dependent on the ATP loss elicited by NO. This affected two distinct steps of the apoptotic cascade. First, the release of cytochromecfrom mitochondria was delayed by NO. Second, processing of procaspases-3/7 to the active proteases was prevented even after cytochrome c had been released. Thus, NO interferes with execution steps of apoptosis both upstream and downstream of cytochromecrelease.
Biochemical and Biophysical Research Communications 05/1999; · 2.48 Impact Factor
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Barbara. Single
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ABSTRACT: Cytochrome c (Cyt c) is located within the mitochondrial intermembrane space, and it is an essential constituent of the respiratory chain. The translocation of Cyt c from mitochondria to the cytosol is an important step in the apoptotic signaling pathway, linking mitochondrial changes to the activation of execution caspases (Liu et al, 1996). Once translocated into the cytosol, Cyt c together with Apaf-1 and procaspase-9 form a multiprotein complex, the apoptosome, which initiates the activation of caspase-3 (Li P et al, 1997). Studies in cell-free sytems have shown that addition of Cyt c to cytosols directly activates caspase-3, whereas immunodepletion of Cyt c from cell homogenates prevents caspase-3 activation. Furthermore, microinjection of Cyt c into intact cells has been shown to induce apoptosis (Li F et al, 1997). Although Cyt c release has been observed in many experimental models of apoptosis, the mechanism of translocation across the outer mitochondrial membrane is unclear. One question is whether Cyt c release occurs by a selective transport mechanism into the cytosol, or by a nonselective change of permeability in the outer mitochondrial membrane. To distinguish between these two possibilities, we monitored the translocation of Cyt c and of the mitochondrial intermembrane space marker adenylate kinase (ADK).
First publ. in: Cell Death and Differentiation 12 (1998), 5, pp. 1001-1003.
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ABSTRACT: Apoptosis and necrosis are two forms of cell death that have been defined on the basis of distinguishable morphological criteria. However, these different types of cell death may involve several common signalling and execution mechanisms. Since various stimuli induce both apoptotic and necrotic death, the mode of cell demise seems to be dependent on intracellular factors. One of these factors is the concentration of ATP. By modulating ATP levels, apoptosis or necrosis can be triggered selectively under otherwise identical conditions. By controlling ATP levels in staurosporine treated Jurkat cells, apoptotic (but not necrotic) cell death was detected selectively, and was quantitated with high sensitivity by the BM Cell Death Detection ELISA or by staining with annexin V.
First publ. in: Biochemica 2 (1998), pp. 25-28.
