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Early events in Bcl-2-enhanced apoptosis

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Abstract

Transfection of PC12 pheochromocytoma cells with bcl-2 potentiates apoptosis induced by the antimitotic agent, neocarzinostatin (NCS). The mechanism of potentiation involves caspase 3-dependent cleavage of Bcl-2 to its pro-apoptotic counterpart, but the cellular events proximal to caspase 3 activation in this system are not known. Two min after initiation of NCS treatment, Bax begins to translocate from cytosol to the mitochondria; the mitochondrial localization of Bax persists for 30 min after NCS treatment. At the same time, cytochrome C is released from the mitochondria to cytosol. The mitochondrial membrane potential exhibits differential change in mock- and bcl-2-transfected PC12 cells. In mock-transfected PC12 cells, the mitochondrial membrane potential increases immediately, peaks at 15 min following initiation of NCS treatment, and drops thereafter. In contrast, in bcl-2-transfected PC12 cells, the membrane potential drops immediately following NCS treatment. Caspase 9 is activated and peaks at 10 min in both mock- and bcl-2 transfected PC12 cells, however, the peak activity of caspase 9 is higher and caspase 9 activation lasts longer (30 min) after the treatment in bcl-2 transfectants. Not until 30 min after initiation of a 1 h treatment with NCS is Bcl-2 protein cleaved in bcl-2-transfected cells. Thus, in bcl-2-transfected cells, the mitochondrial membrane potential drops and cytochrome C is released from the mitochondria despite the presence of large amounts of intact mitochondrial Bcl-2. This makes it unlikely that cleavage of Bcl-2 is the only factor involved in potentiation of NCS-induced apoptosis by Bcl-2.

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Authors and Affiliations

  1. Pediatric Center for Neuroscience and Division of Child Neurology, Department of Pediatrics, University of Pittsburgh, Pittsburgh, PA, 15213, USA

    Y. Liang, C. Yan, K. D. Nylander & N. F. Schor

Authors
  1. Y. Liang
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  2. C. Yan
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  3. K. D. Nylander
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  4. N. F. Schor
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Correspondence to N. F. Schor.

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Liang, Y., Yan, C., Nylander, K.D. et al. Early events in Bcl-2-enhanced apoptosis. Apoptosis 8, 609–616 (2003). https://doi.org/10.1023/A:1026135509274

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