title: Early events in Bcl-2-enhanced apoptosis.
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.
authors.affiliation: Pediatric Center for Neuroscience and Division of Child Neurology, Department of Pediatrics, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Liang
authors.forename: C
authors.initials: C
authors.lastname: Yan
authors.forename: K D
authors.initials: KD
authors.lastname: Nylander
authors.forename: N F
authors.initials: NF
authors.lastname: Schor
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D016716:PC12 Cells; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology*; D051381:Rats; D009353:Zinostatin / Q000494:pharmacology; D051028:bcl-2-Associated X Protein
chemical_list: D000903:Antibiotics, Antineoplastic; C494828:Bax protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D009353:Zinostatin; C506435:Casp9 protein, rat; D053453:Caspase 9; D020169:Caspases