title: Over-expression of Bcl-2 does not protect cells from hypericin photo-induced mitochondrial membrane depolarization, but delays subsequent events in the apoptotic pathway.
abstract: Hypericin (HY) is a powerful photo-inducer of apoptosis in Jurkat cells as measured by caspase-3 activation, cell shrinkage, phosphatidylserine (PS) exposure and the appearance of hypoploid DNA. These processes are preceded by rapid Bcl-2-independent mitochondrial transmembrane depolarization and a drop in cytoplasmic pH. Pre-incubation of cells with inhibitors of the mitochondrial permeability transition pore, such as cyclosporin A or bongkrekic acid, does not protect cells from mitochondrial membrane potential (deltapsim) decrease. However, monitoring of mitochondrial entrapped calcein by confocal fluorescence imaging gives clear evidence of HY photo-induced mitochondrial permeability. This should be considered as the result of a non-specific alteration of mitochondrial membrane integrity brought about by lipid peroxidation. Nevertheless, synthesis of the anti-apoptotic protein Bcl-2 appears to delay the subsequent time course of PS exposure and to reduce caspase-3 activation and the fraction of cells which become hypoploid. We interpret this partially protective effect as the consequence of a direct interaction of Bcl-2 with cytosolic cytochrome c previously released from mitochondria upon deltapsim decrease and/or of Bcl-2 inhibition of the deleterious retro-effect of caspase-3 on the mitochondrial permeability transition pore and/or the mitochondrial membrane components.
authors.affiliation: Laboratoire de Physicochimie Biomoléculaire et Cellulaire (CNRS ESA 7033), Université P. et M. Curie, Paris, France.
authors.forename: R
authors.initials: R
authors.lastname: Chaloupka
authors.forename: P X
authors.initials: PX
authors.lastname: Petit
authors.forename: N
authors.initials: N
authors.lastname: Israël
authors.forename: F
authors.initials: F
authors.lastname: Sureau
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000873:Anthracenes; D017209:Apoptosis / Q000528:radiation effects*; D001865:Bongkrekic Acid / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000528:radiation effects; D016572:Cyclosporine / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation / Q000528:radiation effects; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D005434:Flow Cytometry; D005452:Fluoresceins / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D007425:Intracellular Membranes / Q000378:metabolism / Q000528:radiation effects; D008564:Membrane Potentials / Q000528:radiation effects; D051379:Mice; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism* / Q000528:radiation effects; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010787:Photosensitivity Disorders; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D013997:Time Factors
chemical_list: D000873:Anthracenes; D005452:Fluoresceins; D010718:Phosphatidylserines; D019253:Proto-Oncogene Proteins c-bcl-2; D001865:Bongkrekic Acid; D010569:Perylene; C004965:hypericin; D016572:Cyclosporine; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; C007740:fluorexon