bongkrekic-acid and hypericin

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.

Topics: 3T3 Cells; Animals; Anthracenes; Apoptosis; Bongkrekic Acid; Caspase 3; Caspases; Cell Line; Cell Membrane Permeability; Cyclosporine; Dose-Response Relationship, Radiation; Enzyme Activation; Fibroblasts; Flow Cytometry; Fluoresceins; Humans; Hydrogen-Ion Concentration; Intracellular Membranes; Membrane Potentials; Mice; Microscopy, Confocal; Mitochondria; Perylene; Phosphatidylserines; Photosensitivity Disorders; Proto-Oncogene Proteins c-bcl-2; Time Factors