Over-expression of Bcl-2 does not protect cells from hypericin photo-induced mitochondrial membrane depolarization, but delays subsequent events in the apoptotic pathway

FEBS Lett. 1999 Dec 3;462(3):295-301. doi: 10.1016/s0014-5793(99)01538-0.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Apoptosis / radiation effects*
  • Bongkrekic Acid / pharmacology
  • Caspase 3
  • Caspases / metabolism
  • Cell Line
  • Cell Membrane Permeability / radiation effects
  • Cyclosporine / pharmacology
  • Dose-Response Relationship, Radiation
  • Enzyme Activation / radiation effects
  • Fibroblasts / cytology
  • Fibroblasts / enzymology
  • Flow Cytometry
  • Fluoresceins / metabolism
  • Humans
  • Hydrogen-Ion Concentration / radiation effects
  • Intracellular Membranes / metabolism
  • Intracellular Membranes / radiation effects
  • Membrane Potentials / radiation effects
  • Mice
  • Microscopy, Confocal
  • Mitochondria / metabolism*
  • Mitochondria / radiation effects
  • Perylene / analogs & derivatives*
  • Perylene / metabolism
  • Phosphatidylserines / metabolism
  • Photosensitivity Disorders
  • Proto-Oncogene Proteins c-bcl-2 / biosynthesis*
  • Time Factors


  • Fluoresceins
  • Phosphatidylserines
  • Proto-Oncogene Proteins c-bcl-2
  • Bongkrekic Acid
  • Perylene
  • hypericin
  • Cyclosporine
  • CASP3 protein, human
  • Casp3 protein, mouse
  • Caspase 3
  • Caspases
  • fluorexon