MITOCHONDRIAL PERMEABILITY TRANSITION IS A CENTRAL COORDINATING EVENTOF APOPTOSIS

In a number of experimental systems, the early stage of the apoptotic process, i.e., the stage that precedes nuclear disintegration, is char acterized by the breakdown of the inner mitochondrial transmembrane po tential (Delta Psi(m)). This Delta Psi(m) disruption is mediated by th e opening of permeability transition (PT) pores and appears to be crit ical for the apoptotic cascade, since it is directly regulated by Bcl- 2 and since mitochondria induced to undergo PT in vitro become capable of inducing nuclear chromatinolysis in a cell-free system of apoptosi s. Here, we addressed the question of which apoptotic events are secon dary to mitochondrial PT. We tested the effect of a specific inhibitor of PT, bongkrekic acid (BA), a ligand of the mitochondrial adenine nu cleotide translocator, on a prototypic model of apoptosis: glucocortic oid-induced thymocyte death. In addition to abolishing the apoptotic D elta Psi(m) disruption, BA prevents a number of phenomena linked to ap optosis: depletion of nonoxidized glutathione, generation of reactive oxygen species, translocation of NF kappa B, exposure of phosphatidyls erine residues on the outer Plasma membrane, cytoplasmic vacuolization , chromatin condensation, and oligonucleosomal DNA fragmentation. BA i s also an efficient inhibitor of p53-dependent thymocyte apoptosis ind uced by DNA damage. These data suggest that a number of apoptotic phen omena are secondary to PT. In addition, we present data indicating tha t apoptotic Delta Psi(m) disruption is secondary to transcriptional ev ents. These data connect the PT control point to the p53- and ICE/Ced 3-regulated control points of apoptosis and place PT upstream of nucle ar and plasma membrane features of PCD.