Increased mitochondrial cytochrome c levels and mitochondrial hyperpolarization precede camptothecin-induced apoptosis in Jurkat cells

Mitochondria play a central role in apoptosis through release of cytochrome c and activation of caspases, In the present study, we showed that, in Jur kat human T cells, camptothecin-induced apoptosis is preceded by (i) an inc rease in cytochrome c and subunit IV of cytochrome c oxidase (COX IV) level s in mitochondria; and (ii) an elevation of the mitochondrial membrane pote ntial (Delta Psi (m)). These events are followed by cytochrome c release in to the cytosol, cytochrome c and COX IV depletion from mitochondria, extern alization of phosphatidylserine (PS), disruption of Delta Psi (m),, caspase activation, poly(ADP-ribose)polymerase cleavage and DNA fragmentation. The pan-caspase inhibitor z-VAD.fmk blocked camptothecin-induced PS externaliz ation, disruption of Delta Psi (m) and DNA fragmentation, suggesting that t hese events are mediated by caspase activation. In contrast, z-VAD did not prevent cytochrome c release, despite preventing cytochrome c and COX IV de pletion from mitochondria, Together, these data suggest that mitochondrial cytochrome c and COX IV enrichment are early events preceding the onset of apoptosis and that cytochrome c release is upstream of caspase activation a nd loss of Delta Psi (m). Furthermore, prevention by z-VAD of cytochrome c and COX IV depletion in mitochondria suggests the possibility that a caspas e-like activity in mitochondria is involved in the proteolytic depletion of respiratory chain proteins. Activation of this activity may play an import ant role in drug-induced apoptosis.