Collapse of the inner mitochondrial transmembrane potential is not required for apoptosis of HL60 cells

Apoptotic cell death involves a series of morphological and biochemical cha nges orchestrated by activated proteases belonging to the caspase family. R ecent studies have suggested that the activation of this process of executi on is dependent upon events associated with the loss of mitochondrial inner transmembrane potential (Delta psi(m)), as a consequence of the formation of the permeability transition (PT) pore. This has led to the proposal that mitochondrial depolarization represents a central irreversible checkpoint in the apoptotic program. Here, we present evidence that HL-60 cells underg o apoptosis in response to the cytotoxic insults of actinomycin-D, etoposid e, and staurosporine without showing significant changes in Delta psi(m) In stead, the loss of Delta psi(m) could be detected only later in the cell de ath pathway. In addition, the uncoupling agent CCCP produced an early mitoc hondrial depolarization in HL-60s but these cells showed few signs of apopt osis up to 8 h after the insult. Furthermore, examination of these cells in response to staurosporine revealed the release of mitochondrial cytochrome c into the cytosol over time, corresponding to caspase activation irrespec tive of mitochondrial depolarization. In summary, our data suggest that the collapse of Delta psi(m) as a consequence of PT is not a universal early m arker for apoptosis and, moreover, it is not part of the central apoptotic machinery. (C) 1999 Academic Press.