Intracellular acidification during apoptosis can occur in the absence of a nucleus.

During apoptosis, DNA fragmentation and intracellular acidification occur concurrently. Previous results have shown that intracellular acidification is not required for DNA fragmentation, while the alternative, that acidification is a consequence of DNA fragmentation was analyzed here. To obviate the requirement of any nuclear function in acidification, apoptosis was induced by staurosporine in cytoplasts made from the breast tumor cell line MDA-MB-468. Both cells and cytoplasts demonstrated externalization of phosphatidylserine that was prevented by the pan-caspase inhibitor zVAD-fluoromethylketone or by expression of Bcl-2. Intracellular acidification was observed in both cells and cytoplasts and this was also inhibited by both zVAD-fluoromethylketone and Bcl-2. These results show that intracellular acidification and DNA fragmentation are independent consequences of caspase action during apoptosis. Copyright 1999 Academic Press.