Potentiation of apoptosis by mitochondria in a cell-free system

Using a cell-free system, we show that rat liver mitochondria, but not mito chondrial extracts, potentiated apoptosis triggered by cytosols derived fro m apoptotic cells. Apoptosis potentiated by mitochondria appeared to be inh ibited by caspase 3 but not by caspase 1 inhibitors. A cytosolic caspase-3- like activity was increased by the addition of mitochondria to apoptotic cy tosols; the latter activation was inhibited by the addition of bcl-2. Chela tion of calcium by EGTA significantly and specifically inhibited the apopto sis potentiated by mitochondria as well as the increase of caspase-3-like a ctivity. The incubation of mitochondria with apoptotic cytosols led to the release of cytochrome c, this latter phenomenon being inhibited by EGTA. Ca lcium or cytochrome c and dATP, however, did not reproduce the mitochondria l potentiation in the absence of the organelle. Thus, mitochondria can init iate and potentiate apoptosis through similar but not identical mechanisms. (C) 1998 Academic Press.