Cytochrome c-induced apoptosis is dominant to bcl-2 and activated MAP-KK survival signals and is mediated by caspases. (a) Cytochrome c overrides IL-3, bcl-2, and activated MAP-KK. A2 cells (upper panels) expressing activated MAP-KK and A15 cells (lower panels) coexpressing activated MAP-KK and bcl-2 were electroporated with control protein (left) or bovine cytochrome c at 80 μg/mL (right) and recultured with IL-3. Pre-G1 apoptotic fractions were as follows: A2: control <1%; with cytochrome c 6%; A15: control <1%; with cytochrome c 16%. Apoptotic fractions by direct microscopy are given in Table 2. (b) Cytochrome c-induced apoptosis is dependent on caspases. Bo cells were electroporated with 80 μg/mL apo- or holo-cytochrome c as for Fig 1 and recultured with IL-3, with or without z-Ddcbmk at 50 μg/mL (100 μmol/L). Cells were analyzed after 3 hours. Pre-G1apoptotic fractions were as follows: control cells, 16%; with holo-cytochrome c, 45%; with apo-cytochrome c, 9%; with z-Ddcbmk only, 7%; with holo-cytochrome c and z-Ddcbmk, 4%. z-Ddcmbk abolishes cytochrome c-induced DNA fragmentation. Similar results were obtained with B15, A2, and A15 cells and z-VADfmk (data not shown).