Lack of cytochrome c-dependent activation of pro–caspase-3 in BL cell lines. (A) S-100 cytosols were prepared from the Jurkat and BL cell lines, and exogenous dATP and cytochrome c (dATP/Cyt c) were introduced to initiate caspase activation. Processing of pro–caspase-3 was determined by Western blotting. (B) Measurement of caspase-3–like enzyme activity by DEVD-AMC cleavage in Jurkat and BL cell lines treated as in panel A. □ indicates S-100 cytosols alone; ▪, with exogenous dATP and cytochrome c. Results are depicted as mean values ± SDs (n = 3). (C) Granzyme B (GrB) processing of pro–caspase-3 remains intact in BL-derived cell lines. S-100 cytosols from a panel of BL cell lines were incubated for 30 minutes with recombinant human granzyme B, and samples were assessed for processing of pro–caspase-3 (using specific anti–caspase-3 antibodies) and for caspase-3–like enzyme activity (D), using the fluorogenic DEVD-AMC substrate. Cytosolic extracts from Jurkat cells were included as a positive control. In D, □ indicates S-100 cytosols alone; ▪, with granzyme B. Results in panel D are depicted as mean values ± SDs (n = 3).