Differential activation of caspase-8 and -9 in myeloma cells expressing wt or mutated p53.

(A) ARP-1 (p53 null), (B) U266 (mutated p53) cells, and (C) IM9 and (D) HS-Sultan (wt p53) cells were cultured with ATO and assayed for apoptosis and for caspase activity using FITC-tagged caspase-specific substrate peptides as described above in the legend to Figure6. For more details, see “Materials and methods.” Bars are ± SD of at least 3 experiments. Note the parallel kinetics between apoptosis and caspase activity in the 4 cell lines and the preferential activation of caspase-9 over caspase-8 in cells with wt p53, although the overall extent of apoptosis in these cells was low.