XIAP inhibition enhances TRAIL-induced mitochondrial perturbations in a caspase-dependent manner. Jurkat leukemia cells were treated for 24 hours with 0.4 ng/mL TRAIL and/or 10 nM XIAP inhibitor 2, control compound, or DMSO and 20 μM zVAD.fmk, 50 μM zDEVD.fmk, or DMSO. Mitochondrial transmembrane potential (A) and cytochrome c release (B) were assessed by FACS analysis. Representative experiments of at least 3 experiments are shown in top panels (dotted line indicates no TRAIL; solid line, TRAIL-treated cells); mean and SD of 3 experiments each performed in duplicate are shown in the bottom panels. For statistical analysis, t test was performed. *P < .01.