Bcl-2 overexpression but not FADD deficiency blocks the caspase cascade induced by proteasome inhibitors. (A) Following a 1-hour preincubation with or without zVAD-fmk (100 μM), Bcl-2-overexpressing or vector control Jurkat cells were stimulated with regular medium, epoxomicin (0.4 μM), or MG132 (0.5 μM) for 12 hours. Cleavage of caspase-3, caspase-8, caspase-9, and PARP was detected using immunoblot analysis. (B) WT and FADD-deficient Jurkat cells were preincubated with zVAD-fmk for 1 hour. Subsequently, cells were stimulated with regular medium or epoxomicin (0.4 μM) for 12 hours. Cleavage of caspase-3, caspase-8, caspase-9, and PARP was detected by immunoblotting.