Meis1- and Pbx-mediated apoptosis is caspase dependent. Increasing concentrations of the pan-caspase inhibitor z-VAD-fmk were added to cells transfected with either murine Meis1b (A) or murine Pbx1b (B) and were assayed for cell death. Apoptosis was assayed as previously described. (C-D) Caspase-specific inhibitors were added to cells transfected with murine Meis1b or murine Pbx1b and were assayed for cell death. Results displayed are from the addition of 5 μM of all inhibitors used. (A-D) Transfection efficiency, 36%.