Fig. 3. Rescue of apoptosis using exogenous and endogenous inhibitors. A, proliferation of E1A/ras-transformed cells was assessed 24 h after combined treatment with STP (20 nM) and IR (5 Gy), with or without preincubation with increasing concentrations of Z-VAD-FMK. B, cell proliferation of E1A/ras-transformed MEFs overexpressing bcl-2 (•) and cells carrying only a control vector ({circ}) was measured 24 h after combined treatment with IR (5 Gy) in the presence of increasing doses of STP (5–20 nM). C, caspase-3-like activities were measured in Bcl-2-overexpressing cells ({blacksquare}) and control cells ({square}) as described in the legend to Fig. 2 .