Fig. 6. Strict requirement of caspase-9 for STP-induced radiosensitization. A, formation of active caspase-3 in E1A/ras-transformed caspase 9-deficient cells was determined after the different treatments using an antibody recognizing the cleaved caspase-3 subunit. Compare with Fig. 2 B. B, proliferation in E1A/ras-transformed caspase-9 wild-type cells ({blacksquare}) and caspase-9-deficient cells ({square}) was assessed 24 h after treatment with STP (20 nM), IR (5 Gy), or both in combination.