Down-regulation of DNA-PKcs/pAkt in TRAIL-treated metastatic cancer cells and prevention of caspase-3 dependent DNA-PKcs cleavage by suppression of c-Myc in the cells. (A) The cell lysates obtained from PC3 and PC3-MM2 cells (left) treated with TRAIL (2 or 10 ng/ml for 6 h) or KM12 and KM12L4A cells (right) treated with TRAIL (5 or 25 ng/ml for 8 h) were subjected to Western blot analysis to monitor the levels of DNA-PKcs and its CF, phosphorylated Akt Ser473 (pAkt) and total Akt (tAkt). Actin was used as a loading control. (B) PC3-MM2 cells were transfected with siRNA against c-myc or scrambled siRNA as a control. After 48 h, the transfectants were treated with TRAIL (1 or 5 ng/ml) for 6 h and were subjected to Western blot analysis to monitor the changed levels of c-Myc and DNA-PKcs (left). The cell lysates of PC3-MM2 cells treated with TRAIL (5 ng/ml) for 4 h were subjected to Western blot analysis to monitor levels of caspase-3, DNA-PKcs, PARP and their CFs. Some samples were pretreated with 50 μM Z-DEVD-FMK, a specific caspase-3 inhibitor, for 2 h (right).