Degradation of DNA-PKcs by caspase-3 is a late event in apoptosis induced by proteasome inhibition in PC-3 cells. Representative (n = 3) western blot of lysates from PC-3 prostate cancer cells after 3, 6 and 24 hours incubation with MG-132 (50 μM) or Velcade (100 nM) using a specific antibody against human DNA-PKcs. The antibody recognizes the intact 460 kDa protein as well as the specific 160 kDa fragment observed after caspase-3 dependent cleavage of DNA-PKcs. MG-132 caused no significant change of the DNA-PKcs protein levels over a period of 6 hours. Detection of a caspase-3-cleavage specific 160 kDa fragment coincided with apoptosis at 24 hours, but did not occur during the first 6 hours.