BCL-2 PROTECTS MURINE ERYTHROLEUKEMIA-CELLS FROM P53-DEPENDENT AND -INDEPENDENT RADIATION-INDUCED CELL-DEATH

To better understand the molecular basis of radiation-induced cell dea th, we studied the role of the bcl-2 oncogene and the p53 tumor suppre ssor gene in this process, A temperature-sensitive mutant of murine p5 3 (p53(Val-135)) and/or bcl-2 was transfected into murine erythroleuke mia cells (MEL, DP16-1, which are null in p53), We demonstrate that ra diation-induced cell death occurs by both p53-dependent and -independe nt pathways and overexpression of bcl-2 modulates both pathways, When viability was measured 24 h post-radiation, cells that had been briefl y exposed to wtp53 immediately after X-ray irradiation had decreased s urvival as compared to unirradiated cells expressing wtp53 or X-ray ir radiated DP16-1 cells, However, at later times X-ray irradiated parent al DP16-1 cells also had decreased survival compared to the unirradiat ed control. This decrease in survival began 48 h following radiation. Bcl-2 prevented radiation-induced cell death in DP16-1 cells expressin g wtp53 and delayed radiation-induced cell death in DP16-1 cells witho ut wtp53, X-ray irradiated cells expressing wtp53 displayed microscopi c and biochemical characteristics consistent with cell death due to ap optosis, DP16-1 cells which were untransfected or co-transfected with wtp53 and bcl-2 displayed characteristics of cells undergoing necrosis , These results suggest that radiation-induced cell death occurs by bo th p53-dependent and p53-independent pathways, The p53-dependent pathw ay results in cell death via apoptosis and occurs approximately 24 h f ollowing radiation, The p53-independent pathway does not appear to inv olve apoptosis and occurs at a later time, starting 48 h after X-ray e xposure, Thus, bcl-2 protects cells from p53-dependent radiation-induc ed apoptotic cell death and attenuates p53-independent radiation-induc ed cell death.