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 death, we studied the role of the bcl-2 oncogene and the p53 tumor suppressor gene in this process, A temperature-sensitive mutant of murine p53 (p53(Val-135)) and/or bcl-2 was transfected into murine erythroleukemia cells (MEL, DP16-1, which are null in p53), We demonstrate that radiation-induced cell death occurs by both p53-dependent and -independent pathways and overexpression of bcl-2 modulates both pathways, When viability was measured 24 h post-radiation, cells that had been briefly exposed to wtp53 immediately after X-ray irradiation had decreased survival as compared to unirradiated cells expressing wtp53 or X-ray irradiated DP16-1 cells, However, at later times X-ray irradiated parental DP16-1 cells also had decreased survival compared to the unirradiated control. This decrease in survival began 48 h following radiation. Bcl-2 prevented radiation-induced cell death in DP16-1 cells expressing wtp53 and delayed radiation-induced cell death in DP16-1 cells without wtp53, X-ray irradiated cells expressing wtp53 displayed microscopic and biochemical characteristics consistent with cell death due to apoptosis, 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 both p53-dependent and p53-independent pathways, The p53-dependent pathway results in cell death via apoptosis and occurs approximately 24 h following radiation, The p53-independent pathway does not appear to involve apoptosis and occurs at a later time, starting 48 h after X-ray exposure, Thus, bcl-2 protects cells from p53-dependent radiation-induced apoptotic cell death and attenuates p53-independent radiation-induced cell death.