Radiation-induced apoptosis and cell cycle progression in TP53-deficient human leukemia cell line HL-60

Human promyelocytic leukemia (HL-60) cells were irradiated with 0.5-100 Gy of gamma radiation and studied for 48 h post irradiation to determine the m ode of death and progression of cells through the phases of the cell cycle. HL-60 cells are much more sensitive to radiation-induced loss of clonogeni city (D-0 = 2.2 Gy) than to induction of apoptosis at 6 h (D-0 for nonapopt otic cells = 32.6 Gy). After doses 20-50 Gy, the onset of massive apoptosis occurred and nonapoptotic cells were in G(1)/G(0) phase of the cell cycle. In contrast, 6 h after irradiation with doses 2.5-10 Gy maximum cells were in S-phase and 16-24 h after irradiation were arrested in Gz-phase. Maximu m apoptosis occurred 48 h after irradiation with doses 3.5-10 Gy, and cells that died by necrosis were found in 9-44%.