ABNORMAL G1 ARREST IN THE CELL-LINES FROM LEC STRAIN RATS AFTER X-IRRADIATION

The effect of X-irradiation of cell lines from LEC and WKAH strain rat s on a progression of cell cycle was investigated. When WKAH rat cells were exposed to 5 Gy of X-rays and their cell cycle distribution was determined by a flow cytometer, the proportion of S-phase cells decrea sed and that of GUM-phase cells increased at 8 hr post-irradiation. At 18 and 24 hr post-irradiation, approximately 80% of the cells appeare d in the G1 phase. On the contrary, the proportion of S-phase cells in creased and that of G1-phase cells decreased in LEC rats during 8-24 h r post-irradiation, compared with that at 0 hr post-irradiation. Thus, radiation-induced delay in the progression from the G1 phase to S pha se (G1 arrest) was observed in WKAH rat cells but not in LEC rat cells . In the case of WKAH rat cells, the intensities of the bands of p53 p rotein increased at 1 and 2 hr after X-irradiation at 5 Gy, compared w ith those of unirradiated cells and at 0 hr post-irradiation. In contr ast, the intensities of the bands were faint and did not significantly increase in LEC rat cells during 0-6 hr incubation after X-irradiatio n. Present results suggested that the radioresistant DNA synthesis in LEC rat cells is thought to be due to the abnormal G1 arrest following X-irradiation.