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 rats 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 decreased and that of G2/M-phase cells increased at 8 hr post-irradiation. At 18 and 24 hr post-irradiation, approximately 80% of the cells appeared in the G1 phase. On the contrary, the proportion of S-phase cells increased and that G1-phase cells decreased in LEC rats during 8-24 hr post-irradiation, compared with that at 0 hr post-irradiation. Thus, radiation-induced delay in the progression from the G1 phase to S phase (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 protein increased at 1 and 2 hr after X-irradiation at 5 Gy, compared with those of unirradiated cells and at 0 hr post-irradiation. In contrast, the intensities of the bands were faint and did not significantly increase in LEC rat cells during 0-6 hr incubation after X-irradiation. 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.