Abstract
Radiation-induced G1 checkpoint activation plays a pivotal role in initiating irreversible G1 arrest in cells that have persistent chromatin damage. The ATM-p53-p21 pathway is critical for the initial activation of G1 checkpoint, however, its involvement in the maintenance of G1 arrest remains to be determined. In this study, we hypothesized a signal stabilization mechanism to maintain G1 arrest. To prove this, normal human diploid cells were synchronized in G0 phase, irradiated with 10 Gy of gamma rays, and released immediately following irradiation. Twelve hours after irradiation, the ATM kinase inhibitor, KU55933, was administrated. Cells were fixed at 24 hours, and the percentage of cells in S phase was determined by EdU incorporation. The percentages of EdU positive cells was decreased from 24.6% to 4.8 % by 10 Gy irradiation, while similar decrease was observed in KU55933 treated cells. Then, cells were incubated for up to 96 hours after irradiation with KU55933. We found that continuous inactivation of ATM gradually abandoned G1 arrest. These results indicate that ATM-dependent signal is involved in the maintenance of G1 arrest.
