Ku affects the ATM-dependent S phase checkpoint following ionizing radiation

Abstract

Following exposure to genotoxic stress, proliferating cells actively slow down DNA replication through an S phase checkpoint to provide time for repair. The ATM-dependent pathway plays an important role in the S phase checkpoint response following ionizing irradiation. We report that there is a stronger S phase checkpoint response in irradiated Ku80 7/7 cells as compared with their wild-type counterparts, which has no relationship to DNA-dependent protein kinase (DNA-PK) activity but correlates with a higher ATM activity and with more ATM bound to chromatin DNA in such cells. Wortmannin, a nonspecific inhibitor of ATM, not only reduces the higher activity of ATM kinase, but also abolishes the stronger S phase checkpoint response in Ku80 7/7 cells. Furthermore, a specific ATM antisense oligonucleotide abolishes the stronger S checkpoint response in Ku80 7/7 cells and renders these cells practically indistinguishable from Ku80 +/+ cells for this endpoint. These results in aggregate indicate that the stronger S checkpoint in irradiated Ku80 7/7 cells is due to the higher ATM kinase activity.

Suppression of DNA-PKcs and Ku80 individually and in combination: Different effects of radiobiology in HeLa cells

“…While HeLa cells inhibited Ku80 and DNA-PKcs both individually or in combination, they were arrested in the S phase at 4 h after 6 Gy irradiation, confirmed results reported previously (35). Similar to reasons explained above, the DSB repair was compensated by the HR repair pathway when the NHEJ proteins were inhibited, so the cells were arrested in the S phase in order to allow the DSBs to be repaired by the HR protein that plays a main role in the late S and G2/M phases (6,7,35).…”

Chloroethylnitrosourea-induced cell death and genotoxicity: Cell cycle dependence and the role of DNA double-strand breaks, HR and NHEJ

“…Furthermore, the Ku70/Ku80 dimer has been reported to compete with the ATM kinase for binding to the damaged DNA, thus influencing the regulation of S and G 2 checkpoints. 40 Finally, Ku80 was shown to recruit BRCA1 to sites of DSB. 41 As BRCA1 is a mediator of the HR function of Rad51, 42 lack of Ku80 may have impact also on HR on blocked replication forks.…”

An Overactivated ATR/CHK1 Pathway Is Responsible for the Prolonged G2 Accumulation in Irradiated AT Cells

“…ATM could be activated from a trans-acting process immediately by changes in the structure of chromatin induced by DSBs (50). Alternately, ATM could be activated from combination of a trans-acting (changes in the structure of chromatin) and a cis-acting (DNA-binding) process that either through ATM directly binding to DNA DSBs (51,52) or by other DNA-binding protein formed complexes with ATM (53), thus playing a role in the initiating stage of multicheckpoints following IR. The fact of ATM-regulated S and G 2 -M checkpoints in a dose (IR)-dependent manner is supported more by the model of combined trans-and cis-acting processes.…”