Requirement of ATM-dependent pathway for the repair of a subset of DNA double strand breaks created by restriction endonucleases

Synchronized G1 cells were treated with various restriction endonucleases. DNA double strand breaks were detected by the foci of phosphorylated ATM at serine 1981 and 53BP1. DNA damage was detectable 2 hours after the treatment, and the number of foci decreased thereafter. Repair of the 3'-protruding ends created by Pst I and Sph I was efficient irrespective of ATM function, whereas the repair of a part of the blunt ends caused by Pvu II and Rsa I, and 5'-protruding ends created by Eco RI and Bam HI, respectively, were compromised by ATM inhibition.Our results indicate that ATM-dependent pathway plays a pivotal role in the repair of a subset of DNA double strand breaks with specific end structures.Ionizing radiation induces various types of DNA damage, among which DNA double strand breaks show the most detrimental effects on living cells. DNA double strand breaks are repaired by two major DNA repair pathways, which are non-homologous end-joining (NHEJ) and homologous recombination (HR) [1-6]. While DNA repair pathway efficiently rejoin the broken ends, un-rejoined or mis-rejoined DNA damage provide chances to threaten the integrity of the genome [7-9]. Thus, the cells evolved a sophisticated system, by which stability of the genome is maintained [10,11]. The system referred to as DNA damage checkpoint pathway requires ATM function [12-14], which is activated by dissociation of ATM proteins followed by autophosphorylation [15]. Activated ATM phosphorylates various downstream proteins including those that regulate cell cycle progression, cell death, as well as DNA repair [11,14,16,17]. Thereby, ATM plays a critical role in orchestrating DNA damage signaling and DNA damage repair.Although AT cells were known to be sensitive to ionizing radiation, the mechanism underlying the hyper radio-sensitivity has not yet been fully understood [12-14,18]. AT cells have no gross defect in DNA double strand break repair, however, several studies reported that a fraction of the initi