Targeting double-strand breaks to replicating DNA identifies a subpathway of DSB repair that is defective in ataxia-telangiectasia cells.
The critical cellular defect(s) and basis for cell killing by ionizing radiation in ataxia-telangiectasia (A-T) are unknown. We use the topoisomerase I inhibitor camptothecin (CPT), which kills mainly S-phase cells and induces DSBs predominantly in replication forks, to show that A-T cells are defective in the repair of this particular subclass of DSBs. CPT-treated A-T cells reaching G2 have abnormally high levels of chromatid exchanges (viewed as prematurely condensed G2 chromosomes); aberrations in normal cells are mostly chromatid breaks. Transfectants of A-T cells with the wild-type ATM cDNA are corrected for CPT sensitivity, chromatid aberrations, and the DSB repair defect. These data suggest that in normal cells ATM, the A-T protein, probably recognizes DSBs in active replicons and targets the repair machinery to the breaks; in addition, the ATM protein is involved in the suppression of low-fidelity, adventitious rejoining between replication-associated DSBs. The loss of ATM functions therefore leads to genome destabilization, sensitivity to DSB-inducing agents and to the cancer-promoting illegitimate exchange events that follow.
Johnson
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RT
Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, United Kingdom. johnsort@umdnj.edu
Gotoh
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Mullinger
A M
AM
Ryan
A J
AJ
Shiloh
Y
Y
Ziv
Y
Y
Squires
S
S
D001260:Ataxia Telangiectasia / Q000235:genetics / Q000378:metabolism*; D064007:Ataxia Telangiectasia Mutated Proteins; D002166:Camptothecin / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D012854:Sister Chromatid Exchange / Q000187:drug effects; D059004:Topoisomerase I Inhibitors; D014162:Transfection; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D011506:Proteins; D011994:Recombinant Proteins; D059004:Topoisomerase I Inhibitors; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D002166:Camptothecin