Targeting double-strand breaks to replicating DNA identifies a subpathway of DSB repair that is defective in ataxia-telangiectasia cells

Robert T. Johnson, Eisuke Gotoh, Ann M. Mullinger, Anderson J. Ryan, Yosef Shiloh, Yael Ziv, Shoshana Squires

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Pages (from-to)317-325
Number of pages9
JournalBiochemical and Biophysical Research Communications
Volume261
Issue number2
DOIs
StatePublished - 2 Aug 1999

Keywords

  • Camptothecin
  • Chromatid exchanges
  • Double strand breaks
  • S-phase DNA
  • Topoisomerase I inhibition

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