title: Genome instability in ataxia telangiectasia (A-T) families: camptothecin-induced damage to replicating DNA discriminates between obligate A-T heterozygotes, A-T homozygotes and controls.
abstract: Previously we used the topoisomerase I inhibitor camptothecin (CPT), which kills mainly S-phase cells primarily by inducing double strand breaks (DSBs) in replication forks, to show that ataxia telangiectasia (A-T) fibroblasts 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 (G2 PCC), compared with normal cells where aberrations are mostly chromatid breaks. Here we show that A-T lymphoblastoid cells established from individuals with different mutations in the ATM gene also exhibit increased levels of chromosomal exchanges in response to CPT, indicating that the replication-associated DSBs are misrepaired in all these cells. From family studies we show that the presence of a single mutated allele in obligate A-T heterozygotes leads to intermediate levels of chromosomal exchanges in CPT-treated lymphoblastoid cells, thus providing a functional and sensitive assay to identify these individuals.
authors.affiliation: Coriell Cell Repositories, Coriell Institute for Medical Research, 403 Haddon Avenue, Camden, New Jersey, 08103, USA.
authors.forename: Jay C
authors.initials: JC
authors.lastname: Leonard
authors.forename: Ann M
authors.initials: AM
authors.lastname: Mullinger
authors.forename: John
authors.initials: J
authors.lastname: Schmidt
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Cordell
authors.forename: Robert T
authors.initials: RT
authors.lastname: Johnson
mesh_terms: D001260:Ataxia Telangiectasia / Q000235:genetics*; D002166:Camptothecin / Q000633:toxicity; D002460:Cell Line; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects; D042822:Genomic Instability; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000187:drug effects; D009154:Mutation
chemical_list: D002166:Camptothecin