title: Protection of halogenated DNA from strand breakage and sister-chromatid exchange induced by the topoisomerase I inhibitor camptothecin.
abstract: The fundamental nuclear enzyme DNA topoisomerase I (topo I), cleaves the double-stranded DNA molecule at preferred sequences within its recognition/binding sites. We have recently reported that when cells incorporate halogenated nucleosides analogues of thymidine into DNA, it interferes with normal chromosome segregation, as shown by an extraordinarily high yield of endoreduplication, and results in a protection against DNA breakage induced by the topo II poison m-AMSA [F. Cortés, N. Pastor, S. Mateos, I. Domínguez, The nature of DNA plays a role in chromosome segregation: endoreduplication in halogen-substituted chromosomes, DNA Repair 2 (2003) 719-726; G. Cantero, S. Mateos, N. Pastor; F. Cortés, Halogen substitution of DNA protects from poisoning of topoisomerase II that results in DNA double-strand breaks (DSBs), DNA Repair 5 (2006) 667-674]. In the present investigation, we have assessed whether the presence of halogenated nucleosides in DNA diminishes the frequency of interaction of topo I with DNA and thus the frequency with which the stabilisation of cleavage complexes by the topo I poison camptothecin (CPT) takes place, in such a way that it protects from chromosome breakage and sister-chromatid exchange. This protective effect is shown to parallel a loss in halogen-substituted cells of the otherwise CPT-increased catalytic activity bound to DNA.
authors: Department of Cell Biology, Faculty of Biology, University of Seville, Seville, Spain.
authors: Manuel Luís
authors: ML
authors: Orta
authors: Santiago
authors: S
authors: Mateos
authors: Gloria
authors: G
authors: Cantero
authors: Lisa J
authors: LJ
authors: Wolff
authors: Felipe
authors: F
authors: Cortés
mesh_terms: D000818:Animals; D016466:CHO Cells; D002166:Camptothecin / Q000494:pharmacology*; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006219:Halogens / Q000378:metabolism*; D012854:Sister Chromatid Exchange; D059004:Topoisomerase I Inhibitors
chemical_list: D004791:Enzyme Inhibitors; D006219:Halogens; D059004:Topoisomerase I Inhibitors; D004247:DNA; D002166:Camptothecin