title: Topoisomerase II activity in a DNA double-strand break repair deficient Chinese hamster ovary cell line.
abstract: Topoisomerase II activity was measured in wild-type, Chinese hamster ovary K1 cells, and in the DNA double-strand break repair deficient xrs-6 cell line. Total topoisomerase II activity in a high salt, nuclear extract was found to be the same in both cell lines, as measured by decatenation of kinetoplast DNA networks and catenation of plasmid pBR322 DNA. While at low drug concentrations m-AMSA-induced enzyme cutting of nuclear DNA was 25% less in xrs-6 cells, the frequency of DNA breaks at high concentrations of the drug, and thus the frequency of the topoisomerase II enzyme, was the same in both cell lines. Despite the presence of equivalent enzyme levels in both cell lines, the xrs-6 cell line was 3 times more sensitive to drug-induced cytotoxicity. These results may be due to the fact that, as with X-radiation-induced DNA damage, xrs-6 cells are deficient in the capacity to rejoin topoisomerase II-induced DNA double-strand breaks.
authors.affiliation: Department of Radiology, University of Utah Health Sciences Center, Salt Lake City 84132.
authors.forename: R L
authors.initials: RL
authors.lastname: Warters
authors.forename: B W
authors.initials: BW
authors.lastname: Lyons
authors.forename: T M
authors.initials: TM
authors.lastname: Li
authors.forename: D J
authors.initials: DJ
authors.lastname: Chen
mesh_terms: D000677:Amsacrine / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D004249:DNA Damage; D004260:DNA Repair; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D009154:Mutation
chemical_list: D004277:DNA, Single-Stranded; D000677:Amsacrine; D004250:DNA Topoisomerases, Type II