title: Effects of DNA topoisomerase inhibitors on nonhomologous and homologous recombination in mammalian cells.
abstract: To study the involvement of DNA topoisomerases in recombination in mammalian cells, we used gene transfer assays to examine the effects of DNA topoisomerase inhibitors on nonhomologous (illegitimate) and homologous recombination. The assays were performed by transfecting adenine phosphoribosyltransferase-deficient (APRT-) CHO cells with plasmids carrying the wild-type or mutant aprt genes and by treating the cells with the inhibitors, followed by subsequent cultivation to select for APRT-positive (APRT+) colonies. Treatments with DNA topoisomerase II inhibitors such as VP-16, VM-26, ICRF-193 resulted in a 3- to 5-fold stimulation of integration of both closed-circular and linearized plasmids carrying the wild-type aprt gene into the recipient genome through nonhomologous recombination. The same treatments also increased 6- to 9-fold and 3-fold the number of APRT+ recombinant colonies that were generated by cotransfecting two closed-circular plasmids with nonoverlapping defective aprt genes and their linearized equivalents, respectively. However, this cotransfection assay involved intrinsically nonhomologous recombination processes; normalization of the frequencies by dividing them with those of the above nonhomologous recombination revealed 2-fold enhancement of homologous recombination events between the circular mutant genes but not between the linear ones. In contrast, DNA topoisomerase I inhibitor, camptothecin, showed no such effect on either recombination. From these results, we discuss the function of DNA topoisomerases on recombination in mammalian cells.
authors.affiliation: Kihara Institute for Biolgical Research, Yokohama City University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Aratani
authors.forename: T
authors.initials: T
authors.lastname: Andoh
authors.forename: H
authors.initials: H
authors.lastname: Koyama
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000235:genetics; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000633:toxicity; D016466:CHO Cells / Q000187:drug effects / Q000201:enzymology; D002166:Camptothecin / Q000633:toxicity; D002869:Chromosome Aberrations / Q000235:genetics; D006224:Cricetinae; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D054659:Diketopiperazines; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000633:toxicity*; D005047:Etoposide / Q000633:toxicity; D016296:Mutagenesis; D009152:Mutagenicity Tests; D009692:Nucleic Acid Heteroduplexes; D010879:Piperazines / Q000633:toxicity; D011995:Recombination, Genetic / Q000187:drug effects*; D013713:Teniposide / Q000633:toxicity; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D014162:Transfection
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D054659:Diketopiperazines; D004791:Enzyme Inhibitors; D009692:Nucleic Acid Heteroduplexes; D010879:Piperazines; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D005047:Etoposide; D013713:Teniposide; D000228:Adenine Phosphoribosyltransferase; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin