DNA topoisomerase activities in Chinese hamster radiosensitive mutants after X-ray treatment.
In the last years the attractive hypothesis of a possible involvement of mammalian topoisomerases in DNA repair has been proposed, given their molecular mechanism of action. So far, using asynchronous cultures a lot of controversial results have been reported, without taking into account the frequently dramatic fluctuations of topoisomerase activities depending upon the cell cycle stage and proliferation rate (mainly for topoisomerase II). We have addressed this question making use of G1 synchronous cultures of the Chinese hamster radiosensitive mutants xrs 5 (defective in DNA double strand breaks rejoining) and irs 2 (which shows radioresistant DNA synthesis), as well as their parental lines CHO K1 and V79 respectively, which show a normal radiosensitivity. Cells were irradiated with 5 Gy of X-rays and the activities of topoisomerases I and II in nuclear extracts were studied for comparison with non-irradiated controls in both the mutants and parental cell lines. Our results clearly show a modulation of the topoisomerase activities after irradiation, that varies depending upon the mutation that the different lines bear. While this hypothesis needs further testing, an interesting idea is that DNA topoisomerases might be involved in the cellular response to radiation damage, either through a direct participation in the repair mechanisms or in a preparative step to allow repair to proceed.
Department of Cell Biology, Faculty of Biology, University of Seville, Avda. Reina Mercedes no. 6, 41012 Seville, Spain.
Nuria
N
Pastor
Felipe
F
Cortés
D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells / Q000201:enzymology* / Q000528:radiation effects*; D002453:Cell Cycle / Q000235:genetics / Q000528:radiation effects; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis* / Q000528:radiation effects*; D004249:DNA Damage / Q000235:genetics / Q000528:radiation effects*; D004260:DNA Repair / Q000235:genetics / Q000528:radiation effects*; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000528:radiation effects*; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000528:radiation effects; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics / Q000528:radiation effects; D009154:Mutation / Q000235:genetics / Q000528:radiation effects*; D014176:Protein Biosynthesis / Q000235:genetics / Q000528:radiation effects; D014965:X-Rays
D004247:DNA; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II