title: Altered DNA topoisomerase II activity in Chinese hamster cells resistant to topoisomerase II inhibitors.
abstract: Most DNA intercalators and epipodophyllotoxins inhibit mammalian topoisomerase II by trapping the enzyme within DNA cleavage complexes that can be detected in cells as protein-associated DNA strand breaks. We have characterized previously a line of Chinese hamster cells (DC3F/9-OHE cells) the resistance of which to the cytotoxic effect of intercalators and etoposide is associated with a reduced formation of protein-associated DNA strand breaks. In the present study, topoisomerases of these cells were compared to those of the parental sensitive cells (DC3F). NaCl extracts (0.35 M) of isolated DC3F/9-OHE nuclei did not form 4'-(9-acridinylamino)methanesulfon-m-anisidide-induced DNA-protein linking, whereas DC3F nuclear extracts did. In addition, DC3F/9-OHE nuclear extract had an unusually high level of DNA linking activity in the absence of 4'-(9-acridinylamino)methanesulfon-m-anisidide. Topoisomerases II from DC3F/9-OHE and DC3F nuclei appeared similar qualitatively. DC3F/9-OHE nuclear extract had approximately twice less topoisomerase II molecules than did DC3F nuclear extract but similar topoisomerase II activity. Topoisomerase I activities appeared also similar in sensitive and resistant cells. However, part of DC3F/9-OHE topoisomerase I copurified with a DNA linking activity which was not present in DC3F nuclei. This unusual DNA linking activity was not sensitive to the stimulatory effect of 4'-(9-acridinylamino)methanesulfon-m-anisidide.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000609:Aminoacridines / Q000494:pharmacology; D000677:Amsacrine; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000032:analysis; D004250:DNA Topoisomerases, Type II / Q000032:analysis* / Q000302:isolation & purification; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D005047:Etoposide / Q000494:pharmacology; D008970:Molecular Weight; D059005:Topoisomerase II Inhibitors
chemical_list: D000609:Aminoacridines; D059005:Topoisomerase II Inhibitors; D000677:Amsacrine; D005047:Etoposide; D000255:Adenosine Triphosphate; D004247:DNA; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II