Inhibition of topoisomerase II activity and its effect on nucleolar structure and function.
The relationship between topoisomerase II activity and ribosomal RNA synthesis was investigated using the antitumoral drug VM26, a specific inhibitor of topoisomerase II. For this purpose TG cells, a human tumor cell line, were cultured in the presence of 2.5 microM VM26 for 1 and 3 h; VM26 reduced the topoisomerase II activity, measured in whole cell extracts. In the presence of VM26 the [3H]uridine incorporation into ribosomal RNA was decreased; electron microscopy investigation of nucleoli showed a segregation of nucleolar components. Because VM26 stabilizes the cleavable complex and inhibits the resealing reaction, thus causing potential cleavage sites, we have analyzed the double-strand breaks caused by the drug treatment in the tandem repeat ribosomal DNA (rDNA) genes, by indirect labeling with two probes recognizing the 5' portion of ETS (BES) and the 3' portion of 28S (LS6BE) transcribed gene. In VM26-treated cells rDNA is fragmented and a topoisomerase II preferential cleavage site is present, localized at 1.85 kb in 28S region from 3' EcoRI site.
Govoni
M
M
Dipartimento di Patologia Sperimentale, Università degli Studi di Bologna, Italy.
Farabegoli
F
F
Pession
A
A
Novello
F
F
D002466:Cell Nucleolus / Q000502:physiology* / Q000648:ultrastructure*; D004247:DNA / Q000032:analysis / Q000235:genetics; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008854:Microscopy, Electron; D012313:RNA / Q000032:analysis / Q000235:genetics; D013713:Teniposide / Q000494:pharmacology; D059005:Topoisomerase II Inhibitors; D014316:Tritium; D014407:Tumor Cells, Cultured; D014529:Uridine / Q000378:metabolism
D059005:Topoisomerase II Inhibitors; D014316:Tritium; D012313:RNA; D004247:DNA; D013713:Teniposide; D004250:DNA Topoisomerases, Type II; D014529:Uridine