Ku antigen is required to relieve G2 arrest caused by inhibition of DNA topoisomerase II activity by the bisdioxopiperazine ICRF-193

Munoz, P.; Baus, F.; Piette, J.


2001-04-12 / vol 20 / pages 1990-9


Ku antigen is necessary for DNA double-strand break (DSB) repair through its ability to bind DNA ends with high affinity and to recruit the catalytic subunit of DNA-PK to the DSBs. Ku-deficient cells are hypersensitive to agents causing DSBs in DNA but also to the DNA topoisomerase II (topo II) inhibitor ICRF-193, which does not induce DSBs. This suggests a new role of Ku antigen, that is independent of DSB repair by DNA-PK. Here we characterize the basis for the hypersensitivity of Ku-deficient cells to ICRF-193. Chromosome condensation and segregation, which are dependent on topo II, but also the catalytic activity of topo II in late S-G2 were inhibited to a comparable extent when ICRF-193 was applied to Ku-deficient cells or wild-type cells. However, mutant cells arrested in G2 by ICRF-193 treatment were unable to progress into M phase upon drug removal, although drug-trapped topo II complexes were removed from DNA and the two isoforms of topo II recovered their catalytic activity as in wild-type cells. The reversibility of G2 arrest was recovered by complementation of mutant cells with a human Ku86 cDNA. Notably, chromosome condensation was abnormal in Ku-deficient cells after suppression of the G2 arrest by caffeine, even in the absence of ICRF-193. These results reflect the involvement of Ku-antigen in the cellular response to topo II inhibition, more particularly in relieving G2 arrest caused by topo II inhibition in late S/G2 and the subsequent recovery of chromosome condensation.

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Animals; Enzyme Inhibitors/*pharmacology; Cricetinae; Antineoplastic Agents/pharmacology; *Antigens, Nuclear; *DNA Helicases; DNA Topoisomerases, Type II/*antagonists & inhibitors/metabolism; Piperazines/*pharmacology; Chromosomes/physiology; Cricetulus; DNA-Binding Proteins/deficiency/*physiology; Fibroblasts/drug effects/enzymology/ultrastructure; G2 Phase/drug effects/*physiology; Nuclear Proteins/deficiency/*physiology; S Phase/physiology

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