Hypersensitivity of Ku-deficient cells toward the DNA topoisomerase II inhibitor ICRF-193 suggests a novel role for Ku antigen during the G2 and M phases of the cell cycle.
Ku antigen is a heterodimer, comprised of 86- and 70-kDa subunits, which binds preferentially to free DNA ends. Ku is associated with a catalytic subunit of 450 kDa in the DNA-dependent protein kinase (DNA-PK), which plays a crucial role in DNA double-strand break (DSB) repair and V(D)J recombination of immunoglobulin and T-cell receptor genes. We now demonstrate that Ku86 (86-kDa subunit)-deficient Chinese hamster cell lines are hypersensitive to ICRF-193, a DNA topoisomerase II inhibitor that does not produce DSB in DNA. Mutant cells were blocked in G2 at drug doses which had no effect on wild-type cells. Moreover, bypass of this G2 block by caffeine revealed defective chromosome condensation in Ku86-deficient cells. The hypersensitivity of Ku86-deficient cells toward ICRF-193 was not due to impaired in vitro decatenation activity or altered levels of DNA topoisomerase IIalpha or -beta. Rather, wild-type sensitivity was restored by transfection of a Ku86 expression plasmid into mutant cells. In contrast to cells deficient in the Ku86 subunit of DNA-PK, cells deficient in the catalytic subunit of the enzyme neither accumulated in G2/M nor displayed defective chromosome condensation at lower doses of ICRF-193 compared to wild-type cells. Our data suggests a novel role for Ku antigen in the G2 and M phases of the cell cycle, a role that is not related to its role in DNA-PK-dependent DNA repair.
Muñoz
P
P
Institut de Génétique Moléculaire de Montpellier, CNRS, 34293 Montpellier Cedex 5, France. munoz@igm.cnrs-mop.fr
Zdzienicka
M Z
MZ
Blanchard
J M
JM
Piette
J
J
D000818:Animals; D034961:Antigens, Nuclear; D016466:CHO Cells; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D006224:Cricetinae; D004249:DNA Damage; D004265:DNA Helicases; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D054659:Diketopiperazines; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016195:G2 Phase; D006801:Humans; D000072200:Ku Autoantigen; D008938:Mitosis; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D010879:Piperazines / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors; D014162:Transfection
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D054659:Diketopiperazines; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D010879:Piperazines; D059005:Topoisomerase II Inhibitors; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D004250:DNA Topoisomerases, Type II