Rejoining of isochromatid breaks induced by heavy ions in G2-phase normal human fibroblasts.
We reported previously that exposure of normal human fibroblasts in G2 phase of the cell cycle to high-LET radiation produces a much higher frequency of isochromatid breaks than exposure to gamma rays. We concluded that an increase in the production of isochromatid breaks is a signature of initial high-LET radiation-induced G2-phase damage. In this paper, we report the repair kinetics of isochromatid breaks induced by high-LET radiation in normal G2-phase human fibroblasts. Exponentially growing human fibroblasts (AG1522) were irradiated with gamma rays or energetic carbon (290 MeV/nucleon), silicon (490 MeV/nucleon), or iron (200 MeV/nucleon) ions. Prematurely condensed chromosomes were induced by calyculin A after different postirradiation incubation times ranging from 0 to 600 min. Chromosomes were stained with Giemsa, and aberrations were scored in cells at G2 phase. G2-phase fragments, the result of the induction of isochromatid breaks, decreased quickly with incubation time. The curve for the kinetics of the rejoining of chromatid-type breaks showed a slight upward curvature with time after exposure to 440 keV/microm iron particles, probably due to isochromatid-isochromatid break rejoining. The formation of chromatid exchanges after exposure to high-LET radiation therefore appears to be underestimated, because isochromatid-isochromatid exchanges cannot be detected. Increased induction of isochromatid breaks and rejoining of isochromatid breaks affect the overall kinetics of chromatid-type break rejoining after exposure to high-LET radiation.
Kawata
T
T
NASA Lyndon B. Johnson Space Center, Radiation Biophysics Laboratory, Houston, Texas 77058, USA. tkawata@ems.jsc.nasa.gov
Durante
M
M
Furusawa
Y
Y
George
K
K
Ito
H
H
Wu
H
H
Cucinotta
F A
FA
D002478:Cells, Cultured; D002842:Chromatids / Q000378:metabolism* / Q000528:radiation effects; D004260:DNA Repair / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology / Q000528:radiation effects*; D016195:G2 Phase / Q000235:genetics*; D020450:Heavy Ions / Q000009:adverse effects*; D006801:Humans; D007621:Karyotyping