Phosphorylated histone H2AX foci persist on rejoined mitotic chromosomes in normal human diploid cells exposed to ionizing radiation.
Histone H2AX is phosphorylated and forms foci in response to exposure to ionizing radiation. It has been thought that phosphorylated histone H2AX foci reflect unrepaired DNA double-strand breaks; however, we report here the localization of phosphorylated histone H2AX foci at the site of rejoined DNA double-strand breaks. We observed that phosphorylated histone H2AX foci remained even 96 h after exposure to X rays in interphase cells. To clarify the localization of residual phosphorylated histone H2AX foci, we examined localization of focus formation on mitotic chromosomes irradiated with X rays. We found that phosphorylated histone H2AX foci were located not only on chromosomal fragments but also on intact metaphase chromosomes without fragments. In anaphase cells, chromosomal bridges, which resulted from illegitimate rejoining of DNA broken ends, had phosphorylated histone H2AX foci. These foci were detected as individual small spots 30 min after X irradiation, but foci detected 20 or 96 h after X irradiation were clustered along the chromosomal bridges. These results indicate that phosphorylated histone H2AX foci persist if DNA breaks are rejoined. It is suggested that "residual" foci indicate an aberrant chromatin structure by illegitimate rejoining but not a DNA double-strand break itself.
Division of Radiation Biology, Department of Radiology and Radiation Biology, Nagasaki University, Nagasaki, Japan.
Masatoshi
M
Suzuki
Keiji
K
Suzuki
Seiji
S
Kodama
Masami
M
Watanabe
D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002877:Chromosomes, Human / Q000235:genetics* / Q000528:radiation effects*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004171:Diploidy; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008938:Mitosis / Q000235:genetics* / Q000528:radiation effects; D010766:Phosphorylation / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011839:Radiation, Ionizing; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases