Radiation sensitivity, H2AX phosphorylation, and kinetics of repair of DNA strand breaks in irradiated cervical cancer cell lines.
Six human cervical cancer cell lines [five human papillomavirus (HPV) positive, one HPV negative] for induction and rejoining of DNA strand breaks and for kinetics of formation and loss of serine 139 phosphorylated histone H2AX (gammaH2AX). X-rays induced the same level of DNA breakage for all cell lines. By 8 hours after 20 Gy, <2% of the initial single-strand breaks remained and no double-strand breaks could be detected. In contrast, 24 hours after irradiation, gammaH2AX representing up to 30% of the initial signal still present. SW756 cells showed almost four times higher background levels of gammaH2AX and no residual gammaH2AX compared with the most radiosensitive HPV-negative C33A cells that showed the lowest background and retained 30% of the maximum level of gammaH2AX. Radiation sensitivity, measured as clonogenic-surviving fraction after 2 Gy, was correlated with the fraction of gammaH2AX remaining 24 hours after irradiation. A substantial correlation with gammaH2AX loss half-time measured over the first 4 hours was seen only when cervical cell lines were included in a larger series of p53-deficient cell lines. Interestingly, p53 wild-type cell lines consistently showed faster gammaH2AX loss half-times than p53-deficient cell lines. We conclude that cell line-dependent differences in loss of gammaH2AX after irradiation are related in part to intrinsic radiosensitivity. The possibility that the presence of gammaH2AX foci may not always signify the presence of a physical break, notably in some tumor cell lines, is also supported by these results.
British Columbia Cancer Research Centre, Vancouver, British Columbia, Canada.
Judit P
JP
Banáth
Susan H
SH
Macphail
Peggy L
PL
Olive
D045744:Cell Line, Tumor; D020552:Comet Assay; D004249:DNA Damage; D004260:DNA Repair / Q000502:physiology*; D004273:DNA, Neoplasm / Q000378:metabolism* / Q000528:radiation effects; D005260:Female; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010766:Phosphorylation / Q000528:radiation effects; D011836:Radiation Tolerance / Q000502:physiology*; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000532:radiotherapy*
D004273:DNA, Neoplasm; C468783:H2AX protein, human; D006657:Histones