To quantitatively compare the γ-H₂AX foci formation between DNA-PKcs^{+ /+} and DNA-PKcs^-/-mouse embryonic fibroblast (MEF) cells, and to investigate the dynamic changes in DNA double-strand breaks (DSBs) in human nasopharyngeal carcinoma SUNE-1 cells exposed to X-ray radiation.

The expression of DNA-PKcs was determined by Western blot. The γ-H₂AX foci formation induced by 5 Gy X-ray radiation was detected by cell immunofluorescence. The ImageJ software was used to quantitatively analyze the γ-H₂AX foci formation.

The expression of DNA-PKcs was silenced in DNA-PKcs^-/-MEF cells and normal in DNA-PKcs^{+ /+} MEF cells. According to the dynamic analyses of the numbers of γ-H₂AX foci/cell and γ-H₂AX foci/mm^2, a similar tendency was observed in DSB formation in DNA-PKcs^{+ /+} MEF cells, DNA-PKcs^-/-MEF cells, and SUNE-1 cells exposed to X-ray radiation. A large number of γ-H₂AX foci formed at 0.5-1.0 h after radiation. DSBs were repaired at 6 h after radiation in DNA-PKcs^{+ /+} MEF cells and 24 h after radiation in DNA-PKcs^-/-MEF cells and SUNE-1 cells. The peak values of γ-H₂AX foci/cell and γ-H₂AX foci/mm² were observed at 1.0 and 0.5 h after radiation, respectively. Compared with DNA-PKcs^{+ /+} MEF cells, DNA-PKcs^-/-MEF cells had different numbers of γ-H₂AX foci/cell at 0.5, 1.0, 3.0, 6.0, and 12.0 h after radiation, as well as different numbers of γ-H₂AX foci/mm² at 3.0, 6.0, and 12.0 h after radiation.

Quantitative measurement of the number of γ-H₂AX foci/cell or γ-H₂AX foci/mm² by cell immunofluorescence provides new insights into the quantitative and dynamic study of DSB damage and repair.

Non-homologous terminal connection; DNA dependent protein kinase catalytic subunit; γH₂AX foci formation; SUNE-1 cell line