Abstract
We studied the localization of phosphorylated H2AX (γ-H2AX) in cultured human fibroblasts (NB1RGB) and EGFP-tagged rad51 in Chinese hamster CHO cells after irradiation with heavy ion beams. Asynchronous cells were irradiated with X-rays, carbon ion beam (LET is about 30 or 88 keV/μm), Si (220 keV/μm), Ar (95 keV/μm), and Fe ion beam (440 keV/μm) at room temperature. Gamma-H2AX in irradiated cells was detecteded by immuno-staining from 0 to 24 h after irradiation. Gamma-H2AX monitored by using flow cytometry increased just after irradiation of each radiation and reached maximum around 30 min. Gamma-H2AX was then decreased quickly for cells irradiated with X-rays but presented longer for Si and Fe beams. Comparing the induction of the amount of γ-H2AX at 30 min after irradiation, high LET Si and Fe were more effective than X-rays and C beams. Carbon ion beam with lower LET of 30 keV/μm induced similar to X-rays and C ion with 88 keV/μm was intermediate between High LET group and low LET group. Under the confocal microscopy, foci of γ-H2AX on cell nucleus was not visible just after X-irradiation, but obvious after Fe ion irradiation. Number of foci per nucleus was increased with increasing dose at 30 min after irradiation similarly for all radiation tested. On the other hand, rad51 foci were not visible just after irradiation even for Fe beams. They were observed about 1 h after irradiation, and were co-localized with γ-H2AX foci. They were visible at 20 h after irradiation both for heavy ions and X-rays.
