Phosphorylation of histone H2AX as a measure of radiosensitivity

Abstract

Purpose Phosphorylation of histone H2AX (γH2AX) occurs rapidly in response to the presence of DNA double-strand breaks and is thought to recruit repair enzymes to these sites. We examined the possibility that expression of phosphorylated H2AX could provide information on tumor and/or normal tissue sensitivity to radiation. Methods Flow cytometry of γH2AX antibody-stained single cells was used to measure γH2AX intensity in cultured cell lines, tumor cells, and normal tissues. Results The rate of disappearance of γH2AX during the first few hours after irradiation was generally faster in more radioresistant tumor and normal cell lines, but slower in radiosensitive cells and normal tissues from C3H mice. An exception was testis, which showed a high background and rapid loss rate. Levels of γH2AX were at least three times higher in well-oxygenated cells than in anoxic cells, and the oxygen concentration that produced a half-maximal response was 0.55%. Hypoxic cells could be detected in SiHa xenografts as a subpopulation with lower expression of γH2AX. Conclusions Analysis of γH2AX has the potential to provide useful information on tumor and normal cell response to ionizing radiation after exposure to clinically relevant doses of radiation.