H2AX phosphorylation at the sites of DNA double-strand breaks in cultivated mammalian cells and tissues

A sequence variant of histone H2A called H2AX is one of the key components of chromatin involved in DNA damage response induced by different genotoxic stresses. Phosphorylated H2AX (gamma H2AX) is rapidly concentrated in chromatin domains around DNA double-strand breaks (DSBs) after the action of ionizing radiation or chemical agents and at stalled replication forks during replication stress. gamma H2AX foci could be easily detected in cell nuclei using immunofluorescence microscopy that allows to use gamma H2AX as a quantitative marker of DSBs in various applications. H2AX is phosphorylated in situ by ATM, ATR, and DNA-PK kinases that have distinct roles in different pathways of DSB repair. The gamma H2AX serves as a docking site for the accumulation of DNA repair proteins, and after rejoining of DSBs, it is released from chromatin. The molecular mechanism of gamma H2AX dephosphorylation is not clear. It is complicated and requires the activity of different proteins including phosphatases and chromatin-remodeling complexes. In this review, we summarize recently published data concerning the mechanisms and kinetics of gamma H2AX loss in normal cells and tissues as well as in those deficient in ATM, DNA-PK, and DSB repair proteins activity. The results of the latest scientific research of the low-dose irradiation phenomenon are presented including the bystander effect and the adaptive response estimated by gamma H2AX detection in cells and tissues.