Specific ATM-Mediated Phosphorylation Dependent on Radiation Quality

Abstract

To determine whether the physical differences between high-and low-LET radiation are reflected in the biological responses of exposed cells, we detailed phosphoprotein profiles of three proteins functional in radiation repair and signal transduction.Detailing γH2AX, pATF2 Ser 490/498 and pSMC1 Ser 957 kinetics following X-ray and ironion exposure also provides a window into understanding the underlying cellular responses. Phosphorylated forms of these proteins have been documented to co-localize at sites of double strand breaks (DSBs) after low-LET exposures, and two of these phosphorylations, pATF2 and pSMC1, are specifically ATM dependent. Flow cytometry-based methods were used to quantify total levels of each phospho-protein at various times after radiation. As expected, we observed a greater induction and persistence in γH2AX after iron-ion (high-LET) exposure as compared to X-ray (low-LET). In contrast, pATF2 and pSMC1 showed markedly lower induction levels following Fe exposure as compared to equivalent doses of X-ray. Quantification of pATF2 and pSMC1 foci revealed fewer cells containing foci, and fewer foci per cell after iron-ion compared to X-ray exposure. These findings suggest that ATM responds to DSBs induced by high-LET radiation differently from DSBs induced by low-LET radiation.2

Induction and Processing of the Radiation-Induced Gamma-H2AX Signal and Its Link to the Underlying Pattern of DSB: A Combined Experimental and Modelling Study

“…However, since the analysis of the saturation tendency was not the first aim of the paper, this aspect was not deeply discussed, neither complemented by a modelling analysis as it is here the case. Flow cytometry data of γ H2AX also appear in publications with different aims, but they are usually restricted to low doses (up to few Gy) and therefore not comparable with what we want to discuss here [64–66]. …”

γH2AX: a sensitive molecular marker of DNA damage and repair

“…50 High linear energy transfer exposure leads to greater induction and persistence of gH2AX in cells, as well as larger foci, which may be attributed to further gH2AX formation occurring away from the initial DSB. 51,52 Several mechanisms have been proposed to explain the origin of H2AX phosphorylation. The first involves direct ATM activation that triggers rapid auto-phosphorylation of Ser-1981 on detecting conformational changes in DNA as a result of local chromatin modifications.…”

Carbon Ion Radiotherapy: A Review of Clinical Experiences and Preclinical Research, with an Emphasis on DNA Damage/Repair

“…Reduced survival and cytogenetic differences were also observed between normal and NHEJ-deficient cells after charged particle radiation induced damage [49,50,51]. It has been also shown that clustered DNA damage affects DNA damage response by altering the ataxia telangiectasia mutated (ATM) to ataxia telangiectasia and Rad3 related (ATR) transition at break sites along with persistent ATM/activating transcription factor 2 (ATF2) signaling, a downstream substrate of ATM [52,53]. …”