Specific ATM-mediated Phosphorylation Dependent on Radiation Quality

Radiat Res. 2008 Sep;170(3):353-64. doi: 10.1667/RR1354.1.


To determine whether the physical differences between high- and low-LET radiation are reflected in the biological responses of exposed cells, we detailed phospho-protein profiles of three proteins functional in radiation repair and signal transduction. Detailing gamma-H2AX, pATF2 Ser490/498 and pSMC1 Ser957 kinetics after X-ray and iron-ion 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 radiation exposures, and two of these phosphorylations, pATF2 and pSMC1, are specifically dependent on ATM. Flow cytometry-based methods were used to quantify total levels of each phospho-protein at various times after irradiation. As expected, we observed a greater induction and persistence in gamma-H2AX after iron-ion (high-LET) exposure compared to X-ray (low-LET) exposure. In contrast, pATF2 and pSMC1 showed markedly lower induction levels after iron-ion exposure compared to equivalent doses of X rays. 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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / metabolism*
  • Cell Line
  • DNA / radiation effects*
  • DNA Damage / physiology*
  • DNA-Binding Proteins / metabolism*
  • Dose-Response Relationship, Radiation
  • Fibroblasts / metabolism*
  • Fibroblasts / radiation effects*
  • Humans
  • Phosphoproteins / metabolism*
  • Phosphorylation / radiation effects
  • Protein-Serine-Threonine Kinases / metabolism*
  • Radiation Dosage
  • Tumor Suppressor Proteins / metabolism*


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Phosphoproteins
  • Tumor Suppressor Proteins
  • DNA
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases