Imaging Features That Discriminate Between Foci Induced by High- And low-LET Radiation in Human Fibroblasts

Radiat Res. 2006 May;165(5):505-15. doi: 10.1667/RR3538.1.


In this study, we investigated the formation of radiation-induced foci in normal human fibroblasts exposed to X rays or 130 keV/mum nitrogen ions using antibodies to phosphorylated protein kinase ataxia telangiectasia mutated (ATMp) and histone H2AX (gamma-H2AX). High-content automatic image analysis was used to quantify the immunofluorescence of radiation-induced foci. The size of radiation-induced foci increased for both proteins over a 2-h period after nitrogen-ion irradiation, while the size of radiation-induced foci did not change after exposure to low-LET radiation. The number of radiation-induced ATMp foci showed a more rapid rise and greater frequency after X-ray exposure and was resolved more rapidly such that the frequency of radiation-induced foci decreased by 90% compared to 60% after exposure to high-LET radiation 2 h after 30 cGy. In contrast, the kinetics of radiation-induced gamma-H2AX focus formation was similar for high- and low-LET radiation in that it reached a plateau early and remained constant for up to 2 h. High-resolution 3D images of radiation-induced gamma-H2AX foci and dosimetry computation suggest that multiple double-strand breaks from nitrogen ions are encompassed within large nuclear domains of 4.4 Mbp. Our work shows that the size and frequency of radiation-induced foci vary as a function of radiation quality, dose, time and protein target. Thus, even though double-strand breaks and radiation-induced foci are correlated, the dynamic nature of both contradicts their accepted equivalence for low doses of different radiation qualities.

Publication types

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

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / radiation effects
  • Cells, Cultured
  • DNA / radiation effects*
  • DNA / ultrastructure*
  • DNA Damage / genetics*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / radiation effects
  • Dose-Response Relationship, Radiation
  • Fibroblasts / cytology*
  • Fibroblasts / metabolism
  • Fibroblasts / radiation effects*
  • Histones / genetics
  • Histones / radiation effects
  • Humans
  • Image Interpretation, Computer-Assisted / methods
  • Linear Energy Transfer
  • Micronucleus Tests / methods*
  • Microscopy, Fluorescence / methods*
  • Phosphorylation / radiation effects
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / radiation effects
  • Radiation Dosage
  • Radiation, Ionizing
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / radiation effects


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • H2AX protein, human
  • Histones
  • Tumor Suppressor Proteins
  • DNA
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases