title: Induction and persistence of large γH2AX foci by high linear energy transfer radiation in DNA-dependent protein kinase-deficient cells.
abstract: OBJECTIVE
  To evaluate the cell response to DNA double-strand breaks induced by low and high linear energy transfer (LET) radiations when the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), an essential protein of the nonhomologous end-joining repair pathway, lacks kinase activity.
  
  
  METHODS
  CHO10B2, a Chinese hamster ovary cell line, and its derived radiosensitive mutant cell line, irs-20, lacking DNA-PKcs activity, were evaluated after 0 to 3 Gy of γ-rays, plateau and Bragg peak protons, and lithium beams by clonogenic assay, and as a measurement of double-strand breaks, phosphorylated H2AX (γH2AX) foci number and size were quantified by immunocytofluorescence.
  
  
  RESULTS
  Irs-20 exhibited greater radiosensitivity and a higher amount of γH2AX foci than CHO10B2 at 6 hours after irradiation for all types of radiations. Remarkably, CHO10B2 and irs-20 maintained their difference in radiosensitivity after high-LET radiation. Six hours after low-LET radiations, irs-20 did not reach basal levels of γH2AX at high doses, whereas CHO10B2 recovered basal levels for all doses. After high-LET radiation, only CHO10B2 exhibited a reduction in γH2AX foci, but it never reached basal levels. Persistent foci in irs-20 confirmed a repair deficiency. Interestingly, after 30 minutes of high-LET radiation both cell lines exhibited large foci (size>0.9 μm2) related to the damage nature, whereas at 6 hours irs-20 showed a higher amount of large foci than CHO10B2, with a 7-fold increase at 3 Gy, that could also be associated to radiosensitivity.
  
  
  CONCLUSIONS
  We demonstrated, for the first time, an association between deficient DNA-PKcs activity and not only high levels of H2AX phosphorylation but also persistence and size increase of γH2AX foci after high-LET irradiation.
authors: Departamento de Micro y Nanotecnología, Comisión Nacional de Energía Atómica, San Martín, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
authors: Candelaria
authors: C
authors: Bracalente
authors: Irene L
authors: IL
authors: Ibañez
authors: Beatriz
authors: B
authors: Molinari
authors: Mónica
authors: M
authors: Palmieri
authors: Andrés
authors: A
authors: Kreiner
authors: Alejandro
authors: A
authors: Valda
authors: Jorge
authors: J
authors: Davidson
authors: Hebe
authors: H
authors: Durán
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000172:deficiency*; D005720:Gamma Rays; D006657:Histones / Q000378:metabolism*; D018499:Linear Energy Transfer; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D015415:Biomarkers; C468783:H2AX protein, human; D006657:Histones; D051747:DNA-Activated Protein Kinase