Differential radiosensitivity phenotypes of DNA-PKcs mutations affecting NHEJ and HRR systems following irradiation with gamma-rays or very low fluences of alpha particles.
We have examined cell-cycle dependence of chromosomal aberration induction and cell killing after high or low dose-rate γ irradiation in cells bearing DNA-PKcs mutations in the S2056 cluster, the T2609 cluster, or the kinase domain. We also compared sister chromatid exchanges (SCE) production by very low fluences of α-particles in DNA-PKcs mutant cells, and in homologous recombination repair (HRR) mutant cells including Rad51C, Rad51D, and Fancg/xrcc9. Generally, chromosomal aberrations and cell killing by γ-rays were similarly affected by mutations in DNA-PKcs, and these mutant cells were more sensitive in G1 than in S/G2 phase. In G1-irradiated DNA-PKcs mutant cells, both chromosome- and chromatid-type breaks and exchanges were in excess than wild-type cells. For cells irradiated in late S/G2 phase, mutant cells showed very high yields of chromatid breaks compared to wild-type cells. Few exchanges were seen in DNA-PKcs-null, Ku80-null, or DNA-PKcs kinase dead mutants, but exchanges in excess were detected in the S2506 or T2609 cluster mutants. SCE induction by very low doses of α-particles is resulted from bystander effects in cells not traversed by α-particles. SCE seen in wild-type cells was completely abolished in Rad51C- or Rad51D-deficient cells, but near normal in Fancg/xrcc9 cells. In marked contrast, very high levels of SCEs were observed in DNA-PKcs-null, DNA-PKcs kinase-dead and Ku80-null mutants. SCE induction was also abolished in T2609 cluster mutant cells, but was only slightly reduced in the S2056 cluster mutant cells. Since both non-homologous end-joining (NHEJ) and HRR systems utilize initial DNA lesions as a substrate, these results suggest the possibility of a competitive interference phenomenon operating between NHEJ and at least the Rad51C/D components of HRR; the level of interaction between damaged DNA and a particular DNA-PK component may determine the level of interaction of such DNA with a relevant HRR component.
Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Yu-Fen
YF
Lin
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
Hatsumi
H
Nagasawa
Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts, United States of America.
John B
JB
Little
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
Takamitsu A
TA
Kato
Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Hung-Ying
HY
Shih
Department of Clinical Sciences, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Xian-Jin
XJ
Xie
Department of Biosciences, Brookhaven National Laboratory, Upton, New York, United States of America.
Paul F
PF
Wilson
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
John R
JR
Brogan
Institute of Regenerative Medicine and Biofunction, Graduate School of Medical Science, Tottori University, Tottori, Japan.
Akihiro
A
Kurimasa
Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
David J
DJ
Chen
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
Joel S
JS
Bedford
Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Benjamin P C
BP
Chen
D000512:Alpha Particles; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D002869:Chromosome Aberrations / Q000528:radiation effects*; D003412:Cricetulus; D059766:DNA End-Joining Repair / Q000528:radiation effects*; D051747:DNA-Activated Protein Kinase / Q000235:genetics*; D005720:Gamma Rays; D006801:Humans; D011836:Radiation Tolerance; D059767:Recombinational DNA Repair / Q000528:radiation effects*; D012854:Sister Chromatid Exchange / Q000528:radiation effects
D051747:DNA-Activated Protein Kinase