Identification of DNA double strand breaks at chromosome boundaries along the track of particle irradiation.
Chromosomal translocations arise from misrejoining of DNA double strand breaks (DSBs) between loci located on two chromosomes. One current model suggests that spatial proximity of potential chromosomal translocation partners influences translocation probability. Ionizing radiation (IR) is a potent inducer of translocations. Accumulating evidence demonstrates that particle irradiation more frequently causes translocations compared with X-ray irradiation. This observation has led to the hypothesis that the high frequency of translocations after particle irradiation may be due to the formation of DSBs at chromosome boundaries along the particle track, because such DSBs can be misrejoined between distinct chromosomes. In this study, we simultaneously visualized the site of IR-induced DSBs and chromosome position by combining Immunofluorescence and fluorescence in situ hybridization. Importantly, the frequency of γH2AX foci at the chromosome boundary of chromosome 1 after carbon-ion irradiation was >4-fold higher than that after X-ray irradiation. This observation is consistent with the idea that particle irradiation generates DSBs at the boundaries of two chromosomes along the track. Further, we showed that resolution of γH2AX foci at chromosome boundaries is prevented by inhibition of DNA-PKcs activity, indicating that the DSB repair is NHEJ-dependent. Finally, we found that γH2AX foci at chromosome boundaries after carbon-ion irradiation contain DSBs undergoing DNA-end resection, which promotes repair utilizing microhomology mediated end-joining during translocation. Taken together, our study suggests that the frequency of DSB formation at chromosome boundaries is associated with the incidence of chromosomal translocations, supporting the notion that the spatial proximity between breaks is an important factor in translocation formation. © 2016 Wiley Periodicals, Inc.
Research Program for Heavy Ion Therapy, Division of Integrated Oncology Research, Gunma University Initiative for Advanced Research (GIAR), Gunma, Japan.
Atsuko
A
Niimi
Division of Radiation Biology and Protection, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
Motohiro
M
Yamauchi
Faculty of Pharmacy, Silpakorn University, Nakhon Pathom, Thailand.
Siripan
S
Limsirichaikul
Advanced Scientific Research Leaders Development Unit, Gunma University, Gunma, Japan.
Ryota
R
Sekine
Department of Radiation Oncology, Gunma University, Gunma, Japan.
Takahiro
T
Oike
Department of Radiation Oncology, Gunma University, Gunma, Japan.
Hiro
H
Sato
Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
Keiji
K
Suzuki
Department of Radiation Oncology, Massachusetts General Hospital/Harvard Medical School, Boston, MA.|International Open Laboratory, Gunma University Initiative for Advanced Research (GIAR), Gunma, Japan.
Kathryn D
KD
Held
Research Program for Heavy Ion Therapy, Division of Integrated Oncology Research, Gunma University Initiative for Advanced Research (GIAR), Gunma, Japan.|Department of Radiation Oncology, Gunma University, Gunma, Japan.
Takashi
T
Nakano
Advanced Scientific Research Leaders Development Unit, Gunma University, Gunma, Japan.
Atsushi
A
Shibata
D002250:Carbon Radioisotopes; D002878:Chromosomes, Human, Pair 1 / Q000235:genetics / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004249:DNA Damage / Q000528:radiation effects; D059766:DNA End-Joining Repair / Q000528:radiation effects*; D004260:DNA Repair / Q000528:radiation effects; D005347:Fibroblasts / Q000528:radiation effects; D006657:Histones / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D011839:Radiation, Ionizing; D014178:Translocation, Genetic / Q000528:radiation effects*; D014965:X-Rays
D002250:Carbon Radioisotopes; C468783:H2AX protein, human; D006657:Histones