Induction and rejoining of DNA double-strand breaks in normal human skin fibroblasts after exposure to radiation of different linear energy transfer:Possible roles of track structure and chromatin organization

DNA double-strand breaks are nonrandomly induced by high-LET radiation. Dif ferences in the induction and rejoining of DSBs after irradiation with ions having different LET were detected by fragment analysis, The data obtained indicate that the track structure of the traversing particle and its inter action with the different chromatin structures of the cellular DNA influenc e the yield as well as the distribution of the induced damage, The inductio n and rejoining of clustered DSBs induced by the same nitrogen ion fluence at LETs of 80-225 keV/mum were investigated by a detailed analysis of the D NA fragmentation patterns in normal human fibroblasts. The DSBs in the cell s were allowed to rejoin during incubations for 0-20 h, Two separate pulsed -field gel electrophoresis protocols were used, optimized for separation of fragments in the size ranges 1-6 Mbp and 5 kbp-1.5 Mbp, A strong influence of LET on the level of DSB induction was evident. The DSB yield increased from 4.5 +/- 0.2 to 10.0 +/- 0.3 DSBs per particle traversal through the ce ll nucleus when LET increased from 80 to 225 keV/mum. Further, the size dis tribution of the DNA fragments showed a significant dependence on radiation quality, with an excess of fragments at 50-200 kbp and around 1 Mbp, Diffe rences in repair kinetics were also evident, with slower rejoining for incr easing LET, and the initial nonrandom fragment distributions were still pre sent after 1 h of repair. (C) 2001 by Radiation Research Society.