INDUCTION AND REJOINING OF DNA DOUBLE-STRAND BREAKS AND INTERPHASE CHROMOSOME BREAKS AFTER EXPOSURE TO X-RAYS IN ONE NORMAL AND 2 HYPERSENSITIVE HUMAN FIBROBLAST CELL-LINES

The aim of this work was to measure simultaneously and in a quantitati ve manner double-strand breaks (DSBs), interphase chromosome breaks an d cell lethality either immediately after irradiation, or at various t imes thereafter (up to 24 h), in cells of three nontransformed human f ibroblast cell lines of widely different intrinsic radiosensitivity. W e wished to assess initial damage, repair kinetics and residual damage at the DNA and the chromosome level, and to correlate these parameter s with cell killing. We employed HF19 cells, a normal fibroblast cell line, AT2 cells, a radiosensitive cell line from a patient suffering f rom ataxia telangiectasia (AT), and 180BR cells, a radiosensitive cell line from a patient with no clinical symptoms of AT. AT2 and 180BR ce lls, in addition to being radiosensitive, also display a reduced abili ty to repair potentially lethal damage compared to HF19 cells. The yie ld of DSBs, as measured by pulsed-field gel electrophoresis, is simila r in all three cell Lines (slopes correspond to 1.6-1.7% Gy(-1) of DNA -associated radioactivity released from the gel well into the lane). I n contrast, residual DSBs measured 24 h after irradiation are almost z ero for HF19 cells (0.1% confidence interval = 0-1.4%), but are 12.5% (+/-2.3%) and 43.8% (+/-1.2%) of those measured immediately after irra diation in AT2 and 180BR cells, respectively. Residual interphase chro mosome breaks are 11.6% (+/-1.6%), 29.7% (+/-5.7%) and 41.4% (+/-2.2%) of those measured immediately after irradiation in HF19, AT2 and 180B R cells, respectively. Neither the initial yield of DSBs nor that of e xcess interphase chromosome breaks can explain the differences in radi osensitivity between the three cell lines; however, there is a correla tion between residual DSBs, rate of DSB rejoining at 24 h, residual in terphase chromosome breaks on the one hand and cell survival on the ot her hand. (C) 1995 by Radiation Research Society