RADIATION SENSITIVITY CORRELATES WITH CHANGES IN DNA SUPERCOILING ANDNUCLEOID PROTEIN-CONTENT IN CELLS OF 3 CHINESE-HAMSTER CELL-LINES

We have investigated the composition of nuclear matrix proteins and DN A supercoiling characteristics of cell lines expressing altered radiat ion sensitivity. Chinese hamster ovary cell lines 4364 (wild-type), XR -1 (DSB repair-deficient, radiosensitive) and XR-122 (a radioresistant variant of XR-1 bearing human chromosome 5) were used as a model to s tudy the relationship between intrinsic radiation sensitivity and the level of DNA supercoiling ability within chromatin loops and the compo sition of nuclear matrix proteins. Analysis of the ability of DNA loop domains to undergo changes in DNA supercoiling in the presence of DNA damage revealed that the degree of inhibition of loop rewinding was g reater in the radiation-sensitive cells (XR-1) compared to the radiati on-resistant cells (4364 and XR-122). Furthermore, the loop-rewinding characteristics correlated inversely with the clonogenic survival of t hese cells after exposure to ionizing radiation. Since DNA loops are a nchored to the nuclear matrix by protein-DNA anchor points, a study of the nuclear matrix proteins by high-resolution 2D-PAGE was conducted for these cells to determine whether differential inhibition of loop r ewinding could be due to differences in the DNA loop-protein anchor po ints in these cells. The XR-1 cells showed an overall absence of 13 pr oteins compared to the 4364 cells. Of these 13, 5 were restored in XR- 122 cells. These results are consistent with the hypothesis that stabi lity of the DNA loop domains in the presence of DNA damage contributes to the expression of potentially lethal damage by ionizing radiation.