Rs. Malyapa et al., RADIATION SENSITIVITY CORRELATES WITH CHANGES IN DNA SUPERCOILING ANDNUCLEOID PROTEIN-CONTENT IN CELLS OF 3 CHINESE-HAMSTER CELL-LINES, Radiation research, 140(3), 1994, pp. 312-320
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.