A. Sak et al., Protection of DNA from radiation-induced double-strand breaks: influence of replication and nuclear proteins, INT J RAD B, 76(6), 2000, pp. 749-756
Purpose: To study the protective effect of histone and non-histone proteins
on double-strand break (dsb) induction in replicating S-phase DNA as well
as bulk DNA of plateau phase human tumour cells.
Materials and methods: Induction of dsb was studied in two human adenocarci
noma cell lines: Colo320HSR and MCF-7. To assess the influence of chromatin
structure on radiation-induced DNA dsb, different nuclear preparations of
cells, either continuously labelled with C-14 or pulse labelled with H-3, w
ere assessed by pulsed-field gel electrophoresis (PFGE).
Results and conclusions: Stepwise removal of DNA-bound proteins from the ch
romatin increased the amount of radiation-induced dsb in both cell lines. H
owever, the protective effect of DNA-associated proteins on dsb induction w
as significantly reduced in DNA of replicating S-phase cells compared with
bulk DNA of plateau phase cells. These data show that proteins associated w
ith the DNA have a different protective effect on radiation-induced dsb, re
ndering replicating DNA with open chromatin structure more sensitive to dsb
induction by ionizing radiation.