Protection of DNA from radiation-induced double-strand breaks: influence of replication and nuclear proteins.
OBJECTIVE
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.


METHODS
Induction of dsb was studied in two human adenocarcinoma 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 14C or pulse labelled with 3H, were assessed by pulsed-field gel electrophoresis (PFGE).


CONCLUSIONS
Stepwise removal of DNA-bound proteins from the chromatin increased the amount of radiation-induced dsb in both cell lines. However, the protective effect of DNA-associated proteins on dsb induction was significantly reduced in DNA of replicating S-phase cells compared with bulk DNA of plateau phase cells. These data show that proteins associated with the DNA have a different protective effect on radiation-induced dsb, rendering replicating DNA with open chromatin structure more sensitive to dsb induction by ionizing radiation.
Sak
A
A
Institute of Radiotherapy, Charité, Humboldt-University Berlin, Germany. alis.sak@charite.de
Stuschke
M
M
Wurm
R
R
Budach
V
V
D002843:Chromatin / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004261:DNA Replication; D004273:DNA, Neoplasm / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects*; D016521:Electrophoresis, Gel, Pulsed-Field; D006657:Histones / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016196:S Phase; D014407:Tumor Cells, Cultured
D002843:Chromatin; D004273:DNA, Neoplasm; D006657:Histones; D009687:Nuclear Proteins