Chromatin- and temperature-dependent modulation of radiation-induced double-strand breaks.
OBJECTIVE
To investigate the influence of chromatin organization and scavenging capacity in relation to irradiation temperature on the induction of double-strand breaks (DSB) in structures derived from human diploid fibroblasts.


METHODS
Agarose plugs with different chromatin structures (intact cells+/-wortmannin, permeabilized cells with condensed chromatin, nucleoids and DNA) were prepared and irradiated with X-rays at 2 or 37 degrees C and lysed using two different lysis protocols (new ice-cold lysis or standard lysis at 37 degrees C). Induction of DSB was determined by constant-field gel electrophoresis.


RESULTS
The dose-modifying factor (DMF(temp)) for irradiation at 37 compared with 2 degrees C was 0.92 in intact cells (i.e. more DSB induced at 2 degrees C), but gradually increased to 1.5 in permeabilized cells, 2.2 in nucleoids and 2.6 in naked DNA, suggesting a role of chromatin organization for temperature modulation of DNA damage. In addition, DMF(temp) was influenced by the presence of 0.1 M DMSO or 30 mM glutathione, but not by post-irradiation temperature.


CONCLUSIONS
The protective effect of low temperature was correlated to the indirect effects of ionizing radiation and was not dependent on post-irradiation temperature. Reasons for a dose modifying factor <1 in intact cells are discussed.
Elmroth
K
K
Department of Oncology, Göteborg University Sahlgrenska University Hospital SE-413 45 Göteborg Sweden. kecke.elmroth@oncology.gu.se
Nygren
J
J
Stenerlöw
B
B
Hultborn
R
R
D000730:Androstadienes / Q000494:pharmacology; D002460:Cell Line; D002843:Chromatin / Q000528:radiation effects*; D015925:Cryopreservation / Q000379:methods; D004247:DNA / Q000187:drug effects / Q000528:radiation effects*; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects*; D006801:Humans; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D012062:Relative Biological Effectiveness; D013696:Temperature; D000077191:Wortmannin
D000730:Androstadienes; D002843:Chromatin; D004247:DNA; D000077191:Wortmannin