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Chromatin- and temperature-dependent modulation of radiation-induced double-strand breaks
K Elmroth1, J Nygren, B Stenerlöw
1Department of Oncology, Göteborg University Sahlgrenska University Hospital SE-413 45 Göteborg Sweden. kecke.elmroth@oncology.gu.se
Purpose:
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.
Materials And 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.
Conclusion:
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.