Chromatin organization contributes to non-randomly distributed double-strand breaks after exposure to high-LET radiation.
The influence of higher-order chromatin structure on the non-random distribution of DNA double-strand breaks induced by high-LET radiation was investigated. Five different chromatin structures (intact cells, condensed and decondensed chromatin, nucleoids and naked genomic DNA) from GM5758 cells or K562 cells were irradiated with (137)Cs gamma-ray photons and 125 keV/microm nitrogen ions (16-25 MeV/nucleon). DNA was purified with a modified lysis procedure to avoid release of heat-labile sites, and fragment size distributions and double-strand break yields were analyzed by different pulsed-field gel electrophoresis protocols. Whereas double-strand breaks in photon-irradiated cells were randomly distributed, irradiation of intact K562 cells with high-LET nitrogen ions produced an excess of non-randomly distributed DNA fragments 10 kb-1 Mbp in size. Complete removal of proteins eliminated this non-random component. There was a gradual increase in the yield of double-strand breaks for each chromatin decondensation step, and compared to intact cells, the yields for naked DNA (in buffer without scavengers) increased 83 and 25 times after photon and nitrogen-ion irradiation, respectively. The corresponding relative biological effectiveness decreased from 1.6-1.8 for intact cells to 0.49 for the naked DNA. We conclude that the organization of DNA into chromatin fiber and higher-order structures is responsible for the majority of non-randomly distributed double-strand breaks induced by high-LET radiation. However, our data suggest a complex interaction between track structure and chromatin organization over several levels.
Radulescu
Irina
I
Division of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden. irina_radulescu@yahoo.com
Elmroth
Kecke
K
Stenerlöw
Bo
B
D002843:Chromatin / Q000737:chemistry* / Q000528:radiation effects*; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects*; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000737:chemistry* / Q000528:radiation effects*; D005720:Gamma Rays; D020450:Heavy Ions; D006801:Humans; D020014:K562 Cells; D018499:Linear Energy Transfer; D008970:Molecular Weight; D011829:Radiation Dosage; D012062:Relative Biological Effectiveness
D002843:Chromatin; D004247:DNA