Journal
NUCLEIC ACIDS RESEARCH
Volume 39, Issue 19, Pages 8416-8429Publisher
OXFORD UNIV PRESS
DOI: 10.1093/nar/gkr463
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Funding
- European Space Agency (ESA) [AO-08-IBER]
- Bundesministerium fur Bildung und Forschung (BMBF)
- Kompetenzverbund Strahlenforschung (KVSF) [02NUK005C, 02NUK001B]
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In cells exposed to ionizing radiation (IR), double-strand breaks (DSBs) form within clustered-damage sites from lesions disrupting the DNA sugar-phosphate backbone. It is commonly assumed that these DSBs form promptly and are immediately detected and processed by the cellular DNA damage response (DDR) apparatus. This assumption is questioned by the observation that after irradiation of naked DNA, a fraction of DSBs forms minutes to hours after exposure as a result of temperature dependent, chemical processing of labile sugar lesions. Excess DSBs also form when IR-exposed cells are processed at 50 degrees C, but have been hitherto considered method-related artifact. Thus, it remains unknown whether DSBs actually develop in cells after IR exposure from chemically labile damage. Here, we show that irradiation of 'naked' or chromatin-organized mammalian DNA produces lesions, which evolve to DSBs and add to those promptly induced, after 8-24 h in vitro incubation at 37 degrees C or 50 degrees C. The conversion is more efficient in chromatin-associated DNA, completed within 1 h in cells and delayed in a reducing environment. We conclude that IR generates sugar lesions within clustered-damage sites contributing to DSB formation only after chemical processing, which occurs efficiently at 37 degrees C. This subset of delayed DSBs may challenge DDR, may affect the perceived repair kinetics and requires further characterization.
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