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Live dynamics of 53BP1 DNA damage foci induced by a combination of clustered and dispersed double strand breaks
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. University of Warsaw, Poland.
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Cells react differently to alpha particle-induced clustered DNA damage and X-ray induced dispersed DNA damage. Little is known about how they cope when both types of damage are induced simultaneously. We used live cell microscopy to analyse the formation and motion of the DNA double strand break (DSB) repair factor 53BP1-GFP foci in U2OS cells exposed to a mixed beam of alpha particles and X-rays. We observed that the kinetics of appearance and decline of mixed beam-induced foci resemble that of after alpha particle irradiation. They showed a fast increase and almost no repair during the imaging time, while X-ray-exposed cells showed a strong increase and decline over the observation interval. Secondly, focus sizes were similar to X-ray-induced foci, with both being significantly smaller than those induced by alpha particles; thirdly, they showed a high mean pixel intensity already at early time point after irradiation. Finally, focus mobility was reduced relative to alpha particle and X-ray-induced foci, which was correlated with a delayed appearance of a fraction of mixed beam-induced foci. These results suggest that cells react to a simultaneous induction of clustered and dispersed DNA damage by sequestering the 53BP1 protein in selected foci, possibly at sites of clustered DNA damage. This happens at the cost of foci forming at chromatin areas containing dispersed, simple damage. Our results highlight that the DNA damage response to a combination of dispersed and clustered DNA damage in the same cell differs significantly from the response to exposure with single radiation types.

Keyword [en]
Mixed beam, radiation, DNA damage, 53BP1 foci
National Category
Cell Biology
Research subject
Molecular Bioscience
Identifiers
URN: urn:nbn:se:su:diva-145503OAI: oai:DiVA.org:su-145503DiVA: diva2:1129862
Funder
Swedish Radiation Safety Authority
Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2017-08-10Bibliographically approved
In thesis
1. Cellular responses to combined irradiation with alpha particles and X-rays
Open this publication in new window or tab >>Cellular responses to combined irradiation with alpha particles and X-rays
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mixed radiation fields, where different ionizing particles act together, are very important in radiobiology and in radiation protection. Mixed beams are not only the most common form of radiation exposure, but the prediction of their biological effect is also full of uncertainties. Currently, prediction of the biological damage of exposure to mixed radiation fields is based on the default assumption of simple additivity between the effects of all the radiation in the field. This assumption has been proven to be incorrect. Indeed, the simultaneous effect of different radiation qualities has been shown to be greater than additive, namely synergistic. This implicates that, for instance, the predicted cancer risk for astronauts, that remain a prolonged time in space, is currently underestimated as well as the risk of developing secondary cancer for radiotherapy patients.

This thesis aims at understanding the mechanisms behind the cellular response to simultaneous exposure to alpha particles and X-rays (that is referred as mixed beam).

Paper I describes the cell killing and the mutagenic effect of mixed beam exposure in human lymphoblastoid wild type and in cells with impaired capacity to repair oxidative DNA damage .We found that oxidative DNA damage plays an important role in the lethal, synergistic effect of mixed beams.

Paper II and III investigates whether mixed beams exposure leads to an augmented DNA double strand breaks (DSB) induction or to an altered response of the cellular DSB repair machinery. We found that mixed irradiation resulted in synergistic induction of DSB, and that those lesions were repaired with slow kinetics.

Paper IV focuses on the effect of mixed beams at the level of DNA damage in normal cells. Induction and repair of DNA lesions such as DSB, single strand breaks and apurinic sites was quantified using the alkaline comet assay. We found that alpha particles and X-rays interacted in inducing DNA damage. Moreover, although mixed beam exposure resulted in strong activation of the DNA damage response, it resulted in delayed repair.

Although more research is needed to fully elucidate the mechanisms behind the detected synergistic effects, our results strongly suggest that an overwhelmed DNA-repair system causes delay in repair of damage.

Place, publisher, year, edition, pages
Stockholm: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 2017. 88 p.
Keyword
Radiation, DNA damage, mutations, alpha particles, X-rays, mixed beam
National Category
Biological Sciences
Research subject
Molecular Bioscience
Identifiers
urn:nbn:se:su:diva-145509 (URN)978-91-7649-887-3 (ISBN)978-91-7649-888-0 (ISBN)
Public defence
2017-09-27, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Radiation Safety Authority
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-09-04 Created: 2017-08-07 Last updated: 2017-08-28Bibliographically approved

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