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Studies of DNA repair strategies in response to complex DNA damages
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology. (Centre for Radiation Protection Research)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main aim of this thesis was to study the role of the indirect actions of γ-rays and α-particles on the complexity of primary DNA damages and the repair fidelity of major DNA repair pathways: non-homologous end joining (NHEJ), homologous recombination repair (HRR) and base excision repair (BER). The complexity of radiation-induced damages increases and the proximity between damages decreases with increasing LET due to formation of ionization clusters along the particle track. The complexity of damages formed can be modified by the free radical scavenger dimethyl sulfoxide (DMSO). In addition, the effects of low doses of low dose rate γ-radiation on cellular response in terms of differentiation were investigated.

Paper I investigates the role of the indirect effect of radiation on repair fidelity of HRR, NHEJ and BER when damages of different complexity were induced by radiation or by potassium bromate. We found that potassium bromate induces complex DNA damages through processing of base modifications and that the indirect effect of radiation has a high impact on the NHEJ pathway. Results in paper II confirmed our conclusions in paper I that the indirect effect from both γ-rays and α-particles has an impact on all three repair pathways studied and NHEJ benefits the most when the indirect effect of radiation is removed.

In paper III we investigated the effects of low dose/dose rate γ-radiation on the developmental process of neural cells by using cell models for neurons and astrocytes. Our results suggest that low dose/dose rate γ-radiation attenuates differentiation and down-regulates proteins involved in the differentiation process of neural cells by an epigenetic rather than cytotoxic mechanism.

Place, publisher, year, edition, pages
Department of Genetics, Microbiology and Toxicology, Stockholm University , 2012. , 41 p.
Keyword [en]
ionizing radiation, complex DNA damage, indirect effect of radiation, dimethyl sulfoxide
National Category
Cell Biology
Research subject
Molecular Genetics
Identifiers
URN: urn:nbn:se:su:diva-72472ISBN: 978-91-7447-456-5 (print)OAI: oai:DiVA.org:su-72472DiVA: diva2:503576
Public defence
2012-03-23, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2012-03-01 Created: 2012-02-13 Last updated: 2012-12-14Bibliographically approved
List of papers
1. The indirect effect of radiation reduces the repair fidelity of NHEJ as verified in repair deficient CHO cell lines exposed to different radiation qualities and potassium bromate
Open this publication in new window or tab >>The indirect effect of radiation reduces the repair fidelity of NHEJ as verified in repair deficient CHO cell lines exposed to different radiation qualities and potassium bromate
2012 (English)In: Mutation research, ISSN 0027-5107, E-ISSN 1873-135X, Vol. 731, 125-132 p.Article in journal (Refereed) Published
Abstract [en]

The complexity of DNA lesions induced by ionizing radiation is mainly dependent on radiation quality, where the indirect action of radiation may contribute to different extent depending on the type of radiation under study. The effect of indirect action of radiation can be investigated by using agents that induce oxidative DNA damage or by applying free radical scavengers. The aim of this study was to investigate the role of the indirect effect of radiation for the repair fidelity of non-homologous end-joining (NHEJ), homologous recombination repair (HRR) and base excision repair (BER) when DNA damage of different complexity was induced by gamma radiation, alpha particles or from base damages (8-oxo-dG) induced by  potassium bromate (KBrO3).

CHO cells lines deficient in XRCC3 (HRR) irs1SF, XRCC7 (NHEJ) V3-3 and XRCC1 (BER) EM9 were irradiated in the absence or presence of the free radical scavenger dimethyl sulphoxide (DMSO). The endpoints investigated included rate of cell proliferation by the DRAG assay, clonogenic cell survival and the level of primary DNA damage by the comet assay.

The results revealed that the indirect effect of low-LET radiation significantly reduced the repair fidelity of both NHEJ and HRR pathways. For high-LET radiation the indirect effect of radiation also significantly reduced the repair fidelity for the repair deficient cell lines. The results suggest further that the repair fidelity of the error prone NHEJ repair pathway is more impaired by the indirect effect of high-LET radiation relative to the other repair pathways studied. 

The response to bromate observed for the two DSB repair deficient cell lines strongly support earlier studies that bromate induces complex DNA damages. The significantly reduced repair fidelity of irs1SF and V3-3 suggests that NHEJ as well as HRR are needed for the repair, and that complex DSBs are formed after bromate exposure.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
clustered DNA damage, ionizing radiation, potassium bromate, dimethyl sulfoxide
National Category
Cell Biology
Research subject
Toxicology
Identifiers
urn:nbn:se:su:diva-72470 (URN)10.1016/j.mrfmmm.2011.12.008 (DOI)000300918800016 ()
Available from: 2012-02-27 Created: 2012-02-13 Last updated: 2017-12-07Bibliographically approved
2. The response of HRR-deficient Chinese hamster ovary cell line reveals significant contribution of the indirect effect from both γ-rays and α-particles on NHEJ pathway
Open this publication in new window or tab >>The response of HRR-deficient Chinese hamster ovary cell line reveals significant contribution of the indirect effect from both γ-rays and α-particles on NHEJ pathway
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In order to investigate the relative involvement of the different DNA repair pathways NHEJ, HRR and BER in repair of DNA lesions of different complexity, we have compared clonogenic survival and induction of micronuclei in a panel of repair-deficient CHO cell lines after exposure to γ-rays and α-particle radiation. The complexity of the DNA lesions formed was also modified by exposures to2 MDMSO, a potent radical scavenger, which is known to interact with the lesions produced by direct hits on DNA.

The NHEJ pathway gained the most from scavenging of the free radicals after irradiation to γ-rays or α-particles as evaluated by cell survival and the yields of MN. Results presented here also implicate that clustered base damages were induced by α-radiation and contributed to the yield of DNA double-strand breaks.

Keyword
ionizing radiation, indirect effect, dimethyl sulfoxide, clusterd DNA damage
National Category
Biological Sciences
Research subject
Toxicology
Identifiers
urn:nbn:se:su:diva-72551 (URN)
Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2012-02-16Bibliographically approved
3. Low-Dose/Dose-Rate gamma Radiation Depresses Neural Differentiation and Alters Protein Expression Profiles in Neuroblastoma SH-SY5Y Cells and C17.2 Neural Stem Cells
Open this publication in new window or tab >>Low-Dose/Dose-Rate gamma Radiation Depresses Neural Differentiation and Alters Protein Expression Profiles in Neuroblastoma SH-SY5Y Cells and C17.2 Neural Stem Cells
Show others...
2011 (English)In: Radiation Research, ISSN 0033-7587, E-ISSN 1938-5404, Vol. 175, no 2, 185-192 p.Article in journal (Refereed) Published
Abstract [en]

The effects of low doses of ionizing radiation on cellular development in the nervous system are presently unclear. The focus of the present study was to examine low-dose gamma-radiation-induced effects on the differentiation of neuronal cells and on the development of neural stem cells to glial cells. Human neuroblastoma SH-SY5Y cells were exposed to (137)Cs gamma rays at different stages of retinoic acid-induced neuronal differentiation, and neurite formation was determined 6 days after exposure. When SH-SY5Y cells were exposed to low-dose-rate gamma rays at the onset of differentiation, the number of neurites formed per cell was significantly less after exposure to either 10, 30 or 100 mGy compared to control cells. Exposure to 10 and 30 mGy attenuated differentiation of immature C17.2 mouse-derived neural stem cells to glial cells, as verified by the diminished expression of glial fibrillary acidic protein. Proteomic analysis of the neuroblastoma cells by 2D-PAGE after 30 mGy irradiation showed that proteins involved in neuronal development were downregulated. Proteins involved in cell cycle and proliferation were altered in both cell lines after exposure to 30 mGy; however, the rate of cell proliferation was not affected in the low-dose range. The radiation-induced attenuation of differentiation and the persistent changes in protein expression is indicative of an epigenetic rather than a cytotoxic mechanism. (C) 2011 by Radiation Research Society

National Category
Biophysics Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-67348 (URN)10.1667/RR2090.1 (DOI)000287113500006 ()
Note
authorCount :5Available from: 2011-12-28 Created: 2011-12-28 Last updated: 2017-12-08Bibliographically approved

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