The repair of gamma-radiation-induced DNA damage is inhibited by microcystin-LR, the PP1 and PP2A phosphatase inhibitor
The genotoxic activity of microcystin-LR (MC-LR) is a matter of debate. MC-LR is known to be a phosphatase inhibitor and it may be expected that it is involved in the regulation of the activity of DNA-dependent protein kinase (DNA-PK), the key enzyme involved in the repair of radiation-induced DNA d...
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Published in | Mutagenesis Vol. 21; no. 1; pp. 83 - 90 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Oxford
Oxford University Press
01.01.2006
Oxford Publishing Limited (England) |
Subjects | |
Online Access | Get full text |
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Summary: | The genotoxic activity of microcystin-LR (MC-LR) is a matter of debate. MC-LR is known to be a phosphatase inhibitor and it may be expected that it is involved in the regulation of the activity of DNA-dependent protein kinase (DNA-PK), the key enzyme involved in the repair of radiation-induced DNA damage. We studied the effect of MC-LR on the repair capacity of radiation-induced DNA damage in human lymphocytes and human glioblastoma cell lines MO59J and MO59K. A dose of 0.5 µg/ml of MC-LR was chosen because it induced very little early apoptosis which gives no false positive results in the comet assay. Human lymphocytes in G0-phase of the cell cycle were pre-treated with MC-LR for 3 h and irradiated with 2 Gy of gamma radiation. The kinetics of DNA repair was assessed by the comet assay. In addition the frequencies of chromosomal aberrations were analysed. The pre-treatment with MC-LR inhibited the repair of radiation-induced damage and lead to enhanced frequencies of chromosomal aberrations including dicentric chromosomes. The results of a split-dose experiment, where cells were exposed to two 1.5 Gy doses of radiation separated by 3 h with or without MC-LR, confirmed that the toxin increased the frequency of dicentric chromosomes. We also determined the effect of MC-LR and ionizing radiation on the frequency of γ-H2AX foci. The pre-treatment with MC-LR resulted in reduced numbers of γ-H2AX foci in irradiated cells. In order to elucidate the impact of MC-LR on DNA-PK we examined the kinetics of DNA repair in human glioblastoma MO59J and MO59K cells. Both cell lines were exposed to 10 Gy of X-rays and DNA repair was analysed by the comet assay. A strong inhibitory effect was observed in the MO59K but not in the MO59J cells. These results indicate that DNA-PK might be involved in DNA repair inhibition by MC-LR. |
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Bibliography: | To whom correspondence should be addressed at: Department of Radiobiology and Immunology, Institute of Biology, Swietokrzyska Academy, ul. Swietokrzyska 15, 25-406 Kielce, Poland. Tel: +4841 349 62 98; Fax: +4841 349 62 92; Email: alankoff@pu.kielce.pl ark:/67375/HXZ-ZSJ3FH0K-G istex:677C53E612430F0C25C52E97A84632FC7D4A387A local:gel002 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0267-8357 1464-3804 |
DOI: | 10.1093/mutage/gel002 |