The repair of gamma-radiation-induced DNA damage is inhibited by microcystin-LR, the PP1 and PP2A phosphatase inhibitor

• Published in: Mutagenesis 2006-01, Vol.21 (1), p.83-90
• Main Authors: Lankoff, A., Bialczyk, J., Dziga, D., Carmichael, W.W., Gradzka, I., Lisowska, H., Kuszewski, T., Gozdz, S., Piorun, I., Wojcik, A.
• Format: Article
• Language: English
• Subjects: Apoptosis - drug effects; Apoptosis - radiation effects; Biological and medical sciences; Chromosome Aberrations; Comet Assay; DNA Damage - drug effects; DNA Damage - radiation effects; DNA Repair - drug effects; DNA Repair - radiation effects; DNA-Activated Protein Kinase - metabolism; Enzyme Inhibitors - adverse effects; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Gamma Rays - adverse effects; Glioblastoma - drug therapy; Glioblastoma - pathology; Glioblastoma - radiotherapy; Histones - metabolism; Humans; Kinetics; Lymphocytes - cytology; Lymphocytes - drug effects; Lymphocytes - radiation effects; Marine Toxins - adverse effects; Microcystins; Molecular and cellular biology; Molecular genetics; Mutagenesis. Repair; Peptides, Cyclic - adverse effects; Phosphoprotein Phosphatases - antagonists & inhibitors; Receptors, Neuropeptide Y - antagonists & inhibitors; Resting Phase, Cell Cycle - drug effects; Resting Phase, Cell Cycle - radiation effects
• ISSN: 0267-8357; 1464-3804
• DOI: 10.1093/mutage/gel002

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.