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 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 microg/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 gamma-H2AX foci. The pre-treatment with MC-LR resulted in reduced numbers of gamma-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.
Lankoff
A
A
Department of Radiobiology and Immunology, Institute of Biology, Swietokrzyska Academy, Kielce, Poland. alankoff@pu.kielce.pl
Bialczyk
J
J
Dziga
D
D
Carmichael
W W
WW
Gradzka
I
I
Lisowska
H
H
Kuszewski
T
T
Gozdz
S
S
Piorun
I
I
Wojcik
A
A
D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002869:Chromosome Aberrations; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000009:adverse effects*; D005434:Flow Cytometry; D005720:Gamma Rays / Q000009:adverse effects*; D005909:Glioblastoma / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006657:Histones / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D008387:Marine Toxins / Q000009:adverse effects; D052998:Microcystins; D010456:Peptides, Cyclic / Q000009:adverse effects*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D017476:Receptors, Neuropeptide Y / Q000037:antagonists & inhibitors; D016192:Resting Phase, Cell Cycle / Q000187:drug effects / Q000528:radiation effects
D004791:Enzyme Inhibitors; C468783:H2AX protein, human; D006657:Histones; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D017476:Receptors, Neuropeptide Y; C109491:neuropeptide Y4 receptor; D051747:DNA-Activated Protein Kinase; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR