Mutation induction by okadaic acid, a protein phosphatase inhibitor, in CHL cells, but not in S. typhimurium.
Okadaic acid (OA) is a specific and strong inhibitor of protein phosphatases 1 and 2A present in eukaryotes, and a potent promoter of carcinogenesis in mouse skin. In this study, we examined the mutagenicity of OA. OA did not induce mutations in S. typhimurium TA100 and TA98, with or without a microsomal metabolic activation system. However, it was strongly mutagenic to Chinese hamster lung (CHL) cells without a microsomal activation system, as shown using diphtheria toxin (DT) resistance (DTr) as a selective marker. Treatment of CHL cells with OA at 17.5 ng/ml induced 164 DTr mutants per 10(6) survivors. A plot of the mutation frequency against the OA concentration gave a concave curve, and the mutant frequency was calculated to be 5500/10(6) survivors/micrograms, with OA in the dose range of 10-15 ng/ml. This value was about 680 times that of ethyl methanesulfonate (EMS), and comparable to that of 2-amino-N6-hydroxyadenine, one of the strongest known mutagens. Elongation factor 2 (EF-2) obtained from 4 DTr clones was not ADP-ribosylated by DT fragment A. PCR-direct sequencing revealed that the hot spot of EF-2 for EMS mutagenesis in CHO-K1 cells, the first letter of codon 717, was not a hot spot for OA mutagenesis in CHL cells.
Aonuma
S
S
Carcinogenesis Division, National Cancer Center Research Institute, Tokyo, Japan.
Ushijima
T
T
Nakayasu
M
M
Shima
H
H
Sugimura
T
T
Nagao
M
M
D000818:Animals; D001483:Base Sequence; D002460:Cell Line / Q000187:drug effects; D002470:Cell Survival; D006224:Cricetinae; D004247:DNA; D004167:Diphtheria Toxin / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics; D004988:Ethers, Cyclic / Q000633:toxicity*; D008168:Lung / Q000166:cytology / Q000187:drug effects; D008969:Molecular Sequence Data; D009152:Mutagenicity Tests; D009153:Mutagens / Q000633:toxicity*; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics
D004167:Diphtheria Toxin; D004988:Ethers, Cyclic; D009153:Mutagens; D019319:Okadaic Acid; D004247:DNA; D010749:Phosphoprotein Phosphatases