Aonuma S, Ushijima T, Nakayasu M, Shima H, Sugimura T, Nagao M
Carcinogenesis Division, National Cancer Center Research Institute, Tokyo, Japan.
Mutat Res. 1991 Sep-Oct;250(1-2):375-81. doi: 10.1016/0027-5107(91)90194-s.
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.
冈田酸（OA）是真核生物中存在的蛋白磷酸酶1和2A的特异性强抑制剂，也是小鼠皮肤致癌作用的强效促进剂。在本研究中，我们检测了OA的致突变性。无论有无微粒体代谢活化系统，OA均未在鼠伤寒沙门氏菌TA100和TA98中诱导突变。然而，如使用对白喉毒素（DT）抗性（DTr）作为选择标记所示，在无微粒体活化系统的情况下，它对中国仓鼠肺（CHL）细胞具有强烈的致突变性。用17.5 ng/ml的OA处理CHL细胞，每10⁶个存活细胞诱导出164个DTr突变体。以突变频率对OA浓度作图得到一条凹曲线，在OA浓度为10 - 15 ng/ml的剂量范围内，计算出突变频率为5500/10⁶个存活细胞/微克。该值约为甲磺酸乙酯（EMS）的680倍，与已知最强诱变剂之一的2-氨基-N⁶-羟基腺嘌呤相当。从4个DTr克隆获得的延伸因子2（EF-2）未被DT片段A进行ADP-核糖基化。PCR直接测序显示，在CHO-K1细胞中EMS诱变的EF-2热点，即密码子717的第一个字母，在CHL细胞中不是OA诱变的热点。
