Effects of protein kinase inhibitors on the progression of the cell cycle. especially on the initiation of M phase.

以非洲爪蟾（Xenopus laevis）未受精卵为原料制备促成熟因子硫酸铵组分。研究了K252衍生物和staurosporine对MPF和cdc2激酶活性的抑制作用。K252a和staurosporine抑制MPF活性的IC50分别为15和1.5 ug/ml，抑制cdc2激酶活性的IC50分别为3.5和0.4 ug/ml。K252b和KT5926抑制cdc2激酶活性的IC50分别为0.15和60 ug/ml。蛋白激酶抑制剂抑制作用的强弱顺序依次为K252b> staurosporine> K252a> KT5926。因此，cdc2激酶的性质与其他蛋白激酶明显不同，特别是其对K252b的敏感性比K252a高20倍以上。蛋白激酶抑制剂对MPF激活过程的影响也进行了研究。虽然30 ug/ml K252a和1.5 ug/ml K252b对cdc2激酶的抑制程度大致相同，但前者抑制cdc2蛋白的去磷酸化和p110的硫代磷酸化，而后者没有。因此，负责MPF活化的蛋白激酶可能与cdc2激酶本身不同。对培养细胞M期起始的抑制作用以staurosporine最强，其次是K252a和K252b。这可能是由于K252b通过细胞膜的渗透性较低，但也有可能抑制剂作用于cdc2激酶本身以外的其他靶点。

Ammonium sulfate fraction of maturation-promoting factor (MPF) was prepared from unfertilized eggs of Xenopus laevis. The inhibitory effects of K252 derivatives and staurosporine on MPF and cdc2 Kinase activities of the MPF fraction were examined. K252a and staurosporine inhibited the MPF activity with IC50 of 15 and 1.5 ug/ml, respectively and the cdc2 Kinase activity with IC50 of 3.5 and 0.4 ug/ml, respectively. K252b and KT5926 inhibited the cdc2 kinase activity with IC50 of 0.15 and 60 ug/ml, respectively. The decreasing order of the protein kinase inhibitors in the potency of the inhibitory actions was K252b> staurosporine> K252a> KT5926. Thus, the property of cdc2 kinase is remarkably different from that of the other protein kinases, especially in that its sensitivity to K252b is greater by more than 20 times than to K252a. The effects of the protein kinase inhibitors on the processes leading to the activation of MPF were also examined. Although 30 ug/ml K252a and 1.5 ug/ml K252b inhibited cdc2 kinase approximately to the same extent, the former inhibited the dephosphorylation of cdc2 protein and the thiophosphorylation of p110, whereas the latter did not. Therefore, the protein kinase responsible for the activation of MPF is suggeted to be different from cdc2 kinase itself. As to the inhibitory effects on the initiation of M phase of cultured cells staurosporine was the strongest, followed by K252a and K252b. This may be due to the low permeability of K252b across the cell membrane, but it is also possible that the inhibitors act on other targets than cdc2 kinase itself.