Vigneron Suzanne, Brioudes Estelle, Burgess Andrew, Labbé Jean-Claude, Lorca Thierry, Castro Anna
Centre de Recherche de Biochimie Macromoléculaire, CNRS UMR 5237, IFR 122, Labellisée Ligue Nationale Contre le Cancer, Universités Montpellier 2 et 1, Montpellier, France.
EMBO J. 2009 Sep 16;28(18):2786-93. doi: 10.1038/emboj.2009.228. Epub 2009 Aug 13.
Greatwall (GW) is a new kinase that has an important function in the activation and the maintenance of cyclin B-Cdc2 activity. Although the mechanism by which it induces this effect is unknown, it has been suggested that GW could maintain cyclin B-Cdc2 activity by regulating its activation loop. Using Xenopus egg extracts, we show that GW depletion promotes mitotic exit, even in the presence of a high cyclin B-Cdc2 activity by inducing dephosphorylation of mitotic substrates. These results indicate that GW does not maintain the mitotic state by regulating the cyclin B-Cdc2 activation loop but by regulating a phosphatase. This phosphatase is PP2A; we show that (1) PP2A binds GW, (2) the inhibition or the specific depletion of this phosphatase from mitotic extracts rescues the phenotype induced by GW inactivation and (3) the PP2A-dependent dephosphorylation of cyclin B-Cdc2 substrates is increased in GW-depleted Xenopus egg extracts. These results suggest that mitotic entry and maintenance is not only mediated by the activation of cyclin B-Cdc2 but also by the regulation of PP2A by GW.
长城激酶（GW）是一种新型激酶，在细胞周期蛋白B-Cdc2活性的激活和维持中具有重要作用。尽管其诱导这种效应的机制尚不清楚，但有人提出GW可能通过调节其激活环来维持细胞周期蛋白B-Cdc2的活性。利用非洲爪蟾卵提取物，我们发现即使在细胞周期蛋白B-Cdc2活性较高的情况下，GW的缺失也会通过诱导有丝分裂底物的去磷酸化促进有丝分裂退出。这些结果表明，GW不是通过调节细胞周期蛋白B-Cdc2激活环来维持有丝分裂状态，而是通过调节一种磷酸酶来实现。这种磷酸酶是蛋白磷酸酶2A（PP2A）；我们发现：（1）PP2A与GW结合；（2）在有丝分裂提取物中抑制该磷酸酶或特异性去除该磷酸酶可挽救由GW失活诱导的表型；（3）在缺失GW的非洲爪蟾卵提取物中，细胞周期蛋白B-Cdc2底物的PP2A依赖性去磷酸化增加。这些结果表明，有丝分裂的进入和维持不仅由细胞周期蛋白B-Cdc2的激活介导，还由GW对PP2A的调节介导。
