Thr-161 phosphorylation of monomeric Cdc2 -: Regulation by protein phosphatase 2C in Xenopus oocytes
Thr-161 phosphorylation of monomeric Cdc2 -: Regulation by protein phosphatase 2C in Xenopus oocytes
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DOI：
10.1074/jbc.m202742200
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发表时间：
2002-08-09
影响因子：
4.8
通讯作者：
Ozon, R
中科院分区：
文献类型：
--
作者：
De Smedt, V;Poulhe, R;Ozon, R
发育完全的爪蟾卵母细胞在减数分裂的前期被阻滞。再进入减数分裂取决于MPF （m期促进因子或周期蛋白B.Cdc2复合物）的激活，由孕激素触发。前驱停止的卵母细胞含有Cdc2的储存。大部分蛋白以单体形式存在，而被称为pre-MPF的一小部分被发现与细胞周期蛋白b相关。Cdc2的激活取决于两个关键事件：细胞周期蛋白结合和位于t环上的Thr-161残基的激活磷酸化。为了进一步了解Cdc2在Thr-161磷酸化中的调控作用，我们从前期卵母细胞中分离了Cdc2单体。基于细胞周期蛋白的激活和针对Thr-161磷酸化Cdc2的抗体检测，我们首次发现前期卵母细胞含有大量Thr-161磷酸化的Cdc2单体。PP2C是一种Mg2+依赖性磷酸酶，负性地控制Cdc2的Thr-161磷酸化。已经在Thr-161上磷酸化的游离Cdc2群体的意外存在可能有助于产生启动MPF扩增所需的Cdc2激酶活性阈值。
Fully grown Xenopus oocyte is arrested at prophase I of meiosis. Re-entry into meiosis depends on the activation of MPF (M-phase promoting factor or cyclin B.Cdc2 complex), triggered by progesterone. The prophase-arrested oocyte contains a store of Cdc2. Most of the protein is present as a monomer whereas a minor fraction, called pre-MPF, is found to be associated with cyclin B. Activation of Cdc2 depends on two key events: cyclin binding and an activating phosphorylation on Thr-161 residue located in the T-loop. To get new insights into the regulation of Thr-161 phosphorylation of Cdc2, monomeric Cdc2 was isolated from prophase oocytes. Based on its activation upon cyclin addition and detection by an antibody directed specifically against Cdc2 phosphorylated on Thr-161, we show for the first time that the prophase oocyte contains a significant amount of monomeric Cdc2 phosphorylated on Thr-161. PP2C, a Mg2+-dependent phosphatase, negatively controls Thr-161 phosphorylation of Cdc2. The unexpected presence of a population of free Cdc2 already phosphorylated on Thr-161 could contribute to the generation of the Cdc2 kinase activity threshold required to initiate MPF amplification.