Phosphorylation of Erp1 by p90rsk is required for cytostatic factor arrest in Xenopus laevis eggs
Phosphorylation of Erp1 by p90rsk is required for cytostatic factor arrest in Xenopus laevis eggs
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DOI：
10.1038/nature05696
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发表时间：
2007-04-26
期刊：
影响因子：
64.8
通讯作者：
Kishimoto, Takeo
中科院分区：
文献类型：
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作者：
Nishiyama, Tomoko;Ohsumi, Keita;Kishimoto, Takeo
在受精之前，脊椎动物卵的减数分裂细胞周期被称为细胞生长抑制因子（CSF）的细胞质活性阻滞在减数分裂II的中期（1），这导致后期促进复合物/细胞周期体（APC/C）的抑制，APC/C是一种靶向有丝分裂细胞周期蛋白（减数分裂和有丝分裂的调节蛋白）降解的泛素连接酶（2，3）。最近的研究表明，Erp 1/Erp 2，一种APC/C的抑制蛋白，在建立和维持CSF停滞中具有重要作用（4-6），但其与Mos的关系尚不清楚，Mos是一种促分裂原活化蛋白激酶（MAPK）激酶，通过激活p90核糖体S6激酶（p90 rsk）在建立CSF停滞7中也具有重要作用（8，9）。在这里，我们报告说，在非洲爪蟾卵Erp 1是底物的p90 rsk，和MOS依赖的磷酸化Erp 1的p90 rsk在Thr 336，Ser 342和Ser 344是至关重要的稳定Erp 1和建立CSF逮捕减数分裂II卵母细胞。CSF逮捕的鸡蛋提取物的半定量分析表明，莫斯依赖的Erp 1磷酸化增强，但不产生，Erp 1的活动，维持中期逮捕。我们的研究结果还表明，Erp 1通过在APC/C的羧基末端破坏盒结合APC/C来抑制细胞周期蛋白B降解（10），并且这种结合也通过Mos依赖性磷酸化增强。因此，莫斯和Erp 1合作建立和维持中期II逮捕爪蟾卵。Mos和Erp 1之间的联系为未受精脊椎动物卵中CSF停滞的整体机制提供了分子解释。
Until fertilization, the meiotic cell cycle of vertebrate eggs is arrested at metaphase of meiosis II by a cytoplasmic activity termed cytostatic factor (CSF)(1), which causes inhibition of the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that targets mitotic cyclins - regulatory proteins of meiosis and mitosis - for degradation(2,3). Recent studies indicate that Erp1/ Emi2, an inhibitor protein for the APC/C, has an essential role in establishing and maintaining CSF arrest(4-6), but its relationship to Mos, a mitogen-activated protein kinase ( MAPK) kinase kinase that also has an essential role in establishing CSF arrest 7 through activation of p90 ribosomal S6 kinase (p90rsk)(8,9), is unclear. Here we report that in Xenopus eggs Erp1 is a substrate of p90rsk, and that Mos-dependent phosphorylation of Erp1 by p90rsk at Thr 336, Ser 342 and Ser 344 is crucial for both stabilizing Erp1 and establishing CSF arrest in meiosis II oocytes. Semi-quantitative analysis with CSF-arrested egg extracts reveals that the Mos-dependent phosphorylation of Erp1 enhances, but does not generate, the activity of Erp1 that maintains metaphase arrest. Our results also suggest that Erp1 inhibits cyclin B degradation by binding the APC/C at its carboxy-terminal destruction box(10), and this binding is also enhanced by the Mos-dependent phosphorylation. Thus, Mos and Erp1 collaboratively establish and maintain metaphase II arrest in Xenopus eggs. The link between Mos and Erp1 provides a molecular explanation for the integral mechanism of CSF arrest in unfertilized vertebrate eggs.