Department of Biology, Graduate School of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
Dev Cell. 2011 Sep 13;21(3):506-19. doi: 10.1016/j.devcel.2011.06.029. Epub 2011 Aug 25.
In vertebrates, unfertilized eggs are arrested at metaphase of meiosis II by Mos and Emi2, an inhibitor of the APC/C ubiquitin ligase. In Xenopus, Cdk1 phosphorylates Emi2 and both destabilizes and inactivates it, whereas Mos recruits PP2A phosphatase to antagonize the Cdk1 phosphorylation. However, how Cdk1 phosphorylation inhibits Emi2 is largely unknown. Here we show that multiple N-terminal Cdk1 phosphorylation motifs bind cyclin B1-Cdk1 itself, Plk1, and CK1δ/ε to inhibit Emi2. Plk1, after rebinding to other sites by self-priming phosphorylation, partially destabilizes Emi2. Cdk1 and CK1δ/ε sequentially phosphorylate the C-terminal APC/C-docking site, thereby cooperatively inhibiting Emi2 from binding the APC/C. In the presence of Mos, however, PP2A-B56β/ε bind to Emi2 and keep dephosphorylating it, particularly at the APC/C-docking site. Thus, Emi2 stability and activity are dynamically regulated by Emi2-bound multiple kinases and PP2A phosphatase. Our data also suggest a general role for Cdk1 substrate phosphorylation motifs in M phase regulation.
在脊椎动物中，未受精卵通过 Mos 和 Emi2 阻滞在减数分裂 II 中期，Emi2 是 APC/C 泛素连接酶的抑制剂。在非洲爪蟾中，Cdk1 磷酸化 Emi2，使其失稳并失活，而 Mos 招募 PP2A 磷酸酶来拮抗 Cdk1 的磷酸化。然而，Cdk1 磷酸化如何抑制 Emi2 在很大程度上仍是未知的。在这里，我们表明多个 N 端 Cdk1 磷酸化基序结合 cyclin B1-Cdk1 本身、Plk1 和 CK1δ/ε 以抑制 Emi2。Plk1 通过自我引发的磷酸化重新结合到其他位点后，部分使 Emi2 失稳。Cdk1 和 CK1δ/ε 顺序磷酸化 APC/C docking 位点，从而协同抑制 Emi2 与 APC/C 的结合。然而，在 Mos 存在的情况下，PP2A-B56β/ε 结合到 Emi2 并使其持续去磷酸化，特别是在 APC/C docking 位点。因此，Emi2 的稳定性和活性受到 Emi2 结合的多种激酶和 PP2A 磷酸酶的动态调节。我们的数据还表明 Cdk1 底物磷酸化基序在 M 期调控中的普遍作用。
