Division of Neurosurgery, Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
Mol Cell Biol. 2010 Nov;30(21):5160-7. doi: 10.1128/MCB.00448-10. Epub 2010 Sep 7.
The m(7)G cap binding protein eukaryotic initiation factor 4E (eIF4E) is a rate-limiting determinant of protein synthesis. Elevated eIF4E levels, commonly associated with neoplasia, promote oncogenesis, and phosphorylation of eIF4E at Ser209 is critical for its tumorigenic potential. eIF4E phosphorylation is catalyzed by mitogen-activated protein kinase (MAPK)-interacting serine/threonine kinase (Mnk), a substrate of Erk1/2 and p38 MAPKs. Interaction with the scaffolding protein eIF4G, which also binds eIF4E, brings Mnk and its substrate into physical proximity. Thus, Mnk-eIF4G interaction is important for eIF4E phosphorylation. Through coimmunoprecipitation assays, we showed that MAPK-mediated phosphorylation of the Mnk1 active site controls eIF4G binding. Utilizing a naturally occurring splice variant, we demonstrated that the C-terminal domain of Mnk1 restricts its interaction with eIF4G, preventing eIF4E phosphorylation in the absence of MAPK signaling. Furthermore, using a small-molecule Mnk1 inhibitor and kinase-dead mutant, we established that Mnk1 autoregulates its interaction with eIF4G, releasing itself from the scaffold after phosphorylation of its substrate. Our findings indicate tight control of eIF4E phosphorylation through modulation of Mnk1-eIF4G interaction.
m(7)G 帽结合蛋白真核起始因子 4E(eIF4E)是蛋白质合成的限速决定因素。eIF4E 水平升高，通常与肿瘤发生有关，促进了肿瘤的发生，而 eIF4E 在丝氨酸 209 位的磷酸化对于其致瘤潜能至关重要。eIF4E 的磷酸化由丝氨酸/苏氨酸激酶（Mnk）催化，Mnk 是 Erk1/2 和 p38 MAPK 的底物，是有丝分裂原激活蛋白激酶（MAPK）-相互作用的丝氨酸/苏氨酸激酶。与支架蛋白 eIF4G 的相互作用，eIF4G 也与 eIF4E 结合，将 Mnk 和其底物拉近。因此，Mnk-eIF4G 相互作用对于 eIF4E 磷酸化很重要。通过共免疫沉淀实验，我们表明，MAPK 介导的 Mnk1 活性位点磷酸化控制 eIF4G 的结合。利用天然存在的剪接变体，我们证明 Mnk1 的 C 端结构域限制了其与 eIF4G 的相互作用，从而阻止了 MAPK 信号缺失时 eIF4E 的磷酸化。此外，我们使用小分子 Mnk1 抑制剂和激酶失活突变体，证明 Mnk1 自我调节其与 eIF4G 的相互作用，在其底物磷酸化后从支架上释放出来。我们的研究结果表明，通过调节 Mnk1-eIF4G 相互作用，可以对 eIF4E 磷酸化进行严格控制。
