LMTK1/AATYK1 Is a Novel Regulator of Axonal Outgrowth That Acts via Rab11 in a Cdk5-Dependent Manner
LMTK1/AATYK1 Is a Novel Regulator of Axonal Outgrowth That Acts via Rab11 in a Cdk5-Dependent Manner
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DOI：
10.1523/jneurosci.5317-11.2012
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发表时间：
2012-05
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影响因子：
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通讯作者：
Tetsuya Takano;M. Tomomura;Nozomu Yoshioka;Koji Tsutsumi;Yukichi Terasawa;Taro Saito;H. Kawano;
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文献类型：
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作者：
Tetsuya Takano;M. Tomomura;Nozomu Yoshioka;Koji Tsutsumi;Yukichi Terasawa;Taro Saito;H. Kawano;
轴突生长是细胞骨架动力学和膜运输协调的过程；然而，对负责调节膜供应的蛋白质知之甚少。LMTK1（狐猴激酶1）/AATYK1（凋亡相关酪氨酸激酶1）是一种在神经元中高度表达的丝氨酸/苏氨酸激酶。我们最近报道了LMTK1在CHO-K1细胞的内体运输循环中发挥作用。本研究利用小鼠脑皮质神经元，探讨LMTK1在轴突生长中的作用以及Cdk5对其的调节作用。LMTK1在培养中轴突生长时，在Cdk5磷酸化位点Ser34位点表达并磷酸化，并与Rab11A（调节再循环核内体运输的小GTPase）在核周区域和轴突共定位。过表达未磷酸化的突变体LMTK1-S34A可显著促进培养神经元的轴突生长。由于Rab11A失活，LMTK1位于Rab11A的上游，增强的轴突生长减少。出乎意料的是，通过敲低或基因靶向下调LMTK1也显著增强了轴突伸长。rab11a阳性囊泡在lmtk1缺失神经元轴突中的顺行运输速度比在野生型神经元轴突中的快。这种增强的轴突生长被LMTK1-WT或LMTK1-S34D突变体逆转，而LMTK1-S34A则不能逆转。因此，LMTK1可以通过cdk5依赖的方式调节Rab11A活性负向控制轴突生长，Cdk5-LMTK1-Rab11是参与轴突生长的新信号通路。
Axonal outgrowth is a coordinated process of cytoskeletal dynamics and membrane trafficking; however, little is known about proteins responsible for regulating the membrane supply. LMTK1 (lemur kinase 1)/AATYK1 (apoptosis-associated tyrosine kinase 1) is a serine/threonine kinase that is highly expressed in neurons. We recently reported that LMTK1 plays a role in recycling endosomal trafficking in CHO-K1 cells. Here we explore the role of LMTK1 in axonal outgrowth and its regulation by Cdk5 using mouse brain cortical neurons. LMTK1 was expressed and was phosphorylated at Ser34, the Cdk5 phosphorylation site, at the time of axonal outgrowth in culture and colocalized with Rab11A, the small GTPase that regulates recycling endosome traffic, at the perinuclear region and in the axon. Overexpression of the unphosphorylated mutant LMTK1-S34A dramatically promoted axonal outgrowth in cultured neurons. Enhanced axonal outgrowth was diminished by the inactivation of Rab11A, placing LMTK1 upstream of Rab11A. Unexpectedly, the downregulation of LMTK1 by knockdown or gene targeting also significantly enhanced axonal elongation. Rab11A-positive vesicles were transported anterogradely more quickly in the axons of LMTK1-deficient neurons than in those of wild-type neurons. The enhanced axonal outgrowth was reversed by LMTK1-WT or the LMTK1-S34D mutant, which mimics the phosphorylated state, but not by LMTK1-S34A. Thus, LMTK1 can negatively control axonal outgrowth by regulating Rab11A activity in a Cdk5-dependent manner, and Cdk5–LMTK1–Rab11 is a novel signaling pathway involved in axonal outgrowth.