Physiological role of protein synthesis in nerve growth cone

本研究的目的是阐明局部蛋白质合成在神经生长锥对细胞外刺激的运动和形态变化中的生理作用。在2002年，我们研究了神经生长因子诱导的神经突起生长的作用，使用鸡背根神经节细胞培养层粘连蛋白的局部蛋白质合成。我们首先研究了钙调节蛋白翻译因子真核细胞延伸因子2（eEF 2）的表达和分布模式。我们发现磷酸化的eEF 2分布在细胞体和生长锥中，但表达水平较低。高浓度KCl刺激后，细胞生长锥塌陷，突起生长受到抑制，磷酸化eEF 2表达水平显著升高，并伴随细胞内钙离子浓度的升高，表明生长锥内eEF 2以钙离子依赖的方式磷酸化，参与了调节突起生长的信号级联反应。在2003年，我们研究了本地蛋白质合成的semaphoring 3A（Sema 3A）诱导的生长锥崩溃的作用。Sema 3A诱导eIF 4 E的磷酸化和用茴香霉素阻断蛋白质合成抑制生长锥塌陷。暴露于Fyn激酶抑制剂lavemdustin-A的细胞显示由Sema 3A诱导的eIF 4 E的eIF 4 E磷酸化降低。由于Sema 3A信号被认为是独立的钙信号，这表明，神经突生长和生长锥崩溃介导的局部蛋白质合成的独立调节。

The aim of this study is to clarity the physiological roles of local protein synthesis in change of motility and morphology of nerve growth cone in response to extracellular stimuli. In 2002, we examined the roles of local protein synthesis in neurite outgrowth induced by nerve growth factor using chick dorsal root ganglion cells cultured on laminin. We first investigated the expression and distribution patterns of calcium-regulated protein translational factor, eukaryotic elongation factor-2 (eEF2). We found that phosphorylated eEF2 was distributed in the cell body and the growth cones, but the expression level was low. The cells exposed to high KCl stimulus showed growth cone collapse and inhibition of neurite outgrowth, and the expression level of phosphorylated eEF2 was significantly increased with intracellular calcium transient induced by high KCl stimulus, suggesting that eEF2 within growth cones was phosphorylated in a calcium-dependent manner and was involved in the signal cascade regulating neurite outgrowth. In 2003, we examined the roles of local protein synthesis in growth cone collapse induced by semaphoring 3A (Sema3A). Sema3A induced phosphorylation of eIF4E and blockade of protein synthesis with anisomycin inhibited the growth cone collapse. The cells to expose to Fyn kinase inhibitor, lavemdustin-A showed decrease of eIF4E phosphorylation of eIF4E induced by Sema3A. Since Sema3A signaling is considered to be independent of calcium signaling, it is suggested that neurite outgrowth and growth cone collapse mediated by local protein synthesis are independently regulated.