Regulatory mechanisms of neurotransmitter release by cytokine and growth factors.

神经营养因子和各种生长因子在大脑中表达，在发育和成人大脑中都起着重要的作用。近年来的研究表明，多种营养因子参与了突触可塑性的调节，但其具体机制尚不清楚。为了阐明营养因子介导的突触前功能调控的分子机制，我们研究了表皮生长因子（EGF）和胰岛素样生长因子-1 （IGF-1）对克隆大鼠嗜铬细胞瘤PC12细胞神经递质释放的影响。短暂的EGF和IGF-1处理以浓度依赖的方式增强PC12细胞Ca^<2+>依赖性多巴胺（DA）的释放。EGF激活了丝裂原活化蛋白激酶（MAPK）和磷脂酰肌醇3-激酶（pi3 -激酶）途径，并且EGF依赖的DA释放增强被MAPK激酶抑制剂和pi3激酶抑制剂抑制。与此形成鲜明对比的是，IGF…More -1激活了pi3 -激酶途径而没有激活MAPK途径，并且IGF-1依赖性增强被pi3 -激酶抑制剂抑制而不被MAPK激酶抑制剂抑制。egfp标记的蛋白激酶B （PKB）的PH结构域在PC12细胞中表达，选择性结合磷脂酰肌醇3,4-二磷酸和磷脂酰肌醇3,4,5-三磷酸，在EGF或神经生长因子（NGF）处理后易位到质膜上，而这种易位被有效的pi3激酶抑制剂wortmannin消除。相比之下，IGF-1未引起EGFP-PKB-PH的重分布。EGF和NGF诱导肌动蛋白细胞骨架的重组，尤其是在细胞过程的尖端，而IGF-1仅引起轻微的变化。在EGF或NGF处理后，超过9种细胞蛋白被pi3激酶的下游酶PKB磷酸化，但不同的一组蛋白被IGF-1磷酸化。这些结果表明，pi3激酶通过两种不同的机制参与神经递质释放的增强。少

Neurotrophins and various growth factors are expressed in brain and play important roles both in developing and in adult brains. Recent studies indicate that various trophic factors involve in the regulation of synaptic plasticity underlying learning and memory, however, the precise mechanisms are still remained obscure. In order to elucidate molecular mechanisms of trophic factor-mediated regulation of presynaptic functions, effects of epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1) on neurotransmitter release were studied in clonal rat pheochromocytoma PC12 cells. A brief treatment of EGF and IGF-1 enhanced Ca^<2+> dependent dopamine (DA) release from PC12 cells in concentration-dependent manners. EGF activated both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-kinase) pathways, and EGF-dependent enhancement of DA release was suppressed by a MAPK kinase inhibitor as well as by PI3-kinase inhibitors. By the striking contrast, IGF … More -1 activated PI3-kinase pathway but not MAPK pathway, and IGF-1-dependent enhancement was suppressed by PI3-kinase inhibitor but not by MAPK kinase inhibitor. EGFP-tagged PH domain of protein kinase B (PKB), which selectively bind to phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-triphosphate, expressed in PC12 cells was translocated to plasma membrane after treatments with either EGF or nerve growth factor (NGF), and the translocations were abolished by wortmannin, a potent inhibitor of PI3-kinase. By the contrast, no significant redistribution of EGFP-PKB-PH was induced by IGF-1. EGF as well as NGF induced reorganization of actin cytoskeleton especially in the tip of cell process, however, only slight change was induced by IGF-1. More than nine cellular proteins were phosphorylated by PKB, a downstream enzyme of PI3-kinase, after a treatment with either EGF or NGF, however different set of proteins were phosphorylated by IGF-1. These results indicate that PI3-kinase participates in the enhancement of neurotransmitter release by two distinct mechanisms. Less