神經元發育期間生長相關蛋白GAP-43表現與磷酸化之調控機轉探討

Regulatory Mechanisms of Growth-Associated Protein 43 (GAP-43) Expression and Phosphorylation in Developing Neurons

許敏靖(MinChingHsu)

指導教授 ： 李怡萱

臺北醫學大學/醫學院/醫學科學研究所/碩士(2003年)

摘要

生長相關蛋白(Growth-associated protein 43; GAP-43)在神經發育過程中或是神經受損後的修復過程中，對於神經纖維的生長以及調節神經可塑性等均扮演的重要的角色。先前的研究發現，GAP-43的磷酸化與否與其功能性具有極大的相關性。在此，我們利用P19分化之神經細胞研究GAP-43的磷酸化表現及神經纖維生長之影響，結果發現，在神經分化及發育的過程中，PKC可促進GAP-43的磷酸化表現，並且對於神經纖維的正常發育有促進的作用。我們更進一步探討，在發育期的大腦皮質細胞中，活化麩胺酸受體對於GAP-43的表現及磷酸化是否有所影響，並深入探討是透過何種路徑所調控。結果發現，在KA的作用之下，對於GAP-43的表現產生抑制，但是對於GAP-43的磷酸化卻有促進的作用。我們更進一步的證實， KA對於GAP-43之影響可能經由以下三種路徑所調控：(1)經由細胞內鈣增加活化PKC，促使GAP-43磷酸化增加；(2)經由一非G-protein調控之路徑，降低細胞內cAMP濃度，使得PKA活性降低，因而使GAP-43表現下降；(3)藉由G-protein調控，升高細胞內cAMP濃度，使得PKA活性升高，造成GAP-43表現上升。由於此三種作用的互相消長，使得KA刺激之下，GAP-43的表現可能不變或是降低，但確定可顯著增加具有促進神經生長功能活性的Ser-41-phospho-GAP-43的含量。此外，我們也發現皮質固酮會阻斷紅藻胺酸降低cAMP的作用，而使GAP-43的表現得以維持。而皮質固醇亦可與紅藻胺酸同樣的促進GAP-43的磷酸化，但兩者並無加成作用。因此，紅藻胺酸透過促進GAP-43磷酸化而促進神經發育的作用，而其對GAP-43表現的影響，則可能可藉由皮質固醇的共同作用而得以穩定。

關鍵字

生長相關蛋白 ； 紅藻胺酸 ； 磷酸化

並列摘要

Growth- associated protein 43 (GAP-43) plays an important role on neurite outgrowth and neural plasticity in developing or regenerating neurons. It has been shown previously that GAP-43 phosphorylation is related to its function. We herein apply the P19-derived neurons to investigate the relation of GAP-43 phosporylation and relationship of neurite outgrowth. We found that protein kinase C could facilitate GAP-43 phosphorylation and increase neurite outgrowth. We further examined if activate excitatory glutamate receptors could influence GAP-43 expression and phosphorylation, and mediated by which pathway. We found that activated glutamate receptor subtype AMPA/KA receptor by kainic acid could decrease GAP-43 expression and increase GAP-43 phosphorylation. Furthermore, the mechanism of KA induced GAP-43 change could be mediated by three distinct pathways as follows: (1) increase of intracellular calcium concentration, and in turn activates PKC activity to phosphorylate GAP-43 at Ser41; (2) decrease of cAMP concentration and PKA activity through a non-G-protein-mediated pathway, and in turn reduced GAP-43 expression; (3) increase of cAMP concentration and PKA activity through a G-protein-mediated pathway, and facilitated GAP-43 expression. According to these three different pathways KA-induced GAP-43 expression could be decrease or no change, but profound increase of Ser-41-phospho-GAP-43 is consistent. We further found that the presence of cortisterone blocked KA-decreased cAMP and GAP-43 expression, and also enhance GAP-43 phosphorylation to the similar degree as KA. Therefore glucocorticoids might play an important role in stabilizing GAP-43 expression while glutamate signaling is promoting GAP-43 functions in developing central neurons.

並列關鍵字

Growth-associated protein 43 ； kainic acid ； phosphorylation

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