Cullin3-KLHL20對PDZ-RhoGEF泛素化在神經滋養因子引起神經突生長之探討

Abstract

神經細胞軸突分枝及生長在神經發育及再生過程中扮演重要的角色。在本篇論文中，我們發現在神經細胞中, BTB-kelch蛋白KLHL20藉由與Cul3結合形成泛素接合酉毎複合體而具有促進神經細胞軸突分枝及生長功能。Cul3-KLHL20 接合酉毎複合體會促使一個在腦部高度表現的蛋白PDZ-RhoGEF的泛素化，並造成其降解。我們更進一步發現，神經滋養因子(Neurotrophins)可以藉由影響PDZ-RhoGEF的泛素化進而促使神經元的生長。神經細胞接收到神經滋養因子的刺激後，會活化下游的p38 MAPK，進一步促使PDZ-RhoGEF磷酸化。磷酸化的PDZ-RhoGEF會被KLHL20所辨識，並將其送至Cul3-KLHL20 接合酉毎複合體，促進PDZ-RhoGEF的泛素化，並引發PDZ-RhoGEF蛋白的降解。此一過程會進導致RhoA活性降低，而促使神經元的生長。由於神經滋養因子在神經發育過程中扮演著重要的角色，不僅可以促進神經細胞的存活更具有促進神經元生長的功能。因此，我們的研究提出了神經滋養因子藉由促進PDZ-RhoGEF降解而達到其調控神經分化的功能。

The induction of neurite outgrowth and arborization is critical for developmental and regenerative processes. Here we report that the BTB-kelch protein KLHL20 promoted neurite outgrowth and arborization in hippocampal and cortical neurons through its interaction with Cullin3 to form a ubiquitin ligase complex. This complex targeted PDZ-RhoGEF, a protein abundantly expressed in brain, for ubiquitin-dependent proteolysis, thereby restricting RhoA activity and facilitating growth cone spreading and neurite outgrowth. Importantly, targeting PDZ-RhoGEF to KLHL20 required PDZ-RhoGEF phosphorylation by p38 MAPK. In response to p38-activating neurotrophins, such as brain-derived neurotrophic factor and neurotrophin-3, KLHL20-mediated PDZ-RhoGEF destruction was potentiated, leading to neurotrophin-induced neurite outgrowth. Our study identified a ubiquitin-dependent pathway that targets PDZ-RhoGEF destruction to facilitate neurite outgrowth, and indicates a key role of this pathway in neurotrophin-induced neuronal morphogenesis.