The Exocyst Complex Associates with Microtubules to Mediate Vesicle Targeting and Neurite Outgrowth

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Abstract
During neuronal development, vesicles are targeted to the growth cone to promote neurite outgrowth and synaptogenesis. The Exocyst complex is an essential macromolecule in the secretory pathway that may play a role in vesicle targeting. Although it has been shown that this complex is enriched in rat brain, the molecular mechanism underlying its function is largely unknown. Here, we report that the Exocyst complex coimmunoprecipitates with microtubules from total rat brain lysate. Additionally, the Exocyst complex subcellular localization changes on neuronal differentiation. In undifferentiated pheochromocytoma (PC12) cells, this complex is associated with microtubules at the microtubule organizing center. However, in differentiated PC12 cells and cultured hippocampal neurons, the Exocyst complex and microtubules extend to the growing neurite and colocalize at the growth cone with synaptotagmin. Inhibition of the NGF-activated MAP kinase pathway blocks the Exocyst complex and microtubule redistribution, abolishing neurite outgrowth and promoting cytosolic accumulation of secretory vesicles. Consistently, the overexpression of Exocyst sec10 subunit mutant blocks neurite outgrowth. These results indicate that the Exocyst complex targets secretory vesicles to specific domains of the plasma membrane through its association with the microtubules, promoting neurite outgrowth.