Calcium-regulated Exocytosis in Neuroendocrine Cells: Intersectin-1L Stimulates Actin Polymerization and Exocytosis by Activating Cdc42

Actin cytoskeleton remodeling is a critical step of regulated exocytosis in many secretory cell types, including neuroendocrine cells. While the classical model considers the cortical actin network as a physical barrier preventing the uncontrolled recruitment of secretory granules to the plasma membrane docking sites, recent evidence supports the idea that actin polymerization also plays a more active role in the late stages of exocytosis. However, the molecular machinery underlying this positive function of actin in the course of exocytosis remains largely unknown. Here, we propose that the neuronal guanine nucleotide exchange factor, intersectin-1L, activates the GTPase Cdc42, which in turn provides de novo actin filaments that are important for calcium-regulated exocytosis in PC12 cells.