Phospholipase C2 Activation Redirects Vesicle Trafficking by Regulating F-actin

PI(4,5)P-2 localizes to sites of dense core vesicle exocytosis in neuroendocrine cells and is required for Ca2+-triggered vesicle exocytosis, but the impact of local PI(4,5)P-2 hydrolysis on exocytosis is poorly understood. Previously, we reported that Ca2+-dependent activation of phospholipase C2 (PLC2) catalyzes PI(4,5)P-2 hydrolysis, which affected vesicle exocytosis by regulating the activities of the lipid-dependent priming factors CAPS (also known as CADPS) and ubiquitous Munc13-2 in PC12 cells. Here we describe an additional role for PLC2 in vesicle exocytosis as a Ca2+-dependent regulator of the actin cytoskeleton. Depolarization of neuroendocrine PC12 cells with 56 or 95 mm KCl buffers increased peak Ca2+ levels to approximate to 400 or approximate to 800 nm, respectively, but elicited similar numbers of vesicle exocytic events. However, 56 mm K+ preferentially elicited the exocytosis of plasma membrane-resident vesicles, whereas 95 mm K+ preferentially elicited the exocytosis of cytoplasmic vesicles arriving during stimulation. Depolarization with 95 mm K+ but not with 56 mm K+ activated PLC2 to catalyze PI(4,5)P-2 hydrolysis. The decrease in PI(4,5)P-2 promoted F-actin disassembly, which increased exocytosis of newly arriving vesicles. Consistent with its role as a Ca2+-dependent regulator of the cortical actin cytoskeleton, PLC2 localized with F-actin filaments. The results highlight the importance of PI(4,5)P-2 for coordinating cytoskeletal dynamics with vesicle exocytosis and reveal a new role for PLC2 as a Ca2+-dependent regulator of F-actin dynamics and vesicle trafficking.