Phospholipase Cη2 Activation Redirects Vesicle Trafficking by Regulating F-actin

Abstract

PI(4,5)P2 localizes to sites of dense core vesicle exocytosis in neuroendocrine cells and is required for Ca(2+)-triggered vesicle exocytosis, but the impact of local PI(4,5)P2 hydrolysis on exocytosis is poorly understood. Previously, we reported that Ca(2+)-dependent activation of phospholipase Cη2 (PLCη2) catalyzes PI(4,5)P2 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 PLCη2 in vesicle exocytosis as a Ca(2+)-dependent regulator of the actin cytoskeleton. Depolarization of neuroendocrine PC12 cells with 56 or 95 mm KCl buffers increased peak Ca(2+) levels to ~400 or ~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 PLCη2 to catalyze PI(4,5)P2 hydrolysis. The decrease in PI(4,5)P2 promoted F-actin disassembly, which increased exocytosis of newly arriving vesicles. Consistent with its role as a Ca(2+)-dependent regulator of the cortical actin cytoskeleton, PLCη2 localized with F-actin filaments. The results highlight the importance of PI(4,5)P2 for coordinating cytoskeletal dynamics with vesicle exocytosis and reveal a new role for PLCη2 as a Ca(2+)-dependent regulator of F-actin dynamics and vesicle trafficking.