NCS1 regulates Ca2+-Dependent Focal Exocytosis of Golgi-derived Vesicles to Help Phagocytic uptake in Macrophages

During phagocytic uptake by macrophages, role of Golgi apparatus was previously ruled out. Notably all such reports were limited to Fc{gamma}-receptor mediated phagocytosis. Here we unravel a highly devolved mechanism for recruitment of Golgi-derived secretory vesicles during phagosome biogenesis, which was important for uptake of most cargos except IgG-coated ones. We report recruitment of Mannosidase-II positive Golgi-derived vesicles during uptake of diverse targets including latex beads, E. coli, Salmonella Typhimurium and Mycobacterium tuberculosis in human and mouse macrophages. The recruitment of Mannosidase-II vesicles was an early event mediated by focal exocytosis and coincided with the recruitment of transferrin receptor, VAMP3 and dynamin-2. Brefeldin A treatment inhibited Mannosidase-II recruitment and phagocytic uptake of serum coated or uncoated latex beads and E. coli. However consistent with previous studies, Brefeldin A treatment did not affect uptake of IgG-coated latex beads. Mechanistically recruitment of Mannosidase-II vesicles during phagocytic uptake required Ca2+ from both extra and intra-cellular sources apart from PI3Kinase, microtubules and dynamin-2. Extracellular Ca2+ via voltage-gated Ca2+ channels establish a Ca2+-dependent local PIP3 gradient, which guides the focal movement of Golgi-derived vesicles to the site of uptake. We confirmed Golgi-derived vesicles recruited during phagocytosis were secretory vesicles as their recruitment was sensitive to depletion of VAMP2 or NCS1 however recruitment of recycling endosome marker VAMP3 was unaffected. Both VAMP2 and NCS1 depletion individually resulted in the reduced uptake by macrophages. Together the study provides a previously unprecedented role of Golgi-derived secretory vesicles in phagocytic uptake, the key innate defense function.