Phospholipases stimulate secretion in RBL mast cells

Roles for glycerophospholipids in exocytosis have been proposed, but remain controversial. Phospholipases are stimulated following the activation of t he high-affinity receptor for immunoglobulin E (IgE) in mast cells. To stud y the biochemical sequelae that lead to degranulation, broken cell systems were employed. We demonstrate that the addition of three distinct types of exogenous phospholipases (i.e., bcPLC, scPLD, and tfPLA(2)), all of which h ydrolyze phosphatidylcholine (PC), trigger degranulation in permeabilized R BL-2H3 cells, a mucosal mast cell line. Production of bioactive lipids by t hese phospholipases promotes release of granule contents through the plasma membrane and acts downstream of PKC, PIP-L, and Rho subfamily GTPases in r egulated secretion. These exogenous phospholipase-induced degranulation pat hways circumvent specific factors activated following stimulation of the Ig E receptor as well as in ATP- and GTP-dependent intracellular pathways. Tak en together, these results suggest that regulated secretion may be achieved in vitro in the absence of cytosolic factors via phospholipase activation and that products of PC hydrolysis can promote exocytosis in mast cells.