Muscarine enhances soluble amyloid precursor protein secretion in human neuroblastoma SH-SY5Y by a pathway dependent on protein kinase C α, src-tyrosine kinase and extracellular signal-regulated kinase but not phospholipase C

The signalling pathways by which muscarine and epidermal growth factor (EGF) regulate the secretion of the α-secretase cleavage product (sAPPα) of the amyloid precursor protein (APP) were examined in the human neuroblastoma SH-SY5Y. Using specific inhibitors it was found that over 80% of sAPPα secretion, enhanced by muscarine, occurred via the extracellular signal-regulated kinase (ERK1/2) member of the mitogen-activated protein kinase (MAPK) family and was dependent on protein kinase Cα (PKCα) and a member of the Src family of non-receptor tyrosine kinases (Src-TK). In contrast the stimulation of sAPPα secretion by EGF was not affected by inhibitors of PKC nor Src-TK but was dependent on ERK1/2. In addition muscarine-enhanced sAPPα secretion and ERK1/2 activation were inhibited 60 and 80%, respectively, by micromolar concentrations of the phosphatidylinositol 3 kinase (PI-3K) inhibitor wortmannin. In comparison wortmannin decreased EGF stimulation of sAPPα secretion and ERK 1/2 activation by approximately 40%. Unexpectedly, U73122, an inhibitor of phosphoinositide-specific phospholipase C, did not inhibit muscarine enhancement of sAPPα secretion. These data are discussed in relation to a pathway for the enhancement of sAPPα secretion by muscarine which involves the activation of a Src-TK by G-protein β/γ-subunits leading to activation of PKCα, and ERK1/2 by a mechanism not involving phospholipase C.