SECRETED FORM OF BETA-AMYLOID PRECURSOR PROTEIN ACTIVATES PROTEIN-KINASE-C AND PHOSPHOLIPASE C-GAMMA-1 IN CULTURED EMBRYONIC RAT NEOCORTICAL CELLS

The secreted form of beta-amyloid precursor protein (sAPP) has been re ported to exert various biological activities in cultured neurons. The signal transduction mechanisms underlying these physiological functio ns of sAPP remain unclear. We now report that treatment of neural cell s with the secreted form of APP695 (sAPP695) leads to dose- and time-d ependent increase in phosphorylation of the endogenous substrates with a molecular mass of 80, 57 and 43 kDa. Pretreatment of cells with pro tein kinase C (PKC) inhibitor H-7 reduced phosphorylation of the 80- a nd 43-kDa proteins in a dose-dependent manner. The effect of sAPP695 o n the phosphorylation is mimicked by phorbol 12-myristate-13-acetate ( PMA). Downregulation of PKC by prolonged treatment of cells with PMA a bolished sAPP695-enhanced phosphorylation of the 80- and 43-kDa protei ns, indicating PKC is involved in the sAPP695-enhanced phosphorylation of these proteins in the cells. We also suggest that the 80- and 43-k Da proteins phosphorylated by sAPP695-stimulation are the major PKC su bstrates myristoylated alanine-rich C-kinase substrate and growth-asso ciated protein-43. Furthermore, we demonstrate that tyrosine phosphory lation of phospholipase C gamma 1 and formation of inositol 1,4,5-tris phosphate were increased by sAPP695-stimulation. These observations su ggest that sAPP695 induces the activation of the signaling pathways th rough a stimulation of phosphoinositide-PKC cascade. (C) 1998 Elsevier Science B.V.