RAPID STIMULATION OF AMYLOID PRECURSOR PROTEIN RELEASE BY EPIDERMAL GROWTH-FACTOR - ROLE OF PROTEIN-KINASE-C

The amyloid precursor protein (APP) of Alzheimer's disease is a transm embrane protein that is cleaved by an uncharacterized enzyme known as alpha-secretase within its extracellular/intraluminal domain after the activation of guanine nucleotide-binding protein-coupled receptors li nked to phosphoinositide hydrolysis. The secretory process results in the release of large soluble derivatives of APP (APPs), and, when elic ited by muscarinic receptor activation, exhibits both protein kinase C (PKC)-dependent and tyrosine phosphorylation-dependent components [Sl ack, Breu, Petryniak, Srivastava and Wurtman (1995) J. Biol. Chem. 270 , 8337-8344]. In this report we examine the regulation of the release of APPs by epidermal growth factor (EGF) receptors, which possess intr insic tyrosine kinase activity, and are coupled to a variety of effect ers including phosphoinositide-specific phospholipase C gamma. In A431 cells, EGF caused time-dependent and dose-dependent increases in the formation of inositol phosphates in cultures prelabelled with myo-[H-3 ]inositol, and in the release of APPs into the culture medium; the two responses exhibited similar time courses and EC50 values for EGF. Con comitant with these effects, there were concentration-dependent (3-300 ng/ml) increases in the phosphorylation of tyrosine residues in sever al proteins, including the EGF receptor itself The specific PKC antago nist GF 109203X decreased the effect of EGF by approx. 35 % at a conce ntration that abolished the stimulation of the release of APPs by the PKC activator PMA. Tyrphostin AG 1478, an inhibitor of EGF receptor ty rosine kinase, abolished the EGF-induced release of APPs. These result s demonstrate that in A431 cells, activation of the EGF receptor stimu lates alpha-secretase activity by a mechanism that is partly dependent on PKC activity.