PHYSIOLOGICAL LEVELS OF BETA-AMYLOID PEPTIDE STIMULATE PROTEIN-KINASE-C IN PC12 CELLS

Alzheimer's beta-amyloid peptide (A beta) is normally present at nanom olar concentrations in body fluids and in the medium of cultured cells . In vitro experiments have shown that A beta has neurotrophic effects and can promote neuronal adhesion and elongation of axon-like process es. In an attempt to understand the molecular mechanisms underlying su ch effects, we have recently reported that nanomolar doses of A beta c an stimulate protein tyrosine phosphorylation and activate phosphatidy linositol-3-kinase in neuronal cells. Here we show evidence that A bet a can also activate protein kinase C, a serine/threonine kinase, in PC 12 cells. First, using a serine-containing S6 peptide as an exogenous substrate, we found that nanomolar levels of A beta peptides 1-40 or 1 -42 significantly stimulated an S6 phosphorylating kinase activity, wh ereas the A beta(40-1) reverse sequence peptide had no effect. Down-re gulation of PKC by prolonged (18 h) treatment with 1 mu M PMA prevente d the A beta-induced S6 phosphorylation. Using a more specific PKC sub strate, N-terminal acetylated peptide (4-14) from myelin basic protein , we then demonstrated that A beta indeed increased PKC activity and t hat this activity could be blocked by the PKC inhibitor, staurosporine . Finally, immunoblotting experiments showed that A beta induced trans location of PKC gamma from cytosol to membrane and also significantly reduced cytosolic PKC alpha levels. Taken together, these data suggest that physiological levels of A beta can regulate PKC activity. (C) 19 97 Elsevier Science B.V.