THE RELEASE OF ALZHEIMERS-DISEASE BETA-AMYLOID PEPTIDE IS REDUCED BY PHORBOL TREATMENT

Amyloid precursor protein (APP) is cleaved predominantly within the be ta amyloid peptide (BAP) domain to release a non-amyloidogenic amino-t erminal PN2 fragment. Treatment of cells with phorbol dibutyrate, an a gent which activates protein kinase C, has been shown to increase the release of an amino-terminal fragment. A panel of mutant APP reporter constructs was expressed in which each of the potential phosphorylatio n sites located within the cytoplasmic domain of APP was replaced with alanine residues. Phorbol response patterns were unchanged for each o f these mutants, suggesting that induced cleavage occurs independently of APP substrate phosphorylation. We find that phorbol (a) increases the release of a PN2 fragment that is consistent with the normal secre tase activity, (b) decreases the release of a shorter amino terminal A PP fragment that is cleaved near the amino terminus of BAP, and (c) de creases the release of BAP which was identified based on electrophoret ic mobility, epitope mapping, and radiosequencing. These data demonstr ate that pharmacological treatment can reduce the formation of BAP and suggests that protein kinase C activators could be developed as thera peutic agents to block BAP formation.