The beta amyloid cascade plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Therefore, drugs that regulate amyloid precursor protein (APP) processing toward the nonamyloidgenic pathway may have therapeutic potential. Many anti-dementia drugs can regulate APP processing in addition to their pharmacological properties. Deprenyl is a neuroprotective agent used to treat some neurodegenerative diseases, including AD. In the present study, the effects of deprenyl on APP processing were investigated. Using SK-N-SH and PC12 cells, it was demonstrated that deprenyl stimulated the release of the nonamyloidogenic alpha-secretase form of soluble APP (sAPPalpha) in a dose-dependent manner without affecting cellular APP expression. The increase of sAPPalpha secretion by deprenyl was blocked by the mitogen activated protein (MAP) kinase inhibitor U0126 and PD98059, and by the protein kinase C (PKC) inhibitor GF109203X and staurosporine, suggesting the involvement of these signal transduction pathways. Deprenyl induced phosphorylation of p42/44 MAP kinase, which was abolished by specific inhibitors of MAP kinase and PKC. Deprenyl also phosphorylated PKC and its major substrate, and myristoylated alanine-rich C kinase (MARCKS) at specific amino acid residues. The data also indicated that 10microM deprenyl successfully induced two PKC isoforms involved in the pathogenesis of AD, PKCalpha and PKCepsilon, to translocate from the cytosolic to the membrane fraction. This phenomenon was substantiated by immunocytochemistry staining. These data suggest a novel pharmacological mechanism in which deprenyl regulates the processing of APP via activation of the MAP kinase and PKC pathways, and that this mechanism may underlie the clinical efficacy of the drug in some AD patients.