The microbial alkaloid toxin staurosporine blocks the phorbol ester-induced increase in β-amyloid precursor protein in PC12 cells

The amyloid precursor protein (APP) is abnormally cleaved during the progression of Alzheimer's disease, resulting in production of the toxic beta-amyloid peptide, which forms neuritic plaques in the brain. To develop a pharmacological approach for treatment of Alzheimer's disease, natural compounds which may inhibit APP synthesis and/or beta-amyloid production are required. Staurosporine, a toxin isolated from Streptomyces staurospores bacteria, is widely used as a protein kinase C inhibitor in signal transduction research. Using rat pheochromocytoma PC12 sympathetic neurons, which express APP, we characterised staurosporine effect on APP level by western blotting, using an anti-APP monoclonal antibody. PC12 APP levels were increased or decreased upon exposure to either 50-200 nM or 10-20 nM phorbol 12-myristate 13-acetate (PMA, a protein kinase C activator), respectively. An apparent relationship was found between the change in APP level and a differential down regulation process of different PKC isoforms. The PMA-induced increase in intracellular APP level was dose-dependently inhibited by staurosporine (natural alkaloid) or GF 109203X (synthetic analogue), protein kinase C (PKC) inhibitors. This inhibition was mainly observed upon treatment of the cells before the exposure to PMA. These results suggest PKC regulation of APP levels in PC12 cells, and provide staurosporine as a leader compound for the development of drugs to control the expression of APP in Alzheimer's research.