title: Stimulation of beta-amyloid precursor protein alpha-processing by phorbol ester involves calcium and calpain activation.
abstract: Normal processing of Alzheimer's beta-amyloid precursor protein (APP) is markedly stimulated by phorbol esters, but the underlying mechanisms have yet to be fully understood. In this study, we observed that: (a) Phorbol 12,13-dibutyrate (PDBu)-stimulated APP secretion in cultured SH-SY5Y neuroblastoma and fibroblast cells was blocked by EGTA and calpain inhibitors in a concentration-dependent manner, but not by other protease inhibitors. (b) Secretion of fibronectin, another secretory protein tested for comparison, was enhanced by PDBu, but insensitive to calpain inhibitors. (c) PDBu stimulated intracellular calpain activity as measured by the hydrolysis of a fluorogenic calpain substrate. (d) PDBu also induced rapid proteolysis of two endogenous substrates of calpains, i.e., tau and microtubule-associated protein-2 (MAP-2) and the proteolysis was blocked by EGTA and calpain inhibitors. Taken together, these results suggest that stimulation of APP alpha-processing by PDBu is through a mechanism that involves the activation of Ca(2+) and, most notably, calpain. The implications of the findings are discussed in relation to the regulatory mechanism of APP alpha-processing.
authors.affiliation: Neurobiology of Aging Research Laboratory, Medical Research Service, Bay Pines VA Medical Center, FL 33744, USA. ming.chen@med.va.gov
authors.forename: Ming
authors.initials: M
authors.lastname: Chen
authors.forename: Hugo L
authors.initials: HL
authors.lastname: Fernandez
mesh_terms: D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D016875:tau Proteins / Q000378:metabolism
chemical_list: C545487:APP protein, human; D016564:Amyloid beta-Protein Precursor; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005353:Fibronectins; D008869:Microtubule-Associated Proteins; D010446:Peptide Fragments; D016875:tau Proteins; D015240:Phorbol 12,13-Dibutyrate; D004533:Egtazic Acid; D002154:Calpain; D002118:Calcium