title: Protein kinase C activation potentiates the rapid secretion of the amyloid precursor protein from rat cortical synaptosomes.
abstract: In this study we have used the presynaptic-rich rat cerebrocortical synaptosomal preparation to investigate the proteolytic cleavage of the amyloid precursor protein (AbetaPP) by the alpha-secretase pathway within the betaA4 domain to generate a soluble secreted N-terminal fragment (AbetaPPs). AbetaPP was detected in crude cortical synaptosomal membranes, although at a lower density than that observed in whole-tissue homogenates. Protein kinase C (PKC) activation induced a translocation of the conventional PKC isoform beta1 and novel PKCepsilon from cytosol to membrane fractions, but there was no alteration in the proportion of AbetaPP associated with the Triton-soluble and -insoluble fractions. AbetaPPs was constitutively secreted from cortical synaptosomes, with this secretion being enhanced significantly by the direct activation of PKC with phorbol ester. The PKC-induced secretion of AbetaPPs was only partially blocked by the PKC inhibitor GF109203X (2.5 microM), whereas the phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein was significantly inhibited by GF109203X. The differential sensitivities of the MARCKS phosphorylation and AbetaPPs secretion to GF109203X may imply that different PKC isoforms are involved in these two events in the synaptosomal system. These findings strongly suggest that the alpha-secretase activity leading to the secretion of AbetaPPs can occur at the level of the presynaptic terminal.
authors.affiliation: Department of Pharmacology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, Scotland, UK.
authors.forename: M
authors.initials: M
authors.lastname: McLaughlin
authors.forename: K C
authors.initials: KC
authors.lastname: Breen
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000096:biosynthesis / Q000378:metabolism*; D000818:Animals; D002458:Cell Fractionation; D002540:Cerebral Cortex / Q000378:metabolism*; D003902:Detergents; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D017830:Octoxynol; D010766:Phosphorylation; D017729:Presynaptic Terminals / Q000201:enzymology / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D012995:Solubility; D013574:Synaptosomes / Q000201:enzymology* / Q000378:metabolism
chemical_list: D016564:Amyloid beta-Protein Precursor; D003902:Detergents; D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D008565:Membrane Proteins; D017830:Octoxynol; D011493:Protein Kinase C; C070515:bisindolylmaleimide I