Background
Amyloid β-protein (Aβ), the major constituent of amyloid deposits found in Alzheimer’s disease, is derived from the β-amyloid precursor protein (βPP). Constitutive proteolysis by α-secretase and secretion of soluble βPP (βPPs) are stimulated by protein kinase C (PKC) activation, whereas Aβ production and release are inhibited. The cellular mechanism that underlies the PKC-mediated down-regulation of Aβ generation is unclear. Because endocytic processing of βPP from the cell surface is a major pathway of Aβ production, the effect of PKC activation by phorbol 12,13-dibutyrate (PDBu) on endocytic trafficking of βPP was examined.
Materials and Methods
In this study, trafficking of βPP was assayed in Chinese hamster ovary cells (CHO) cells stably transfected with full-length βPP751.
Results
Treatment with PDBu resulted in a rapid and striking reduction of up to 80% in the amount of βPP at the cell surface. This loss of cell-surface molecules could not be accounted for by changes in the trafficking of cell-surface βPP molecules, as determined by a radiolabeled antibody assay. Rather, the decrease in βPP was due primarily to a reduction in the sorting of βPP to the cell surface. This alteration was correlated with accelerated intracellular α-secretase-mediated βPP cleavage and accelerated βPP trafficking in the exocytic pathway.
Conclusions
The data suggest that the displacement of βPP away from the cell surface after phorbol ester treatment reduces the substrate available for endocytic processing and, in turn, results in the inhibition of Aβ production.