Phorbol esters affect multiple steps in beta-amyloid precursor protein trafficking and amyloid beta-protein production.
BACKGROUND
Amyloid beta-protein (A beta), the major constituent of amyloid deposits found in Alzheimer's disease, is derived from the beta-amyloid precursor protein (beta PP). Constitutive proteolysis by alpha-secretase and secretion of soluble beta PP (beta PPs) are stimulated by protein kinase C (PKC) activation, whereas A beta production and release are inhibited. The cellular mechanism that underlies the PKC-mediated down-regulation of A beta generation is unclear. Because endocytic processing of beta PP from the cell surface is a major pathway of A beta production, the effect of PKC activation by phorbol 12,13-dibutyrate (PDBu) on endocytic trafficking of beta PP was examined.


METHODS
In this study, trafficking of beta PP was assayed in Chinese hamster ovary cells (CHO) cells stably transfected with full-length beta PP751.


RESULTS
Treatment with PDBu resulted in a rapid and striking reduction of up to 80% in the amount of beta PP at the cell surface. This loss of cell-surface molecules could not be accounted for by changes in the trafficking of cell-surface beta PP molecules, as determined by a radiolabeled antibody assay. Rather, the decrease in beta PP was due primarily to a reduction in the sorting of beta PP to the cell surface. This alteration was correlated with accelerated intracellular alpha-secretase-mediated beta PP cleavage and accelerated beta PP trafficking in the exocytic pathway.


CONCLUSIONS
The data suggest that the displacement of beta PP away from the cell surface after phorbol ester treatment reduces the substrate available for endocytic processing and in turn, results in the inhibition of A beta production.
Koo
E H
EH
Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000096:biosynthesis*; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D006224:Cricetinae; D004789:Enzyme Activation; D018604:Epitope Mapping; D008969:Molecular Sequence Data; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D014162:Transfection
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C