Proteasome-mediated degradation of the C-terminus of the Alzheimer's disease beta-amyloid protein precursor: effect of C-terminal truncation on production of beta-amyloid protein.
The beta-amyloid protein (Abeta) is derived by proteolytic processing of the amyloid protein precursor (APP). Cleavage of APP by beta-secretase generates a C-terminal fragment (APP-CTFbeta), which is subsequently cleaved by gamma-secretase to produce Abeta. Our previous studies have shown that the proteasome can cleave the C-terminal cytoplasmic domain of APP. To identify proteasome cleavage sites in APP, two peptides homologous to the C-terminus of APP were incubated with recombinant 20S proteasome. Cleavage of the peptides was monitored by reversed phase high-performance liquid chromatography and mass spectrometry. Proteasome cleaved the APP C-terminal peptides at several sites, including a region around the sequence YENPTY that interacts with several APP-binding proteins. To examine the effect of this cleavage on Abeta production, APP-CTFbeta and mutant forms of APP-CTFbeta terminating on either side of the YENPTY sequence were expressed in CHO cells. Truncation of APP-CTFbeta on the N-terminal side of the YENPTY sequence at residue 677 significantly decreased the amount of Abeta produced, whereas truncation on the C-terminal side of residue 690 had little effect. The results suggest that proteasomal cleavage of the cytosolic domain of APP at the YENPTY sequence decreases gamma-secretase processing, and consequently inhibits Abeta production. Therefore, the proteasome-dependent trafficking pathway of APP may be a valid therapeutic target for altering Abeta production in the Alzheimer's disease brain.
Nunan
Janelle
J
Department of Pathology, University of Melbourne, Victoria, Australia.
Williamson
Nicholas A
NA
Hill
Andrew F
AF
Sernee
M Fleur
MF
Masters
Colin L
CL
Small
David H
DH
D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D013058:Mass Spectrometry / Q000379:methods; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D016296:Mutagenesis; D010053:Ovary; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D026801:Synteny; D014162:Transfection
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D009097:Multienzyme Complexes; D010446:Peptide Fragments; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex