Deletion of an Endosomal/Lysosomal Targeting Signal Promotes the Secretion of Alzheimer's Disease Amyloid Precursor Protein (APP)

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Abstract
Alzheimer's disease amyloid precursor protein (APP) generates a β-amyloid protein (Aβ) that is a main component of the senile plaques found in the brains of Alzheimer's disease patients. APP is thought to undergo proteolysis via two different pathways, the amyloidogenic pathway which produces Aβ, and the non-amyloidogenic pathway which releases a large N-terminal fragment into the medium. The proteases that mediate these processes remain unidentified. The physiological function of APP is not clear yet. Therefore, the cytoplasmic region of APP has attracted much interest, because this region is highly conserved among species, and members of the amyloid precursor-like protein (APLP) family. Several potentially functional sequences exist in the region, including signal sequences for protein sorting and a Go -protein binding sequence. We constructed two mutants, 695ΔNPTY and 6957Delta;GYEN. They lack potential endosome/lysosome targeting signals, NPTY and GY, in the cytoplasmic domain of APP695, respectively. The mutant APPs had longer half-lives and were secreted more easily into the medium than the wild type, suggesting that these sequences are important for the secretion and metabolism of APP.

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