Rapid and Direct Transport of Cell Surface APP to the Lysosome defines a novel selective pathway
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RESEARCH
Rapid and Direct Transport of Cell Surface APP to the Lysosome defines a novel selective pathway Research
Angela Lorenzen1, Jonathan Samosh1, Kenneth Vandewark1, Pieter H Anborgh1, Claudia Seah1, Ana C Magalhaes1, Sean P Cregan1,3, Stephen SG Ferguson1,3 and Stephen H Pasternak*1,2
Abstract Background: A central feature of Alzheimer's disease is the cleavage of the amyloid precursor protein (APP) to form beta-amyloid peptide (Aβ) by the β-secretase and γ-secretase enzymes. Although this has been shown to occur after endocytosis of APP from the cell surface, the exact compartments of APP processing are not well defined. We have previously demonstrated that APP and γ-secretase proteins and activity are highly enriched in purified rat liver lysosomes. In order to examine the lysosomal distribution and trafficking of APP in cultured cells, we generated constructs containing APP fused to a C-terminal fluorescent protein tag and N-terminal HA-epitope tag. These were co-transfected with a panel of fluorescent-protein tagged compartment markers. Results: Here we demonstrate using laser-scanning confocal microscopy that although APP is present throughout the endosomal/lysosomal system in transfected Cos7 and neuronal SN56 cell lines as well as in immunostained cultured mouse neurons, it is enriched in the lysosome. We also show that the Swedish and London mutations reduce the amount of APP in the lysosome. Surprisingly, in addition to its expected trafficking from the cell surface to the early and then late endosomes, we find that cell-surface labelled APP is transported rapidly and directly from the cell surface to lysosomes in both Cos7 and SN56 cells. This rapid transit to the lysosome is blocked by the presence of either the London or Swedish mutations. Conclusions: These results demonstrate the presence of a novel, rapid and specific transport pathway from the cell surface to the lysosomes. This suggests that regulation of lysosomal traffic could regulate APP processing and that the lysosome could play a central role in the pathophysiology of Alzheimer's disease. Background One of the pathological hallmarks of Alzheimer's disease (AD) is the production and cerebral deposition of the βamyloid (Aβ) peptides. Aβ peptides are generated by the sequential proteolysis of the Amyloid Precursor Protein (APP). β-Secretase (BACE) performs the first cleavage of APP at an extracellular/luminal 'β-site' which removes the bulky extracellular domain of APP [1,2]. This initial cleavage is followed by a second cleavage at a 'γ-site' within the transmembrane domain of APP by γ-secretase to yield the 40-42 amino acid Aβ peptide [3,4]. APP is a type 1 transmembrane protein that is transported to the cell surface where it undergoes rapid endo* Correspondence: [email protected] 1 J. Allyn Taylor Centre for Cell Biology, Molecular Brain Research Group, Robarts
Research Institute, Schulich School of Medicine, the University of Western Ontario, London, Ontario, N6A 5K8, Canada Full list of author information is ava
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