title: Rapid and direct transport of cell surface APP to the lysosome defines a novel selective pathway.
abstract: BACKGROUND
  A central feature of Alzheimer's disease is the cleavage of the amyloid precursor protein (APP) to form beta-amyloid peptide (Abeta) by the beta-secretase and gamma-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 gamma-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.
authors.affiliation: 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.
authors.forename: Angela
authors.initials: A
authors.lastname: Lorenzen
authors.forename: Jonathan
authors.initials: J
authors.lastname: Samosh
authors.forename: Kenneth
authors.initials: K
authors.lastname: Vandewark
authors.forename: Pieter H
authors.initials: PH
authors.lastname: Anborgh
authors.forename: Claudia
authors.initials: C
authors.lastname: Seah
authors.forename: Ana C
authors.initials: AC
authors.lastname: Magalhaes
authors.forename: Sean P
authors.initials: SP
authors.lastname: Cregan
authors.forename: Stephen S G
authors.initials: SS
authors.lastname: Ferguson
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Pasternak
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D051381:Rats
chemical_list: D016564:Amyloid beta-Protein Precursor
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