title: Late compartments of amyloid precursor protein transport in SY5Y cells are involved in beta-amyloid secretion.
abstract: Amyloid plaques, composed mainly of the 39-43 amino acid betaA4 peptide, are a characteristic feature of Alzheimer's disease. Generation of betaA4 by proteolytic processing of the amyloid precursor protein (APP) is thought to occur in a pathway that includes the activity of two as yet unknown proteases, with beta-secretase cleaving at the N terminus and gamma-secretase releasing the C terminus of betaA4. Inhibition studies and the finding that cell surface APP can serve as a direct precursor of betaA4 suggest that the endosomal/lysosomal compartment is involved in the proteolysis of APP into betaA4. In this study we targeted APP695 chimeric proteins directly into the endosomal/lysosomal compartment. This decreased the amount of released betaA4, while the generation of the betaA4 N terminus continued. APP695 proteins were constructed also, which carried sorting signals responsible for recycling between the trans-Golgi network (TGN) and the cell surface. These proteins were processed into secreted betaA4 at even higher levels than wild-type APP695. Moreover, retention of APP695 proteins in the endoplasmic reticulum led to neither betaA4 secretion nor to processing by beta-secretase in human SH-SY5Y neuroblastoma cells. These data suggest that a beta-cleavage activity resides in a late endosomal compartment and that a gamma-cleavage occurs in early endosomes, resulting in the generation of betaA4 peptides with the majority ending at residue 40.
authors.affiliation: Center for Molecular Biology Heidelberg, The University of Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: G C
authors.initials: GC
authors.lastname: Peraus
authors.forename: C L
authors.initials: CL
authors.lastname: Masters
authors.forename: K
authors.initials: K
authors.lastname: Beyreuther
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000096:biosynthesis; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D016922:Cellular Senescence; D002678:Chimera; D004721:Endoplasmic Reticulum / Q000378:metabolism; D058851:GPI-Linked Proteins; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D015388:Organelles / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000682:Amyloid; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D015816:Cell Adhesion Molecules, Neuronal; D058851:GPI-Linked Proteins; D011993:Recombinant Fusion Proteins; C095362:limbic system-associated membrane protein