Presenilin-1, Nicastrin, Amyloid Precursor Protein, and γ-Secretase Activity Are Co-localized in the Lysosomal Membrane

• Published in: The Journal of biological chemistry 2003-07, Vol.278 (29), p.26687-26694
• Main Authors: Pasternak, Stephen H., Bagshaw, Richard D., Guiral, Marianne, Zhang, Sunqu, Ackerley, Cameron A., Pak, Brian J., Callahan, John W., Mahuran, Don J.
• Format: Article
• Language: English
• Subjects: Alzheimer Disease - etiology; Alzheimer Disease - metabolism; Amino Acid Sequence; Amyloid beta-Protein Precursor - genetics; Amyloid beta-Protein Precursor - metabolism; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Cell Fractionation - methods; Endopeptidases - metabolism; Endosomes - metabolism; Humans; Intracellular Membranes - metabolism; Lysosomes - metabolism; Membrane Glycoproteins - metabolism; Membrane Proteins - metabolism; Microscopy, Immunoelectron; Models, Biological; Peptide Fragments - genetics; Peptide Fragments - metabolism; Polyethylene Glycols; Presenilin-1; Rats; Rats, Sprague-Dawley; Substrate Specificity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M304009200

Alzheimer's disease (AD) is caused by the cerebral deposition of β-amyloid (Aβ), a 38–43-amino acid peptide derived by proteolytic cleavage of the amyloid precursor protein (APP). Initial studies indicated that final cleavage of APP by the γ-secretase (a complex containing presenilin and nicastrin) to produce Aβ occurred in the endosomal/lysosomal system. However, other studies showing a predominant endoplasmic reticulum localization of the γ-secretase proteins and a neutral pH optimum of in vitro γ-secretase assays have challenged this conclusion. We have recently identified nicastrin as a major lysosomal membrane protein. In the present work, we use Western blotting and immunogold electron microscopy to demonstrate that significant amounts of mature nicastrin, presenilin-1, and APP are co-localized with lysosomal associated membrane protein-1 (cAMP-1) in the outer membranes of lysosomes. Furthermore, we demonstrate that these membranes contain an acidic γ-secretase activity, which is immunoprecipitable with an antibody to nicastrin. These experiments establish APP, nicastrin, and presenilin-1 as resident lysosomal membrane proteins and indicate that γ-secretase is a lysosomal protease. These data reassert the importance of the lysosomal/endosomal system in the generation of Aβ and suggest a role for lysosomes in the pathophysiology of AD.