Presenilin-1, nicastrin, amyloid precursor protein, and gamma-secretase activity are co-localized in the lysosomal membrane.
Alzheimer's disease (AD) is caused by the cerebral deposition of beta-amyloid (Abeta), 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 gamma-secretase (a complex containing presenilin and nicastrin) to produce Abeta occurred in the endosomal/lysosomal system. However, other studies showing a predominant endoplasmic reticulum localization of the gamma-secretase proteins and a neutral pH optimum of in vitro gamma-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 gamma-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 gamma-secretase is a lysosomal protease. These data reassert the importance of the lysosomal/endosomal system in the generation of Abeta and suggest a role for lysosomes in the pathophysiology of AD.
Pasternak
Stephen H
SH
Research Institute, The Hospital for Sick Children, University of Toronto, Toronto M5G 1X8, Canada.
Bagshaw
Richard D
RD
Guiral
Marianne
M
Zhang
Sunqu
S
Ackerley
Cameron A
CA
Pak
Brian J
BJ
Callahan
John W
JW
Mahuran
Don J
DJ
D000544:Alzheimer Disease / Q000209:etiology / Q000378:metabolism; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D002458:Cell Fractionation / Q000379:methods; D010450:Endopeptidases / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008954:Models, Biological; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011092:Polyethylene Glycols; D053764:Presenilin-1; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
D016564:Amyloid beta-Protein Precursor; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D010446:Peptide Fragments; D053764:Presenilin-1; C413604:nicastrin protein; D011092:Polyethylene Glycols; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; C016811:tyloxapol