title: Lysosomal processing of amyloid precursor protein to A beta peptides: a distinct role for cathepsin S.
abstract: To investigate the potential contribution of the lysosomal compartment in the processing of amyloid precursor protein (APP) to amyloid beta-peptides (A beta s), we stably overexpressed a series of lysosomal proteases (the cysteine proteases, cathepsins B, L and S, and the aspartic protease, cathepsin D) in a human kidney epithelial cell line (293) transfected to express high levels of beta APP. Preliminary experiments indicated that 293 cells endogenously synthesize cathepsins B, L and D, but not cathepsin S. A beta secretion was assessed by immunoprecipitation and ELISA and found to be increased approximately 2-fold following cathepsin S expression, but to be unchanged (cathepsins B, L) or decreased (cathepsin D) in the other double transfectants. E-64d, an inhibitor of lysosomal cysteine proteases, significantly reduced A beta secretion by the cathepsin S transfectants, but had no effect on cells expressing the other proteases. Radiosequencing of A beta secreted by cathepsin S-expressing cells revealed that a previously unreported variant beginning at Met -1 (relative to the most common A beta N-terminus, Asp -1) accounted for most of the increase in A beta secretion. Immunostaining of human brain sections revealed cathepsin S in cortical neurons and glia in samples of brain from patients with Alzheimer's disease. These results provide evidence in living cells for a pathway in which cathepsin S generates A beta from amyloidogenic fragments of beta APP in the endosomal/lysosomal compartment. This pathway appears to be inducible, distinct from a constitutive pathway used by 293 and other cells to generate A beta, and may be relevant to the pathogenesis of Alzheimer's disease.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Munger
authors.forename: C
authors.initials: C
authors.lastname: Haass
authors.forename: C A
authors.initials: CA
authors.lastname: Lemere
authors.forename: G P
authors.initials: GP
authors.lastname: Shi
authors.forename: W S
authors.initials: WS
authors.lastname: Wong
authors.forename: D B
authors.initials: DB
authors.lastname: Teplow
authors.forename: D J
authors.initials: DJ
authors.lastname: Selkoe
authors.forename: H A
authors.initials: HA
authors.lastname: Chapman
mesh_terms: D000544:Alzheimer Disease / Q000201:enzymology; D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D001921:Brain / Q000201:enzymology; D002401:Cathepsin B / Q000235:genetics / Q000378:metabolism; D002402:Cathepsin D / Q000235:genetics / Q000378:metabolism; D056668:Cathepsin L; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney; D008247:Lysosomes / Q000201:enzymology*; D008969:Molecular Sequence Data; D009457:Neuroglia / Q000201:enzymology; D009474:Neurons / Q000201:enzymology; D014162:Transfection
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C028217:cathepsin S; D002402:Cathepsin D