title: Presenilin 1 stabilizes the C-terminal fragment of the amyloid precursor protein independently of gamma-secretase activity.
abstract: The cleavage of the transmembrane amyloid precursor protein (APP) by beta-secretase leaves the C-terminal fragment of APP, C99, anchored in the plasma membrane. C99 is subsequently processed by gamma-secretase, an unusual aspartyl protease activity largely dependent on presenilin (PS), generating the amyloid beta-peptide (Abeta) that accumulates in the brain of patients with Alzheimer's disease. It has been suggested that PS proteins are the catalytic core of this proteolytic activity, but a number of other proteins mandatory for gamma-secretase cleavage have also been discovered. The exact role of PS in the gamma-secretase activity remains a matter of debate, because cells devoid of PS still produce some forms of Abeta. Here, we used insect cells expressing C99 to demonstrate that the expression of presenilin 1 (PS1), which binds C99, not only increases the production of Abeta by these cells but also increases the intracellular levels of C99 to the same extent. Using pulse-chase experiments, we established that this results from an increased half-life of C99 in cells expressing PS1. In Chinese hamster ovary cells producing C99 from full-length human APP, similar results were observed. Finally, we show that a functional inhibitor of gamma-secretase does not alter the ability of PS1 to increase the intracellular levels of C99. This finding suggests that the binding of PS1 to C99 does not necessarily lead to its immediate cleavage by gamma-secretase, which could be a spatio-temporally regulated or an induced event, and provides biochemical evidence for the existence of a substrate-docking site on PS1.
authors.affiliation: Laboratoire de Pharmacologie Expérimentale, Université Catholique de Louvain, 1200 Brussels, Belgium.
authors.forename: Didier
authors.initials: D
authors.lastname: Pitsi
authors.forename: Jean-Noël
authors.initials: JN
authors.lastname: Octave
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000096:biosynthesis; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D010450:Endopeptidases / Q000502:physiology*; D049692:History, Early Modern 1451-1600; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D010446:Peptide Fragments / Q000737:chemistry*; D053764:Presenilin-1; D014280:Triglycerides / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D010446:Peptide Fragments; D053764:Presenilin-1; D014280:Triglycerides; D005680:gamma-Aminobutyric Acid; C057077:1,2-dilinolenoyl-3-(4-aminobutyryl)propane-1,2,3-triol; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human