The X11α Protein Slows Cellular Amyloid Precursor Protein Processing and Reduces Aβ40 and Aβ42 Secretion*
- From the ‡Howard Hughes Medical Institute,¶Department of Internal Medicine and Biological Chemistry, and§Department of Neurology, University of Michigan Medical Center, Ann Arbor, Michigan 48109 and ‖Veterans Affairs Medical Center Geriatric Research, Education, and Clinical Center, Ann Arbor, Michigan 48105
Abstract
Constitutive amyloid precursor protein (APP) metabolism results in the generation of soluble APP (APPs) and Aβ peptides, including Aβ40 and Aβ42–the major component of amyloid plaques in Alzheimer’s disease brain. The phosphotyrosine binding (PTB) domain of X11 binds to a peptide containing a YENPTY motif found in the carboxyl terminus of APP. We have cloned the full-lengthX11 gene now referred to as X11α.Coexpression of X11α with APP results in comparatively greater levels of cellular APP and less APPs, Aβ40, and Aβ42 recovered in conditioned medium of transiently transfected HEK 293 cells. These effects are impaired by a single missense mutation of either APP (Y682G within the YENPTY motif) or X11α (F608V within the PTB domain), which diminishes their interaction, thus demonstrating specificity. The inhibitory effect of X11α on Aβ40 and Aβ42 secretion is amplified by coexpression with the Swedish mutation of APP (K595N/M596L), which promotes its amyloidogenic processing. Pulse-chase analysis demonstrates that X11α prolongs the half-life of APP from ∼2 h to ∼4 h. The effects of X11α on cellular APP and APPs recovery were confirmed in a 293 cell line stably transfected with APP. The specific binding of the PTB domain of X11α to the YENPTY motif-containing peptide of APP appears to slow cellular APP processing and thus reduces recovery of its soluble fragments APPs, Aβ40, and Aβ42 in conditioned medium of transfected HEK 293 cells. X11α may be involved in APP trafficking and metabolism in neurons and thus may be implicated in amyloidogenesis in normal aging and Alzheimer’s disease brain.
Footnotes
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↵* The work was supported by a pilot of National Institutes of Health Grant P50 AG08671.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF047347 and AF047348.
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↵‡ To whom correspondence and reprint requests should be addressed: VAMC GRECC, 2215 Fuller Rd., Ann Arbor, MI 48105. Tel.: 734-761-7686; Fax: 734-761-7489; E-mail: raymondt{at}umich.edu.
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↵** An investigator of the Howard Hughes Medical Institute.
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↵1 The abbreviations used are: AD Alzheimer’s disease; Aβ, amyloid-β protein; APPc, cellular APP; APPswe, Swedish mutation of APP; APP, β-amyloid precursor protein; APPsα, soluble APP cleaved by α-secretase, APPsβ, soluble APP cleaved by β-secretase; PDZ, PSD-95/Dlg/ZO-1; PI, protein interaction; PTB, phosphotyrosine binding; HEK, human embryonic kidney cells; PAGE, polyacrylamide gel electrophoresis; ELISA, enzyme-linked immunosorbent assay.
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↵2 J.-P. Borg and B. Margolis, unpublished data.
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- Received February 10, 1998.
- Revision received April 7, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
