Systematic Evaluation of Candidate Ligands Regulating
Ectodomain Shedding of Amyloid Precursor Protein
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Abstract
Despite
intense interest in the proteolysis of the β-Amyloid
Precursor Protein (APP) in Alzheimer’s disease, how the normal
processing of this type I receptor-like glycoprotein is physiologically
regulated remains ill-defined. In recent years, several candidate
protein ligands for APP, including F-spondin, Reelin, β1 Integrin,
Contactins, Lingo-1, and Pancortin, have been reported. However, a
cognate ligand for APP that regulates its processing by α- or
β-secretase has yet to be widely confirmed in multiple laboratories.
Here, we developed new assays in an effort to confirm a role for one
or more of these candidate ligands in regulating APP ectodomain shedding
in a biologically relevant context. A comprehensive quantification
of APPsα and APPsβ, the immediate products of secretase
processing, in both non-neuronal cell lines and primary neuronal cultures
expressing endogenous APP yielded no evidence that any of these published
candidate ligands stimulate ectodomain shedding. Rather, Reelin, Lingo-1,
and Pancortin-1 emerged as the most consistent ligands for significantly
inhibiting ectodomain shedding. These findings led us to conduct further
detailed analyses of the interactions of Reelin and Lingo-1 with APP