Phosphorylation Regulates Intracellular Trafficking of β-Secretase

Jochen Walter,Regina Fluhrer,Bianka Hartung,Michael Willem,Christoph Kaether,Anja Capell,Sven Lammich,Gerd Multhaup,Christian Haass

doi:10.1074/jbc.m011116200

Jochen Walter, Regina Fluhrer + Show 7 more

Open Access

https://doi.org/10.1074/jbc.m011116200

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Abstract

beta-Secretase (BACE) is a transmembrane aspartyl protease, which generates the N terminus of Alzheimer's disease amyloid beta-peptide. Here, we report that BACE can be phosphorylated within its cytoplasmic domain at serine residue 498 by casein kinase 1. Phosphorylation exclusively occurs after full maturation of BACE by propeptide cleavage and complex N-glycosylation. Phosphorylation/dephosphorylation affects the subcellular localization of BACE. BACE wild type and an S498D mutant that mimics phosphorylated BACE are predominantly located within juxtanuclear Golgi compartments and endosomes, whereas nonphosphorylatable BACE S498A accumulates in peripheral EEA1-positive endosomes. Antibody uptake assays revealed that reinternalization of BACE from the cell surface is independent of its phosphorylation state. After reinternalization, BACE wild type as well as BACE S498D are efficiently retrieved from early endosomal compartments and further targeted to later endosomal compartments and/or the trans-Golgi network. In contrast, nonphosphorylatable BACE S498A is retained within early endosomes. Our results therefore demonstrate regulated trafficking of BACE within the secretory and endocytic pathway.

Highlights

␤-Secretase (BACE) is a transmembrane aspartyl protease, which generates the N terminus of Alzheimer’s disease amyloid ␤-peptide
BACE Is Phosphorylated at Serine 498 —To investigate whether BACE is posttranslationally modified by phosphorylation, we used human embryonic kidney (HEK) 293 cells stably overexpressing human BACE
By testing several protein kinases in vitro, we found that casein kinase (CK)-1 can phosphorylate BACE at the in vivo phosphorylation site at serine residue 498

Summary

Introduction

␤-Secretase (BACE) is a transmembrane aspartyl protease, which generates the N terminus of Alzheimer’s disease amyloid ␤-peptide. A close homologue was identified and termed as BACE-2, Asp, DRAP, or memapsin 1 [4, 5, 9].2 Both enzymes are type I membrane proteins sharing significant homology with other members of the aspartyl protease family [5,6,7,8]. The acidic pH optimum of BACE [5,6,7,8] indicates that it is predominantly active within late Golgi compartments and/or endosomes/lysosomes This is consistent with previous findings demonstrating that ␤-secretase cleavage of ␤APP can occur in all of these acidic compartments [15,16,17,18]

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