The Low Density Lipoprotein Receptor-related Protein (LRP) Is a Novel β-Secretase (BACE1) Substrate

Christine A.F Von Arnim,Ayae Kinoshita,Ithan D Peltan,Michelle M Tangredi,Lauren Herl,Bonny M Lee,Robert Spoelgen,Tammy T Hshieh,Sripriya Ranganathan,Frances D Battey,Chun-Xiang Liu,Brian J Bacskai,Sanja Sever,Michael C Irizarry,Dudley K Strickland,Bradley T Hyman

doi:10.1074/jbc.m414248200

Abstract

BACE is a transmembrane protease with beta-secretase activity that cleaves the amyloid precursor protein (APP). After BACE cleavage, APP becomes a substrate for gamma-secretase, leading to release of amyloid-beta peptide (Abeta), which accumulates in senile plaques in Alzheimer disease. APP and BACE are co-internalized from the cell surface to early endosomes. APP is also known to interact at the cell surface and be internalized by the low density lipoprotein receptor-related protein (LRP), a multifunctional endocytic and signaling receptor. Using a new fluorescence resonance energy transfer (FRET)-based assay of protein proximity, fluorescence lifetime imaging (FLIM), and co-immunoprecipitation we demonstrate that the light chain of LRP interacts with BACE on the cell surface in association with lipid rafts. Surprisingly, the BACE-LRP interaction leads to an increase in LRP C-terminal fragment, release of secreted LRP in the media and subsequent release of the LRP intracellular domain from the membrane. Taken together, these data suggest that there is a close interaction between BACE and LRP on the cell surface, and that LRP is a novel BACE substrate.

Highlights

BACE is a transmembrane protease with ␤-secretase activity that cleaves the amyloid precursor protein (APP)
Using a new fluorescence resonance energy transfer (FRET)based assay of protein proximity, fluorescence lifetime imaging (FLIM), and co-immunoprecipitation we demonstrate that the light chain of lipoprotein receptor-related protein (LRP) interacts with BACE on the cell surface in association with lipid rafts
Using both a FRET-based assay of protein proximity and co-immunoprecipitation, we demonstrate that the LRP-ICD interacts with BACE and that this interaction seems to take place in lipid rafts on the cell surface

Summary

Introduction

BACE is a transmembrane protease with ␤-secretase activity that cleaves the amyloid precursor protein (APP). The BACE-LRP interaction leads to an increase in LRP C-terminal fragment, release of secreted LRP in the media and subsequent release of the LRP intracellular domain from the membrane Taken together, these data suggest that there is a close interaction between BACE and LRP on the cell surface, and that LRP is a novel BACE substrate. The low density lipoprotein receptor-related protein, LRP, is a type I integral membrane protein with a 515-kDa extracellular ␣-chain non-convalently bound to the 85 kDa membranespanning ␤-chain It is found on the cell surface and cycles between the cell membrane and endosomes. Instead BACE induces LRP extracellular domain cleavage and subsequent release of the LRP intracellular domain from the membrane Taken together, these data suggest a close interaction between BACE and LRP on the cell surface

Methods

Results

Conclusion