Nerve Growth Factor Induces Rapid Increases in Functional Cell Surface Low Density Lipoprotein Receptor-related Protein

Guojun Bu,Yuling Sun,Alan L Schwartz,David M Holtzman

doi:10.1074/jbc.273.21.13359

Abstract

The low density lipoprotein receptor-related protein (LRP) is a large endocytic receptor that binds multiple ligands and is highly expressed in neurons. Several LRP ligands, including apolipoprotein E/lipoproteins and amyloid precursor protein, have been shown to participate either in Alzheimer's disease pathogenesis or pathology. However, factors that regulate LRP expression in neurons are unknown. In the current study, we analyzed the effects of nerve growth factor (NGF) treatment on LRP expression, distribution, and function within neurons in two neuronal cell lines. Our results show that NGF induces a rapid increase of cell surface LRP expression in a central nervous system-derived neuronal cell line, GT1-1 Trk, which was seen within 10 min and reached a maximum at about 1 h of NGF treatment. This increase of cell surface LRP expression is concomitant with an increase in the endocytic activity of LRP as measured via ligand uptake and degradation assays. We also found that the cytoplasmic tail of LRP is phosphorylated and that NGF rapidly increases the amount of phosphorylation. Furthermore, we detected a significant increase of LRP expression at the messenger RNA level following 24 h of NGF treatment. Both rapid and long term induction of LRP expression were also detected in peripheral nervous system-derived PC12 cells following NGF treatment. Taken together, our results demonstrate that NGF regulates LRP expression in neuronal cells.

Highlights

The low density lipoprotein receptor-related protein (LRP)1 is a large multiligand endocytic receptor expressed abundantly in liver and brain [1]
To analyze whether LRP expression is regulated in neuronal cells, we examined the effects of nerve growth factor (NGF) treatment on LRP expression in both a central nervous system-derived neuronal cell line, GT1–1 Trk, and a neuronal crest-derived neuronal cell line, PC12 cells
Since we have previously shown that LRP is expressed by these cells and that NGF-mediated neurite outgrowth is augmented by apoE3-containing lipoproteins through LRP [22, 41], we asked whether NGF treatment results in a change in the amount of LRP on the surface of these cells

Summary

Introduction

The low density lipoprotein receptor-related protein (LRP)1 is a large multiligand endocytic receptor expressed abundantly in liver and brain [1]. Since we have previously shown that LRP is expressed by these cells and that NGF-mediated neurite outgrowth is augmented by apoE3-containing lipoproteins through LRP [22, 41], we asked whether NGF treatment results in a change in the amount of LRP on the surface of these cells. GT1–1 Trk cells were treated with NGF (100 ng/ml) for different periods of time, and the amount of 125I-␣2M* (0.4 nM) binding in the presence or absence of RAP (500 nM) was performed at 4 °C to determine the amount of cell surface LRP.

Results

Conclusion