SCAMP5 Links Endoplasmic Reticulum Stress to the Accumulation of Expanded Polyglutamine Protein Aggregates via Endocytosis Inhibition

Jee-Yeon Noh,Huikyong Lee,Sungmin Song,Nam Soon Kim,Wooseok Im,Manho Kim,Hyemyung Seo,Chul-Woong Chung,Jae-Woong Chang,Robert J Ferrante,Young-Jun Yoo,Hoon Ryu,Yong-Keun Jung

doi:10.1074/jbc.m807620200

Abstract

Accumulation of expanded polyglutamine proteins is considered to be a major pathogenic biomarker of Huntington disease. We isolated SCAMP5 as a novel regulator of cellular accumulation of expanded polyglutamine track protein using cell-based aggregation assays. Ectopic expression of SCAMP5 augments the formation of ubiquitin-positive and detergent-resistant aggregates of mutant huntingtin (mtHTT). Expression of SCAMP5 is markedly increased in the striatum of Huntington disease patients and is induced in cultured striatal neurons by endoplasmic reticulum (ER) stress or by mtHTT. The increase of SCAMP5 impairs endocytosis, which in turn enhances mtHTT aggregation. On the contrary, down-regulation of SCAMP5 alleviates ER stress-induced mtHTT aggregation and endocytosis inhibition. Moreover, stereotactic injection into the striatum and intraperitoneal injection of tunicamycin significantly increase mtHTT aggregation in the striatum of R6/2 mice and in the cortex of N171-82Q mice, respectively. Taken together, these results suggest that exposure to ER stress increases SCAMP5 in the striatum, which positively regulates mtHTT aggregation via the endocytosis pathway.

Highlights

Taining huntingtin is the main aggregate component in the affected neurons [3]
When these polyQ track constructs were expressed in cells, Green fluorescent protein (GFP) allowed the detection of expression, aggregation, and subcellular localization of the chimera under a fluorescence microscope
Transfection efficiency, which was normalized by co-transfection with monomeric RFP, was relatively even for the clones, and GFP-positive dots were counted as aggregates of the polyQ track protein

Summary

Introduction

Taining huntingtin is the main aggregate component in the affected neurons [3]. molecular chaperones, such as Hsp70, Hsp40/HDJ1 (dHDJ1), and chaperonin TRiC, perturb the aggregation of polyQ track protein and reduce polyQ track cytotoxicity in yeast and cell lines (4 – 6) and in Drosophila and mouse models [4, 7]. GFP-positive cells were observed for 18, 24, and 36 h under a fluorescence microscope for the aggregation of polyQ track protein. Functional Isolation of SCAMP5 as an Enhancer of mtHTT Aggregation—To find out new regulators of polyQ track protein aggregation, we screened 4,200 human full-length cDNAs in the expression vector with cell-based assays.

Results

Conclusion