α1-Syntrophin Modulates Turnover of ABCA1

Youichi Munehira,Tomohiro Ohnishi,Shinobu Kawamoto,Akiko Furuya,Kenya Shitara,Michihiro Imamura,Toshifumi Yokota,Shin'Ichi Takeda,Teruo Amachi,Michinori Matsuo,Noriyuki Kioka,Kazumitsu Ueda

doi:10.1074/jbc.m313436200

Abstract

ABCA1 (ATP-binding cassette transporter A1) mediates the release of cellular cholesterol and phospholipid to form high density lipoprotein. Functions of ABCA1 are highly regulated at the transcriptional and post-transcriptional levels, and the synthesized ABCA1 protein turns over rapidly with a half-life of 1-2 h. To examine whether the functions of ABCA1 are modulated by associated proteins, a yeast two-hybrid library was screened with the C-terminal 120 amino acids of ABCA1. Two PDZ (PSD95-Discs large-ZO1) proteins, alpha1-syntrophin and Lin7, were found to interact with ABCA1. Immunoprecipitation revealed that alpha1-syntrophin interacted with ABCA1 strongly and that the interaction was via the C-terminal three amino acids SYV of ABCA1. Co-expression of alpha1-syntrophin in human embryonic kidney 293 cells retarded degradation of ABCA1 and made the half-life of ABCA1 five times longer than in the cells not expressing alpha1-syntrophin. This effect is not common among PDZ-containing proteins interacting with ABCA1, because Lin7, which was also found to interact with the C terminus region of ABCA1, did not have a significant effect on the half-life of ABCA1. Co-expression of alpha1-syntrophin significantly increased the apoA-I-mediated release of cholesterol. ABCA1 was co-immunoprecipitated with alpha1-syntrophin from mouse brain. These results suggest that alpha1-syntrophin is involved in intracellular signaling, which determines the stability of ABCA1 and modulates cellular cholesterol release.

Highlights

ABCA1 (ATP-binding cassette transporter A1) mediates the release of cellular cholesterol and phospholipid to form high density lipoprotein
These results suggest that ␣1syntrophin is involved in intracellular signaling, which determines the stability of ABCA1 and modulates cellular cholesterol release
The importance of ABCA1 in this active cholesterol-releasing pathway for regulating cholesterol homeostasis became apparent with the finding that it is impaired in the cells from patients with Tangier disease, a genetic deficiency of circulating high density lipoprotein (HDL) [3, 4]

Summary

Introduction

ABCA1 (ATP-binding cassette transporter A1) mediates the release of cellular cholesterol and phospholipid to form high density lipoprotein. By yeast two-hybrid screening with the Cterminal 120 amino acids of ABCA1, two PDZ (PSD95-Discs large-ZO1)-binding proteins, ␣1-syntrophin and Lin7, were found to interact with ABCA1. ABCA1 was not precipitated with mouse IgG control from any of the lysates in which the expression of ABCA1 (Fig. 1) and FLAG-tagged proteins (data not shown) were detected by immunoblotting.

Results

Conclusion