Stomatin-like Protein-1 Interacts with Stomatin and Is Targeted to Late Endosomes

Mario Mairhofer,Marianne Steiner,Ulrich Salzer,Rainer Prohaska

doi:10.1074/jbc.m109.014993

Mario Mairhofer, Marianne Steiner + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m109.014993

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Abstract

The human stomatin-like protein-1 (SLP-1) is a membrane protein with a characteristic bipartite structure containing a stomatin domain and a sterol carrier protein-2 (SCP-2) domain. This structure suggests a role for SLP-1 in sterol/lipid transfer and transport. Because SLP-1 has not been investigated, we first studied the molecular and cell biological characteristics of the expressed protein. We show here that SLP-1 localizes to the late endosomal compartment, like stomatin. Unlike stomatin, SLP-1 does not localize to the plasma membrane. Overexpression of SLP-1 leads to the redistribution of stomatin from the plasma membrane to late endosomes suggesting a complex formation between these proteins. We found that the targeting of SLP-1 to late endosomes is caused by a GYXXPhi (Phi being a bulky, hydrophobic amino acid) sorting signal at the N terminus. Mutation of this signal results in plasma membrane localization. SLP-1 and stomatin co-localize in the late endosomal compartment, they co-immunoprecipitate, thus showing a direct interaction, and they associate with detergent-resistant membranes. In accordance with the proposed lipid transfer function, we show that, under conditions of blocked cholesterol efflux from late endosomes, SLP-1 induces the formation of enlarged, cholesterol-filled, weakly LAMP-2-positive, acidic vesicles in the perinuclear region. This massive cholesterol accumulation clearly depends on the SCP-2 domain of SLP-1, suggesting a role for this domain in cholesterol transfer to late endosomes.

Highlights

Vienna, Vienna A-1090, Austria. 2 To whom correspondence should be addressed: Dr Bohr-Gasse 9/3, Vienna brain, heart, and skeletal muscle [7, 8] and can be identified in most other tissues [1]
Nothing is known about the molecular and cell biological characteristics of the human stomatin-like protein stomatin-like protein-1 (SLP-1) except for its bipartite structure consisting of a stomatin and sterol carrier protein-2 (SCP-2)/nonspecific lipid transfer protein domain [7]
Our present study shows that SLP-1 and stomatin co-localize well in late endosomes but not at the plasma membrane, which is only positive for stomatin

Summary

Introduction

Vienna A-1090, Austria. 2 To whom correspondence should be addressed: Dr Bohr-Gasse 9/3, Vienna brain, heart, and skeletal muscle [7, 8] and can be identified in most other tissues [1]. Overexpression of SLP-1 Causes Redistribution of Stomatin from the Plasma Membrane to the Late Endosomal Compartment—Because of the late endosomal localization of both stomatin and SLP-1, we transiently transfected HeLa cells with myc- or GFP-tagged SLP-1 and analyzed their co-distribution with endogenous stomatin.

Results

Conclusion