Acid-sensing ion channel (ASIC) 4 predominantly localizes to an early endosome-related organelle upon heterologous expression.

Verena Schwartz,Stefan Gründer,Katharina Friedrich,Georg Polleichtner

doi:10.1038/srep18242

Verena Schwartz, Stefan Gründer + Show 2 more

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https://doi.org/10.1038/srep18242

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Abstract

Acid-sensing ion channels (ASICs) are voltage-independent proton-gated amiloride sensitive sodium channels, belonging to the DEG/ENaC gene family. Six different ASICs have been identified (ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3, ASIC4) that are activated by a drop in extracellular pH, either as homo- or heteromers. An exception is ASIC4, which is not activated by protons as a homomer and which does not contribute to functional heteromeric ASICs. Insensitivity of ASIC4 to protons and its comparatively low sequence identity to other ASICs (45%) raises the question whether ASIC4 may have different functions than other ASICs. In this study, we therefore investigated the subcellular localization of ASIC4 in heterologous cell lines, which revealed a surprising accumulation of the channel in early endosome-related vacuoles. Moreover, we identified an unique amino-terminal motif as important for forward-trafficking from the ER/Golgi to the early endosome-related compartment. Collectively, our results show that heterologously expressed ASIC4 predominantly resides in an intracellular endosomal compartment.

Highlights

Acid-sensing ion channels (ASICs) are voltage-independent proton-gated amiloride sensitive sodium channels, belonging to the DEG/ENaC gene family
We examined cells after different times of transfection (12, 24 and 48 h) to investigate whether GFP-ASIC4 might accumulate in the vacuolar structures after passage through a different cellular compartment
Resembling these findings, it has previously been reported that transient receptor potential mucolipin-1 (TRPML1), a resident protein of lysosomes[29], when over-expressed in HeLa cells localizes in vacuolar structures containing lysosomal markers[30], showing that fusion of vesicles is not an indication for mislocalization of an over-expressed channel

Summary

Introduction

Acid-sensing ion channels (ASICs) are voltage-independent proton-gated amiloride sensitive sodium channels, belonging to the DEG/ENaC gene family. An exception is ASIC4, which is not activated by protons as a homomer and which does not contribute to functional heteromeric ASICs. Insensitivity of ASIC4 to protons and its comparatively low sequence identity to other ASICs (45%) raises the question whether ASIC4 may have different functions than other ASICs. In this study, we investigated the subcellular localization of ASIC4 in heterologous cell lines, which revealed a surprising accumulation of the channel in early endosome-related vacuoles. ASIC1a, ASIC1b, ASIC2a, and ASIC3 form functional homomeric channels[1,3,4,5,7], while ASIC2b and ASIC4 do not[6,8,9].

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