The first intracellular loop of GLUT4 contains a retention motif.

Maya Talantikite,Marjorie Poggi,Roland Govers,Teresa Gonzalez,Franck Peiretti,Marion Berenguer,Marie Christine Alessi

doi:10.1242/jcs.183525

Abstract

Glucose transporter GLUT4 (also known as SLC2A4) plays a major role in glucose homeostasis and is efficiently retained intracellularly in adipocytes and myocytes. To simplify the analysis of its retention, here, various intracellular GLUT4 domains were fused individually to reporter molecules. Of the four short cytoplasmic loops of GLUT4, only the first nine-residue-long loop conferred intracellular retention of truncated forms of the transferrin receptor and CD4 in adipocytes. In contrast, the same loop of GLUT1 was without effect. The reporter molecules to which the first loop of GLUT4 was fused localized, unlike GLUT4, to the trans-Golgi network (TGN), possibly explaining why these molecules did not respond to insulin. The retention induced by the GLUT4 loop was specific to adipocytes as it did not induce retention in preadipocytes. Of the SQWLGRKRA sequence that constitutes this loop, mutation of either the tryptophan or lysine residue abrogated reporter retention. Mutation of these residues individually into alanine residues in the full-length GLUT4 molecule resulted in a decreased retention for GLUT4-W105A. We conclude that the first intracellular loop of GLUT4 contains the retention motif WLGRK, in which W105 plays a prominent role.

Highlights

Glucose transporter GLUT4 plays a crucial role in glucose homeostasis and is an important target for the treatment of type 2 diabetes
The adipocytes did not RESULTS Intracellular retention in 3T3-L1 adipocytes GLUT4 with an HA epitope tag within its first extracellular domain (Fig. 1) has been used extensively to study the intracellular localization of GLUT4 and is virtually absent from the plasma membrane in 3T3-L1 adipocytes (Fig. 2A, two left panels of second accumulate any substantial amount of anti-HA antibody at the cell surface or intracellularly (Fig. 2A, two right panels of second row), indicating that during these 10 min there was very little GLUT4 appearing at the cell surface
Compared with TfR, GLUT1 was retained intracellularly, but to a lesser extent than GLUT4 (Fig. 2A, fourth row). Another molecule that is efficiently retained intracellularly in adipocytes is a chimeric molecule consisting of the cytoplasmic domain of IRAP fused to the transmembrane and extracellular domains of the transferrin receptor (IRAP–TfRΔ, known as vpTR; Fig. 2A, fifth row)

Summary

Introduction

Glucose transporter GLUT4 ( known as SLC2A4) plays a crucial role in glucose homeostasis and is an important target for the treatment of type 2 diabetes. GLUT4 mediates the uptake of glucose in muscle and fat. In the absence of insulin stimulation, GLUT4 is efficiently retained intracellularly. GLUT4 translocates to the cell surface of myocytes and adipocytes where it transports glucose into these cells (Bogan, 2012; Govers, 2014). The combination of these two features, retention and insulin sensitivity, are highly unique to GLUT4. The intracellular trafficking of GLUT4 has been studied for decades, exactly how GLUT4 is retained intracellularly and how insulin impinges on this retention mechanism remains largely unknown

Methods

Results

Conclusion