GLUT4 retention in adipocytes requires two intracellular insulin-regulated transport steps.
Insulin regulates glucose uptake into fat and muscle by modulating the distribution of the GLUT4 glucose transporter between the surface and interior of cells. The GLUT4 trafficking pathway overlaps with the general endocytic recycling pathway, but the degree and functional significance of the overlap are not known. In this study of intact adipocytes, we demonstrate, by using a compartment-specific fluorescence-quenching assay, that GLUT4 is equally distributed between two intracellular pools: the transferrin receptor-containing endosomes and a specialized compartment that excludes the transferrin receptor. These pools of GLUT4 are in dynamic communication with one another and with the cell surface. Insulin-induced redistribution of GLUT4 to the surface requires mobilization of both pools. These data establish a role for the general endosomal system in the specialized, insulin-regulated trafficking of GLUT4. Trafficking through the general endosomal system is regulated by rab11. Herein, we show that rab11 is required for the transport of GLUT4 from endosomes to the specialized compartment and for the insulin-induced translocation to the cell surface, emphasizing the importance of the general endosomal pathway in the specialized trafficking of GLUT4. Based on these findings we propose a two-step model for GLUT4 trafficking in which the general endosomal recycling compartment plays a specialized role in the insulin-regulated traffic of GLUT4. This compartment-based model provides the framework for understanding insulin-regulated trafficking at a molecular level.
Department of Biochemistry, Biophysics and Molecular Medicine, Weill Medical College of Cornell University, New York, New York 10021, USA.
Anja
A
Zeigerer
Michael A
MA
Lampson
Ola
O
Karylowski
David D
DD
Sabatini
Milton
M
Adesnik
Mindong
M
Ren
Timothy E
TE
McGraw
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D011990:Receptors, Transferrin / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
D005456:Fluorescent Dyes; D005947:Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D014168:Transferrin; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse