Insulin Stimulation of GLUT4 Translocation

Abstract

Semiz et al. discovered that insulin treatment increased the frequency of movement along microtubules of the glucose transporter protein GLUT4 independently of phosphatidylinositol 3-kinase (PI3K). Insulin enhances glucose transport in muscle cells and adipocytes by stimulating the translocation and fusion to the plasma membrane of intracellular vesicles containing GLUT4; at least some steps in this process involve the type of PI3K with p85 and p110 subunits. Although evidence suggests that elements of the cytoskeleton are involved in vesicle translocation, the details have remained controversial. The authors used time-lapse fluorescence microscopy to visualize GLUT4-containing vesicles moving along complex networks of microtubules in 3R3-L1 adipocytes expressing yellow fluorescent protein-labeled GLUT4 (GLUT4-YFP) and cyan fluorescent protein-labeled tubulin (tubulin-CFP). Vesicles moved to and from the perinuclear region over distances as long as 20 μm. Insulin increased the frequency--but not the velocity--of long-range GLUT4-YFP movement, but not that of short-range movement. The effect on outward movement was greater than that on inward movement. Pharmacological analysis with the PI3K inhibitor wortmannin indicated that insulin's effect on GLUT4 translocation along microtubules was independent of PI3K. Wortmannin did, however, inhibit insulin-stimulated appearance of GLUT4 in the plasma membrane. Genomic screening in combination with Western analysis, mass spectrometry of immunoprecipitates, and expression of dominant-negative mutant proteins indicated that conventional kinesin KIF5B mediated GLUT4-containg vesicle transport along microtubules. Thus, the PI3K-dependent step appears to occur late in the GLUT4 trafficking pathway, with regulation of KIF5B occurring through a distinct signaling pathway. S. Semiz, J. G. Park, S. M. C. Nicoloro, P. Furcinitti, C. Zhang, A. Chawla, J. Leszek, M. P. Czech, Conventional kinesin KIF5B mediates insulin-stimulated GLUT4 movements on microtubules. EMBO J . 22 , 2387-2399 (2003). [Abstract] [Full Text]