Molecular machinery involved in the insulin-regulated fusion of GLUT4-containing vesicles with the plasma membrane

The GLUT4 facilitative glucose transporter protein is primarily expressed in muscle and adipose tissue and accounts for the majority of post-prandial glucose uptake. In the basal or nonstimulated state, GLUT4 is localized to intracellular membrane compartments sequestered away from circulating glucose. However, in response to agonist stimulation, there is a marked redistribution of the GLUT4 protein to the cell surface membrane providing a transport route for the uptake of glucose. This GLUT4 translocation can be divided into four general steps: (i) GLUT4 vesicle trafficking out of the storage pool, (ii) docking just below the cell surface, (iii) priming via the interactions of the SNARE proteins present on the vesicular and plasma membranes, and (iv) fusion of the GLUT4 vesicle with the plasma membrane. This review focuses on recent advances made in identification and characterization of the molecular events and protein interactions involved in these steps of insulin-stimulated GLUT4 translocation.