Insulin Receptor (IR) and Glucose Transporter 2 (GLUT2) Proteins Form a Complex on the Rat Hepatocyte Membrane

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Abstract
The hepatic glucose transporter, GLUT2, facilitates bidirectional glucose transport across the hepatocyte plasma membrane under insulin regulation. We studied the interactions of IR and GLUT2 proteins to determine whether they are physically coupled in a receptor-transporter complex. By comparing endosome and plasma membrane IR and GLUT2 ratios before and after feeding, it was determined that IR and GLUT2 are internalized in a fixed ratio. When solubilized hepatocytes were immunoprecipitated with antibodies against either IR or GLUT2, both proteins co-precipitated. The association of IR and GLUT2 was further assessed by confocal microscopy. Sections of fed liver were incubated with fluorescein-tagged anti-GLUT2 or Texas Red-tagged anti-IR. Colocalization was observed both at the plasma membrane and in the cytosol. Fluorescence-resonance energy transfer studies further confirmed this association. We conclude that IR and GLUT2 form a receptor-transporter complex in hepatocytes, which forms a mechanism of insulin-mediated hepatic glucose regulation.