Aldolase mediates the association of F-actin with the insulin-responsive glucose transporter GLUT4

Abstract

To identify potential proteins interacting with the insulin-responsive glucose transporter (GLUT4), we generated fusion proteins of glutathione S- transferase (GST) and the final 30 amino acids from GLUT4 (GST-G4) or GLUT1 (GST-G1). Incubation of these carboxylterminal fusion proteins with adipocyte cell extracts revealed a specific interaction of GLUT4 with fructose 1,6- bisphosphate aldolase. In the presence of aldolase, GST-G4 but not GST-G1 was able to co-pellet with filamentous (F)-actin. This interaction was prevented by incubation with the aldolase substrates, fructose 1,6-bisphosphate or glyceraldehyde 3-phosphate. Immunofluorescence confocal microscopy demonstrated a significant co-localization of aldolase and GLUT4 in intact 3T3L1 adipocytes, which decreased following insulin stimulation. Introduction into permeabilized 3T3L1 adipocytes of fructose 1,6-bisphosphate or the metabolic inhibitor 2-deoxyglucose, two agents that disrupt the interaction between aldolase and actin, inhibited insulin-stimulated GLUT4 exocytosis without affecting GLUT4 endocytosis. Furthermore, microinjection of an aldolase-specific antibody also inhibited insulin-stimulated GLUT4 translocation. These data suggest that aldolase functions as a scaffolding protein for GLUT4 and that glucose metabolism may provide a negative feedback signal for the regulation of glucose transport by insulin.