EXPRESSION OF THE LIVER-TYPE GLUCOSE-TRANSPORTER (GLUT2) IN 3T3-L1 ADIPOCYTES - ANALYSIS OF THE EFFECTS OF INSULIN ON SUBCELLULAR-DISTRIBUTION

We have expressed the liver-type facilitative glucose transporter, GLU T2, in the insulin-sensitive 3T3-L1 adipocyte clonal cell line in an e ffort to address the importance of transporter isoform and cellular en vironment on the ability of insulin to mediate glucose-transporter tra nslocation. Analysis of non-differentiated fibroblastic cell clones tr ansfected with the GLUT2 cDNA identified the presence of this isoform in several independent clones. These clones exhibited increased deoxyg lucose and fructose transport rates compared with control cells. Upon differentiation, the fibroblastic clones selected for study achieved > 95% phenotypic conversion into adipocytes. Expression of the GLUT2 pr otein was maintained throughout the differentiation protocol. Subcellu lar fractionation revealed that in response to insulin, unlike the nat ive GLUT4, GLUT2 protein did not undergo significant translocation to the plasma membrane; furthermore, the subcellular distribution of the expressed GLUT2 was quite distinct from that of the endogenous GLUT4. 3T3-L1 adipocytes expressing GLUT2 only exhibited a 2-fold increase in insulin-stimulated fructose uptake, further suggesting that GLUT2 doe s not undergo insulin-stimulated translocation.