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, GLUT2, in the insulin-sensitive 3T3-L1 adipocyte clonal cell line in an effort to address the importance of transporter isoform and cellular environment on the ability of insulin to mediate glucose-transporter translocation. Analysis of non-differentiated fibroblastic cell clones transfected with the GLUT2 cDNA identified the presence of this isoform in several independent clones. These clones exhibited increased deoxyglucose 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 protein was maintained throughout the differentiation protocol. Subcellular fractionation revealed that in response to insulin, unlike the native 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 does not undergo insulin-stimulated translocation.