REGULATION OF GLUCOSE TRANSPORT AND GLUCOSE TRANSPORTER GENE EXPRESSION BY GRAWTH FACTORS IN ANIMAL CELLS

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GLUT1, a 55 kDa glycoprotein glucose transporter present in the plasma membranes of braink erythrocytes and several fibroblasts, mediates glucose uptake of memmalian cells in a facilitative diffusion manner. In the present studies we observed that the expression of GLUT1 mRNA and protein in the mouse 3T3 fibroblasts were stimulated by an active growth factor TGF-beta1. TGF-beta1 also modulated the glycosylation of the GLUT1 protein, which resulted in the expression of a larger 65 kDa GLUT1 with a higher affinity for D-glucose. Studies with glycosidases and lectins indicated that the asparagine-loinked oligosaccharides of the GLUT1 protein were altered by TGF-beta1 leading to more branched and/or repeated polylactosamine chains.Modulation of the GLUT1 glycosylation with the increased affinity for D-glucose was also found in malignant human cell lines and this was strongly associated with an unidentified tumor suppressor gene present in the human chromosome11. Futher studies on the analysis of the modulated glycosylation of the GLUT1 protein and on the tumor suppressor function are in progress.