Alteration by transforming growth factor-beta 1 of asparagine-linked sugar chains in glucose transporter protein in Swiss 3T3 cells.

GLUT1 protein in Swiss 3T3 cells is a 55-kDa glycoprotein with an N-linked oligosaccharide chain. We previously showed that the 65-kDa GLUT1 protein with modulated glycosylation was induced by transforming growth factor-beta 1 (TGF-beta 1) in Swiss 3T3 cells. To further investigate the altered structures of these sugar chains, the membrane glycoproteins solubilized with Triton X-100 were fractionated by lectin-affinity chromatography. The 55-kDa GLUT1 in control and TGF-beta 1-treated cells showed partial binding to Datura stramonium agglutinin (DSA), whereas the 65-kDa GLUT1 exclusively bound to DSA- and wheat germ agglutinin (WGA)-agarose. The 65-kDa GLUT1 in TGF-beta 1-treated cells was sensitive to endo-beta-galactosidase, which cleaves unsubstituted polylactosamine chains. While the 55-kDa GLUT1 in control 3T3 cells was similarly digested by endo-beta-galactosidase, that in TGF-beta 1-treated cells was resistant to this enzyme. These results suggest that the N-linked oligosaccharides of GLUT1 in Swiss 3T3 cells were altered by TGF-beta 1 to forms with more branched and/or repeated polylactosamines as well as with some substitution in the polylactosamines, resulting in a larger GLUT1 molecule. These GLUT1 proteins were exclusively located at the plasma membrane and served as a glucose transporter. However, the affinity to 2-deoxyglucose was significantly increased by TGF-beta 1, associated with the altered glycosylation of GLUT1 protein.