Abstract
N-linked oligosaccharides appear to be important for the function of the epidermal growth factor (EGF) receptor. In a previous study (Rebbaa, A., Yamamoto, H., Moskal, J. R., and Bremer, E. G. (1996) J. Neurochem. 67, 2265-2272), we showed that binding of the erythroagglutinating phytohemagglutin lectin from Phaseolus vulgaris to the bisecting structures on the EGF receptor from U373 MG glioma cells blocked EGF binding and receptor autophosphorylation. In this study we examined the consequences of overexpression of the bisecting structure on the EGF receptor by gene transfection of U373 MG cells with the N-acetylglucosaminyltransferase III (GnT-III). This modification leads to a significant decrease in EGF binding and EGF receptor autophosphorylation. In addition, the cellular response to EGF was found to be altered. Proliferation of U373 MG cells in serum-free medium is inhibited by EGF. In contrast, proliferation of the GnT-III-transfected cells was stimulated by EGF. These data demonstrate that changes in EGF receptor glycosylation by GnT-III transfection reduces the number of the active receptors in U373 MG cells and that this change results in change in the cellular response to EGF.
Highlights
epidermal growth factor (EGF) receptors expressed in the human glioma cell line, U373 MG, contain bisecting oligosaccharide structure recognized by E-PHA lectin, as well as the tri- or tetra-antennary structure recognized by leucoaglutinating lectin from Phaseolus vulgaris [5]
The role of the oligosaccharide portion in the modulation of the EGF receptor function has been mainly examined by inducing transient modifications in receptor glycosylation, by incubation of cells with glycosylation inhibitors [2] or lectins [4, 11]
The function of EGF receptor was abolished in cells where glycosyltransferases were inhibited as well as when the cells were treated with certain lectins
Summary
EGF receptors expressed in the human glioma cell line, U373 MG, contain bisecting oligosaccharide structure recognized by E-PHA lectin, as well as the tri- or tetra-antennary structure recognized by leucoaglutinating lectin from Phaseolus vulgaris [5]. The expression of the bisecting structures at the cell surface as well as on EGF receptors, EGF binding, the receptor autophosphorylation, and the cell proliferation were compared between nontransfected and GnT-III-transfected U373 MG cells. In a human glioma cell line, U373 MG, EGF receptors contain the bisecting oligosaccharide structure, and interaction of this structure with E-PHA lectin was found to inhibit ligand recognition by the receptor [5].
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