Binding of erythroagglutinating phytohemagglutinin lectin from Phaseolus vulgaris to the epidermal growth factor receptor inhibits receptor function in the human glioma cell line, U373 MG

Little is known about the role of the N-linked oligosaccharides in the function of the epidermal growth factor (EGF) receptor (EGF-R). In a human glioma cell line, U373 MG, EGF-Rs contain the bisecting N-linked oligosaccharide sequence recognized by erythroagglutinating phytohemagglutinin lectin from Phaseolus vulgaris (E-PHA). Incubation of E-PHA with cultured U373 MG cells results in inhibition of EGF binding to its receptor and consequently inhibition of EGF-induced autophosphorylation of the receptor. Consistent with the inhibitory effects on the EGF-R, phenotypic events that depend on EGF-R signaling, such as cell spreading and proliferation, were also found to be modified. The effect of this lectin seems to be specific because leukoagglutinating phytohemagglutinin lectin from P. vulgaris (L-PHA), an isolectin of E-PHA, had no effect on EGF-R activity or the biological functions of these cells even though L-PHA was able to bind to the EGF-R. These findings suggest the presence of an important bisecting N-linked oligosaccharide structure in close proximity to the EGF binding site on the receptor. Furthermore, these results suggest the possibility that E-PHA lectin binding may provide an additional approach to blocking EGF-dependent glioma cell growth.