Epidermal Growth Factor Induces Phosphorylation on Growth Factor Receptor-Binding Protein-2 (GRB2) in A431 Epidermal Carcinoma Cells

Abstract

Growth factor receptor-binding protein-2 (GRB2) is a key molecule in growth factor signal transduction. GRB2 is an 'adapter protein,' linking tyrosine kinase receptors to guanine nucleotide-releasing factor, Son of sevenless (Sos). Recent studies have demonstrated that Platelet-derived growth factor (PDGF) induces phosphorylation on GRB2. Herein it has been demonstrated that Epidermal growth factor (EGF) also induces phosphorylation on GRB2. Lysates from A431 epidermal carcinoma cells stimulated with EGF and resolved by SDS-PAGE were analyzed with an antibody to GRB2, revealing a shift in the electrophoretic mobility of GRB2. A series of radioactive labeling experiments confirmed that the observed mobility shift was due to phosphorylation. Phosphorylation on GRB2 was in accordance with receptor activation, in both a time- and concentration- dependent manner. Further investigation revealed that phosphorylated GRB2 associates with activated EGF receptor, demonstrating the importance of phosphorylated GRB2 in signal transduction.