A VARIANT EPIDERMAL GROWTH-FACTOR RECEPTOR EXHIBITS ALTERED TYPE-ALPHA TRANSFORMING GROWTH-FACTOR BINDING AND TRANSMEMBRANE SIGNALING

Epidermal growth factor (EGF) and type alpha transforming growth facto r (TGF-alpha) bind to a specific region in subdomain III of the extrac ellular portion of the EGF receptor (EGFR). Binding leads to receptor dimerization, auto- and transphosphorylation on intracellular tyrosine residues, and activation of signal transduction pathways. We compared the binding and biological actions of EGF and TGF-alpha in Chinese ha mster ovary (CHO) cells expressing either wild-type human EGFR (HER497 R) or a variant EGFR that has an arginine-to-lysine substitution in th e extracellular domain at codon 497 (HER497K) within subdomain IV of E GFR. Both receptors exhibited two orders of binding sites with radioio dinated EGF (I-125-EGF). Similar results were obtained with I-125-TGF- alpha in cells expressing HER497R. In contrast, only one order of low- affinity binding sites was seen with I-125-TGF alpha in the case of HE R497K. Although EGF and TGF-alpha enhanced tyrosine phosphorylation of both receptors, CHO cells expressing HER497K exhibited an attenuated growth response to EGF and TGF-alpha and a reduced induction of the pr otooncogenes FOS, JUN, and MYC. Moreover, high concentrations of TGF-a lpha (5 nM) inhibited growth in these cells but not in cells expressin g HER497R. These findings indicate that a region in subdomain IV of EG FR regulates signal transduction across the cell membrane and selectiv ely modulates the binding characteristics of TGF-alpha.