Inhibition of epidermal growth factor receptor aggregation by an antibody directed against the epidermal growth factor receptor extracellular domain.

Abstract

We have examined the perturbation of epidermal growth factor (EGF) receptor-receptor interactions by a monoclonal antibody (13A9) that binds to the receptor extracellular domain. While 13A9 did not inhibit EGF binding, it inhibited energy transfer between fluorescent-labeled EGF molecules bound to receptors in membranes from human A431 cells by 70-100%. This antibody also inhibited EGF-stimulated receptor dimerization in membranes as assessed by chemical cross-linking and Fab fragments of the antibody strongly inhibited the EGF-stimulated dimerization of solubilized receptors when assessed by velocity sedimentation. However, under conditions where 13A9 inhibited receptor-receptor interactions within the plasma membranes, the antibody had no effect on EGF-stimulated receptor autophosphorylation or tyrosine kinase activity toward an exogenous substrate. Moreover, although the antibody significantly inhibited receptor dimerization in A431 cells, it had no effect on EGF-stimulated changes in cytosolic free [Ca2+] or 125I-EGF uptake in these cells, or on EGF-stimulated DNA synthesis in Swiss 3T3 cells. We conclude that the dimerization of the EGF receptors in a membrane environment is not required for full activation of tyrosine kinase activity and that inhibition of the dimerization of a large fraction of EGF receptors in cells does not necessarily inhibit several EGF-mediated cellular responses.