The linear C-terminal regions of epidermal growth factor (EGF) and transforming growth factor-α bind to different epitopes on the human EGF receptor

Abstract

Epidermal growth factor (EGF) and transforming growth factor-α (TGFα) bind with similar affinities in a competitive fashion to the human EGF receptor, and basically induce similar mitogenic responses. In spite of the fact that EGF and TGFα are structurally alike, it is still not clear if the two growth factors bind the receptor in an identical manner. The observation that the 13A9 antibody blocks binding of TGFα, but not that of EGF, to the human EGF receptor [Winkler, O'Connor, Winget and Fendly (1989) Biochemistry 28, 6373–6378] suggests that their binding characteristics are not identical. In the present study we have made use of a set of EGF/TGFα chimaeric molecules to show that the 13A9 antibody blocks receptor binding of ligands with TGFα sequences, but not of ligands with EGF sequences, in their C-terminal linear regions. Using HaCaT human keratinocyte cells in culture, it was determined that ligands that are able to bind the EGF receptor in the presence of 13A9 are also able to induce calcium release from intracellular stores in these cells, indicating that these ligands have the ability to activate the EGF receptor in the presence of the antibody. From these data it is concluded that the flexible C-terminal linear domains of EGF and TGFα bind to separate sequences on the EGF receptor, such that the binding domain of TGFα, but not that of EGF, overlaps with the binding epitope of the 13A9 antibody.