A non-mitogenic analogue of epidermal growth factor enhances the phosphorylation of endogenous membrane proteins

The cyanogen bromide cleaved analogue of Epidermal Growth Factor (EGF) binds to EGF receptors with reduced affinity but fails to induce DNA synthesis. However, at similar receptor occupancy, cyanogen bromide cleaved EGF is as potent as EGF in enhancing the phosphorylation of endogenous membrane proteins mediated by the EGF specific, cyclic nucleotide independent protein kinase. Two possibilities arise concerning the biological role of the EGF induced membrane protein phosphorylation: 1) it is not related to the triggering of DNA synthesis by EGF and does not serve as “second messenger” for the growth factor. 2) it is a necessary but not sufficient biochemical signal for the activation of DNA synthesis by EGF.