Superagonistic activation of ErbB-1 by EGF-related growth factors with enhanced association and dissociation rate constants

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alp ha) are mitogenic hormones that exert their activity primarily by binding t o the EGF receptor, also known as ErbB-1, We have recently characterized a set of EGF/TGF alpha chimeric molecules with similar high affinity for ErbB -1 as EGF and TGF alpha and shown that three of these chimeras induce mitog enic cell stimulation at already a 10-fold lower concentration than their w ild-type counterparts (Lenferink, A. E,, Kramer, R, H,, van Vugt, M. J., Ko nigswieser, M., DiFiore, P, P,, van Zoelen, E, J,, and van de Poll, M. L. ( 1997) Biochem. J, 327, 859-865), In the present study we show that these so -called superagonistic chimeras do not differ from EGF and TGF alpha in the ir ability to induce ErbB-1 tyrosine phosphorylation but are considerably m ore potent in activation of mitogen-activated protein kinase phosphorylatio n. Direct cell binding studies and analysis of ligand-receptor interaction by surface plasmon resonance measurements revealed that both the associatio n rate constant (k(on)) and the dissociation rate constant (k(off)) of thes e superagonists is 3-5-fold higher in comparison with the wild-type ligands and nonsuperagonistic chimeras. These data indicate that the dynamic on an d off rate constants for receptor binding may be more specific parameters f or determining the mitogenic activity of peptide hormones than their consta nts for equilibrium receptor binding.