Regulatory control of the epidermal growth factor receptor tyrosine kinase.

The epidermal growth factor (EGF) receptor has been shown to posses an intrinsic tyrosine protein kinase activity that is stimulated by the binding ofEGF [1]. In addition, two other ligands for the EGF receptor can stimulate the tyrosine protein kinase activity in intact cells: TGF-(X (transforming growth factor (X) and a soluble biosynthetic precursor of TGF-(X [2, 3]. Analysis of the kinetics of autophosphorylation and of the activity of the receptor to phosphorylate exogenous substrates indicates that the autophosphorylation of the receptor causes an increase in its tyrosine protein kinase activity [4]. This increase in the tyrosine protein kinase activity of the receptor caused by phosphorylation represents a mechanism by which amplification of the signaling mechanism of the EG F receptor can occur subsequent to the binding of EG F to the receptor.