Abstract
The epidermal growth factor receptor (EGF-R) on human epidermoid carcinoma cells, A431, was found to be predominantly associated with the detergent-insoluble cytoskeleton, where it retained both a functional ligand-binding domain and an intrinsic tyrosine kinase activity. The EGF-R was constitutively associated with the A431 cytoskeleton; this association was not a consequence of adventitious binding. The EGF-R was associated with cytoskeletal elements both at the cell surface, within intracellular vesicles mediating the internalization of the hormone-receptor complex, and within lysosomes. The EGF-R became more stably associated with cytoskeletal elements after its internalization. The cytoskeletal association of the EGF-R was partially disrupted on suspension of adherent cells, indicating that alteration of cellular morphology influences the structural association of the EGF-R, and that the EGF-R is not intrinsically insoluble. Cytoskeletons prepared from EGF-treated A431 cells, when incubated with gamma-32P-ATP, demonstrated enhanced autophosphorylation of the EGF-R in situ as well as the phosphorylation of several high molecular weight proteins. In this system, phosphorylation occurs between immobilized kinase and substrate. The EGF-R and several high molecular weight cytoskeletal proteins were phosphorylated on tyrosine residues; two of the latter proteins were phosphorylated transiently as a consequence of EGF action, suggesting that EGF caused the active redistribution of the protein substrates relative to protein kinases. The ability of EGF to stimulate protein phosphorylation in situ required treatment of intact cells at physiological temperatures; addition of EGF directly to cytoskeletons had no effect. These data suggest that the structural association of the EGF-R may play a role in cellular processing of the hormone, as well as in regulation of the EGF-R kinase activity and in specifying its cellular substrates.