Epidermal growth factor receptor in human epidermal cells: direct demonstration in cultured cells

The interaction of [125I] labeled murine epidermal growth factor (EGF)( with cultured human keratinocytes has been studied. Epidermal cells from neonatal foreskins were propagated to confluence in 24-well culture trays and incubated with [125I] EGF for binding assays. Association reached equilibrium within 2-4 hr at 4 degrees and slightly earlier at 37 degrees. EGF bound at 37 degrees dissociates very slowly from cells, since it can be shown to enter cells and is degraded to trichloracetic-acid-soluble material. Cells exposed to chloroquine, an inhibitor of lysosomal enzymes, fail to degrade internalized [125I] EGF. Scatchard plots of the binding data yield a dissociation constant of 1 X 10(-9) m and show that epidermal cells bind approximately 3-4 X 10(4) molecules of EGF. Cells exposed to EGF alter their ability to bind EGF by decreasing the number of binding sites in a time- and concentration-dependent manner. Differentiation of epidermal cells in culture poses a problem in assessment of binding of EGF and possibly of other biologically active ligands, since cells lose the ability to bind EGF as they differentiate. These findings indicate that isolated epidermal cells possess a functional receptor for EGF which binds and responds to EGF in a manner similar to that described for other cells.