Autophosphorylation of EGF receptors in the A431 cell line with an increased intracellular concentration of Ca(2+) ions

The increase in the intracellular concentration of Ca2+ in A431 cells induced by the calcium ionophore A23187 leads to phosphorylation of epidermal growth factor (EGF) receptors at serine and/or threonine residues. This process is accompanied by the decrease in the level of EGF receptor autophosphorylation at tyrosine residues. Preincubation of cells in a A23187-containing medium in the presence of phorbol-12-myristoyl-13-acetate leads to a further decrease of the phosphotyrosine content in EGF receptors. At increased intracellular concentrations of Ca2+ preincubation of A431 cells with the protein kinase C inhibitor H-7 has no effect on the degree of EGF receptor autophosphorylation. Down-regulation of cellular protein kinase C does not change the A23187-induced effect either. The data obtained suggest that the decreased autophosphorylation of EGF receptors induced by Ca2+ is not due to the activation of cellular protein kinase C.