Epidermal growth factor-receptor-protein kinase interactions. Co-purification of receptor and epidermal growth factor-enhanced phosphorylation activity

Abstract

Membranes may be prepared from A-431 human epidermoid carcinoma cells which have the ability to bind 125I-labeled epidermal growth factor (EGF) in a specific manner and which, in the presence of EGF, catalyze the phosphorylation of a number of endogenous membrane proteins. The activation of the membrane associated protein kinase by EGF appears to be a reversible phenomenon. The membrane preparation may be solubilized by a number of nonionic detergents with the retention of both 125I-labeled EGF-binding activity and EGF-enhanced phosphorylation of specific membrane proteins. The solubilized membrane preparation may be purified by affinity chromatography using EGF covalently linked to Affi-Gel. The purified preparation retains both EGF-binding activity and EGF-enhanced phosphorylation activity. Analysis of the affinity-purified preparation by sodium dodecyl sulfate-gel electrophoresis indicates the presence of one major protein band of molecular weight 150,000 and several trace bands. The evidence suggests that the major 150,000 protein band is the receptor for EGF and is a substrate of the phosphorylation reaction. The co-purification of EGF-binding activity and EGF-stimulated phosphorylation activity suggests an inherent close relationship.