Characterization of the action of epidermal growth factor in three different biological systems

In general, these studies characterized in each system one or more of the following aspects of EGF's biological action: EGF binding, EGF-induced phosphorylation, or EGF-stimulated DNA synthesis. In human corneal fibroblasts (HCF), EGF binds to specific, saturable, high affinity receptors and stimulated [3H]-thymidine incorporation, and in vitro measurement of DNA synthesis, approximately 2.5 fold above control cultures, with maximal stimulation occurring at approximately 1 nM EGF. In addition, fibroblasts growth factor (FGF) and insulin stimulated maximal [3H]-thymidine incorporation in HCF at approximately 100 ng ml-1 and 1 nM, respectively. In combination with dexamethasone (5 nM), the stimulation of [3H]-thymidine incorporation by EGF was maintained. However, dexamethasone abolished the stimulatory action of FGF. Highly purified preparations of human placental outer cell membranes and intracellular organelles were assayed for functional EGF binding proteins (EGF-receptors). Functionality of a protein was determined by covalent labeling with [125I]-EGF and EGF-stimulated autophosphorylation