Growth stimulation of A431 cells by epidermal growth factor: identification of high-affinity receptors for epidermal growth factor by an anti-receptor monoclonal antibody.

Abstract

Epidermal growth factor (EGF) at 3 nM maximally inhibits the proliferation of A431 epidermoid carcinoma cells. We show that at lower concentrations, in the range of 3-100 pM, EGF has a mitogenic effect on A431 cells. In Epidermal growth factor (EGF) promotes the growth of many cell types in vitro (1-3) and inhibits proliferation of several cell types-e.g., GH4 rat pituitary tumor cells (4), A431 epidermoid carcinoma cells (5, 6), and certain human breast cancer cells (7). EGF initially binds to receptors homogeneously distributed on the cell surface. Subsequent events have been described by various investigators and include receptor phosphorylation, aggregation, internalization, and degradation in lysosomes (1). The mechanism by which these events induce DNA synthesis and cytokinesis is unknown.It has been found that at least 6-8 hr of EGF exposure are required to stimulate DNA synthesis (8). Das and Fox have suggested that EGF-induced internalization and degradation of the EGF receptor are rate-limiting factors for EGF-induced mitogenesis (9, 10), perhaps through production of a second messenger. Recent studies showed enhancement of EGF stimulation of DNA synthesis by amine compounds, which inhibited clustering of receptors in coated pits (11), and by phorbol esters, which reduced both the affinity of EGF receptors for EGF and its subsequent degradation (12)(13)(14). These results suggest that EGF stimulation of cell growth might only require the presence of EGF-EGF receptor complexes at the cell surface in contradiction to the above hypothesis.Shechter et al., on the other hand, suggested that the stimulatory effect of EGF might be mediated by small amounts of high-affinity EGF receptors, which remain at the cell surface for more than 8 hr when occupied by EGF (15). King and Cuatrecasas also have suggested that the accumulation of stable intracellular complexes between high-affinity receptors and EGF are involved in growth stimulation, but the role of these highaffinity receptors in mitogenesis remains unclear (16).A431 cells lend themselves to the study of EGF interactions with receptors because of their extremely high number of EGF receptors (1-3 x 10' per cell) (1,17,18

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Epiregulin binds to epidermal growth factor receptor and ErbB-4 and induces tryosine phosphorylation of epidermal growth factor receptor, ErbB-2, ErbB-3 and ErbB-4

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