Analysis of morphology and receptor metabolism in clonal variant A431 cells with differing growth responses to epidermal growth factor

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Abstract
Human epidermoid carcinoma A431 cell clones have been obtained whose growth is inhibited, stimulated, or unaffected by epidermal growth factor (EGF). In clones exhibiting each type of growth response, EGF induced similar morphologic changes consisting of aggregation of cells into dense clusters with baring of large areas of the culture dish. The similarity of the clones' morphologic responses, despite their differing growth responses, indicates that the effects of EGF on morphology are distinct from effects on growth. Cells whose growth was inhibited by EGF contained high numbers of EGF receptors, whereas the concentration of EGF receptors was reduced in cells whose growth was stimulated or unaffected by EGF. There were, however, no consistent differences in EGF receptor concentrations between stimulated or null clones. Cells that exhibited each type of growth response displayed similar rates of EGF binding to receptors, rates of internalization of EGF, and rates and extent of EGF‐induced receptor down‐regulation. Changes in EGF‐stimulated tyrosine‐specific protein kinase activity paralleled changes in EGF receptors, both between clones and upon down‐regulation. These studies indicate that a reduction in the concentration of EGF receptors in A431 cells allows escape from the growth inhibitory effects of EGF, but suggest that the pattern of growth response depends on biochemical events subsequent to EGF‐receptor metabolism and activation of tyrosine‐specific protein kinase.