Mobility of epidermal growth factor surface receptors and modulation by cytoplasmic actin

Epidermal growth factor (EGF) receptors were demonstrated in cultured bovine odontogenic epithelial and ectomesenchymal cells and in rat embryonic and foetal lung fibroblasts by immunofluorescent reactivity with EGF and anti-EGF traced with a fluorescein-isothiocyanate-labelled goat anti-rabbit globulin. Mobility of EGF receptors, either alone or cross linked by anti-EGF, was manifest as sequential changes in staining patterns progressing from a random pattern to clusters, supranuclear caps and large perinuclear globules. Double fluorochrome studies showed that supranuclear caps of EGF receptors occurred in sites closely related to those occupied by cytoplasmic actin; the latter was demonstrated by anti-actin antibody traced with a rhodamine-labelled goat anti-human globulin. Prior treatment of cells with 2 x 10-5 M cytochalasin B for 10-120 min promoted capping of EGF receptors, while its presence throughout the staining procedure inhibited capping. The dual opposing effects of cytochalasin B on capping suggest that actin may have roles in the opposing functions of EGF receptor anchorage and mobility.