The effects of epidermal growth factor (EGF) on the cytokeratin filaments of cultured murine epithelial cells were studied by the indirect immunofluorescence technique with affinity-purified antibodies. Mouse epithelial cells (MMC-E), grown on glass cover slips, and viewed by immunofluorescence microscopy, showed keratin-specific fluorescence as typical bright perinuclear aggregates corresponding to dense paracrystalline granules seen in electron microscopy. Within minutes after an exposure to EGF, the keratin granules in the MMC-E cells decreased. After 10 min of incubation, the cells had spread fibrillar keratin. Such an effect could not be found after a similar exposure to insulin, dexamethasone, dibutyryl cyclic AMP, or antimitotic drugs. EGF, therefore, has a relatively direct effect on the cytoskeletal organization of cultured epithelial cells. These rapid effects on the keratin filaments may explain the simultaneous EGF-induced ultrastructural surface changes of the cells. EGF may thus function as a regulatory factor in the migration of epithelial cells and in the mobility of their cell membranes. The epithelial cell line, MMC-E, should prove a useful model for studies on the action of EGF on nontransformed epithelial cells in vitro.

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