Rapid rounding of human epidermoid carcinoma cells A-431 induced by epidermal growth factor

Abstract

Epidermal growth factor (EGF) induces rapid rounding of A-431 human epidermoid carcinoma cells in Ca++-free medium. Cell rounding is not induced by a variety of other polypeptide hormones, antiserum to cell membranes, local anesthetics, colchicine, cytochalasin B, oe cyclic nucleotides. However, trypsin, like EGF, induces rounding of A-431 cells in the absence of Ca++. Both trypsin- and EGF-induced rounding are temperature dependent, appear to be energy dependent, and are inhibited by cytochalasins, suggesting the active participation of microfilaments in cell rounding. However, a medium transfer experiment suggests that EGF-induced rounding is not attributable to secretion of a protease, and a number of serine protease inhibitors have no effect on the EGF-induced rounding process. Cell rounding is not attributable to the slight stimulation by EGF of the release of Ca++ that is observed in Ca++-free medium, as stimulation of such release by the ionophore A23187 neither induces cell rounding nor blocks EGF-induced rounding. Cells that have rounded up after treatment with EGF or trypsin spread out upon addition of Ca++ to the medium, even in the continuing presence of EGF or trypsin. Like the cell-rounding process, the cell-spreading process is temperature dependent, appears to be energy dependent, and is inhibited by cytochalasin B. Thus, EGF does not destroy the ability of the cell to spread; rather, in the presence of EGF (or trypsin), cell spreading and the maintenance of the flattened state become dependent on external Ca++. Because untreated cells remain flattened in the absence of Ca++, the data suggest that EGF may disrupt Ca++-independent mechanisms of adhesion normally present in A-431 cells.