| Abstract: | We studied the effects of a series of drugs on A431, a cell line with well-characterized growth factor requirements and epidermal growth factor (EGF) receptors. The major 32PO4]-labeled protein immunoprecipitated with anti-phosphotyrosine antibodies from EGF-stimulated A431 cells was the EGF receptor. Both the quantity of 32PO4]-labeled EGF receptor immunoprecipitated and the phosphotyrosine content of total 32PO4]-labeled proteins were reduced by the addition during EGF stimulation of trifluoperazine (TFP). TFP had little effect on the binding, internalization, and processing of 125I]-EGF. In addition to the effects on phosphorylation, TFP inhibited cell growth both in the presence and absence of EGF. Morphologically, TFP blocked EGF-induced ruffling. TFP did not alter the EGF-stimulated phosphatidylinositol turnover. In an in vitro experiment using A431 cell membranes, TFP did not inhibit phosphorylation of the EGF receptor. |
