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Inhibition of epidermal growth factor-induced phosphorylation by trifluoperazine
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.
Insights
Trifluoperazine (TFP) reduces epidermal growth factor (EGF) receptor phosphorylation and inhibits A431 cell growth. TFP affects EGF receptor phosphorylation but not EGF binding or processing.
Area of Science:
- Cell biology
- Molecular pharmacology
Background:
- A431 cells possess well-characterized epidermal growth factor (EGF) receptors.
- EGF stimulation leads to phosphorylation of the EGF receptor in A431 cells.
Purpose of the Study:
- To investigate the effects of trifluoperazine (TFP) on EGF receptor signaling and A431 cell behavior.
- To determine if TFP impacts EGF receptor phosphorylation, binding, internalization, or processing.
Main Methods:
- Utilized A431 cell line for experiments.
- Employed [32PO4] labeling to assess protein phosphorylation.
- Used anti-phosphotyrosine antibodies for immunoprecipitation of phosphorylated proteins.
- Measured [125I]-EGF binding, internalization, and processing.
- Observed morphological changes and cell growth inhibition.
- Assessed phosphatidylinositol turnover and in vitro receptor phosphorylation.
Main Results:
- Trifluoperazine (TFP) reduced the quantity of phosphorylated EGF receptor and total phosphotyrosine content in EGF-stimulated A431 cells.
- TFP inhibited A431 cell growth irrespective of EGF presence.
- TFP blocked EGF-induced cell ruffling but did not affect EGF binding, internalization, processing, or phosphatidylinositol turnover.
- In vitro experiments showed TFP did not inhibit EGF receptor phosphorylation in A431 cell membranes.
Conclusions:
- Trifluoperazine (TFP) interferes with epidermal growth factor (EGF) receptor phosphorylation in intact A431 cells.
- TFP exhibits anti-proliferative effects on A431 cells and inhibits EGF-induced morphological changes.
- The mechanism of TFP's action on EGF receptor phosphorylation appears to be downstream of EGF binding and upstream of phosphatidylinositol turnover.