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Modulation of type alpha transforming growth factor receptors by a phorbol ester tumor promoter
Abstract:
Epidermal growth factor (EGF) and an EGF-like transforming growth factor (eTGF) from retrovirally transformed cells bind to a common receptor type in A431 cells. We have investigated the effects of the tumor promoter phorbol myristate acetate [PMA] on EGF/eTGF receptors in intact A431 cells. Treatment with PMA at 37 degrees C induces a complete loss of high-affinity (Kd = 35-50 pM) binding sites for eTGF and EGF on the cell surface of A431 cells. This effect is half-maximal at 0.1 nM PMA, exhibits rapid kinetics, and persists for at least 4 hr in the presence of PMA. eTGF and PMA added to intact A431 cells induce the phosphorylation of immunoprecipitable 170kd EGF/eTGF receptors. The EGF/eTGF receptor isolated from control cells was found to contain phosphoserine and phosphothreonine. PMA and eTGF caused a marked increase in the level of these two phosphoamino acids. In addition, eTGF but not PMA caused the appearance of phosphotyrosine in the EGF/eTGF receptor in vivo. We conclude that the tumor-promoting phorbol diester regulates both the affinity and phosphorylation state of the A431 cell receptor for the type alpha transforming growth factors, eTGF and EGF.
Insights
Phorbol myristate acetate (PMA), a tumor promoter, reduces epidermal growth factor (EGF) and EGF-like transforming growth factor (eTGF) binding to A431 cell receptors. PMA also alters receptor phosphorylation, impacting cell signaling pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Epidermal growth factor (EGF) and EGF-like transforming growth factor (eTGF) bind to a common receptor on A431 cells.
- Tumor promoters can influence cellular signaling pathways.
Purpose of the Study:
- To investigate the effects of phorbol myristate acetate (PMA) on EGF/eTGF receptors in A431 cells.
- To understand how PMA affects receptor binding affinity and phosphorylation.
Main Methods:
- Treatment of intact A431 cells with PMA and/or eTGF.
- Measurement of high-affinity binding sites for EGF/eTGF.
- Immunoprecipitation and analysis of receptor phosphorylation (phosphoserine, phosphothreonine, phosphotyrosine).
Main Results:
- PMA treatment caused a complete loss of high-affinity EGF/eTGF binding sites.
- PMA induced phosphorylation of the EGF/eTGF receptor, increasing phosphoserine and phosphothreonine levels.
- eTGF, but not PMA, induced phosphotyrosine in the receptor.
Conclusions:
- PMA regulates both the affinity and phosphorylation state of the A431 cell receptor for EGF and eTGF.
- These findings shed light on the molecular mechanisms by which tumor promoters can affect growth factor signaling.