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Transforming growth factor beta modulates phosphorylation of the epidermal growth factor receptor and proliferation
1Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
Abstract:
Transforming growth factor beta (TGF-beta) increased the phosphorylation of the epidermal growth factor (EGF) receptor and inhibited the growth of A431 cells. Incubation with TGF-beta induced maximal EGF receptor phosphorylation to levels 1.5-fold higher than controls. Phosphorylation increased more prominently (4-5-fold) on tyrosine residues as determined by phosphoamino acid analysis and antiphosphotyrosine antibody immunoblotting. The kinase activity of EGF receptor was also elevated 2.5-fold when cells were cultured in the presence of TGF-beta. The antiproliferative effect of TGF-beta on A431 cells was accompanied by prolongation of G0-G1 phase and by morphological changes. TGF-beta augmented the growth inhibition of A431 cells which could be induced by EGF. In parallel, the specific EGF-induced increase in total phosphorylation of the EGF receptor was also augmented in the presence of TGF-beta. In cells cultured with TGF-beta, the phosphorylation of EGF receptor tyrosines induced by 20-min exposure to EGF was further increased 2-3-fold, suggesting additive effects upon receptor phosphorylation. EGF receptor activation by TGF-beta is characterized by kinetics quite distinct from that induced by EGF and therefore appears to take place through an independent mechanism. The TGF-beta-induced elevation in the phosphorylation of the EGF receptor may have a role in the augmented growth inhibition of A431 cells observed in the presence of EGF and TGF-beta.
Insights
Transforming growth factor beta (TGF-beta) enhances epidermal growth factor (EGF) receptor phosphorylation and inhibits A431 cell growth. This TGF-beta effect on EGF receptor signaling contributes to augmented growth inhibition when combined with EGF.
Area of Science:
- Cellular signaling pathways
- Receptor tyrosine kinases
- Cancer cell proliferation
Background:
- Epidermal growth factor (EGF) receptor signaling is crucial for cell growth.
- Transforming growth factor beta (TGF-beta) is known to regulate cell proliferation and differentiation.
- Cross-talk between TGF-beta and EGF receptor pathways is implicated in various cellular processes.
Purpose of the Study:
- To investigate the effect of TGF-beta on EGF receptor phosphorylation and kinase activity.
- To determine the impact of TGF-beta on A431 cell proliferation.
- To explore the interplay between TGF-beta and EGF in regulating A431 cell growth and EGF receptor signaling.
Main Methods:
- A431 cells were treated with TGF-beta and/or EGF.
- EGF receptor phosphorylation was assessed using phosphoamino acid analysis and antiphosphotyrosine antibody immunoblotting.
- Kinase activity of EGF receptor was measured.
- Cell proliferation was evaluated by monitoring cell cycle progression (G0-G1 phase) and morphological changes.
Main Results:
- TGF-beta treatment increased EGF receptor phosphorylation, particularly on tyrosine residues (4-5-fold increase).
- TGF-beta elevated EGF receptor kinase activity by 2.5-fold.
- TGF-beta inhibited A431 cell proliferation, causing G0-G1 phase prolongation and morphological changes.
- TGF-beta augmented EGF-induced growth inhibition and EGF receptor phosphorylation, suggesting additive effects.
Conclusions:
- TGF-beta activates the EGF receptor through a mechanism distinct from EGF.
- The observed TGF-beta-induced EGF receptor phosphorylation plays a role in the enhanced growth inhibition of A431 cells in the presence of both TGF-beta and EGF.