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Modulation of epidermal growth factor receptor gene expression by transforming growth factor-beta in a human breast
Abstract:
Modulation of epidermal growth factor (EGF) receptor expression determines cellular responsiveness to EGF and might play an important role in growth inhibition. We have investigated the actions of EGF and/or transforming growth factor type beta (TGF beta) on EGF receptor gene expression in MDA-468 human breast carcinoma cell line, which responds to EGF and/or TGF beta with growth inhibition. Using the cDNA clone pE7, which encodes 2.4 kilobases of the human EGF receptor mRNA, as a hybridization probe, we have found that exposure of MDA-468 cells to EGF results in elevated levels of EGF receptor mRNA. This increase in mRNA accumulation showed time and dose dependence. Addition of TGF beta enhances the accumulation of EGF receptor mRNA induced by EGF. Under this condition, stimulation could be detected after 1 h exposure to TGF beta with a maximum at 6-8 h. A concentration of 10 pM TGF beta gave detectable stimulation with maximal stimulation occurring at 300 pM in the presence of EGF (50 ng/ml). In contrast, TGF beta alone had no significant effect on EGF receptor mRNA accumulation. In the presence of cycloheximide, the EGF receptor mRNA was super-induced in response to EGF. Treatment of the cells with TGF beta enhances the EGF-dependent superinduction of EGF receptor mRNA produced by cycloheximide, suggesting that the stimulatory action of TGF beta does not depend on continuous protein synthesis. The results described here are consistent with the hypothesis that the growth inhibitory action of TGF beta in MDA-468 cells may be mediated, at least in part, by modulation of EGF receptor gene expression.
Insights
Epidermal Growth Factor (EGF) increases EGF receptor mRNA in breast cancer cells. Transforming Growth Factor beta (TGF-β) enhances this effect, suggesting a role in growth inhibition.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Cellular response to growth factors is crucial in cancer.
- Epidermal Growth Factor (EGF) receptor (EGFR) expression influences cell behavior.
- Transforming Growth Factor beta (TGF-β) can inhibit cancer cell growth.
Purpose of the Study:
- To investigate the effect of EGF and TGF-β on EGFR gene expression in human breast carcinoma cells (MDA-468).
- To understand the role of EGFR modulation in TGF-β-mediated growth inhibition.
Main Methods:
- Utilized a cDNA clone (pE7) for human EGFR mRNA detection via hybridization.
- Exposed MDA-468 cells to EGF and/or TGF-β under various conditions (time, dose, cycloheximide).
- Quantified EGFR mRNA levels using hybridization assays.
Main Results:
- EGF exposure elevated EGFR mRNA levels in a time- and dose-dependent manner.
- TGF-β enhanced EGF-induced EGFR mRNA accumulation, with effects seen after 1h and peaking at 6-8h.
- TGF-β alone did not significantly affect EGFR mRNA; it enhanced EGF-dependent superinduction in the presence of cycloheximide, indicating protein synthesis is not required for TGF-β's action.
Conclusions:
- EGF upregulates EGFR mRNA expression in MDA-468 cells.
- TGF-β potentiates EGF-induced EGFR mRNA accumulation, suggesting a mechanism for growth inhibition.
- Modulation of EGFR gene expression by TGF-β may contribute to its growth inhibitory effects in breast cancer.