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Oestrogen and epidermal growth factor down-regulate erbB-2 oncogene protein expression in breast cancer cells by
S Antoniotti1, D Taverna, P Maggiora
1Department of Animal Biology, University of Torino, Italy.
Abstract:
Mitogen-induced mammary cell growth is often accompanied by decreased levels of expression of the p185erbB-2 protein. We have previously reported that oestrogen inhibits erbB-2 mRNA and protein expression in breast cancer cells, while epidermal growth factor (EGF) treatment has been shown to decrease p185erbB-2 levels in normal mouse mammary epithelial cells. In the present work, we studied the effect of oestrogen and EGF on erbB-2 expression in oestrogen-responsive breast cancer cells. We observed that both oestrogen and EGF comparably down-regulated p185erbB-2 levels, while stimulating growth of T47D and ZR75.1 cells. Oestrogens, but not EGF, concomitantly down-regulated erbB-2 mRNA. Run-on analysis showed a reduced erbB-2 transcription rate in the presence of oestrogens. Furthermore, the transcriptional activity of a 219 bp proximal fragment of the human erbB-2 promoter was repressed by oestrogens, whereas it was enhanced by EGF. EGF stimulated both tyrosine phosphorylation and autokinase activity of p185erbB-2 down-regulates p185erbB-2 at a post-translational level. Thus, two factors converging in terms of effects on cell growth, display divergent mechanisms of regulation of erbB-2 expression.
Insights
Estrogen and epidermal growth factor (EGF) both reduce p185erbB-2 protein in breast cancer cells, but through different mechanisms. Estrogen acts transcriptionally, while EGF acts post-translationally.
Area of Science:
- Molecular Biology
- Cell Biology
- Endocrinology
Background:
- Mitogen-induced mammary cell growth often correlates with reduced p185erbB-2 protein expression.
- Estrogen and epidermal growth factor (EGF) have been previously shown to inhibit erbB-2 expression through different mechanisms.
Purpose of the Study:
- To investigate the distinct effects of estrogen and EGF on erbB-2 expression in estrogen-responsive breast cancer cells.
- To elucidate the regulatory mechanisms underlying erbB-2 expression modulation by these growth factors.
Main Methods:
- Cell culture of estrogen-responsive breast cancer cell lines (T47D and ZR75.1).
- Analysis of erbB-2 mRNA and protein levels following estrogen and EGF treatment.
- Run-on assays to assess erbB-2 transcription rates.
- Reporter gene assays using a human erbB-2 promoter fragment.
- Western blot analysis for tyrosine phosphorylation and autokinase activity of p185erbB-2.
Main Results:
- Both estrogen and EGF down-regulated p185erbB-2 protein levels and stimulated cell growth.
- Estrogen reduced erbB-2 mRNA levels and transcription rate, repressing erbB-2 promoter activity.
- EGF did not affect erbB-2 mRNA or transcription but enhanced erbB-2 promoter activity.
- EGF stimulated p185erbB-2 tyrosine phosphorylation and autokinase activity, indicating post-translational regulation.
Conclusions:
- Estrogen and EGF exhibit divergent mechanisms in regulating erbB-2 expression, despite converging on cell growth.
- Estrogen regulates erbB-2 at the transcriptional level, while EGF acts post-translationally.
- These findings highlight the complex interplay between growth factors and oncogene expression in breast cancer.