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Stabilization of mammary-derived growth inhibitor messenger RNA by antiestrogens
1Departments of Medicine and Oncology, Lady Davis Research Institute, McGill University, Montreal, Quebec, Canada H3T 1E2.
Abstract:
Mammary-derived growth inhibitor (MDGI) is a tumor suppressor gene that is maximally expressed in terminally differentiated mammary epithelial cells. The MDGI gene is silenced in human breast cancer cell lines and in many primary human and experimental breast tumors. We demonstrate that the antiestrogens 4-hydroxytamoxifen (4-OH tamoxifen) and ICI 182780 (ICI) stimulate MDGI expression in vitro. Dose-dependent MDGI mRNA accumulation was observed when ICI was added to the culture medium of mammary explants. Both 4-OH tamoxifen and ICI stabilized MDGI mRNA without affecting the transcription rate of the MDGI gene. Under estrogen-free conditions, the half-life of MDGI mRNA in control explants was approximately 6 h. This half-life was increased to 7.5 h in the presence of 10(-7) M 4-OH tamoxifen and to greater than 12 h in the presence of 10(-7) M ICI. There was a positive correlation between the antiproliferative activity of antiestrogens and their ability to stabilize MDGI mRNA. The up-regulation of expression of the MDGI tumor suppressor gene in normal breast tissue by antiestrogens may contribute to the protective activity of these compounds that is seen in mammary gland carcinogenesis experimental systems and to the decreased risk of contralateral cancer that is seen in women receiving tamoxifen therapy.
Insights
Antiestrogens like tamoxifen can increase the expression of the mammary-derived growth inhibitor (MDGI) tumor suppressor gene. This stabilization of MDGI mRNA by antiestrogens may explain their protective effects against breast cancer.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Mammary-derived growth inhibitor (MDGI) is a tumor suppressor gene crucial for differentiated mammary epithelial cells.
- MDGI gene silencing is observed in various breast cancers, indicating its role in tumorigenesis.
Purpose of the Study:
- To investigate the effect of antiestrogens on MDGI gene expression.
- To explore the mechanism by which antiestrogens influence MDGI expression and its potential role in breast cancer prevention.
Main Methods:
- Treatment of mammary explants with antiestrogens (4-hydroxytamoxifen and ICI 182780).
- Measurement of MDGI mRNA levels and stability.
- Assessment of MDGI gene transcription rates.
- Correlation analysis between antiestrogen antiproliferative activity and MDGI mRNA stabilization.
Main Results:
- Antiestrogens 4-hydroxytamoxifen and ICI 182780 were found to stimulate MDGI expression in vitro.
- Both compounds significantly stabilized MDGI mRNA, increasing its half-life without altering transcription rates.
- A positive correlation was observed between the antiproliferative effects of antiestrogens and their capacity to stabilize MDGI mRNA.
Conclusions:
- Antiestrogens up-regulate the expression of the MDGI tumor suppressor gene in normal breast tissue.
- MDGI mRNA stabilization by antiestrogens may contribute to their chemopreventive effects in mammary gland carcinogenesis.
- This mechanism could be relevant to the reduced risk of contralateral breast cancer observed in women undergoing tamoxifen therapy.