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Phytoestrogen interaction with estrogen receptors in human breast cancer cells
Abstract:
The interactions of phytoestrogens with estrogen receptors were studied in the human breast cancer cell line, MCF-7. The compounds tested were coumestrol, genistein, and formononetin and the mycotoxins, zearalenone and its reduced derivative, zearalenol. All but formononetin compete for binding of [3H]-estradiol to unfilled cytoplasmic estrogen receptor or unfilled nuclear estrogen receptor sites. Relative binding affinities are zearalenol HMP (high melting point isomer) greater than zearalenol LMP (low melting point isomer) greater than zearalenone = coumestrol greater than genistein greater than formononetin. Dissociation constants estimated from competition curves show that binding affinities are high. In contrast to estradiol, phytoestrogens bind only weakly to sex steroid-binding globulin; they also do not bind to corticosteroid-binding globulin. These compounds translocate the cytoplasmic estrogen receptor and bind to unfilled nuclear estrogen receptors in whole cells. Bound nuclear receptors are then processed in a manner similar to estradiol in a step which rapidly decreases total cellular estrogen receptors. The phytoestrogens are also biologically active; they can markedly enhance tumor cell proliferation. In sum, phytoestrogens interact with the estrogen receptors of human breast cancer cells in culture and, therefore, may affect estrogen-mediated events in these cells.
Insights
Phytoestrogens like coumestrol and genistein bind to estrogen receptors in human breast cancer cells. This interaction can enhance tumor cell proliferation, suggesting a role in estrogen-mediated events.
Area of Science:
- Endocrinology
- Molecular Biology
- Cancer Research
Background:
- Phytoestrogens are plant-derived compounds with estrogenic activity.
- Estrogen receptors play a crucial role in the growth and development of breast cancer.
Purpose of the Study:
- To investigate the binding interactions of specific phytoestrogens and mycotoxins with estrogen receptors in MCF-7 human breast cancer cells.
- To determine the biological activity of these compounds in relation to estrogen receptor binding.
Main Methods:
- Competition binding assays using [3H]-estradiol to assess binding affinities to cytoplasmic and nuclear estrogen receptors.
- Whole-cell studies to evaluate receptor translocation and processing.
- Cell proliferation assays to measure biological activity.
Main Results:
- Coumestrol, genistein, zearalenone, and zearalenol competed for estrogen receptor binding, with varying affinities.
- Phytoestrogens translocated cytoplasmic estrogen receptors to the nucleus and decreased total cellular estrogen receptors.
- These compounds significantly enhanced MCF-7 breast cancer cell proliferation.
Conclusions:
- Phytoestrogens interact with estrogen receptors in human breast cancer cells.
- The binding and subsequent nuclear translocation suggest a mechanism for phytoestrogen-mediated effects on estrogen-responsive genes.
- Phytoestrogens exhibit biological activity by promoting tumor cell proliferation, highlighting their potential impact on estrogen-mediated events in breast cancer.