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Modulation of estrogen receptor mRNA expression by melatonin in MCF-7 human breast cancer cells
T M Molis1, L L Spriggs, S M Hill
1Department of Anatomy, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Abstract:
Melatonin, the hormonal product of the pineal gland, has been shown to inhibit the development of mammary tumors in vivo and the proliferation of MCF-7 human breast cancer cells in vitro by mechanisms not yet identified. However, previous studies have demonstrated that melatonin significantly decreased estrogen-binding activity and the expression of immunoreactive estrogen receptor (ER) in MCF-7 breast cancer cells. To determine the mechanism(s) by which melatonin regulates ER expression in MCF-7 cells, the relationship between the level of steady state ER mRNA and the rate of ER gene transcription were examined in response to melatonin. Physiological concentrations of melatonin decreased steady state levels of ER mRNA expression in a dose- and time-specific manner. This decrease was not dependent upon the presence of estrogen since similar decreases in steady state ER mRNA levels were seen in MCF-7 cells cultured in both complete and estrogen-depleted media. The decreased expression of ER mRNA in response to melatonin appears to be directly related to the suppression of transcription of the ER gene. This regulation is independent of the synthesis of new proteins, as cycloheximide was unable to block the melatonin-induced decrease of steady-state ER mRNA levels. The down-regulation of ER by melatonin appears to not be mediated via a direct interaction with the ER and subsequent feedback on its own expression, since melatonin treatment did not alter the transcriptional regulatory ability of the fully activated wild type ER or a constitutively active hormone-binding domain-deleted ER variant. In addition, the stability of the ER transcript was unaffected by melatonin. Thus, it appears that the antiproliferative actions of this pineal indoleamine are mediated, at least in part, through the suppression of the transcription of the ER gene in MCF-7 human breast cancer cells.
Insights
Melatonin, a pineal hormone, inhibits breast cancer cell proliferation by suppressing estrogen receptor (ER) gene transcription. This mechanism reduces ER mRNA levels, independent of protein synthesis or direct ER interaction.
Area of Science:
- Endocrinology
- Molecular Biology
- Cancer Research
Background:
- Melatonin, a pineal gland hormone, inhibits mammary tumor development and breast cancer cell proliferation.
- Previous studies indicate melatonin reduces estrogen-binding activity and estrogen receptor (ER) expression in MCF-7 cells.
- The precise mechanisms by which melatonin affects ER expression remain unidentified.
Purpose of the Study:
- To elucidate the mechanisms underlying melatonin's regulation of ER expression in MCF-7 human breast cancer cells.
- To investigate the relationship between steady-state ER mRNA levels and ER gene transcription in response to melatonin.
- To determine if melatonin's effects are mediated by direct interaction with the ER or protein synthesis.
Main Methods:
- Examined steady-state ER mRNA levels and ER gene transcription rates in MCF-7 cells treated with melatonin.
- Utilized estrogen-depleted media to assess melatonin's effects independent of estrogen.
- Employed cycloheximide to investigate the role of new protein synthesis.
- Assessed the impact of melatonin on the transcriptional regulatory ability of wild-type and variant ER.
Main Results:
- Physiological melatonin concentrations decreased steady-state ER mRNA levels in a dose- and time-dependent manner.
- Melatonin suppressed ER gene transcription, independent of estrogen presence or new protein synthesis.
- Melatonin did not affect ER transcript stability or the transcriptional regulatory ability of the ER.
- The antiproliferative effects of melatonin in MCF-7 cells are partly mediated by suppressing ER gene transcription.
Conclusions:
- Melatonin's antiproliferative action on MCF-7 breast cancer cells is, in part, achieved by suppressing ER gene transcription.
- This suppression of ER gene transcription is a key mechanism by which melatonin exerts its effects.
- The findings provide insight into the molecular pathways targeted by melatonin in breast cancer therapy.