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Updated: Jun 13, 2026
Systems Biology of Metabolic Regulation by Estrogen Receptor Signaling in Breast Cancer
Published on: March 17, 2016
Selective estrogen receptor down-regulator and selective estrogen receptor modulators differentially regulate
Sanjay Kansra1, Shenglin Chen, Madhavi Latha Yadav Bangaru
1Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America.
Background:
We recently reported that estrogen receptor alpha (ERalpha), even in absence of estrogen (E2), plays a critical role in lactotroph homeostasis. The anti-estrogen ICI 182780 (ICI), but not tamoxifen or raloxifene, rapidly promoted the degradation of ERalpha, and inhibited cell proliferation. However, all three ER antagonists suppressed PRL release, suggesting that receptor occupation is sufficient to inhibit prl gene expression whereas receptor degradation is required to suppress lactotroph proliferation. In this study our objective was to determine whether ERalpha degradation versus occupation, differentially modulates the biological outcome of anti-estrogens.
Principal Findings:
Using the rat lactotroph cell line, GH3 cells, we report that ICI induced proteosome mediated degradation of ERalpha. In contrast, an ERalpha specific antagonist, MPP, that does not promote degradation of ERalpha, did not inhibit cell proliferation. Further, ICI, but not MPP, abolished anchorage independent growth of GH3 cells. Yet, both ICI and MPP were equally effective in suppressing prl expression and release, as well as ERE-mediated transcriptional activity.
Conclusion:
Taken together, our results demonstrate that in lactotrophs, ERalpha degradation results in decreased cell proliferation, whereas ERalpha occupation by an antagonist that does not promote degradation of ERalpha is sufficient to inhibit prl expression.
Insights
Estrogen receptor alpha (ERalpha) degradation inhibits lactotroph proliferation, while occupation suppresses prolactin (PRL) expression. This highlights distinct biological outcomes of ERalpha modulation in lactotrophs.
Area of Science:
- Endocrinology
- Cell Biology
- Molecular Biology
Background:
- Estrogen receptor alpha (ERalpha) is crucial for lactotroph homeostasis, even without estrogen (E2).
- Anti-estrogens like ICI 182780 (ICI) induce ERalpha degradation and inhibit cell proliferation, while suppressing prolactin (PRL) release.
- Tamoxifen and raloxifene suppress PRL release but do not promote ERalpha degradation.
Purpose of the Study:
- To investigate whether ERalpha degradation versus occupation differentially modulates biological outcomes of anti-estrogens.
- To clarify the distinct roles of ERalpha degradation and occupation in lactotroph function.
Main Methods:
- Utilized the rat lactotroph cell line, GH3 cells.
- Compared the effects of ICI 182780 (ICI) and an ERalpha-specific antagonist, MPP, which does not induce ERalpha degradation.
- Assessed proteasome-mediated degradation, cell proliferation, anchorage-independent growth, PRL expression and release, and ERE-mediated transcriptional activity.
Main Results:
- ICI induced proteasome-mediated degradation of ERalpha in GH3 cells.
- MPP did not inhibit cell proliferation or abolish anchorage-independent growth.
- Both ICI and MPP equally suppressed PRL expression and release, and ERE-mediated transcriptional activity.
Conclusions:
- ERalpha degradation in lactotrophs leads to reduced cell proliferation.
- ERalpha occupation by antagonists that do not induce degradation is sufficient to inhibit PRL expression.
- Distinct mechanisms of ERalpha modulation yield different biological outcomes in lactotrophs.
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