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Updated: Sep 27, 2026
Profiling of Estrogen-regulated MicroRNAs in Breast Cancer Cells
Published on: February 21, 2014
Decrease of estrogen receptor expression and associated ERE-dependent transcription in MCF-7 breast cancer cells
Hye-Sook Seo1, Fabrice Journé, Denis Larsimont
1Laboratoire J.-C. Heuson de Cancérologie Mammaire, Service de Médecine Interne, Institut Jules Bordet, Université Libre de Bruxelles, Brussels, Belgium.
Abstract:
Oligomycin at 0.01 microM produces very rapid decrease of [3H]estradiol (E2)-binding capacity in MCF-7 cells maintained in culture in glucose- and serum-free medium. Loss of binding capacity was associated with elimination of the estrogen receptor (ER) as well as a decrease of basal expression of ERE-luciferase reporter gene. These effects were not due to major cell death as shown by MTT assay. Hence, the inhibition of ATP synthesis produced by oligomycin seems to influence ER turnover, resulting in very rapid loss of receptor. Withdrawal of oligomycin and maintenance of glucose in the medium led to only a partial reappearance of ER and failed to restore optimal ERE-dependent transcription. Oligomycin significantly down-regulated progesterone receptor (PR) level and partially abrogated E2-induced PR up-regulation, indicating that this drug also affects other nuclear receptors. Treatment of cytosol from MCF-7 cells with acid and alkaline phosphatases decreased [3H]E2-binding capacity, indicating the requirement of ER phosphorylation for optimal hormone binding. On the other hand, oligomycin-induced ER loss was partly compensated by E2 and partial anti-estrogens (AEs; 4-OH-TAM or RU 39 411); i.e. oligomycin failed to improve the E2-induced ER down-regulation and very weakly suppressed partial AE-induced receptor up-regulation. The known ability of these ligands to stabilize ER in the cell nucleus before regulating ER level may explain this phenomenon since such antagonism was not recorded with pure AE RU 58 668, which is known to impede nuclear translocation of the receptor. Interestingly, ligands able to down-regulate ER (i.e. E2 or RU 58 668) increased ER phosphorylation while 4-OH-TAM which up-regulate the receptor had little effect in this regard. Oligomycin failed to strongly affect such phosphorylation enhancements while it produced a weak decrease of basal phosphorylation level. Hence, phosphorylations/dephosphorylations of specific sites on ER and/or co-regulators seem to govern its turnover.
Insights
Oligomycin rapidly decreases estrogen receptor (ER) levels and function in MCF-7 cells by inhibiting ATP synthesis, impacting ER turnover and transcription. This suggests ER phosphorylation regulates its stability and response to ligands.
Area of Science:
- Cell Biology
- Molecular Endocrinology
- Biochemistry
Background:
- Estrogen receptor (ER) is crucial for regulating gene expression in hormone-responsive cells.
- ER activity is modulated by ligand binding, post-translational modifications like phosphorylation, and protein turnover.
- Understanding factors influencing ER stability and function is key to developing targeted therapies.
Purpose of the Study:
- To investigate the effect of oligomycin, an ATP synthesis inhibitor, on ER expression and function in MCF-7 cells.
- To explore the role of ER phosphorylation in oligomycin-induced changes and ligand interactions.
- To determine if oligomycin affects other nuclear receptors.
Main Methods:
- MCF-7 cells were treated with oligomycin in glucose- and serum-free medium.
- Estrogen receptor (ER) binding capacity was measured using [3H]estradiol.
- ER levels were assessed, along with ERE-luciferase reporter gene expression.
- Cell viability was evaluated using MTT assay.
- Progesterone receptor (PR) levels and phosphorylation status were analyzed.
Main Results:
- Oligomycin rapidly decreased ER binding capacity and levels, independent of major cell death.
- Basal ERE-luciferase activity was reduced, indicating impaired transcriptional function.
- Oligomycin down-regulated PR levels and interfered with E2-induced PR upregulation.
- ER phosphorylation was required for hormone binding, and oligomycin affected ER phosphorylation patterns.
- Ligand-specific effects on ER phosphorylation and turnover were observed, with partial rescue by E2 and partial anti-estrogens.
Conclusions:
- Oligomycin-induced ATP synthesis inhibition accelerates ER turnover, leading to rapid loss of receptor and function.
- ER phosphorylation plays a critical role in regulating ER stability and hormone binding.
- Oligomycin impacts multiple nuclear receptors, suggesting broader effects on endocrine signaling.
- These findings highlight the intricate regulation of ER by cellular energy status and post-translational modifications.
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