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Rapid estrogen signaling negatively regulates PTEN activity through phosphorylation in endometrial cancer cells
Melanie M Scully1, Leslie K Palacios-Helgeson, Lah S Wah
1Department of Obstetrics and Gynecology, School of Medicine, University of Colorado, Anschutz Medical Campus, Aurora, CO, 80045, USA, melanie.scully@UCDenver.edu.
Abstract:
Hyperestrogenicity is a risk factor for endometrial cancer. 17β-estradiol (E2) is known to stimulate both genomic and nongenomic estrogen receptor-α (ERα) actions in a number of reproductive tissues. However, the contributions of transcription-independent ERα signaling on normal and malignant endometrium are not fully understood. Phosphatase and tensin homolog (PTEN) is a tumor suppressor that decreases cellular mitosis primarily through negative regulation of the phosphoinositide 3-kinase/AKT signaling axis. PTEN levels are elevated during the E2 dominated, mitotically active, proliferative phase of the menstrual cycle, indicating possible hormonal regulation of PTEN in the uterus. In order to determine if rapid E2 signaling regulates PTEN, we used ERα-positive, PTEN-positive, endometrial cells. We show that cytosolic E2/ERα signaling leads to increased phosphorylation of PTEN at key regulatory residues. Importantly, E2 stimulation decreased PTEN lipid phosphatase activity and caused consequent increases in phospho-AKT. We further demonstrate that cytosolic ERα forms a complex with PTEN in an E2-dependent manner, and that ERα constitutively complexes with protein kinase2-α (CK2α), a kinase previously shown to phosphorylate the C-terminal tail of PTEN. These results provide mechanistic support for an E2-dependent, ERα cytosolic signaling complex that negatively regulates PTEN activity through carboxy terminus phosphorylation. Using an animal model, we show that sustained E2 signaling results in increased phospho-PTEN (S380, T382, and T383), total PTEN, and phospho-AKT (S473). Taken together, we provide a novel mechanism in which transcription-independent E2/ERα signaling may promote a pro-tumorigenic environment in the endometrium.
Insights
Rapid estrogen signaling (E2) activates estrogen receptor-alpha (ERα) to phosphorylate and inhibit PTEN tumor suppressor activity, potentially promoting endometrial cancer. This non-genomic pathway involves a cytosolic ERα-PTEN complex.
Area of Science:
- Endocrinology
- Molecular Biology
- Cancer Research
Background:
- Hyperestrogenicity is a known risk factor for endometrial cancer.
- Estrogen (E2) exerts effects via genomic and nongenomic estrogen receptor-alpha (ERα) signaling.
- The role of transcription-independent ERα signaling in endometrial physiology and pathology remains unclear.
Purpose of the Study:
- To investigate the rapid, transcription-independent effects of E2 on PTEN activity in endometrial cells.
- To elucidate the molecular mechanism by which E2 signaling regulates PTEN.
- To determine the in vivo relevance of these findings in an animal model.
Main Methods:
- Utilized ERα-positive and PTEN-positive human endometrial cells.
- Stimulated cells with E2 and analyzed PTEN phosphorylation and activity.
- Investigated the formation of ERα-PTEN and ERα-CK2α complexes using co-immunoprecipitation.
- Administered sustained E2 signaling in an animal model and assessed PTEN and AKT phosphorylation.
Main Results:
- E2 stimulation of cytosolic ERα signaling increased PTEN phosphorylation.
- E2 reduced PTEN lipid phosphatase activity, leading to increased phospho-AKT.
- Cytosolic ERα formed an E2-dependent complex with PTEN, which also associates with CK2α.
- In vivo, sustained E2 signaling increased phospho-PTEN, total PTEN, and phospho-AKT.
Conclusions:
- A novel, transcription-independent E2/ERα signaling pathway negatively regulates PTEN activity in the endometrium.
- This pathway involves cytosolic ERα complex formation with PTEN and CK2α, leading to PTEN inhibition.
- These findings suggest a mechanism by which E2 signaling may contribute to a pro-tumorigenic endometrial environment.