THYROID HORMONE RECEPTOR Β KNOCKDOWN REDUCES SUPPRESSION OF PROGESTINS BY ACTIVATING THE MTOR PATHWAY IN ENDOMETRIAL CANCER CELLS
2Department of Gynecology, Shanghai Key Laboratory of Female Reproductive Endocrine Related Diseases,, Obstetrics and Gynecology Hospital, Fudan University, Shanghai
3Lab of Reproductive Pharmacology, NHC Key Lab of Reproduction Regulation, Shanghai Institute for Biomedical and Pharmaceutical Technologies, Shanghai
Problem statement: Progestin resistance is a major obstacle to conservative therapy in patients with endometrial cancer (EC) and endometrial atypical hyperplasia (EAH). However, the related inducing factor is yet unclear.
Methods: In the study, we assayed the levels of thyroid hormone in plasma of patients with EC and EAH, and evaluated the expression of thyroid receptor α (TRα) and β (TRβ) in the endometrium tissues via immunohistochemistry. THRB-silenced RL95-2 and KLE EC cells were cultured to investigate the response of progestins, including medroxyprogesterone acetate (MPA) and nomegestrol acetate. Cell migration and invasion assay were performed. Transcriptomics and Western blotting were conducted to investigate the changes in signaling pathways.
Results: We found that the serum levels of triiodothyronine (T3) were significantly lower in patients with EC compared with healthy women. A strong expression of TRβ was observed in most patients with EC and EAH sensitive to progestin treatment. In contrast, TRα positive expression was detected in less than half of the patients sensitive to progestin therapy. Importantly, THRB, rather than THRA, knockdown promoted the viability and motilities of RL95-2 cells but not KLE cells. The suppressive effect of progestins on cell growth and motility significantly decreased in THRB-silenced RL95-2 cells. Multiple proliferation-related signaling pathways were enriched, and the activities of mammalian targets of rapamycin (mTOR)/4e-binding protein 1 (4EBP1)/eukaryotic translation initiation factor 4G (eIF4G) rather than phosphorylated protein kinase B (Akt) were remarkably boosted. Progestin treatment enhanced the effects, and the augmentation was partially abated on supplementation with T3. In THRB-knockdown KLE cells, the progestins-activated partial signaling pathway expression (either mTOR or eIF4G), and supplementation with T3 did not induce noticeable alterations.
Conclusion THRB knockdown enhanced the viability and motility of type I EC cells and attenuated the suppressive effects of progestins by activating the mTOR-4EBP1/eIF4G pathway. The status of THRB may play an important role in regulating the sensitivity of type I EC towards progestin therapy and lower expression of THRB is likely correlated with progesterone resistance. Our study opens a new window to explore the mechanisms of progestin resistance.
Conflict of interest statement: The author declares no conflict of interest.
