δEF1 down-regulates ER-α expression and confers tamoxifen resistance in breast cancer

Area of Science:

• Endocrinology
• Molecular Biology
• Oncology

Background:

• Tamoxifen resistance is a significant challenge in breast cancer treatment.
• Reduced estrogen receptor alpha (ER-α) levels are a primary mechanism of resistance.
• Understanding ER-α regulation is crucial for developing new therapeutic strategies.

Purpose of the Study:

• To investigate the role of δEF1 in regulating ER-α expression.
• To explore the potential of targeting δEF1 to overcome tamoxifen resistance.
• To elucidate the molecular mechanisms linking δEF1, ER-α, and tamoxifen sensitivity.

Main Methods:

• Investigated δEF1 regulation by 17β-estradiol (E2) in MCF-7 cells.
• Analyzed ER-α promoter activity and δEF1 binding.
• Assessed the impact of δEF1 and ER-α levels on tamoxifen sensitivity in cell lines.
• Utilized RNA interference to deplete δEF1 in MDA-MB-231 cells.

Main Results:

• δEF1 expression is upregulated by E2 via PI3K or NF-κB pathways in an ER-α-dependent manner.
• δEF1 represses ER-α transcription by binding to the ER-α promoter.
• A strong inverse correlation exists between δEF1 and ER-α expression in breast cancer tissues.
• Elevated δEF1 reduces tamoxifen sensitivity, while ER-α overexpression restores it.
• δEF1 depletion in MDA-MB-231 cells restores ER-α expression and tamoxifen sensitivity.

Conclusions:

• δEF1 plays a critical role in the development of tamoxifen resistance in breast cancer.
• Restoring ER-α expression by inhibiting δEF1 is a potential therapeutic strategy for endocrine resistance.
• Targeting δEF1 may offer a novel approach to improve breast cancer treatment outcomes.