Estrogen receptor variants ERdelta5 and ERdelta7 down-regulate wild-type estrogen receptor activity

Area of Science:

• Molecular Biology
• Endocrinology
• Cancer Research

Background:

• The estrogen receptor (ER) is crucial for estrogen effects and a key target in endocrine therapies, particularly for breast cancer.
• ER variants, often lacking domains, can significantly alter receptor activity and response to hormone therapy.
• Understanding ER variant function is vital for improving cancer treatment strategies.

Purpose of the Study:

• To investigate how ER variants ERdelta5 and ERdelta7 influence the activity of wild-type ER (wtER) in response to estrogen and antiestrogens.
• To elucidate the mechanism by which ER variants affect wtER function, specifically examining potential heterodimerization.

Main Methods:

• Utilized yeast systems for co-expression of ER variants (ERdelta5, ERdelta7) with wtER and an ERE-LacZ reporter.
• Assessed the transcriptional activity of wtER in the presence of ER variants and ligands (estrogen, antiestrogens).
• Employed the yeast two-hybrid system to evaluate protein-protein interactions (homodimerization and heterodimerization) between ER variants and wtER.

Main Results:

• ERdelta5 and ERdelta7 significantly decreased wtER response to 17beta-estradiol (by 41-43% and 24-34%, respectively).
• ERdelta5 showed weak, ligand-independent activity, unaffected by tamoxifen or ICI 182,780; ERdelta7 exhibited no constitutive activity or ligand response.
• Yeast two-hybrid assays confirmed that ERdelta5 and ERdelta7 do not form homodimers or heterodimers with wtER.

Conclusions:

• ERdelta5 and ERdelta7 modulate wtER activity, reducing its response to estrogen.
• The inhibitory effect of ERdelta5 and ERdelta7 on wtER is not mediated through heterodimerization, suggesting alternative inhibitory mechanisms.
• Further research is needed to identify the precise molecular mechanisms underlying ER variant interference with wtER function.