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Different nuclear binding sites for antiestrogen and estrogen receptor complexes
Endocrinology
|February 1, 1977
Summary
Estrogen receptor nuclear translocation differs between estrogens and anti-estrogens. Estrogens form a salt-resistant nuclear estrogen receptor (ERC) essential for uterine growth, while anti-estrogens only form a salt-extractable form.
Area of Science:
- Endocrinology
- Molecular Biology
- Reproductive Science
Background:
- Estrogen receptors (ERs) mediate the effects of estrogens.
- Understanding ER nuclear translocation and retention is key to comprehending estrogenic and anti-estrogenic actions.
- The in vivo dynamics of ERs in response to different ligands are not fully elucidated.
Purpose of the Study:
- To investigate the in vivo effects of estrogens and anti-estrogens on estrogen receptor nuclear accumulation, cytoplasmic levels, and nuclear receptor forms in immature rat uteri.
- To differentiate the roles of salt-resistant and salt-extractable nuclear estrogen receptor forms in mediating estrogenic responses.
Main Methods:
- Immature rats were injected with estradiol-17beta (E2), diethylstilbestrol (DES), or anti-estrogens (U-11,100A, zuclomiphene, enclomiphene).
- Uterine tissues were analyzed for cytoplasmic and nuclear estrogen receptor levels at various time points post-injection.
- Nuclear estrogen receptors were fractionated into salt-extractable and salt-resistant forms using 0.3M KCl.
Main Results:
- Estrogens (E2, DES) induced rapid nuclear translocation of estrogen receptor complexes (ERC, DRC) within 1 hour, followed by depletion and subsequent replenishment of cytoplasmic receptors.
- Anti-estrogens induced slower nuclear accumulation, with limited cytoplasmic receptor replenishment.
- Estrogens generated both salt-extractable and salt-resistant nuclear ERC, with the salt-resistant form correlating with uterine growth.
- Anti-estrogens primarily formed only salt-extractable nuclear receptors.
Conclusions:
- The salt-resistant nuclear estrogen receptor form, generated by estrogens, is crucial for sustained uterine growth.
- The salt-extractable nuclear estrogen receptor form may mediate short-term estrogenic effects.
- Estrogens and anti-estrogens exhibit distinct mechanisms in regulating estrogen receptor nuclear localization and function.