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Molecular classification of estrogens

V C Jordan1, J M Schafer, A S Levenson

  • 1Robert H. Lurie Comprehensive Cancer Center, Northwestern University Medical School, Chicago, Illinois 60611, USA. vcjordan@northwestern.edu

Cancer Research
|September 18, 2001
PubMed

Insights

Different estrogens induce distinct estrogen receptor alpha (ER) conformations, influencing gene activation. This suggests classifying estrogens based on their ER interaction may predict selective actions and carcinogenic potential.

Area of Science:

  • Endocrinology
  • Molecular Biology
  • Cancer Research

Background:

  • Estrogens play crucial roles in target tissues like the uterus, breast, and pituitary gland, where hormone-responsive tumors frequently arise.
  • The precise conformational changes induced in estrogen receptor alpha (ER) by various estrogens remain incompletely understood.
  • Understanding ER conformation is vital for deciphering selective estrogen actions and carcinogenic potential.

Purpose of the Study:

  • To investigate whether different estrogens induce distinct conformations of estrogen receptor alpha (ER).
  • To explore the impact of these distinct ER conformations on the activation of the transforming growth factor alpha (TGF-alpha) gene.
  • To propose a classification of estrogens based on their ER interaction and potential functional outcomes.

Main Methods:

  • Utilized a novel in vitro assay to assess TGF-alpha gene activation in MDA-MB-231 cells expressing specific ER variants (D351 ER and D351G ER).
  • Tested the effects of three distinct estrogen types: estradiol, diethylstilbestrol, and a triphenylethylene (TPE) derivative.
  • Employed computer molecular modeling to interpret experimental data and elucidate ER-ligand interactions.

Main Results:

  • Flat estrogens (estradiol, diethylstilbestrol) activated TGF-alpha via the canonical activating function 2 (AF2) domain, facilitating SRC-1 binding.
  • The TPE derivative, however, activated TGF-alpha through an alternative pathway (AF2b), as evidenced by differential activation of D351 ER but not D351G ER.
  • This differential activation highlights distinct ER conformational responses to different estrogen structures.

Conclusions:

  • Propose the existence of two distinct classes of estrogens based on their ability to form different ER complexes.
  • These distinct ER complexes may recruit different coactivators, leading to varied downstream effects.
  • Estrogen structure dictates ER conformation, influencing selective actions and potentially carcinogenic outcomes of phytoestrogens and xenoestrogens.

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