Synthetic 19-nortestosterone derivatives as estrogen receptor alpha subtype-selective ligands induce similar receptor conformational changes and steroid receptor coactivator recruitment than natural estrogens

The binding of estradiol (E2) to estrogen receptors (ER) is followed by conformational changes resulting in coactivator or corepressor recruitment that influences gene transcription. A series of synthetic A-ring reduced 19-nortestosterone-derived progestins has the capacity to selectively bind and activate transcription through the ERα. Herein, the molecular mechanisms involved in ER subtype-selective interactions of these compounds as assessed by their effects upon both ERα and ERβ structural conformation and their ability to induce recruitment of steroid receptor coactivator-1 (SRC-1) to ERα were investigated. The results demonstrated that all synthetic A-ring 3β,5α-tetrahydro-reduced derivatives of 19-nortestosterone induced an ERα trypsin digestion pattern similar to that seen with E2, without effects upon ERβ. In addition, these compounds had the ability to recruit SRC-1 to the ligand-binding domain of ERα similar to E2. Our data indicate that A-ring 3β,5α-tetrahydro-reduced 19-nortestosterone-derived progestins behave as selective ERα agonists with ligand–receptor structural and functional responses similar to those induced with natural E2.