The third class of nuclear receptors (Nuclear, Class 3, Estrogen Receptor-like) includes estrogen and estrogen-related receptors (ER), as well as the 3-ketosteroid receptors (progesterone (PR), androgen (AR), gluco- and mineralocorticoid (GR and MR, respectively) receptors).
The progesterone receptor (PR) is a progestin-activated steroid receptor with two subtypes known to date (A and B). It plays a central role in diverse reproductive events associated with establishment and maintenance of pregnancy, alveolar development in the breast and sexual behavior. PR dysfunction has been associated with cancer (ovarian cancer, breast cancer, endometrial cancer, prostate cancer), metabolic disorders (progesterone resistance, obesity, osteoporosis), cardiovascular defects (aortic aneurysm), neurological defects (migraine, vertigo) and reproductive conditions (endometriosis, infertility)[1]. Noteworthy, Org OD-2 (Axon 2085) is a selective agonist of the membrane bound progesterone receptor (mPR). Although mPRs typically consist of 7-TM domains, mPRs do not belong to the large family of GPCRs, nor do they belong to the family of nuclear PRs, even though they are sharing the same endogenous ligand.[2]