Abstract
Estrogen-related receptor (ERR) was studied in the placenta and uterine endometrium, especially endometrial cancers, among reproductive organs. In the placenta, the estrogen receptor (ER) alpha and beta mRNA levels increased from the first to the second trimester, and then decreased until normal term delivery. Estrogen-related receptor alpha, beta and gamma mRNA levels gradually increased up to the second trimester, and then comparatively rapidly increased until normal term delivery. In endometrial cancers, ER alpha and beta mRNA levels decreased with clinical stage, myometrial invasion and dedifferentiation. Estrogen-related receptor alpha levels increased with clinical stage and myometrial invasion, and the ERR gamma levels increased with myometrial invasion. Estrogen-related receptors can bind to the steroid receptor coactivator family without any ligands, and drive transcription activity of the target genes. The manner of ERR and ER gene expressions might show a competitive interaction associated with the use of common cofactors. It is speculated that the upregulation of ERR is related to the placental growth after the downregulation of ER from the second trimester until delivery, and that ERR alpha and gamma are candidates for prognostic factors in endometrial cancer, although ERR are not directly related to tumor growth and advancement of endometrial cancer. (Reprod Med Biol 2005; 4: 129-131).