[Estrogen receptor: superfamily of thyroid hormone receptors].

Estrogen signal transduction plays an important role in mammary tissue. The principal mechanism by which the effects of estrogen are mediated by target tissues is via an initial interaction with the estrogen receptor (ER), a member of the steroid/thyroid/retinoid receptor gene superfamily. The ER can be isolated from the cytosol of target cell extracts as a large nontransformed 7-8S oligomeric complex, which contains hsp 90 and hsp 70. Like other steroid receptors, ER has six regions, A-F. The DNA-binding (region c) and the ligand binding (region) domains of ER alpha and beta show 96% and 55% amino acid sequence homology, respectively. The other regions (the hypervariable A/b domain, the hinge region D, and the C-terminal F-domain) are less conserved. The heat-shock proteins function help fold the ER protein properly and to protect the hydrophobic hormone binding domain from inappropriate interactions. Recently, a novel ER, referred to as ER-beta was cloned and characterized rat prostate.