Subcellular distribution, properties and interrelationship of oestrogen receptors in endometrium and other target tissues.

ABSTRACT

More than half of the extranuclear receptor content of resting cells is associated with cytoplasmic structures. Subfractionation of microsomes reveals a preponderance of "basic" (low electrophoretic mobility) receptor in rough endoplasmic reticulum. Surfynol-dithiothreitol extracts of smooth membranes are rich in "acidic" (high electrophoretic mobility) receptor. Trypsin increases the yields up to seven-fold, and this increase is correlated (r = 0.993) with the acidic receptor content and 5'-nucleotidase activity of these microsomal preparations. Acidic microsomal "cytosolic" and nuclear receptor can be degraded to the "basic" variety of streptomyces hyaluronidase. All forms give rise to a tryptic fragment with unchanged affinity for oestradiol and dimerization ability. Basic receptor isolated after enzymatic conversion of acidic receptor is microheterogenous on isoelectric focusing, but gives rise to only one precipitation arc versus the IgG fraction of a polyclonal antiserum. The precipitation arc can be recharged with labelled oestradiol and autoradiographed. Non-immune IgG's from (unspecific) soluble complexes with oestrogen receptors, but not with their tryptic fragments. The polyclonal antioestrogen receptor IgG fraction precipitates the oestradiol-tagged tryptic receptor fragment from all subcellular sources of all homologous (porcine) and heterologous (human, ovine, bovine, goat, rabbit, guinea pig, rat) target tissues tested. Organ specificity can therefore be excluded and a high degree of phylogenetic conservation of the oestrogen receptor's protein moiety is implied. The presence, in the immune IgG fraction, of steroid releasing antibodies, which apparently distort the binding site, should spur the search for monoclonal antibodies with similar properties.