Antibodies to estrogen receptor: Immunochemical similarity of estrophilin from various mammalian species

Immunoglobulin obtained from the serum of rabbits immunized with a highly purified preparation of estradiol-receptor complex from calf uterine nuclei has been shown to contain specific antibodies to the receptor protein (estrophilin) by four criteria: (a) precipitation of the radioactive steroid upon addition of goat antibody against rabbit gamma globulin to a mixture of the tritiated estradiol-receptor complex and the immunoglobulin, (b) adsorption of the estradiol-receptor complex by the immunoglobulin linked to Sepharose, (c) adsorption of the estradiol-receptor complex in the presence of the immunoglobulin by Staphylococcus aureus protein-A linked to Sepharose, and (d) the ability of the immunoglobulin to increase the sedimentation rate of the estradiol-receptor complex. Antibodies to calf nuclear estrophilin were shown to crossreact with the nuclear receptor of rat uterus, as well as with the extranuclear receptor of calf, rat, mouse, and guinea pig uterus and of human breast cancer. The antibodies do not react with either the nuclear or extranuclear dihydrotestosterone-receptor complexes of rat prostate or with the extranuclear progesterone-receptor complex of chick oviduct. These findings indicate an immunochemical similarity among estrophilins from several mammalian species, as well as between extranuclear and nuclear forms of the receptor, but not among receptor proteins for different steroid hormones.