A MONOCLONAL-ANTIBODY TO THE ESTROGEN-RECEPTOR DISCRIMINATES BETWEEN THE NONACTIVATED AND ACTIVATED ESTROGEN-RECEPTOR AND ANTI-ESTROGEN-RECEPTOR COMPLEXES

An IgM-class monoclonal antibody (B36) raised against the calf uterine estrogen receptor (R) was used to probe the structure of R bound to estradiol or to 4-hydroxytamoxifen, a nonsteroidal antiestrogen which displays a high affinity for R. This antibody does not noticeably modify the interaction of R with these ligands, but R, when bound to B36, is markedly displaced in both low- and high-salt sucrose gradients. The B36 antibody interacts more strongly with activated cytosol estradiol-R and 4-hydroxytamoxifen-R complexes than with nonactivated (molybdate-stabilized) complexes. This antibody also interacts strongly with the nuclear forms of R bound to estradiol or to the anti-estrogen. The affinity of B36 for the nonactivated R-4-hydroxytamoxifen complex is 3-fold greater than for the nonactivated R-estradiol complex. The difference is slightly less pronounced for activated complexes. Preincubation of activated R with saturing amounts of B36 partially (.ltoreq. 60%) inhibits the binding of R-ligand complexes to DNA adsorbed onto cellulose. The B36 and DNA binding domains of R apparently are related. R may have different external structures when activated or nonactivated and when bound to an anti-estrogen or to estradiol.