A monoclonal antibody to the estrogen receptor discriminates between the nonactivated and activated estrogen- and anti-estrogen-receptor complexes.

An IgM-class monoclonal antibody ( B36 ) [Greene, G. L., Fitch, F. W., & Jensen, E.V. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 157-161] 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 anti-estrogen 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. We found the following: The B36 antibody interacts more strongly with activated cytosol estradiol- 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 non-activated R-estradiol complex. The difference is slightly less pronounced for activated complexes. Preincubation of activated R with saturating amounts of B36 partially (less than or equal to 60%) inhibits the binding of R-ligand complexes to DNA adsorbed onto cellulose. These results suggest that the B36 and DNA binding domains of R are related and strengthen the hypothesis that R has different external structures when activated or nonactivated and when bound to an anti-estrogen or to estradiol.