A monoclonal antibody to the estrogen receptor inhibits in vitro criteria of receptor activation by an estrogen and an anti-estrogen.

Abstract

The effect of an IgM class monoclonal antibody (B36) (Greene, G. L., Fitch, F. W., and Jensen, E. V. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 157-161) raised against the calf uterine estrogen receptor was tested in vitro on certain parameters of estrogen receptor activation by estradiol or 4-hydroxytamoxifen, a potent anti-estrogen. The following results were obtained. The antibody prevented the decrease in the dissociation rate of the receptor-estradiol complex which results from activation of the complex, whereas it did not affect the dissociation rate of the receptor-4-hydroxytamoxifen complex, which remains unchanged upon activation. The antibody also increased the dissociation rate of the preactivated receptor-estradiol complex. The antibody protected the naked estrogen receptor against heat-inactivation. B36 partially inhibited the binding of the estradiol- and 4-hydroxy-tamoxifen-receptor complexes to DNA adsorbed onto cellulose, but did not reverse the receptor-DNA binding. This inhibition was not overcome by higher DNA concentrations and was more pronounced for the receptor interacting with estrogen than with anti-estrogen. All these effects were specific since they were related to antibody/antigen recognition and were dose-dependent. These results indicate that the binding of the antibody to the estrogen-activated receptor induces a conformational change in the receptor and that the antibody can prevent and overcome the effect of activation whatever its mechanism. They also confirm that the conformations of the estrogen receptor differ when bound to estradiol or to 4-hydroxytamoxifen.