Studies on the activation of the oestrogen receptor bound to the anti-oestrogens 4-hydroxytamoxifen and ICI 164,384 by using three monoclonal antibodies
Three monoclonal antibodies, H222, H226 and D547, which provided evidence of the structural transformation and change in exposure of the functional domains of the oestrogen receptor from fetal guineapig uterus upon activation, were used to study the receptor bound to the anti-oestrogens 4-hydroxytamoxifen and ICI 164,384. No differences in the structure of non-activated 4-hydroxytamoxifen— and ICI 164,384—receptor complexes, as compared with the oestradiol—receptor complex, were detected by the three monoclonal antibodies. When heated at 28°C, both anti-oestrogen—receptor complexes became capable of binding the D547 antibody, which reacts selectively with the activated receptor; however, this binding was lower than that of the oestradiol-receptor complex. The interaction with the H226 antibody showed that anti-oestrogens can induce receptor dimerization, but to a lesser extent than oestradiol. In addition, both anti-oestrogen—receptor complexes can bind to DNA—cellulose and are retained in nuclei from intact cells at 28°C, but less efficiently than the oestradiol—receptor complex. On the other hand, the nuclear receptor seems to have a similar dimeric structure when bound to either anti-oestrogens or oestradiol, as detected by the three monoclonal antibodies. The data suggest that 4-hydroxytamoxifen and ICI 164,384 induce an impaired activation of the oestrogen receptor; this difference, although quantitative rather than qualitative, might be related to the partial agonistic action of these anti-oestrogens in the fetal guinea-pig uterus.