[Characterization of activated and non-activated estrogen receptor using monoclonal antibodies]

Three monoclonal antibodies (D547, H222 and H226) prepared against the human estrogen receptor interact with the estrogen receptor from fetal guinea pig uterus depending on its activation state. The D547 antibody, whose epitope is located between the hormone-binding and DNA-binding domains, recognizes only the activated receptor. The H226 antibody, whose epitope is in the N-terminal region of the receptor ("A/B" region), recognizes both the activated and non-activated receptor. However, the H226 epitope seems to be partially masked in the non-activated receptor (oligomeric form 9 S) but completely exposed following activation. This antibody detects the formation of an activated dimer, which is the only form retained in the nuclei. The H222 antibody, whose epitope is in the hormone-binding domain, reacts with all the hormone-binding subunits present in the non-activated receptor. However, only one H222 epitope is accessible in the activated dimer, suggesting that this epitope and consequently the hormone-binding domain, are located close to the dimerization site. According to these results, the activation process involves a structural transformation of the receptor that modifies the exposure of functional domains.