Characteristics of different cytoplasmic and nuclear estrogen receptors appearing with continuous hormonal exposure

Biochemical properties of cytosol estrogen receptor (ER(C)) and nuclear estrogen receptor (ER(N)) from rat uteri continuously exposed in vivo to 17β-[2,4,6,7-³H]estradiol ([³H]E₂) for 6 h have been studied on the basis of immunological recognition and chromatographic elution patterns. Overall concentrations of ER(C) and ER(N) did not change during this time period when receptor-saturating concentrations of [³H]E₂ were maintained; however, biochemical characteristics were different in ER(C) and ER(N) after short or long term hormonal exposure. When ER(C) from rats treated with estradiol for 30 min was applied to HAP or DEAE columns, two different ER binding components were seen. DNA binding in a cell-free system revealed that these binding components represented an activated had a nonactivated ER(C) population. After long term hormonal exposure (6 h), only one component of ER(C) with low DNA binding could be shown despite the preservation of an equivalent quantity of cytoplasmic binding activity. This binder does not react with a monoclonal antibody directed against extranuclear estrogen receptor species. These data suggest disappearance of the activated ER(C) population, with appearance of a new, immunologically nonrecognizable ER(C) species with 6 h of continuous hormonal exposure. Elution profiles of ER(N) on HAP chromatography reveal 2 different binding components at 30 min and at 6 h of continuous [³H]E₂ exposure. There is an increase of the population eluted at higher molarity after 6 h of in vivo treatment. This later eluting binding component is the major DNA binder in vitro. ER(N) from both time points are recognized immunologically by monoclonal antibody. After reaction with the antibody, the sedimentation coefficient shifted to 8-9 S on sucrose gradients, but the previously described faster sedimentation of ER(N) extracted 6 h after injection persisted. We conclude that ER in both cellular compartments undergoes time-dependent alterations, which may be involved in the initiation of hormone action.