Cytosol estrogen receptor (ER(C)) and nuclear estrogen receptor (ER(N)) levels were investigated in rat uteri under different conditions of hormonal exposure. The amount of directly assayable receptor was closely related to the serum concentration of 17β-[2,4,6,7,3H]estradiol ([3H]E2). A double injection technique was established to maintain serum levels of [3H]E2 which were sufficient to saturate receptor sites. Under these conditions, stable ER(C) and ER(N) levels are maintained throughout the study period. 30% of the total ER remains cytoplasmic in localization despite continuous hormonal exposure. Properties of ER(C) and ER(N) after 6 h of continuous hormonal exposure were investigated and found to be different from receptors found in these subcellular compartments 30 min after hormone injections. ER(C) from uteri 30 min after injection showed a faster sedimentation coefficient than ER(C) prepared 6 h after hormone treatment. ER(C) after 6 h of hormonal exposure showed a reduction of binding to calf thymus DNA adsorbed on cellulose in a cell-free system. ER(C) 30 min after [3H]E2 treatment had a biphasic dissociation pattern consistent with two different receptor populations, whereas uterine ER(C) obtained after 6 h of in vivo exposure to estradiol showed virtually no dissociation at 22 and 28°C. In contrast to ER(C), ER(N) 6 h after hormone injection sedimented faster than ER(N) obtained 30 min after treatment. KCl extractable ER(N) obtained either at 30 min or 6 h posthormone treatment showed biphasic dissociation kinetics at 22 and 28° C, whereas KCl nonextractable ER(N) showed virtually no dissociation. Virtually all of the specifically bound ligand in cytosol and nuclear preparations was proven to be authentic E2. We conclude that total cellular receptor is quantitatively conserved during 6 h of continuous hormonal treatment. Nuclear receptor loss is not a requisite for receptor-mediated steroid function, although important time-dependent changes in receptor properties in both cytoplasmic and nuclear compartments do occur.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|State||Published - 1983|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology