title: Hydrodynamic characterizations of estrogen receptors complexed with [3H]-4-hydroxytamoxifen: evidence in support of contrasting receptor transitions mediated by different ligands.
abstract: Size-exclusion high-performance liquid chromatography was used to characterize the hydrodynamic molecular properties of estrogen receptors complexed with estradiol and the antiestrogen 4-hydroxytamoxifen. Cytoplasmic estrogen receptors complexed with [3H]-4-hydroxytamoxifen did not undergo reductions in hydrodynamic size after exposure to KCl or urea. Nuclear receptors complexed with 4-hydroxytamoxifen eluted as hydrodynamically larger molecules than nuclear receptors complexed with estradiol. Because identical hydrodynamic characterizations were obtained with the covalent ligand [3H]tamoxifen aziridine, these differences in chromatographic behavior are due to differences in ligand-mediated receptor properties and are not the result of ligand dissociation. When estrogen receptors, complexed with either [3H]estradiol or [3H]-4-hydroxytamoxifen, were exposed to trypsin, the receptors complexed with 4-hydroxytamoxifen eluted as larger hydrodynamic forms than receptors complexed with estradiol. These observations are interpreted to indicate that estradiol and 4-hydroxytamoxifen mediate contrasting transitions in the molecular orientation of estrogen receptors. The consequences of the transitions mediated by 4-hydroxytamoxifen appear to be that intermolecular associations become difficult to disrupt with KCl or urea and that the accessibility of trypsin-sensitive proteolytic sites becomes altered. Chromatin fractionation using DNase I and hypotonic Mg2+ solubilization identified a chromatin region that was less readily penetrated by receptors complexed with 4-hydroxytamoxifen than receptors complexed with estradiol.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002851:Chromatography, High Pressure Liquid; D004958:Estradiol / Q000378:metabolism; D004965:Estrogen Antagonists / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D008024:Ligands; D051379:Mice; D011960:Receptors, Estrogen / Q000378:metabolism*; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000378:metabolism; D014599:Uterus / Q000378:metabolism*
chemical_list: D004965:Estrogen Antagonists; D008024:Ligands; D011960:Receptors, Estrogen; D013629:Tamoxifen; C016601:afimoxifene; D004958:Estradiol