title: Activation of transcriptionally inactive human estrogen receptors by cyclic adenosine 3',5'-monophosphate and ligands including antiestrogens.
abstract: We show that some transcriptionally inactive human estrogen receptor (ER) mutants can be activated by 17 beta-estradiol (E2), and sometimes by antiestrogens, in the presence of elevated levels of intracellular cAMP. ER-deficient Chinese hamster ovary or 3T3 mouse fibroblast cells were transfected with mutant ERs (the point mutant L540Q, the frameshift mutant S554fs, or the carboxy-terminal truncated receptor ER1-530) and various estrogen response element-containing reporter genes. Individual treatments with E2, the antiestrogens trans-hydroxytamoxifen and ICI 164,384, or with 3-isobutyl-1-methyl-xanthine plus cholera toxin (IBMX plus CT) which raise intracellular cAMP, generally do not activate the mutant receptors. However, cotreatment with IBMX/CT and one of the three ligands (E2, trans-hydroxytamoxifen, or ICI164,384) results in the unexpected recovery of strong activation of the L540Q or S554fs receptors, the magnitude of which is dependent upon promoter- and cell-contexts. Unlike L540Q and S554fs, the transcriptionally inactive ER1-530 is not activated by any combination of ligands and IBMX/CT. These data demonstrate that some ER mutants that form transcriptionally nonproductive ER-E2 complexes can be successfully activated by the combination of an agonist or antagonist ligand and an agent thought to act via phosphorylation pathways. Also highlighted is the promoter- and cell-specific nature of the transcriptional response to different ligand-ER complexes. Lastly, the enhanced transcriptional activity of wild type ER and some ER mutants in the presence of antiestrogens and elevated intracellular cAMP may provide a partial explanation of the ability of some estrogen-dependent human breast tumors to resist antiestrogen therapies currently employed.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
authors.forename: B A
authors.initials: BA
authors.lastname: Ince
authors.forename: M M
authors.initials: MM
authors.lastname: Montano
authors.forename: B S
authors.initials: BS
authors.lastname: Katzenellenbogen
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002772:Cholera Toxin / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D017930:Genes, Reporter / Q000187:drug effects; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D011960:Receptors, Estrogen / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D004965:Estrogen Antagonists; D011960:Receptors, Estrogen; D004958:Estradiol; D002772:Cholera Toxin; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine