title: Role of activation function domain-1, DNA binding, and coactivator GRIP1 in the expression of partial agonist activity of glucocorticoid receptor-antagonist complexes.
abstract: The determinants of the partial agonist activity of most antisteroids complexed with steroid receptors are not well understood. We now examine the role of the N-terminal half of the glucocorticoid receptor (GR) including the activation domain (AF-1), the DNA binding site sequence, receptor contact with DNA, and coactivator binding on the expression of partial agonist activity in two cell lines for GRs bound by five antiglucocorticoids: dexamethasone mesylate (Dex-Mes), dexamethasone oxetanone (Dex-Ox), progesterone (Prog), deoxycorticosterone (DOC), and RU486. Using truncated GRs, we find that the N-terminal half of GR and the AF-1 domain are dispensable for the partial agonist activity of antiglucocorticoids. This contrasts with the AF-1 domain being required for the partial agonist activity of antisteroids with most steroid receptors. DNA sequence (MMTV vs a simple GRE enhancer) and cell-specific factors (CV-1 vs Cos-7) exert minor effects on the level of partial agonist activity. Small activity differences for some complexes of GAL4/GR chimeras with GR- vs GAL-responsive reporters suggest a contribution of DNA-induced conformational changes. A role for steroid-regulated coactivator binding to GRs is compatible with the progressively smaller increase in partial agonist activity of Dex-Mes > Prog > RU486 with added GRIP1 in CV-1 cells. This hypothesis is consistent with titration experiments, where low concentrations of GRIP1 more effectively increase the partial agonist activity of Dex-Mes than Prog complexes. Furthermore, ligand-dependent GRIP1 binding to DNA-bound GR complexes decreases in the order of Dex > Dex-Mes > Prog > RU486. Thus, the partial agonist activity of a given GR-steroid complex in CV-1 cells correlates with its cell-free binding of GRIP1. The ability to modify the levels of partial agonist activity through changes in steroid structure, DNA sequence, specific DNA-induced conformational changes, and coactivator binding suggests that useful variations in endocrine therapies may be possible by the judicious selection of these parameters to afford gene and tissue selective results.
authors.affiliation: Steroid Hormones Section, NIDDK/LMCB, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Sehyung
authors.initials: S
authors.lastname: Cho
authors.forename: John A
authors.initials: JA
authors.lastname: Blackford
authors.forename: S Stoney
authors.initials: SS
authors.lastname: Simons
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D003900:Desoxycorticosterone / Q000737:chemistry / Q000378:metabolism; D003907:Dexamethasone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D005938:Glucocorticoids / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008024:Ligands; D015735:Mifepristone / Q000737:chemistry / Q000378:metabolism; D051958:Nuclear Receptor Coactivator 2; D010446:Peptide Fragments / Q000819:agonists / Q000502:physiology; D011374:Progesterone / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology*; D020218:Response Elements; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D015854:Up-Regulation / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D005938:Glucocorticoids; D008024:Ligands; D051958:Nuclear Receptor Coactivator 2; D010446:Peptide Fragments; D011965:Receptors, Glucocorticoid; D015534:Trans-Activators; D014157:Transcription Factors; D015735:Mifepristone; C041706:dexamethasone oxetanone; D003900:Desoxycorticosterone; D011374:Progesterone; D003907:Dexamethasone; C031710:dexamethasone 21-methanesulfonate