title: Modulation of glucocorticoid receptor phosphorylation and transcriptional activity by a C-terminal-associated protein phosphatase.
abstract: The glucocorticoid receptor (GR) is phosphorylated at three major sites on its N terminus (S203, S211, and S226), and phosphorylation modulates GR-regulatory functions in vivo. We examined the phosphorylation site interdependence, the contribution of the receptor C-terminal ligand-binding domain, and the participation of protein phosphatases in GR N-terminal phosphorylation and gene expression. We found that GR phosphorylation at S203 was greater when S226 was not phosphorylated and vice versa, indicative of intersite dependency. We also observed that a GR derivative lacking the ligand-binding domain, which no longer binds the heat shock protein 90 (Hsp90) complex, exhibits increased GR phosphorylation at all three sites as compared with the full-length receptor. A GR mutation (F602S) that produces a receptor less dependent on Hsp90 for function as well as treatment with the Hsp90 inhibitor geldanamycin also increased basal GR phosphorylation at a subset of sites. Pharmacological inhibition of serine/threonine protein phosphatases increased GR basal phosphorylation. Likewise, a reduction in protein phosphatase 5 protein levels enhanced GR phosphorylation at a subset of sites and selectively reduced the induction of endogenous GR target genes. Together, our findings suggest that GR undergoes a phosphorylation/dephosphorylation cycle that maintains steady-state receptor phosphorylation at a low basal level in the absence of ligand. Our findings also suggest that the ligand-dependent increase in GR phosphorylation results, in part, from the dissociation of a ligand-binding domain-linked protein phosphatase(s), and that changes in the intracellular concentration of protein phosphatase 5 differentially affect GR target gene expression.
authors.affiliation: Department of Microbiology, New York University Cancer Institute, New York University School of Medicine, 550 First Avenue, New York, New York 10016, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Weiwei
authors.initials: W
authors.lastname: Chen
authors.forename: Evelyn
authors.initials: E
authors.lastname: Kono
authors.forename: Thoa
authors.initials: T
authors.lastname: Dang
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Garabedian
mesh_terms: D001665:Binding Sites; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011965:Receptors, Glucocorticoid / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D009687:Nuclear Proteins; D011965:Receptors, Glucocorticoid; D010749:Phosphoprotein Phosphatases; C089641:protein phosphatase 5