Pin1 promotes GR transactivation by enhancing recruitment to target genes

T M Poolman,L Matthews,D W Ray,A S Loudon,S N Farrow

doi:10.1093/nar/gkt624

Abstract

The glucocorticoid receptor (GR) is a ligand activated transcription factor, serving to regulate both energy metabolism and immune functions. Factors that influence cellular sensitivity to glucocorticoids (GC) are therefore of great interest. The N-terminal of the GR contains numerous potential proline-directed phosphorylation sites, some of which can regulate GR transactivation. Unrestricted proline isomerisation can be inhibited by adjacent serine phosphorylation and requires a prolyl isomerise, Pin1. Pin1 therefore determines the functional outcome of proline-directed kinases acting on the GR, as cis/trans isomers are distinct pools with different interacting proteins. We show that Pin1 mediates GR transactivation, but not GR trans-repression. Two N-terminal GR serines, S203 and S211, are targets for Pin1 potentiation of GR transactivation, establishing a direct link between Pin1 and the GR. We also demonstrate GC-activated co-recruitment of GR and Pin1 to the GILZ gene promoter. The Pin1 effect required both its WW and catalytic domains, and GR recruitment to its GRE was Pin1-dependent. Therefore, Pin1 is a selective regulator of GR transactivation, acting through N-terminal phospho-serine residues to regulate GR recruitment to its target sites in the genome. As Pin1 is dysregulated in disease states, this interaction may contribute to altered GC action in inflammatory conditions.

Highlights

Glucocorticoids (GCs) are highly potent anti-inflammatory agents and exert important effects on carbohydrate metabolism, resulting in off-target phenomena including diabetes and obesity
Initial studies used the Pin1 inhibitor juglone to screen for Pin1 effects on glucocorticoid receptor (GR) transactivation (Supplementary Figure S1)
We showed that the Pin1 effect on GR was dependent on phosphoserines in the N-terminal domain, and not the site of interaction between GR and the SRC family of co-activators in the C-terminal domain, additional studies were focussed on a potential role for SRC-3

Summary

Introduction

Glucocorticoids (GCs) are highly potent anti-inflammatory agents and exert important effects on carbohydrate metabolism, resulting in off-target phenomena including diabetes and obesity. There is considerable interest in identifying how the broad spectrum of glucocorticoid activities can be targeted, to retain the beneficial anti-inflammatory actions, but minimize metabolic offtarget effects. The best characterized modifications lie in the N-terminal domain, and consist of proline-directed serine phosphorylation sites. The importance of individual modifications has been defined, e.g. transactivation of IGFBP1 requires phosphorylation of serine 211 (S211), and thereby recruitment of the co-activator MED14 [2]. Some GR phosphorylation sites have been shown to enhance, for example, S211 and S203 [3], whereas others inhibit GR transactivation, for example, at S226 [4] and S404 [5] [reviewed in [6]]

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