Functional Characterization of the hGRαT556I Causing Chrousos Syndrome

Eur J Clin Invest. 2016 Jan;46(1):42-9. doi: 10.1111/eci.12563. Epub 2015 Dec 15.

Abstract

Background: Chrousos syndrome is a rare pathologic condition characterized by generalized, partial resistance of target tissues to glucocorticoids and caused by inactivating mutations of the human glucocorticoid receptor (hGR) gene. A novel case of Chrousos syndrome has been reported in a patient with adrenal incidentaloma, who harboured a heterozygous point mutation in the hGR gene, which resulted in threonine (T) to isoleucine (I) substitution at amino acid position 556 in the ligand-binding domain of the receptor.

Objective: To delineate the molecular mechanisms through which the mutant receptor hGRαT556I causes Chrousos syndrome.

Design and results: Compared with the wild-type receptor, the mutant receptor hGRαT556I demonstrated 50% reduction in its ability to transactivate glucocorticoid-responsive genes and in the affinity for the ligand, 30% increase in the ability to transrepress the nuclear factor-κB-target genes and a 3,4-fold delay in the cytoplasmic-to-nuclear translocation. The mutant receptor hGRαT556I did not exert a dominant negative effect upon the hGRα-mediated transcriptional activity; it preserved its ability to bind to DNA and interacted with the glucocorticoid receptor-interacting protein 1 coactivator mostly through its activation function-1 domain. Structural biology studies revealed that the T556I mutation caused disruption of the hydrogen bond formed by the T556 with the =O group of P637 backbone, which resulted in a significant relocation of the P637-bearing loop. This conformational alteration affected the local 3D arrangement of the receptor and hence the electrostatic surface of the region.

Conclusions: The hGRαT556I causes Chrousos syndrome by impairing multiple steps of the glucocorticoid signal transduction pathway.

Keywords: Chrousos syndrome; glucocorticoid receptor; glucocorticoid signalling; hGR mutations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • COS Cells
  • Chlorocebus aethiops
  • Dexamethasone / metabolism
  • Glucocorticoids / metabolism
  • HCT116 Cells
  • HeLa Cells
  • Humans
  • Metabolism, Inborn Errors / genetics*
  • Nuclear Receptor Coactivator 2 / metabolism
  • Point Mutation
  • Receptors, Glucocorticoid / deficiency*
  • Receptors, Glucocorticoid / genetics
  • Receptors, Glucocorticoid / metabolism
  • Signal Transduction

Substances

  • Glucocorticoids
  • NCOA2 protein, human
  • Nuclear Receptor Coactivator 2
  • Receptors, Glucocorticoid
  • glucocorticoid receptor alpha
  • Dexamethasone

Supplementary concepts

  • Glucocorticoid Receptor Deficiency