The thyroid hormone receptor-coactivator interface mediates negative feedback regulation of the human pituitarythyroid axis
C. Moran1, M. Agostini1, E. Schoenmakers1, C. Mitchell1, J. Gregory2, M. Gurnell1 & K. Chatterjee1
Corepressors and coactivators mediate thyroid hormone receptor-dependent repression and transactivation of positively-regulated target genes respectively, but their role in negative regulation is not understood.
A 4 years old boy was born at 31 weeks. He was jittery at birth, with neonatal respiratory distress. Childhood features included poor weight gain, heat intolerance, tachycardia and hyperactivity. Ongoing problems are low frequency hearing loss, poor sight, impaired coordination and learning disability. His circulating free thyroid hormones are consistently elevated (FT4 47.1 pmol/l (RR 9.823.1), FT3 13.7 pmol/l (RR 3.56.5) together with non-suppressed TSH (8.0 mU/l (RR 0.355.50)) levels; parental thyroid function is normal.
The proband is heterozygous for a novel mutation (E457Q) in the TRβ gene, involving a highly conserved residue located in its carboxyterminal transactivation domain; the mutation occurs de novo, with wild type parental TRβ sequence, consistent with their normal thyroid function. Although the mutant receptor binds T3 normally (WT Ka=1.29×1010 M−1; E457Q Ka=1.26×1010 M−1) hormone-dependent negative regulation (hTSHα) by E457Q TRβ is markedly impaired; in addition, when coexpressed, E457Q TRβ is a strong dominant negative inhibitor of WT receptor function. In protein-protein interaction assays, E457Q TRβ binds and dissociates from corepressors (NCoR, SMRT) normally; however, the mutant receptor fails to recruit coactivators (TRAP 220, SRC-1, RIPI40, LCoR). Crystallographic modelling indicates that substitution of glutamine for the negatively-charged glutamic acid at codon 457 abrogates electrostatic receptor-coactivator interactions.
Elevated thyroid hormones with non-suppressed TSH in the proband indicate impaired negative feedback in the pituitarythyroid axis in vivo. consistent with impaired negative regulation of the TSHα promoter by E457Q TRβ seen in vitro. Together these observations suggest that proteins recruited to the thyroid receptor-coactivator interface mediate negative transcriptional regulation of target genes in the human pituitarythyroid axis.
*Please note C Moran and M Agostini contributed equally to this work.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This work was supported, however funding details are unavailable.