Negative regulation by thyroid hormone receptor requires an intact coactivator-binding surface

Abstract

Thyroid hormone (TH) action is mediated by TH receptors (TRs), which are members of the nuclear hormone receptor superfamily. In vitro studies have demonstrated that TR activity is regulated by interactions with corepressor and coactivator proteins (CoRs and CoAs, respectively). TH stimulation is thought to involve dissociation of CoRs and recruitment of CoAs to the liganded TR. In contrast, negative regulation by TH is thought to occur via recruitment of CoRs to the liganded TR. The physiological role of CoAs bound to TRs, however, has yet to be defined. In this study, we used gene-targeting techniques to mutate the TR-β locus within its activation function-2 (AF-2) domain (E457A). This mutation was chosen because it completely abolished CoA recruitment in vitro, while preserving normal triiodothyronine (T 3 ) binding and CoR interactions. As expected, THstimulated gene expression was reduced in homozygous E457A mice. However, these animals also displayed abnormal regulation of the hypothalamic-pituitary-thyroid axis. Serum thyroxine, T 3 , and thyroid-stimulating hormone (TSH) levels and pituitary Tshb mRNA levels were inappropriately elevated compared with those of WT animals, and L-T 3 treatment failed to suppress serum TSH and pituitary Tshb mRNA levels. Therefore, the AF-2 domain of TR-β is required for positive and, paradoxically, for negative regulation by TH in vivo.

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…Recently, similar mutations in the human THRA gene have been identified that generate dominant negative TRa1 proteins (459,460). The Thrb and Thra knockin mouse models display a range of tissueselective phenotypes and offer the opportunity to investigate the cellular and molecular defects underlying the disease symptoms in specific tissues (456,(461)(462)(463)(464)(465).…”

A thyroid hormone receptor mutation that dissociates thyroid hormone regulation of gene expression in vivo

“…Paradoxically, CoRs may increase transcription of the TSH subunit and TRH genes (16,17), whereas CoAs may have a role in ligand-dependent repression of negatively regulated genes. Both SRC-1 knockout mice and helix 12 mutant knock-in (KI) mice (which have TR that is unable to interact with coactivators) exhibit defective negative gene regulation by TH (18,19). The molecular mechanisms by which the same proteins that mediate gene activation on positively regulated genes also mediate gene repression on negatively regulated target genes are not well understood.…”

Role of co-regulators in metabolic and transcriptional actions of thyroid hormone

“…Mice expressing THRB with E457A mutation in AF-2 that does not affect ligand binding but completely abolishes recruitment of co-activators to LBD also demonstrate profound RTH phenotype at peripheral tissues and HPT axis (Ortiga-Carvalho et al 2005). Surprisingly, disruption of Src1 in the Thrb E457A/E457A mice worsened the degree of resistance to TH, resulting in increased serum T 4 and TSH at baseline.…”

“…Mice expressing Thrb E457A mutation that abolishes co-activator binding and homozygous Thrb knockout animals also demonstrate various degrees of resistance to TH (Ortiga-Carvalho et al 2005), reviewed in Flamant and Samarut (2003). Thra knock-in mouse models carrying mutations analogous to those found in patients with THRB RTH were generated before identification of patients with THRA gene mutations (Thra PV , Thra R384C , Thra L400R , Thra P398H , Thra R384C ) and display varying phenotypes, with some of them being similar to patients with THRA RTH (Kaneshige et al 2001, Liu et al 2003, Quignodon et al 2007, Tinnikov et al 2002, reviewed in van Mullem et al (2014) and Vennstrom et al (2008).…”