Structure-guided approach to relieving transcriptional repression inResistance to Thyroid Hormone α.

Mutations in thyroid hormone receptor α (TRα), a ligand-inducible transcription factor, cause Resistance to Thyroid Hormone α (RTHα). This disorder is characterised by tissue-specific hormone refractoriness and hypothyroidism, due to inhibition of target gene expression by mutant TRα-corepressor complexes. Using biophysical approaches, we show that RTHα-associated TRα mutants devoid of ligand-dependent transcription activation function, unexpectedly retain the ability to bind thyroid hormone. Visualisation of ligand (T3) within the crystal structure of a prototypic TRα mutant, validates this notion. This finding prompted synthesis of different thyroid hormone analogues, identifying a lead compound (ES08) which dissociates corepressor from mutant human TRα more efficaciously than T3. ES08 rescues developmental anomalies in a zebrafish model of RTHα and induces target gene expression in TRα mutation-containing cells from an RTHα patient, more effectively than T3. Our observations provide proof-of-principle for developing synthetic ligands that can relieve transcriptional repression by the mutant TRα-corepressor complex, for treatment of RTHα.