Alteration of a single amino acid residue in retinoic acid receptor causes dominant-negative phenotype.

Thyroid hormone receptor (TR) and retinoic acid receptor (RAR) are closely related not only in their structures but also in their modes of action. TR and RAR share many amino acids in the functionally important DNA binding domain, ligand binding domain, and heterodimeric interface. To function, both receptors dimerize with retinoid X receptor, recognize their cognate hormone response elements, and then respond to the ligand, leading to the activation of the target genes. Genetic analysis has revealed mutated TRs in thyroid hormone resistance syndrome, which displays autosomal dominant inheritance. Eventually, the mutated TRs show the dominant-negative phenotype on the wild-type TR. The mutations have been observed mostly in conserved amino acids between TR and RAR in the ligand binding domain and produce hormone-insensitive receptors. In this report, we demonstrate that the dominant-negative phenotype is transferable to RAR by a single amino acid substitution identified in the syndromes of thyroid hormone resistance. The mutated RAR can suppress the wild-type RAR function, especially at the physiological concentration of retinoic acid. Consistently, the mutated RAR is an absolute requirement of intact dimeric and DNA binding capacities for the dominant-negative phenotype, indicating the necessity of the maintenance of a machinery for correct recognition of the targets. Thus, the hormone-insensitive receptor may be interfering with the access of functional receptors to the hormone response elements. The dominant-negative RAR will serve as a molecular tool to elucidate physiological roles of RAR by blocking RAR-mediated signaling pathways.