Saitou M, Narumiya S, Kakizuka A
Department of Pharmacology, Kyoto University Faculty of Medicine, Japan.
J Biol Chem. 1994 Jul 22;269(29):19101-7.
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.
甲状腺激素受体（TR）和视黄酸受体（RAR）不仅在结构上密切相关，而且在作用方式上也密切相关。TR和RAR在功能重要的DNA结合结构域、配体结合结构域和异二聚体界面中共享许多氨基酸。为了发挥功能，这两种受体都与视黄酸X受体二聚化，识别它们的同源激素反应元件，然后对配体作出反应，从而导致靶基因的激活。遗传分析揭示了甲状腺激素抵抗综合征中的TR突变，该综合征表现为常染色体显性遗传。最终，突变的TR在野生型TR上表现出显性负性表型。这些突变大多发生在配体结合结构域中TR和RAR之间的保守氨基酸处，并产生激素不敏感受体。在本报告中，我们证明了显性负性表型可通过在甲状腺激素抵抗综合征中鉴定出的单个氨基酸取代转移至RAR。突变的RAR可以抑制野生型RAR的功能，尤其是在视黄酸的生理浓度下。一致地，突变的RAR对于显性负性表型而言是完整的二聚体和DNA结合能力的绝对要求，这表明维持正确识别靶标的机制的必要性。因此，激素不敏感受体可能会干扰功能性受体与激素反应元件的结合。显性负性RAR将作为一种分子工具，通过阻断RAR介导的信号通路来阐明RAR的生理作用。
