Collingwood T N, Rajanayagam O, Adams M, Wagner R, Cavaillès V, Kalkhoven E, Matthews C, Nystrom E, Stenlof K, Lindstedt G, Tisell L, Fletterick R J, Parker M G, Chatterjee V K
Department of Medicine, University of Cambridge, Addenbrooke's Hospital, United Kingdom.
Proc Natl Acad Sci U S A. 1997 Jan 7;94(1):248-53. doi: 10.1073/pnas.94.1.248.
The syndrome of resistance to thyroid hormone is characterized by elevated serum free thyroid hormones, failure to suppress pituitary thyrotropin secretion, and variable peripheral refractoriness to hormone action. Here we describe a novel leucine to valine mutation in codon 454 (L454V) of the thyroid hormone beta receptor (TR beta) in this disorder, resulting in a mutant receptor with unusual functional properties. Although the mutant protein binds ligand comparably to wild-type receptor and forms homo- and heterodimers on direct repeat, everted repeat, or palindromic thyroid response elements, its ability to activate transcription via these elements is markedly impaired. The hydrophobic leucine residue lies within an amphipathic alpha-helix at the carboxyl terminus of TR beta and the position of the homologous residue in the crystal structure of TR alpha indicates that its side chain is solvent-exposed and might interact with other proteins. We find that two putative transcriptional mediators (RIP140 and SRC-1) exhibit hormone-dependent association with wild-type TR. In comparison, the interaction of this natural mutant (L454V) and artificial mutants (L454A, E457A) with RIP140 and SRC-1 is markedly reduced. Furthermore, coexpression of SRC-1 is able to restore the transcriptional activity of the L454V mutant receptor, indicating that the interaction of this residue with accessory proteins is critical for transcriptional activation. Finally, the occurrence of the L454V mutation in resistance to thyroid hormone, together with impaired negative regulation of the thyroid-stimulating hormone alpha promoter by this mutant, suggests that the amphipathic alpha-helix also mediates hormone-dependent transcriptional inhibition, perhaps via interaction with these or other accessory factors.
甲状腺激素抵抗综合征的特征是血清游离甲状腺激素升高、垂体促甲状腺激素分泌未能被抑制以及外周对激素作用的抵抗程度各异。在此，我们描述了该疾病中甲状腺激素β受体（TRβ）第454密码子（L454V）处一个新的亮氨酸到缬氨酸的突变，导致产生具有异常功能特性的突变受体。尽管突变蛋白与野生型受体结合配体的能力相当，并且在直接重复、反向重复或回文甲状腺反应元件上形成同源二聚体和异源二聚体，但其通过这些元件激活转录的能力明显受损。疏水的亮氨酸残基位于TRβ羧基末端的一个两亲性α螺旋内，TRα晶体结构中同源残基的位置表明其侧链暴露于溶剂中，可能与其他蛋白质相互作用。我们发现两种假定的转录调节因子（RIP140和SRC-1）与野生型TR表现出激素依赖性结合。相比之下，这种天然突变体（L454V）和人工突变体（L454A、E457A）与RIP140和SRC-1的相互作用明显减弱。此外，SRC-1的共表达能够恢复L454V突变受体的转录活性，表明该残基与辅助蛋白的相互作用对于转录激活至关重要。最后，甲状腺激素抵抗中L454V突变的出现，以及该突变体对促甲状腺激素α启动子负调控的受损，表明两亲性α螺旋也可能通过与这些或其他辅助因子相互作用介导激素依赖性转录抑制。
