Ando S, Nakamura H, Sasaki S, Nishiyama K, Kitahara A, Nagasawa S, Mikami T, Natsume H, Genma R, Yoshimi T
Department of Internal Medicine, Hamamatsu University School of Medicine, Shizuoka, Japan.
J Endocrinol. 1996 Nov;151(2):293-300. doi: 10.1677/joe.0.1510293.
Clinical resistance to thyroid hormone (RTH) has been classified into generalized resistance to thyroid hormone (GRTH) and pituitary resistance to thyroid hormone (PRTH) types. Since similar mutations have been identified in tri-iodothyronine (T3) receptor (TR) beta gene in GRTH and PRTH, and since considerable overlap has been seen in the clinical manifestations in patients with GRTH and PRTH, two subtypes of RTH are now considered to be a continuous spectrum with the same genetic defect. A point mutation at amino acid Arg 338 to Trp (R338W) which we identified in a patient with PRTH is very interesting, since R338W has been found in several other patients with PRTH, raising the possibility that this mutation may tend to associate with a phenotype of PRTH. In our previous study, we found that R338W had relatively less impaired transcriptional potency, weaker dominant negative activity on various T3 response elements and poor homodimer formation, as compared with another GRTH mutant. In this study, to investigate the functional properties of R338W further, especially in terms of the relation between transcriptional activity and dimer formations, we introduced the R338W mutation into the mutant receptors, K443E and F451X, constructing the double mutants, R338W/K443E and R338W/ F451X. Both R338W/K443E and R338W/F451X showed negligible T3 binding and transcriptional activities. The dominant negative activities of K443E and F451X were, however, significantly weakened by introducing the R338W mutation. As a control, a double mutant G345R/K443E was constructed by introducing a point mutation, G345R, located in the same exon 9 as R338W, into the K443E mutant. Dominant negative activity did not differ between G345R/K443E and K443E. Homodimer formation was significantly reduced in the double mutants containing R338W, but not G345R. In summary, introducing the R338W mutation, but not G345R, into the mutant TR significantly weakened the dominant negative activity, despite further impairment of the T3 binding and transcriptional activities.
甲状腺激素临床抵抗（RTH）已被分为全身性甲状腺激素抵抗（GRTH）和垂体性甲状腺激素抵抗（PRTH）类型。由于在GRTH和PRTH患者的三碘甲状腺原氨酸（T3）受体（TR）β基因中已鉴定出相似的突变，并且由于GRTH和PRTH患者的临床表现存在相当大的重叠，现在认为RTH的两个亚型是具有相同遗传缺陷的连续谱。我们在一名PRTH患者中鉴定出的氨基酸Arg 338突变为Trp（R338W）的点突变非常有趣，因为在其他几名PRTH患者中也发现了R338W，这增加了这种突变可能倾向于与PRTH表型相关的可能性。在我们之前的研究中，我们发现与另一个GRTH突变体相比，R338W的转录能力受损相对较小，对各种T3反应元件的显性负活性较弱，且同源二聚体形成较差。在本研究中，为了进一步研究R338W的功能特性，特别是在转录活性与二聚体形成之间的关系方面，我们将R338W突变引入突变受体K443E和F451X中，构建了双突变体R338W/K443E和R338W/F451X。R338W/K443E和R338W/F451X均显示出可忽略不计的T3结合和转录活性。然而，通过引入R338W突变，K443E和F451X的显性负活性显著减弱。作为对照，通过将位于与R338W相同的第9外显子中的点突变G345R引入K443E突变体中，构建了双突变体G345R/K443E。G345R/K443E和K443E之间的显性负活性没有差异。在含有R338W的双突变体中，同源二聚体形成显著减少，但在含有G345R的双突变体中没有减少。总之，将R338W突变而非G345R引入突变型TR中，尽管T3结合和转录活性进一步受损，但显著减弱了显性负活性。
