Tagami T, Nakamura H, Sasaki S, Miyoshi Y, Imura H
Department of Internal Medicine, Kyoto University School of Medicine, Japan.
Endocrinology. 1993 Jan;132(1):275-9. doi: 10.1210/endo.132.1.8419128.
Recent studies of the expression of c-erbA/thyroid hormone receptor (TR) mRNAs have revealed a dissociation between T3-binding activity and the behavior of the mRNAs that code the functional TRs in some tissues. Compared with T3-binding activity, TR(alpha 1 + beta 1) mRNA is disproportionally high in the brain and low in the liver. Using anti-TR antiserum, 4BII, which recognizes TR alpha 1 and beta 1, but not the alpha 2-variant, we measured TR protein content in rat tissues by Western blotting. Two protein bands of 47 and 55 kilodaltons (kDa) were specifically identified as TR proteins. The positions of the in vitro transcription/translation products of c-erbA/TR alpha 1 and beta 1 cDNA on the gel were consistent with those of the 47- and 55-kDa bands, respectively. The 47- and 55-kDa proteins in nuclear proteins extracted with 0.4 M KCl from rat tissues were analyzed by Western blotting, and the intensity of TR protein bands in each tissue was measured by a densitometer. The relative TR protein concentration was highest in liver, followed by brain, kidney, and testis. We compared the TR protein level measured by Western blotting with the maximal T3-binding capacity (Cmax) in the same aliquot of samples from liver and brain. Both the TR protein level and the Cmax in the brain were about 40% of those in the liver, suggesting that the Cmax per receptor molecule is constant in these two tissues, and an abundant amount of functional TR proteins exists in the liver, corresponding to the high level of T3-binding activity.
最近对c-erbA/甲状腺激素受体（TR）mRNA表达的研究表明，在某些组织中，T3结合活性与编码功能性TR的mRNA行为之间存在分离。与T3结合活性相比，TR（α1 + β1）mRNA在脑中异常高，而在肝脏中低。使用识别TRα1和β1但不识别α2变体的抗TR抗血清4BII，我们通过蛋白质印迹法测量了大鼠组织中的TR蛋白含量。两条47和55千道尔顿（kDa）的蛋白带被特异性鉴定为TR蛋白。c-erbA/TRα1和β1 cDNA的体外转录/翻译产物在凝胶上的位置分别与47 kDa和55 kDa条带的位置一致。用0.4 M KCl从大鼠组织中提取的核蛋白中的47 kDa和55 kDa蛋白通过蛋白质印迹法进行分析，并用密度计测量每个组织中TR蛋白条带的强度。相对TR蛋白浓度在肝脏中最高，其次是脑、肾和睾丸。我们将蛋白质印迹法测得的TR蛋白水平与来自肝脏和脑的同一样品等分试样中的最大T3结合能力（Cmax）进行了比较。脑中的TR蛋白水平和Cmax均约为肝脏中的40%，这表明这两个组织中每个受体分子的Cmax是恒定的，并且肝脏中存在大量功能性TR蛋白，这与高水平的T3结合活性相对应。
