Toyoda N, Nishikawa M, Horimoto M, Yoshikawa N, Mori Y, Yoshimura M, Masaki H, Tanaka K, Inada M
Second Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
Endocrinology. 1990 Sep;127(3):1199-205. doi: 10.1210/endo-127-3-1199.
The effects of T3 and T4 on the iodothyronine 5'-deiodinase (5'-D) activity in FRTL-5 rat thyroid cells were investigated. T3 and T4 stimulated the 5'-D activity in a dose-dependent manner. Kinetic studies showed that the stimulation of the 5'-D by T3 was associated with an increase in maximum velocity (Vmax) in [11.9 +/- 0.2 (mean +/- SE) and 25.4 +/- 0.9 pmol I-released/mg protein.min, respectively, in control and cultured with 10(-9) M T3 for four days] but without a change in apparent Michaelis-Menten constant (Km) (94.8 +/- 5.3 nM and 105.4 +/- 12.1 nM, respectively). Furthermore, cycloheximide (5 microM) completely abolished the stimulatory effect of T3 on the 5'-D activity. T3 and T4 also enhanced the 5'-D activity stimulated by TSH in a dose-dependent manner. Kinetic studies showed that the stimulatory effect of T3 on the 5'-D stimulated by TSH was again associated with an increase in Vmax (86.0 +/- 4.0 and 166.5 +/- 1.9 pmol I- released/mg protein.min, respectively, cultured with 0.3 U/liter TSH and cultured with TSH plus 10(-9) M T3 for four days) without a change in apparent Km (114.0 +/- 7.4 nM and 111.6 +/- 12.5 nM, respectively). Cycloheximide (5 microM) completely abolished the stimulatory effect of TSH plus T3 on the 5'-D activity. There were no significant differences observed between cells cultured with TSH and with TSH plus T3 in either the intra- or extracellular cAMP contents. Furthermore, T3 enhanced the 5'-D activity stimulated by (Bu)2 cAMP. These results strongly suggest that T3 or T4 was synergistic with TSH in stimulating the 5'-D activity in FRTL-5 cells, and that cAMP production would be an important component of the synergism.
研究了T3和T4对FRTL-5大鼠甲状腺细胞中碘甲状腺原氨酸5'-脱碘酶（5'-D）活性的影响。T3和T4以剂量依赖的方式刺激5'-D活性。动力学研究表明，T3对5'-D的刺激与最大速度（Vmax）的增加有关（对照组和用10^(-9) M T3培养四天后的细胞中，Vmax分别为[11.9±0.2（平均值±标准误）和25.4±0.9 pmol碘释放/毫克蛋白·分钟]），但表观米氏常数（Km）没有变化（分别为94.8±5.3 nM和105.4±12.1 nM）。此外，放线菌酮（5 μM）完全消除了T3对5'-D活性的刺激作用。T3和T4也以剂量依赖的方式增强了促甲状腺激素（TSH）刺激的5'-D活性。动力学研究表明，T3对TSH刺激的5'-D的刺激作用再次与Vmax的增加有关（分别用0.3 U/升TSH培养和用TSH加10^(-9) M T3培养四天后的细胞中，Vmax分别为86.0±4.0和166.5±1.9 pmol碘释放/毫克蛋白·分钟），表观Km没有变化（分别为114.0±7.4 nM和111.6±12.5 nM）。放线菌酮（5 μM）完全消除了TSH加T3对5'-D活性的刺激作用。在细胞内或细胞外cAMP含量方面，用TSH培养的细胞和用TSH加T3培养的细胞之间没有观察到显著差异。此外，T3增强了（Bu）2 cAMP刺激的5'-D活性。这些结果强烈表明，T3或T4与TSH在刺激FRTL-5细胞中的5'-D活性方面具有协同作用，并且cAMP的产生将是这种协同作用的一个重要组成部分。
