Metabolic effect of 3,3',5'-triiodothyronine in cultured growth hormone-producing rat pituitary tumor cells. Evidence for a unique mechanism of thyroid hormone action.
Metabolic effect of 3,3',5'-triiodothyronine in cultured growth hormone-producing rat pituitary tumor cells. Evidence for a unique mechanism of thyroid hormone action.
复制标题
DOI：
10.1172/jci112049
复制
发表时间：
1985-08
期刊：
影响因子：
--
通讯作者：
D L St Germain
中科院分区：
文献类型：
--
作者：
D L St Germain
一般认为生理水平的3，3 '，5'-三碘甲状腺原氨酸（rT 3）对脑垂体和其他组织的代谢影响最小。本研究在生长激素产生的大鼠垂体瘤细胞系（GH 3细胞）中研究了rT 3和其他甲状腺激素对碘甲腺原氨酸5 ′-脱碘酶（I5 ′ D）活性的调节作用。I5 ′ D活性是硫醇依赖性的，并显示出非线性反应动力学，表明存在两种酶促过程，一种具有低米氏常数（甲状腺素[T4]的Km为2 nM），第二种具有高Km值（0.9 μ M）。细胞在去酶培养基中生长导致低Km I5 'D活性增加2 - 3.5倍（P小于0.001）。向培养基中添加甲状腺激素导致对低Km I5 'D活性的快速、剂量依赖性抑制，类似物效力顺序如下：rT 3大于或等于T4大于3，5，3'-三碘甲腺原氨酸（T3）。使用无血清培养条件，rT 3的活性比T3高约50倍。这些抑制作用在激素添加后15分钟内被注意到，并且不能归因于与T4的底物竞争。这些研究结果表明，T4到T3转换的甲状腺激素在垂体前叶的控制是由一个独特的细胞机制，是独立的核T3受体介导的，在某些情况下，rT 3可能发挥调节作用，在控制这种酶的过程。
Physiologic levels of 3,3',5'-triiodothyronine (rT3) are generally believed to have minimal metabolic effects in the pituitary gland and other tissues. In the present studies, the regulatory role of rT3 and other thyroid hormones on iodothyronine 5'-deiodinase (I5'D) activity was studied in a growth hormone-producing rat pituitary tumor cell line (GH3 cells). I5'D activity was thiol-dependent and displayed nonlinear reaction kinetics suggesting the presence of two enzymatic processes, one having a low Michaelis constant (Km for thyroxine [T4] of 2 nM) and a second with a high Km value (0.9 microM). Growth of cells in hormone-depleted medium resulted in a two- to 3.5-fold increase in low Km I5'D activity (P less than 0.001). The addition of thyroid hormones to the culture medium resulted in a rapid, dose-dependent inhibition of low Km I5'D activity with the following order of analogue potency: rT3 greater than or equal to T4 greater than 3,5,3'-triiodothyronine (T3). Using serum-free culture conditions, rT3 was approximately 50 times more active than T3. These inhibitory effects were noted within 15 min of hormone addition and could not be attributed to substrate competition with T4. These findings suggest that the control of T4 to T3 conversion by thyroid hormones in the anterior pituitary gland is mediated by a unique cellular mechanism that is independent of the nuclear T3 receptor; and under some circumstances, rT3 may play a regulatory role in controlling this enzymatic process.