PHYSIOLOGICAL ROLE OF THYROXINE-BINDING PROTEINS

甲状腺素（T4）是激素原活化的第一步，是它的5'单脱碘为T3， 1型和2型碘甲腺原氨酸脱碘酶。3型脱碘酶（D3）催化内环的去除 碘使T4或T3失活。这三种酶有两个共同的特点： 蛋白质和所有的稀有氨基酸硒代半胱氨酸在其活性中心，作为碘 接受者它们赋予甲状腺激素作用的调节两个一般优点。首先是在 胚胎发育，甲状腺激素的激活和失活程序发生在 在特定细胞中的特定时间，以允许诱导或抑制甲状腺激素依赖性基因 表情其次，在整个生命过程中，D2在下丘脑-垂体-甲状腺轴中的重要作用 允许陆生脊椎动物适应碘缺乏症通过监测T4的浓度， 流通这使得TRH和TSH分泌的增加，早在活性物质的浓度之前， 激素T3减少在人类中，长期以来一直认为，D1，存在于高浓度的 肝脏和肾脏是循环T3的主要来源。D2表达模式的最新分析 与较早的体内结果一起表明，情况并非如此， 可能是由D2激活T4引起的。这种酶在人类中广泛表达，但在 啮齿动物本文主要从三个方面对脱碘酶的分子生理学进行了研究。 具体目的我将分析D1、D2和D3独特的拓扑结构和亚细胞定位的原因 使用共聚焦显微镜和细胞生物学技术。具体目标II将采用细胞 表达内源性或重组D1和D2，以了解为什么D2是催化 人类甲状腺外T3的产生。我们还将确定为什么由D2催化的T4 5 '- 脱碘作用进入细胞核，而D1产生的脱碘作用则不进入细胞核。具体目标三将解决 三种酶的活性形式问题。它们是同源二聚体还是与其他蛋白质相互作用？ 我们还将分析这种相互作用的功能效应。因此，这些研究将解决基本的 甲状腺激素激活和失活的调节机制， 病理状态。

The first step in the activation of the prohormone, thyroxine (T4), is its 5' monodeiodination to T3, catalyzed by the types 1 and 2 iodothyronine deiodinase. Type 3 deiodinase (D3) catalyzes removal of an inner ring iodine inactivating T4 or T3. These three enzymes have two common features; they are integralmembrane proteins and all have the rare amino acid selenocysteine in their active center to serve as the iodine acceptor. They confer two general advantages to the regulation of thyroid hormone action. First, during embryological development, activation and inactivation of thyroid hormone is programmed to occur at specific times in specific cells to allow either induction or repression of thyroid hormone-dependent gene expression. Second, throughout life, the important role of D2 in the hypothalamic-pituitary-thyroid axis permits the terrestrial vertebrate to adapt to iodine deficiency by monitoring the concentration of T4 in the circulation. This permits increases in TRH and TSH secretion, long before the concentrations of the active hormone, T3, decrease. In humans, it has long been assumed that D1, present in high concentrations in the liver and kidney, is the major source of circulating T3. More recent analyses of D2 expression patterns together with older in vivo results suggest that this is not the case and that most plasma T3 in humans probably derives from the activation of T4 by D2. This enzyme is widely expressed in humans, but not in rodents. The present proposal will focus on 3 aspects of the molecular physiology of the deiodinases. Specific Aim I will analyze the causes of the unique topology and subcellular localizations of D1, D2 andD3 in the cell using confocal microscopy and cell biological techniques. Specific Aim II will employ cells expressing endogenous or recombinant D1 and D2 to understand why D2 is the major enzyme catalyzing extrathyroidal T3 production in humans. We also will determine why the T3 produced by D2-catalyzed T4 5'- deiodination enters the nucleus whereas that generated by D1 does not. Specific Aim III will address the issue of the active form of the three enzymes. Are they homodimers or do they interact with other proteins? We will also analyze the functional effects of this interaction. These studies will thus address the basic mechanisms by which thyroid hormone activation and inactivation are regulated in both normal and pathological states.