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Functional analysis of a novel signaling cascade activated by thyroid hormone: Role of PI3 kinase→PKB→mTOR→ZAKI-4αactivation by thyroid hormone

甲状腺激素激活的新型信号级联的功能分析：甲状腺激素激活PI3激酶→PKB→mTOR→ZAKI-4α的作用

基本信息

批准号：
16390269
负责人：
SEO Hisao
金额：
$ 8.9万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

Thyroid hormone (TH) is essential for normal development, growth and metabolism. Its effects are mediated through triiodothyronine (T_3), which acts as a ligand for the TH receptors (TRs). In the classical model of genes positively regulated by TH, the TR first binds as a heterodimer or homodimer on TH response elements (TRE) located in the promoter regions of target genes, where it interacts with corepressors. Upon ligand binding, the TR homodimers are dissociated in favor of heterodimer formation with the retinoid-X receptor (RXR), resulting in release of the corepressors and recruitment of coactivators. This new complex attracts a large number of proteins which engage the RNA polymerase II in the transcription of the targeted gene. In addition to the classical, "nuclear" mode of TH action, we demonstrated that TH also activates PI3K-Akt signaling pathway rapidly through a non-genomic mechanism. It was found that 1) TH treatment induced sequential phosphorylation and activation of th … More e serine/threonine kinase Akt, the mammalian target of rapamycin (mTOR) and its substrate p70^<S6K> and 2) phosphorylation of these proteins was abrogated by both PI3K inhibitors, LY294002 and wortmannin, and by a dominant negative regulatory subunit of PI3K (p85a). This TH action is very rapid and independent of protein synthesis, suggesting that it does not involve the typical nuclear action of TR. It is of note that this rapid TH action was abrogated by the introduction of a dominant negative TRP (TRG345R) into the cells expressing the wild type TRβ, indicating the participation of TRβ. It was demonstrated that TRβ directly interacts with the regulatory subunit of PI3K, p85a in human skin fibroblasts. The interaction is independent of ligand binding, while PI3K can be activated only in the presence of TH. We and others identified several genes under the control of this action, including ZAKI-4a, hypoxia-inducible factor-la, glucose transporter 1, phosphofructokinase, and the monocarboxylate transporter 4. ZAKI-4 gene was originally identified by us as a thyroid hormone (TH) responsive gene which locates on human chromosome 6. We later found that three transcripts, a, β1 and β2, were generated by the single ZAKI-4 gene through differential splicing. The β1 and β2 isoforms encode the same protein product ZAKI-4β, which shares the common carboxyl terminal region with ZAKI-4a. Both ZAKI-4a and β belong to a family of small structurally related proteins which bind to, and down-regulate the activity of calcineurin (protein phosphatase 2B). It was demonstrated in human and rodents that the expression of only a isoform is upregulated. by TH. Since it is known that calcineurin is involved in neuronal plasticity, TH may play the role in neuronal plasticity through regulating calcineurin activity. Less

甲状腺激素（TH）对于正常发育、生长和新陈代谢至关重要。其作用是通过三碘甲状腺原氨酸 (T_3) 介导的，三碘甲状腺原氨酸是 TH 受体 (TR) 的配体。在受 TH 正向调节的基因的经典模型中，TR 首先作为异二聚体或同二聚体结合在位于靶基因启动子区域的 TH 响应元件 (TRE) 上，并与辅阻遏物相互作用。配体结合后，TR 同二聚体解离，有利于与类维生素A-X 受体 (RXR) 形成异二聚体，从而释放辅阻遏物并招募共激活剂。这种新的复合物吸引大量蛋白质，使 RNA 聚合酶 II 参与目标基因的转录。除了 TH 作用的经典“核”模式外，我们还证明 TH 还通过非基因组机制快速激活 PI3K-Akt 信号通路。结果发现，1) TH 处理诱导丝氨酸/苏氨酸激酶 Akt（雷帕霉素 (mTOR) 的哺乳动物靶点及其底物 p70^<S6K>）的连续磷酸化和激活，2) 这些蛋白质的磷酸化被 PI3K 抑制剂 LY294002 和渥曼青霉素以及显性失活所消除。 PI3K (p85a) 的调节亚基。 TH 作用非常迅速且独立于蛋白质合成，表明它不涉及 TR 的典型核作用。值得注意的是，这种快速的 TH 作用通过将显性失活 TRP (TRG345R) 引入表达野生型 TRβ 的细胞中而被消除，表明 TRβ 的参与。研究表明，TRβ 直接与人皮肤成纤维细胞中 PI3K 的调节亚基 p85a 相互作用。这种相互作用与配体结合无关，而 PI3K 仅在 TH 存在的情况下才能被激活。我们和其他人鉴定了几个受此作用控制的基因，包括ZAKI-4a、缺氧诱导因子-la、葡萄糖转运蛋白1、磷酸果糖激酶和单羧酸转运蛋白4。ZAKI-4基因最初被我们鉴定为甲状腺激素（TH）反应基因，位于人类6号染色体上。后来我们发现了三个转录物，a、β1和 β2是由单个ZAKI-4基因通过差异剪接产生的。 β1 和 β2 亚型编码相同的蛋白质产物 ZAKI-4β，其与 ZAKI-4a 具有共同的羧基末端区域。 ZAKI-4a 和 β 均属于结构相关的小蛋白家族，可与钙调神经磷酸酶（蛋白磷酸酶 2B）结合并下调其活性。在人类和啮齿类动物中证明只有同种型的表达上调。由TH。由于已知钙调神经磷酸酶参与神经元可塑性，TH可能通过调节钙调神经磷酸酶活性在神经元可塑性中发挥作用。较少的