Crosstalk between Ca^<2+>-calcineurin-pathway and thyroid hormone action

我们在培养的人皮肤成纤维细胞中发现了一个甲状腺激素（T3）应答基因ZAKI-4。它属于一个编码含有保守基序的蛋白质的基因家族。基序结合并抑制钙调磷酸酶（CN）。在本研究中，我们通过5′和3′-RACE鉴定了人脑中3种不同的ZAKI-4转录本α、β1和β2。1个转录本与我们最初克隆的完全相同，另外两个是新的。这三种转录本是由6号染色体短臂上的单个基因交替起始和剪接而产生的。预测β1和β2编码相同的蛋白产物β，但其n端与a不同。这两种同工异构体都与CN结合，并通过相同的c端区域抑制其活性。对三种转录本的表达谱分析表明，a转录本仅在大脑中表达，而b转录本在大脑、心脏、骨骼肌和肾脏中表达最丰富。研究还表明，人皮肤成纤维细胞同时表达α和β转录本，这提出了一个问题，即哪个转录本被T3上调。结果表明，T3能显著诱导一种异构体的表达，但不能诱导β的表达。t3介导的a异构体的增加与内源性CN活性的显著降低有关。我们进一步探讨了T3如何调节人皮肤成纤维细胞中同种异构体的表达。首先，研究了钙调磷酸酶抑制剂FK506及其类似物雷帕霉素对t3介导的ZAKI-4α调控的影响，因为有报道称CN的激活会导致ZAKI-4家族基因DSCR1的表达增加。结果表明，t3介导的ZAKI-4表达的增加不受FK506的抑制，而被雷帕霉素完全消除。由于雷帕霉素是哺乳动物雷帕霉素靶蛋白（mTOR）的特异性抑制剂，我们研究了mTOR参与T3的作用。结果表明，T3通过非基因组作用激活mTOR激酶。这些数据首次证明了T3信号通过mTOR级联到钙调磷酸酶抑制剂ZAKI-4α。少

We identified a thyroid hormone (T3)-responsive gene, ZAKI-4 in cultured human skin fibroblasts. It belongs to a family of genes that encode proteins containing a conserved motif. The motif binds to and inhibits calcineurin (CN). In this study, we identified three different ZAKI-4 transcripts, α, β1 and β2 in human brain by 5'-and 3'-RACE. The a transcript was identical to that we originally cloned and the other two were novel. The three transcripts are generated by alternative initiation and splicing from a single gene on the short arm of chromosome 6. It is predicted that β1 and β2 encode an identical protein product β, which differs from a in its N-terminus. Both isoforms associate with CN and inhibit its activity through an identical C-terminal region. An examination of expression profile of the three transcripts revealed that a transcript is expressed exclusively in brain, while b transcripts are expressed ubiquitously, most abundantly in brain, heart, skeletal muscle and kidney. … More It was also demonstrated that human skin fibroblasts express both α and β transcripts, raising a question which transcript is upregulated by T3. It was revealed that T3 markedly induced the expression of a isoform but not of β. This T3-mediated increase in the a isoform was associated with a significant decrease in endogenous CN activity. We further explored how T3 regulates the expression of a isoform in human skin fibroblasts. First, effect of calcineurin inhibitor FK506 and its analog rapamycin on T3-mdeiated regulation of ZAKI-4α was studied, because activation of CN was reported to cause an increased expression of a ZAKI-4 family gene, DSCR1. It was demonstrated that T3-mediated increase in ZAKI-4 expression was not inhibited by FK506 but completely abrogated by rapamycin. Since rapamycin is a specific inhibitor of mammalian target of rapamycin (mTOR), we investigated the involvement of mTOR in T3 action. It was demonstrated that T3 activates mTOR kinase through non-genomic action. These data for the first time demonstrated that T3 signaling cascade through mTOR to calcineurin inhibitor ZAKI-4α. Less