Expression of nodal, lefty-A, and lefty-B in undifferentiated human embryonic stem cells requires activation of Smad2/3
Expression of nodal, lefty-A, and lefty-B in undifferentiated human embryonic stem cells requires activation of Smad2/3
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DOI：
10.1074/jbc.m404979200
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发表时间：
2004-10-22
影响因子：
4.8
通讯作者：
Besser, D
中科院分区：
文献类型：
--
作者：
Besser, D
人胚胎干细胞在条件培养基或非条件培养基中分别生长时将保持未分化或经历分化。控制未分化状态维持的因子和信号事件还没有很好地表征，它们的鉴定是非常重要的。基于全球表达分析的数据，我们着手确定在分化过程的早期阶段受到调控的基因和控制它们的信号通路。这项研究表明，Nodal和Nodal信号传导的抑制剂lefty-A和lefty-B在分化后很早就下调。这些基因在未分化细胞中的高表达通过激活素连接激酶（ALK）4/5/7下游的转录因子Smad 2/3的激活来维持。用激活素A处理分化细胞导致Smad 2/3的激活和nodal、lefty-A和lefty-B的表达，而激酶抑制剂SB-431542抑制ALK 4/5/7阻断Smad 2/3的激活和这些基因在未分化状态下的表达。此外，当细胞通过用GSK 3抑制剂BIO处理而保持未分化时，nodal、lefty-A和lefty-B的高表达也需要ALK 4/5/7的活化。相反，通过ALK 2/3/6导致Smad 1/5/8活化的BMP信号传导在未分化细胞中被阻断，并在分化时被活化。综上所述，这些观察结果表明Smad 2/3在未分化的hESC中被激活，并且是控制Nodal信号传导的基因表达所必需的。此外，在抑制GSK 3（Wnt信号传导的标志）和激活素/Nodal途径之间似乎存在串扰。
Human embryonic stem cells will remain undifferentiated or undergo differentiation when grown in conditioned or non-conditioned medium, respectively. The factors and signaling events that control the maintenance of the undifferentiated state are not well characterized and their identification is of major importance. Based on the data from global expression analyses, we set out to identify genes and the signaling pathways controlling them that are regulated in the early phase of the differentiation process. This study shows that nodal and the inhibitors of Nodal signaling, lefty-A and lefty-B, are down-regulated very early upon differentiation. High expression of these genes in undifferentiated cells is maintained by activation of the transcription factor Smad2/3, downstream of the activin-linked kinases (ALK) 4/5/7. Treatment of differentiating cells with Activin A leads to activation of Smad2/3 and expression of nodal, lefty-A and lefty-B, while inhibition of ALK4/5/7 by the kinase inhibitor SB-431542 blocks activation of Smad2/3 and expression of these genes in the undifferentiated state. In addition, when cells are maintained undifferentiated by treatment with the GSK3-inhibitor, BIO, high expression of nodal, lefty-A, and lefty-B also requires activation of ALK4/5/7. Conversely, BMP signaling leading to Smad1/5/8 activation via ALK2/3/6 is blocked in undifferentiated cells and becomes activated upon differentiation. Taken together, these observations establish that Smad2/3 is activated in undifferentiated hESCs and required for the expression of genes controlling Nodal signaling. Moreover, there appears to be cross-talk between inhibition of GSK3, a hallmark of Wnt signaling and the Activin/Nodal pathway.