p53 regulates cell cycle and microRNAs to promote differentiation of human embryonic stem cells.
p53 regulates cell cycle and microRNAs to promote differentiation of human embryonic stem cells.
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DOI：
10.1371/journal.pbio.1001268
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发表时间：
2012
期刊：
影响因子：
9.8
通讯作者：
Barton MC
中科院分区：
文献类型：
--
作者：
Jain AK;Allton K;Iacovino M;Mahen E;Milczarek RJ;Zwaka TP;Kyba M;Barton MC
多项研究表明，肿瘤抑制因子p53是去分化的障碍;这是否是严格由于抑制增殖仍然是一个争论的主题。在这里，我们表明，p53在促进人类胚胎干细胞（hESC）的分化和反对自我更新的特定靶基因和microRNA的调节中发挥着积极的作用。与小鼠胚胎干细胞相反，hESC中的p53在细胞核中维持在低水平，尽管处于脱乙酰化的非活性状态。响应于视黄酸，CBP/p300在赖氨酸373处乙酰化p53，这导致从E3-泛素连接酶HDM 2和TRIM 24解离。稳定的p53结合CDKN 1A以建立细胞周期的G1期而不激活细胞死亡途径。与此同时，p53激活miR-34 a和miR-145的表达，这反过来又抑制干细胞因子OCT 4、KLF 4、LIN 28 A和SOX 2，并防止向多能性倒退。p53水平的诱导是一个关键步骤：RNA干扰介导的p53敲低延迟分化，而p53的负调节因子的耗竭或p53的异位表达产生hESC的自发分化，独立于视黄酸。p53 R175 H是一种不结合DNA或调节转录的p53突变形式，其异位表达未能诱导分化。这些研究强调了p53调控网络在决定人类干细胞状态中的重要性。生物体中的大多数细胞类型都是由胚胎干细胞（ESC）产生的，胚胎干细胞能够增殖无限次，并有潜力产生该生物体的任何类型的细胞（这种能力称为多能性）。为了保持这些特性，ESCs必须保持在增殖状态，这是通过多种因素的协作来实现的。在分化的细胞中表达这些因子的组合可以产生ESC样品质;这些诱导多能干细胞（iPSC）然后可以像ESC一样发挥功能。先前的研究表明，p53通常以其通过调节细胞周期和细胞死亡途径来维持基因组完整性的作用而闻名，也可以在iPSC的产生过程中作为重编程成体细胞的屏障;这是否严格归因于增殖的抑制仍然是一个争论的主题。在这里，我们表明，p53在积极促进人类胚胎干细胞（hESCs）的分化中起着重要作用。我们发现，在分化之前，p53在hESC中以非常低的水平表达，由两个负调节因子HDM 2和TRIM 24控制，这两个负调节因子触发p53降解。在诱导分化时，p53的赖氨酸373被乙酰化，这破坏了与负调节因子的现有相互作用，从而允许p53的稳定和活化。活性p53反过来促进细胞周期调节因子p21的表达，以减缓hESC细胞周期;细胞周期的差距（G1）期细胞积聚，阻止分裂。与此同时，p53激活特定的microRNA，miR-34 a和miR-145，抑制几种干细胞因子的表达，并防止分化的细胞倒退到多能性。我们的研究结果突出了p53在决定人类干细胞状态中的新功能。
Multiple studies show that tumor suppressor p53 is a barrier to dedifferentiation; whether this is strictly due to repression of proliferation remains a subject of debate. Here, we show that p53 plays an active role in promoting differentiation of human embryonic stem cells (hESCs) and opposing self-renewal by regulation of specific target genes and microRNAs. In contrast to mouse embryonic stem cells, p53 in hESCs is maintained at low levels in the nucleus, albeit in a deacetylated, inactive state. In response to retinoic acid, CBP/p300 acetylates p53 at lysine 373, which leads to dissociation from E3-ubiquitin ligases HDM2 and TRIM24. Stabilized p53 binds CDKN1A to establish a G1 phase of cell cycle without activation of cell death pathways. In parallel, p53 activates expression of miR-34a and miR-145, which in turn repress stem cell factors OCT4, KLF4, LIN28A, and SOX2 and prevent backsliding to pluripotency. Induction of p53 levels is a key step: RNA-interference-mediated knockdown of p53 delays differentiation, whereas depletion of negative regulators of p53 or ectopic expression of p53 yields spontaneous differentiation of hESCs, independently of retinoic acid. Ectopic expression of p53R175H, a mutated form of p53 that does not bind DNA or regulate transcription, failed to induce differentiation. These studies underscore the importance of a p53-regulated network in determining the human stem cell state. Most cell types in an organism are generated from embryonic stem cells (ESCs), which are able to proliferate an unlimited number of times and have the potential to produce any kind of cell of that organism (this ability is called pluripotency). In order to maintain these properties, ESCs have to remain in a proliferate state, which is achieved by the collaboration of several factors. Expressing combinations of these factors in differentiated cells can result in ESC-like qualities; these induced pluripotent stem cells (iPSCs) can then function like ESCs. Previous studies suggested that p53, generally known for its roles in maintaining genomic integrity by regulating cell cycle and cell death pathways, also acts as a barrier to reprogramming adult cells during the creation of iPSCs; whether this is strictly due to repression of proliferation remains a subject of debate. Here, we show that p53 plays a significant role in actively promoting differentiation of human ESCs (hESCs). We find that, prior to differentiation, p53 is expressed at very low levels in hESCs, held in check by two negative regulators, HDM2 and TRIM24, that trigger p53 degradation. Upon induction of differentiation, lysine 373 of p53 is acetylated, and this disrupts the existing interactions with negative regulators, thus allowing stabilization and activation of p53. Active p53 in turn promotes expression of the cell cycle regulator p21 to slow down the hESC cell cycle; cells in the gap (G1) phase of the cell cycle accumulate, preventing division. In parallel, p53 activates specific microRNAs, miR-34a and miR-145, that inhibit the expression of several stem cell factors and prevent differentiated cells from backsliding to pluripotency. Our results highlight a novel function of p53 in determining the human stem cell state.
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