Instituto de Biomedicina (IBIOMED) and Departamento de Biología Molecular, University of León, University of Leon, Campus de Vegazana, Leon, Spain.
Research Programs Unit, Molecular Neurology, Biomedicum Stem Cell Center, University of Helsinki, Haartmaninkatu 8, Helsinki, Finland.
Cell Death Dis. 2017 Sep 7;8(9):e3034. doi: 10.1038/cddis.2017.432.
The generation of induced pluripotent stem cells (iPSCs) by somatic cell reprogramming holds great potential for modeling human diseases. However, the reprogramming process remains very inefficient and a better understanding of its basic biology is required. The mesenchymal-to-epithelial transition (MET) has been recognized as a crucial step for the successful reprogramming of fibroblasts into iPSCs. It has been reported that the p53 tumor suppressor gene acts as a barrier of this process, while its homolog p63 acts as an enabling factor. In this regard, the information concerning the role of the third homolog, p73, during cell reprogramming is limited. Here, we derive total Trp73 knockout mouse embryonic fibroblasts, with or without Trp53, and examine their reprogramming capacity. We show that p73 is required for effective reprogramming by the Yamanaka factors, even in the absence of p53. Lack of p73 affects the early stages of reprogramming, impairing the MET and resulting in altered maturation and stabilization phases. Accordingly, the obtained p73-deficient iPSCs have a defective epithelial phenotype and alterations in the expression of pluripotency markers. We demonstrate that p73 deficiency impairs the MET, at least in part, by hindering BMP pathway activation. We report that p73 is a positive modulator of the BMP circuit, enhancing its activation by DNp73 repression of the Smad6 promoter. Collectively, these findings provide mechanistic insight into the MET process, proposing p73 as an enhancer of MET during cellular reprogramming.
体细胞重编程产生诱导多能干细胞（iPSCs）在人类疾病建模方面具有巨大的潜力。然而，重编程过程仍然非常低效，需要更好地了解其基本生物学。间质到上皮的转变（MET）已被认为是将成纤维细胞成功重编程为 iPSCs 的关键步骤。据报道，p53 肿瘤抑制基因作为该过程的障碍，而其同源物 p63 则作为促进因素。在这方面，关于细胞重编程过程中第三个同源物 p73 的信息有限。在这里，我们获得了总 Trp73 敲除的小鼠胚胎成纤维细胞，无论是否存在 Trp53，并检查了它们的重编程能力。我们表明，p73 是由 Yamanaka 因子进行有效重编程所必需的，即使没有 p53 也是如此。缺乏 p73 会影响重编程的早期阶段，损害 MET，并导致成熟和稳定阶段发生改变。因此，获得的 p73 缺陷型 iPSCs 具有有缺陷的上皮表型和多能性标志物表达的改变。我们证明，p73 缺乏通过阻碍 BMP 途径的激活至少部分地损害了 MET。我们报告说，p73 是 BMP 回路的正调节剂，通过抑制 DNp73 对 Smad6 启动子的抑制来增强其激活。总的来说，这些发现为 MET 过程提供了机制上的见解，提出 p73 是细胞重编程过程中 MET 的增强子。
