Institute of Molecular Medicine and Cell Research, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Faculty of Biology, University of Freiburg, Freiburg, Germany.
Int J Cancer. 2020 Apr 15;146(8):2229-2242. doi: 10.1002/ijc.32644. Epub 2019 Sep 18.
The transcription factor SNAIL1 is a master regulator of epithelial-to-mesenchymal transition (EMT), a process entailing massive gene expression changes. To better understand SNAIL1-induced transcriptional reprogramming we performed time-resolved transcriptome analysis upon conditional SNAIL1 expression in colorectal cancer cells. Gene set variation analyses indicated that SNAIL1 strongly affected features related to cell cycle and Wnt/β-Catenin signalling. This correlated with upregulation of LEF1, a nuclear binding partner of β-Catenin. Likewise, transcriptomes of cell lines and colorectal cancers, including poor-prognosis mesenchymal tumours, exhibit positively correlated SNAI1 and LEF1 expression, and elevated LEF1 levels parallel increased patient mortality. To delineate the functional contribution of LEF1 to SNAIL1-induced EMT, we used the CRISPR/Cas9 system to knock-out LEF1 in colorectal cancer cells, and to engineer cells that express LEF1 mutants unable to interact with β-Catenin. Both complete LEF1-deficiency and prevention of the β-Catenin-LEF1 interaction impaired the ability of SNAIL1 to elicit expression of an alternative set of Wnt/β-catenin targets, and to promote cancer cell invasion. Conversely, overexpression of wildtype, but not of mutant LEF1, stimulated alternative Wnt/β-Catenin target gene expression, and caused cell-cycle arrest. Moreover, like SNAIL1, LEF1 retarded tumour growth in xenotransplantations. Thus, LEF1 phenocopies SNAIL1 with respect to several critical aspects of EMT. Indeed, comparative transcriptomics suggested that 35% of SNAIL1-induced transcriptional changes are attributable to LEF1. However, LEF1 did not autonomously induce EMT. Rather, LEF1 appears to be a strictly β-Catenin-dependent downstream effector of SNAIL1. Apparently, SNAIL1 employs β-Catenin-LEF1 complexes to redirect Wnt/β-Catenin pathway activity towards pro-invasive and anti-proliferative gene expression.
转录因子 SNAIL1 是上皮间质转化 (EMT) 的主要调节因子，这是一个涉及大量基因表达变化的过程。为了更好地理解 SNAIL1 诱导的转录重编程，我们在结直肠癌细胞中条件性表达 SNAIL1 后进行了时间分辨的转录组分析。基因集变异分析表明，SNAIL1 强烈影响与细胞周期和 Wnt/β-连环蛋白信号相关的特征。这与核结合伴侣β-连环蛋白的 LEF1 的上调相关。同样，包括预后不良的间充质肿瘤在内的细胞系和结直肠癌的转录组显示 SNAI1 和 LEF1 的表达呈正相关，并且 LEF1 水平的升高与患者死亡率的增加平行。为了描绘 LEF1 对 SNAIL1 诱导的 EMT 的功能贡献，我们使用 CRISPR/Cas9 系统敲除结直肠癌细胞中的 LEF1，并构建表达不能与β-连环蛋白相互作用的 LEF1 突变体的工程细胞。完全缺失 LEF1 或阻止β-连环蛋白-LEF1 相互作用均会损害 SNAIL1 引发另一组 Wnt/β-连环蛋白靶基因表达并促进癌细胞侵袭的能力。相反，过表达野生型 LEF1（而非突变型 LEF1）可刺激替代 Wnt/β-连环蛋白靶基因的表达并引起细胞周期停滞。此外，与 SNAIL1 一样，LEF1 在异种移植中也会抑制肿瘤生长。因此，LEF1 在 EMT 的几个关键方面模拟了 SNAIL1。事实上，比较转录组学表明，SNAIL1 诱导的转录变化中有 35%归因于 LEF1。然而，LEF1 本身并不能自主诱导 EMT。相反，LEF1 似乎是 SNAIL1 的严格依赖β-连环蛋白的下游效应因子。显然，SNAIL1 利用β-连环蛋白-LEF1 复合物将 Wnt/β-连环蛋白途径的活性重新定向到促侵袭和抗增殖基因表达。
