β-Catenin-Independent Activation of TCF1/LEF1 in Human Hematopoietic Tumor Cells through Interaction with ATF2 Transcription Factors
β-Catenin-Independent Activation of TCF1/LEF1 in Human Hematopoietic Tumor Cells through Interaction with ATF2 Transcription Factors
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DOI：
10.1371/journal.pgen.1003603
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发表时间：
2013-08-01
期刊：
影响因子：
4.5
通讯作者：
Aaronson, Stuart A.
中科院分区：
文献类型：
--
作者：
Grumolato, Luca;Liu, Guizhong;Aaronson, Stuart A.
Wnt 信号传导在胚胎发育和干细胞维持中的作用已得到充分证实，导致该通路组成性上调的畸变在几种类型的人类癌症中很常见。在配体介导的激活后，Wnt 受体促进 β-连环蛋白的稳定，β-连环蛋白易位到细胞核并与转录因子的 T 细胞因子/淋巴增强因子 (TCF/LEF) 家族结合，从而调节 Wnt 靶基因的表达。当不与 β-连环蛋白结合时，TCF/LEF 蛋白被认为充当转录抑制因子。使用特定的慢病毒报告基因，我们鉴定了在缺乏 β-连环蛋白稳定的情况下表现出组成型 TCF/LEF 转录激活的造血肿瘤细胞。由诱导型显性失活 TCF4 (DN-TCF4) 介导的 TCF/LEF 活性抑制可抑制细胞生长和 Wnt 靶基因的表达。此外，TCF1 和 LEF1（而非 TCF4）的表达刺激某些人类细胞系中的 TCF/LEF 报告基因活性，与 β-连环蛋白无关。通过体内互补方法，缺乏与β-连环蛋白结合能力的TCF1突变体诱导非洲爪蟾胚胎轴复制（Wnt激活的标志）以及Wnt靶基因Xnr3的表达。通过生成不同的 TCF1-TCF4 融合蛋白，我们鉴定了三个不同的 TCF1 结构域，它们参与该转录因子的不依赖于 β-连环蛋白的活性。 TCF1 和 LEF1 与转录因子激活转录因子 2 (ATF2) 家族的成员在物理上相互作用并在功能上协同作用。此外，淋巴瘤细胞中 ATF2 表达的敲低反映了 DN-TCF4 对与 Wnt 通路相关的靶基因表达和细胞生长的抑制作用。总之，我们的研究结果表明，通过与 ATF2 因子的相互作用，TCF1/LEF1 在缺乏 β-连环蛋白稳定的情况下促进造血系统恶性肿瘤的生长，从而建立了一种不同于典型 Wnt 信号传导相关的 TCF1/LEF1 转录活性的新机制。
The role of Wnt signaling in embryonic development and stem cell maintenance is well established and aberrations leading to the constitutive up-regulation of this pathway are frequent in several types of human cancers. Upon ligand-mediated activation, Wnt receptors promote the stabilization of beta-catenin, which translocates to the nucleus and binds to the T-cell factor/lymphoid enhancer factor (TCF/LEF) family of transcription factors to regulate the expression of Wnt target genes. When not bound to b-catenin, the TCF/LEF proteins are believed to act as transcriptional repressors. Using a specific lentiviral reporter, we identified hematopoietic tumor cells displaying constitutive TCF/LEF transcriptional activation in the absence of b-catenin stabilization. Suppression of TCF/LEF activity in these cells mediated by an inducible dominant-negative TCF4 (DN-TCF4) inhibited both cell growth and the expression of Wnt target genes. Further, expression of TCF1 and LEF1, but not TCF4, stimulated TCF/LEF reporter activity in certain human cell lines independently of b-catenin. By a complementary approach in vivo, TCF1 mutants, which lacked the ability to bind to b-catenin, induced Xenopus embryo axis duplication, a hallmark of Wnt activation, and the expression of the Wnt target gene Xnr3. Through generation of different TCF1-TCF4 fusion proteins, we identified three distinct TCF1 domains that participate in the beta-catenin-independent activity of this transcription factor. TCF1 and LEF1 physically interacted and functionally synergized with members of the activating transcription factor 2 (ATF2) family of transcription factors. Moreover, knockdown of ATF2 expression in lymphoma cells phenocopied the inhibitory effects of DN-TCF4 on the expression of target genes associated with the Wnt pathway and on cell growth. Together, our findings indicate that, through interaction with ATF2 factors, TCF1/LEF1 promote the growth of hematopoietic malignancies in the absence of b-catenin stabilization, thus establishing a new mechanism for TCF1/LEF1 transcriptional activity distinct from that associated with canonical Wnt signaling.