It is well established that transforming growth factor-β (TGFβ) switches its function from being a tumor suppressor to a tumor promoter during the course of tumorigenesis, which involves both cell-intrinsic and environment-mediated mechanisms. We are interested in breast cancer cells, in which SMAD mutations are rare and interactions between SMAD and other transcription factors define pro-oncogenic events. Here, we have performed chromatin immunoprecipitation (ChIP)-sequencing analyses which indicate that the genome-wide landscape of SMAD2/3 binding is altered after prolonged TGFβ stimulation. De novo motif analyses of the SMAD2/3 binding regions predict enrichment of binding motifs for activator protein (AP)1 in addition to SMAD motifs. TGFβ-induced expression of the AP1 component JUNB was required for expression of many late invasion-mediating genes, creating a feed-forward regulatory network. Moreover, we found that several components in the WNT pathway were enriched among the late TGFβ-target genes, including the invasion-inducing WNT7 proteins. Consistently, overexpression of WNT7A or WNT7B enhanced and potentiated TGFβ-induced breast cancer cell invasion, while inhibition of the WNT pathway reduced this process. Our study thereby helps to explain how accumulation of pro-oncogenic stimuli switches and stabilizes TGFβ-induced cellular phenotypes of epithelial cells.

中文翻译：

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JUNB控制着TGFβ信号的前馈网络，加剧了乳腺癌的侵袭

公认的是，在肿瘤发生过程中，转化生长因子-β（TGFβ）将其功能从抑癌作用转变为肿瘤启动子，这涉及细胞内在和环境介导的机制。我们对乳腺癌细胞感兴趣，在乳腺癌细胞中，SMAD突变很少见，SMAD与其他转录因子之间的相互作用定义了促癌事件。在这里，我们进行了染色质免疫沉淀（ChIP）测序分析，这些分析表明，长时间的TGFβ刺激后，SMAD2 / 3结合的全基因组格局发生了变化。从头开始除SMAD基序外，SMAD2 / 3结合区的基序分析还预测了激活蛋白（AP）1结合基序的富集。TGFβ诱导的AP1组分JUNB的表达是许多晚期入侵介导基因的表达所必需的，从而建立了前馈调控网络。此外，我们发现WNT途径中的某些成分在晚期TGFβ靶基因中富集，包括诱导入侵的WNT7蛋白。一致地，WNT7A或WNT7B的过表达增强并增强了TGFβ诱导的乳腺癌细胞侵袭，而对WNT途径的抑制则减少了该过程。因此，我们的研究有助于解释促癌性刺激的积累如何转换和稳定TGFβ诱导的上皮细胞表型。