An alternative splicing switch in FLNB promotes the mesenchymal cell state in human breast cancer.
An alternative splicing switch in FLNB promotes the mesenchymal cell state in human breast cancer.
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DOI：
10.7554/elife.37184
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发表时间：
2018-07-30
期刊：
影响因子：
7.7
通讯作者：
Hahn WC
中科院分区：
文献类型：
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作者：
Li J;Choi PS;Chaffer CL;Labella K;Hwang JH;Giacomelli AO;Kim JW;Ilic N;Doench JG;Ly SH;Dai C;Hagel K;Hong AL;Gjoerup O;Goel S;Ge JY;Root DE;Zhao JJ;Brooks AN;Weinberg RA;Hahn WC
mRNA前体的选择性剪接代表了关键的基因表达调控步骤，并允许产生具有不同功能的不同蛋白质产物。在基因组规模的表达筛选诱导上皮间质转化（EMT），我们发现了一个惊人的丰富的RNA结合蛋白。我们验证了QKI和RBFOX 1是诱导中间间充质细胞状态和增加致瘤性的必要和充分条件。利用RNA-seq和eCLIP分析，我们发现QKI和RBFOX 1协同调节肌动蛋白结合蛋白FLNB的剪接和功能，FLNB在EMT的调节中起着因果作用。具体而言，FLNB外显子30的跳跃通过释放FOXC 1转录因子诱导EMT。此外，FLNB外显子30的跳跃与基底样乳腺癌患者样品中的EMT基因特征密切相关。这些观察结果确定了一种特定的剪接失调，它调节肿瘤细胞的可塑性，并经常在人类癌症中观察到。随着人体的发育，无数的细胞从一种状态转变为另一种状态。两种重要的细胞状态被称为上皮细胞和间充质细胞。上皮状态的细胞往往紧密连接并形成屏障，如皮肤细胞。间充质状态的细胞组织松散，移动更多，并组成结缔组织。一些细胞通过上皮-间充质转化（简称EMT）在这些状态之间交替。如果没有这种转变，某些器官就不会发育，伤口也不会愈合。然而，癌细胞也利用这种转变扩散到身体的远处。这类癌症通常是最具侵略性的，因此也是最致命的。上皮细胞向间充质细胞的转化以可逆的方式动态调节。例如，某些蛋白质的基因可能只在上皮状态下活跃，并通过打开其他“上皮基因”来进一步加强这种状态。或者，mRNA分子（DNA和蛋白质之间的中间分子）的加工可能存在差异，导致上皮细胞和间充质细胞产生不同的蛋白质。Li，Choi等人想知道数千个人类基因中的哪一个可以赋予上皮状态细胞间充质特征。更好地理解这个开关可以帮助预防经历上皮细胞向间充质细胞转化的癌症。Li，Choi等人在人类乳腺癌细胞中进行的一项大规模实验中发现，一组结合和修饰mRNA分子的蛋白质对上皮细胞向间充质细胞的转化非常重要。特别是两种蛋白质促进了这种转变，最有可能的是通过与第三种蛋白质FLNB的mRNA结合并去除其中的一小部分。FLNB通常可以阻止上皮细胞向间充质细胞的转变，但是由较短的mRNA编码的较小的蛋白质通过开启“间充质基因”促进了这种转变。不同FLNB蛋白之间的这种转换发生在一些更具侵袭性的乳腺癌中，这些乳腺癌也含有间充质细胞。找出特定癌症中产生的FLNB蛋白质可以提供其侵袭性的指示。此外，寻找可以靶向mRNA结合蛋白或FLNB的药物可能有一天会导致一些最具侵袭性的乳腺癌的新治疗方法。
Alternative splicing of mRNA precursors represents a key gene expression regulatory step and permits the generation of distinct protein products with diverse functions. In a genome-scale expression screen for inducers of the epithelial-to-mesenchymal transition (EMT), we found a striking enrichment of RNA-binding proteins. We validated that QKI and RBFOX1 were necessary and sufficient to induce an intermediate mesenchymal cell state and increased tumorigenicity. Using RNA-seq and eCLIP analysis, we found that QKI and RBFOX1 coordinately regulated the splicing and function of the actin-binding protein FLNB, which plays a causal role in the regulation of EMT. Specifically, the skipping of FLNB exon 30 induced EMT by releasing the FOXC1 transcription factor. Moreover, skipping of FLNB exon 30 is strongly associated with EMT gene signatures in basal-like breast cancer patient samples. These observations identify a specific dysregulation of splicing, which regulates tumor cell plasticity and is frequently observed in human cancer. As the human body develops, countless cells change from one state into another. Two important cell states are known as epithelial and mesenchymal. Cells in the epithelial state tend to be tightly connected and form barriers, like skin cells. Mesenchymal state cells are loosely organized, move around more and make up connective tissues. Some cells alternate between these states via an epithelial-to-mesenchymal transition (EMT for short) and back again. Without this transition, certain organs would not develop and wounds would not heal. Yet, cancer cells also use this transition to spread to distant sites of the body. Such cancers are often the most aggressive, and therefore the most deadly. The epithelial-to-mesenchymal transition is dynamically regulated in a reversible manner. For example, the genes for some proteins might only be active in the epithelial state and further reinforce this state by turning on other ‘epithelial genes’. Alternatively, there might be differences in the processing of mRNA molecules – the intermediate molecules between DNA and protein – that result in the production of different proteins in epithelial and mesenchymal cells. Li, Choi et al. wanted to know which of the thousands of human genes can endow epithelial state cells with mesenchymal characteristics. A better understanding of the switch could help to prevent cancers undergoing an epithelial-to-mesenchymal transition. From a large-scale experiment in human breast cancer cells, Li, Choi et al. found that a group of proteins that bind and modify mRNA molecules are important for the epithelial-to-mesenchymal transition. Two proteins in particular promoted the transition, most likely by binding to the mRNA of a third protein called FLNB and removing a small piece of it. FLNB normally works to prevent the epithelial-to-mesenchymal transition, but the smaller protein encoded by the shorter mRNA promoted the transition by turning on ‘mesenchymal genes’. This switching between different FLNB proteins happens in some of the more aggressive breast cancers, which also contain mesenchymal cells. Finding out which FLNB protein is made in a given cancer may provide an indication of its aggressiveness. Also, looking for drugs that can target the mRNA-binding proteins or FLNB may one day lead to new treatments for some of the most aggressive breast cancers.