Wnt信号-HNF4α组成双负反馈环在肝细胞肝癌上皮-间质转化（EMT）形成中的作用机制研究

Wnt signaling relates to EMT in several cancer types; however, this relationship and the underlying molecular mechanism in HCC is not completely defined. Moreover, the regulation of Wnt signaling during EMT process in HCC also remains largely unknown, which reflects the cellular context dependence and tissue specificity. Our previous experiments of this proposal indicated that Wnt signaling may mediate EMT phenotypes and inhibit HNF4α expression via Slug and Snail. On the other hand,HNF4α was found to associates with TCF4 to compete with β-Catenin, but facilitate transcription co-repressor activities, hence inhibit Wnt signaling induced EMT. Moreover, HNF4α may control the switch between the transcriptional and adhesive functions of β-catenin. In this proposal, we will systematically study the mechanism and function of the Double-Negative Feedback Loop between Wnt Signaling and HNF4α, in molecular, cellular, rat tumor model and clinical tumor sample levels. Our study will reveal a complex association between HNF4α and the central EMT driving signaling and highlights the role of inhibiting Wnt signaling or restoring HNF4α in reverting HCC malignant phenotype.

Wnt信号在多种肿瘤细胞中介导EMT过程，然而在HCC细胞EMT过程中的下游分子机理仍然不十分明确，并且Wnt信号在HCC细胞EMT过程中的调节机制也不清楚，这反映了细胞背景的差异性与组织/肿瘤特异性。我们的前期实验表明，Wnt信号通过Slug以及Snail介导HCC细胞EMT表型并抑制HNF4α的表达；另一方面，HNF4α能够与β-catenin竞争性结合TCF4，从而抑制Wnt信号输出。这样就形成一个"Wnt信号-HNF4α双负反馈环"，从而在Wnt信号激活的HCC细胞EMT过程中，Wnt信号能够解除HNF4α对于自身的抑制而发挥作用。本课题将从分子、细胞、大鼠肝癌模型以及临床标本分析等几个方面，系统研究"Wnt信号-HNF4α双负反馈环"形成机理以及在HCC细胞EMT形成中的作用。

Wnt-β-catenin信号通路参与多种癌症表皮到间质的转化过程（EMT）；然而Wnt-β-catenin信号通路是如何参与肝癌的形成，下游分子机理到底是什么还没有完全研究清楚。HNF4α是肝细胞系分化的重要的因子，而且还是一个肝癌细胞潜在的EMT调控因子。然而，HNF4α在肝分化中的作用机制和抑制EMT的分子机制没有研究清楚。在我们的研究中，我们在肝癌细胞EMT的过程中系统的探索了Wnt-β-catenin信号通路和HNF4α的相互关系。我们的研究结果表明在肝癌细胞EMT中，Wnt-β-catenin信号通路通过Snail和Slug负调控HNF4α的表达。反向的，HNF4α与β-catenin竞争结合TCF4，抑制EMT有关的Wnt-β-catenin的靶基因的表达。HNF4α可以调控β-catenin作为转录因子和粘附因子之间的功能转换。过表达HNF4α可以逆转Wnt-β-catenin信号通路诱导的EMT表型。最后，我们在大鼠肿瘤模型中验证了Wnt-β-catenin信号通路与HNF4α之间的调控模型。我们的研究得出在肝癌的EMT中，无论在体外还是体内都存在一个HNF4α与Wnt-β-catenin信号通路之间双向负反馈调节环。通过抑制Wnt-β-catenin信号通路或者表达HNF4α可以阻止肝癌细胞的EMT，这为治疗肝癌侵袭带来了新思路。