Smad7的转录调控作用与分子机制研究

Smad7 is a key negative regulator of TGF-β signaling. It has been shown that both TGF-β and Smad7 play critical roles in the progression of heptocellular carcinoma. Previouly we found that Smad7 could bind DNA in the nucleus and interfere with the TGF-β-induced gene transcription, implicating that Smad7 may act as a transcription factor and regulate gene expression. However, the mechanisms whereby Smad7 regulate gene transcription remain unclear, and the relationship between Smad7 and TGF-β/Smads in gene transcription needs further investigation. To address these questions, using RNA-Seq technology, we have systematically identified the target genes of TGF-β and Smad7 in hepatocellular carcinoma cells. In this proposal, we plan to carry out ChIP-Seq experiments and further identify the DNA-binding sites of Smad7 and Smad3 on a genome-wide scale in hepatoma cells. By integrating the RNA-Seq and ChIP-Seq data, we hope to understand the role of Smad7 in gene transcription regulation and the underlying mechanisms, and the relationship between Smad7 and Smad3 in binding DNA and gene transcription regulation at the whole genome level. Finally, we will also explore whether Smad7 could regulate the expression of some of its target genes independently of TGF-β. We hope that our study will shed light on the function of Smad7 in the progression of heptocellular carcinoma.

Smad7是TGF-β信号通路的关键负调控因子之一，在肝癌的发生与发展中具有重要作用。前期我们发现Smad7能在细胞核内结合DNA并抑制TGF-β诱导的基因转录，提示Smad7可能作为转录因子调控基因表达。但是，Smad7调控基因转录的分子机制仍然不清楚；在转录水平，Smad7与TGF-β/Smad的关系有待于更深入的研究。立足于解决这些问题，前期我们使用转录组测序技术鉴定了TGF-β和Smad7在肝癌细胞中的靶基因。在本申请中，我们拟进一步通过ChIP-Seq技术高通量鉴定Smad7和Smad3在在肝癌细胞基因组上的结合位点；结合转录组测序数据，重点研究Smad7作为转录因子介导基因转录的作用与分子机制，及其在全基因组范围内对TGF-β/Smad3诱导基因转录的影响；并探讨Smad7能否独立于TGF-β调控基因转录。我们希望本研究有助于理解Smad7作为转录因子在肝癌中的功能。

信号调控对于TGF-β发挥多种生理和病理功能具有重要意义。Smad7蛋白是TGF-β信号的关键负调控因子之一，但对其分子功能与生理功能的了解仍然在不断深化之中。本项目阐述了Smad7蛋白在Smad蛋白水平调控TGF-β信号的一个新机制，相关成果于2016年发表在J Biol Chem杂志；发现CXXC5蛋白是TGF-β信号的正反馈调控因子，它能在肝癌细胞中促进TGF-β诱导的靶基因表达和细胞生长抑制，从而抑制肝癌发生，相关成果于2018年发表在J Mol Cell Biol杂志；此外，项目主持人作为共同客座编辑，为Acta Biochim Biophys Sin杂志组织一期TGF-β细胞信号转导专刊，于2018年第一期出版。本项目共发表SCI论文4篇，相关成果有助于理解Smad7和CXXC5蛋白在TGF-β信号调控中的作用与机制，对于理解肝癌发生的分子机制有较大贡献，为后续转化研究提供了基础；此外，TGF-β专刊出版促进了国内外同行的交流，有利于提升国内专业期刊的学术影响力和国际影响力。