BRG1/BRM异常切换促肝细胞恶性转变机制研究

Both BRM and BRG1 are the catalytic subunits of the SWI/SNF complex, which acts crucial role in chromatin remodeling and transcriptional regulation. BRG1 often highly expresses in non-mature hepatocytes including fetal liver and hepatic progenitors in the mature liver, on the contrary, BRM always highly expresses in mature hepatocytes. The relay expressing manner of BRM and BRG1 coordinately controls liver differentiation and function. We have found that the liver selective deletion of BRG1 alone does not disturb the development and regeneration of the liver, although both of them had undergone a progress of intensive chromatin remodeling. However, in human and mouse liver cancer (HCC) tissues, BRM was found significantly decreased while BRG1 was significantly increased, suggesting that the disorder expression of BRM/BRG1 is closely related to the occurrence of HCC. Intriguingly, when induced by DEN injection, BRG1 deficient mice were more likely to be tumorigenic and showed early lung metastases. SWI/SNF is involved in the transcriptional regulation of many genes by controlling chromatin remodeling, but the target genes regulated by BRM/BRG1 subunits remain unclear. In this study, we will generate BRM or/and BRG1 knockout mice and treat the mice with carcinogenic chemicals or induce spontaneous HCC tumors by cross-breeding with Mdr2-/- mice, and then explore the roles of BRM/BRG1 in hepatic proliferation, differentiation, epithelial-mesenchymal transition as well as malignant transformation of hepatocytes. Our work will be helpful to provide experimental foundation for elucidating the mechanism of HCC and reasonable intervention.

BRM/BRG1是关键染色体重构复合物SWI/SNF的催化活性亚基，通常BRG1高表达于非成熟肝细胞而BRM正好相反，二者呈“接力”表达现象，协调控制着肝脏分化和各种功能。但我们发现BRG1单独缺失对肝脏发育及再生并无影响，尽管两者都经历了剧烈的染色质重构过程。然而，在人和小鼠肝癌（HCC）组织中，BRM显著下降而BRG1明显上升，提示二者表达时象紊乱与HCC发生密切相关，其功能并不能完全互补。有趣的是BRG1敲除小鼠在DEN诱导下更易成瘤并早发肺转移。SWI/SNF通过染色质构象参与众多基因的转录调控，但BRM/BRG1亚基调控的靶基因并不清楚。本研究将通过BRM/BRG1单独和联合敲除小鼠，建立化学诱导及Mdr2-/-自发HCC小鼠模型，探究BRM/BRG1在肝细胞增殖、分化、EMT及恶性转化中的作用及分子机制，为阐明HCC发生机制及合理干预提供实验基础。

肝脏疾病是危害国人健康的主要疾病，其发生与基因表达异常密切相关；SWI/SNF复合体，作为关键染色质重构复合物之一，除改变染色质构象的功能外，还具有调控基因表达的生物学功能。目前已报道SWI/SNF复合体关键亚基的突变与肿瘤发生密切相关，然而该复合物在肝癌及胆管癌中的作用并不清楚。因此，我们首先利用数据库资源，探究了SWI/SNF复合体15个关键亚基在HCC患者中的表达模式以及与患者预后的相关性。研究结果显示，除BRM外，各亚基均在HCC肿瘤组织中高表达；通过风险预测模型构建和预后分析，我们发现，根据ARID1A、SMARCC1、SMARCD1及ACTL6A四个亚基的表达情况，可作为HCC患者预后的评价指标；此外，通过细胞、分子生物学实验，我们深入探索了SMARCD1调控HCC发生、发展的分子机制。Brg1作为SWI/SNF复合体的关键ATPase亚基之一，在肝脏发育早期高表达，肝脏发育成熟后，表达主要集中于肝脏前体细胞或胆管细胞。当肝脏受到慢性损伤时，会出现大量的前体细胞增生，同时伴随肝纤维化的发生，即胆管反应。通过构建Brg1胆管细胞特异性敲除小鼠，我们发现Brg1的缺失大大减弱了前体细胞的扩增，降低细胞干性相关基因，如SOX9、EpCAM等的表达。在TAA构建的肝内胆管癌模型中，特异性敲除或靶向抑制Brg1可显著延缓肝内胆管癌的发生；最后通过临床标本检测，我们发现Brg1高表达患者预后更差。在本基金的资助下，我们深入探究了SWI/SNF复合体在肝脏疾病，尤其是肝癌和胆管癌，中的表达情况；同时重点深入研究了SMARCD1及Brg1在HCC和ICC演进过程中的作用及分子机制，为临床治疗肝脏肿瘤提供了新靶点和思路。