SWI/SNF染色质重塑复合物成分ARID1A异常在肝癌代谢重编程的作用及分子机制研究

Inactivation of tumor suppressor genes (TSGs), which could be triggered by genetic and epigenetic events, such as DNA mutations, insertion and deletion (indel), and epigenetic modification, play important roles in initiation and progression of hepatocellular carcinoma (HCC). In addition to the deregulated cellular signaling pathways, these TSGs and oncogenes also lead to the altered cellular metabolisms, metabolic reprogramming, as the consequence of the genetic and epigenetic mutations. The altered cellular metabolisms are characterized by lipid accumulation, hepatic steatosis and related hepatitis, similar to non alcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH), which are frequently associated with HCC development. However, the underlying molecular mechanisms by which the metabolic reprogramming contributes to HCC tumorigenesis and progression still remain obscure and should be explored. Very interestingly, our laboratory previously demonstrated that some genes, including ARID1A and other members encoding the subunits of SWI/SNF chromatin remodeling complex, are frequently mutated in hepatitis B virus (HBV)-related HCC. These genes encoding SWI/SNF complex, which also have been frequently found in many cancers, including cancers from gastrointestinal tract, lung cancer, kidney, bladder and ovary, represent the new type of TSGs. Herein, it should be pointed out that we generated hepatocyte-specific Arid1a knockout (Arid1aLKO) mice by crossing mice carrying loxP-flanked Arid1a exon 8 alleles (Arid1af/f) with albumin promoter-Cre transgenic mice. Significantly, the hepatocyte-specific Arid1a deficiency results in the spontaneous hepatic steatosis, steatohepatitis, mitochondrial damage, cell dysplasia and finally HCC development, along with the deregulated genes related to glucose, lipid metabolism, and fatty acid oxidation, as well as the increased reactive oxygen species (ROS) generation, suggesting that ARID1A may play the crucial role in controlling metabolism reprogramming process for cancer development, although the underlying mechanisms is unclear. In the planning project, we aim to elucidate the underlying mechanisms by which the altered ARID1A due to somatic mutations (high frequent mutations in HCC) leads to the metabolic and epigenetic reprogramming, and their role in HCC initiation and progression, based on the effect of normal SWI/SNF complex on glucose, lipid mechanism, fatty acid oxidation, and mitochondrion. Furthermore, our study is to develop the new strategies for the HCC prevention and therapy by modulating metabolism and chromatin remodeling based on molecular classification, through comparing the metabolic and epigenetic changes among liver-specific Arid1a, Tp53 and PTEN deficient mice.

肝癌发生发展涉及癌基因和抑癌基因突变，除导致分子信号异常外，也导致细胞代谢紊乱，脂肪沉积和脂肪性肝炎成为特征之一，但其作用和分子机制不清楚。最近我们发现编码SWI/SNF染色质重塑复合物成分的ARID1A基因在肝癌存在高频率突变；肝脏ARID1A特异剔除小鼠发生脂肪性肝炎、脂质和糖代谢基因表达失衡、线粒体异常以及肝癌发生。目前，ARID1A控制代谢过程的机制不清楚，其异常导致的细胞代谢重编程特征及对肿瘤作用和分子机制有待阐明。本课题拟在阐述肝脏ARID1A调控糖、脂、线粒体等代谢过程的遗传和表观遗传学机制基础上，利用体内外模型研究ARID1A异常导致的细胞代谢重编程特征、SWI/SNF染色质重塑复合物改变和染色质修饰变化及对肝癌细胞性状的影响; 在揭示ARID1A异常导致代谢紊乱和染色质修饰异常特征基础上，探讨靶向代谢和染色质修饰方案对肝癌防疗作用,为基于分子分型的肝癌治疗奠定理论支撑。

本课题根据前期发现ARID1A在人类肝癌样本高频率失活性突变；Arid1a缺失可以导致小鼠脂质代谢异常，脂肪性肝炎和肝癌发生。因此，本课题拟利用体内外模型研究SWI/SNF染色质重塑复合物成分ARID1A在肿瘤细胞代谢重编程及对肿瘤发生发展的作用和机制，并与正常肝脏生理状态下SWI/SNF染色质重塑复合物调节模式进行对比分析，探讨ARID1A对代谢相关基因包括糖代谢、脂质代谢、线粒体三羧酸循环代谢和脂肪酸氧化等代谢相关基因表达调控的影响; 鉴定突变后导致的关键代谢重编程特征和染色质重塑修饰特征及对肝癌发生发展的影响；并评价靶向代谢和表观遗传修饰相关分子对肝癌治疗的作用。通过本项目的实施，发现肝脏特异性Arid1a缺失降低了小鼠对胰岛素的敏感性, 导致了脂质在肝脏细胞累积, 同时也加剧了高脂饮食（HFD）诱导的小鼠脂肪性肝炎。在分子机制上，发现Arid1a缺失直接导致胰岛素信号传递受阻以及损害脂肪酸氧化过程。在分子遗传机制上，揭示了ARID1A调控代谢的新机制：ARID1A一方面通过调控表观遗传调控方式，包括改变染色质可接近性及降低H3K4me3在关键酶处的修饰作用来调控脂肪酸氧化过程；另一方面通过降低调控脂肪酸氧化关键性转录因子PPAR的表达而实现。有趣的是，PPAR过表达可以恢复Arid1a缺陷引起的脂滴累积和胰岛素信号传递受阻现象，是潜在的治疗ARID1A突变相关疾病的靶标。本研究ARID1A相关机制以及脂肪性肝炎和肝癌发病机制及临床上发现有效的靶点具有重要意义。截止至目前，本项目已发表研究论文7篇，授权专利1项，申请专利2项，培养博士研究生4名，硕士研究生3名。新加入2名博士生支持本项目研究。目前还有部分实验数据正在整理过程中，预计1-2年将会发表，本项目在申请时所设定的研究目标已按期完成。