胞苷脱氨酶与突变修复分子功能失衡在乙肝致癌中的作用

Chronic infection with hepatitis B virus (HBV) is the prominent cause of hepatocellular carcinoma (HCC). During HBV-induced hepatocarcinogenesis, cytidine deaminases such as apolioprotein B mRNA-editing enzyme catalytic polypeptides (APOBECs) can bridge chronic inflammation and cancers via inducing viral and somatic mutations. This project is designed to elucidate the mechanisms by which APOBECs whose expression is trans-activated by proimflammatory factors promote the founctional dysequilibrium between APOBECs and uracil-DNA glycosylase (UNG) / fragile histidine triad (FHIT). Systemic biology assay for megadata, deep sequencing, mutagenesis assay of APOBECs, functional assay of the genetic polymorphisms as well as population-based epidemiological studies including case-control study and cohort studies will be sequencially applied in this study. The mechanisms of founctional dysequilibrium between APOBECs and UNG / FHIT, which is driven by proinflammatory factors, will be firstly elucidated. The major somatic mutations, HBV mutation signature, and mitochondrial DNA (mtDNA) mutation in the D-loop region that are induced by extrusive APOBECs will be serially identified. Proinflammatory molecules-reduced APOBECs-affected signaling networks will be constructed to elucidate their roles in promoting HCC occurrence and postoperative recurrence. We will evaluate the associations of the functional genetic polymorphisms in the putative regions of APOBECs, UNG, and FHIT, HBV mutations, serum mtDNA mutations, and inflammatory signaling molecules with the occurrence of HCC. We will identify the above molecular events that can predict the occurrence and recurrence of HBV-HCC, and develop specific prophylactic steps to reduce or postpone hepatocarcinogenesis and to improve the postoperative prognosis of HCC. This study will be of importance to consummate Cancer Evo-Dev theoretically and to precisely prevent and control HCC.

乙肝病毒（HBV）慢性感染是肝细胞癌（HCC）主要原因。在乙肝致癌过程中，胞苷脱氨酶（APOBEC）通过诱导病毒和体细胞变异发挥炎-癌转化桥梁作用。本课题的关键科学问题是阐明慢性炎症刺激导致APOBEC与变异修复分子UNG和FHIT等之间功能失衡在HCC进化发育中的作用机理。拟采用大数据系统生物学分析、深度测序、促突变机制和多态功能研究、流行病学病例-对照研究和队列研究等方法，阐明炎症因子调控APOBEC与UNG/FHIT之间功能失衡机制；确定APOBEC驱动的体细胞变异、HBV变异和线粒体D环变异；阐明受变异激活的信号网络在促进HCC发生和再发的作用；探索三种分子启动子多态性、HBV变异、血清线粒体D环变异及网络分子表达与HCC发生的关联性；确定以上分子事件对HCC发生及复发的预测作用，探索预防HCC并改善预后新措施。对完善癌症进化发育理论、精准防控HCC具有重要意义。

本项目旨在阐明炎症因子导致胞苷脱氨酶（APOBECs）与修复分子(UNG)功能失衡进而促进肝细胞癌（HCC）进化的作用。通过系统生物学分析、高通量测序检测、细胞和动物机制实验以及分子流行病学研究，在HCC中阐明了核心科学问题，并在肾癌、胆管癌、胆囊癌和结直肠癌中进行了扩展，明确了APOBECs促癌作用在不同组织类型中的异同。.通过100例HCC样本的多水平测序分析，发现乙肝病毒（HBV）整合突变数量随着HCC进化显著增加，其水平升高提示预后不良。HBV整合数量与APOBEC3的表达呈正相关关系，而与UNG呈负相关关系。HBV整合显著富集在mTOR信号通路和代谢相关通路。联合使用mTOR抑制剂与糖代谢药物（苯乙双胍）可以有效降低靶向治疗耐药。APOBEC3表达水平与HBV基因组的多样性程度成正相关关系。HBV基因多样性随着HCC进化逐渐降低，体现微环境的选择作用。外州血和HCC组织中的APOBEC3相关HBV变异，其对HCC复发风险的关联性相反。阐明了炎症因子诱导的APOBEC3-UNG失衡是HCC进化的关键。IL-6上调APOBEC3B表达同时抑制UNG表达，APOBEC3B启动子遗传多态性rs2267401-G、UNG增强子rs3890995-C可以增强IL-6导致的APOBEC3B-UNG失衡，进而促进HBV高危突变频率和HCC风险。在多种癌症细胞系中共同证实ETS1和TFAP2A分别是结合APOBEC3A和APOBEC3B启动子的转录抑制因子。IL-6和TNFα可以下调TFAP2A进而解除APOBEC3B的表达抑制。由于TFAP2A表达水平的差异，APOBEC3B rs2267401-G对于胆管癌和胆囊癌发生风险的影响相反。APOBEC3A的致突变活性显著高于APOBEC3B，过表达APOBEC3A导致细胞凋亡增加，而APOBEC3B对细胞凋亡无显著作用。说明可耐受的致突变水平是促进癌症进化的主要因素。APOBECs标签突变也是CRC中的主要类型，但导致CRC突变的APOBEC亚型是AID和APOBEC3G而非APOBEC3A/B，体现了APOBECs促进癌症进化的异质性。.本项目阐明了APOBEC3对HBV-HCC进化的作用机制，发现了APOBECs致癌效果在不同癌症中的异同点，丰富了癌症进化发育学理论。为进一步完善HCC的防控策略提供了理论支撑。