长链非编码RNA-CASC8基因扩增诱导食管鳞癌转移的分子机制

Metastasis is the most prominent factor for cancer-induced death. Identifying the key long non-coding RNA and elucidating the mechanism in metastasis would be of great value for early diagnosis and targeted therapy. Recently, using the RNA sequencing method, we found that CASC8 is one of the most significantly upregulated lncRNA in esophageal cancer tissues with lymph node metastasis. Furthermore, the RNA and protein immunoprecipitation assays revealed that CASC8 interacted with p65/p50 complex. We then demonstrated that CASC8 increased the transcriptional activity of NF-κB, and upregulated multiple genes including MMP9, VEGFC and CCR7, leading to lymph node metastasis in vivo. Surprisingly, we observed that CASC8 interacted with RNA transporting protein HNRNPA2B1, and was incorporated into exosomes. CASC8 was then able to be transmitted into fibroblast cells, and activated NF-κB signaling in fibroblast to induce cytokines expression. Moreover, CASC8 created inflammatory micro-environment in lymph node and lung tissues, facilitating tumor colonization and growth in distant metastasis sites. Hence, in the current project, we aim to explore the biological roles and underlying mechanisms in which CASC8 promotes ESCC metastasis via exosomes and NF-κB activation, which might provide new biomarkers and targets for the diagnosis and treatment of cancer.

转移是肿瘤致死的最主要原因，寻找其关键的调控长链非编码RNA（lncRNA），阐明其功能及分子机制，对晚期恶性肿瘤的诊治具有重要意义。近期，我们筛选到在淋巴结转移性食管癌中表达最显著上调的lncRNA-CASC8。进一步发现：① CASC8能够与NF-κB转录因子复合体p65/p50相结合，增强其转录活性；② CASC8上调MMP9、VEGF-C和CCR7等基因，增强食管癌细胞的迁移和侵袭能力，并诱导淋巴管新生、促进肿瘤淋巴结转移；③ 更为重要的是，CASC8与RNA转运蛋白HNRNPA2B1结合，并被组装进肿瘤外泌体中、活化成纤维细胞，激活其细胞内的NF-κB通路而上调多种炎症因子的表达，从而诱导远处器官炎症微环境形成并诱发肿瘤转移。本项目将承前启后，利用多种技术和方法深层次解析CASC8多层面诱导食管鳞癌转移的分子机制，并结合临床数据分析，探讨CASC8在食管鳞癌临床诊治中的意义。

转移和耐药是肿瘤致死的最主要原因；鉴定关键调控长链非编码RNA并阐明其作用机制，将为肿瘤临床诊治提供新型分子标志物和靶点。围绕该研究主线，本项目取得的主要成果包括：1、lncRNA CASC8在食管癌中存在基因扩增并高表达，CASC8结合p65、p50而促进NF-κB转录复合物的组装，转录上调MMP9、VEGF-C、CCR7等基因，增强肿瘤细胞的侵袭能力并诱导肿瘤相关淋巴管新生，进而促进食管癌淋巴结转移；Wnt/β-Catenin信号激活诱导lncRNA DGCR5选择性剪接生成短的DGCR5-S，DGCR5-S通过阻止TTP的去磷酸化而保护炎性细胞因子的mRNA不被降解，促进炎性细胞因子分泌，塑造炎性微环境而促进食管癌进展；在尼古丁成瘾性食管癌患者中，OTUD3表达下调促进ZFP36蛋白降解，从而稳定VEGF-C的mRNA，进而诱导食管癌淋巴管新生和淋巴结转移（Nature Communications，2021）。2、肿瘤干细胞特性维持是肿瘤转移和耐药的重要原因。AKIP1结合并促进β-Catenin的磷酸化激活，增强肿瘤干性，导致肿瘤的复发和转移（Oncogene，2019）；近期，我们发现RNA结合蛋白ILF2参与出核复合体的组装，促进多潜能基因mRNA的出核和表达，从而增强食管癌干细胞样特性和化疗耐受（Cancer Research，2021a）；TBX19转录上调MFF而促进线粒体分裂，降低线粒体内的活性氧（ROS）水平，抑制由ROS介导的OCT4氧化降解，从而增强肿瘤细胞干性和肿瘤复发（Cancer Research，2021b）。3、肿瘤耐药相关研究上，我们发现肿瘤中ZNF711表达下调引起转运蛋白SLC31A1低表达，抑制肿瘤细胞摄取化疗药物，从而增加肿瘤的化疗抵抗（EBioMedicine，2021）；治疗压力诱导TRIM3磷酸化入核，TRIM37通过单泛素化NEMO促使其从细胞核内输出，解除NEMO对NF-κB转录复合物的抑制作用，从而促进肿瘤化疗抵抗（Cancer Research，2018）；SALL2基因甲基化诱导ER表达下调，促进乳腺癌他莫昔芬治疗抵抗（EMBO Mol Med, 2019）。这些研究成果揭示了肿瘤转移和耐药的新机制，为临床肿瘤诊治提供了潜在的新策略。项目资助发表第一/通讯作者论文12篇，申请国家发明专利2项。