肝癌中tRNA甲基转移酶TRMT6的失调及其功能

Liver cancer (Hepatocellular carcinoma, HCC) is one of the most common cancers in the world. It is particularly prevalent in our country due to the frequent HBV infection. Unfortunately, treatment options for liver cancer patients are very limited. Liver cancer is the third lethal cancer and caused more than 700,000 deaths annually. Liver carcinogenesis is a multistep process driven by the accumulation of genetic alterations. However, the detailed molecular mechanisms of liver carcinogenesis remain largely unknown. In addition to somatic mutations, epigenetic alterations are also playing an equally important role in human carcinogenesis. Previous studies have firmly established the critical roles of aberrant DNA and histone methylation in liver cancer development. Most recently, reversible chemical methylations on RNA is emerging as a new frontier of epigenetic research. RNA modifications can regulate RNA stability and impact on gene expression. Interestingly, RNA modifications are particularly enriched in transfer RNA (tRNA). tRNA is an essential component for protein synthesis, which translates the genetic code in mRNA to synthesize protein. Our preliminary data suggested that tRNA methyltransferase TRMT6 was frequently up-regulated in human liver cancer and associated with more aggressive tumor behaviors. TRMT6 regulates N1-methyladenosine (m1A) modification at position 58 of tRNA. This modification controls the proper folding and structural stability of tRNA. Our preliminary data also showed that depletion of TRMT6 suppressed liver cancer growth and metastasis both in vitro and in vivo. We also showed that knockout of TRMT6 reduced protein synthesis rate. Specifically, proteomic analysis revealed that knockout of TRMT6 inhibited live cancer stem cell marker CD44 expression and suppressed liver cancer sphere formation. Based on the above preliminary data, we hypothesized that deregulation of TRMT6 may alter tRNA m1A modification and contribute to cancer stem cell properties. In this study, we aim to comprehensively analyze the functional and pathological roles of TRMT6 in liver carcinogenesis. The impact of TRMT6 on tRNA deregulation and liver cancer stem cell formation will be investigated. We believe that our findings will substantially enhance our understanding on the molecular mechanisms of liver carcinogenesis and shed light on the development of novel diagnostic and therapeutic strategies for liver cancer patients.

肝癌是世界上致死率第三高的恶性肿瘤。除基因突变外，表观遗传异常也是引发癌症的重要机制。前人的研究证实了DNA和组蛋白甲基化失调在肝癌发生中的重要功能。近年来，发生在RNA水平的可逆化学修饰被认定为表观遗传学的新分支。tRNA是胞内蛋白合成过程中负责翻译mRNA密码子的基本组分。有趣的是，tRNA携带着尤为丰富的化学修饰。我们的前期数据显示tRNA甲基转移酶TRMT6在肝癌中表达频繁上调并且跟多个肝癌临床表征相关。TRMT6催化tRNA m1A 修饰，从而调控tRNA的折叠和稳定性。我们的前期数据还显示，敲低TRMT6会抑制肝癌体内外的生长与转移。同时，敲除TRMT6会降低肝癌细胞的蛋白合成速率。蛋白质组学分析进一步显示敲除TRMT6会降低肝癌干细胞标记CD44的表达并抑制干细胞潜能。在这项研究中，我们将会全面分析TRMT6在肝癌中的功能和病理意义。本研究将会为肝癌发生的分子机制提供新的见解

研究背景及研究目的：可逆的RNA修饰在调节RNA稳定性、可变剪接和蛋白质翻译中起到十分重要的作用。最近有大量的研究表明，失调的RNA修饰对癌症的发展至关重要。tRNA有非常多种的RNA修饰类型，然而对于这些tRNA的修饰在癌症发生发展中的作用并不清楚。肝细胞癌（HCC）是全球致死率排名前四的恶性肿瘤。本项目以肝细胞癌为研究模型，探索了tRNA修饰相关的基因，并鉴定出tRNA m1A修饰的RNA甲基转移酶TRMT6，是促进肝癌发生发展的重要驱动因素。. 方法： 本项目通过高通量测序技术在配对的肝癌患者组织样本中绘制tRNA修饰酶的表达谱。结合多种肝癌细胞系和小鼠模型，在体内外水平对TRMT6的功能进行了验证。进一步地，联合tRNA测序、翻译组学以及蛋白组学等，采用多组学整合分析策略对其机制进行深入探讨。. 结果：我们发现在肝癌患者组织中TRMT6明显高表达，并伴随着不良的预后。实验证明，敲除TRMT6可以减少肝癌细胞的形成、肿瘤的生长和转移。TRMT6在tRNA的表达以及蛋白翻译中起到重要作用。敲除TRMT6后会导致tRNA池的重编程，并以tRNA-密码子依赖性途径抑制细胞干性因子CD44和Nestin的蛋白翻译，从而减少肿瘤细胞的发生。我们进一步阐明了TRMT6在维持肝癌细胞的干性特征包括肿瘤细胞的自我更新，肿瘤发生以及索拉非尼耐药等多方面中都扮演了十分重要的角色。. 结论：综上所述，本项研究过程中揭示了肿瘤表观调控的新视角--tRNA修饰，并且筛选和鉴定出甲基转移酶TRMT6可以作为癌症的潜在治疗靶点