METTL1 promotes tumorigenesis through tRNA-derived fragment biogenesis in prostate cancer

Newly growing evidence highlights the essential role that epitranscriptomic marks play in the development of cancer; however, little is known about the role and implications of altered epitranscriptome deposition in prostate cancer. Here, we show that the transfer RNA N7-methylguanosine (m7G) transferase METTL1 is highly expressed in primary and advanced prostate tumours. Mechanistically, we find that METTL1 depletion causes the loss of m7G tRNA methylation and promotes the biogenesis of a novel class of small non-coding RNAs derived from 5'tRNA fragments. 5' tRNA-derived small RNAs steer translation control to favour the synthesis of key regulators of tumour growth suppression, interferon pathway, and immune effectors. Knockdown of Mettl1 in prostate cancer preclinical models increases intratumoural infiltration of pro-inflammatory immune cells and enhances responses to immunotherapy, leading to decreased tumour progression. Collectively, our findings reveal a therapeutically actionable role of METTL1-directed m7G tRNA methylation in cancer cell translational control and tumour biology. Overall design: Sequences of RNAs bound to METTL1 in prostate cancer cell lines PC3. Photoactivatable-ribonucleoside-enhanced cross-linking immunoprecipitation (PAR-CLIP) was applied to PC3 cells expressing HA-METTL1.Empty vector was used as control. METTL1 was IP using anti-HA antibodies. RNAs bound to METTL1 were extracted and sequenced.

越来越多的新证据凸显表观转录组标记（epitranscriptomic mark）在癌症发生发展中的核心作用，但目前对于表观转录组沉积异常在前列腺癌中的作用与意义仍知之甚少。本研究证实，转运RNA N7-甲基鸟苷（m7G）转移酶METTL1在原发性及晚期前列腺肿瘤中均呈高表达。机制层面研究发现，METTL1表达缺失会导致m7G tRNA甲基化水平丧失，并促进一类源自5'端tRNA片段的新型小非编码RNA的生物发生。这类5'端tRNA来源的小RNA可调控翻译过程，优先合成肿瘤生长抑制、干扰素通路及免疫效应分子的关键调控因子。在前列腺癌临床前模型中敲低Mettl1，可增加瘤内促炎性免疫细胞浸润，并增强免疫治疗应答，最终延缓肿瘤进展。综上，本研究揭示了METTL1介导的m7G tRNA甲基化在癌细胞翻译调控及肿瘤生物学中具有可靶向干预的治疗价值。整体实验设计：对前列腺癌细胞系PC3中与METTL1结合的RNA进行测序分析。本研究对表达HA-METTL1的PC3前列腺癌细胞实施光活化核糖核苷增强交联免疫沉淀（PAR-CLIP，Photoactivatable-ribonucleoside-enhanced cross-linking immunoprecipitation），以转染空载体的细胞作为对照。通过抗HA抗体免疫沉淀METTL1蛋白，提取结合于METTL1的RNA并进行测序。