ERP138238 PRJEB53441 d1084246-fcbd-4202-83c0-e439923e3d0a METTL1 KO tRNA fragments Newly growing evidence highlights the essential role that epitranscriptomic marks play in the development of cancer. Here we show that the transfer RNA N7-methylguanosine (m7G) transferase METTL1 is highly expressed in primary and advanced prostate tumours and increased expression correlates with poor prognosis. Knockdown of METTL1 dramatically inhibits prostate cancer cell growth and tumour progression in vivo. In contrast, overexpression of the wild type but not the catalytically inactive METTL1 potentiates cell growth. Thus, METTL1-mediated methylation is important for prostate tumorigenesis. Mechanistically we find that METTL1 depletion causes loss of m7G tRNA methylation and increases endonucleolytic cleavage of tRNAs leading to an accumulation of 5' tRNA-derived small RNA fragments. 5' tRNA fragments steer translation control to favour synthesis of key regulators of tumour growth suppression and immune rejection. In summary, our findings uncover a critical function of m7G tRNA methylation in directing translation control in cancer cells with important implications for tumour growth and microenvironment crosstalk and unveil METTL1 inhibition as a promising anti-cancer therapeutic strategy. METTL1 promotes tumorigenesis through tRNA-derived fragment biogenesis and translational control in prostate cancer Newly growing evidence highlights the essential role that epitranscriptomic marks play in the development of cancer. Here we show that the transfer RNA N7-methylguanosine (m7G) transferase METTL1 is highly expressed in primary and advanced prostate tumours and increased expression correlates with poor prognosis. Knockdown of METTL1 dramatically inhibits prostate cancer cell growth and tumour progression in vivo. In contrast, overexpression of the wild type but not the catalytically inactive METTL1 potentiates cell growth. Thus, METTL1-mediated methylation is important for prostate tumorigenesis. Mechanistically we find that METTL1 depletion causes loss of m7G tRNA methylation and increases endonucleolytic cleavage of tRNAs leading to an accumulation of 5' tRNA-derived small RNA fragments. 5' tRNA fragments steer translation control to favour synthesis of key regulators of tumour growth suppression and immune rejection. In summary, our findings uncover a critical function of m7G tRNA methylation in directing translation control in cancer cells with important implications for tumour growth and microenvironment crosstalk and unveil METTL1 inhibition as a promising anti-cancer therapeutic strategy. ENA-FIRST-PUBLIC 2023-08-15 ENA-LAST-UPDATE 2023-08-15