METTL1 promotes hepatocarcinogenesis via m7G tRNA modification-dependent translation control

Background N-7-methylguanosine (m(7)G) modification is one of the most common transfer RNA (tRNA) modifications in humans. The precise function and molecular mechanism of m(7)G tRNA modification in hepatocellular carcinoma (HCC) remain poorly understood. Methods The prognostic value and expression level of m(7)G tRNA methyltransferase complex components methyltransferase-like protein-1 (METTL1) and WD repeat domain 4 (WDR4) in HCC were evaluated using clinical samples and TCGA data. The biological functions and mechanisms of m(7)G tRNA modification in HCC progression were studied in vitro and in vivo using cell culture, xenograft model, knockin and knockout mouse models. The m(7)G reduction and cleavage sequencing (TRAC-seq), polysome profiling and polyribosome-associated mRNA sequencing methods were used to study the levels of m(7)G tRNA modification, tRNA expression and mRNA translation efficiency. Results The levels of METTL1 and WDR4 are elevated in HCC and associated with advanced tumour stages and poor patient survival. Functionally, silencing METTL1 or WDR4 inhibits HCC cell proliferation, migration and invasion, while forced expression of wild-type METTL1 but not its catalytic dead mutant promotes HCC progression. Knockdown of METTL1 reduces m(7)G tRNA modification and decreases m(7)G-modified tRNA expression in HCC cells. Mechanistically, METTL1-mediated tRNA m(7)G modification promotes the translation of target mRNAs with higher frequencies of m(7)G-related codons. Furthermore, in vivo studies with Mettl1 knockin and conditional knockout mice reveal the essential physiological function of Mettl1 in hepatocarcinogenesis using hydrodynamics transfection HCC model. Conclusions Our work reveals new insights into the role of the misregulated tRNA modifications in liver cancer and provides molecular basis for HCC diagnosis and treatment.