N7-methylguanosine tRNA modification enhances oncogenic mRNA translation and promotes intrahepatic cholangiocarcinoma progression

The cancer cells selectively promote translation of specific oncogenic transcripts to facilitate cancer survival and progression, while the underlying mechanisms are poorly understood. N7-methylguanosine (m7G) tRNA modification and its methyltransferase complex METTL1/WDR4 are significantly up-regulated in intrahepatic cholangiocarcinoma (ICC) and associated with poor prognosis. We developed tRNA reduction and cleavage sequencing (TRAC-Seq) to reveal the m7G tRNA methylome inICC cell line and ribosome nascent-chain complex-bound mRNAs sequencing(RNC-seq) and ribosome profiling(Ribo-seq) to study the differential translated genes and reveal the ribosome pausing. A subset of 22 tRNAs is modified at a ‘RAGGU’ motif within the variable loop. We observe increased ribosome occupancy at the corresponding codons in the Mettl1 knockdown ICC cell line implying widespread effects on tRNA function, ribosome pausing, and mRNA translation. Translation of cell cycle genes and EGFR signaling pathway genes is particularly affected. Our study uncovers the important physiological function and mechanism of METTL1-mediated m7G tRNA modification in the regulation of cancer progression. TRAC-Seq was developed to identify the tRNA m7G methylome in the intrahepatic cholangiocarcinoma cell line. RNC-seq and Ribo-seq were used to study the differential translated genes in the Mettl1 knockdown and control cells.