Although the function of tRNAs in the translational process is well established, it remains controversial whether tRNA abundance is tightly associated with translational efficiency (TE) in mammals. Moreover, how critically the expression of tRNAs contributes to the establishment of tissue-specific proteomes in mammals has not been well addressed. Here, we measured both tRNA expression using demethylase-tRNA sequencing (DM-tRNA-seq) and TE of mRNAs using ribosome-tagging sequencing (RiboTag-seq) in the brain, heart, and testis of mice. Remarkable variation in the expression of tRNA isodecoders was observed among different tissues. When the statistical effect of isodecoder-grouping on reducing variations is considered through permutating the anticodons, we observed an expected reduction in the variation of anticodon expression across all samples, an unexpected smaller variation of anticodon usage bias, and an unexpected larger variation of tRNA isotype expression at amino acid level. Regardless of whether or not they share the same anticodons, the isodecoders encoding the same amino acids are co-expressed across different tissues. Based on the expression of tRNAs and the TE of mRNAs, we find that the tRNA adaptation index (tAI) and TE are significantly correlated in the same tissues but not between tissues; and tRNA expression and the amino acid composition of translating peptides are positively correlated in the same tissues but not between tissues. We therefore hypothesize that the tissue-specific expression of tRNAs might be due to post-transcriptional mechanisms. This study provides a resource for tRNA and translation studies, as well as novel insights into the dynamics of tRNAs and their roles in translational regulation.
Animals ; Mice ; Anticodon/genetics* ; Transcriptome ; Protein Biosynthesis ; RNA, Transfer/chemistry* ; Amino Acids/metabolism* ; Mammals/metabolism*

N ⁶-methyladenosine (m⁶A) modification is critical for mRNA splicing, nuclear export, stability and translation. Fat mass and obesity-associated protein (FTO), the first identified m⁶A demethylase, is critical for cancer progression. Herein, we developed small-molecule inhibitors of FTO by virtual screening, structural optimization, and bioassay. As a result, two FTO inhibitors namely 18077 and 18097 were identified, which can selectively inhibit demethylase activity of FTO. Specifically, 18097 bound to the active site of FTO and then inhibited cell cycle process and migration of cancer cells. In addition, 18097 reprogrammed the epi-transcriptome of breast cancer cells, particularly for genes related to P53 pathway. 18097 increased the abundance of m⁶A modification of suppressor of cytokine signaling 1 (SOCS1) mRNA, which recruited IGF2BP1 to increase mRNA stability of SOCS1 and subsequently activated the P53 signaling pathway. Further, 18097 suppressed cellular lipogenesis via downregulation of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBPα), and C/EBPβ. Animal studies confirmed that 18097 can significantly suppress in vivo growth and lung colonization of breast cancer cells. Collectively, we identified that FTO can work as a potential drug target and the small-molecule inhibitor 18097 can serve as a potential agent against breast cancer.