A novel tRNA-derived fragment tRF-3022b modulates cell apoptosis and M2 macrophage polarization via binding to cytokines in colorectal cancer

Abstract tRNA-derived fragments (tRFs) are a class of small RNAs that occur when tRNAs are broken down by enzymes due to stress. Increasing reports have shown that tRFs are associated with multiple physiological and pathological processes, especially in cancers; however, very little is known of the effects and mechanisms of tRFs. Therefore, further investigation on the biological roles and clinical value of tRFs is required. In this study, we utilized whole-transcriptome sequencing to profile tRFs expression in the tissues and plasma exosomes of patients with colorectal cancer (CRC). Three tRFs (tRF-3022b, tRF-3030b and tRF-5008b) showed an increasing trend in CRC tissues compared to adjacent normal tissues. They also tended to be elevated in plasma exosomes of CRC patients compared to healthy controls. These results indicated that they may be upregulated in cancer cells and then secreted by exosomes. The knockdown of tRF-regulated factors such as AlkB homolog 3 (ALKBH3), tRNA aspartic acid methyltransferase 1 (DNMT2), angiogenin (ANG), and argonaute RISC catalytic component 2 (AGO2) could affect the expression of tRFs. Notably, we found that the decrease in the three tRFs arrests the progression of the CRC cell cycle and induces cell apoptosis. Silencing tRF-3022b could facilitate M2 macrophage polarization. Mechanistically, we found that tRF-3022b binds to galectin 1 (LGALS1) and macrophage migration inhibitory factor (MIF) in CRC cells and reduces polarization by regulating MIF in M2 macrophages. In conclusion, our study revealed the expression pattern of tRFs in both tissue and plasma exosomes and identified a novel tRF, tRF-3022b, which may affect CRC tumor growth and M2 macrophage polarization by binding to LGALS1 and MIF.