BackgroundExosomes are extracellular vesicles secreted by most cells to deliver functional cargoes to recipient cells. MicroRNAs (miRNAs) constitute a significant part of exosomal contents. The ease of diffusion of exosomes renders them speedy and highly efficient vehicles to deliver functional molecules. Cancer cells secrete more exosomes than normal cells. Reports have showed that exosomal miRNAs of cancer cells facilitate cancer progression. Yet the complexity of cancer dictates that many more functional exosomal miRNAs remain to be discovered.MethodsIn this study, we analyzed miRNA expression profiles of tissue and plasma exosome samples collected from 10 colorectal cancer (CRC) patients and 10 healthy individuals. We focused on hsa-miR-101-3p (101-3p), a profoundly up-regulated miRNA enriched in plasma exosomes of patients bearing CRC. We performed target analysis of 101-3p and pursued functional studies of this microRNA in two colorectal cancer cell lines, namely HCT116 and SW480.ResultsOur results indicated that inhibiting 101-3p slowed cell growth and retarded cell migration in vivo in two colorectal cancer cell lines. Target analysis showed that Homeodomain-interacting protein kinase (HIPK3) is a target of miR-101-3p. HCT116 and SW480 cells stably overexpressing HIPK3 showed increased level of phosphorylated FADD, as well as retarded cell growth, migration, and increased sensitivity to 5-FU. In-depth analysis revealed increased mitochondrial membrane potential upon HIPK3 overexpression along with increased production of reactive oxygen species, number of mitochondria, and expression of respiratory complexes. Measurements of glycolytic parameters and enzymes revealed decreased level of glycolysis upon HIPK3 overexpression in these two cell lines. Xenograft model further confirmed a profoundly improved potency of the synergistic treatment combining both 5-FU and 101-3p inhibitor compared to 5-FU alone.ConclusionThis study unraveled an oncogenic nature of the exosomal 101-3p and suggested a relationship between the 101-3p-HIPK3 axis and metabolic homeostasis in colorectal cancer. Expression level of 101-3p is positively correlated with glycolytic capacity in CRC and therefore 101-3p itself is an oncomiR. Combining 101-3p inhibitor with chemotherapeutic agents is an effective strategy against CRC.

AbstracttRNA-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.

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