Hypoxia plays a key role in colorectal cancer (CRC) metastasis, but its underlying mechanism remains largely unknown. Dicer1, an RNase, has been considered as a tumor regulator in many tumors. However, whether Dicer1 affects CRC progression under hypoxia remains uncertain. In this study, we found that Dicer1 expression was induced by hypoxia in CRC cells and it mediates hypoxia-induced CRC cell progression. Furthermore, we found that the expression of tRF-20-MEJB5Y13, a small non-coding RNA derived from tRNA, was increased under hypoxic conditions, and its upregulation by Dicer1 resulted in hypoxia-induced CRC cell invasion and migration. These results advance the current understanding of the role of Dicer1 in regulating hypoxia signals and provide a new pathway for the development of therapeutic interventions for inhibiting cancer progression.

Background: Hypoxia is a key driving factor for the tumour microenvironment restructuring, which leading to the variation of gene expression profiling in cancer cells. Increasing evidence reveals the initial action of hypoxia in the epitranscriptomics including RNA methylation. The role of tRNA-derived fragments (tRFs) in regulating tumour metastasis potential has attracted attention. Methods: The expression of tRFs in colon cancer cells under hypoxia were evaluated based on full-transcript sequencing and bioinformatics analysis and their effects on colon cancer metastasis were detected by transwell assays. The role of C34 was verified by introducing mutation and artificial m5C modification. The effects of NSUN2 on the biological characteristics of colon cancer cells were investigated on the basis of gain-of-function and loss-of function analyses. Lung metastasis model further uncovered the roles of NSUN2 and key tRF in tumour progression. Assays of RNA immunoprecipitation-qPCR (RIP-qPCR) were performed to identify that NSUN2 is a key methyltransferase for cysteine modification at C34 of tRNA-Arg.Results: The present study verified the up-expression of tRF (tRF-20-MEJB5Y13) and down-expression of tRFs (tRF-20-M0NK5Y93 and tRF-21-3OPP6N7KE) in colon cancer cells under hypoxia, and all of them were derived from different tRNA-Arg. Contradictory effects of these three tRNA-Arg-derived tRFs on metastatic potential of colon cancer were demonstrated in this study. The sequence differences and the key nucleotide bases of tRNA with the methylation modification potential among the source tRNAs were analysed. Notably, our data identified C34 of tRNA-Arg as a key site that may play an important role in hypoxia-mediated tRNA-Arg discrepant cleavage. We further investigated that NSUN2 mediated specific site methylation of tRNA-Arg at C34, thereby protecting tRNA from cleavage by endonuclease and subsequently promoting the colon cancer metastasis both in vitro and in vivo. Conclusion: The present study elaborates on the precise regulatory mechanism of m5C methylation and the role in the selective cleavage of tRNA from the perspective of noncoding RNA methylation epitranscriptomics, providing a novel insight into the molecular basis of selective expression of tRFs in colon cancer under hypoxia.

Background: Colon cancer is a malignant gastrointestinal tumor and is still a worldwide leading cause of cancer-related mortality. Owing to the development of high-throughput sequencing technologies, large-scale data have become available in public databases. We devoted to construct and validate a gene signature that can predict patients’ outcomes for colon cancer using bioinformatics methods. Methods: We integrated GSE44076 and GSE39582 to identify differentially expressed genes (DEGs). Timer 2.0 was used to analysis CTHRC1 expression in various types of cancer. The relationship of clinicopathological features and CTHRC1 expression was explored based on TCGA database. Hub genes were identified by String database and Cytoscape software. The gene prognostic signature was established based on the Cox regression analysis.Results: We obtained 170 common DEGs and confirmed CTHRC1 was significantly overexpressed in colon cancer samples (P < 0.001). High CTHRC1 level was associated with advanced stage and shorter overall survival (OS) time and relapse-free survival (RFS) time in colon cancer patients. We identified thirteen hub genes among 516 genes co-expressed with CTHRC1 and subsequently constructed a 14-gene risk signature, which associated advanced stage and poor OS (log-rank test p < 0.01). Multivariate Cox regression indicated that high risk score was an independent risk factor for poor prognosis (p < 0.01). Finally, Receiver operating characteristic curve analysis was performed to further confirm the validity of the signature. Conclusions: We confirmed the important role of CTHRC1 in colon cancer and further constructed a 14-gene risk signature with promising prognostic accuracy for colon cancer patients.