Background The mitogen‐activated protein kinase (MAPK) pathway is highly associated with the progression and metastasis of various solid tumours. MAPK14, a core molecule of the MAPK pathway, plays vital roles in the colorectal cancer (CRC). Recent studies have shown that circRNAs can affect tumour progression by encoding peptides. However, little is known regarding the potential protein translated from circMAPK14 and whether it plays a role in the carcinogenesis of colorectal cancer. Methods The RNA level and translatable potential of circMAPK14 in CRC was verified using qRT‐PCR and public databases. RNase R digestion assay, qRT‐PCR, sanger sequencing and FISH assays were utilised to verify the circular characteristics and subcellular localisation of circMAPK14. The suppressive role of circMAPK14 on the progression and metastasis of CRC was verified in vivo and in vitro. LC/MS analysis combined with western blotting demonstrated the presence and relative expression of circMAPK14‐175aa. The underlying mechanism of circMAPK14‐175aa action to inhibit CRC was identified by co‐IP analysis. The binding of U2AF2 within the flanking introns of circMAPK14 was evaluated by RNA pull‐down assay and RIP assay. Ultimately, luciferase reporter gene assays and ChIP assays confirmed that FOXC1 suppressed transcription of U2AF2 by binding to the U2AF2 promoter in the –400 bp to –100 bp region. Results We identified that hsa_circ_0131663 (termed circMAPK14) showed significantly decreased expression level in cells and tissue samples of CRC, and was primarily localised in the cytoplasm. A series of function experiments demonstrated that circMAPK14 influenced CRC progression and metastasis by encoding a peptide of 175 amino acids (termed circMAPK14‐175aa). We also found that circMAPK14‐175aa reduced nuclear translocation of MAPK14 by competitively binding to MKK6, thus facilitating ubiquitin‐mediated degradation of FOXC1. Moreover, we described a positive feedback loop in CRC in which elevated FOXC1 expression was caused by reduced circMAPK14‐175aa expression. This, in turn, decreased circMAPK14 biogenesis by suppressing U2AF2 transcription. Conclusion In summary, we reported for the first time that circMAPK14 functioned as a tumour‐suppressor by encoding circMAPK14‐175aa, which blocked the progression and metastasis of colorectal cancer.

BackgroundThough circular RNAs, new non‐coding RNA classes have demonstrated that they have an essential role in the initiation as well as development of CRC (colorectal cancer), whereas in CRC the function and mechanism of hsa_circ_0001666 are less known.MethodsHsa_circ_0001666 was identified by bioinformatics analysis of a circRNA microarray from the GEO database, and its expression in both CRC cell lines and tissues was analysed. A series of in vitro along with in vivo experiments were carried out for exploring the hsa_circ_0001666 functions, including transwell, wound healing, flow cytometry, colony formation, Edu, CCK‐8, soft agar colony formation, tumor xenografts and lung/liver metastasis in mice. RNA pull‐down, RIP (RNA immunoprecipitation), luciferase reporter assay, FISH (fluorescence in situ hybridization) and rescue experiments were used for determining the correlation among hsa_circ_0001666, miR‐576‐5p and PCDH10.ResultsHsa_circ_0001666 was downregulated in both CRC cell lines along with tumour tissues. A higher expression level of hsa_circ_0001666 indicated a better clinical prognosis in patients with CRC. Hsa_circ_0001666 knockdown significantly supported CRC cell proliferation along with invasion and inhibited cell apoptosis in vitro. Hsa_circ_0001666 knockdown accelerated the CRC growth and metastasis in vivo. Moreover, the mechanistic study showed that hsa_circ_0001666, acting as ‘ceRNA’ of miR‐576‐5p, prevented PCDH10 downregulation, as well as suppressed EMT and stemness of CRC cells, and the Wnt/β‐catenin signalling pathway. Inhibiting miR‐576‐5p or overexpressing PCDH10 could reverse phenotypic changes caused by knocking down of hsa_circ_0001666.ConclusionsHsa_circ_0001666 suppresses CRC progression through the miR‐576‐5p/PCDH10 axis and may provide a new insight for the diagnosis and treatment of CRC.

Background N4-acetylcytidine (ac4C) as a significant RNA modification has been reported to maintain the stability of mRNA and to regulate the translation process. However, the roles of both ac4C and its ‘writer’ protein N-acetyltransferase 10 (NAT10) played in the disease especially colorectal cancer (CRC) are unclear. At this point, we discover the underlying mechanism of NAT10 modulating the progression of CRC via mRNA ac4C modification. Methods The clinical significance of NAT10 was explored based on the TCGA and GEO data sets and the 80 CRC patients cohort of our hospital. qRT-PCR, dot blot, WB, and IHC were performed to detect the level of NAT10 and ac4C modification in CRC tissues and matched adjacent tissues. CCK-8, colony formation, transwell assay, mouse xenograft, and other in vivo and in vitro experiments were conducted to probe the biological functions of NAT10. The potential mechanisms of NAT10 in CRC were clarified by RNA-seq, RIP-seq, acRIP-seq, luciferase reporter assays, etc. Results The levels of NAT10 and ac4C modification were significantly upregulated. Also, the high expression of NAT10 had important clinical values like poor prognosis, lymph node metastasis, distant metastasis, etc. Furthermore, the in vitro experiments showed that NAT10 could inhibit apoptosis and enhance the proliferation, migration, and invasion of CRC cells and also arrest them in the G2/M phase. The in vivo experiments discovered that NAT10 could promote tumor growth and liver/lung metastasis. In terms of mechanism, NAT10 could mediate the stability of KIF23 mRNA by binding to its mRNA 3’UTR region and up-regulating its mRNA ac4c modification. And then the protein level of KIF23 was elevated to activate the Wnt/β-catenin pathway and more β-catenin was transported into the nucleus which led to the CRC progression. Besides, the inhibitor of NAT10, remodelin, was applied in vitro and vivo which showed an inhibitory effect on the CRC cells. Conclusions NAT10 promotes the CRC progression through the NAT10/KIF23/GSK-3β/β-catenin axis and its expression is mediated by GSK-3β which forms a feedback loop. Our findings provide a potential prognosis or therapeutic target for CRC and remodelin deserves more attention. Graphical Abstract