Circular RNAs (circRNAs) have been implicated in cancer progression through largely unknown mechanisms. Herein, we identify an N6-methyladenosine (m6A) modified circRNA, circNSUN2, frequently upregulated in tumor tissues and serum samples from colorectal carcinoma (CRC) patients with liver metastasis (LM) and predicts poorer patient survival. The upregulated expression of circNSUN2 promotes LM in PDX metastasis models in vivo and accelerates cancer cells invasion in vitro. Importantly, N6-methyladenosine modification of circNSUN2 increases export to the cytoplasm. By forming a circNSUN2/IGF2BP2/HMGA2 RNA-protein ternary complex in the cytoplasm, circNSUN2 enhances the stability of HMGA2 mRNA to promote CRC metastasis progression. Clinically, the upregulated expressions of circNSUN2 and HMGA2 are more prevalent in LM tissues than in primary CRC tissues. These findings elucidate that N6-methyladenosine modification of circNSUN2 modulates cytoplasmic export and stabilizes HMGA2 to promote CRC LM, and suggest that circNSUN2 could represent a critical prognostic marker and/or therapeutic target for the disease.

MicroRNAs (miRNAs) are endogenous non-coding RNAs that contain approximately 22 nucleotides. They serve as key regulators in various biological processes and their dysregulation is implicated in many diseases including cancer and autoimmune disorders. It has been well established that the maturation of miRNAs occurs in the cytoplasm and miRNAs exert post-transcriptional gene silencing (PTGS) via RNA-induced silencing complex (RISC) pathway in the cytoplasm. However, numerous studies reaffirm the existence of mature miRNA in the nucleus, and nucleus-cytoplasm transport mechanism has also been illustrated. Moreover, active regulatory functions of nuclear miRNAs were found including PTGS, transcriptional gene silencing (TGS), and transcriptional gene activation (TGA), in which miRNAs bind nascent RNA transcripts, gene promoter regions or enhancer regions and exert further effects via epigenetic pathways. Based on existing interaction rules, some miRNA binding sites prediction software tools are developed, which are evaluated in this article. In addition, we attempt to explore and review the nuclear functions of miRNA in immunity, tumorigenesis and invasiveness of tumor. As a non-canonical aspect of miRNA action, nuclear miRNAs supplement miRNA regulatory networks and could be applied in miRNA based therapies.

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We conclude that elevated survivin, MMP7, and TROP2 expression levels are related to decreased survival. In addition, elevated MMP7 and TROP2 expression levels are predictors of disease recurrence and liver metastasis, respectively.

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Overexpressed DNA methyltransferase 1 (DNMT1) strongly contributes to tumor suppressor gene silencing in colorectal cancer (CRC). However, the underlying mechanism of DNMT1 overexpression is still unclear. MicroRNAs (miRNA) have been implicated as gene regulators controlling diverse biological processes, including carcinogenesis. In this study, we investigated whether some miRNA is involved in the regulation of DNMT1 and thus play a functional role in CRC. Our results showed that miR-342 was downregulated in CRC tissues and cell lines. Restoration of miR-342 resulted in a dramatic reduction of the expression of DNMT1 at both messenger RNA and protein levels by directly targeting its 3' untranslated region. This in turn reactivated ADAM23, Hint1, RASSF1A and RECK genes via promoter demethylation. Furthermore, the enhanced expression of miR-342 could significantly inhibit SW480 cell proliferation in vitro (P = 0.006). Further investigation demonstrated G(0)/G(1) cell cycle arrest in SW480 cells, which was associated with an upregulation of p21 and downregulation of cyclinE and CDK2. Overexpression of miR-342 also inhibited SW480 cell invasion. The in vivo antitumor effect was evaluated in SW480 cells with lentivirus-mediated expression of miR-342. Results showed that overexpression of miR-342 significantly inhibited tumor growth and lung metastasis in nude mice (P = 0.034). Our findings describe a new mechanism for the regulation of DNMT1 and aberrant DNA hypermethylation in CRC. This is also the first report to demonstrate that miR-342 may act as a tumor suppressor gene in CRC development. The newly identified miR-342/DNMT1 link provides a new, potential therapeutic target for the treatment of CRC.

Background & Aims Known Genetic factors explain only a small fraction of genetic variation in colorectal cancer (CRC). We conducted a genome-wide association study (GWAS) to identify risk loci for CRC. Methods This discovery stage included 8027 cases and 22577 controls of East-Asian ancestry. Promising variants were evaluated in studies including as many as 11044 cases and 12047 controls. Tumor-adjacent normal tissues from 188 patients were analyzed to evaluate correlations of risk variants with expression levels of nearby genes. Potential functionality of risk variants were evaluated using public genomic and epigenomic databases. Results We identified 4 loci associated with CRC risk; P values for the most significant variant in each locus ranged from 3.92×10−8 to 1.24×10−12: 6p21.1 (rs4711689), 8q23.3 (rs2450115, rs6469656), 10q24.3 (rs4919687), and 12p13.3 (rs11064437). We also identified 2 risk variants at loci previously associated with CRC: 10q25.2 (rs10506868) and 20q13.3 (rs6061231). These risk variants, conferring an approximate 10%–18% increase in risk per allele, are located either inside or near protein-coding genes that include TFEB (lysosome biogenesis and autophagy), EIF3H (initiation of translation), CYP17A1 (steroidogenesis), SPSB2 (proteasome degradation), and RPS21 (ribosome biogenesis). Gene expression analyses showed a significant association (P <.05) for rs4711689 with TFEB, rs6469656 with EIF3H, rs11064437 with SPSB2, and rs6061231 with RPS21. Conclusions We identified susceptibility loci and genes associated with CRC risk, linking CRC predisposition to steroid hormone, protein synthesis and degradation, and autophagy pathways and providing added insight into the mechanism of CRC pathogenesis.

Background Precise methods for postoperative risk stratification to guide the administration of adjuvant chemotherapy (ACT) in localized colorectal cancer (CRC) are still lacking. Here, we conducted a prospective, observational, and multicenter study to investigate the utility of circulating tumor DNA (ctDNA) in predicting the recurrence risk. Methods From September 2017 to March 2020, 276 patients with stage II/III CRC were prospectively recruited in this study and 240 evaluable patients were retained for analysis, of which 1290 serial plasma samples were collected. Somatic variants in both the primary tumor and plasma were detected via a targeted sequencing panel of 425 cancer-related genes. Patients were treated and followed up per standard of care. Results Preoperatively, ctDNA was detectable in 154 of 240 patients (64.2%). At day 3–7 postoperation, ctDNA positivity was associated with remarkably high recurrence risk (hazard ratio [HR], 10.98; 95%CI, 5.31–22.72; P < 0.001). ctDNA clearance and recurrence-free status was achieved in 5 out of 17 ctDNA-positive patients who were subjected to ACT. Likewise, at the first sampling point after ACT, ctDNA-positive patients were 12 times more likely to experience recurrence (HR, 12.76; 95%CI, 5.39–30.19; P < 0.001). During surveillance after definitive therapy, ctDNA positivity was also associated with extremely high recurrence risk (HR, 32.02; 95%CI, 10.79–95.08; P < 0.001). In all multivariate analyses, ctDNA positivity remained the most significant and independent predictor of recurrence-free survival after adjusting for known clinicopathological risk factors. Serial ctDNA analyses identified recurrence with an overall accuracy of 92.0% and could detect disease recurrence ahead of radiological imaging with a mean lead time of 5.01 months. Conclusions Postoperative serial ctDNA detection predicted high relapse risk and identified disease recurrence ahead of radiological imaging in patients with stage II/III CRC. ctDNA may be used to guide the decision-making in postsurgical management.