N6-methyladenosine (m6A) is identified as the most common, abundant and conserved internal transcriptional modification, especially within eukaryotic messenger RNAs (mRNAs). M6A modification is installed by the m6A methyltransferases (METTL3/14, WTAP, RBM15/15B and KIAA1429, termed as “writers”), reverted by the demethylases (FTO and ALKBH5, termed as “erasers”) and recognized by m6A binding proteins (YTHDF1/2/3, IGF2BP1 and HNRNPA2B1, termed as “readers”). Acumulating evidence shows that, m6A RNA methylation has an outsize effect on RNA production/metabolism and participates in the pathogenesis of multiple diseases including cancers. Until now, the molecular mechanisms underlying m6A RNA methylation in various tumors have not been comprehensively clarified. In this review, we mainly summarize the recent advances in biological function of m6A modifications in human cancer and discuss the potential therapeutic strategies.

Non-coding RNAs (ncRNAs) have been shown to regulate gene expression involved in tumor progression of multiple malignancies. Our previous studies indicated that large tumor suppressor kinase 1 (LATS1), a core part of Hippo signaling pathway, functions as a tumor suppressor in gastric cancer (GC). But, the underlying molecular mechanisms by which ncRNAs modulate LATS1 expression in GC remain undetermined. The correlation of LATS1 and has-miR-424-5p (miR-424) expression with clinicopathological characteristics and prognosis of GC patients was analyzed by TCGA RNA-sequencing data. A novel circular RNA_LARP4 (circLARP4) was identified to sponge miR-424 by circRNA expression profile and bioinformatic analysis. The binding site between miR-424 and LATS1 or circLARP4 was verified using dual luciferase assay and RNA immunoprecipitation (RIP) assay. The expression and localization of circLARP4 in GC tissues were investigated by fluorescence in situ hybridization (FISH). MTT, colony formation, Transwell and EdU assays were performed to assess the effects of miR-424 or circLARP4 on cell proliferation and invasion. Increased miR-424 expression or decreased LATS1 expression was associated with pathological stage and unfavorable prognosis of GC patients. Ectopic expression of miR-424 promoted proliferation and invasion of GC cells by targeting LATS1 gene. Furthermore, circLARP4 was mainly localized in the cytoplasm and inhibited biological behaviors of GC cells by sponging miR-424. The expression of circLARP4 was downregulated in GC tissues and represented an independent prognostic factor for overall survival of GC patients. circLARP4 may act as a novel tumor suppressive factor and a potential biomarker in GC.

Background: N6-methyladenosine (m⁶A) RNA methylation and circular RNAs (circRNAs) have been shown to act vital roles in multiple malignancies including gastric cancer (GC). However, there is little knowledge about how m⁶A modification of circRNAs contributes to GC progression.Methods: The association of METTL14 expression with the clinicopathological characteristics and prognosis in patients with GC was assessed by Western blot, Immunohistochemistry and public datasets. In vitro and vivo function experiments were conducted to investigate the role of METTL14 in GC. Furthermore, m⁶A-circRNA epitranscriptomic microarray was utilized to identify METTL14-mediated m⁶A modification of circRNAs, which were validated by methylated RNA immunoprecipitation (Me-RIP), RT-qPCR and rescue experiments in GC cells. The sponge of circORC5 with miR-30c-2-3p was confirmed by luciferase gene report and RNA immunoprecipitation assays. The expression, localization and prognosis of circORC5 in GC were evaluated by fluorescence in situ hybridization. The effects of METTL14 and (or) circORC5 on miR-30c-2-3p-mediated AKT1S1 and EIF4B were estimated by RT-qPCR and Western blot analyses.Results: We found that METTL14 was downregulated in GC tissue samples and its low expression acted as a prognostic factor of poor survival in patients with GC. Ectopic expression of METTL14 markedly repressed growth and invasion of GC cellsin vitroandin vivo, whereas knockdown of METTL14 harbored the opposite effects. Mechanically, m⁶A-circRNA epitranscriptomic microarray and Me-RIP identified circORC5 as the downstream target of METTL14. Silencing of METTL14 reduced the m⁶A level of circORC5, but increased circORC5 expression. Moreover, circORC5 could sponge miR-30c-2-3p, and reverse METTL14-caused upregulation of miR-30c-2-3p and downregulation of AKT1S1 and EIF4B. In addition, circORC5 possessed a negative correlation with miR-30c-2-3p and indicated a poor survival in GC.Conclusion: Our findings demonstrate that METTL14-mediated m⁶A modification of circORC5 suppresses gastric cancer progression by regulating miR-30c-2-3p/AKT1S1 axis.

N6-methyladenosine (m⁶A) is one of the most common RNA modifications in eukaryotes, mainly in messenger RNA (mRNA). Increasing evidence shows that m⁶A methylation modification acts an essential role in various physiological and pathological bioprocesses. Noncoding RNAs (ncRNAs), including miRNAs, lncRNAs and circRNAs, are known to participate in regulating cell differentiation, angiogenesis, immune response, inflammatory response and carcinogenesis. m⁶A regulators, such as METTL3, ALKBH5 and IGF2BP1 have been reported to execute a m⁶A-dependent modification of ncRNAs involved in carcinogenesis. Meanwhile, ncRNAs can target or modulate m⁶A regulators to influence cancer development. In this review, we provide an insight into the interplay between m⁶A modification and ncRNAs in cancer.

Patients with gastric cancer commonly have a poor prognosis, owing to its invasiveness and distant metastasis. Recent studies have confirmed the pivotal role of long non-coding RNAs (lncRNAs) in tumorigenesis and the progression of malignant tumors, including gastric cancer. However, little is known about the molecular mechanism by which lncRNA AK023391 contributes to gastric cancer. A lncRNA microarray was used to identify the differentially expressed lncRNA AK023391 in gastric cancer and adjacent normal tissues. In addition, RNA fluorescence in situ hybridization (FISH) was used to investigate the association between AK023391 expression and the clinicopathological characteristics and prognosis of patients with gastric cancer. Subsequently, a series of in vitro assays and a xenograft tumor model were used to observe the functions of lncRNA AK023391 in gastric cancer cells. A cancer pathway microarray, bioinformatic analysis, western blotting, and immunochemistry were carried out to verify the regulation of AK023391 and its downstream PI3K/Akt signaling pathway. Expression of lncRNA AK023391 was significantly upregulated in gastric cancer samples and cell lines in comparison to adjacent normal tissues, and was positively correlated with poor survival in patients with gastric cancer. The multivariate Cox regression model revealed that AK023391 expression acted as an independent prognostic factor for survival in patients with gastric cancer. Knockdown of AK023391 inhibited cell growth and invasion both in vitro and in vivo, and induced apoptosis and cell cycle arrest in gastric cancer cells, whereas its overexpression reversed these effects. Mechanistically, PI3K/Akt signaling mediated the NF-κB, FOXO3a, and p53 pathways. Moreover, downstream transcription factors, such as c-myb, cyclinB1/G2, and BCL-6 might be involved in AK023391-induced tumorigenesis in gastric cancer. The novel oncogenic lncRNA AK023391 in gastric cancer exerts its effects through activation of the PI3K/Akt signaling pathway, and may act as a potential biomarker for survival in patients with gastric cancer.

Circular RNAs (circRNAs) are a new type of non-coding RNAs and their functions in gastric cancer (GC) remain unclear. Recent studies have revealed that circRNAs play an important role in cancer development and certain types of pathological responses, acting as microRNA (miRNA) sponges to regulate gene expression. CircNet was used to screen potential circRNAs and validated circYAP1 expression levels in 17 GC tissues by quantitative real-time PCR (qRT-PCR) and another 80 paired GC tissues by FISH. CircYAP1 overexpression and knockdown experiments were conducted to assess the effects of circYAP1 in vitro and in vivo, and its molecular mechanism was demonstrated by RNA in vivo precipitation assays, western blotting, luciferase assay and rescue experiments. CircYAP1 expression level was significantly lower in GC tissues than the adjacent normal tissues, and GC patients with circYAP1 low expression had shorter survival times as compared with those with circYAP1 high expression. Functionally, circYAP1 overexpression inhibited cell growth and invasion in vitro and in vivo, but its knockdown reversed these effects. Further analysis showed that circYAP1 sponged miR-367-5p to inhibit p27 Kip1 expression and GC progression. Our findings demonstrate that circYAP1 functions as a tumor suppressor in GC cells by targeting the miR-367-5p/p27 Kip1 axis and may provide a prognostic indicator of survival in GC patients.