METTL3 is known to be involved in all stages in the life cycle of RNA. It affects the tumor formation by the regulation the m6A modification in the mRNAs of critical oncogenes or tumor suppressors. In bladder cancer, METTL3 could promote the bladder cancer progression via AFF4/NF-κB/MYC signaling network by an m6A dependent manner. Recently, METTL3 was also found to affect the m6A modification in non-coding RNAs including miRNAs, lincRNAs and circRNAs. However, whether this mechanism is related to the proliferation of tumors induced by METTL3 is not reported yet. Quantitative real-time PCR, western blot and immunohistochemistry were used to detect the expression of METTL3 in bladder cancer. The survival analysis was adopted to explore the association between METTL3 expression and the prognosis of bladder cancer. Bladder cancer cells were stably transfected with lentivirus and cell proliferation and cell cycle, as well as tumorigenesis in nude mice were performed to assess the effect of METTL3 in bladder cancer. RNA immunoprecipitation (RIP), co-immunoprecipitations and RNA m6A dot blot assays were conducted to confirm that METTL3 interacted with the microprocessor protein DGCR8 and modulated the pri-miR221/222 process in an m6A-dependent manner. Luciferase reporter assay was employed to identify the direct binding sites of miR221/222 with PTEN. Colony formation assay and CCK8 assays were conducted to confirm the function of miR-221/222 in METTL3-induced cell growth in bladder cancer. We confirmed the oncogenic role of METTL3 in bladder cancer by accelerating the maturation of pri-miR221/222, resulting in the reduction of PTEN, which ultimately leads to the proliferation of bladder cancer. Moreover, we found that METTL3 was significantly increased in bladder cancer and correlated with poor prognosis of bladder cancer patients. Our findings suggested that METTL3 may have an oncogenic role in bladder cancer through interacting with the microprocessor protein DGCR8 and positively modulating the pri-miR221/222 process in an m6A-dependent manner. To our knowledge, this is the first comprehensive study that METTL3 affected the tumor formation by the regulation the m6A modification in non-coding RNAs, which might provide fresh insights into bladder cancer therapy.

Background: As a rate‐limiting enzyme of glycolysis, pyruvate kinase muscle isozyme M2 (PKM2) participates in tumor metabolism and growth. The regulatory network of PKM2 in cancer is complex and has not been fully studied in bladder cancer. The 5‐methylcytidine (m5C) modification in PKM2 mRNA might participate in the pathogenesis of bladder cancer and need to be further clarified. This study aimed to investigate the biological function and regulatory mechanism of PKM2 in bladder cancer. Methods: The expression of PKM2 and Aly/REF export factor (ALYREF) was measured by Western blotting, qRT‐PCR, and immunohistochemistry. The bioprocesses of bladder cancer cells were demonstrated by a series of experiments in vitro and in vivo . RNA immunoprecipitation, RNA‐sequencing, and dual‐luciferase reporter assays were conducted to explore the potential regulatory mechanisms of PKM2 in bladder cancer. Results: In bladder cancer, we first demonstrated that ALYREF stabilized PKM2 mRNA and bound to its m5C sites in 3′‐untranslated regions. Overexpression of ALYREF promoted bladder cancer cell proliferation by PKM2‐mediated glycolysis. Furthermore, high expression of PKM2 and ALYREF predicted poor survival in bladder cancer patients. Finally, we found that hypoxia‐inducible factor‐1alpha (HIF‐1α) indirectly up‐regulated the expression of PKM2 by activating ALYREF in addition to activating its transcription directly. Conclusions: The m5C modification in PKM2 mRNA in the HIF‐1α/ALYREF/PKM2 axis may promote the glucose metabolism of bladder cancer, providing a new promising therapeutic target for bladder cancer.

The M6A methyltransferase METTL3: acting as a tumor suppressor in renal cell carcinoma The M6A methyltransferase METTL3: acting as a tumor suppressor in renal cell carcinoma

The RNA methyltransferase NSUN2 has been involved in the cell proliferation and senescence, and is upregulated in various types of cancers. However, the role and potential mechanism of NSUN2 in gastric cancer remains to be determined. Our study showed that NSUN2 was significantly upregulated in gastric cancers, compared to adjacent normal gastric tissues. Moreover, NSUN2 could promote gastric cancer cell proliferation both in vitro and in vivo. Further study demonstrated that CDKN1C (p57^Kip2) was the potential downstream gene of regulated by NSUN2 in gastric cancer. NSUN2 could promote gastric cancer cell proliferation through repressing p57^Kip2 in an m⁵C-dependent manner. Our findings suggested that NSUN2 acted as an oncogene through promoting gastric cancer development by repressing p57^Kip2 in an m⁵C-dependent manner, which may provide a novel therapeutic target against gastric cancer.