Spermine synthase (SMS) is an enzyme participating in polyamine synthesis; however, its function and role in pancreatic cancer remains elusive. Here we report that SMS is upregulated in pancreatic cancer and predicts a worse overall survival and significantly promotes the proliferation and migration of pancreatic cancer cells. Excessive SMS reduces the accumulation of spermidine by converting spermidine into spermine, which activates the phosphorylation of serine/threonine kinase (AKT) and epithelial-mesenchymal transition (EMT) signaling pathway, thereby inhibiting pancreatic cancer cell proliferation and invasion. Moreover, SMS was identified as the direct target of both methyltransferase like 3 (METTL3) and insulin like growth factor 2 mRNA binding protein 3 (IGF2BP3), which directly bind to the m6A modification sites of SMS and inhibit mRNA degradation. Knockdown of METTL3 or IGF2BP3 significantly reduced the SMS protein expression and inhibited the migration of pancreatic cancer. We propose a novel regulatory mechanism in which the METTL3-IGF2BP3 axis mediates the mRNA degradation of SMS in an m6A-dependent manner to regulate spermine/spermidine conversion, which regulates AKT phosphorylation and EMT activation, thereby inducing tumor progression and migration in pancreatic cancer.

Background Pancreatic cancer (PC) is highly malignant. Chemotherapy is the main treatment strategy, especially for patients with advanced PC. However, chemoresistance has always been a frequently encountered bottleneck. Hence, there is an urgent need to enhance the sensitivity of PC to gemcitabine (GEM). Results We demonstrated that SH3BP5-AS1 was significantly upregulated in GEM-resistant PC and predicted a poorer prognosis. SH3BP5-AS1 stability was regulated by ALKBH5/IGF2BP1-mediated m6A modification. Loss of SH3BP5-AS1 reduced PC cell migration and invasion and enhanced the sensitivity of PC to GEM, as confirmed by gain- and loss-of-function assays in vitro and in vivo. Bioinformatics analysis revealed that SH3BP5-AS1 acted as a ceRNA against miR-139-5p and directly targeted CTBP1, affecting the biological behavior of PC cells. The mechanistic studies revealed that the upregulation of SH3BP5-AS1 increased CTBP1 expression by directly activating the Wnt signaling pathway, promoting GEM resistance. Conclusions This study revealed that SH3BP5-AS1 activated Wnt signaling pathway by sponging miR-139-5p, upregulating CTBP1 expression, and contributing to the sensitivity of PC cells to GEM. SH3BP5-AS1 might be a potential target for PC therapy.

The aim of the present study was to clarify the mechanism of how METTL3 regulated pancreatic ductal adenocarcinoma (PDAC) progression by m6A modification of its downstream target mRNA and signaling pathway. Immunoblotting and qRT-PCR assays was employed to determine the expression levels of METTL3. In situ fluorescence hybridization was conducted to localize the cellular distribution of METTL3 and DEAD-box helicase 23 (DDX23). CCK8, colony formation, EDU incorporation, TUNEL, wound healing and Transwell assays were carried out accordingly to study the viability, proliferation, apoptosis, and mobility of cells under different treatments in vitro. Xenograft and animal lung metastasis experiments were also conducted to study the functional role of METTL3 or DDX23 on tumor growth and lung metastasis in vivo. MeRIP-qPCR and bioinformatical analyses were used to obtain the potential direct targets of METTL3. It was shown that m6A methyltransferase METTL3 was upregulated in PDAC tissues with gemcitabine resistance, and its knockdown sensitized pancreatic cancer cells to chemotherapy. Furthermore, silencing METTL3 remarkably reduced pancreatic cancer cell proliferation, migration, and invasion both in vitro and in vivo. Mechanistically, validation experiments confirmed that DDX23 mRNA was a direct target of METTL3 in YTHDF1-dependent manner. Additionally, DDX23 silence resulted in the suppression of pancreatic cancer cell malignancy and PIAK/Akt signaling inactivation. Strikingly, rescuse experiments demonstrated the inhibitive effects of METTL3 silence on cell phenotypes and gemcitabine resistance were partially reversed by forcibly expressed DDX23. In summary, METTL3 promotes PDAC progression and gemcitabine resistance by modifying DDX23 mRNA m6A methylation and enhancing PI3K/Akt signaling activation. Our findings establish a potential tumor promotive and chemo-resistant role for METTL3/DDX23 axis in PDAC.

Background Alternative splicing (AS) of genes has been found to affect gene stability, and its abnormal regulation can lead to tumorigenesis. CELF2 is a vital splicing factor to participate in mRNA alternative splicing. Its downregulation has been confirmed to promote the occurrence and development of pancreatic cancer (PC). However, the regulatory role and mechanisms in PC has not been elucidated. Results CELF2 was downregulated in PC tissues, which affected tumor TNM stage and tumor size, and low expression of CELF2 indicated a poor prognosis of PC. In vivo and in vitro experiments showed that abnormal expression of CELF2 affected the stemness, apoptosis, and proliferation of PC cells. Furthmore, we also found that CELF2 was targeted by ALKBH5 for m6A modification, leading to CELF2 degradation by YTHDF2. Bioinformatic analysis of AS model based on the TCGA database indicated that CELF2 could target CD44 to form different spliceosomes, thereby affecting the biological behavior of PC cells. The conversion of CD44s to CD44V is the key to tumorigenesis. Transcriptomic analysis was conducted to reveal the mechanism of CELF2-mediated CD44 AS in PC. We found that CELF2-mediated splicing of CD44 led to changes in the level of endoplasmic reticulum stress, further regulating the endoplasmic reticulum-associated degradation (ERAD) signaling pathway, thereby affecting apoptosis and cell stemness. In addition, ERAD signaling pathway inhibitor, EerI, could effectively reverse the effect of CD44 on tumors. Conclusions This study indicates that N6-methyladenosine-mediated CELF2 promotes AS of CD44, affecting the ERAD pathway and regulating the biological behavior of PC cells. CELF2 is expected to be a new target for targeted-drug development.