CircRTN4 promotes pancreatic cancer progression through a novel CircRNA-miRNA-lncRNA pathway and stabilizing epithelial-mesenchymal transition protein

Abstract

Background Circular RNAs (circRNAs) play important roles in many biological processes. However, the detailed mechanism underlying the critical roles of circRNAs in cancer remains largely unexplored. We aim to explore the molecular mechanisms of circRTN4 with critical roles in pancreatic ductal adenocarcinoma (PDAC). Methods CircRTN4 expression level was examined in PDAC primary tumors. The oncogenic roles of circRTN4 in PDAC tumor growth and metastasis were studied in mouse tumor models. Bioinformatics analysis, luciferase assay and miRNA pulldown assay were performed to study the novel circRTN4-miRNA-lncRNA pathway. To identify circRTN4-interacting proteins, we performed circRNA-pulldown and mass spectrometry in PDAC cells. Protein stability assay and 3-Dimensional structure modeling were performed to reveal the role of circRTN4 in stabilizing RAB11FIP1. Results CircRTN4 was significantly upregulated in primary tumors from PDAC patients. In vitro and in vivo functional studies revealed that circRTN4 promoted PDAC tumor growth and liver metastasis. Mechanistically, circRTN4 interacted with tumor suppressor miR-497-5p in PDAC cells. CircRTN4 knockdown upregulated miR-497-5p to inhibit the oncogenic lncRNA HOTTIP expression. Furthermore, we identified critical circRTN4-intercting proteins by circRNA-pulldown in PDAC cells. CircRTN4 interacted with important epithelial-mesenchymal transition (EMT)- driver RAB11FIP1 to block its ubiquitination site. We found that circRTN4 knockdown promoted the degradation of RAB11FIP1 by increasing its ubiquitination. Also, circRTN4 knockdown inhibited the expression of RAB11FIP1-regulating EMT-markers Slug, Snai1, Twist, Zeb1 and N-cadherin in PDAC. Conclusion The upregulated circRTN4 promotes tumor growth and liver metastasis in PDAC through the novel circRTN4-miR-497-5p-HOTTIP pathway. Also, circRTN4 stabilizes RAB11FIP1 to contribute EMT. Graphical abstract

Long Noncoding RNA and Circular RNA: Two Rising Stars in Regulating Epithelial-Mesenchymal Transition of Pancreatic Cancer

“…Their results also suggested that circRTN4 may function as a sponge of miR-497-5p, which can also bind with lnc-HOTTIP. Thus circRTN4 can also contribute to the EMT via the miR-497-5p/ HOTTIP/HOXA13 pathway in PDAC (147,150).…”

The Role of MicroRNA in the Regulation of Tumor Epithelial–Mesenchymal Transition

“…Ultimately, it slowed the proliferation and metastasis of glioma cells and alleviated the cellular EMT process [134]. Interestingly, circular RNA (circRTN4) interacted with miR-497-5P to regulate the downstream RAB11FIP1 protein to block the ubiquitination, which inhibited Snail1/2, Twist, ZEB1, and N-cadherin to promote the metastasis of pancreatic ductal carcinoma cells [135]. miR-139-5p regulates the transcription factor Twist and the mesenchymal marker proteins N-cadherin and vimentin by targeting the sex-determining region Y-box protein 5 (SOX5) to achieve EMT inhibition [136].…”

Critical Roles of Circular RNA in Tumor Metastasis via Acting as a Sponge of miRNA/isomiR

“…Pancreatic ductal adenocarcinoma (PDAC) has been the seventh leading cause of cancer death worldwide [92]. The researchers found that circ-0001666 acts as a sponge of miR-1251, the circRNA-associated ceRNA network further up-regulates SOX4 [93], and circRTN4 regulates the expression of Slug, Snai1, Twist, Zeb1, and N-cadherin in the EMT pathway by interacting with tumor suppressor miR-497-5p [94]. Circ-000510 acts as a sponge of miR-20a-3p and indirectly regulates the expression of COL11A1 [95]; circ-0092314 can promote the proliferation, migration, and invasion of pancreatic cancer cells by binding to miR-671 and alleviating the inhibition of its downstream target S100P [96]; circNEIL3 regulates the expression of ADAR1 by acting as a sponge of miR-432-5p, so as to induce RNA editing of GLI1, and ultimately affect the cell cycle progress and promote EMT [97].…”