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

Chi Hin Wong,Yangchao Chen,Frederic Khe-Cheong Fung,Ka-Fai To,Stephen Lam Chan,Ut Kei Lou,Chang-Hua Zhang,Joanna H M Tong

doi:10.1186/s12943-021-01481-w

Abstract

BackgroundCircular 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).MethodsCircRTN4 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.ResultsCircRTN4 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.ConclusionThe 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

Highlights

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer mortality worldwide [1]
CircRTN4 was upregulated in pancreatic ductal adenocarcinoma (PDAC) CircRNAs profiling in non-tumor Human pancreatic ductal epithelial (HPDE) cell and PDAC PANC-1, SW1990 cells was performed to identify Circular RNA (circRNA) that play critical roles in PDAC [9]
We found that circRTN4 was significantly upregulated in 60% of the PDAC primary tumors (53 out of 88), while 18% of PDAC patients showed downregulated circRTN4 (16 out of 88), and 22% of PDAC patients showed unchanged circRTN4 (19 out of 88) (Fig. 1B)

Summary

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer mortality worldwide [1]. Understanding the mechanism underlying PDAC initiation and progression is crucial for the development of novel diagnostic biomarkers and therapeutic targets. Emerging studies identified important roles of circRNAs dysregulation in cancer progression [5,6,7]. The detailed functions and critical mechanisms by circRNAs in PDAC are still largely unexplored. Circular RNAs (circRNAs) play important roles in many biological processes. 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)

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