School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong.
Mol Cancer. 2022 Jan 4;21(1):10. doi: 10.1186/s12943-021-01481-w.
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).
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.
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.
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.
环状 RNA（circRNAs）在许多生物过程中发挥重要作用。然而，circRNAs 在癌症中发挥关键作用的详细机制在很大程度上仍未得到探索。我们旨在探索在胰腺导管腺癌（PDAC）中具有关键作用的环状 RTN4 的分子机制。
检测 PDAC 原发肿瘤中 circRTN4 的表达水平。在小鼠肿瘤模型中研究 circRTN4 在 PDAC 肿瘤生长和转移中的致癌作用。进行生物信息学分析、荧光素酶测定和 miRNA 下拉测定，以研究新型 circRTN4-miRNA-lncRNA 通路。为了鉴定 circRTN4 的相互作用蛋白，我们在 PDAC 细胞中进行了 circRNA 下拉和质谱分析。进行蛋白稳定性测定和三维结构建模，以揭示 circRTN4 在稳定 RAB11FIP1 中的作用。
circRTN4 在 PDAC 患者的原发肿瘤中显著上调。体外和体内功能研究表明，circRTN4 促进 PDAC 肿瘤生长和肝转移。机制上，circRTN4 在 PDAC 细胞中与肿瘤抑制 miR-497-5p 相互作用。circRTN4 敲低可上调 miR-497-5p 抑制致癌 lncRNA HOTTIP 的表达。此外，我们通过 PDAC 细胞中的 circRNA 下拉鉴定了关键的 circRTN4 相互作用蛋白。circRTN4 与重要的上皮-间充质转化（EMT）驱动因子 RAB11FIP1 相互作用，阻止其泛素化位点。我们发现，circRTN4 敲低通过增加其泛素化促进 RAB11FIP1 的降解。此外，circRTN4 敲低抑制了 PDAC 中 RAB11FIP1 调节 EMT 标志物 Slug、Snai1、Twist、Zeb1 和 N-钙粘蛋白表达。
上调的 circRTN4 通过新型 circRTN4-miR-497-5p-HOTTIP 通路促进 PDAC 中的肿瘤生长和肝转移。此外，circRTN4 稳定 RAB11FIP1 以促进 EMT。
