circPVT1 Facilitates Invasion and Metastasis by Regulating miR-205-5p/c-FLIP Axis in Osteosarcoma

Background: As a key subtype of non-coding RNAs, circular RNA (circRNA) has been well documented to play a key role in the tumorigenesis of osteosarcoma (OS). circPVT1 was revealed to participate in the progression of multiple human tumors; however, the roles of circPVT1 in OS invasion and metastasis and its potential mechanisms remain elusive. Methods: RNA expression in OS tissues and cells was examined by qRT-PCR, protein expression was measured by Western blot. circPVT1 knockdown in vitro was achieved by transfecting OS cells with specific siRNAs. OS cell proliferation was assessed via CCK-8 and colony formation assays. OS cell migration and invasion were evaluated by transwell assay. Interaction between miR-205-5p and circPVT1 or c-FLIP was validated through dualluciferase reporter assay. Rescue experiments were performed to explore the regulatory net among circPVT1, miR-205-5p and c-FLIP in OS progression in vitro. Results: circPVT1 and c-FLIP were highly expressed, while miR-205-5p was lowly expressed in OS tissues and cell lines. Knockdown of circPVT1 repressed cell proliferation, migration and invasion via inhibiting epithelial-mesenchymal transition (EMT) in OS. circPVT1 functioned as a sponge of miR-205-5p, and c-FLIP was targeted by miR-205-5p in OS cells. Furthermore, circPVT1 indirectly regulated c-FLIP expression through competitively binding to miR-205-5p. Inhibition of miR-205-5p or overexpression of c-FLIP abolished the effects of si-circPVT1 on cell proliferation, migration and invasion. Conclusion: Our study demonstrated circPVT1 functions as a sponge for miR-205-5p to promote c-FLIP expression, thereby enhancing EMT and inducing OS invasion and metastasis in vitro, implying that circPVT1 might be a potential therapeutic target for further clinical therapy of OS.