Circular RNA circVRK1 suppresses the proliferation, migration and invasion of osteosarcoma cells by regulating zinc finger protein ZNF652 expression via microRNA miR-337-3p.

Circular RNA is an innovative kind of endogenous non-coding RNA, which could take part in tumorigenesis. Nonetheless, the potential molecular mechanisms of circVRK1 in the progression of osteosarcoma remain unresolved. In the current study, we initially investigated circVRK1 levels in osteosarcoma clinical samples and cell lines by qRT-PCR analysis and northern blot assay. RNase R treatments, RNA stability assay and nucleoplasmic separation assay were conducted to identify the characteristics of circVRK1. We adopted CCK-8, colony formation, wound-healing, and transwell assays to assess the biological effects of circVRK1 on the proliferation, migration, and invasiveness of osteosarcoma cells in vitro. We then constructed a xenograft model in nude mice to confirm the suppressive role of circVRK1 in vivo. Moreover, dual-luciferase reporter, RNA immunoprecipitation, and RNA pull-down assays were utilized to elucidate the underlying molecular mechanisms mediated by circVRK1. We demonstrated that circVRK1 was a stable circular transcript localized in the cytoplasm of osteosarcoma cells, and the down-regulation of circVRK1 in osteosarcoma tissues was related to poor outcome of patients. Meanwhile, over-expressed circVRK1 obviously restrained the growth, migration, and invasion of osteosarcoma in vitro and in vivo. Mechanistically, circVRK1 was assumed to be a microRNA sponge for miR-337-3p, and ZNF652 was the downstream gene of miR-337-3p. CircVRK1 overexpression or miR-337-3p knockdown accelerated ZNF652 expression, and up-regulated miR-337-3p efficiently abolished the promotion of ZNF652 induced by circVRK1. Moreover, rescue experiments have proved that circVRK1 inhibits the progression of osteosarcoma by modulating the miR-337-3p/ZNF652 axis. Therefore, we conclude that circVRK1 promotes ZNF652 expression by sponging miR-337-3p. CircVRK1 serves as a molecule sponge for miR-337-3p and mediates the ceRNA network to promote the expression of ZNF652, thus suppresses osteosarcoma proliferation, migration and invasion.