CircABCC3 knockdown inhibits glioblastoma cell malignancy by regulating miR-770-5p/SOX2 axis through PI3K/AKT signaling pathway

Background: Circular RNAs (circRNAs) are found to regulate glioblastoma evolution. However, the role of circ-ATP binding cassette subfamily C member 3 (circABCC3) in glioblastoma process is still unknown. In this study, the effects of circABCC3 on glioblastoma tumorigenesis and underlying mechanism were revealed.

Methods: The expression levels of circABCC3, microRNA-770-5p (miR-770-5p) and sex determining region Y-box protein 2 (SOX2) mRNA were determined by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway-related proteins and SOX2 protein was detected by western blot analysis. Cell proliferation and invasion were severally investigated by cell colony formation and transwell invasion assays. Cell migration was demonstrated by transwell migration and wound-healing assays. Cell apoptosis was revealed by flow cytometry analysis. Tube formation was investigated by tube formation assay. The associated relationship between miR-770-5p and circABCC3 or SOX2 was predicted by starbase or targetscan online database, and identified by dual-luciferase reporter assay, RNA immunoprecipitation assay or RNA pull-down assay. The impacts of circABCC3 knockdown on glioblastoma growth in vivo were revealed by in vivo assay.

Results: CircABCC3 and SOX2 expression were dramatically upregulated, while miR-770-5p expression was apparently downregulated in glioblastoma tissues and cells compared with control groups. CircABCC3 expression was higher in stage III glioblastoma tissues than in stage I + II glioblastoma tissues with close correlation with tumor-node-metastasis (TNM) stage. CircABCC3 absence inhibited cell proliferation, migration, invasion, tube formation and the activation of PI3K/AKT pathway, whereas induced cell apoptosis in glioblastoma. Additionally, circABCC3 acted as a sponge for miR-770-5p, and miR-770-5p targeted SOX2. MiR-770-5p inhibitors impaired the impacts of circABCC3 silencing on glioblastoma progression, angiogenesis and PI3K/AKT pathway. Furthermore, circABCC3 knockdown repressed tumor growth in vivo.

Conclusion: CircABCC3 regulated glioblastoma development via miR-770-5p/SOX2 axis through PI3K/AKT pathway. This finding lays a theoretical foundation for studying circRNA-directed therapy for glioblastoma.