Hsa_circ_0008259 modulates miR-21-5p and PDCD4 expression to restrain osteosarcoma progression

Osteosarcoma (OS) is one of the most common primary bone tumors in children and adolescents. However, the molecular mechanism of OS tumorigenesis is still little known. Circular RNA (circRNA) is a key player in the progression of many cancers. This study is performed to decipher the role and mechanism of circ_0008259 in the progression of OS. A differentially expressed circRNA, circ_0008259, was screened out by analyzing the expression profile of circRNA in OS tissue. Circ_0008259, miR-21-5p and programmable cell death 4 (PDCD4) mRNA expression levels in OS tissues and cells were detected by qRT-PCR. Cell viability, metastatic potential and apoptosis were evaluated by cell counting kit-8 assay, Transwell and flow cytometry. The targeting relationship between circ_0008259 and miR-21-5p, and miR-21-5p and PDCD4 mRNA was analyzed and probed by bioinformatics analysis and dual-luciferase reporter assay, RNA-binding protein immunoprecipitation assay and RNA-pull down assay. The regulatory effects of circ_0008259 and miR-21-5p on PDCD4 protein expression in OS cells were detected by Western blot assay. Circ_0008259 expression and PDCD4 expression were down-regulated and miR-21-5p expression was elevated in the OS tissues and cells. Functional experiments showed that circ_0008259 overexpression significantly inhibited the proliferation and metastatic potential of OS cells and promoted the apoptosis. Besides, PDCD4 was validated as the target gene of miR-21-5p, and circ_0008259 could competitively bind to miR-21-5p, thus up-regulating PDCD4 expression in OS cells. Circ_0008259 suppresses OS progression via regulating miR-21-5p/PDCD4 axis.