Objective: Osteosarcoma (OS) is the most common malignant bone tumor in the pediatric population. The main goal of this study is to investigate the role of hsa_circ_0005909 and the underlying signaling pathway involved in OS.

Methods: Cell proliferation was measured using a CCK-8 assay kit and clone formation assay. Change of RNA and protein expression was determined using RNA extract and quantitative real time PCR (RT-qPCR) assay and Western blotting, respectively. CircInteractome was used to predict the target of circRNA and starBase v2.0 was used to predict the target of miRNAs. Luciferase assay was used to confirm the predicted results from CircInteractome, starBase v2.0, and MirTarget2.

Results: Expression of circ_0005909 was upregulated in both OS tissues and cell lines. The predicted results from CircInteractome, starBase v2.0, and MirTarget2 demonstrated that circ_0005909 could sponge miR-338-3p and that HGMA1 was the direct target of miR-338-3p. Cell viability and cell clones were inhibited by knockdown of circ_0005909 but increased by dual inhibition of circ_0005909 and miR-338-3p. Phosphorylation of ERK, Akt, and PI3K was inhibited by sh-circ_0005909, while this inhibition was repressed by co-transfection of sh-circ_0005909 and HGMA1.

Conclusion: Expression of circ_0005909 was upregulated in both OS tissues and cell lines which upregulated expression of HGMA1 through sponging miR-338-3p, resulting in the activation of MAPK-ERK and PI3K-Akt signaling pathways to promote the development of OS.