miR‑23b‑3p promotes the apoptosis and inhibits the proliferation and invasion of osteosarcoma cells by targeting SIX1.

Osteosarcoma (OS) is the most common primary malignant bone tumor and the third most common cancer that occurs during childhood and adolescence. Increasing evidence has suggested that microRNA (miR)‑23b‑3p has an important role in OS tumorigenesis; however, the underlying molecular mechanisms remain unknown. The aim of the present study was to investigate the expression levels of miR‑23b‑3p and sine oculis homeobox homolog 1 (SIX1) in OS tissues and cell lines (MG‑63, SaOS‑2 and U2OS), as well as to observe the effects of miR‑23b‑3p on U2OS cell viability, cell cycle, apoptosis and invasive ability. The results revealed that the expression levels of miR‑23b‑3p were significantly decreased in OS tissues and cell lines compared with tumor‑adjacent normal tissues and a non‑cancerous human fetal osteoblastic cell line (hFOB1.19). To investigate the underlying mechanisms of miR‑23b‑3p in OS tumorigenesis and progression, human U2OS cell lines over‑ or under expressing miR‑23b‑3p were established. The effects of miR‑23b‑3p on U2OS cell viability, cell cycle, apoptosis and invasion properties were determined by performing Cell Counting Kit‑8, flow cytometry and Transwell invasion assays. miR‑23b‑3p was revealed to suppress cell viability, proliferation and invasion, and to enhance the levels of cell apoptosis. Furthermore, SIX1 mRNA and protein expression levels in OS tissues and cell lines were significantly upregulated when compared with tumor‑adjacent normal tissues and hFOB 1.19 cells, which suggested that SIX1 expression levels may be inversely associated with miR‑23b‑3p levels in OS. Luciferase reporter system analysis demonstrated that miR‑23b‑3p binds to the SIX1 3'‑untranslated region. miR‑23b‑3p downregulation contributed to SIX1 upregulation, which facilitated the potentiation of cyclin D1 and vascular endothelial growth factor‑C expression levels, as well as the inhibition of caspase‑3 expression. Collectively, these results suggested that miR‑23b‑3p is downregulated and SIX1 is upregulated in OS cells, and that miR‑23b‑3p inhibition may suppress the proliferation and invasion of OS cells, and contribute to cell apoptosis via negative regulation of SIX1. miR‑23b‑3p/SIX1 may therefore represent a potential target for the treatment of OS.