MicroRNA-93 promotes cell proliferation by directly targeting P21 in osteosarcoma cells

MicroRNAs (miRNAs) are small, non-coding RNAs that are key regulators of gene expression by directly binding to the 3'-untranslated region of their target mRNAs, resulting in translational repression or degradation of mRNA. It has been demonstrated that miRNAs have key roles in a variety of human malignancies, including osteosarcoma. The present study aimed to assess the molecular mechanism of miR-93 in the regulation of osteosarcoma cell proliferation. Reverse-transcription quantitative PCR and western blot assays were used to examine mRNA and protein expression. An MTT assay and flow cytometry were performed to determine the cell proliferation and cell cycle distribution. A luciferase reporter assay was performed to confirm the direct targeting of cyclin-dependent kinase inhibitor 1A (CDKN1A), also known as P21, by miR-93, which was suggested by a bioinformatics analysis. The results showed that the expression of miR-93 was frequently and significantly increased in a total of 19 osteosarcoma tissues compared to their matched adjacent non-tumor tissues, and the upregulation of miR-93 was associated with the malignant progression of osteosarcoma. Furthermore, miR-93 was also upregulated in the human osteosarcoma cell lines Saos-2, U2OS, SW1353 and MG63 when compared with that in the human osteoblast cell line hFOB1.19. Transfection with miR-93 inhibitor significantly reduced the miR-93 levels and inhibited the proliferation of U2OS and MG63 osteosarcoma cells. The protein levels of P21 were negatively regulated by miR-93 in U2OS and MG63 cells. Knockdown of miR-93 caused cell cycle arrest at G1 stage in U2OS and MG63 cells, identical to the effect of P21 overexpression. Finally, P21 was found to be significantly downregulated in osteosarcoma tissues compared to their matched adjacent non-tumor tissues, suggesting that the inhibition of P21 may be due to increased miR-93 expression in osteosarcoma tissues. In conclusion, the present study demonstrated that miR-93 enhances the proliferation of osteosarcoma cells, at least in part via inhibiting P21 expression and thus promoting cell cycle progression.