MicroRNA-145 inhibits tumour growth and metastasis in osteosarcoma by targeting cyclin-dependent kinase, CDK6.

Osteosarcoma (OS) is reported to be one of the most familiar forms of the primary malignant tumor to adolescents and adults, which is usually found in their long bones. Evidence and data have shown that abnormality in micro-RNA expression is closely related to tumorigenesis. The aim of this study is to investigate the expression, function and underlying mechanism of miR-145 in OS.MiR-145 expression in tumor tissues of patients and cell lines were detected by SYBR green qPCR. Kaplan-Meier method and log-rank test were applied to analyze the overall survival of patients with different miR-145 expression. MG-63 and U2OS cells were transfected with miR-145 or miR-NC, after which we recorded and analyzed the proliferation, migration and invasion respectively. Potential binding sites of miR-145 in CDK6 was identified using TargetScan 6.2. Meanwhile, OS cells were transfected with miR-NC, miR-145, or transfected with miR-145 and CDK6 vector together to find out whether the effect of miR-145 inhibit growth and mobility of OS cells were via targeting CDK6. Moreover, the expression of miR-145 was mediated by a constructed lentivirus vector to inoculate nude mice to observe the inhibiting effect of miR-145 in OS in vivo.MiR-145 downregulation was remarkably related with the occurrence of a phenotype of OS with more aggressiveness. The univariate analysis was applied which showed that with a lower miR-145 level in OS patients led to a more unfavorable prognosis, or, a lower overall survival rate. In OS cells, cell proliferation, motility and invasion were inhibited by ectopic overexpression of miR-145 in vitro. Further studies into the mechanism indicated that its expression probably has a close interrelationship with the 3'- untranslated region (3'-UTR) of CDK6 mRNA, whose mRNA and expression levels were inhibited. And it is found that CDK6 expression was also reversely related to miR-145 expression in clinical specimens. In in vivo experiment, the miR-145 inhibits the growth of OS tumor.miR-145 plays a crucial role in inhibiting invasive and metastatic of OS, whose underlying mechanism probably is directly targeting CDK6. Therefore, MiR-145 is believed to have an important role in growth and metastasis of OS.