MicroRNA-29a suppresses the invasion and migration of osteosarcoma cells by regulating the SOCS1/NF-κB signalling pathway through negatively targeting DNMT3B

The present study aimed to investigate the roles of the microRNA-29a/DNA methyltransferase 3B/suppressor of cytokine signalling 1 (miR-29a/DNMT3B/SOCS1) axis in the invasion and the migration of osteosarcoma (OS). The expression levels of miR-29a, DNMT3B and SOCS1 were determined in tissue samples and OS cell lines by reverse transcription-quantitative polymerase chain reaction (PCR). Apoptosis was measured using flow cytometry analysis. Transwell and wound healing assays were conducted to measure the invasion and migration abilities of OS cells, respectively. A dual-luciferase reporter assay was also conducted to determine the interaction between DNMT3B and miR-29a, while methylation-specific PCR was used to detect the methylation of SOCS1. Western blotting was performed to determine the protein levels of DNMT3B and SOCS1, as well as the levels of proteins associated with epithelial-mesenchymal transition (EMT), apoptosis and the nuclear factor (NF)-κB signalling pathway. The results demonstrated that miR-29a and SOCS1 were downregulated, and DNMT3B was upregulated in both OS tissues and cell lines. The expression of miR-29a and SOCS1 was found to be associated with advanced clinical stage and distant metastasis. In addition, the dual-luciferase reporter assay revealed that DNMT3B was a direct target of miR-29a. Overexpression using miR-29a mimics decreased DNMT3B expression and the methylation level of SOCS1, which resulted in the upregulation of SOCS1 in U2OS and MG-63 cells, while miR-29a inhibition led to the opposite results. Transfection with miR-29a mimics also promoted the apoptosis, and inhibited the invasion, migration and EMT process of OS cells, while it markedly reduced the nuclear translocation of p65 and IκB-α degradation. Treatment with 5-aza-2′-deoxycytidine worked together with miR-29a mimics to synergistically enhance the aforementioned effects. By contrast, the effects induced by miR-29a were partly reversed upon co-transfection with SOCS1 siRNA. In conclusion, miR-29a promoted the apoptosis, and inhibited the invasion, migration and EMT process of OS cells via inhibition of the SOCS1/NF-κB signalling pathway by directly targeting DNMT3B.