DNA Methylation Mediated Down-Regulation of miR-370 Regulates Cell Growth through Activation of the Wnt/β-Catenin Signaling Pathway in Human Osteosarcoma Cells

MicroRNA-370 (miR-370) has been observed to act as a tumor suppressor through the targeting of different proteins in a variety of tumors. Our previous study indicated that miR-370 was able to target forkhead box protein M1 (FOXM1) to inhibit cell growth and metastasis in human osteosarcoma cells. In this study, we reported that FOXM1 interacted with beta-catenin in vitro and in vivo. Similar to FOXM1, critical components of the Wnt signaling pathway, including beta-catenin, c-Myc, and Cyclin D1, were also highly expressed in different human osteosarcoma cells lines. Pharmacological inhibition of FOXM1 or beta-catenin but not of c-Myc was associated with the increased expression of miR-370. Ectopic expression of miR-370 inhibited the downstream signaling of beta-catenin. Moreover, osteosarcoma cells treated with 5-AZA-2'-deoxycytidine (AZA), a DNA methylation inhibitor, exhibited increased levels of miR-370 and decreased levels of a-catenin downstream targets, which resulted in inhibition of cell proliferation and colony formation ability. In conclusion, our results supported a model in which the DNA methylation-mediated down-regulation of miR-370 reduced its inhibitory effect on FOXM1, thereby promoting FOXM1-beta-catenin interaction and activating the Wnt/beta-Catenin signaling pathway in human osteosarcoma cells.