MicroRNA-106b inhibits osteoclastogenesis and osteolysis by targeting RANKL in giant cell tumor of bone

Giant cell tumor (GCT) of bone consists of three major cell types: giant cells, monocytic cells, and stromal cells. From microarray analysis, we found that miR-106b was down-regulated in GCT clinical samples and further determined by fluorescence in situ hybridization. In addition, the expression of novel potential target of miR-106b, RANKL, was elevated in GCT along with previously determined targets in other tumors such as IL-8, MMP2 and TWIST. In a RANKL 3'UTR luciferase reporter assays, agomiR-106b repressed the luciferase activity and the effect was eliminated when the targeting site in the reporter was mutated, suggesting a direct regulation of miR-106b on RANKL mRNA. Moreover, overexpression of miR-106b in GCTSCs through TALEN-mediated site-specific knockin clearly inhibited osteoclastogenesis and osteolysis. By grafting the GCT onto the chick CAM, we confirmed the inhibitory effect of miR-106b on RANKL expression and giant cell formation. Furthermore, in an OVX mouse model, silencing of miR-106b increased RANKL protein expression and promoted bone resorption, while up-regulation of miR-106b inhibited bone resorption. These results suggest that miR-106b is a novel suppressor of osteolysis by targeting RANKL and some other cytokines, which indicates that miR-106b may be a potential therapeutic target for the treatment of GCT.