Platelet-rich miR-21 is a predictive biomarker in osteosarcoma and promotes osteosarcoma cell malignancyM

Platelet-derived microRNAs (miRNAs) are regarded as diagnostic biomarkers as well as potent regulators of cancer development. The expression of miR-21, a vital miRNA, is elevated in the tumor tissues of osteosarcoma (OS) patients. However, platelet-derived miR-21 in OS is unknown. Here, we found that the level of miR-21 is increased in the serum of OS patients. The miR-21 level is associated with advanced tumor stages and poorer clinical outcomes in OS patients. Moreover, platelet-derived microvesicles (PMVs) from OS patients (OS-PMVs) significantly enhanced the miR-21 profile in MG63 OS cells. Functional assays revealed that the proliferation and migration of MG63 cells were promoted by OS-PMV incubation or the transfection of miR-21 mimics, whereas the sensitivity of MG63 cells to methotrexate (MTX), doxorubicin (ADM), and cisplatin (DDP) was reduced. However, inhibiting miR-21 partially reversed the OS-PMV-mediated effects. Furthermore, programmed cell death 4 (PDCD4) was identified as a potential target of miR-21 in OS. miR-21 considerably inhibited PDCD4 expression in MG63 cells and reversed the antitumor effects mediated by PDCD4 overexpression. In conclusion, our results suggest that platelet-rich miR-21 may promote the development of OS by targeting PDCD4.