MicroRNA cloning and sequencing in osteosarcoma cell lines: differential role of miR-93. Studies show that abnormalities in non-coding genes can contribute to carcinogenesis; microRNA levels may modulate cancer growth and metastatic diffusion.MicroRNA libraries were built and sequenced from two osteosarcoma cell lines (MG-63 and 143B), which differ in proliferation and transmigration. By cloning and transfection, miR-93, expressed in both cell lines, was then investigated for its involvement in osteosarcoma progression.Six of the 19 miRNA identified were expressed in both cell lines with higher expression levels of miR-93 in 143B and in primary osteosarcoma cultures compared to normal osteoblasts. Interestingly, levels of miR-93 were significantly higher in metastases from osteosarcoma than in paired primary tumours. When 143B and MG-63 were transfected with miR-93, clones appeared to respond differently to microRNA overexpression. Ectopic expression of miR-93 more significantly increased cell proliferation and invasivity in 143B than in MG-63 clones. Furthermore, increased mRNA and protein levels of E2F1, one of the potential miR-93 targets, were seen in osteosarcoma cellular clones and its involvement in 143B cell proliferation was confirmed by E2F1 silencing.Although further studies are needed to evaluate miRNA involvement in osteosarcoma progression, miR-93 overexpression seems to play an important role in osteosarcoma cell growth and invasion.