miRNA expression profile in human osteosarcoma: role of miR-1 and miR-133b in proliferation and cell cycle control.

miRNA profile deregulation affecting downstream signaling pathways activates endpoints that represent potential biomarkers for prognosis and treatment of tumor patients. In the past 20 years conventional therapy for osteosarcoma (OS) reached a survival plateau, highlighting the need for new therapeutic approaches. In this study, microarray unsupervised and supervised analysis identified, respectively, 100 and 40 differentially expressed miRNAs in OS samples with different grades of malignancy compared to normal bone. When analyzing low-grade and high-grade OS by unsupervised analysis, 12 miRNAs were found to be differentially expressed. Real­time PCR performed on a larger series of OS confirmed a significant lower expression of miR-1, miR­133b and miR-378* in tumors with respect to control, also showing lower mRNA levels in 31 high-grade OS than in 25 low-grade and in metastatic versus non­metastatic patients. We demonstrated that miR-1 and miR133b were downregulated in OS cell lines compared to normal osteoblasts. Secondly, by transfection with miRNA precursor molecules, we demonstrated that the ectopic expression of miR-1 and miR-133b in U2-OS cell lines significantly reduced cell proliferation and MET protein expression and negatively regulated cell invasiveness and motility in a short-term assay. Cell cycle distribution revealed block in G(1) and delay of cell cycle progression associated with increased apoptosis in miR-1- and miR­133b­transfected cells, respectively. Our data assessed specific miRNA profiling deregulation in OS clinical samples and suggest that the expression of miR-1 and miR-133b may control cell proliferation and cell cycle through MET protein expression modulation.