Down-regulation of miR-183 promotes migration and invasion of osteosarcoma by targeting Ezrin. Recent studies have emphasized causative links between aberrant microRNA expression patterns and cancer progression. miR-183 is dysregulated in certain types of human cancers. The expression pattern, clinical significance, and biological role of miR-183 in osteosarcoma, however, remain largely undefined. In this paired analysis, we found that miR-183 was markedly down-regulated in osteosarcoma cells and tissues compared with matching normal bone tissues using RT-qPCR. Statistical analyses revealed that the expression levels of miR-183 significantly correlated with lung metastasis as well as with local recurrence of osteosarcoma. miR-183 expression was inversely correlated with Ezrin mRNA and protein expression levels in osteosarcoma cells as well as in a subset of primary osteosarcoma. Ectopically expressed miR-183 inhibited migratory and invasive abilities of osteosarcoma cells, whereas knockdown of endogenous miR-183 significantly enhanced these abilities. Using a luciferase reporter carrying the 3'-untranslated region (3'-UTR) of Ezrin, we identified Ezrin as a direct target of miR-183. Moreover, ectopic expression of Ezrin could significantly rescue miR-183-suppressed migration and invasion. Of interest, suppression of Ezrin by miR-183 caused a reduction of phosphorylated p44/42 (p-p44/42). Finally, suppression of Ezrin by RNAi mimicked miR-183 action in the suppression of migration and invasion, which was associated with down-regulation of p-p44/42. Taken together, these results suggest that as a tumor suppressor miRNA, miR-183 plays an important role in the aggressiveness of osteosarcoma.Copyright © 2012 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.