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Background MicroRNAs (miRNAs) contribute to tumorigenesis by acting as either oncogenes or tumor suppressor genes.In this study,we investigated the role of miR-145 in the pathogenesis of uveal melanoma.Methods Expression profiles of miRNAs in uveal melanoma were performed using Agilent miRNA array.Quantitative real-time polymerase chain reaction was used to screen the expression levels of miR-145 in normal uveal tissue,uveal melanoma tissue,and uveal melanoma cell lines.Lenti-virus expression system was used to construct MUM-2B and OCM-1 cell lines with stable overexpression of miR-145.Cell proliferation,cell cycle,and cell apoptosis of these miR-145 overexpression cell lines were examined by MTT assay and flow cytometry respectively.The target genes of miR-145 were predicted by bioinformatics and confirmed using a luciferase reporter assay.The expression of insulin-like growth factor-1 receptor (IGF-1R),insulin receptor substrate-1 (IRS-1) proteins was determined by West blotting analysis.IRS-1 was knocked down in OCM-1 cells.TUNEL,BrdU,and flow cytometry assay were performed in IRS-1 knocked down OCM-1 cell lines to analyze its function.Results Forty-seven miRNAs were up regulated in uveal melanoma and 61 were down regulated.miR-145 expression was significantly lower in uveal melanoma sample and the cell lines were compared with normal uveal sample.Overexpression of miR-145 suppressed cell proliferation by blocking the G1 phase entering S phase in uveal melanoma cells,and promoted uveal melanoma cell apoptosis.IRS-1 was identified as a potential target of miR-145 by dual luciferase reporter assay.Knocking down of IRS-1 had similar effect as overexpression of miR-145.Conclusion miR-145 might act as a tumor suppressor in uveal melanoma,and downregulation of the target IRS-1 might be a potential mechanism.