BackgroundmiR-126 plays an important role in the proliferation, invasion, migration, and chemotherapeutics resistance in cancer. Epigallocatechin-3-gallate (EGCG), as the major polyphenolic constituent present in green tea, is a promising anticancer agent. However, the role of miR-126 in EGCG anticancer remains unclear. Here, we investigated the effects of miR-126 and EGCG on cell viability, apoptosis, cell cycle distribution of osteosarcoma cells and the sensitization of miR-126 on osteosarcoma cells to EGCG.MethodsThe cell viability, apoptosis and cycle distribution were analyzed using MTT assay and flow cytometry.ResultsOur results showed that EGCG (0.025, 0.05, 0.1, 0.2 g/L) suppresses proliferation of osteosarcoma MG63 and U2OS cells in a concentration-dependent and time-dependent manner and the inhibitory effects of 0.05 g/L EGCG on U2OS cells were roughly equivalent to 20 μM cisplatin (DDP); miR-126 could promote apoptosis and inhibit proliferation in U2OS cells but without significant effects on cell cycle G1 phase arrest; EGCG suppressed proliferation of U2OS cells through induction of cell cycle G1 arrest and apoptotic death; overexpression of miR-126 enhanced the inhibitory effects of EGCG on proliferation in U2OS cells via promotion of apoptosis.ConclusionsOur results demonstrate that enhanced expression of miR-126 increased the sensitivity of osteosarcoma cells to EGCG through induction of apoptosis.

Osteosarcoma (OS) has become one of the most common primary malignant tumors in the children and adolescents with a poor prognosis mainly due to high metastasis. A disintegrin and metalloprotease 9 (ADAM-9) plays a role in tumorigenesis, invasion, and metastasis in several tumors. miR-126 has been reported to be downregulated in OS tumor. However, the involvement of ADAM-9 in the pathology of OS and the relationship between miR-126 and ADAM-9 in OS cells remain unclear. In this study, using quantitative reverse-transcribed PCR (qRT-PCR) analysis on 37 pairs of OS tumors and matched adjacent normal bone tissues, we found that ADAM-9 is significantly upregulated, while miR-126 is downregulated in human OS tumors. Association analysis revealed that upregulation of ADAM-9 and downregulation of miR-126 are significantly involved in advanced clinical stage development and distant metastasis. Luciferase reporter assay revealed that miR-126 could directly target ADAM-9 3' untranslated region (UTR) and inhibit its expression in U2OS and MG-63 cells. Functional experiments revealed that downregulating ADAM-9 by miR-126 inhibited cellular growth, invasion, and migration in U2OS and MG-63 cells. In rescue experiments, restored ADAM-9 expression attenuated miR-126-mediated suppression, while knockdown of ADAM-9 by small interfering RNA (siRNA) represented similar results with miR-126-mediated tumor suppression in U2OS cells. Taken together, our data indicated that miR-126 inhibits cell growth, invasion, and migration of OS cells by downregulating ADAM-9.

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