MiR-503 regulates cisplatin resistance of human gastric cancer cell lines by targeting IGF1R and BCL2.

Abstract Studies have shown that the drug resistance of gastric cancer cells can be modulated by abnormal expression of microRNAs (miRNAs). We investigated the role of miR-503 in the development of cisplatin resistance in human gastric cancer cell lines. MiR-503 expression was measured by quantitative real-time PCR. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) and clonogenic assays were used to examine changes in cell viability and the drug resistance phenotype of cancer cells associated with upregulation or downregulation of the miRNA. A dual-luciferase activity assay was used to verify target genes of miR-503. Immunohistochemistry, Western blotting analysis, and a flow cytometric apoptosis assay were used to elucidate the mechanism by which miR-503 modulates drug resistance in cancer cells. MiR-503 was significantly downregulated in gastric cancer tissues and several gastric cancer cell lines. Additionally, downregulation of miR-503 in the cisplatin (DDP)-resistant gastric cancer cell line SGC7901/DDP was concurrent with the upregulation of insulin-like growth factor-1 receptor (IGF1R) and B-cell lymphoma 2 (BCL2) expression compared with the parental SGC7901 cell line. An in vitro drug sensitivity assay showed that overexpression of miR-503 sensitized SGC7901/DDP cells to cisplatin. The luciferase activity of reporters driven by IGF1R and BCL2 3'-untranslated regions in SGC7901/DDP cells suggested that IGF1R and BCL2 were both direct target genes of miR-503. Enforced miR-503 expression in SGC7901/DDP cells reduced expression of the target proteins, inhibited proliferation, and sensitized the cells to DDP-induced apoptosis. Our findings suggest that hsa-miR-503 modulates cisplatin resistance of human gastric cancer cells at least in part by targeting IGF1R and BCL2.