MicroRNA-223 functions as an oncogene in human gastric cancer by targeting FBXW7/hCdc4

The aim of this study was (a) to determine the role of micro-223 (miR-223) in gastric cancer and (b) to elucidate its regulatory mechanism on the FBXW7/hCdc4 gene. Artificial miR-223 and control oligonucleotide was transfected into gastric cancer cell line SGC7901 by using Lipofectamine2000. Apoptosis of miR-223 group and control group cells was analyzed by flow cytometry, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and colony formation assays were performed to detect the cell viability, to survey migration of miR-223 group and control group cells; scratch wound-healing motility assays, Transwell Assay, and Western blot test were performed to measure the variance of hFBXW7. Luciferase Reporter Assay, which was done by pLUC-hFBXW7 WT-3'-UTR co-transfected with pLMP-hsa-miR-223 or pLMP plasmid (as control) into HEK293T cells, used to detect whether hFBXW7 is a direct target gene of miR-223. Gastric cancer cell line SGC7901 transfected with miR-223 or control oligonucleotide was resuspended in ECM gel and then was injected into the flank of nude mice, 4 weeks later, the nude mice were euthanized. The tumors were excised then were measured and weighted. SYBR-Green I-based real-time RT-PCR study was used to detect the level of miR-223 in 22 gastric cancer tissue and corresponding gastric mucosa tissues. Immunohistochemical method was applied to detect the protein of hFBXW7. Gastric cancer cell line SGC7901, transfected with miR-223, showed significant reduction in cellular apoptosis and increased proliferation and invasion in vitro. Similar results were found in tumorigenesis assays performed in nude mice. Moreover, 19 of 22 cancer tissue samples highly expressed miR-223, when compared with patient-matched normal gastric mucosa. Specifically, patients with lymph node metastasis or metastatic disease (M1) at an advanced pathological stage showed significantly higher expression of miR-223. FBXW7/hCdc4 protein (FBW7) levels in gastric cancer cases were inversely correlated with miR-223 expression. Overexpression of miR-223 in gastric cancer cell lines decreased FBW7 expression at the translational level and decreased FBXW7/hCdc4-driven luciferase-reporter activity. In summary, the data indicated that miR-223 targets FBXW7/hCdc4 expression at the post-transcriptional level and appears to regulate cellular apoptosis, proliferation, and invasion in gastric cancer. MiR-223 may serve as a novel therapeutic target in gastric cancer.