Putative Tumor Suppressor miR-145 Inhibits Colon Cancer Cell Growth by Targeting Oncogene Friend Leukemia Virus Integration 1 Gene

BACKGROUND: Tumor suppressor microRNA miR-145 is commonly down-regulated in colon carcinoma tissues, but its specific role in tumors remains unknown. METHODS: In this study, the authors identified the Friend leukemia virus integration 1 gene (FLI1) as a novel target of miR-145. FLI1 is involved in t(11;22)(q24:q12) reciprocal chromosomal translocation in Ewing sarcoma, and its expression appears to be associated with biologically more aggressive tumors. RESULTS: The authors demonstrated that miR-145 targets a putative microRNA regulatory element in the 3'-untranslated region (UTR) of FLI1, and its abundance is reversely associated with FLI1 expression in colon cancer tissues and cell lines. By using a luciferase/FLI1 3'-UTR reporter system, they found that miR-145 down-regulated the reporter activity, and this down-regulation was reversed by anti-miR-145. Mutation of the miR-145 microRNA regulatory element sequence in the FLI1 3'-UTR abolished the activity of miR-145. miR-145 decreased FLI1 protein but not FLI1 mRNA, suggesting a mechanism of translational regulation. Furthermore, the authors demonstrated that miR-145 inhibited cell proliferation and sensitized LS174T cells to 5-fluorouracil-induced apoptosis. CONCLUSIONS: Taken together, these results suggest that miR-145 functions as a tumor suppressor by down-regulating oncogenic FLI1 in colon cancer. Cancer 2011;117:86-95. (C) 2010 American Cancer Society.