miR-16 binds COX-2 mRNA and inhibits its translation.
(A) WRL68 cell extracts (500 µg per lane) were immunoprecipitated with Ago-2 or IgG antibodies. Bound RNA was harvested with TRIzol reagent, reverse transcriptased, and PCR amplified with COX-2 primers. PCR products were visualized by electrophoresis in SYBR Safe DNA gel stain agarose gels. The presence of COX-2 mRNA in WRL68 cell transfected with miR-16 or Lipofectamine after Ago2 immunoprecipitation was assessed, and fold differences were plotted. Input, total mRNA in cell extract; and control, bound mRNA after immunoprecipitation with IgG antiboby. (B) Scheme of pGL3-empty, pGL3-seed and pGL3-mut reporter vectors. In pGL3-seed, the putative binding site of miR-16 on COX-2 mRNA 3′-UTR region (as detected by RNAhybrid software) was introduced downstream luciferase gene. In pGL3-mut this region was mutated in order to avoid the binding between miR-16 and Luc mRNA. (C–D) A luciferase assay was carried out on HuH-7 and HepG2 cell lines using pGL3-seed and pGL3-mut reporter vectors. Firefly luciferase activity was evaluated 48 h after co-transfection with pGL3-empty/seed/mut (750 ng), miR-16 (50 nM), In-miR-16 (50 nM) and miR-NC (50 nM) as indicated. Data were normalized against renilla luciferase activity (all samples were co-transfected with 50 ng pRL vector and refer to the positive control, pGL3 empty vector). Data are reported as means±SD of three independent experiments. *p< 0.05 vs. the pGL3-empty condition and # p< 0.05 vs. the miR-16 transfection condition.