<p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRNAs) are endogenously expressed noncoding RNAs with important biological and pathological functions. Although several studies have shown that microRNA-31 (miR-31) is obviously up-regulated in colorectal cancer (CRC), there is no study on the functional roles of miR-31 in CRC.</p> <p>Methods</p> <p>Anti-miR™ miRNA 31 inhibitor (anti-miR-31) is a sequence-specific and chemically modified oligonucleotide to specifically target and knockdown miR-31 molecule. The effect of anti-miR-31 transfection was investigated by real-time PCR. HCT-116<sup>p53+/+ </sup>and HCT-116<sup>p53-/-</sup>colon cancer cells were treated by anti-miR-31 with or without 5-fluorouracil (5-FU), cell proliferation was determined by MTT assay; apoptosis was detected by DAPI staining; cell cycle was evaluated by flow cytometry; colony formation, migration and invasion assays were performed to investigate the effect of suppression of miR-31 on the cell lines.</p> <p>Results</p> <p>Real-time PCR results showed that anti-miR-31 was efficiently introduced into the cells and reduced miR-31 levels to 44.1% in HCT-116<sup>p53+/+ </sup>and 67.8% in HCT-116<sup>p53-/-</sup>cell line (<it>p </it>= 0.042 and 0.046). MTT results showed that anti-miR-31 alone had no effect on the proliferation of HCT-116<sup>p53+/+ </sup>or HCT-116<sup>p53-/-</sup>. However, when combined with 5-FU, anti-miR-31 inhibited the proliferation of the two cell lines as early as 24 h after exposure to 5-FU (<it>p </it>= 0.038 and 0.044). Suppression of miR-31 caused a reduction of the migratory cells by nearly 50% compared with the negative control in both HCT-116<sup>p53+/+ </sup>and HCT-116<sup>p53-/-</sup>(<it>p </it>= 0.040 and 0.001). The invasive ability of the cells were increased by 8-fold in HCT-116<sup>p53+/+ </sup>and 2-fold in HCT-116<sup>p53-/- </sup>(<it>p </it>= 0.045 and 0.009). Suppression of miR-31 had no effect on cell cycle and colony formation (<it>p </it>> 0.05).</p> <p>Conclusions</p> <p>Suppression of miR-31 increases sensitivity to 5-FU at an early stage, and affects cell migration and invasion in HCT-116 colon cancer cells.</p
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