Role of miR-19b and its target mRNAs in 5-fluorouracil resistance in colon cancer cells

Background Drug resistance in colorectal cancers is assumed to be mediated by changes in the expression of microRNAs, but the specific identities and roles of microRNAs are largely unclear. We examined the effect of 5-fluorouracil (5-FU) resistance on microRNA expression. Methods Two types of 5-FU-resistant colon cancer cells were derived from the DLD-1 and KM12C cell lines. The expressions of microRNAs were profiled with a microarray containing 723 microRNAs and validated by quantitative real-time polymerase chain reaction (qRT-PCR). To survey the downstream mediators of microRNA, we used a microRNA:mRNA immunoprecipitation (RIP)-Chip and pathway analysis tool to identify potential direct targets of microRNA. Results In response to 5-FU, miR-19b and miR-21 were over-expressed in 5-FU-resistant cells. Of note, miR-19b was up-regulated 3.47-fold in the DLD-1 resistant cells, which exhibited no alteration in cell cycle profiles despite exposure to 5-FU. After transfection of miR-19b, specific mRNAs were recruited to microRNA:mRNA complexes isolated with Ago2 antibody and subjected to whole-genome transcriptional analysis. In this analysis, 66 target mRNAs were enriched by at least 5.0-fold in the microRNA:mRNA complexes from DLD-1 resistant cells. Ingenuity pathway analysis of mRNA targets significantly ( P