Ionizing radiation is genotoxic to the cell, and p53 is commonly considered to be a key regulator that controls gene expression responding to the genotoxity of radiation. The expression profiles of microRNAs (miRNAs), which are small non-coding RNAs regulating the translation of target mRNAs, were analyzed to determine whether any correlation exists between miRNA expression, radiation response, and/or p53. The miRNA profiles were analyzed by microarray containing 470 human miRNA probes in HCT116 human colon carcinoma cells and their p53-null derivative. Thirty-eight miRNAs among the 138 flagged human miRNAs were selected by fold-change analysis. The expression levels of these 38 miRNAs were changed more than two-fold, and a total of 12 miRNAs were significantly affected by p53, radiation, and the combination of both. All 12 miRNAs had expression patterns correlated to p53, while two miRNAs were affected by radiation or the combined action of radiation and p53. In bioinformatics studies, these miRNAs had p53-binding sites with scores higher than 85% in their upstream regions, and some of their target genes were found to be involved in genotoxic responses. In conclusion, we have identified miRNAs influenced significantly by p53 and/or radiation in the HCT116 human colon carcinoma cell line model, and these miRNAs may have important roles in the regulation of genes involved the cellular responses to radiation.

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