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Using multiple parallel sequencing on Illumina platform, we identified eight microRNAs that showed significant opposite changes of gene expression in cells of the hormone-sensitive LNCaP prostate cancer cell line and in cells of the hormone-resistant DU-145 cell line, in comparison to the microRNA expression in the normal prostate tissue cells. We found that the insulin-like growth factor 1 receptor (IGF1R) gene is a target of five microRNAs whose expression is increased in LNCaP cells and reduced in DU-145 cells.

The dependence of expression of miRNAs and their precursors (pre-miRNAs) on the DNA methylation level in HeLa cells 8 days after mitomycin C treatment was studied. A massive parallel DNA sequencing method was applied to analyze miRNA expression. 5-Azacytidine (DNA methylation inhibitor) was added to the medium 6 days after mutagenic agent exposure. The results indicated that the change in expression for some mature miRNAs (39 of 61) was accompanied by the change in the expression of their pre-miRNAs, while there were no significant changes in the expression of pre-miRNA for other mature miRNAs (22 of 61). The aberrant expression was maintained by 8 of 61 mature miRNAs and 6 of 55 pre-miRNAs in the induced HeLa cells after 5-azacytidine treatment. In addition, the expression of more than 90% of miRNAs, which indicated a significant change in expression after mitomycin C treatment, does not depend or depends slightly on the DNA methylation level in HeLa cells without mitomycin C treatment. The results suggest that mitomycin C induces aberrant DNA methylation which affects maintenance of changes in the miRNA expression in cell generations after mutagen treatment.

It was first shown that DNA damage induction in mitomycin C-treated HeLa cells leads to a change in the selection of 5p and 3p microRNA duplex strands in the formation of the RNA-induced silencing complex (RISC).

Applying the method of multiple parallel sequencing on the MiSeq platform (Illumina, United States), a comparative analysis of miRNA expression in tumor and normal colon tissuie cells was performed. Forty miRNAs aberrantly expressed in cancer were detected. Among them, 15 and 25 miRNAs showed increased arid decreased expression, respectively, for all or most of the cases. Sixteen miRNA clusters were identified, which showed a coordinated or incompletely coordinated aberrant expression in colorectal cancer cells. In two (miR-183/182 and miR-106b/25) and four (miR-143/145, miR-497/195, miR-30e/30c-1, and miR-30a/30c-2) miRNA clusters, respectively, a statistically significant coordinated increase or decrease in expression was iegistered for all miRNAs withini the corresponding cluster. Three aberrantly expressed well-known miRNAs (miR-100-5p, mil-30d-5p, and miR-204-5p) were identified, which, however, had never 'before been associated with coloreictal cancer. The obtained results demonstrate the potential and promising application of 6 miRNA clusters with' coordinated aberrant expression as markers for colorectal cancer.

We identified 40 miRNAs with inherited aberrant expression by multiple parallel sequencing of human HeLa cells irradiated with X rays and mitomycin C. Twenty-two miRNAs were repressed and 15 miRNAs were induced after radiation and mytomycin C treatment. The expression of three miRNAs (miR-10b-5p, miR-148a-3p, and miR-340-5p) decreased after X-ray exposure and increased after mitomycin C treatment. The spectrum of aberrantly expressed miRNAs after X-ray and mitomycin C treatment is different, except for three miRNAs (mir-100-5p, miR-99b-5p, miR-501-3p), which showed the inherited decreased expression after both mutagens. It has been ascertained that for five miRNAs (miR-21-3p, miR-182-5p, miR-19b-3p, miR-30a-3p, and miR-30e-3p) with increased inherited expression, the targets are well-described tumor suppressor genes. For 9 miRNAs (miR-99b-5p, miR-148a-3p, miR-365a-3p, miR-193a-3p, miR-100-5p, miR-99a-5p, miR-29b-3p, miR-340-5p, and miR-23b-3p) with reduced inherited expression, the targets are oncogenes. The obtained results provide further support of the idea that induced epigenetic changes in the genome should be considered when assessing the long-term genetic effects of ionizing radiation and chemical compounds.