Features of iso-miR expression in colon tumor tissue.

Abstract

e13518 Background: With the advent of deep sequencing, enormous variability in miRNA biogenesis was detected, which means that many different sequences can potentially be generated from the same miRNA precursor, potentially having different targets and opposite changes in expression. These variable forms of micro-RNA that differ from the reference sequence are called iso-miR. To date, features of iso-miR expression have not been studied in patients with colorectal cancer (CRC). The aim of the study was to analyze the differential expression of iso-miR in the tumor and normal tissues of patients with CRC. Methods: For iso-miR identification by method of multiple parallel sequencing, 18 patients with CRC (colon adenocarcinoma, G2-3) were selected. The mirVana miRNA Isolation Kit protocol (Ambion, Life Science Technologies, USA) was used to isolate small RNA fractions. The library was prepared using the TruSeq Small RNASample Preparation Kit (Illumina, USA). Sequencing of the nucleotide sequences of cDNA libraries was performed using a MiSeq (Illumina, USA). The determination of iso-miR expression was carried out by comparing the nucleotide sequence of the sequenced molecules in each sample with the known nucleotide sequences of micro-RNA presented in the databases. When analyzing the iso-miR differential expression, the DESeq method implemented in R medium was used. Results: Several iso-miR classes were found (exact, lv3p, mv (multiple variant), nta#T#1 (non-templated T addition)). The most represented is the exact class (corresponding to the canonical miRBase sequence) and lv3pE (3 'extended: it starts from the same position as the canonical sequence, but is longer than the canonical sequence). Statistically significant (p < 0.001) differences in the expression of tumor tissue relative to normal were found for hsa-miR-143 (exact), hsa-miR-26a (exact) and hsa-miR-27b (exact) - a decrease in expression in 3, 32 and 6 times respectively, for hsa-miR-10a (lv3p), hsa-miR-10b (lv3p), hsa-miR-10b (mv) - a decrease of 2 times, for hsa-miR-143 (lv3p) - an increase of 2 times, hsa-miR-143 (nta # T # 1) - a decrease of 5 times, for hsa-miR-192 (lv3p) and (nta # T # 1) - a decrease of 16 and 3 times, respectively. Conclusions: Differential expression of 4 iso-miR classes (exact, lv3p, mv, nta # T) hsa-miR-26a, hsa-miR-27b, hsa-miR-10a, hsa-miR-10b, hsa-miR-143 and hsa-miR-192 was found in patients with CRC, which probably can affect the transcriptional activity of the genes they target. These iso-miRs are also likely to act as potential tumor markers.