Small RNA sequencing revealed aberrant piRNA expression profiles in colorectal cancer

Piwi-interacting RNAs (piRNAs), a novel class of non-coding RNAs, are enriched in germ cells and implicated in spermatogenesis. Emerging evidence demonstrated deregulated expression of piRNAs in numerous tumor types. However, changes in piRNA expression profiles in colorectal cancer (CRC) have not yet been investigated. In the present study, small RNA sequencing was used to evaluate the differences in piRNA expression profiles between CRC and adjacent non-tumor tissues, as well as to screen for differentially expressed piRNAs. The present results demonstrated that the percentage of unique piRNA reads had no notable difference between the paired CRC and adjacent non-tumor samples (0.12% vs. 0.13%); however, the counts of total piRNA reads in CRC samples were increased, compared with those in adjacent non-tumor samples (0.15% vs. 0.07%). Differential expression analysis identified 33 upregulated piRNAs and 2 downregulated piRNAs in CRC samples, among which piR-18849, piR-19521 and piR-17724 were the top three upregulated piRNAs. Reverse transcription-quantitative polymerase chain reaction further confirmed that the expression levels of piR-18849, piR-19521 and piR-17724 were increased in 80 CRC tissues, compared with paired adjacent non-tumor tissues. Furthermore, the high expression of piR-18849 and piR-19521 was associated with a poor degree of differentiation. The increased expression of piR-18849 was also associated with high lymph node metastasis. However, no associations were determined between piR-17724 expression and clinicopathological characteristics of patients. In summary, the present study is the first to provide an overview of the changes in piRNA expression patterns in CRC, shedding new light on the regulatory roles of piRNAs in colorectal carcinogenesis. piR-18849 and piR-19521 may be prognostic biomarkers for patients with CRC.