The possibility of piRNAs sysem to control transposons in cancer cells

Abstract

Down-regulation of Piwil2 (P-element induced wimpy testis like 2) expression induced hypomethylation, the loss of methylation levels, of long interspersed nuclear element-1 (LINE-1 or L1) sequences in the testes of mutant mice. Moreover, the expression of Piwil2 can be found in various cancers. The levels of LINE-1 hypomethylation in cancers are not only generally varied, but also possess a locus-specific pattern. This study focused on the association between Piwil2 and LINE-1 methylation. Eleven WSU-HN cancer cell lines were examined for the expression of Piwil2 using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Genome-wide and specific loci LINE-1 methylation levels were measured using Combined Bisulfite Restriction Analysis (COBRA) and COBRA for unique LINE-1 (CU-L1), respectively. Moreover, inhibit Piwil2 expression used siRNAs. The levels of Piwil2 expression and LINE-1 methylation were varied. Significant association between Piwil2 RNA and LINE-1 methylation of two loci, L1-EPHA3IVS5 and L1-SPOCK3, was observed (Pearson r = 0.7332; P  0.01 and r = 0.6124; P < 0.05, respectively). There was no association with both genome wide LINE-1 methylation and the other 15 loci. We also reported transient inhibition of Piwil2 expression. Unfortunately due to cell death, we can not establish stable cell line. We found no association between short term down-regulated Piwil2 expression effect on methylation levels of LINE-1 in genome-wide and specific loci in HeLa. We suggested that Piwil2 expression may be associated with LINE-1 methylation of selective loci in type of cancer cells.