The association between Piwil2 expression and LINE-1 methylation in cancer cells

ABSTRACT

Background: 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. Objective: This study focused on the association between Piwil2 and LINE-1 methylation. Methods: 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. Results: 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’s 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. Conclusion: Piwil2 expression may be associated with LINE-1 methylation of selective loci in cancer cells.