Abstract
We have previously demonstrated that long-term low-dose sodium arsenite exposure induced cellular transformation and aberrant gene expression in human urothelial cell lines. Since epigenetic alterations play critical roles in the regulation of gene expression, we performed systematic analysis to compare the DNA methylation profiles between arsenic-exposed human urothelial cells and untreated cells. By aid of the Infinium Assay, we selected 61 genes with promoter methylation differences between parental and arsenic-exposed cells over 75%. Among them, 40 genes showed hypomethylated in arsenic-exposed cells, whereas 21 genes hypermethylated. To identify genes whose expression associated with DNA methylation, we performed the quantitative real-time PCR analysis after treatment of cells with 5-aza-2'-deoxycytidine. The results showed that 76% of hypomethylated gene expression levels in arsenic-exposed cells are higher than parental cells. However, only 42% hypermethylated genes consistently expressed lower levels of transcripts in arsenic-exposed cells than control cells. Bisulfite sequencing analysis was performed to confirm the methylation status in arsenic-exposed cells. In all of the genes analyzed in this study, lipocalin-2 (LCN2), also known as oncogene 24p3 or NGAL, is one of the most highly expressed in long-term arsenic-exposed cells as compared to-untreated cells. By siRNA technique, we found that silencing of LCN2 in arsenic-exposed cells exhibited reduced oncogenic potential and decreased production of pro-inflammatory cytokines. Taken together, our present results showed that long-term low dose arsenic exposure could be through epigenetic mechanism to alter the gene expression profile and hence induce cell transformation.
