Exposure of hepatocellular carcinoma cells to low-level As2O3‎ causes an extra toxicity pathway via L1 retrotransposition ‎induction

Various mechanisms have been proposed for toxicity and carcinogenesis pattern of arsenic, a naturally occurring metalloid. The extent to which the long interspersed element-1 (LINE-1) retrotransposon, an ubiquitous retroelement with autonomous mobility, can be influenced upon exposure to low-level arsenic remains to be elucidated. The aim of this study was to evaluate the possible effect of low-level As2O3 on L1 retrotransposition alteration in human hepatocellular carcinoma cells (HepG2). L1 retrotransposition in HepG2 cells was performed by the in vitro retrotransposition assay using an EGFP-tagged L1RP. Following determination of non-cytotoxic concentrations of arsenic by a MTT assay, the cells were transfected with pL1RP-EGFP and then exposed to 0.25, 0.50 and 0.75 μM of As2O3. The amount of EGFP and its copy number in retrotransposed cells were evaluated by FACS and qPCR analysis in treated vs. control cells, respectively. Significant increase in retrotransposition frequency was found after 12 days exposure to 0.50 and 0.75 μM of As2O3 by FACS analysis (P < 0.05). Obtained results were further confirmed by real time PCR, which showed significant induction of retrotransposition in all mentioned concentrations. Our findings indicate that low-level long-term As2O3 exposure may pave activation of L1 retrotransposon.