Evaluating the Extent of LINE-1 Mobility Following Exposure to Heavy Metals in HepG2 Cells

Abstract

The long interspersed elements-1 (LINE1 or L1 retrotransposon) constitute 17% of the human genome and retain mobility properties within the genome. At present, 80-100 human L1 elements are thought to be active in the genome. The mobilization of these active elements may be influenced upon exposure to the heavy metals. In the present study, we evaluated the association of aluminum, lead, and copper exposure with L1 retrotransposition in human hepatocellular carcinoma (HepG2) cell line. An in vitro retrotransposition assay using an enhanced green fluorescent protein (EGFP)-tagged L1RP cassette was established to track EGFP shining as the mark of retrotransposition. Following determination of noncytotoxic concentrations of these metals, pL1RP-EGFP-transfected HepG2 cells were subjected to long-term treatment. Flow cytometry analysis of cells treated with various concentrations of these metals along with quantitative real-time PCR was used to quantify L1 retrotransposition frequencies. Aluminum significantly increased L1 retrotransposition frequency, while no significant association was found concerning lead exposure and L1 retrotransposition. Copper treatment downregulated L1 retrotransposition as a result of EGFP-tagged L1RP expression. Our findings suggest that aluminum might have the potential to cause genomic instability by the enhancement of L1 mobilization. Thus, the risk of induced L1 retrotransposition should be considered during drug safety evaluation and risk assessments of exposure to toxic environmental agents. Further studies are needed for a more robust assay to evaluate any associations between long-term lead exposure and L1 mobility in cell culture assay.

Altering Genomic Integrity: Heavy Metal Exposure Promotes Transposable Element-Mediated Damage

“…Not all types of heavy metals increase TE activity; an indication that the influence observed on TEs is unlikely the result of a generalized metal-induced stress response. LINE-1 retrotransposition increases when treated with mercury [90,91], arsenic trioxide [92], aluminum [93], cadmium [91,94] and nickel [95]. Zinc and magnesium can reverse the effects of cadmium- and nickel-driven increases in LINE-1 retrotransposition [94].…”

A comparative study of Long Interspersed Element-1 Protein Immunoreactivity in Cutaneous Malignancies

“…Previous reports have shown that some environmental factors like Gamma irradiation and X-rays some environmental triggers like benzo[a]pyrene (B[a]P), organochlorine pesticides, food-borne carcinogens, extremely low-frequency magnetic fields (ELF-MF) and some heavy metals like mercury, arsenic, aluminum increase L1 retrotransposition events [31][32][33]. Since the skin is the first line of defense for mentioned factors, so the higher expression of the level of ORF1 due to the exposure to agents is plausible.…”

Long INterspersed element‐1 mobility as a sensor of environmental stresses

“…Karimi et al . (Karimi et al ., ) evaluated the possible effect of copper on human L1 retrotransposition by using in vitro retrotransposition assays on HepG2 cells which were transfected with EGFP‐tagged L1 vector. They observed a decrease of percentage EGFP positive cells in samples treated with a dose of copper (Cu) of 50 μM or 75 μM as compared to control cells, and they confirmed this result evaluating the copy number of EGF gene inserted in the genome.…”

“…Karimi et al . (Karimi et al ., ) evaluated the possible effect of aluminum on human L1 retrotransposition. In vitro retrotransposition assays were performed in human hepatocellular carcinoma cells (HepG2) transfected with EGFP‐tagged L1 vector.…”

“…It did not induce any significant enhancement in L1 activity in the experimental conditions used by Karimi et al . (Karimi et al ., ). However, Wright et al .…”