Mercury Induces Cytotoxicity and Transcriptionally Activates Stress Genes in Human Liver Carcinoma (HepG2) Cells

Abstract

Abstract:Mercury is a non-essential element that exhibits a high degree of toxicity to humans and animals. Exposure to mercury has been associated with a significant number of adverse health effects including: cardiovascular disease, anemia, developmental abnormalities, neurobehavioral disorders, kidney and liver damage, and cancer in some cases. In several studies, the toxicity of mercury has been attributed to its high affinity to protein-containing sulfhydryl groups. However, little is known regarding the molecular mechanisms by which mercury exerts its toxicity, mutagenesis, and carcinogenesis. This research was therefore designed to assess the cellular and molecular responses of human liver carcinoma cells following exposure to mercury. Cytotoxicity was evaluated using the MTT-assay for cell viability, while the gene profile assay was performed to measure the transcriptional activation of stress genes in thirteen different recombinant cell lines generated from HepG 2 cells. Cytotoxicity experiment yielded a LD 50 value of 3.5 ± 0.6 µg/mL upon 48 hours of exposure, indicating that mercury is highly toxic. A dose response relationship was recorded with respect to both cytotoxicity and gene induction. Overall, nine out of the thirteen recombinant cell lines tested showed inductions to statistically significant levels (p<0.05). At 2.5 µg/mL of mercury, the average fold inductions were 5.2 ± 0.9, 21.4 ± 3.9, 7.0 ± 6.2, 6.8 ± 1.1, 2.7 ± 1.0, 4.5 ± 2.0, 7.5 ± 6.0, 2.2 ± 0.7, and 2.5 ± 0.3, for GSTYa, HMTIIA, c-fos, HSP70, CRE, p53RE, GADD153, GADD45, and GRP78, respectively. These results indicate the potential of mercury to undergo Phase II biotransformation in the liver (GSTYa), and to cause protein damage (HMTIIA, HSP70, and GRP78), cell proliferation (c-fos), metabolic perturbation (CRE), growth arrest and DNA Int. J. Mol. Sci. 2002, 3 966 damage (GADD153, GADD45), and apoptosis (p53RE). No significant inductions (p> 0.05) were observed for CYP1A1, XRE, NFkBRE, and RARE.

Hormetic Effects of Acute Methylmercury Exposure on GRP78 Expression in Rat Brain Cortex

“…Qian et al (2001) demonstrated the hormetic effects of lead and mercury on Grp78 mRNA in C6 rat glioma cells. Low-level inorganic mercury also transcriptionally activated Grp78 in HepG2 cells (Sutton et al 2002). Though obtained from in vitro cultured cells, these data corroborate MeHg's ability to induce a hormetic dose-response effect in ER stress responses.…”

Evaluation of comparative effect of pre‐ and posttreatment of selenium on mercury‐induced oxidative stress, histological alterations, and metallothionein mRNA expression in rats

“…Exposure to mercury has been associated with adverse health effects especially nephrotoxicity and neurobehavioral disorders. It has been observed that probably it affects the inherent protein structure, which may interfere with functions relating to protein production [1]. Mercury is also known to induce reactive oxygen species (ROS) in animals.…”

Quantitation of p53 nuclear relocation in response to stress using a yeast functional assay: effects of irradiation and modulation by heavy metal ions

“…We found that Hg 2 þ (HgCl 2 ), with a maximum effect at 300 nM, but not Cd 2 þ (CdCl 2 ) (see below), Pb 2 þ (PbAc) nor Co 2 þ (CoSO 4 ) (data not shown), induced nuclear accumulation of p53, similar to UVB or g-rays (Figure 3c). HgCl 2 is a weak inducer of DNA damage in Saccharomyces cerevisiae at concentrations within the range used here (Kungolos et al, 1999) and can also activate the p53-dependent transcription of stress-response genes in human liver cells (Sutton et al, 2002). The combination of stress by HgCl 2 and girradiation induced a 13-fold p53 nuclear accumulation (Figure 3c), more than the sum effects mediated by HgCl 2 and g-irradiation separately.…”