OBJECTIVETo compare the DNA methylation-related alteration induced by trichloroethylene (TCE) in human hepatic L-02 cells (L-02 cells) and SET deficient cells, and reveal the role of SET on the mechanisms in TCE-induced epigenetic pathway.

METHODSThe L-02 cells and pre-established SET deficient cells were treated with different TCE concentrations, and the changes of total cell viability, DNA methylation level and DNA methyltransferases (DNMTs) activity were measured, respectively. In addition, the TCE-induced alteration in the protein expression of DNMT1, DNMT3a and DNMT3b were analyzed by Western blotting.

RESULTSAfter treatment with TCE for 24 h, the cell proliferation level was significantly decreased in both cell lines. When concentrations of TCE were 0, 1.0, 2.0, 4.0 and 8.0 mmol/L, the proliferation levels of L-02 cells were 100.00±2.70, 83.34±2.38, 75.56±4.51, 71.67±2.77 and 66.67±1.63, respectively (F = 58.29, P < 0.001); the cell proliferation levels of SET deficient cells were 101.12±1.67, 85.01±2.33, 79.44±1.67, 78.337±3.89 and 76.11±3.33, respectively (F = 42.41, P < 0.001). When concentration of TCE reached 4.0 mmol/L, the difference of cell proliferation level between two groups was statistically significant (t = -3.51; P = 0.013). After treated by TCE for 24 h, the global DNA methylation significantly decreased in both cell lines (F value was 212.87 and 79.32, respectively, P < 0.001). The difference between two groups was not statistically significant. After treated by TCE for 24 h, the methyltransferases activities were significantly decreased in both cell cells (F values were 77.92 and 113.80, respectively, P-0.001). The SET deficiency could inhibit the decrease of methyltransferases activity under TCE treatment. When the concentration of TCE reached 8.0 mmol/L, the enzymatic activity of L-02 cells and SET deficient cells decreased to 67.61%±2.85% and 72.97%± 1.94%, respectively. The difference between two groups was statistically significant (t = -3.94, P = 0.008). After treated with TCE for 24 h, concentrations of TCE were 0, 1.0, 2.0, 4.0 and 8.0 mmol/L, and the relative protein levels of DNMT1 in normal L-02 cells increased significantly to 1.00±0.03, 1.28±0.04, 1.20±0.04, 1.62±0.05, 1.43±0.04 (F = 103.00, P < 0.001); In SET deficient cells, the expressions of DNMT1 were 1.00±0.04, 0.96±0.02, 1.19±0.05, 0.85±0.03, 0.83±0.03, which was significantly down-regulated under TCE treatment (F = 44.18, P < 0.001).

CONCLUSIONSET deficiency can significantly attenuate the TCE-induced decreases of cell viability and DNMTs activity, as well as alteration of protein expression of DNMT1 in L-02 cells, which indicated that SET was involved in the mechanism of TCE-induced cytotoxicity and epigenetic pathway in L-02 cells.