中文摘要：

[目的]观察亚砷酸钠（NaAsO2）对人永生化皮肤角质形成细胞（HacaT细胞）DNA双链断裂损伤、组蛋白H4第20位赖氨酸一、二甲基化（H4K20me1、H4K20me2）修饰水平的影响，探讨H4K20me1、H4K20me2修饰在砷致DNA双键断裂损伤中的作用。[方法]体外常规培养HaCaT细胞，以0．00、1．25、2．50、5．00、10．00μmol/LNaAsO2连续处理HaCaT细胞24h，10．00μmol／LNaAs02处理HaCaT细胞0、6、12、24h，其中以0．00μmol／L浓度组和0h为空白对照组。采用中性单细胞凝胶电泳法检测各组HaCaT细胞DNA双链断裂损伤水平（尾部DNA百分含量、Olive尾矩）；免疫印迹法检测各组H4K20me1、H4K20me2蛋白表达水平。[结果]HaCaT细胞染砷24h后，DNA双链断裂程度在5．00、10．00μmol／L浓度组高于对照组（P〈0．05）；H4K20me1／me2蛋白表达水平在2．50、5．00、10．00μmol／L浓度组低于对照组（P〈0．05）。10．00μmol／LNaAsO2处理HaCaT细胞0、6、12和24h后，DNA双链断裂程度在12、24h染砷组高于对照组（P〈0．05），H4K20mel、H4K20me2蛋白表达水平在6、12、24h较对照组降低（P〈0．05）.尾部DNA百分含量与H4K20me1、H4K20me2修饰水平呈负相关（r=-0．955、-0．855，均P〈0．05），Olive尾矩与二者亦呈负相关（r=--0．940、-0．841，均P〈0．05）.[结论]砷可导致HaCaT细胞DNA双键断裂损伤和H4K20me1、H4K20me2表达改变，提示砷所致DNA损伤可能与组蛋白H4K20甲基化修饰有关。

英文摘要：

[ Objective ] To investigate the effects of sodium arsenite （NaAsO2） on DNA double-strand break and the expression of histone H4 lysine 20 monomethylation and dimethylation （H4K20me 1 and H4K20me2） in immortalized human keratinocytes （HaCaT ceils）, and to study the roles of H4K2Omel and H4K20me2 in DNA double-strand break induced by arsenic. [ Methods ] HaCaT cells were conventionally cultured in vitro and treated continuously with different concentrations of NaAsO2 （0.00, 1.25, 2.50, 5.00, and 10.00 μmol/L） for 24 h, or treated with 10.00 μmol/L NaAsO2 for 0, 6, 12, and 24h, respectively. The 0.00 μmol/L and 0 h treatments were used as blank control group. The damage degree of DNA double-strand break （DSB） （tail DNA% and Olive tail moment） in HaCaT cells were measured by neutral single cell gel electrophoresis. Western blot was used to observe the protein expression levels of H4K20mel and H4K20me2.[ Results ] After exposure to NaAsO2 for 24 h, the degrees of DSB in HaCaT cells of the 5.00 and 10.00 μmol/L groups were higher than that of the blank control group （P 〈 0.05）, and the protein expression levels of H4K20me 1 and H4K20me2 in HaCaT cells of the 2.50, 5.00, and 10.00 ~mol/L groups were lower than that of the blank control group （P〈 0.05）. Regarding treatment with 10.00 limol/L NaAsO2 for different time periods, compared with the blank control group, the degrees of DSB in HaCaT cells at 12 and 24h were significantly increased （P〈0.05）, and the H4K20mel and H4K20me2 protein expression levels in HaCaT cells at 6, 12, and 24h were reduced （P 〈 0.05）. Tail DNA% was negatively associated with the protein expression level of H4K2Ome 1 and H4K2Ome2 （r=-0.955, -0.855, both Ps 〈 0.05）. Olive tail moment was also negatively associated （r=-0.940, -0.841, both Ps 〈 0.05）. [ Conclusion ] Arsenic can cause DNA double-strand break damage and changes in the expression of H4K20mel and YI4K20me2 in HaCaT cells, suggesting that DNA damage induced by arsenic may