Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Mutat Res. 2011 Oct 9;725(1-2):43-9. doi: 10.1016/j.mrgentox.2011.07.004. Epub 2011 Jul 18.
3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a chlorine disinfection by-product in drinking water, is carcinogenic in rats and genotoxic in mammalian cells in vitro. In the current study, the mechanism of genotoxicity of MX in human lymphoblastoid TK6 cells was investigated by use of the Comet assay, the micronucleus test, and the thymidine kinase (TK) gene-mutation assay. MX induced a concentration-dependent increase in micronuclei and TK mutations. The lowest effective concentrations in the MN test and the TK gene-mutation assay were 37.5μM and 25μM, respectively. In the Comet assay, a slight although not statistically significant increase was observed in the level of DNA damage induced by MX in the concentration range of 25-62.5μM. Molecular analysis of the TK mutants revealed that MX induced primarily point mutations or other small intragenic mutations (61%), while most of the remaining TK mutants (32%) were large deletions at the TK locus, leading to the hemizygous-type loss-of-heterozygosity (LOH) mutations. These findings show that aside from inducing point mutations, MX also generates LOH at the TK locus in human cells and may thus cause the inactivation of tumour-suppressor genes by LOH.
3-氯-4-(二氯甲基)-5-羟基-2(5H)-呋喃酮（MX）是饮用水中一种含氯消毒副产物，对大鼠具有致癌性，对体外哺乳动物细胞具有遗传毒性。在本研究中，通过彗星试验、微核试验和胸苷激酶（TK）基因突变试验，研究了 MX 对人淋巴母细胞 TK6 细胞遗传毒性的作用机制。MX 诱导微核和 TK 基因突变呈浓度依赖性增加。在 MN 试验和 TK 基因突变试验中，最低有效浓度分别为 37.5μM 和 25μM。在彗星试验中，在 25-62.5μM 的浓度范围内，观察到 MX 诱导的 DNA 损伤水平略有但无统计学意义的增加。TK 突变体的分子分析表明，MX 主要诱导点突变或其他小的基因内突变（61%），而其余大多数 TK 突变体（32%）是 TK 基因座的大片段缺失，导致半合子型杂合性丢失（LOH）突变。这些发现表明，MX 除了诱导点突变外，还在人细胞中的 TK 基因座产生 LOH，因此可能通过 LOH 使肿瘤抑制基因失活。
