Department of Molecular Cell Biology and Toxicology, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China.
Toxicol Sci. 2010 Jul;116(1):174-82. doi: 10.1093/toxsci/kfq109. Epub 2010 Apr 7.
Inorganic arsenic is a ubiquitous environmental contaminant associated with an increased risk of skin hyperkeratosis and cancer. Although several hypotheses that relate to arsenic-induced carcinogenesis have been suggested, the mechanism of action remains obscure. In the present study, molecular mechanisms underlying the inactivation of p53 function and the genomic instability in malignant transformation of the human keratinocyte cell line, HaCaT, induced by low levels of arsenic were investigated. Our results show that long-term exposure of HaCaT cells to sodium arsenite (1.0 microM) increases their proliferation, causes DNA double-strand breaks, and induce anchorage-independent growth. In arsenite-exposed cells, the levels of phospho-p53, p21, and mdm2 increase at early times after exposure. The levels, however, decrease with longer times. Interaction of the promoter of mot-2 (a p53 inhibitor) with nuclear factor kappaB (NF-kappaB) was established by Southwestern and Western blot assays. Blockage of NF-kappaB prevents the increases of arsenite-induced mot-2 levels, and knockdown of mot-2 facilitates the nuclear translocation of p53, indicating that, in HaCaT cells exposed to arsenite, NF-kappaB inhibits p53 function by mot-2. Moreover, inactivation of NF-kappaB facilitated p53-mediated DNA repair and prevented arsenite-induced malignant transformation. Together, the results suggest that the repressive effect of NF-kappaB on p53 by mot-2 leads to genomic instability, which is involved in arsenite-induced malignant transformation of human keratinocytes.
无机砷是一种普遍存在的环境污染物，与皮肤过度角化和癌症风险增加有关。尽管已经提出了几种与砷致癌有关的假说，但作用机制仍不清楚。在本研究中，研究了低水平砷诱导的人角质形成细胞系 HaCaT 恶性转化中 p53 功能失活和基因组不稳定性的分子机制。我们的结果表明，HaCaT 细胞长期暴露于亚砷酸钠（1.0 μM）会增加其增殖，导致 DNA 双链断裂，并诱导非锚定依赖性生长。在暴露于砷的细胞中，磷酸化 p53、p21 和 mdm2 的水平在暴露后的早期时间增加。然而，随着时间的延长，水平下降。通过西南印迹和 Western blot 分析证实了 mot-2（p53 抑制剂）启动子与核因子 kappaB（NF-kappaB）的相互作用。NF-kappaB 的阻断可防止砷诱导的 mot-2 水平增加，并且 mot-2 的敲低促进了 p53 的核易位，表明在暴露于亚砷酸钠的 HaCaT 细胞中，NF-kappaB 通过 mot-2 抑制 p53 功能。此外，NF-kappaB 的失活促进了 p53 介导的 DNA 修复，并防止了砷诱导的恶性转化。总之，这些结果表明，NF-kappaB 通过 mot-2 对 p53 的抑制作用导致基因组不稳定性，这与砷诱导的人角质形成细胞恶性转化有关。
