Arsenic at very low concentrations alters glucocorticoid receptor (GR)-mediated gene activation but not GR-mediated gene repression: Complex dose-response effects are closely correlated with levels of activated GR and require a functional GR DNA binding domain
Arsenic at very low concentrations alters glucocorticoid receptor (GR)-mediated gene activation but not GR-mediated gene repression: Complex dose-response effects are closely correlated with levels of activated GR and require a functional GR DNA binding domain
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DOI：
10.1021/tx0499113
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发表时间：
2004-08-01
影响因子：
4.1
通讯作者：
Hamilton, JW
中科院分区：
文献类型：
--
作者：
Bodwell, JE;Kingsley, LA;Hamilton, JW
饮用水中的砷(As)污染被认为是全世界主要的环境健康威胁。长期摄入会增加患癌症、糖尿病和心血管疾病的风险，最近的研究表明，低至5-10 ppb的水平会增加健康风险。本文报道0.05-1UM(6-120 ppb)对糖皮质激素受体(GR)介导的大鼠EDR3肝癌细胞内源性酪氨酸氨基转移酶(TAT)基因和含有TAT糖皮质激素反应元件的报告基因的激活均有刺激作用。当浓度稍高时(1-3um)，As的作用变得抑制。因此，在这个狭窄的浓度范围内，AS的作用从2到4倍的刺激变为2倍以上的活性抑制。有趣的是，GR对AP1和NF-kappaB介导的基因激活的抑制作用不受AS的影响。AS对GR的刺激和抑制程度高度依赖于激素激活的GR的细胞水平。突变缺失研究表明，GR的中心DNA结合域(DBD)是AS效应所需的最小区域，不需要游离巯基。位于DBD内的点突变具有已知的结构后果，显著改变了GR对AS的反应。特别是，DBD上的点突变提供了DNA结合的GR确认，取消了低剂量的刺激效应，但增强了抑制反应，进一步表明DBD在介导这些AS效应方面是重要的。
Arsenic (As) contamination of drinking water is considered a principal environmental health threat throughout the world. Chronic intake is associated with an increased risk of cancer, diabetes, and cardiovascular disease, and recent studies suggest increased health risks at levels as low as 5-10 ppb. We report here that 0.05-1 muM (6-120 ppb) As showed stimulatory effects on glucocorticoid receptor (GR)-mediated gene activation in rat EDR3 hepatoma cells of both the endogenous tyrosine aminotransferase (TAT) gene and the reporter genes containing TAT glucocorticoid response elements. At slightly higher concentrations (1-3 muM), the effects of As became inhibitory. Thus, over this narrow concentration range, the effects of As changed from a 2- to 4-fold stimulation to a greater than 2-fold suppression in activity. Interestingly, the inhibitory effect of GR on both AP1- and NF-kappaB-mediated gene activation was not affected by As. The magnitude of GR stimulation and inhibition by As was highly dependent on the cellular level of hormone-activated GR. Mutational deletion studies indicated that the central DNA binding domain (DBD) of GR is the minimal region required for the As effect and does not require free sulfhydryls. Point mutations located within the DBD that have known structural consequences significantly altered the GR response to As. In particular, point mutations in the DBD that confer a DNA-bound GR confirmation abolished the low dose As stimulatory effect but enhanced the inhibitory response, further indicating that the DBD is important for mediating these As effects.