Noreault Trisha L, Jacobs Judith M, Nichols Ralph C, Trask Heidi W, Wrighton Steven A, Sinclair Peter R, Evans Ronald M, Sinclair Jacqueline F
Veterans Administration Medical Center, White River Junction, VT 05009, USA.
Toxicol Appl Pharmacol. 2005 Dec 1;209(2):174-82. doi: 10.1016/j.taap.2005.04.008.
Arsenic is a naturally occurring, worldwide contaminant implicated in numerous pathological conditions in humans, including cancer and several forms of liver disease. One of the contributing factors to these disorders may be the alteration of cytochrome P450 (CYP) levels by arsenic. In rat and human hepatocyte cultures, arsenic, in the form of arsenite, decreases the induction of several CYPs. The present study investigated whether arsenite utilizes transcriptional or post-transcriptional mechanisms to decrease CYP3A23 in primary cultures of rat hepatocytes. In these cultures, a 6-h treatment with 5 microM arsenite abolished dexamethasone (DEX)-mediated induction of CYP3A23 protein and activity, but did not inhibit general protein synthesis. However, arsenite treatment only reduced DEX-induced levels of CYP3A23 mRNA by 30%. The effects of arsenite on CYP3A23 transcription were examined using a luciferase reporter construct containing 1.4 kb of the CYP3A23 promoter. Arsenite caused a 30% decrease in DEX-induced luciferase expression of this reporter. Since arsenite abolished induction of CYP3A23 protein, but caused only a small decrease in CYP3A23 mRNA, the effects of arsenite on translation of CYP3A23 mRNA were investigated. Polysomal distribution analysis showed that arsenite decreased translation by decreasing the DEX-mediated increase in CYP3A23 mRNA association with polyribosomes. Arsenite did not decrease intracellular glutathione or increase lipid peroxidation, suggesting that the effect of arsenite on CYP3A23 does not involve oxidative stress. Overall, the results suggest that low-level arsenite decreases both transcription and translation of CYP3A23 in primary rat hepatocyte cultures.
砷是一种天然存在的、遍布全球的污染物，与人类的多种病理状况有关，包括癌症和几种肝病。这些疾病的一个促成因素可能是砷对细胞色素P450（CYP）水平的改变。在大鼠和人类肝细胞培养物中，亚砷酸盐形式的砷会降低几种CYP的诱导。本研究调查了亚砷酸盐是否利用转录或转录后机制来降低大鼠原代肝细胞培养物中CYP3A23的水平。在这些培养物中，用5 microM亚砷酸盐处理6小时可消除地塞米松（DEX）介导的CYP3A23蛋白诱导和活性，但不抑制一般蛋白质合成。然而，亚砷酸盐处理仅使DEX诱导的CYP3A23 mRNA水平降低了30%。使用含有1.4 kb CYP3A23启动子的荧光素酶报告构建体检查了亚砷酸盐对CYP3A23转录的影响。亚砷酸盐使该报告基因的DEX诱导的荧光素酶表达降低了30%。由于亚砷酸盐消除了CYP3A23蛋白的诱导，但仅使CYP3A23 mRNA略有下降，因此研究了亚砷酸盐对CYP3A23 mRNA翻译的影响。多核糖体分布分析表明，亚砷酸盐通过减少DEX介导的CYP3A23 mRNA与多核糖体的结合增加来降低翻译。亚砷酸盐不会降低细胞内谷胱甘肽或增加脂质过氧化，表明亚砷酸盐对CYP3A23的作用不涉及氧化应激。总体而言，结果表明低水平的亚砷酸盐会降低大鼠原代肝细胞培养物中CYP3A23的转录和翻译。
