Arginine decarboxylase: A novel biological target of mercury compounds identified in PC12 cells
Arginine decarboxylase: A novel biological target of mercury compounds identified in PC12 cells
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精氨酸脱羧酶：PC12 细胞中发现的汞化合物的新生物靶标
DOI：
10.1016/j.bcp.2016.08.019
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发表时间：
2016
影响因子：
5.8
通讯作者：
Zhang Hui
中科院分区：
文献类型：
--
作者：
Wang Sufang;Lv Qiyan;Yang Yu;Guo Liang-Hong;Wan Bin;Ren Xiaomin;Zhang Hui
汞化合物是众所周知的有毒环境污染物，对人类和实验动物具有严重的神经毒性作用。以往的研究表明，汞化合物神经毒性的机制之一是由于谷氨酸释放增加引起的N-甲基天冬氨酸（NMDA）型谷氨酸受体的过度激活。本研究旨在通过确定汞化合物在细胞中的生物学靶点，探讨汞化合物神经毒性的分子机制。首先，研究了四种汞化合物（三种有机汞（甲基汞、乙基汞和苯基汞）和一种无机汞（Hg ~（2+）对中枢精氨酸能系统中关键酶精氨酸脱羧酶（ADC）活性的抑制作用。发现它们显著抑制ADC活性，其中甲基汞（MeHg）最强（IC 50 = 7.96 nM）。此外，它们对PC 12细胞中ADC活性显示出显著的抑制作用（MeHg > EtHg > PhHg > HgCl 2），并导致选择性阻断NMDA受体活化的内源性神经调节和神经保护剂胍丁胺水平的显著损失。甲基汞从细胞的免疫沉淀ADC中检测到，提供了明确的证据，直接结合的甲基汞与ADC在细胞中。分子动力学模拟结果表明，汞化合物不仅能与ADC的辅因子PLP形成配位键，还能与底物精氨酸形成配位键。结果表明，甲基汞可通过抑制其新的细胞靶点ADC而减弱胍丁胺的神经保护作用，这可能与甲基汞神经毒性的分子机制有关。
Mercury compounds are well-known toxic environmental pollutants and potently induce severe neurotoxicological effects in human and experimental animals. Previous studies showed that one of the mechanisms of mercury compounds neurotoxicity arose from the over-activation of the N-methyld-aspartate (NMDA)-type glutamate receptor induced by increased glutamate release. In this work, we aimed to investigate the molecular mechanisms of Hg compounds neurotoxicities by identifying their biological targets in cells. Firstly, the inhibitory effects of four Hg compounds, including three organic (methyl-, ethyl- and phenyl-mercury) and one inorganic (Hg2+) Hg compounds, on the activity of arginine decarboxylase (ADC), a key enzyme in the central agmatinergic system, were evaluated. They were found to inhibit the ADC activity significantly with methylmercury (MeHg) being the strongest (IC50= 7.96 nM). Furthermore, they showed remarkable inhibitory effects on ADC activity in PC12 cells (MeHg > EtHg > PhHg > HgCl2), and led to a marked loss in the level of agmatine, an endogenous neuromodulatory and neuroprotective agent that selectively blocks the activation of NMDA receptors. MeHg was detected in the immunoprecipitated ADC from the cells, providing unequivocal evidence for the direct binding of MeHg with ADC in the cell. Molecular dynamics simulation revealed that Hg compounds could form the coordination bond not only with cofactor PLP of ADC, but also with substrate arginine. Our finding indicated that MeHg could attenuate the neuroprotective effects of agmatine by the inhibition of ADC, a new cellular target of MeHg, which might be implicated in molecular mechanism of MeHg neurotoxicity.