Ramesh Govindarajan T, Ghosh Debabrata, Gunasekar Palur G
Molecular Neurotoxicology Laboratory, Department of Biology, College of Science and Technology, Texas Southern University, Houston, TX 77004, USA.
Toxicol Lett. 2002 Dec 15;136(2):151-8. doi: 10.1016/s0378-4274(02)00332-6.
Occupational and environmental exposure to manganese (Mn(2+)) is an increasing problem. It manifests neuronal degeneration characterized by dyskinesia resembling Parkinson's disease. The study was performed to test the hypotheses whether exposure to Mn(2+) alters cellular physiology and promotes intracellular signaling mechanism in dopaminergic neuronal cell line. Since transcription factors have been shown to play an essential role in the control of cellular proliferation and survival, catecholaminergic rich pheochromocytoma (PC12) cells were used to measure changes in the DNA binding activities of nuclear factor kappa B (NF-kappaB) by electrophoretic mobility shift assay (EMSA) following Mn(2+) (0.1-10 microM) exposure. Cells that were exposed to Mn(2+) produced five-fold-activation of transcription factor NF-kappaB DNA binding activity. This remarkable increase was seen within 30-60 min period of Mn(2+) exposure. Activation of NF-kappaB DNA binding activity by Mn(2+) at 1.0 microM correlated with proteolytic degradation of the inhibitory subunit IkappaB(alpha) as evidenced in cytosol. Additional experiments on NF-kappaB reporter gene assay also showed increased NF-kappaB gene expression at 1.0 and 5.0 microM Mn(2+) and this was completely blocked in the presence of NF-kappaB translocation inhibitor, IkappaB(alpha)-DN supporting that NF-kappaB induction occurred during Mn(2+) exposure. In addition, Mn(2+) exposure to PC 12 cells led to activation of signal responsive mitogen activated protein kinase kinase (MAPKK). These results suggest that Mn(2+) at a low dose appears to induce the expression of immediate early gene, NF-kappaB through MAPKK by a mechanism in which IkappaB(alpha) phosphorylation may be involved.
职业性和环境性接触锰离子（Mn(2+)）正成为一个日益严重的问题。它表现为以类似帕金森病的运动障碍为特征的神经元变性。本研究旨在检验以下假设：接触Mn(2+)是否会改变细胞生理并促进多巴胺能神经元细胞系中的细胞内信号传导机制。由于转录因子已被证明在细胞增殖和存活的控制中起重要作用，因此使用富含儿茶酚胺能的嗜铬细胞瘤（PC12）细胞，通过电泳迁移率变动分析（EMSA）来测量在暴露于Mn(2+)（0.1 - 10 microM）后核因子κB（NF-κB）的DNA结合活性变化。暴露于Mn(2+)的细胞产生了转录因子NF-κB DNA结合活性的五倍激活。这种显著增加在Mn(2+)暴露的30 - 60分钟内可见。1.0 microM的Mn(2+)对NF-κB DNA结合活性的激活与抑制亚基IκB(α)的蛋白水解降解相关，这在细胞质中得到了证实。关于NF-κB报告基因分析的额外实验还表明，在1.0和5.0 microM的Mn(2+)浓度下，NF-κB基因表达增加，并且在存在NF-κB易位抑制剂IκB(α)-DN的情况下这种增加被完全阻断，这支持了在Mn(2+)暴露期间发生了NF-κB诱导。此外，Mn(2+)暴露于PC12细胞导致信号响应性丝裂原活化蛋白激酶激酶（MAPKK）的激活。这些结果表明，低剂量的Mn(2+)似乎通过可能涉及IκB(α)磷酸化的机制，通过MAPKK诱导即刻早期基因NF-κB的表达。
