Activation of early signaling transcription factor, NF-κB following low-level manganese exposure

Occupational and environmental exposure to manganese (Mn2+) 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 Mn2+ 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 Mn2+ (0.1-10 muM) exposure. Cells that were exposed to Mn2+ produced five-fold-activation of transcription factor NF-kappaB DNA binding activity. This remarkable increase was seen within 30-60 min period of Mn2+ exposure. Activation of NF-kappaB DNA binding activity by Mn2+ at 1.0 muM correlated with proteolytic degradation of the inhibitory subunit IkappaBalpha 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 muM Mn2+ and this was completely blocked in the presence of NF-kappaB translocation inhibitor, IkappaBalpha-DN supporting that NF-kappaB induction occurred during Mn2+ exposure. In addition, Mn2+ exposure to PC 12 cells led to activation of signal responsive mitogen activated proteinexposure. In addition, Mn2+ exposure to PC 12 cells led to activation of signal responsive mitogen activated protein kinase kinase (MAPKK). These results suggest that Mn2+ at a low dose appears to induce the expression of immediate early gene, NF-kappaB through MAPKK by a mechanism in which IKBoc phosphorylation may be involved.) (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.