Activation of nuclear factor-κB in C6 rat glioma cells after transfection with glia maturation factor

The 17-kDa endogenous brain protein glia maturation factor (GMF) was transfected into C6 rat glioma cells using a replication-defective human adenovirus vector. The cells overexpressed GMF but did not secrete the protein into the medium. Transfection with GMF led to the activation of the transcription factor nuclear factor-kappa B (NF-kappa B), as evidenced by electrophoretic mobility shift assay of the nuclear extract, using a double-stranded oligonucleotide probe containing the consensus binding sequence for NF-kappa B, The specificity of binding was demonstrated by competition with unlabeled probe and by the nonbinding of the mutant probe. Binding was delectable as early as 3 h after transfection, peaked at 6 and 12 h, and gradually declined thereafter. The observed NF-kappa B activation was reduced by cotransfection with catalase and by the presence of high concentrations of pyruvate in the medium, suggesting the involvement of H2O2. The p38 mitogen-activated protein kinase inhibitor SB-203580 also suppressed the GMF-activated NF-kappa B, suggesting the involvement of the p38 signal transduction cascade. On the other hand, the phorbol ester phorbol 12-myristate 13-acetate activated NF-kappa B whether or not GMF was overexpressed. Along with NF-kappa B activation was an enhanced expression of superoxide dismutase (SOD), which was suppressed if NF-kappa B nuclear translocation was blocked by its specific decoy DNA, implicating NF-kappa B as an upstream mediator of this antioxidant enzyme. The p38 inhibitor SB-203580 also blocked the GMF-activated SOD, As NF-kappa B and SOD are both pro-survival signals, the results suggest a cytoprotective role for endogenous GMF in glial cells.