Role of ascorbate in the activation of NF-κB by tumour necrosis factor-α in T-cells

The first product of ascorbate oxidation, the ascorbate free radical (AFR), acts in biological systems mainly as an oxidant, and through its role in the plasma membrane redox system exerts different effects on the cell. We have investigated the role of ascorbate, AFR and dehydroascorbate (DHA) in the activation of the NF-κB transcription factor in Jurkat T-cells stimulated by tumour necrosis factor-α (TNF-α). Here we show, by electrophoretic mobility shift assays, that ascorbate increases the binding of NF-κB to DNA in TNF-α-stimulated Jurkat cells. The ability of ascorbate to enhance cytoplasmic inhibitory IkBα protein degradation correlates completely with its capacity to induce NF-κB binding to DNA and to potentiate NF-κB-mediated transactivation of the HIV-1 long terminal repeat promoter in TNF-α-stimulated Jurkat cells but not in cells stimulated with PMA plus ionomycin. AFR behaves like ascorbate, while DHA and ascorbate phosphate do not affect TNF-α-mediated NF-κB activation. These results provide new evidence for a possible relationship between the activation of the electron-transport system at the plasma membrane by ascorbate or its free radical and redox-dependent gene transcription in T-cells.