Inhibition of I kappa B-alpha phosphorylation and degradation and subsequent NF-kappa B activation by glutathione peroxidase overexpression.

Abstract

Abstract. We report here that both KB-dependent transactivation of a reporter gene and NF-KB activation in response to tumor necrosis factor (TNFc 0 or H202 treatments are deficient in human T47D cell transfectants that overexpress seleno-glutathione peroxidase (GSHPx). These cells feature low reactive oxygen species (ROS) levels and decreased intracellular ROS burst in response to TNFot treatment. Decreased ROS levels and NF-KB activation were likely to result from GSHPx increment since these phenomena were no longer observed when GSHPx activity was reduced by selenium depletion. The cellular contents of the two NF-KB subunits (p65 and p50) and of the inhibitory subunit IKB-a were unaffected by GSHPx overexpression, suggesting that increased GSHPx activity interfered with the activation, but not the synthesis or stability, of NF-KB. Nuclear translocation of NF-KB as well as IKB-ot degradation were inhibited in GSHPx-overexpressing cells exposed to oxidative stress. Moreover, in control T47D cells exposed to TNFa, a time correlation was observed between elevated ROS levels and IKB-ot degradation. We also show that, in growing T47D cells, GSHPx overexpression altered the isoform composition of IKB-et, leading to the accumulation of the more basic isoform of this protein. GSHPx overexpression also abolished the TNFe~-mediated transient accumulation of the acidic and highly phosphorylated IKB-et isoform. These results suggest that intracellular ROS are key elements that regulate the phosphorylation of IKB-~, a phenomenon that precedes and controls the degradation of this protein, and then NF-KB activation.T rtE transcription factor NF-KB plays a pivotal role in the regulation of a wide variety of cellular genes, particularly those involved in immune and inflammatory responses, and also participates in the regulation of viral promoters, including the human immunodeficiency virus long terminal repeat (HIV-1 LTR) (3,7,29,51,66). Five different subunits of NF-KB have been described that can homo-and heterodimerize (21, 53). These polypeptides belong to the rel family of transcription factors, and the more frequent and therefore prototypical form of NF-KB is a heterodimer complex containing the p50 and p65/RelA subunits (6,11,28,59,67). Unlike most transcription factors, these proteins reside in the cytoplasm in a latent form and must therefore translocate into the nucleus to function (5). In unstimulated cells, the nuclear import of the NF-KB DNA-binding dimer p65/RelAp50 is prevented by high-affinity association of the p65/ RelA subunit with a cytoplasmic inhibitor called IKB (4,13,57,71 family of distinct proteins (62) and interacts, through its ankyrin-like repeats, with the nuclear localization signals of p50 and p65/RelA (9, 34). The prototypical IKB protein involved in cytoplasmic retention of NF-KB dimers is IKB-a, encoded by the MAD-3 gene (32). The inactive NF-KB-IKB-ot complexes are dissociated in response to a variety of extracellular stimuli, thereby allowing free NF-KB dimers to translocate to the nucleus ...

Distinct Promoters Determine Alternative Transcription of gpx-4 into Phospholipid-Hydroperoxide Glutathione Peroxidase Variants

“…It is thus extremely unlikely that PHGPx, which is less abundant than any of its congeners, is of vital importance because of its antioxidant potential. Modulation of cytokine responses, as reported for gpx-4 overexpression, cannot likely be reconciled with embryogenesis either, because it has been similarly reported for GPx-1 (42), and needless to say, the role of PHGPx as a structural protein of spermatozoa is irrelevant to embryonic development. Rather a unique role of PHGPx in cellular differentiation would be compatible with the outcome of the reverse genetics approach.…”

Impairment of synaptic transmission by transient hypoxia in hippocampal slices: Improved recovery in glutathione peroxidase transgenic mice

“…The target cellular mechanisms protected in the synaptic transmission and the LTP signaling pathways and machinery remain to be identified. Candidate mechanisms may include prevention of signaling interference involving kinase activation (or tyrosine phosphatase inhibition by free radicals) that may culminate, for example, in the inhibition of both I B phosphorylation and NF B activation (35); inhibition of peroxide-mediated activation of phospholipase A2 (36); and prevention of oxygen free radicalmediated damage to glutamate-uptake systems (37). Hypoxic insults were reported to transiently augment the extracellular concentration of glutamate (38).…”

Redox signaling: hydrogen peroxide as intracellular messenger

“…In vitro and in vivo studies of oxidized OxyR revealed that the transcriptional factor is activated through the formation of a disulfide bond and is deactivated by reduction with glutaredoxin (Zheng et al, 1998). N F-κB was the first eukaryotic transcription factor shown to respond directly to oxidative stress Baeuerle and Baltimore, 1996;Kretz-Remy et al, 1996). The transactivator plays a crucial role in the regulation of numerous genes involved in immune and inflammatory processes.…”