c-Jun NH2-terminal kinase-mediated redox-dependent degradation of I kappa B - Role of thioredoxin in NF-kappa B activation

NF-kappaB is a redox-sensitive transcription factor known to be activated b y oxidative stress as well as chemical and biological reductants, Its DNA b inding activity requires reduced cysteines present in the p65 subunit of th e dimer, Thioredoxin (Trx) is an endogenous disulfide oxidoreductase known to modulate several redox-dependent functions in the cell. NF-kappaB was ac tivated by addition of Escherichia coli thioredoxin in a redox-dependent ma nner in A549 cells. Such activation was accompanied by degradation of I kap paB in the cytosol. In addition, only the reduced form of thioredoxin activ ated NF-kappaB, whereas the oxidized form was without any effect. Overexpre ssion of human thioredoxin also caused activation of NF-kappaB and degradat ion of I kappaB. On the contrary, dominant-negative redox-inactive mutant t hioredoxin expression did not activate NF-kappaB, further confirming the re dox-dependent activation of NF-kappaB. We also investigated the mechanism o f activation of NF-kappaB by thioredoxin, We demonstrate that thioredoxin a ctivates c-Jun NH2-terminal kinase (JNK)-signaling cascade, and dominant-ne gative expression of mitogen-activated protein kinase kinase kinase 1 (MEKK 1), JNK kinase, or JNK inhibits NF-kappaB activation by thioredoxin. In con trast, wild-type MEKK1 or JNK kinase induced NF-kappaB activation alone or in combination with thioredoxin expression plasmid. These findings were als o confirmed by NF-kappaB-dependent luciferase reporter gene transcription.