Suboptimal action of NF-kappa B in Fanconi anemia cells results from low levels of thioredoxin

Electrophoretic mobility shift assays (EMSA) revealed that under standard cell culture conditions NF- B was induced in Fanconi anemia fibroblasts in contrast to control cells. Dithiothreitol, a potent synthetic redox potential-delivering compound, when added to growing cells, prevented this induction of NF- B and, simultaneously, chromosomal instability was reduced. Fanconi anemia cells possess low endogenous levels of the naturally occurring antioxidant thioredoxin. Transfection of Fanconi anemia cells with thioredoxin cDNA containing a nuclear localization signal prevented both spontaneous as well as mitomycin C-induced chromosomal instability. A promotor construct with two NF- B binding sites in front of the CAT gene induced little CAT expression in cells with low thioredoxin content in spite of induced NF-[kappa]B. In cells with higher thioredoxin content CAT expression was increased. Cotransfection of the NF-[kappa]B-dependent CAT plasmid with the Trx/nuc-plasmid into FA fibroblasts increased the CAT expression to almost that of control cells, indicating that in this model system with diminished thioredoxin content NF-[kappa]B requires thioredoxin for binding to its specific promotor. Since Fanconi anemia cells have low thioredoxin contents, NF-[kappa]B-dependent genes are expressed insufficiently. This explains part of the pathophysiological processes observed in Fanconi anemia