Thioredoxin reductase (TrxR) is a flavoprotein that contains a C-terminal penultimate selenocysteine (Sec) and has an ability to reduce thioredoxin (Trx), which regulates the activity of NF-kappa B. To date, three TrxR isozymes, TrxR1, TrxR2, and TrxR3, have been identified. In the present study, we found that among these isozymes only TrxR1 was induced by tumor necrosis factor-alpha (TNF alpha) in vascular endothelial cells. Furthermore, the overexpression of TrxR1 enhanced TNF alpha-induced DNA-binding activity of NF-kappa B and NF-kappa B-dependent gene expression. The catalytic Sec residue of TrxR1, which is essential for reducing Trx, was required for this NF-kappa B activation, and aurothiomalate, an inhibitor of TrxR, suppressed TNF alpha-induced activation of NF-kappa B and the expression of NF-kappa B-targeted proinflammatory genes such as E-selectin and cyclooxygenase-2. These results suggest that TrxR1 may act as a positive regulator of NF-kappa B and may play an important role in the cellular inflammatory response.

Selenium (Se) is an essential trace element and functions primarily in the form of selenoproteins. [1][2][3][4][5] Se is incorporated into selenoproteins in the form of selenocysteine, and its incorporation is directed by a specific UGA codon, which normally functions as a stop codon in both prokaryocytes and eukaryocytes. 6) In mammals, 14 selenoproteins have been found to date.2,3) These include four types of glutathione peroxidase (GPx), 7) three types of thyroid hormone deiodinase, 8) three types of thioredoxin reductase (TrxR), 9,10) selenophosphate synthetase 2, 11) selenoprotein W, 12) selenoprotein P (SelP), 13) and the 15-kDa selenoprotein. 14) In addition to these selenoproteins, a computational screening identified three other new mammalian selenoproteins. 15,16) Se deficiency causes a fall in the activities and mRNA levels of selenoproteins. 4,5) In humans, severe Se deficiency is associated with cardiac disease (Keshan disease) in some provinces of China. 5,17) It has also been reported that deficiency of Se is associated with an increased incidence of myocardial infarction and other atherosclerotic cardiovascular diseases. 18,19) Reactive oxygen species (ROS) have been implicated in the pathogenesis of many cardiovascular diseases including atherosclerosis.20) The vascular endothelium represents a critical cell target in these disorders. ROS stimulate endothelial lipid peroxidation, 21) perturb the barrier function of vascular endothelial cells (EC), 22) and then interfere with endothelial functions. Selenoproteins such as GPx isozymes, TrxR isozymes and SelP have an activity to scavenge ROS and lipid peroxides. 23,24) Thomas et al. found that Se supplementation confers resistance on EC to oxidative injury.25) The possible mechanism for this protection is considered to be through the expression of selenoproteins. However, the expression and the regulation of selenoproteins in vascular EC have not yet been well understood.In the present study, we detected the expression of several selenoproteins including TrxR isozymes, GPx isozymes and SelP in cultured bovine arterial EC (BAEC) and then investigated the effect of Se depletion on the expression of these selenoproteins. MATERIALS AND METHODSCell Culture BAEC were kindly provided by Dr. M. Masuda of the National Cardiovascular Research Institute (Osaka, Japan). BAEC were cultured and maintained in Dulbecco's modified Eagle's medium (DMEM) containing 10% fetal calf serum (FCS). In order to prepare Se-sufficient and Se-deficient cells, the cells were grown in 0.5% FCS-containing DMEM supplemented either with insulin (5 mg/ml), transferrin (0.5 mg/ml) and sodium selenite (100 nM) (Se-sufficient medium) or with insulin and transferrin (Se-deficient medium) alone.Measurement of Sensitivity of BAEC to tert-Butylhydroperoxide (t-BuOOH) The sensitivity of BAEC to tBuOOH was determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay as described previously.26) BAEC cultured in Se-deficient or Se-sufficient medium for 6 d were resu...