| 1. |
- Madeja, Zbigniew, et al.
(författare)
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The role of thioredoxin reductase activity in selenium-induced cytotoxicity
- 2005
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Ingår i: Biochemical Pharmacology. - : Elsevier. - 0006-2952 .- 1356-1839. ; 69:12, s. 1765-1772
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Tidskriftsartikel (refereegranskat)abstract
- The selenoprotein thioredoxin reductase is a key enzyme in selenium metabolism, reducing selenium compounds and thereby providing selenide to synthesis of all selenoproteins. We evaluated the importance of active TrxR1 in selenium-induced cytotoxicity using transfected TrxR1 over-expressing stable Human Embryo Kidney (HEK-293) cells and modulation of activity by pretreatment with low concentration of selenite. Treatment with sodium selenite induced cytotoxity in a dose-dependent manner in both TrxR1 over-expressing and control cells. However, TrxR1 over-expressing cells, which were preincubated for 72h with 0.1 microM selenite, were significantly more resistant to selenite cytotoxicity than control cells. To demonstrate the early effects of selenite on behaviour of HEK-293 cells, we also investigated the influence of this compound on cell motility. We observed inhibition of cell motility by 50 microM selenite immediately after administration. Moreover, TrxR1 over-expressing cells preincubated with a low concentration of selenite were more resistant to the inhibitory effect of 50 microM selenite than those not preincubated. It was also observed that the TrxR over-expressing cells showed higher TrxR1 activity than control cells and the preincubation of over-expressing cells with 0.1 microM selenite induced further significant increase in the activity of TrxR1. On the other hand, we demonstrated that TrxR1 over-expressing cells showed decreased glutathione peroxidase activity compared to control cells. These data strongly suggest that TrxR1 may be a crucial enzyme responsible for cell resistance against selenium cytotoxicity.
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| 2. |
- Nalvarte, Ivan
(författare)
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Functional characterization of cytosolic and mitochondrial thioredoxin reductases
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mammalian thioredoxin reductases (TrxRs) are homodimeric selenoproteins belonging to the nucleotide oxidoreductase family. They contain a C-terminal penultimate selenocysteine residue, which is kept reduced by the N-terminal redox active site, CVNVGC, of the adjacent subunit. The low pKa, of the selenocysteine residue, in combination with its Cterminal accessibility, gives TrxRs broad substrate specificity. The main substrates of TrxRs are thioredoxins (Trxs), which are reduced using NADPH as an electron donor. Trx can then act as a general protein-disulfide reductase and reduce a variety of substrates. This constitutes the thioredoxin system. Apart from the classical cytosolic thioredoxin system, there exists a complete thioredoxin system exclusively in mitochondria with its own thioredoxin (Trx2) and thioredoxin reductase (TrxR2). In this thesis, we describe the functional characterization of the cytosolic and mitochondrial thioredoxin reductases. It has been suggested that there exists a link between selenium and vitamin E in the protection against lipid membrane peroxidation. Here, we present evidence that TrxR1 is a major reducer of ubiquinone, a regenerator of vitamin E. This reduction is entirely selenium dependent, and puts forward TrxR1 as an important enzyme in the antioxidant defence of lipid membranes. Furthermore, we show that cell lines overexpressing TrxR2 have a higher viability than control cells upon complex III inhibition. This effect may be ascribed to the reduction of cytochrome c by TrxR2, since this would allow electrons to bypass complex III via TrxR2. Indeed, we demonstrate that TrxR2 is a potent reducer of cytochrome c. In addition, we show that cells overexpressing TrxRs have a surprising elevated expression of markers associated with differentiation, compared to control cells. This effect is evident for both the classic cytosolic form, TrxR1a, and its cytosolic splice variant TrxR1b. Expression of TrxR1a and TrxR1b apparently preceds the expression of the genes associated with differentiation, suggesting TrxRs to be involved in the early onset of differentiation. Furthermore, some genes are oppositely regulated by TrxR1a and TrxR1b, implying attentiveness in future TrxR1 gene silencing experiments. In summary, the results presented in this thesis give better understanding of the functions of TrxRs. Our work illustrates the diverse roles of TrxRs, from mediators of redox homeostasis in distinct cellular compartments to their implications in gene expression pathways. The role of TrxRs in these redox regulatory mechanisms are far from resolved and, as reflected in this thesis, much more work is needed in this field of research.
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| 3. |
- Sroka, Jolanta, et al.
(författare)
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Overexpression of thioredoxin reductase 1 inhibits migration of HEK-293 cells
- 2007
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Ingår i: Biology of the Cell. - : John Wiley & Sons. - 0248-4900 .- 1768-322X. ; 99:12, s. 677-687
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND INFORMATION:TrxR (thioredoxin reductase), in addition to protecting against oxidative stress, plays a role in the redox regulation of intracellular signalling pathways controlling, among others, cell proliferation and apoptosis. The aim of the present study was to determine whether TrxR1 is involved in the regulation of cell migration.RESULTS:Stably transfected HEK-293 (human embryonic kidney) cells which overexpress cytosolic TrxR1 (HEK-TrxR15 and HEK-TrxR11 cells) were used in the present study. We found that the stimulation of cell motility induced by PKC (protein kinase C) activators, PMA and DPhT (diphenyltin), was inhibited significantly in the HEK-TrxR15 and HEK-TrxR11 cells compared with control cells. The overexpression of TrxR1 also inhibited characteristic morphological changes and reorganization of the F-actin cytoskeleton induced by PMA and DPhT. In addition, the selective activation of PKCdelta by DPhT was inhibited in cells that overexpressed cytosolic TrxR1. Furthermore, rottlerin, a selective inhibitor of PKCdelta, and PKCdelta siRNA (small interfering RNA), suppressed the morphological changes induced by DPhT in the control cells.CONCLUSIONS:The overexpression of TrxR1 inhibits migration of HEK-293 cells stimulated with PMA and DPhT. Moreover, our observations suggest that this effect is mediated by the inhibition of PKCdelta activation.
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