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Background: The thioredoxin system maintains redox balance through the action of thioredoxin and thioredoxin reductase. Thioredoxin regulates the activity of various substrates, including those that function to counteract cellular oxidative stress. These include the peroxiredoxins, methionine sulfoxide reductase A and specific transcription factors. Of particular relevance is Redox Factor-1, which in turn activates other redox-regulated transcription factors., Scope of Review: Experimentally defined transcription factor binding sites in the human thioredoxin and thioredoxin reductase gene promoters together with promoters of the major thioredoxin system substrates involved in regulating cellular redox status are discussed. An in silico approach was used to identify potential putative binding sites for these transcription factors in all of these promoters., Major Conclusions: Our analysis reveals that many redox gene promoters contain the same transcription factor binding sites. Several of these transcription factors are in turn redox regulated. The ARE is present in several of these promoters and is bound by Nrf2 during various oxidative stress stimuli to upregulate gene expression. Other transcription factors also bind to these promoters during the same oxidative stress stimuli, with this redundancy supporting the importance of the antioxidant response. Putative transcription factor sites were identified in silico, which in combination with specific regulatory knowledge for that gene promoter may inform future experiments., General Significance: Redox proteins are involved in many cellular signalling pathways and aberrant expression can lead to disease or other pathological conditions. Therefore understanding how their expression is regulated is relevant for developing therapeutic agents that target these pathways., (© 2013.)

Thioredoxin is a redox-active protein that plays multiple roles in regulating cell growth, cell signalling and apoptosis. Here, we have demonstrated that a complex mechanism involving multiple regulatory elements is involved in the tBHQ [tert-butylhydroquinone or 2,5-di-(t-butyl)-1,4-hydroquinone]-mediated activation of the thioredoxin gene. Luciferase assays, utilizing various wild-type and mutated thioredoxin promoter fragments, revealed roles for the ORE (oxidative stress responsive element), ARE (antioxidant responsive element), three Sp1 (specificity protein 1)-binding sites and the TATA box in the activation of the thioredoxin gene by tBHQ. The ORE required the presence of the ARE to elicit its response, whereas the independent removal of three Sp1-binding sites and the TATA box also decreased activation of the thioredoxin gene, with mutation of the TATA box having the greatest effect. Real-time RT (reverse transcriptase)-PCR analysis also revealed varying roles for two TSSs (transcription start sites) in the activation of the thioredoxin gene by tBHQ. Transcription was initiated from both TSSs; however, different response rates and fold inductions were observed. Together, these results suggest that the thioredoxin gene is controlled by a novel arrangement of two overlapping core promoter regions, one containing a TATA box and the other TATA-less. Altering the intracellular levels of thioredoxin in a breast cancer cell line also influenced the induction of thioredoxin transcription in response to tBHQ. Stable transfections with a redox-inactive thioredoxin mutant produced 3.6 times higher induction levels of thioredoxin transcription compared with control cells, indicating an intrinsic form of control of promoter activity by the thioredoxin system itself.