title: Substrate and inhibitor specificities differ between human cytosolic and mitochondrial thioredoxin reductases: Implications for development of specific inhibitors.
abstract: The cytosolic and mitochondrial thioredoxin reductases (TrxR1 and TrxR2) and thioredoxins (Trx1 and Trx2) are key components of the mammalian thioredoxin system, which is important for antioxidant defense and redox regulation of cell function. TrxR1 and TrxR2 are selenoproteins generally considered to have comparable properties, but to be functionally separated by their different compartments. To compare their properties we expressed recombinant human TrxR1 and TrxR2 and determined their substrate specificities and inhibition by metal compounds. TrxR2 preferred its endogenous substrate Trx2 over Trx1, whereas TrxR1 efficiently reduced both Trx1 and Trx2. TrxR2 displayed strikingly lower activity with dithionitrobenzoic acid (DTNB), lipoamide, and the quinone substrate juglone compared to TrxR1, and TrxR2 could not reduce lipoic acid. However, Sec-deficient two-amino-acid-truncated TrxR2 was almost as efficient as full-length TrxR2 in the reduction of DTNB. We found that the gold(I) compound auranofin efficiently inhibited both full-length TrxR1 and TrxR2 and truncated TrxR2. In contrast, some newly synthesized gold(I) compounds and cisplatin inhibited only full-length TrxR1 or TrxR2 and not truncated TrxR2. Surprisingly, one gold(I) compound, [Au(d2pype)(2)]Cl, was a better inhibitor of TrxR1, whereas another, [(iPr(2)Im)(2)Au]Cl, mainly inhibited TrxR2. These compounds also inhibited TrxR activity in the cytoplasm and mitochondria of cells, but their cytotoxicity was not always dependent on the proapoptotic proteins Bax and Bak. In conclusion, this study reveals significant differences between human TrxR1 and TrxR2 in substrate specificity and metal compound inhibition in vitro and in cells, which may be exploited for development of specific TrxR1- or TrxR2-targeting drugs.
authors.affiliation: Western Australian Institute for Medical Research, Centre for Medical Research, University of Western Australia, Perth, WA 6000, Australia.
authors.forename: Oliver
authors.initials: O
authors.lastname: Rackham
authors.forename: Anne-Marie J
authors.initials: AM
authors.lastname: Shearwood
authors.forename: Ross
authors.initials: R
authors.lastname: Thyer
authors.forename: Elyshia
authors.initials: E
authors.lastname: McNamara
authors.forename: Stefan M K
authors.initials: SM
authors.lastname: Davies
authors.forename: Bernard A
authors.initials: BA
authors.lastname: Callus
authors.forename: Antonio
authors.initials: A
authors.lastname: Miranda-Vizuete
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Berners-Price
authors.forename: Qing
authors.initials: Q
authors.lastname: Cheng
authors.forename: Elias S J
authors.initials: ES
authors.lastname: Arnér
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Filipovska
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002945:Cisplatin / Q000378:metabolism / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D004228:Dithionitrobenzoic Acid / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000201:enzymology; D009285:Naphthoquinones / Q000378:metabolism; D050607:Organogold Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D008063:Thioctic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D054481:Thioredoxin Reductase 1 / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054482:Thioredoxin Reductase 2 / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000975:Antioxidants; D004791:Enzyme Inhibitors; D009285:Naphthoquinones; D050607:Organogold Compounds; D011994:Recombinant Proteins; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D013879:Thioredoxins; D008063:Thioctic Acid; C013091:lipoamide; D004228:Dithionitrobenzoic Acid; C516124:TXNRD1 protein, human; C516127:TXNRD2 protein, human; D054481:Thioredoxin Reductase 1; D054482:Thioredoxin Reductase 2; D002945:Cisplatin; C005134:juglone