Article

Substrate and inhibitor specificities differ between human cytosolic and mitochondrial thioredoxin reductases: Implications for development of specific inhibitors.

Western Australian Institute for Medical Research, Centre for Medical Research, University of Western Australia, Perth, WA 6000, Australia.
Free Radical Biology and Medicine (Impact Factor: 5.27). 03/2011; 50(6):689-99. DOI: 10.1016/j.freeradbiomed.2010.12.015
Source: PubMed

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.

0 Bookmarks
 · 
134 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Thioredoxin reductase (TrxR) is overpressed in many human tumors and has a key role in regulating intracellular redox balance. Recently, thioredoxin system has emerged as a valuable target for anticancer drug development. Herein we demonstrate that selenocystine (SeC) could enhance auranofin (AF)-induced A549 human lung adenocarcinoma cell apoptosis in vitro and in vivo through synergetic inhibition of TrxR1. SeC pretreatment significantly enhanced AF-induced loss of mitochondrial membrane potential (Δψm) by regulating Bcl-2 family proteins. The combined treatment with SeC and AF also resulted in enhanced intracellular reactive oxygen species (ROS) accumulation, DNA damage, and inactivation of ERK and AKT. Inhibitors of ERK and AKT effectively enhanced combined treatment-induced apoptotic cell death. However, inhibition of ROS reversed the apoptosis induced by SeC and AF, and recovered the inactivation of ERK and AKT, which revealed the importance of ROS in cell apoptosis and regulation of ERK and AKT pathways. Moreover, xenograft lung tumor growth in nude mice was more effectively inhibited by combined treatment with SeC and AF by induction of apoptosis through targeting TrxR1 in vivo. Taken together, our results suggest the strategy to use SeC and AF in combination could be a highly efficient way to achieve anticancer synergism by targeting TrxR1.
    Cell Death & Disease 04/2014; 5:e1191. · 6.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Botulinum neurotoxins consist of a metalloprotease linked via a conserved interchain disulfide bond to a heavy chain responsible for neurospecific binding and translocation of the enzymatic domain in the nerve terminal cytosol. The metalloprotease activity is enabled upon disulfide reduction and causes neuroparalysis by cleaving the SNARE proteins. Here, we show that the thioredoxin reductase-thioredoxin protein disulfide-reducing system is present on synaptic vesicles and that it is functional and responsible for the reduction of the interchain disulfide of botulinum neurotoxin serotypes A, C, and E. Specific inhibitors of thioredoxin reductase or thioredoxin prevent intoxication of cultured neurons in a dose-dependent manner and are also very effective inhibitors of the paralysis of the neuromuscular junction. We found that this group of inhibitors of botulinum neurotoxins is very effective in vivo. Most of them are nontoxic and are good candidates as preventive and therapeutic drugs for human botulism.
    Cell Reports 09/2014; · 7.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The molecular mechanisms by which Entamoeba histolytica causes amebic liver abscess (ALA) are still not fully understood. Amebic mechanisms of adherence and cytotoxic activity are pivotal for amebic survival but apparently do not directly cause liver abscess. Abundant evidence indicates that chronic inflammation (resulting from an inadequate immune response) is probably the main cause of ALA. Reports referring to inflammatory mechanisms of liver damage mention a repertoire of toxic molecules by the immune response (especially nitric oxide and reactive oxygen intermediates) and cytotoxic substances released by neutrophils and macrophages after being lysed by amoebas (e.g., defensins, complement, and proteases). Nevertheless, recent evidence downplays these mechanisms in abscess formation and emphasizes the importance of peroxynitrite (ONOO(-)). It seems that the defense mechanism of amoebas against ONOO(-), namely, the amebic thioredoxin system (including peroxiredoxin), is superior to that of mammals. The aim of the present text is to define the importance of ONOO(-) as the main agent of liver abscess formation during amebic invasion, and to explain the superior capacity of amoebas to defend themselves against this toxic agent through the peroxiredoxin and thioredoxin system.
    BioMed research international. 01/2014; 2014:324230.

Full-text

Download
14 Downloads
Available from
May 22, 2014