Das K C, Lewis-Molock Y, White C W
Department of Pediatrics, National Jewish Medical and Research Center, Denver, Colorado 80206, USA.
Am J Respir Cell Mol Biol. 1997 Dec;17(6):713-26. doi: 10.1165/ajrcmb.17.6.2809.
Manganese superoxide dismutase (MnSOD) is a mitochondrial enzyme that dismutates potentially toxic superoxide radical into hydrogen peroxide and dioxygen. This enzyme is critical for protection against cellular injury due to elevated partial pressures of oxygen. Thioredoxin (TRX) is a potent protein disulfide reductase found in most organisms that participates in many thiol-dependent cellular reductive processes and plays an important role in antioxidant defense, signal transduction, and regulation of cell growth and proliferation. Here we describe induction of manganese superoxide dismutase by thioredoxin. MnSOD mRNA and activity were increased dramatically by low concentrations of TRX (28 microM). Elevation of MnSOD mRNA by TRX was inhibited by actinomycin D, but not cycloheximide, occurring both in cell lines and primary human lung microvascular endothelial cells. mRNAs for other antioxidant enzymes including copper-zinc superoxide dismutase and catalase were not elevated, demonstrating specificity of induction of MnSOD by TRX. Thiol oxidation by diamide or alkylation by chlorodinitrobenzene inhibited MnSOD induction, further indicating a requirement for reduced TRX. Because both oxidized and reduced thioredoxin (28 microM) induced MnSOD mRNA, the intracellular redox status of externally added Escherichia coli oxidized TRX was determined. About 45% of internalized E. coli TRX was reduced, with 8% in fully reduced form and about 37% in partially reduced form. However, when TRX reductase and nicotinamide adenine dinucleotide (NADPH) were added to the extracellular medium with TRX, more than 80% of E. coli TRX was found to be in a fully reduced state in human adenocarcinoma (A549) cells. Although lower concentrations of oxidized TRX (7 microM) did not induce MnSOD mRNA, this concentration of TRX, when reduced by NADPH and TRX reductase, increased MnSOD mRNA six-fold. In additional studies, MCF-7 cells stably transfected with the human TRX gene had elevated expression of MnSOD mRNA relative to vector-transfected controls. Thus, both endogenously produced and exogenously added TRX elevate MnSOD gene expression. These findings suggest a novel mechanism involving reduced TRX in regulation of MnSOD.
锰超氧化物歧化酶（MnSOD）是一种线粒体酶，它可将具有潜在毒性的超氧阴离子自由基歧化为过氧化氢和氧气。该酶对于保护细胞免受因氧分压升高导致的损伤至关重要。硫氧还蛋白（TRX）是一种在大多数生物体中都存在的强效蛋白质二硫键还原酶，它参与许多硫醇依赖性的细胞还原过程，并在抗氧化防御、信号转导以及细胞生长和增殖的调节中发挥重要作用。在此，我们描述了硫氧还蛋白对锰超氧化物歧化酶的诱导作用。低浓度的TRX（28微摩尔）可使MnSOD的mRNA和活性显著增加。TRX对MnSOD mRNA的升高作用被放线菌素D抑制，但不被环己酰亚胺抑制，这种现象在细胞系和原代人肺微血管内皮细胞中均有发生。包括铜锌超氧化物歧化酶和过氧化氢酶在内的其他抗氧化酶的mRNA并未升高，这表明TRX对MnSOD的诱导具有特异性。二酰胺引起的硫醇氧化或氯二硝基苯引起的烷基化抑制了MnSOD的诱导，进一步表明需要还原型的TRX。由于氧化型和还原型硫氧还蛋白（28微摩尔）均可诱导MnSOD mRNA，因此测定了外源添加的大肠杆菌氧化型TRX在细胞内的氧化还原状态。内化的大肠杆菌TRX约有45%被还原，其中8%为完全还原形式，约37%为部分还原形式。然而，当将硫氧还蛋白还原酶和烟酰胺腺嘌呤二核苷酸（NADPH）与TRX一起添加到细胞外培养基中时，在人腺癌（A549）细胞中发现超过80%的大肠杆菌TRX处于完全还原状态。尽管较低浓度的氧化型TRX（7微摩尔）不会诱导MnSOD mRNA，但当该浓度的TRX被NADPH和硫氧还蛋白还原酶还原后，可使MnSOD mRNA增加6倍。在其他研究中，稳定转染了人TRX基因的MCF-7细胞相对于载体转染的对照细胞，MnSOD mRNA的表达有所升高。因此，内源性产生的和外源添加的TRX均可提高MnSOD基因的表达。这些发现提示了一种涉及还原型TRX对MnSOD进行调节的新机制。
