Anestål Karin, Arnér Elias S J
Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institute, 171 77 Stockholm, Sweden.
J Biol Chem. 2003 May 2;278(18):15966-72. doi: 10.1074/jbc.M210733200. Epub 2003 Feb 6.
Mammalian thioredoxin reductases are selenoproteins. For native catalytic activity, these enzymes utilize a C-terminal -Gly-Cys-Sec-Gly-COOH sequence (where Sec is selenocysteine) forming a redox active selenenylsulfide/selenolthiol motif. A range of cellular systems depend upon or are regulated by thioredoxin reductase and its major protein substrate thioredoxin, including apoptosis signal-regulating kinase 1, peroxiredoxins, methionine sulfoxide reductase, and several transcription factors. Cytosolic thioredoxin reductase 1 (TrxR1) is moreover inhibited by various electrophilic anticancer compounds. TrxR1 is hence generally considered to promote cell viability. However, several recent studies have suggested that TrxR1 may promote apoptosis, and the enzyme was identified as GRIM-12 (gene associated with retinoid interferon-induced mortality 12). Transient transfection with GRIM-12/TrxR1 was also shown to directly induce cell death. To further analyze such effects, we have here employed lipid-mediated delivery of recombinant TrxR1 preparations into human A549 cells, thereby bypassing selenoprotein translation to facilitate assessment of the protein-related effects on cell viability. We found that selenium-deficient TrxR1, having a two-amino acid-truncated C-terminal -Gly-Cys-COOH motif, rapidly induced cell death (38 +/- 29% apoptotic cells after 4 h; p < 0.005 compared with controls). Cell death induction was also promoted by selenium-compromised TrxR1 derivatized with either cis-diamminedichloroplatinum (II) (cisplatin) or dinitrophenyl moieties but not by the structurally related non-selenoprotein glutathione reductase. In contrast, TrxR1 with intact selenocysteine could not promote cell death. The direct cellular effects of selenium-compromised forms of TrxR1 may be important for the pathophysiology of selenium deficiency as well as for the efficacy of antiproliferative drugs targeting the selenocysteine moiety of this enzyme.
哺乳动物硫氧还蛋白还原酶是硒蛋白。为了具备天然催化活性，这些酶利用一个C端-Gly-Cys-Sec-Gly-COOH序列（其中Sec是硒代半胱氨酸）形成一个氧化还原活性的硒代亚磺酰基/硒醇硫醇基序。一系列细胞系统依赖于硫氧还蛋白还原酶及其主要蛋白质底物硫氧还蛋白，或受其调节，其中包括凋亡信号调节激酶1、过氧化物酶体增殖物激活受体、甲硫氨酸亚砜还原酶以及几种转录因子。此外，胞质硫氧还蛋白还原酶1（TrxR1）受到多种亲电子抗癌化合物的抑制。因此，TrxR1通常被认为可促进细胞活力。然而，最近的几项研究表明，TrxR1可能促进细胞凋亡，并且该酶被鉴定为GRIM-12（与类视黄醇干扰素诱导的死亡率12相关的基因）。用GRIM-12/TrxR1进行瞬时转染也显示可直接诱导细胞死亡。为了进一步分析此类效应，我们在此采用脂质介导的方法将重组TrxR1制剂导入人A549细胞，从而绕过硒蛋白翻译过程，以便于评估该蛋白对细胞活力的相关影响。我们发现，缺乏硒的TrxR1具有截短了两个氨基酸的C端-Gly-Cys-COOH基序，可迅速诱导细胞死亡（4小时后凋亡细胞达38±29%；与对照组相比，p<0.005）。用顺二氨二氯铂（II）（顺铂）或二硝基苯基部分衍生的硒缺乏的TrxR1也可促进细胞死亡诱导，但结构相关的非硒蛋白谷胱甘肽还原酶则无此作用。相比之下，具有完整硒代半胱氨酸的TrxR1不能促进细胞死亡。硒缺乏形式的TrxR1对细胞的直接作用可能对硒缺乏的病理生理学以及靶向该酶硒代半胱氨酸部分的抗增殖药物的疗效具有重要意义。
