Superoxide and hydrogen peroxide-dependent inhibition of iron regulatory protein activity: A protective stratagem against oxidative injury
Superoxide and hydrogen peroxide-dependent inhibition of iron regulatory protein activity: A protective stratagem against oxidative injury
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DOI：
10.1096/fasebj.10.11.8836047
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发表时间：
1996-09-01
期刊：
影响因子：
4.8
通讯作者：
BernelliZazzera, A
中科院分区：
文献类型：
--
作者：
Cairo, G;Castrusini, E;BernelliZazzera, A
细胞内铁稳态受细胞质铁调节蛋白（IRP）调节，IRP与mRNA的铁响应元件（IRE）结合，分别调节铁的摄取和螯合。当铁缺乏时，IRP与IRE结合，协同增加转铁蛋白受体的合成并减少铁蛋白的合成，从而为细胞提供易于利用的游离铁。当铁过量时，IRP不结合，铁螯合胜过铁吸收。我们发现，孵育大鼠肝裂解物与黄嘌呤氧化酶（XO），产生超氧化物（O-2（.-））和过氧化氢（H2 O2）对IRP活性产生了显着但可逆的抑制，因为IRE-IRP的形成减少了70-80%，但在暴露于2-巯基乙醇等还原剂后恢复到基线值。IRP抑制被阻止单独或同时加入超氧化物歧化酶和过氧化氢酶，表明这两个O-2（.-）。和H2 O2都参与其中。相反，铁螯合剂和羟基自由基清除剂并不阻碍IRP的抑制，这表明O-2（.-）H_2O_2的作用不依赖于铁源。铁蛋白增强IRP抑制，但这一过程涉及紧密结合的铁中心，从XO分流还原当量，并返回到氧气，从而增加O-2（.-）的形成。与O-2（.-）的专属作用一致H_2O_2、XO在缺铁条件下也能抑制重组人IRP。这些结果表明O2（.-）.和H2 O2可以直接但可逆地下调IRP的RNA结合活性，引起游离铁的短暂减少，否则游离铁将转化为更有效的氧化剂，如羟基自由基或同样具有攻击性的铁-过氧复合物。这建立了一种新的保护策略，防止氧化损伤的病理生理条件下，其特征是过度产生的O2（.-）和H2 O2。
Cellular iron homeostasis is regulated by the cytoplasmic iron regulatory protein (IRP), which binds to iron-responsive elements (IRE) of mRNAs, modulating iron uptake and sequestration, respectively. When iron is scarce, IRP binds to IRE and coordinately increases the synthesis of transferrin receptor and decreases that of ferritin, thus providing the cell with readily available free iron. When iron is in excess, IRP does not bind and iron sequestration prevails over iron uptake. We have found that incubation of rat liver lysates with xanthine oxidase (XO), which generates superoxide (O-2(.-)) and hydrogen peroxide (H2O2), caused a remarkable but reversible inhibition of IRP activity, as the formation of IRE-IRP decreased by 70-80% but returned to baseline values upon exposure to a reducing agent like 2-mercaptoethanol. IRP inhibition was prevented by separate or simultaneous addition of superoxide dismutase and catalase, showing that both O-2(.-). and H2O2 were involved. By contrast, iron chelators and hydroxyl radical scavengers did not impede the inhibition of IRP, suggesting that O-2(.-) and H2O2 acted independently of fi ee iron sources. Ferritin enhanced IRP inhibition, but this process involved tightly bound iron centers that shunted reducing equivalents from XO and returned them to oxygen, thus increasing the formation of O-2(.-). In agreement with the exclusive role of O-2(.-) and H2O2, XO also inhibited recombinant human IRP in the absence of iron. These results demonstrate that O2(.-). and H2O2 can directly but reversibly down-regulate the RNA-binding activity of IRP, causing transient decrease of free iron that otherwise would convert them into more potent oxidants such as hydroxyl radicals or equally aggressive iron-peroxo complexes. This establishes a novel protective stratagem against oxidative injury under pathophysiologic conditions characterized by the excessive generation of O2(.-) and H2O2.