Malorni W, Testa U, Rainaldi G, Tritarelli E, Peschle C
Department of Ultrastructures, Istituto Superiore di Sanita, Rome, Italy.
Exp Cell Res. 1998 May 25;241(1):102-16. doi: 10.1006/excr.1998.4020.
Several studies have demonstrated that perturbations of intracellular oxidative balance play a key role in numerous physiological as well as pathological conditions leading to various morbidity states. In previous studies we have shown that the free radical inducer menadione rapidly and specifically downmodulates the membrane transferrin receptor (TfR) by blocking receptor recycling. This modulation is due to receptor redistribution and not to receptor loss. Here we show that other oxidant compounds, such as hydrogen peroxide, also induce a rapid downmodulation of membrane TfR and that pretreatment of cells with the antioxidant, thiol supplier, N-acetylcysteine inhibits the downmodulation of these receptors elicited by either menadione or hydrogen peroxide. This observation suggests that intracellular thiol redox status may be a critical determinant of TfR downmodulation induced by oxidative stress. Furthermore, immunocytochemical results show that, in menadione-treated cells, TfRs are associated with the Golgi complex, where normally only 20% of total cellular TfRs is found and is mainly detected in the cytoplasm as scattered punctuations. Accordingly, menadione and hydrogen peroxide also elicited a downmodulation of low density lipoprotein receptor (LDLR) which mediates, like TfR, the transport of nutrients to the cell and is endocytosed through clathrin-coated pits. Finally, experiments carried out using okadaic acid, an inhibitor of phosphatases, suggest that H2O2 and menadione downmodulate surface TfR via different biochemical pathways. Taken together these results suggest the existence of a potentially important protective mechanism through which iron uptake is prevented in oxidatively imbalanced cells. Iron uptake can in fact give rise to the formation of highly toxic hydroxyl radicals reacting with hydrogen peroxide and leading to cytotoxicity. Downmodulation of surface TfR may thus represent the physiological control mechanism for reducing iron uptake in diverse pathological conditions including hypoxia-reperfusion injury, acquired immunodeficiency syndrome, and aging.
多项研究表明，细胞内氧化平衡的扰动在导致各种发病状态的众多生理和病理状况中起关键作用。在先前的研究中，我们已经表明自由基诱导剂甲萘醌通过阻断受体再循环迅速且特异性地下调膜转铁蛋白受体（TfR）。这种调节是由于受体重新分布而非受体丢失。在这里，我们表明其他氧化剂化合物，如过氧化氢，也会诱导膜TfR的快速下调，并且用抗氧化剂、硫醇供应剂N - 乙酰半胱氨酸对细胞进行预处理可抑制由甲萘醌或过氧化氢引起的这些受体的下调。这一观察结果表明细胞内硫醇氧化还原状态可能是氧化应激诱导TfR下调的关键决定因素。此外，免疫细胞化学结果表明，在甲萘醌处理的细胞中，TfR与高尔基体复合体相关，而在高尔基体复合体中，通常仅发现总细胞TfR的20%，并且主要在细胞质中作为散在的斑点被检测到。相应地，甲萘醌和过氧化氢也引起低密度脂蛋白受体（LDLR）的下调，LDLR与TfR一样介导营养物质向细胞的转运，并通过网格蛋白包被小窝进行内吞。最后，使用磷酸酶抑制剂冈田酸进行的实验表明，H2O2和甲萘醌通过不同的生化途径下调表面TfR。综合这些结果表明存在一种潜在重要的保护机制，通过该机制可防止氧化失衡细胞摄取铁。事实上，铁摄取会导致与过氧化氢反应并导致细胞毒性的高毒性羟基自由基的形成。因此，表面TfR的下调可能代表了在包括缺氧 - 再灌注损伤、获得性免疫缺陷综合征和衰老在内的多种病理状况下减少铁摄取的生理控制机制。
