Vieira O, Escargueil-Blanc I, Jürgens G, Borner C, Almeida L, Salvayre R, Nègre-Salvayre A
INSERM U.466, Biochemistry Department, University Paul Sabatier, Toulouse, France.
FASEB J. 2000 Mar;14(3):532-42. doi: 10.1096/fasebj.14.3.532.
Oxidized low-density lipoproteins (oxLDL) play a role in the genesis of atherosclerosis. OxLDL are able to induce apoptosis of vascular cells, which is potentially involved in the formation of the necrotic center of atherosclerotic lesions, plaque rupture, and subsequent thrombotic events. Because oxLDL may induce structural modifications of cell protein and altered proteins may impair cell viability, the present work aimed to evaluate the extent of protein alterations, the degradation of modified proteins through the ubiquitin-proteasome system (a major degradative pathway for altered and oxidatively modified proteins) and their role during apoptosis induced by oxLDL. This paper reports the following: 1) oxLDL induce derivatization of cell proteins by 4-hydroxynonenal (4-HNE) and ubiquitination. 2) Toxic concentrations of oxLDL elicit a biphasic effect on proteasome activity. An early and transient activation of endogenous proteolysis is followed rapidly by a subsequent decay (resulting probably from the 26S proteasome inhibition) and followed later by the inhibition of the 20S proteasome (as assessed by inhibition of sLLVY-MCA hydrolysis). 3) Specific inhibitors of proteasome (lactacystin and proteasome inhibitor I) potentiated considerably the toxicity of oxLDL (nontoxic doses of oxLDL became severely toxic). The defect of the ubiquitination pathway (in temperature-sensitive mutants) also potentiated the toxicity of oxLDL. This suggests that the ubiquitin-proteasome pathway plays a role in the cellular defenses against oxLDL-induced toxicity. 4) Dinitrophenylhydrazine (DNPH), an aldehyde reagent, prevented both the oxLDL-induced derivatization of cell proteins and subsequent cytotoxicity. Altogether, the reported data suggest that both derivatization of cell proteins (by 4-HNE and other oxidized lipids) and inhibition of the proteasome pathway are involved in the mechanism of oxLDL-induced apoptosis.
氧化型低密度脂蛋白（oxLDL）在动脉粥样硬化的发生过程中起作用。oxLDL能够诱导血管细胞凋亡，这可能参与动脉粥样硬化病变坏死中心的形成、斑块破裂及随后的血栓形成事件。由于oxLDL可能诱导细胞蛋白的结构修饰，而改变的蛋白可能损害细胞活力，因此本研究旨在评估蛋白改变的程度、通过泛素-蛋白酶体系统（改变的和氧化修饰蛋白的主要降解途径）对修饰蛋白的降解及其在oxLDL诱导的凋亡过程中的作用。本文报道了以下内容：1）oxLDL诱导细胞蛋白经4-羟基壬烯醛（4-HNE）衍生化和泛素化。2）oxLDL的毒性浓度对蛋白酶体活性产生双相效应。内源性蛋白水解的早期短暂激活之后迅速是随后的衰减（可能是由于26S蛋白酶体抑制所致），随后是20S蛋白酶体的抑制（通过抑制sLLVY-MCA水解评估）。3）蛋白酶体的特异性抑制剂（乳胞素和蛋白酶体抑制剂I）显著增强了oxLDL的毒性（oxLDL的无毒剂量变得具有严重毒性）。泛素化途径缺陷（在温度敏感突变体中）也增强了oxLDL的毒性。这表明泛素-蛋白酶体途径在细胞抵御oxLDL诱导的毒性中起作用。4）醛试剂二硝基苯肼（DNPH）可防止oxLDL诱导的细胞蛋白衍生化及随后的细胞毒性。总之，所报道的数据表明细胞蛋白的衍生化（通过4-HNE和其他氧化脂质）和蛋白酶体途径的抑制均参与oxLDL诱导的凋亡机制。
