Severity or duration of endoplasmic reticulum (ER) stress leads to two different cellular events: cell survival and apoptosis. Drug-induced ER stress or neurotoxicity has been observed as one of the main side effects. However, how ER stress affects cellular signaling cascades leading to neuronal damage is still not well understood. In this study, the toxicological mechanisms of two typical ER stress inducers, tunicamycin (Tm) and dithiothreitol (DTT), were investigated by cell viability, unfolded protein response, apoptosis and proteomic responses in mouse neuro-2a cells. A large portion of differentially expressed proteins (DEPs) that participate in protein synthesis and folding were identified in the Tm treated group, indicating adaptive cellular responses like the unfolded protein response were activated, which was not the case in the DTT treated group. Interestingly, KEGG pathway analysis and validation experiments revealed that proteins involved in proteasomal degradation were down-regulated by both inducers, while proteins involved in ubiquitination were up-regulated by Tm and down-regulated by DTT. A protein responsible for delivering ubiquitinated proteins to the proteasome, the UV excision repair protein RAD23 homolog A (HR23 A), was discovered as a DEP altered by both Tm and DTT. This protein was down-regulated in the Tm treated group and up-regulated in the DTT treated group, which explained the differences we observed in the ubquintination and proteasomal degradation pathways. Autophagy was activated in the Tm treated group, suggesting that it may serve as a compensatory effect to proteasomal degradation. Our work provides new insights into the neurotoxicity generated by various ER stress inducers and the underlying mechanisms.

内质网（ER）应激的严重程度或持续时间会导致两种不同的细胞事件：细胞存活和细胞凋亡。已经观察到药物诱导的ER应激或神经毒性是主要的副作用之一。然而，内质网应激如何影响导致神经元损伤的细胞信号级联反应尚不清楚。在这项研究中，通过小鼠神经2a细胞中的细胞活力，未折叠的蛋白应答，细胞凋亡和蛋白质组学应答，研究了两种典型的ER应激诱导剂，衣霉素（Tm）和二硫苏糖醇（DTT）的毒理机制。在Tm处理组中鉴定出大部分参与蛋白质合成和折叠的差异表达蛋白质（DEP），这表明诸如未折叠的蛋白质反应之类的适应性细胞反应已被激活，在DTT治疗组中情况并非如此。有趣的是，KEGG通路分析和验证实验表明，蛋白酶体降解所涉及的蛋白质均被两种诱导剂下调，而泛素化所涉及的蛋白质被Tm上调并被DTT所下调。发现了一种负责将泛素化蛋白传递到蛋白酶体的蛋白，即紫外线切除修复蛋白RAD23同源物A（HR23 A），它是被Tm和DTT改变的DEP。在Tm治疗组中该蛋白下调，而在DTT治疗组中该蛋白上调，这解释了我们在泛素化和蛋白酶体降解途径中观察到的差异。自噬在Tm治疗组中被激活，表明它可以作为蛋白酶体降解的补偿作用。