Oxidative stress mechanisms related to ribotoxic stress and endoplasmic reticulum stress

神经纤维缠结（NFT）和神经元细胞死亡是阿尔茨海默病（AD）的标志，异常高磷酸化的tau蛋白是NFT的主要亚基。然而，tau蛋白磷酸化在阿尔茨海默病神经退行性过程中的作用机制尚不清楚。我们研究了用多肽转移酶抑制剂（包括大霉素和t2 -三醇）处理SY5Y人神经母细胞瘤细胞时tau蛋白磷酸化和神经元细胞死亡的变化。Western blot分析显示，大霉素和t2 -三醇诱导SAPK和p38 MAPK活化，M4 （Thr-231/Ser-235）、PHF-1 （Ser-396/404）和S422 （Ser-422）位点的tau蛋白过度磷酸化。p38抑制剂SB203580在这种反应中减弱了tau蛋白的磷酸化，而GSK-3抑制剂锂则没有。在该反应中，Hoechst33342显示的凋亡细胞数量小于Live/ dead kit （Molecular Probe）显示的总死亡细胞数量的*，提示可能涉及非凋亡细胞死亡机制。这种肽基转移酶抑制是一种核毒性胁迫。进一步用玫瑰花和光处理细胞，单线态氧诱导。在这种情况下，核糖体RNA被氧化，tau蛋白被磷酸化，可能是通过核糖体毒性应激。在阿尔茨海默病中，脑tau蛋白的过度磷酸化和神经元细胞的死亡可能与这种核毒性应激机制有关。

Neurofibliraly tangles (NFTs) and neuronal cell death are hallmark of Alzheimer's disease (AD) and abnormal hyperphospholylated tau protein is the major subunit of NFT. However the mechanisms of phosphorylation of tau in neurodegenerative process of AD is unknown. We investigated the changes of phosphorylation of tau protein and neuronal cell death in SY5Y human neuroblastoma cells treated with peptidyltransferase inhibitors including anisomycin and T2-triol. Western blot analysis revealed that anisomycin and T2-triol induced activation of SAPK and p38 MAPK and hyperphosphorylation of tau protein at the M4 (Thr-231/Ser-235), the PHF-1 (Ser-396/404) and the S422 (Ser-422) site. The inhibitor of p38, SB203580, attenuated the phosphorylation of tau protein in this response, whereas an inhibition of GSK-3, lithium, did not. In this response the number of apoptotic cells visualized by Hoechst33342 was less than *he number of total dead cells visualized by Live/Dead kit (Molecular Probe), suggesting the non-apoptotoc cell death mechanism might be involved. This peptidyltransferase-inhibition is one kind of ribotoxic stresses. Further the cells were treated with rose bengal and light, and singlet oxygen was induced. Under this condition, ribosomal RNA was oxidized and tau protein was phosphorylated, probably through ribotoxic stress. In AD brain hyperphosphorylation of tau protein and neuronal cell death might be explained by this ribotoxic stress mechanism.