Phosphorylation inhibits turnover of the tau protein by the proteasome:: influence of RCAN1 and oxidative stress
Phosphorylation inhibits turnover of the tau protein by the proteasome:: influence of RCAN1 and oxidative stress
复制标题
DOI：
10.1042/bj20060463
复制
发表时间：
2006-12-15
影响因子：
4.1
通讯作者：
Grune, Tilman
中科院分区：
文献类型：
--
作者：
Poppek, Diana;Keck, Susi;Grune, Tilman
过度磷酸化的tau蛋白聚集在神经元缠结的成对螺旋丝中，见于阿尔茨海默病等tau蛋白病。在本文中，我们表明，tau蛋白营业额是依赖于降解的蛋白酶体（抑制MG 132）在HT 22神经元细胞。重组人tau蛋白在体外被20 S蛋白酶体迅速降解，但由GSK 3 β（糖原合成酶激酶3 β）引起的tau蛋白磷酸化显著抑制蛋白水解。通过OA [冈田酸;其抑制PP（蛋白磷酸酶）1和PP 2A]或CsA [环孢菌素A;其抑制PP 2B（钙调神经磷酸酶）]在HT 22细胞中增加Tau磷酸化，并且通过诱导tet-off依赖性RCAN 1转基因（其也抑制PP 2B）在PC 12细胞中增加Tau磷酸化。OA对PP 1/PP 2A的抑制是这些治疗中最有效的，OA诱导的tau过度磷酸化几乎完全阻断了HT 22细胞（以及加入纯化蛋白酶体的细胞裂解物）中的tau降解，尽管蛋白酶体活性实际上增加了。许多tau蛋白病涉及tau蛋白过度磷酸化和慢性炎症的氧化应激。我们测试了细胞氧化应激和体外直接tau氧化修饰对tau蛋白水解的影响。在HT 22细胞中，单独的氧化应激没有引起tau磷酸化的增加，但确实微妙地改变了tau磷酸化的模式。Tau实际上比大多数细胞蛋白更不容易受到直接氧化修饰，并且氧化的Tau的降解并不比未处理的Tau好。氧化应激加OA处理的组合引起广泛的tau磷酸化和tau降解的显著抑制。用tau-CFP（青色荧光蛋白）/tau-GFP（绿色荧光蛋白）构建体转染的HT 22细胞在tau过度磷酸化和氧化应激后表现出显著的毒性，整个细胞质中纤维状tau结构丧失。我们认为，tau蛋白磷酸化和tau蛋白氧化的组合，这也发生在tau蛋白病，可能是直接负责的tau蛋白聚集体的积累。
Hyperphosphorylated tau proteins accumulate in the paired helical filaments of neurofibrillary tangles seen in such tauopathies as Alzheimer's disease. In the present paper we show that tau turnover is dependent on degradation by the proteasome (inhibited by MG132) in HT22 neuronal cells. Recombinant human tau was rapidly degraded by the 20 S proteasome in vitro, but tau phosphorylation by GSK3 beta (glycogen synthase kinase 3 beta) significantly inhibited proteolysis. Tau phosphorylation was increased in HT22 cells by OA [okadaic acid; which inhibits PP (protein phosphatase) 1 and PP2A] or CsA [cyclosporin A; which inhibits PP2B (calcineurin)], and in PC12 cells by induction of a tet-off dependent RCAN1 transgene (which also inhibits PP2B). Inhibition of PP1/PP2A by OA was the most effective of these treatments, and tau hyperphosphorylation induced by OA almost completely blocked tau degradation in HT22 cells (and in cell lysates to which purified proteasome was added) even though proteasome activity actually increased. Many tauopathies involve both tau hyperphosphorylation and the oxidative stress of chronic inflammation. We tested the effects of both cellular oxidative stress, and direct tau oxidative modification in vitro, on tau proteolysis. In HT22 cells, oxidative stress alone caused no increase in tau phosphorylation, but did subtly change the pattern of tau phosphorylation. Tau was actually less susceptible to direct oxidative modification than most cell proteins, and oxidized tau was degraded no better than untreated tau. The combination of oxidative stress plus OA treatment caused extensive tau phosphorylation and significant inhibition of tau degradation. HT22 cells transfected with tau-CFP (cyan fluorescent protein)/tau-GFP (green fluorescent protein) constructs exhibited significant toxicity following tau hyperphosphorylation and oxidative stress, with loss of fibrillar tau structure throughout the cytoplasm. We suggest that the combination of tau phosphorylation and tau oxidation, which also occurs in tauopathies, may be directly responsible for the accumulation of tau aggregates.