Ser9 phosphorylation causes cytoplasmic detention of I2PP2A/SET in Alzheimer disease
Ser9 phosphorylation causes cytoplasmic detention of I2PP2A/SET in Alzheimer disease
复制标题
Ser9 磷酸化导致阿尔茨海默病中 I2PP2A/SET 的细胞质滞留
DOI：
10.1016/j.neurobiolaging.2012.12.025
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发表时间：
2013-07-01
影响因子：
4.2
通讯作者：
Wang, Xiaochuan
中科院分区：
文献类型：
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作者：
Yu, Guang;Yan, Tonghai;Wang, Xiaochuan
核蛋白I-2(PP2A)/SET是蛋白磷酸酶2a （PP2A）的内源性抑制剂，在阿尔茨海默病（AD）大脑神经元中增加并易位到细胞质中，并且细胞质中的PP2A活性受到损害。然而，SET如何保留在细胞质中尚不完全清楚。通过产生磷酸化位点特异性抗体，我们在本研究中发现SET在Ser9位点磷酸化，从而在AD脑的细胞质中积累。进一步的研究表明，磷酸化模拟物和酪蛋白激酶（CK） ii介导的Ser9磷酸化都会干扰SET/importin- α /importin- β复合物的形成，从而抑制SET核输入并诱导SET的细胞质滞留。有趣的是，Ser9嵌套在SET序列(6)AKVSKK（11）的中心，这与经典的核定位信号（NLS）一致。为了检验(6)AKVSKK（11）是否为SET的新NLS，我们将SET赖氨酸7、赖氨酸10和赖氨酸11分别突变为丙氨酸（K7A、K10A、K11A），并在HEK293/tau细胞中表达这些突变体。我们发现SET （K11A）的表达导致SET的核输入缺陷，并且应用一种合成的肽Tat-AAKVSKKE，可以竞争性地结合输入α / β，导致SET的细胞质滞留。最后，SET的磷酸化加重了PP2A抑制并导致tau过度磷酸化。总之，目前的研究已经确定了一种新的机制，通过新的nns依赖性CKII相关的Ser9磷酸化导致SET的细胞质滞留，这表明CKII的抑制可以阻止SET的细胞质积累，从而保持AD大脑中PP2A的活性。(C) 2013爱思唯尔公司版权所有。
The nuclear protein I-2(PP2A)/SET, an endogenous inhibitor of protein phosphatase-2A (PP2A), is increased and translocated to the cytoplasm in the neurons of Alzheimer's disease (AD) brains, and PP2A activity in cytoplasm is compromised. However, it is not fully understood how SET is retained in the cytoplasm. By generating a phosphorylation site-specific antibody, we found in the present study that SET is phosphorylated at Ser9, by which it is accumulated in the cytoplasm of the AD brains. Further studies demonstrate that both the phosphor-mimic and casein kinase (CK) II-mediated phosphorylation at Ser9 interferes with the formation of the SET/importin-alpha/importin-beta complex, and thus inhibits SET nuclear import and induces the cytoplasmic detention of SET. Interestingly, Ser9 is nested in the center of the sequence (6)AKVSKK(11) of SET, which is consistent with a classical nuclear localization signal (NLS). To test whether (6)AKVSKK(11) is a new NLS of SET, we mutated SET lysine 7, lysine 10, and lysine 11 to alanine acid (K7A, K10A, K11A) respectively, and expressed these mutants in HEK293/tau cells. We found that expression of SET (K11A) led to a nuclear import defect of SET, and application of a synthesized peptide Tat-AAKVSKKE that can competitively bind to importin alpha/beta resulted in cytoplasmic detention of SET. Finally, phosphorylation of SET aggravates PP2A inhibition and leads to tau hyperphosphorylation. In conclusion, the current study has identified a novel mechanism that causes cytoplasmic detention of SET with a new NLS-dependent CKII-associated phosphorylation of Ser9, suggesting that inhibition of CKII arrests cytoplasmic accumulation of SET and thus preserves PP2A activity in AD brains. (C) 2013 Elsevier Inc. All rights reserved.