Lau Kwok-Fai, Chan Wing-Man, Perkinton Michael S, Tudor Elizabeth L, Chang Raymond C C, Chan H-Y Edwin, McLoughlin Declan M, Miller Christopher C J
Department of Biochemistry and Molecular Biotechnology Programme, Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR.
J Biol Chem. 2008 Dec 12;283(50):34728-37. doi: 10.1074/jbc.M801874200. Epub 2008 Oct 15.
FE65 is an adaptor protein that binds to and forms a transcriptionally active complex with the gamma-secretase-derived amyloid precursor protein (APP) intracellular domain. The regulatory mechanisms of FE65-APP-mediated transcription are still not clear. In this report, we demonstrate that Dexras1, a Ras family small G protein, binds to FE65 PTB2 domain and potently suppresses the FE65-APP-mediated transcription. The suppression is not via competition for binding of FE65 between Dexras1 and APP because the two proteins can simultaneously bind to the FE65 PTB2 domain. Phosphorylation of FE65 tyrosine 547 within the PTB2 domain has been shown to enhance FE65-APP-mediated transcription but not to influence binding to APP. Here we find that this phosphorylation event reduces the binding between Dexras1 and FE65. We also demonstrate that Dexras1 inhibits the FE65-APP-mediated transcription of glycogen synthase kinase 3beta (GSK3 beta). Moreover, small interfering RNA knockdown of Dexras1 enhances GSK3 beta expression and increases phosphorylation of Tau, a GSK3 beta substrate. Thus, Dexras1 functions as a suppressor of FE65-APP-mediated transcription, and FE65 tyrosine 547 phosphorylation enhances FE65-APP-mediated transcription, at least in part, by modulating the interaction between FE65 and Dexras1. These findings reveal a novel regulatory mechanism for FE65-APP-mediated signaling.
FE65是一种衔接蛋白，它与γ-分泌酶衍生的淀粉样前体蛋白（APP）细胞内结构域结合并形成转录活性复合物。FE65-APP介导的转录调控机制仍不清楚。在本报告中，我们证明Dexras1（一种Ras家族小G蛋白）与FE65的PTB2结构域结合，并强烈抑制FE65-APP介导的转录。这种抑制不是通过Dexras1和APP竞争与FE65的结合，因为这两种蛋白可以同时结合到FE65的PTB2结构域。已表明PTB2结构域内FE65酪氨酸547的磷酸化可增强FE65-APP介导的转录，但不影响与APP的结合。在这里我们发现，这种磷酸化事件会减少Dexras1与FE65之间的结合。我们还证明Dexras1抑制FE65-APP介导的糖原合酶激酶3β（GSK3β）转录。此外，通过小干扰RNA敲低Dexras1可增强GSK3β的表达并增加GSK3β底物Tau的磷酸化。因此，Dexras1作为FE65-APP介导转录的抑制剂发挥作用，而FE65酪氨酸547的磷酸化至少部分地通过调节FE65与Dexras1之间的相互作用来增强FE65-APP介导的转录。这些发现揭示了FE65-APP介导信号传导的一种新的调控机制。
