Dexras1 Interacts with FE65 to Regulate FE65-Amyloid Precursor Protein-dependent Transcription

Abstract

FE65 is an adaptor protein that binds to and forms a transcriptionally active complex with the ␥-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-APPmediated 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 3␤ (GSK3␤). Moreover, small interfering RNA knockdown of Dexras1 enhances GSK3␤ expression and increases phosphorylation of Tau, a GSK3␤ 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 is an adaptor protein with multiple protein-protein interaction domains including a WW domain and two C-terminal PTB domains (1). It is believed that FE65 functions as a "scaffold" protein to recruit various binding partners together to form a functional complex. In fact, FE65 has been shown to interact with a number of proteins. For example, transcription factors CP2 and Tip60 interact with the FE65 PTB1 (2, 3), c-Abl tyrosine kinase and Mena are FE65 WW domain binding partners (4, 5) and the nucleosome assembly factor SET binds FE65 (6). Of great interest, the Alzheimer disease amyloid precursor protein (APP) 2 has been shown to interact with the FE65 PTB2 domain (7-10).APP is a ubiquitously expressed type I integral transmembrane protein with a large ectodomain and a short intracellular domain (11,12). The functions of APP are not properly understood. However, APP is known to be processed first by either ␣-or ␤-secretase and then by ␥-secretase. Cleavage of APP by ␤-and ␥-secretases results in the generation of the 4-kDa ␤-amyloid peptide (A␤). Aggregation of A␤ to form neuritic plaques in brains is a pathological hallmark of Alzheimer disease (for reviews, see Refs. 1 and 13). FE65 has been shown to modulate the production of A␤ (14 -16). In addition to A␤ generation, cleavage of the APP by ␥-secretase releases the APP intracellular domain (AICD). Importantly, AICD has been shown to translocate to the nucleus as a complex with FE65 and the FE65⅐AICD complex strongly stimulates transcription of a GAL4-dependent reporter system (3,(17)(18)(19)(20). However, the control mechanism(s) of FE65-AICD nuclear transcription is currently unclear.Nuclear trans...

Fe65 matters: New light on an old molecule

“…Phosphorylation of Thr-668 of APP has been shown to impair Fe65 binding, suggesting a possible ''molecular switch'' mechanism to regulate the Fe65-APP interaction (10). Recently, another ligand of Fe65 PTB2 domain, the small G-protein Dexras1, has been shown to bind Fe65, in a noncompetitive way with APP, and this binding is reduced by the phosphorylation of Y547 within the Fe65 PTB2 (11). Differently, the N-terminal PTB domain of Fe65 (PTB1) binds several proteins, such as the transcription factor CP2/LSF/LBP1 (12), the histone acetyltransferase Tip60 (13), and the lipoprotein receptors (14).…”

AICD Nuclear Signaling and Its Possible Contribution to Alzheimers Disease

“…AFT complexes have been localized at endogenous KAI1 promoter sites by fluorescence in situ hybridization and SET-AFT (SAFT) complexes were shown to bind the KAI1 promoter in two-step chromatin immunoprecipitation experiments [55,63]. Likewise, the AICD-regulated expression of GSK3 has been replicated [54,64]. A series of experiments has focused on neprilysin (NEP) as it is a major enzyme degrading A .…”

“…In addition to these stimulatory interactions, proteins that inhibit AICD-mediated transcription have also been described. The Ras family member Dexras1 was shown to bind to the Fe65 PTB2 domain simultaneously with APP and to suppress Fe65-APP mediated transcription [64]. This suppression can be reversed by phosphorylation of Y547 in the PTB2 domain which results in reduced Dexras1 binding and increased APP-mediated transcription.…”

<i>Rasd1</i> is an estrogen-responsive immediate early gene and modulates expression of late genes in rat anterior pituitary cells

“…However, whether a change in CRE-containing promoter activity or a combination of changes in CRE, AP-1 and SRE promoter activities shown to be accompanied by Rasd1 knockdown is responsible for the changes in mRNA expression of the estrogen-responsive late genes such as Pim3 and Fosl1 genes is unclear. Rasd1 was recently shown to have a novel function of interacting with other proteins such as FE65-amyloid precursor protein [36] and the transcription factor Ear2 [37] to regulate gene expression. Therefore, it is likely that…”