Growth Factor Receptor-bound Protein 2 Interaction with the Tyrosine-phosphorylated Tail of Amyloid β Precursor Protein Is Mediated by Its Src Homology 2 Domain

The sequential processing of the familial disease gene product amyloid beta precursor protein (AbetaPP) by beta- and gamma-secretases generates amyloid beta, which is considered to be the pathogenic factor of Alzheimer's disease, and the AID peptide (AbetaPP intracellular domain). The AID peptide acts as a positive regulator of apoptosis and modulates transcription and calcium release. To gain clues about the molecular mechanisms regulating the function of AbetaPP and AID, proteins interacting with the AID region of AbetaPP have been isolated using the yeast two-hybrid system. Recent evidence indicates that AbetaPP undergoes post-translational modification events in the AID region and that phosphorylation might regulate its affinity for interacting proteins. To test this possibility and to uncover AbetaPP-binding partners whose interaction depends on AbetaPP phosphorylation, we used a proteomic approach. Here we describe a protein, growth factor receptor-bound protein 2 (Grb2), that specifically binds AbetaPP, phosphorylated in Tyr(682). Furthermore, we show that this interaction is direct and that Grb2 binds to phospho-AbetaPP via its Src homology 2 region. Together with the evidence that Grb2 is in complex with AbetaPP in human brains and that these complexes are augmented in brains from Alzheimer's cases, our data indicate that Grb2 may mediate some biological and possibly pathological AbetaPP-AID function

CD74 interacts with APP and suppresses the production of Aβ

<p>Abstract</p> <p>Background</p> <p>Alzheimer disease (AD) is characterized by senile plaques, which are mainly composed of β amyloid (Aβ) peptides. Aβ is cleaved off from amyloid precursor protein (APP) with consecutive proteolytic processing by β-secretase and γ-secretase.</p> <p>Results</p> <p>Here, we show that CD74, the invariant chain of class II major histocompatibility complex, interacts with APP and serves as a negative regulator of Aβ. CD74 resembles other APP interacters such as BRI2 and BRI3, since all of them reduce the level of Aβ. However, unlike BRIs, CD74 does not reduce the secretion of sAPPα or sAPPβ. Interestingly, in HeLa cells, over expression of CD74 steers APP, but not Notch, to large vacuoles created by CD74.</p> <p>Conclusion</p> <p>Taken together, we propose that CD74 inhibits Aβ production by interacting with and derailing normal trafficking of APP.</p

The interactome of the amyloid β precursor protein family members is shaped by phosphorylation of their intracellular domains

<p>Abstract</p> <p>Background</p> <p>Brain tissue from patients with Alzheimer's disease has shown an increase of phosphorylation of Tyr-682, located on the conserved Y682ENPTY motif, and Thr-668 residues, both in the intracellular domain (AID) of amyloid β precursor protein (APP), although the role of these two residues is not yet known.</p> <p>Results</p> <p>Here, we report that the phosphorylation status of Tyr-682, and in some cases Thr-668, shapes the APP interactome. It creates a docking site for SH2-domain containing proteins, such as ShcA, ShcB, ShcC, Grb7, Grb2, as well as adapter proteins, such as Crk and Nck, that regulate important biological processes, cytosolic tyrosine kinases, such as Abl, Lyn and Src, which regulate signal transduction pathways, and enzymes that control phosphatidylinositols levels and signaling, such as PLC-γ. At the same time, it either reduces (like for JIP1, NUMB, NUMBL and ARH) or abolishes (like for Fe65, Fe65L1 and Fe65L2) binding of other APP interactors. Phosphorylation of Thr-668, unlike Tyr-682, does not seem to affect APP's ability to interact with the various proteins, with Pin1 and X11 being the exclusions. We also found that there are some differences between the interactions to AID and to ALID1 and ALID2, its two homologues.</p> <p>Conclusion</p> <p>Our data indicates that APP can regulate diverse cellular processes and that, vice versa, a network of signaling events can impact APP processing. Our results also suggest that phosphorylation of the APP Intracellular Domain will dramatically shape the APP interactome and, consequently, will regulate APP processing, APP transport and APP/AID-mediated functions.</p

Hyperphosphorylation of JNK-interacting Protein 1, a Protein Associated with Alzheimer Disease

The c-Jun N-terminal kinase (JNK) group of mitogen-activated protein (MAP) kinases are activated by pleiotropic signals including environmental stresses, growth factors, and hormones. JNK-interacting protein 1 (JIP1) is a scaffold protein that assembles and facilitates the activation of the mixed lineage kinase-dependent JNK module and also establishes an interaction with beta-amyloid precursor protein that has been partially characterized. Here we show that, similarly to other proteins involved in various neurological diseases, JIP1 becomes hyperphosphorylated following activation of stress-activated and MAP kinases. By immobilized metal affinity chromatography and a combined microcapillary LC/MALDI-TOF/ESI-ion trap mass spectrometry approach, we identified 35 sites of mitotic phosphorylation within JIP1, among which eight were present within (Ser/Thr)-Pro sequence. This motif is modified by various kinases in aggregates of the microtubule-associated protein tau, which generates typical intraneuronal lesions occurring in Alzheimer disease. Most of the post-translational modifications found were located within the JNK, MAP kinase kinase, and RAC-alpha Ser/Thr protein kinase binding regions; no modifications occurred in protein Src homology 3 and phosphotyrosine interaction domains, which are essential for binding to kinesin, beta-amyloid precursor protein, and MAP kinase kinase kinase. Protein phosphorylation is known to affect stability and protein-protein interactions. Thus, the findings that JIP1 is extensively phosphorylated after activation of stress-activated and MAP kinases indicate that these signaling pathways might modulate JIP1 signaling by regulating its stability and association with some, but not all, interacting proteins

Autosomal Recessive Hypercholesterolemia Protein Interacts with and Regulates the Cell Surface Level of Alzheimer's Amyloid β Precursor Protein *

The familial Alzheimer's disease gene product amyloid beta protein precursor (A beta PP) is sequentially processed by beta- and gamma-secretases to generate the A beta peptide. Although much is known about the biochemical pathway leading to A beta formation, because extracellular aggregates of A beta peptides are considered the cause of Alzheimer's disease, the biological role of A beta PP processing is only recently being investigated. Cleavage of A beta PP by gamma-secretase releases, together with A beta, a COOH-terminal A beta PP intracellular domain, termed AID. Hoping to gain clues about proteins that regulates A beta PP processing and function, we used the yeast two-hybrid system to identify proteins that interact with the AID region of A beta PP. One of the interactors isolated is the autosomal recessive hypercholesterolemia (ARH) adapter protein. This molecular interaction is confirmed in vitro and in vivo by fluorescence resonance energy transfer and in cell lysates. Moreover, we show that reduction of ARH expression by RNA interference results in increased levels of cell membrane A beta PP. These data assert a physiological role for ARH in A beta PP internalization, transport, and/or processing

Alternative, Non-secretase Processing of Alzheimer's β-Amyloid Precursor Protein during Apoptosis by Caspase-6 and -8

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Although the pathogenesis of AD is unknown, it is widely accepted that AD is caused by extracellular accumulation of a neurotoxic peptide, known as Abeta. Mutations in the beta-amyloid precursor protein (APP), from which Abeta arises by proteolysis, are associated with some forms of familial AD (FAD) and result in increased Abeta production. Two other FAD genes, presenilin-1 and -2, have also been shown to regulate Abeta production; however, studies examining the biological role of these FAD genes suggest an alternative theory for the pathogenesis of AD. In fact, all three genes have been shown to regulate programmed cell death, hinting at the possibility that dysregulation of apoptosis plays a primary role in causing neuronal loss in AD. In an attempt to reconcile these two hypotheses, we investigated APP processing during apoptosis and found that APP is processed by the cell death proteases caspase-6 and -8. APP is cleaved by caspases in the intracellular portion of the protein, in a site distinct from those processed by secretases. Moreover, it represents a general effect of apoptosis, because it occurs during cell death induced by several stimuli both in T cells and in neuronal cells

Jun NH2-terminal Kinase (JNK) Interacting Protein 1 (JIP1) Binds the Cytoplasmic Domain of the Alzheimer's β-Amyloid Precursor Protein (APP)

The familial Alzheimer's disease gene product amyloid beta precursor protein (APP) is sequentially processed by beta- and gamma-secretases to generate the Abeta peptide. The biochemical pathway leading to Abeta formation has been extensively studied since extracellular aggregates of Abeta peptides are considered the culprit of Alzheimer's disease. Aside from its pathological relevance, the biological role of APP processing is unknown. Cleavage of APP by gamma-secretase releases, together with Abeta, a COOH-terminal APP intracellular domain, termed AID. This peptide has recently been identified in brain tissue of normal control and patients with sporadic Alzheimer's disease. We have previously shown that AID acts as a positive regulator of apoptosis. Nevertheless, the molecular mechanism by which AID regulates this process remains unknown. Hoping to gain clues about the function of APP, we used the yeast two-hybrid system to identify interaction between the AID region of APP and JNK-interacting protein-1 (JIP1). This molecular interaction is confirmed in vitro, in vivo by fluorescence resonance energy transfer (FRET), and in mouse brain lysates. These data provide a link between APP and its processing by gamma-secretase, and stress kinase signaling pathways. These pathways are known regulators of apoptosis and may be involved in the pathogenesis of Alzheimer's disease

LTP and memory impairment caused by extracellular A\u3b2 and Tau oligomers is APP-dependent

The concurrent application of subtoxic doses of soluble oligomeric forms of human amyloid-beta (oA\u3b2) and Tau (oTau) proteins impairs memory and its electrophysiological surrogate long-term potentiation (LTP), effects that may be mediated by intra-neuronal oligomers uptake. Intrigued by these findings, we investigated whether oA\u3b2 and oTau share a common mechanism when they impair memory and LTP in mice. We found that as already shown for oA\u3b2, also oTau can bind to amyloid precursor protein (APP). Moreover, efficient intra-neuronal uptake of oA\u3b2 and oTau requires expression of APP. Finally, the toxic effect of both extracellular oA\u3b2 and oTau on memory and LTP is dependent upon APP since APP-KO mice were resistant to oA\u3b2- and oTau-induced defects in spatial/associative memory and LTP. Thus, APP might serve as a common therapeutic target against Alzheimer's Disease (AD) and a host of other neurodegenerative diseases characterized by abnormal levels of A\u3b2 and/or Tau