Interaction of Cytosolic Adaptor Proteins with Neuronal Apolipoprotein E Receptors and the Amyloid Precursor Protein

Abstract

Apolipoprotein E, ␣ 2 -macroglobulin, and amyloid precursor protein (APP) are involved in the development of Alzheimer's disease. All three proteins are ligands for the low density lipoprotein (LDL) receptor-related protein (LRP), an abundant neuronal surface receptor that has also been genetically linked to Alzheimer's disease. The cytoplasmic tails of LRP and other members of the LDL receptor gene family contain NPxY motifs that are required for receptor endocytosis. To investigate whether these receptors may have functions that go beyond ligand internalization, e.g. possible roles in cellular signaling, we searched for proteins that might interact with the cytoplasmic tails of the receptors. A family of adaptor proteins containing protein interaction domains that can interact with NPxY motifs has previously been described. Using yeast 2-hybrid and protein coprecipitation approaches in vitro, we show that the neuronal adaptor proteins FE65 and mammalian Disabled bind to the cytoplasmic tails of LRP, LDL receptor, and APP, where they can potentially serve as molecular scaffolds for the assembly of cytosolic multiprotein complexes. FE65 contains two distinct protein interaction domains that interact with LRP and APP, respectively, raising the possibility that LRP can modulate the intracellular trafficking of APP. Tyrosinephosphorylated mammalian Disabled can recruit nonreceptor tyrosine kinases, such as src and abl, to the cytoplasmic tails of the receptors to which it binds, suggesting a molecular pathway by which receptor/ligand interaction on the cell surface could generate an intracellular signal.

Apolipoprotein E and Apolipoprotein E Receptors: Normal Biology and Roles in Alzheimer Disease

“…However, they harbor a variety of short conserved sequence stretches, such as the tetra-amino acid NPxY motif, which serve as docking sites for a wide array of cytoplasmic adaptor and scaffolding proteins (Trommsdorff et al 1998;Gotthardt et al 2000;Beffert et al 2005;Hoe et al 2006a;Hoe et al 2006b). The receptors can also interact as coreceptors through their extracellular domains with other types of signaling proteins and modules, and thereby modulate their intrinsic activity (Boucher et al 2002;Loukinova et al 2002;Huang et al 2003;Lillis et al 2008;Zurhove et al 2008), including that of the N-methyl-D-aspartate (NMDA) receptor Beffert et al 2005;Hoe et al 2006b).…”

“…Both receptors bind the large homo-oligomeric signaling protein Reelin with high affinity (D'Arcangelo et al 1999;Hiesberger et al 1999), resulting in their clustering at the plasma membrane (Strasser et al 2004). The simultaneous interaction of the adapter protein Disabled 1 (Dab1) with NPxY motifs in their intracellular domains (ICDs) (Trommsdorff et al 1998;Stolt et al 2005) results in the progressive recruitment and transphosphorylation of Src family tyrosine kinases (SFKs) Arnaud et al 2003;Bock and Herz 2003). This in turn initiates a kinase casade inside the neuron, starting with the activation of phosphoinositide-3-kinase (PI3K), which subsequently activates protein kinase B (also known as Akt), and ending with the inhibition of glycogen synthase 3b (GSK3b) , one of the primary kinases that phosphorylate the microtubule stabilizing protein tau on the same sites that are typically abnormally phosphorylated in the neurofibrillary tangles in the AD-afflicted brain.…”

“…Further studies showed that LRP1 also interacts with the neuronal isoform of APP lacking the KPI domain (APP695). Two different phosphotyrosinebinding (PTB) domains within the adaptor protein FE65 bind to the NPxY motifs within APP and LRP1, thus bridging an interaction between these two membrane proteins intracellularly (Trommsdorff et al 1998;Kinoshita et al 2001;Pietrzik et al 2004). Because of the rapid endocytosis rate of LRP1 compared with that of APP (Cam et al 2005), the consequence of APP and LRP1 interaction is accelerated APP endocytic trafficking and processing to Ab (Ulery et al 2000;Zerbinatti et al 2004;Cam et al 2005;Zerbinatti et al 2006).…”

Restoration of positioning control following Disabled-2 expression in ovarian and breast tumor cells

“…Mice that are de®cient in both the apolipoprotein E receptor 2 (apoER2) and VLDL receptor have an indistinguishable phenotype from reeler and Dab1 defective mice (Trommsdor et al, 1999). Moreover, Dab1 has been shown to associate with the cytoplasmic tail of these and other receptors, including the amyloid precursor protein and other members of the LDL receptor gene family (Rice et al, 1998;Trommsdor et al, 1998;Howell et al, 1999). Thus, Dab1 has been proposed to interact with cell surface receptor glycoproteins to mediate the intracellular signal of the ECM protein reelin in determining the positioning of brain cells (Go net, 1997;Rice et al, 1998;Trommsdorf et al, 1999;Howell et al, 1999).…”

A missed exit: Reelin sets in motion Dab1 polyubiquitination to put the break on neuronal migration: Figure 1.

“…The binding of Reelin to its receptors induces the tyrosine phosphorylation of the cytoplasmic adaptor protein Dab1, which interacts with the conserved motif NPxY in the cytoplasmic tails of VLDLR and ApoER2 (Trommsdorff et al 1998;Howell et al 1999).…”