Apolipoprotein E Receptors Are Required for Reelin-induced Proteasomal Degradation of the Neuronal Adaptor Protein Disabled-1

Abstract

Dab1 consists of an aminoterminal phosphotyrosine binding domain followed by a stretch of tyrosyl residues and a large carboxyl-terminal domain. At least two of the tyrosine residues are phosphorylated in vivo by the Src family kinase Fyn (2, 3) in response to Reelin. Tyrosine phosphorylation of Dab1 at these residues is essential for the transduction of the Reelin signal (4) and requires binding of Reelin to its receptors, apolipoprotein E receptor 2 (apoER2) and VLDL receptor, two members of the low density lipoprotein (LDL) receptor gene family (reviewed in Ref. 5). Tyrosinephosphorylated Dab1 triggers the activation of class I phosphatidylinositol 3 (PI3)-kinase (6, 7), which has been shown to be necessary for the formation of a normal cortical plate (8).The conserved phosphotyrosine binding domain mediates the interaction of Dab1 with unphosphorylated NPXY tetraamino acid sequences in the cytosolic domains of transmembrane receptors, including members of the LDL receptor family (9, 10), and with phosphoinositides at the inner leaflet of the plasma membrane (10 -12). The function of the carboxyl-terminal sequence is less well defined. It is not required for the tyrosine phosphorylation of Dab1 or the activation of Src family kinases and PI3-kinase by Reelin (7). Mice expressing a carboxyl-terminal truncated Dab1 protein (p45) display normal brain development (13), although haploinsufficiency of the p45 allele causes a restricted phenotype characterized by positioning defects of late-born cortical plate neurons and hippocampal CA1 pyramidal cells. Interestingly, a serine residue near the carboxyl terminus of Dab1 is phosphorylated by Cdk5 in vivo (14), a proline-directed serine/threonine kinase, which is also essential for the correct positioning of postmitotic neurons (reviewed in Ref. 15), but the functional significance of this biochemical cross-talk remains unclear.How the Reelin signal in migrating neurons is terminated is not known. The Reelin-induced tyrosine phosphorylation of Dab1 declines only after prolonged incubation periods (16). Treatment of neurons with sodium orthovanadate did not significantly increase Dab1 tyrosine phosphorylation, suggesting that phosphotyrosine phosphatases do not play a major role in limiting the response to Reelin (16). Up-regulation of Dab1 protein levels is a common feature in mice carrying dysfunctional mutations of genes that encode key Reelin signaling molecules, namely Reelin itself (17), its receptors apoER2 and VLDLR (18), and its kinase Fyn (2, 3), as well as in mice that * This work was supported in part by National Institutes of Health Grants HL20948, HL63762, and NS43408, the Alzheimer's Association, the Wolfgang-Paul Award of the Humboldt Foundation, the Perot Family Foundation (to J. H.), and an Emmy Noether fellowship of the Deutsche Forschungsgemeinschaft (to P. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Secti...

Age-related accumulation of Reelin in amyloid-like deposits

“…This hypothesis is supported by studies in transgenic animals showing ectopic accumulations of Dab1 in Reelin-, ApoER2-, and VLDLR-deficient mice (Rice and Curran, 2001;Trommsdorff et al, 1999). In-vitro studies showed that internalization of Reelin-ApoER2 complexes is required for endocytosis and proteasomal degradation of Dab1 (Bock et al, 2004;D'Arcangelo et al, 1999). A direct role of Reelin in APP processing is demonstrated by the increased co-immunoprecipitation of Dab1 with ApoER2 and APP and decreased Aβ production (Hoe et al, 2006a), indicating that reduced Reelin levels might favor the production of neurotoxic Aβ species.…”

“…Transduction of the signal involves the interaction of the adapter protein Dab1 with the intracellular NPxY motiv of these receptors, resulting in tyrosine phosphorylation of Dab1, activation of Src family of non-receptor tyrosine kinases, and triggering a downstream cytosolic kinase cascade beginning with the activation of phosphatidylinositol-3-kinase (PI3K) and ending with the inhibition of glycogen synthase kinase 3β (GSK3β; for recent review, see Herz and Cheng, 2006). The signal is terminated with Reelin targeted to the lysosome and Dab1 degraded by the proteasome (Arnaud et al, 2003;Bock et al, 2004;Morimura et al, 2005). In the adult brain, Reelin expression is maintained by GABAergic interneurons and glutamatergic pyramidal neurons in layer II of the entorhinal cortex (Alcantara et al, 1998;Miettinen et al, 2005;Pesold et al, 1998;Ramos-Moreno et al, 2006) and the same signalling cascade is used in adult synapses to modulate neuronal function and synaptic plasticity by regulating glutamate receptor activity through the phosphorylation of intracellular tyrosine residues (Beffert et al, , 2006Chen et al, 2005;Weeber et al, 2002).…”

Both the phosphoinositide and receptor binding activities of Dab1 are required for Reelin-stimulated Dab1 tyrosine phosphorylation

“…3A). Because neuron cultures contain low levels of Reelin [25], and Dab1 turnover is increased following Reelin-stimulated tyrosine phosphorylation [26,27], increased levels of K45Q and S114T are consistent with decreased Reelin-dependent phosphorylation. Following acute Reelin stimulation, endogenous Dab1 in all cultures and wildtype, S19A and K45Q mutant Dab1-EGFP were tyrosine phosphorylated at increased levels (Fig.…”

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

“…Several recent advances provide further understanding of the mechanism of this posttranscriptional down-regulation of Dab1. Arnaud et al (2003a) and Bock et al (2004) previously showed in primary neuronal cultures that Dab1 is down-regulated through polyubiquitination and targeting to the proteasome in the presence of Reelin, and that this modification requires tyrosine phosphorylation of Dab1. Moreover, inhibition of Dab1 tyrosine phosphorylation and inhibition of SFK activation blocks Dab1 down-regulation (Arnaud et al 2003b;Bock et al 2004;Kuo et al 2005).…”

“…Arnaud et al (2003a) and Bock et al (2004) previously showed in primary neuronal cultures that Dab1 is down-regulated through polyubiquitination and targeting to the proteasome in the presence of Reelin, and that this modification requires tyrosine phosphorylation of Dab1. Moreover, inhibition of Dab1 tyrosine phosphorylation and inhibition of SFK activation blocks Dab1 down-regulation (Arnaud et al 2003b;Bock et al 2004;Kuo et al 2005). Feng et al (2007) identified two critical Dab1 tyrosine phosphorylation sites (primary Tyr198, and also Tyr185), both at YQxI sequences, essential for the Dab1 degradation in response to Reelin, in an embryonic cortical neuron culture system.…”