Syndecan 3 Intramembrane Proteolysis Is Presenilin/γ-Secretase-dependent and Modulates Cytosolic Signaling

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Neurotrophins are trophic factors that regulate important neuronal functions. They bind two unrelated receptors, the Trk family of receptor-tyrosine kinases and the p75 neurotrophin receptor (p75). p75 was recently identified as a new substrate for ␥-secretase-mediated intramembrane proteolysis, generating a p75-derived intracellular domain (p75-ICD) with signaling capabilities. Using PC12 cells as a model, we studied how neurotrophins activate p75 processing and where these events occur in the cell. We demonstrate that activation of the TrkA receptor upon binding of nerve growth factor (NGF) regulates the metalloprotease-mediated shedding of p75 leaving a membranebound p75 C-terminal fragment (p75-CTF). Using subcellular fractionation to isolate a highly purified endosomal fraction, we demonstrate that p75-CTF ends up in endosomes where ␥-secretase-mediated p75-CTF cleavage occurs, resulting in the release of a p75-ICD. Moreover, we show similar structural requirements for ␥-secretase processing of p75 and amyloid precursor protein-derived CTFs. Thus, NGF-induced endocytosis regulates both signaling and proteolytic processing of p75.Neurotrophins belong to a small family of neurotrophic factors that include nerve growth factor (NGF), 4 brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3), and neurotrophin-4 (NT4). They regulate different aspects of the developing and adult nervous system by binding to specific members of the Trk family of receptor-tyrosine kinases (TrkA, -B, and -C) or to the p75 neurotrophin receptor (p75). Their involvement includes neuronal migration, cell death, axonal elongation, myelinization, neuronal differentiation, and synaptic plasticity (1-3). p75 is a multifunctional type I transmembrane protein that is structurally related to the tumor necrosis factor receptor superfamily. It binds all neurotrophins, alone or in complex with Trk receptors, but also other ligands such as amyloid peptides and pro-neurotrophins (4, 5). The association of p75 with different receptors shapes the outcome of a signaling event. For example, binding of p75 to TrkA in the presence of NGF promotes neuronal survival, whereas interaction with the Nogo receptor (NgR) in the presence of its ligands, such as Nogo and myelin-associated glycoprotein (MAG), results in growth cone collapse and the inhibition of axonal regeneration (1, 4, 5). In addition, different downstream p75-associated signaling cascades are triggered through the interaction of its cytosolic portion with multiple adaptor proteins (6). Neurotrophin binding to p75 also induces accumulation of p75 in recycling endosomes where it associates with specific p75 downstream signaling effectors (7-9). Hence trafficking of p75 in the cell body or in axons (10, 11) may determine downstream signaling of p75 as previously shown for Trk receptors (12). The regulation of p75 signaling becomes even more complicated with the finding that p75 is subject to a dual processing starting with shedding of the ectodomain and followed by ␥-secretase cleavage. Thi...

Section: Discussionmentioning

confidence: 87%

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confidence: 99%

TrkA Receptor Activation by Nerve Growth Factor Induces Shedding of the p75 Neurotrophin Receptor Followed by Endosomal γ-Secretase-mediated Release of the p75 Intracellular Domain

Urra

Escudero²,

Ramos³

et al. 2007

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“…To demonstrate that Alc secretes an A␤-like peptide by the secondary cleavage of CTF1 by ␥-secretase, we designed the Alc␣⌬E construct, which lacks the sequence between Pro 40 and Met 815 in FLAG-Alc␣1 and mimics CTF1 (Fig. 2A).…”

Section: Secretion Of A␤-like Peptide and Release Of The Intracellulamentioning

confidence: 99%

“…Supporting this, we demonstrated here that Alc is a novel substrate of ␥-secretase. Recent publications have reported that a number of membrane proteins can act as ␥-secretase substrates (31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41). Thus, it is now clear that there are a variety of ␥-secretase substrates and that ␥-secretase is not specific for APP and Notch (42).…”

Section: Stabilization and Localization Of Alcicd By Interacting Withmentioning

confidence: 99%

Coordinated Metabolism of Alcadein and Amyloid β-Protein Precursor Regulates FE65-dependent Gene Transactivation

Araki

Miyagi

Kato

et al. 2004

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The Alcadeins (Alcs)/calsyntenins and the amyloid ␤-protein precursor (APP) associate with each other in the brain by binding via their cytoplasmic domains to X11L (the X11-like protein). We previously reported that the formation of this APP-X11L-Alc tripartite complex suppresses the metabolic cleavages of APP. We show here that the metabolism of the Alcs markedly resembles that of APP. The Alcs are subjected to a primary cleavage event that releases their extracellular domain. Alcs then undergo a secondary presenilin-dependent ␥-cleavage that leads to the secretion of the amyloid ␤-protein-like peptide and the liberation of an intracellular domain fragment (AlcICD). However, when Alc is in the tripartite complex, it escapes from these cleavages, as does APP. We also found that AlcICD suppressed the FE65-dependent gene transactivation activity of the APP intracellular domain fragment, probably because AlcICD competes with the APP intracellular domain fragment for binding to FE65. We propose that the Alcs and APP are coordinately metabolized in neurons and that their cleaved cytoplasmic fragments are reciprocally involved in the regulation of FE65-dependent gene transactivation. Any imbalance in the metabolism of Alcs and APP may influence the FE65-dependent gene transactivation, which together with increased secretion of amyloid ␤-protein may contribute to neural disorders.The deposition and accumulation of amyloid ␤-protein (A␤) 1 in the human brain are hallmarks of Alzheimer's disease (AD)(1). Amyloid ␤-protein precursor (APP) is the precursor of A␤. It has a receptor-like transmembrane protein structure that consists of an extracellular domain, a transmembrane domain, and a short carboxyl-terminal cytoplasmic domain (2). The cytoplasmic domain of APP controls its metabolism and various physiological functions by interacting with cytoplasmic adaptor proteins (3-8). One of these adaptor proteins is X11L (the X11-like protein), which associates with the cytoplasmic domain of APP and stabilizes APP metabolism (5, 9). During our previous research that aimed to reveal the molecular mechanism by which X11L regulates APP metabolism, we found that the Alcadeins, which form cadherin-related membrane protein family, are X11-and X11L-binding proteins (9). These proteins are also known as calsyntenins, which were originally isolated as postsynaptic Ca 2ϩ -binding membrane proteins, but whose functions were not identified (10, 11). The Alcadeins (Alcs) consist of two Alc␣ isoforms (Alc␣1 and Alc␣2) and Alc␤ and Alc␥, all of which are type I transmembrane proteins and contain a conserved X11L-binding motif in their single cytoplasmic domains, similar to APP (9).Alc does not directly interact with the cytoplasmic domain of APP. Rather, the association between the two molecules is bridged by the phosphotyrosine interaction domain of X11L. This results in the formation of a tripartite complex in the brain (9). The formation of this complex enhances the X11L-mediated stabilization of APP metabolism and suppresses the generation...

“…More recently, this mechanism of secretase proteolysis has been extended to a second tyrosine kinase, the CSF-1 receptor (23) and several adhesion receptors, including CD44 (24), several cadherins (25)(26)(27), nectin-1␣ (28), syndecan 3 (29), and Deleted in Colorectal Cancer (30). In many of these systems, the secretase-liberated ICD fragment is found in the nucleus and is associated with transcriptional activity.…”

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confidence: 99%

Secretase-dependent Tyrosine Phosphorylation of Mdm2 by the ErbB-4 Intracellular Domain Fragment

Arasada

Carpenter

2005

Heregulin activation of the endogenous receptor tyrosine kinase ErbB-4 in ZR-75-1 breast cancer cells provokes tyrosine phosphorylation of Hdm2 in a manner that is sensitive to inhibition of ␣-or ␥-secretase activity, indicating that liberation of the tyrosine kinase intracellular domain (ICD) fragment is required. Similar results are obtained when Erbb-4 is exogenously expressed in 32D cells, which do not otherwise express any ErbB family members. Expression of the ErbB-4 ICD fragment leads to its constitutive association with Mdm2 and tyrosine phosphorylation of Mdm2, a protein that is predominantly localized in the nucleus and that regulates p53 levels. When the ErbB-4 ICD fragment was expressed in H1299 cells, it promoted Hdm2 ubiquitination and increased the levels of p53 and p21, a transcriptional target of p53. In addition, expression of the ICD fragment increased p53 activity toward the p21 promoter in a luciferase reporter assay.ErbB-4 is a receptor tyrosine kinase that is activated by the binding of its cognate ligands, such as heregulin (neuregulin) (1). As with other ErbB receptors, ligand binding provokes homo-and heterodimerization, particularly with ErbB-2, leading to tyrosine kinase activation and the initiation of signal transduction pathways. Although ErbB-4 activation can provoke a mitogenic response, frequently the cellular response is the promotion of cell differentiation. Genetic studies in mice reveal an ErbB-4 requirement for differentiation of the mammary gland in the adult (2-4) and for neural and cardiac development during embryogenesis (5). In cell culture ErbB-4 activation is required for the differentiation of mammary cells (6) and PC12 cells (7). The molecular basis for the capacity of ErbB-4 to influence cell differentiation pathways is not known.ErbB-4 is also novel within this receptor family in regard to its sequential proteolytic processing by ␣-and ␥-secretases. Treatment of cells with heregulin (8) or 12-O-tetradecanoylphorbol-13-acetate (9) initiates a metalloprotease-dependent ectodomain cleavage of ErbB-4 between His-651 and Ser-652 (10), placing this initial cleavage site eight residues prior to the transmembrane domain, which is typical of an ␣-secretase activity. Ectodomain cleavage or ErbB-4 is abrogated in TACE (ADAM17) null cells (11), and recombinant TACE is able to cleave a peptide representing ErbB-4 residues 646 -657 between His-651 and Ser-652 (10). Therefore, it seems likely that tumor necrosis factor alpha converting enzyme (TACE) executes this cleavage in vivo. There are two products of ectodomain cleavage: a 120-kDa ectodomain fragment, which can be recovered in the medium, and a membrane-associated 80-kDa (m80) fragment that begins with Ser-652 and includes the transmembrane and cytoplasmic domains of ErbB-4 (9, 10).The m80 fragment is utilized as a substrate by ␥-secretase activity that cleaves within the transmembrane domain at a site(s) unknown and releases a soluble 80-kDa fragment (s80) into the cytoplasm (12, 13). This s80 (intracellular domain, ICD)...