Fibulin‐1 binds the amino‐terminal head of β‐amyloid precursor protein and modulates its physiological function

Abstract

Genetic studies have implicated amyloid precursor protein (APP) in the pathogenesis of Alzheimer's disease. While accumulating lines of evidence indicate that APP has various functions in cells, little is known about the proteins that modulate its biological activity. Toward this end, we employed a two-hybrid system to identify potential interacting factors. We now report that ®bulin-1, which contains repetitive Ca 21 -binding EGF-like elements, binds to APP at its aminoterminal growth factor-like domain, the region that is responsible for its neurotrophic activities. Fibulin-1 expression in the brain is con®ned to neurons, and is not expressed signi®cantly by astrocytes or microglia. Direct binding of ®bulin-1 to the secreted form of APP (sAPP) was demonstrated with a pull-down assay using fragments of both ®bulin-1 fused with glutathione-S transferase and sAPP, produced in bacteria and yeast, respectively. The ®bulin-1/sAPP heteromer was shown to form in the conditioned medium of transfected COS-7 cells. Furthermore, ®bulin-1 blocks sAPP-mediated proliferation of primary cultured rat neural stem cells. These results suggest that ®bulin-1 may play a signi®cant role in modulating the neurotrophic activities of APP. Keywords: Alzheimer's disease, amyloid precursor protein, binding protein, ®bulin-1, neural stem cells, proliferation.Amyloid precursor protein (APP) is an integral membrane glycoprotein expressed in the brain and CNS. Genetic studies implicate APP in the pathogenesis of Alzheimer's disease (AD) via b-amyloid (Ab), which is derived from APP. The nonamyloidogenic metabolism of APP involves an enzymatic cleavage within the Ab sequence, releasing the secreted form of APP (sAPP) (reviewed in Selkoe 1994). A possible role for APP and sAPP in the brain is suggested by a number of observations. In neurons, APP is present at synaptic sites and in vesicular structures within the cell body, axon and dendrites (Koo et al. 1990), and while APP-de®cient mice show decreased locomotor activity and learning impairment (Zheng et al. 1995), overexpression of APP in transgenic mice results in increased numbers of presynaptic terminals (Mucke et al. 1994). In addition, intraventricular administration of sAPP protects hippocampal neurons against ischemic injury (Smith et al. 1994) and enhances memory performance (Roch et al. 1994). Also, in vitro studies show that sAPP enhances neuronal survival, neurite outgrowth, and cell adhesiveness (reviewed in Saitoh and Mook-Jung 1996). Finally, sAPP has been shown to enhance proliferation of neural stem cells (Ohsawa et al. 1999) and thyroid epithelial cells (Pietrzik et al. 1998). In total, these ®ndings suggest that APP, and in particular sAPP, has neurotrophic/growth factor-like functions.Proteins of the APP family share a highly conserved region known as C in the cytoplasmic tail, and two highly conserved regions known as E1 and E2 in the extracellular region (Rosen et al. 1989). Secreted APP includes E1 and E2 regions and has a multidomain structure that may facilita...

Shotgun proteomics implicates extracellular matrix proteins and protease systems in neuronal development induced by astrocyte cholinergic stimulation

“…4). Several of these proteins are involved in neuritogenesis including prosaposin (O'Brien et al 1994), fibronectin (Gundersen 1987;Matthiessen et al 1989), fibulin-1 (Ohsawa et al 2001), thrombospondin 1 (Adams 1997), PAI-1 (Soeda et al 2006), galectin-3 (Pesheva et al 1998), monocyte chemoattractant protein-1 (Bianchi et al 2005), neural cell adhesion molecule 1 (Ronn et al 1998), and Plau (Pittman et al 1989). …”

Interaction of amyloid precursor protein with contactins and NgCAM in the retinotectal system

“…Binding has been reported for extracellular matrix components, including heparan sulfate (Multhaup, 1994;Small et al, 1994), collagen (Beher et al, 1996) and fibulin 1 (Ohsawa et al, 2001); zinc and copper ions (Turner et al, 2003); and the lipoprotein receptors, scavenger receptor A (SantiagoGarcia et al, 2001) and LRP (Kounnas et al, 1995). More recently identified extracellular proteins that can interact with APP include F-spondin (also known as spondin 1) (Ho and Sudhof, 2004;Hoe et al, 2005), Drosophila FASII (Ashley et al, 2005), BRI2 (ITM2B) (Fotinopoulou et al, 2005;Matsuda et al, 2005), APLP1, APLP2 and APP itself (Soba et al, 2005), Notch family members (Fassa et al, 2005;Fischer et al, 2005;Oh et al, 2005;Chen et al, 2006), LRRTM3 (Majercak et al, 2006) and NgR (RTN4R) (Park et al, 2006).…”

Tol2 gene trap integrations in the zebrafish amyloid precursor protein genes appa and aplp2 reveal accumulation of secreted APP at the embryonic veins

“…Release of the intracellular domain of APP by the γ-secretase pathway is stimulated by binding of the extracellular domain to the GPI-linked ligand TAG1 (Ma et al, 2008), similar to the processing of other type-1 transmembrane proteins such as Notch. Fibulin-1, a member of the fibulin family of secreted glycoproteins that are components of basement membrane, has been shown to bind APP's amino-terminal growth factor-like domain; this interaction contributes to the neurotrophic activities of APP (Ohsawa et al, 2001). In addition, Fibulin-1 and fibulin-5 have been shown to suppress angiogenesis in tumors derived from mice injected with HT1080 cancer cells (Xie et al, 2008).…”