P3-296 FE65 constitutes the functional link between the LDL receptor-related protein (LRP) and APP

Ectodomain shedding of the amyloid precursor protein (APP) by the two proteases ␣-and ␤-secretase is a key regulatory event in the generation of the Alzheimer disease amyloid ␤ peptide (A␤). At present, little is known about the cellular mechanisms that control APP shedding and A␤ generation. Here, we identified a novel protein, transmembrane protein 59 (TMEM59), as a new modulator of APP shedding. TMEM59 was found to be a ubiquitously expressed, Golgi-localized protein. TMEM59 transfection inhibited complex N-and O-glycosylation of APP in cultured cells. Additionally, TMEM59 induced APP retention in the Golgi and inhibited A␤ generation as well as APP cleavage by ␣-and ␤-secretase cleavage, which occur at the plasma membrane and in the endosomes, respectively. Moreover, TMEM59 inhibited the complex N-glycosylation of the prion protein, suggesting a more general modulation of Golgi glycosylation reactions. Importantly, TMEM59 did not affect the secretion of soluble proteins or the ␣-secretase like shedding of tumor necrosis factor ␣, demonstrating that TMEM59 did not disturb the general Golgi function. The phenotype of TMEM59 transfection on APP glycosylation and shedding was similar to the one observed in cells lacking conserved oligomeric Golgi (COG) proteins COG1 and COG2. Both proteins are required for normal localization and activity of Golgi glycosylation enzymes. In summary, this study shows that TMEM59 expression modulates complex N-and O-glycosylation and suggests that TMEM59 affects APP shedding by reducing access of APP to the cellular compartments, where it is normally cleaved by ␣-and ␤-secretase. Processing of the amyloid precursor protein (APP)3 by two different proteases, called ␣-and ␤-secretase, is a central regulatory event in the generation of the amyloid ␤ peptide (A␤), which has a key role in Alzheimer disease (AD) pathogenesis (1). Both ␣-and ␤-secretase cleave the type I membrane protein APP within its ectodomain close to its transmembrane domain (2). This leads to the secretion of soluble forms of APP (APPs) and is referred to as APP shedding. The ␤-secretase is the aspartyl protease BACE1 and cleaves APP at the N terminus of the A␤ peptide domain, thus catalyzing the first step in A␤ peptide generation (3, 4). After the initial cleavage of APP by BACE1, the remaining C-terminal APP fragment is cleaved by ␥-secretase within its transmembrane domain at the C terminus of the A␤ domain, leading to the secretion of the A␤-peptide (5). In contrast to ␤-secretase, ␣-secretase cleaves within the A␤-sequence of APP, and thereby precludes A␤ peptide generation. Additionally, ␣-but not ␤-secretase cleavage generates a secreted form of APP (APPs␣), which has neurotrophic and neuroprotective properties (6 -8). The ␣-secretase is a member of the ADAM family (A disintegrin and metalloprotease) of proteases (9 -12). At present little is known about how the cell controls access of APP to its secretases and the amount of ␣-and ␤-secretase cleavage (reviewed in Refs. 13 and 14). Recent studies increasingl...

Section: Tmem59 Modulates Maturation and Shedding Of App-tosupporting

confidence: 69%

The Novel Membrane Protein TMEM59 Modulates Complex Glycosylation, Cell Surface Expression, and Secretion of the Amyloid Precursor Protein

Ullrich

Münch

Neumann

et al. 2010

“…Various studies have concluded that Fe65 either inhibits or promotes secretion of APP s␣ (10,12,18). The results of our analysis of AICD production indicate that Fe65 promotes cleavage of APP by ␣-secretase, a conclusion that implies that Fe65 should increase rather than decrease production of APP s␣ .…”

Section: Discussionmentioning

confidence: 49%

“…Furthermore, LRP association with APP, mediated by Fe65, regulates proteolytic processing and AICD generation (10,11). This suggests that Fe65 could stimulate ␥-secretase-mediated liberation of AICD-GV16 by promoting processing of APP by ␣-and/or ␤-secretase, thereby increasing the concentration of substrate for ␥-secretase-mediated cleavage.…”

Section: Fe65 Stimulation Of App Proteolysis Is Dependent On Ptb1-mentioning

confidence: 99%

“…The intracellular interaction between APP and the carboxyl-terminal portion of the low density lipoprotein-related protein 1 (LRP) is mediated by Fe65 via its two PTB domains (10). The LRP interaction with APP, mediated by Fe65, may coordinate numerous aspects of APP proteolytic processing, including APP carboxyl-terminal fragment generation and ␤-amyloid secretion (11).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Fe65 Stimulates Proteolytic Liberation of the β-Amyloid Precursor Protein Intracellular Domain

Wiley

Smith

Hudson

et al. 2007

The ␤-amyloid precursor protein (APP)-binding protein Fe65 is involved in APP nuclear signaling and several steps in APP proteolytic processing. In this study, we show that Fe65 stimulates ␥-secretase-mediated liberation of the APP intracellular domain (AICD). The mechanism of Fe65-mediated stimulation of AICD formation appears to be through enhanced production of the carboxyl-terminal fragment substrates of ␥-secretase and direct stimulation of processing by ␥-secretase. The stimulatory capacity of Fe65 is isoform-dependent, as the non-neuronal and a2 isoforms promote APP processing more effectively than the exon 9 inclusive neuronal form of Fe65. Intriguingly, Fe65 stimulation of AICD production appears to be inversely related to pathogenic ␤-amyloid production as the Fe65 isoforms profoundly stimulate AICD production and simultaneously decrease A␤42 production. Despite the capacity of Fe65 to stimulate ␥-secretase-mediated APP proteolysis, it does not rescue the loss of proteolytic function associated with the presenilin-1 familial Alzheimer disease mutations. These data suggest that Fe65 regulation of APP proteolysis may be integrally associated with its nuclear signaling function, as all antecedent proteolytic steps prior to release of Fe65 from the membrane are fostered by the APP-Fe65 interaction.

“…The production and clearance of amyloid-␤ (A␤), a pathogenic peptide of Alzheimer disease, are also dependent on the LRP1-mediated endocytosis. Thus, amyloid precursor protein (APP), a membrane protein, is intracellularly bridged with LRP1 by FE65 (36,37). APP also binds to LRP1 extracellularly (38).…”

Section: Discussionmentioning

confidence: 99%

Premature Ligand-Receptor Interaction during Biosynthesis Limits the Production of Growth Factor Midkine and Its Receptor LDL Receptor-related Protein 1

Sakamoto¹,

Chen³

et al. 2011

Protein production within the secretory pathway is accomplished by complex but organized processes. Here, we demonstrate that the growth factor midkine interacts with LDL receptor-related protein 1 (LRP1) at high affinity (K d value, 2.7 nM) not only at the cell surface but also within the secretory pathway during biosynthesis. The latter premature ligand-receptor interaction resulted in aggregate formation and consequently suppressed midkine secretion and LRP1 maturation. We utilized an endoplasmic reticulum (ER) retrieval signal and an LRP1 fragment, which strongly bound to midkine and the LRP1-specialized chaperone receptor-associated protein (RAP), to construct an ER trapper. The ER trapper efficiently trapped midkine and RAP and mimicked the premature ligand-receptor interaction, i.e. suppressed maturation of the ligand and receptor. The ER trapper also diminished the inhibitory function of LRP1 on platelet-derived growth factor-mediated cell migration. Complementary to these results, an increased expression of RAP was closely associated with midkine expression in human colorectal carcinomas (33 of 39 cases examined). Our results suggest that the premature ligand-receptor interaction plays a role in protein production within the secretory pathway.