Aph-2/Nicastrin: an essential component of gamma-secretase and regulator of Notch signaling and Presenilin localization.
ABSTRACT The Notch signaling pathway plays a role in cell fate specification in many metazoans. A critical aspect of Notch activation involves proteolysis of the Notch receptor. This cleavage event requires Presenilin as a component of a large multiprotein complex, gamma-secretase. This complex mediates a similar cleavage event of the beta-amyloid precursor protein (APP). The transmembrane protein Nicastrin has been found to associate with Presenilin, Notch, and APP. Recent biochemical and genetic studies have focused on elucidating the function of this protein.
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ABSTRACT: Abstract Abundant biochemical and genetic evidence suggests that presenilins are catalytic components of γ-secretase, the protease responsible for generating the Alzheimer amyloid β-protein. However, the differential localization of presenilins to early secretory compartments and γ-secretase substrates to late secretory compartments and the plasma membrane (the ‘spatial paradox’) argues against this view. We investigated this issue by studying the localization of nicastrin, another putative γ-secretase component, and its association with presenilin-1 into proteolytically active complexes. Glycosidase digests revealed that nicastrin exists in multiple glycoforms and is terminally sialylated, a modification often associated with the trans-Golgi network. Trafficking of nicastrin to the trans-Golgi network was confirmed by density gradient fractionation and immunofluorescence microscopy. In presenilin-deficient cells, however, nicastrin trafficking and maturation were abnormal, as the protein was restricted to early secretory compartments and failed to be sialylated. Mature sialylated nicastrin in trans-Golgi network fractions was complexed quantitatively with N- and C-terminal fragments of presenilin-1, whereas immature nicastrin present in early secretory compartments was not. Additionally, trans-Golgi network fractions contained the γ-secretase substrate β-amyloid precursor protein C83 and were enriched in presenilin-dependent γ-secretase proteolytic activity. The results resolve the apparent spatial paradox by demonstrating that presenilin–nicastrin complexes and presenilin-dependent γ-secretase activity are co-localized to a late secretory compartment. The findings provide further evidence that presenilin-containing complexes are the γ-secretase, and indicate that presenilins also regulate γ-secretase assembly.Journal of Neurochemistry 03/2003; 84(5):1143-1153. DOI:10.1046/j.1471-4159.2003.01616.x · 4.24 Impact Factor
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ABSTRACT: Production of Aβ by γ-secretase is a key event in Alzheimer's disease (AD). The γ-secretase complex consists of Presenilin (PS) 1 or 2, Nicastrin (ncstn), Pen-2 and Aph-1 and cleaves type I transmembrane proteins, including the amyloid precursor protein (APP). Although ncstn is widely accepted as an essential component of the complex required for γ-secretase activity, recent in vitro studies have suggested that ncstn is dispensable for APP processing and Aβ production. The focus of this study was to answer this controversy and evaluate the role of ncstn in Aβ generation and the development of the amyloid-related phenotype in the mouse brain. To eliminate ncstn expression in the mouse brain we used a ncstn conditional knock-out mouse that we mated with an established AD transgenic mouse model (5XFAD) and a neuronal Cre expressing transgenic mouse (CamKIIα-iCre), to generate AD mice (5XFAD/CamKIIα-iCre/ncstn(f/f) mice) where ncstn was conditionally inactivated in the brain. 5XFAD/CamKIIα-iCre/ncstn(f/f) mice at 10 week of age developed a neurodegenerative phenotype with a significant reduction in Aβ production and formation of Aβ aggregates, and absence of amyloid plaques. Inactivation of nctsn resulted in substantial accumulation of APP-CTFs and altered PS1 expression. These results reveal a key role for ncstn in modulating Aβ production and amyloid plaque formation in vivo and suggest ncstn as a target in AD therapeutics. This article is protected by copyright. All rights reserved.Aging cell 07/2013; DOI:10.1111/acel.12131 · 7.55 Impact Factor
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ABSTRACT: γ-Secretase is a membrane-bound protease that cleaves within the transmembrane region of amyloid precursor protein to generate the C-termini of the Aβ peptides which are believed to play a central role in the neuropathology of Alzheimer’s disease. An in vitro γ-secretase assay using a recombinant substrate C100Flag has been developed to facilitate the characterization and identification of this enigmatic protease. Biochemical studies establish that γ-secretase activity is catalyzed by a PS1-containing macromolecular complex. Moreover, the fact that the photoreactive active γ-secretase inhibitor directed to the active site labels PS1 suggests that PS1 contains the active site of the protease. Presenilin/γ-secretase as a potential target for AD therapy and its role in regulated intramembrane proteolysis are discussed.Neurobiology of Aging 11/2002; 23(6):1023-1030. DOI:10.1016/S0197-4580(02)00126-4 · 4.85 Impact Factor