A presenilin-1-dependent gamma-secretase-like protease mediates release of Notch intracellular domain.
TL;DR: It is reported that, in mammalian cells, PS1 deficiency also reduces the proteolytic release of NICD from a truncated Notch construct, thus identifying the specific biochemical step of the Notch signalling pathway that is affected by PS1.
Abstract: Signalling through the receptor protein Notch, which is involved in crucial cell-fate decisions during development, requires ligand-induced cleavage of Notch. This cleavage occurs within the predicted transmembrane domain, releasing the Notch intracellular domain (NICD), and is reminiscent of gamma-secretase-mediated cleavage of beta-amyloid precursor protein (APP), a critical event in the pathogenesis of Alzheimer's disease. A deficiency in presenilin-1 (PS1) inhibits processing of APP by gamma-secretase in mammalian cells, and genetic interactions between Notch and PS1 homologues in Caenorhabditis elegans indicate that the presenilins may modulate the Notch signalling pathway. Here we report that, in mammalian cells, PS1 deficiency also reduces the proteolytic release of NICD from a truncated Notch construct, thus identifying the specific biochemical step of the Notch signalling pathway that is affected by PS1. Moreover, several gamma-secretase inhibitors block this same step in Notch processing, indicating that related protease activities are responsible for cleavage within the predicted transmembrane domains of Notch and APP. Thus the targeting of gamma-secretase for the treatment of Alzheimer's disease may risk toxicity caused by reduced Notch signalling.
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TL;DR: Evidence that the presenilin proteins, mutations in which cause the most aggressive form of inherited AD, lead to altered intramembranous cleavage of the beta-amyloid precursor protein by the protease called gamma-secretase has spurred progress toward novel therapeutics and provided discrete biochemical targets for drug screening and development.
Abstract: Rapid progress in deciphering the biological mechanism of Alzheimer's disease (AD) has arisen from the application of molecular and cell biology to this complex disorder of the limbic and association cortices. In turn, new insights into fundamental aspects of protein biology have resulted from research on the disease. This beneficial interplay between basic and applied cell biology is well illustrated by advances in understanding the genotype-to-phenotype relationships of familial Alzheimer's disease. All four genes definitively linked to inherited forms of the disease to date have been shown to increase the production and/or deposition of amyloid β-protein in the brain. In particular, evidence that the presenilin proteins, mutations in which cause the most aggressive form of inherited AD, lead to altered intramembranous cleavage of the β-amyloid precursor protein by the protease called γ-secretase has spurred progress toward novel therapeutics. The finding that presenilin itself may be the long-sought γ-...
5,890 citations
TL;DR: Overexpression of a transmembrane aspartic protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of beta-secretase cleavage products, and these were cleaved exactly and only at known beta- secretase positions.
Abstract: Cerebral deposition of amyloid beta peptide (Abeta) is an early and critical feature of Alzheimer's disease. Abeta generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: beta-secretase and gamma-secretase. These proteases are prime therapeutic targets. A transmembrane aspartic protease with all the known characteristics of beta-secretase was cloned and characterized. Overexpression of this protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of beta-secretase cleavage products, and these were cleaved exactly and only at known beta-secretase positions. Antisense inhibition of endogenous BACE messenger RNA decreased the amount of beta-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as beta-secretase. Finally, the expression pattern and subcellular localization of BACE were consistent with that expected for beta-secretase. Future development of BACE inhibitors may prove beneficial for the treatment of Alzheimer's disease.
3,879 citations
TL;DR: The results indicate that the two transmembrane aspartate residues are critical for both presenilin-1 endoproteolysis and γ-secretase activity, and suggest that presenILin 1 is either a unique diaspartyl cofactor for ιsecretase or is itselfγ- secretase, an autoactivated intramembranous aspartyl protease.
Abstract: Accumulation of the amyloid-beta protein (Abeta) in the cerebral cortex is an early and invariant event in the pathogenesis of Alzheimer's disease. The final step in the generation of Abeta from the beta-amyloid precursor protein is an apparently intramembranous proteolysis by the elusive gamma-secretase(s). The most common cause of familial Alzheimer's disease is mutation of the genes encoding presenilins 1 and 2, which alters gamma-secretase activity to increase the production of the highly amyloidogenic Abeta42 isoform. Moreover, deletion of presenilin-1 in mice greatly reduces gamma-secretase activity, indicating that presenilin-1 mediates most of this proteolytic event. Here we report that mutation of either of two conserved transmembrane (TM) aspartate residues in presenilin-1, Asp 257 (in TM6) and Asp 385 (in TM7), substantially reduces Abeta production and increases the amounts of the carboxy-terminal fragments of beta-amyloid precursor protein that are the substrates of gamma-secretase. We observed these effects in three different cell lines as well as in cell-free microsomes. Either of the Asp --> Ala mutations also prevented the normal endoproteolysis of presenilin-1 in the TM6 --> TM7 cytoplasmic loop. In a functional presenilin-1 variant (carrying a deletion in exon 9) that is associated with familial Alzheimer's disease and which does not require this cleavage, the Asp 385 --> Ala mutation still inhibited gamma-secretase activity. Our results indicate that the two transmembrane aspartate residues are critical for both presenilin-1 endoproteolysis and gamma-secretase activity, and suggest that presenilin 1 is either a unique diaspartyl cofactor for gamma-secretase or is itself gamma-secretase, an autoactivated intramembranous aspartyl protease.
1,915 citations
TL;DR: This work shows a rapid, massive conversion of proliferative crypt cells into post-mitotic goblet cells after conditional removal of the common Notch pathway transcription factor CSL/RBP-J and indicates that γ-secretase inhibitors, developed for Alzheimer's disease, might be of therapeutic benefit in colorectal neoplastic disease.
Abstract: The self-renewing epithelium of the small intestine is ordered into stem/progenitor crypt compartments and differentiated villus compartments. Recent evidence indicates that the Wnt cascade is the dominant force in controlling cell fate along the crypt-villus axis. Here we show a rapid, massive conversion of proliferative crypt cells into post-mitotic goblet cells after conditional removal of the common Notch pathway transcription factor CSL/RBP-J. We obtained a similar phenotype by blocking the Notch cascade with a gamma-secretase inhibitor. The inhibitor also induced goblet cell differentiation in adenomas in mice carrying a mutation of the Apc tumour suppressor gene. Thus, maintenance of undifferentiated, proliferative cells in crypts and adenomas requires the concerted activation of the Notch and Wnt cascades. Our data indicate that gamma-secretase inhibitors, developed for Alzheimer's disease, might be of therapeutic benefit in colorectal neoplastic disease.
1,555 citations
TL;DR: Why Aβ accumulates in the brains of elderly individuals is unclear but could relate to changes in APP metabolism or Aβ elimination, which will be crucial to the development of therapeutic targets to treat AD.
Abstract: Alzheimer's disease (AD), the leading cause of dementia worldwide, is characterized by the accumulation of the β-amyloid peptide (Aβ) within the brain along with hyperphosphorylated and cleaved forms of the microtubule-associated protein tau. Genetic, biochemical, and behavioral research suggest that physiologic generation of the neurotoxic Aβ peptide from sequential amyloid precursor protein (APP) proteolysis is the crucial step in the development of AD. APP is a single-pass transmembrane protein expressed at high levels in the brain and metabolized in a rapid and highly complex fashion by a series of sequential proteases, including the intramembranous γ-secretase complex, which also process other key regulatory molecules. Why Aβ accumulates in the brains of elderly individuals is unclear but could relate to changes in APP metabolism or Aβ elimination. Lessons learned from biochemical and genetic studies of APP processing will be crucial to the development of therapeutic targets to treat AD.
1,486 citations
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TL;DR: This research was supported by grants from the National Institutes of Health (HL20948) and the Perot Family Foundation.
3,626 citations
TL;DR: The results indicate that mutations in PS1 that manifest clinically cause a gain of function and that inhibition of PS1 activity is a potential target for anti-amyloidogenic therapy in Alzheimer's disease.
Abstract: Point mutations in the presenilin-1 gene (PS1) are a major cause of familial Alzheimer's disease. They result in a selective increase in the production of the amyloidogenic peptide amyloid-beta(1-42) by proteolytic processing of the amyloid precursor protein (APP). Here we investigate whether PS1 is also involved in normal APP processing in neuronal cultures derived from PS1-deficient mouse embryos. Cleavage by alpha- and beta-secretase of the extracellular domain of APP was not affected by the absence of PS1, whereas cleavage by gamma-secretase of the transmembrane domain of APP was prevented, causing carboxyl-terminal fragments of APP to accumulate and a fivefold drop in the production of amyloid peptide. Pulse-chase experiments indicated that PS1 deficiency specifically decreased the turnover of the membrane-associated fragments of APP. As in the regulation of cholesterol metabolism by proteolysis of a membrane-bound transcription factor, PS1 appears to facilitate a proteolytic activity that cleaves the integral membrane domain of APP. Our results indicate that mutations in PS1 that manifest clinically cause a gain of function and that inhibition of PS1 activity is a potential target for anti-amyloidogenic therapy in Alzheimer's disease.
1,797 citations
TL;DR: It is shown that signalling by a constitutively active membrane-bound Notch-1 protein requires the proteolytic release of the Notch intracellular domain (NICD), which interacts preferentially with CSL.
Abstract: Notch proteins are ligand-activated transmembrane receptors involved in cell-fate selection throughout development1,2,3. No known enzymatic activity is contained within Notch and the molecular mechanism by which it transduces signals across the cell membrane is poorly understood. In many instances, Notch activation results in transcriptional changes in the nucleus through an association with members of the CSL family of DNA-binding proteins (where CSL stands for CBF1, Su(H), Lag-1)1,2,3,4. As Notch is located in the plasma membrane and CSL is a nuclear protein, two models have been proposed to explain how they interact (Fig. 1) . The first suggests that the two interact transiently at the membrane1,5,6,7. The second postulates that Notch is cleaved by a protease, enabling the cleaved fragment to enter the nucleus6,8,9,10,11,12,13,14. Here we show that signalling by a constitutively active membrane-bound Notch-1 protein requires the proteolytic release of the Notch intracellular domain (NICD), which interacts preferentially with CSL. Very small amounts of NICD are active, explaining why it is hard to detect in the nucleus in vivo. We also show that it is ligand binding that induces release of NICD.
1,625 citations
TL;DR: Results show that PS1 is required for proper formation of the axial skeleton, normal neurogenesis, and neuronal survival.
969 citations
TL;DR: The results confirm and extend recent reports indicating that the Notch receptor exists at the plasma membrane as a heterodimeric molecule, but disagree as to the nature of the protease that is responsible for the cleavage that takes place in the extracellular region.
Abstract: The Notch receptor, which is involved in numerous cell fate decisions in invertebrates and vertebrates, is synthesized as a 300-kDa precursor molecule (p300). We show here that proteolytic processing of p300 is an essential step in the formation of the biologically active receptor because only the cleaved fragments are present at the cell surface. Our results confirm and extend recent reports indicating that the Notch receptor exists at the plasma membrane as a heterodimeric molecule, but disagree as to the nature of the protease that is responsible for the cleavage that takes place in the extracellular region. We report here that constitutive processing of murine Notch1 involves a furin-like convertase. We show that the calcium ionophore A23187 and the α1-antitrypsin variant, α 1-PDX, a known inhibitor of furin-like convertases, inhibit p300 processing. When expressed in the furin-deficient Lovo cell line, p300 is not processed. In vitro digestion of a recombinant Notch-derived substrate with purified furin allowed mapping of the processing site to the carboxyl side of the sequence RQRR (amino acids 1651–1654). Mutation of these four amino acids (and of two secondary dibasic furin sites located nearby) completely abolished processing of the Notch1 receptor.
755 citations