Unraveling the complexity of γ-secretase.
Ontology highlight
ABSTRACT:
SUBMITTER: Wolfe MS
PROVIDER: S-EPMC7371508 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:γ-Secretase is an intramembrane-cleaving protease responsible for the generation of amyloid-β (Aβ) peptides. Recently, a series of compounds called γ-secretase modulators (GSMs) has been shown to decrease the levels of long toxic Aβ species (i.e., Aβ42), with a concomitant elevation of the production of shorter Aβ species. In this study, we show that a phenylimidazole-type GSM allosterically induces conformational changes in the catalytic site of γ-secretase to augment the proteolytic activity. Analyses using the photoaffinity labeling technique and systematic mutational studies revealed that the phenylimidazole-type GSM targets a previously unidentified extracellular binding pocket within the N-terminal fragment of presenilin (PS). Collectively, we provide a model for the mechanism of action of the phenylimidazole-type GSM in which binding at the luminal side of PS induces a conformational change in the catalytic center of γ-secretase to modulate Aβ production.
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Project description:Over two decades, γ-secretase has been the target for extensive therapeutic development due to its pivotal role in pathogenesis of Alzheimer's disease and cancer. However, it has proven to be a challenging task owing to its large set of substrates and our limited understanding of the enzyme's structural and mechanistic features. The scientific community is taking bigger strides towards solving this puzzle with recent advancement in techniques like cryogenic electron microscopy (cryo-EM) and photo-affinity labelling (PAL). This review highlights the significance of the PAL technique with multiple examples of photo-probes developed from γ-secretase inhibitors and modulators. The binding of these probes into active and/or allosteric sites of the enzyme has provided crucial information on the γ-secretase complex and improved our mechanistic understanding of this protease. Combining the knowledge of function and regulation of γ-secretase will be a decisive factor in developing novel γ-secretase modulators and biological therapeutics.
| S-EPMC7483676 | biostudies-literature
Project description:Selective lowering of Abeta42 levels (the 42-residue isoform of the amyloid-beta peptide) with small-molecule gamma-secretase modulators (GSMs), such as some non-steroidal anti-inflammatory drugs, is a promising therapeutic approach for Alzheimer's disease. To identify the target of these agents we developed biotinylated photoactivatable GSMs. GSM photoprobes did not label the core proteins of the gamma-secretase complex, but instead labelled the beta-amyloid precursor protein (APP), APP carboxy-terminal fragments and amyloid-beta peptide in human neuroglioma H4 cells. Substrate labelling was competed by other GSMs, and labelling of an APP gamma-secretase substrate was more efficient than a Notch substrate. GSM interaction was localized to residues 28-36 of amyloid-beta, a region critical for aggregation. We also demonstrate that compounds known to interact with this region of amyloid-beta act as GSMs, and some GSMs alter the production of cell-derived amyloid-beta oligomers. Furthermore, mutation of the GSM binding site in the APP alters the sensitivity of the substrate to GSMs. These findings indicate that substrate targeting by GSMs mechanistically links two therapeutic actions: alteration in Abeta42 production and inhibition of amyloid-beta aggregation, which may synergistically reduce amyloid-beta deposition in Alzheimer's disease. These data also demonstrate the existence and feasibility of 'substrate targeting' by small-molecule effectors of proteolytic enzymes, which if generally applicable may significantly broaden the current notion of 'druggable' targets.
| S-EPMC2678541 | biostudies-literature
Project description:Gamma-secretase mediates the final proteolytic cleavage, which liberates amyloid beta-peptide (Abeta), the major component of senile plaques in the brains of Alzheimer disease patients. Therefore, gamma-secretase is a prime target for Abeta-lowering therapeutic strategies. gamma-Secretase is a protein complex composed of four different subunits, presenilin (PS), APH-1, nicastrin, and PEN-2, which are most likely present in a 1:1:1:1 stoichiometry. PS harbors the catalytically active site, which is critically required for the aspartyl protease activity of gamma-secretase. Moreover, numerous familial Alzheimer disease-associated mutations within the PSs increase the production of the aggregation-prone and neurotoxic 42-amino acid Abeta. Nicastrin may serve as a substrate receptor, although this has recently been challenged. PEN-2 is required to stabilize PS within the gamma-secretase complex. No particular function has so far been assigned to APH-1. The four components are sufficient and required for gamma-secretase activity. At least six different gamma-secretase complexes exist that are composed of different variants of PS and APH-1. All gamma-secretase complexes can exert pathological Abeta production. Assembly of the gamma-secretase complex occurs within the endoplasmic reticulum, and only fully assembled and functional gamma-secretase complexes are transported to the plasma membrane. Structural analysis by electron microscopy and chemical cross-linking reveals a water-containing cavity, which allows intramembrane proteolysis. Specific and highly sensitive gamma-secretase inhibitors have been developed; however, they interfere with the physiological function of gamma-secretase in Notch signaling and thus cause rather significant side effects in human trials. Modulators of gamma-secretase, which selectively affect the production of the pathological 42-amino acid Abeta, do not inhibit Notch signaling.
| S-EPMC2662049 | biostudies-literature
Project description:Alzheimer's disease (AD) is caused by synaptic and neuronal loss in the brain. One of the characteristic hallmarks of AD is senile plaques containing amyloid β-peptide (Aβ). Aβ is produced from amyloid precursor protein (APP) by sequential proteolytic cleavages by β-secretase and γ-secretase, and the polymerization of Aβ into amyloid plaques is thought to be a key pathogenic event in AD. Since γ-secretase mediates the final cleavage that liberates Aβ, γ-secretase has been widely studied as a potential drug target for the treatment of AD. γ-Secretase is a transmembrane protein complex containing presenilin, nicastrin, Aph-1, and Pen-2, which are sufficient for γ-secretase activity. γ-Secretase cleaves >140 substrates, including APP and Notch. Previously, γ-secretase inhibitors (GSIs) were shown to cause side effects in clinical trials due to the inhibition of Notch signaling. Therefore, more specific regulation or modulation of γ-secretase is needed. In recent years, γ-secretase modulators (GSMs) have been developed. To modulate γ-secretase and to understand its complex biology, finding the binding sites of GSIs and GSMs on γ-secretase as well as identifying transiently binding γ-secretase modulatory proteins have been of great interest. In this review, decades of findings on γ-secretase in AD are discussed.
| S-EPMC9076685 | biostudies-literature
Project description:Protein ubiquitination, the covalent attachment of ubiquitin to target proteins, has emerged as one of the most prevalent posttranslational modifications (PTMs), regulating nearly every cellular pathway. The diversity of signaling associated with this particular PTM stems from the myriad ways in which a target protein can be modified by ubiquitin, e.g., monoubiquitin, multi-monoubiquitin, and polyubiquitin linkages. In this Review, we focus on developments in both enzymatic and chemical methods that engender ubiquitin with new chemical and physical properties. Moreover, we highlight how these methods have enabled studies directed toward (i) characterizing enzymes responsible for reversing the ubiquitin modification, (ii) understanding the influence of ubiquitin on protein function and crosstalk with other PTMs, and (iii) uncovering the impact of polyubiquitin chain linkage and length on downstream signaling events.
| S-EPMC4805399 | biostudies-literature
Project description:BACKGROUND:γ-Secretase is a multiprotein protease that cleaves amyloid protein precursor (APP) and other type I transmembrane proteins. It has two catalytic subunits, presenilins 1 and 2 (PS1 and 2). In our previous report, we observed subtle differences in PS1- and PS2-mediated cleavages of select substrates and slightly different potencies of PS1 versus PS2 inhibition for select γ-secretase inhibitors (GSIs) on various substrates. In this study, we investigated whether γ-secretase modulators (GSMs) and inverse γ-secretase modulators (iGSMs) modulate γ-secretase processivity using multiple different substrates. We next used HEK 293T cell lines in which PSEN1 or PSEN2 was selectively knocked out to investigate processivity and response to GSMs and iGSMs. METHODS:For cell-free γ-secretase cleavage assay, recombinant substrates were incubated with CHAPSO-solubilized CHO or HEK 293T cell membrane with GSMs or iGSMs in suitable buffer. For cell-based assay, cDNA encoding substrates were transfected into HEK 293T cells. Cells were then treated with GSMs or iGSMs, and conditioned media were collected. Aβ and Aβ-like peptide production from cell-free and cell-based assay were measured by ELISA and mass spectrometry. RESULT:These studies demonstrated that GSMs are highly selective for effects on APP, whereas iGSMs have a more promiscuous effect on many substrates. Surprisingly, iGSMs actually appear to act as like GSIs on select substrates. The data with PSEN1 or PSEN2 knocked out HEK 293T reveal that PS1 has higher processivity and response to GSMs than PS2, but PS2 has higher response to iGSM. CONCLUSION:Collectively, these data indicate that GSMs are likely to have limited target-based toxicity. In addition, they show that iGSMs may act as substrate-selective GSIs providing a potential new route to identify leads for substrate-selective inhibitors of certain γ-secretase-mediated signaling events. With growing concerns that long-term β-secretase inhibitor is limited by target-based toxicities, such data supports continued development of GSMs as AD prophylactics.
| S-EPMC7236921 | biostudies-literature
Project description:The numerous processes involved in the etiology of breast cancer such as cell survival, metabolism, proliferation, differentiation, and angiogenesis are currently being elucidated. However, underlying mechanisms that drive breast cancer progression and drug resistance are still poorly understood. As we discuss here in detail, the Notch signaling pathway is an important regulatory component of normal breast development, cell fate of normal breast stem cells, and proliferation and survival of breast cancer initiating cells. Notch exerts a wide range of critical effects through a canonical pathway where it is expressed as a type I membrane precursor heterodimer followed by at least two subsequent cleavages induced by ligand engagement to ultimately release an intracellular form to function as a transcriptional activator. Notch and its ligands are overexpressed in breast cancer, and one method of effectively blocking Notch activity is preventing its cleavage at the cell surface with ?-secretase inhibitors. In the context of Notch signaling, the application of clinically relevant anti-Notch drugs in treatment regimens may contribute to novel therapeutic interventions and promote more effective clinical response in women with breast cancer.
| S-EPMC3726525 | biostudies-literature
Project description:γ-Secretase catalyzes the final cleavage of the amyloid precursor protein (APP), resulting in the production of amyloid-β (Aβ) peptides with different carboxyl termini. Presenilin (PSEN) and amyloid precursor protein (APP) mutations linked to early onset familial Alzheimer's disease modify the profile of Aβ isoforms generated, by altering both the initial γ-secretase cleavage site and subsequent processivity in a manner that leads to increased levels of the more amyloidogenic Aβ42 and in some circumstances Aβ43. Compounds termed γ-secretase modulators (GSMs) and inverse GSMs (iGSMs) can decrease and increase levels of Aβ42, respectively. As GSMs lower the level of production of pathogenic forms of long Aβ isoforms, they are of great interest as potential Alzheimer's disease therapeutics. The factors that regulate GSM modulation are not fully understood; however, there is a growing body of evidence that supports the hypothesis that GSM activity is influenced by the amino acid sequence of the γ-secretase substrate. We have evaluated whether mutations near the luminal border of the transmembrane domain (TMD) of APP alter the ability of both acidic, nonsteroidal anti-inflammatory drug-derived carboxylate and nonacidic, phenylimidazole-derived classes of GSMs and iGSMs to modulate γ-secretase cleavage. Our data show that point mutations can dramatically reduce the sensitivity to modulation of cleavage by GSMs but have weaker effects on iGSM activity. These studies support the concept that the effect of GSMs may be substrate selective; for APP, it is dependent on the amino acid sequence of the substrate near the junction of the extracellular domain and luminal segment of the TMD.
| S-EPMC3985764 | biostudies-literature
Project description:Fifteen human healthy volunteers, divided into three groups, received a single dose of placebo or either 140 mg or 280 mg of the γ-secretase inhibitor semagacestat (LY450139). Endogenous peptides in CSF, sampled prior to administration of the drug and at six subsequent time points, were analyzed by liquid chromatography coupled to mass spectrometry, using isobaric labeling based on the tandem mass tag approach for relative quantification.
2016-03-14 | PXD003075 | Pride