Non-Linear and Flexible Regions of the Human Notch1 Extracellular Domain Revealed by High-Resolution Structural Studies

Progression of Notch signaling regulation of B cells under radiation exposure

With the continuous development of nuclear technology, the radiation exposure caused by radiation therapy is a serious health hazard. It is of great significance to further develop effective radiation countermeasures. B cells easily succumb to irradiation exposure along with immunosuppressive response. The approach to ameliorate radiation-induced B cell damage is rarely studied, implying that the underlying mechanisms of B cell damage after exposure are eager to be revealed. Recent studies suggest that Notch signaling plays an important role in B cell-mediated immune response. Notch signaling is a critical regulator for B cells to maintain immune function. Although accumulating studies reported that Notch signaling contributes to the functionality of hematopoietic stem cells and T cells, its role in B cells is scarcely appreciated. Presently, we discussed the regulation of Notch signaling on B cells under radiation exposure to provide a scientific basis to prevent radiation-induced B cell damage.

NOTCH Signaling Pathway: Occurrence, Mechanism, and NOTCH-Directed Therapy for the Management of Cancer

It is now well understood that many signaling pathways are vital in carrying out and controlling essential pro-survival and pro-growth cellular functions. The NOTCH signaling pathway, a highly conserved evolutionary signaling pathway, has been thoroughly studied since the discovery of NOTCH phenotypes about 100 years ago in Drosophila melanogaster. Abnormal NOTCH signaling has been linked to the pathophysiology of several diseases, notably cancer. In tumorigenesis, NOTCH plays the role of a "double-edged sword," that is, it may act as an oncogene or as a tumor suppressor gene depending on the nature of the context. However, its involvement in several cancers and inhibition of the same provides targeted therapy for the management of cancer. The use of gamma (γ)-secretase inhibitors and monoclonal antibodies for cancer treatment involved NOTCH receptors inhibition, leading to the possibility of a targeted approach for cancer treatment. Likewise, several natural compounds, including curcumin, resveratrol, diallyl sulfide, and genistein, also play a dynamic role in the management of cancer by inhibition of NOTCH receptors. This review outlines the functions and structure of NOTCH receptors and their associated ligands with the mechanism of the signaling pathway. In addition, it also emphasizes the role of NOTCH-targeted nanomedicine in various cancer treatment strategies.

Soluble and multivalent Jag1 DNA origami nanopatterns activate Notch without pulling force

The Notch signaling pathway has fundamental roles in embryonic development and in the nervous system. The current model of receptor activation involves initiation via a force-induced conformational change. Here, we define conditions that reveal pulling force-independent Notch activation using soluble multivalent constructs. We treat neuroepithelial stem-like cells with molecularly precise ligand nanopatterns displayed from solution using DNA origami. Notch signaling follows with clusters of Jag1, and with chimeric structures where most Jag1 proteins are replaced by other binders not targeting Notch. Our data rule out several confounding factors and suggest a model where Jag1 activates Notch upon prolonged binding without appearing to need a pulling force. These findings reveal a distinct mode of activation of Notch and lay the foundation for the development of soluble agonists.

Regulation of the Notch signaling pathway by natural products for cancer therapy

The Notch signaling pathway is an evolutionarily conserved pathway that modulates normal biological processes involved in cellular differentiation, apoptosis, and stem cell self-renewal in a context-dependent fashion. Attributed to its pleiotropic physiological roles, both overexpression and silencing of the pathway are associated with the emergence, progression, and poorer prognosis in various types of cancer. To decrease disease incidence and promote survival, targeting Notch may have chemopreventive and anti-cancer effects. Natural products with profound historical origins have distinguished themselves from other therapies due to their easy access, high biological compatibility, low toxicity, and reliable effects at specific physiological sites in vivo. This review describes the Notch signaling pathway, particularly its normal activation process, and some main illnesses related to Notch signaling pathway dysregulation. Emphasis is placed on the effects and mechanisms of natural products targeting the Notch signaling pathway in diverse cancer types, including curcumin, ellagic acid (EA), resveratrol, genistein, epigallocatechin-3-gallate (EGCG), quercetin, and xanthohumol and so on. Existing evidence indicates that natural products are feasible solution to fight against cancer by targeting Notch signaling, either alone or in combination with current therapeutic agents.

Mutations observed in somatic evolution reveal underlying gene mechanisms

Highly sensitive DNA sequencing techniques have allowed the discovery of large numbers of somatic mutations in normal tissues. Some mutations confer a competitive advantage over wild-type cells, generating expanding clones that spread through the tissue. Competition between mutant clones leads to selection. This process can be considered a large scale, in vivo screen for mutations increasing cell fitness. It follows that somatic missense mutations may offer new insights into the relationship between protein structure, function and cell fitness. We present a flexible statistical method for exploring the selection of structural features in data sets of somatic mutants. We show how this approach can evidence selection of specific structural features in key drivers in aged tissues. Finally, we show how drivers may be classified as fitness-enhancing and fitness-suppressing through different patterns of mutation enrichment. This method offers a route to understanding the mechanism of protein function through in vivo mutant selection.

1H, 15N, 13C backbone and sidechain resonance assignments and secondary structure of mouse NOTCH1 EGF27

NOTCH1 is a transmembrane receptor in metazoans that is linked to a variety of disorders. The receptor contains an extracellular domain (ECD) with 36 tandem epidermal growth factor-like (EGF) repeats. The ECD is responsible for intercellular signaling via protein-ligand interactions with neighboring cells. Each EGF repeat consists of approximately 40 amino acids and 3 conserved disulfide bonds. The Abruptex region (EGF24-29) is critical for NOTCH1 signaling and is known for its missense mutations. Certain EGF repeats are modified with the addition of O-linked glycans and many have calcium binding sites, which give each EGF repeat a unique function. It has been shown that the loss of the O-fucose site of EGF27 alters NOTCH1 activity. To investigate the role of glycosylation in the NOTCH1 signaling pathway, nuclear magnetic resonance spectroscopy has been employed to study the structures of EGF27 and its glycoforms. Here, we report the backbone and sidechain 1H, 15N, and 13C-resonance assignments of the unmodified EGF27 protein and the predicted secondary structure derived from the assigned chemical shifts.

The biology of SCUBE

The SCUBE [Signal peptide-Complement C1r/C1s, Uegf, Bmp1 (CUB)-Epithelial growth factor domain-containing protein] family consists of three proteins in vertebrates, SCUBE1, 2 and 3, which are highly conserved in zebrafish, mice and humans. Each SCUBE gene encodes a polypeptide of approximately 1000 amino acids that is organized into five modular domains: (1) an N-terminal signal peptide sequence, (2) nine tandem epidermal growth factor (EGF)-like repeats, (3) a large spacer region, (4) three cysteine-rich (CR) motifs, and (5) a CUB domain at the C-terminus. Murine Scube genes are expressed individually or in combination during the development of various tissues, including those in the central nervous system and the axial skeleton. The cDNAs of human SCUBE orthologs were originally cloned from vascular endothelial cells, but SCUBE expression has also been found in platelets, mammary ductal epithelium and osteoblasts. Both soluble and membrane-associated SCUBEs have been shown to play important roles in physiology and pathology. For instance, upregulation of SCUBEs has been reported in acute myeloid leukemia, breast cancer and lung cancer. In addition, soluble SCUBE1 is released from activated platelets and can be used as a clinical biomarker for acute coronary syndrome and ischemic stroke. Soluble SCUBE2 enhances distal signaling by facilitating the secretion of dual-lipidated hedgehog from nearby ligand-producing cells in a paracrine manner. Interestingly, the spacer regions and CR motifs can increase or enable SCUBE binding to cell surfaces via electrostatic or glycan-lectin interactions. As such, membrane-associated SCUBEs can function as coreceptors that enhance the signaling activity of various serine/threonine kinase or tyrosine kinase receptors. For example, membrane-associated SCUBE3 functions as a coreceptor that promotes signaling in bone morphogenesis. In humans, SCUBE3 mutations are linked to abnormalities in growth and differentiation of both bones and teeth. In addition to studies on human SCUBE function, experimental results from genetically modified mouse models have yielded important insights in the field of systems biology. In this review, we highlight novel molecular discoveries and critical directions for future research on SCUBE proteins in the context of cancer, skeletal disease and cardiovascular disease.

Combined proteomic and biochemical analyses redefine the consensus sequence requirement for epidermal growth factor-like domain hydroxylation

Epidermal growth factor-like domains (EGFDs) have important functions in cell-cell signaling. Both secreted and cell surface human EGFDs are subject to extensive modifications, including aspartate and asparagine residue C3-hydroxylations catalyzed by the 2-oxoglutarate oxygenase aspartate/asparagine-β-hydroxylase (AspH). Although genetic studies show AspH is important in human biology, studies on its physiological roles have been limited by incomplete knowledge of its substrates. Here, we redefine the consensus sequence requirements for AspH-catalyzed EGFD hydroxylation based on combined analysis of proteomic mass spectrometric data and mass spectrometry-based assays with isolated AspH and peptide substrates. We provide cellular and biochemical evidence that the preferred site of EGFD hydroxylation is embedded within a disulfide-bridged macrocycle formed of 10 amino acid residues. This definition enabled the identification of previously unassigned hydroxylation sites in three EGFDs of human fibulins as AspH substrates. A non-EGFD containing protein, lymphocyte antigen-6/plasminogen activator urokinase receptor domain containing protein 6B (LYPD6B) was shown to be a substrate for isolated AspH, but we did not observe evidence for LYPD6B hydroxylation in cells. AspH-catalyzed hydroxylation of fibulins is of particular interest given their important roles in extracellular matrix dynamics. In conclusion, these results lead to a revision of the consensus substrate requirements for AspH and expand the range of observed and potential AspH-catalyzed hydroxylation in cells, which will enable future study of the biological roles of AspH.

Signalling dynamics in embryonic development

In multicellular organisms, cellular behaviour is tightly regulated to allow proper embryonic development and maintenance of adult tissue. A critical component in this control is the communication between cells via signalling pathways, as errors in intercellular communication can induce developmental defects or diseases such as cancer. It has become clear over the last years that signalling is not static but varies in activity over time. Feedback mechanisms present in every signalling pathway lead to diverse dynamic phenotypes, such as transient activation, signal ramping or oscillations, occurring in a cell type- and stage-dependent manner. In cells, such dynamics can exert various functions that allow organisms to develop in a robust and reproducible way. Here, we focus on Erk, Wnt and Notch signalling pathways, which are dynamic in several tissue types and organisms, including the periodic segmentation of vertebrate embryos, and are often dysregulated in cancer. We will discuss how biochemical processes influence their dynamics and how these impact on cellular behaviour within multicellular systems.

Notch-Jagged signaling complex defined by an interaction mosaic

The Notch signaling system links cellular fate to that of its neighbors, driving proliferation, apoptosis, and cell differentiation in metazoans, whereas dysfunction leads to debilitating developmental disorders and cancers. Other than a five-by-five domain complex, it is unclear how the 40 extracellular domains of the Notch1 receptor collectively engage the 19 domains of its canonical ligand, Jagged1, to activate Notch1 signaling. Here, using cross-linking mass spectrometry (XL-MS), biophysical, and structural techniques on the full extracellular complex and targeted sites, we identify five distinct regions, two on Notch1 and three on Jagged1, that form an interaction network. The Notch1 membrane-proximal regulatory region individually binds to the established Notch1 epidermal growth factor (EGF) 8-EGF13 and Jagged1 C2-EGF3 activation sites as well as to two additional Jagged1 regions, EGF8-EGF11 and cysteine-rich domain. XL-MS and quantitative interaction experiments show that the three Notch1-binding sites on Jagged1 also engage intramolecularly. These interactions, together with Notch1 and Jagged1 ectodomain dimensions and flexibility, determined by small-angle X-ray scattering, support the formation of nonlinear architectures. Combined, the data suggest that critical Notch1 and Jagged1 regions are not distal but engage directly to control Notch1 signaling, thereby redefining the Notch1-Jagged1 activation mechanism and indicating routes for therapeutic applications.

Current Views on the Roles of O-Glycosylation in Controlling Notch-Ligand Interactions

The 100th anniversary of Notch discovery in Drosophila has recently passed. The Notch is evolutionarily conserved from Drosophila to humans. The discovery of human-specific Notch genes has led to a better understanding of Notch signaling in development and diseases and will continue to stimulate further research in the future. Notch receptors are responsible for cell-to-cell signaling. They are activated by cell-surface ligands located on adjacent cells. Notch activation plays an important role in determining the fate of cells, and dysregulation of Notch signaling results in numerous human diseases. Notch receptors are primarily activated by ligand binding. Many studies in various fields including genetics, developmental biology, biochemistry, and structural biology conducted over the past two decades have revealed that the activation of the Notch receptor is regulated by unique glycan modifications. Such modifications include O-fucose, O-glucose, and O-N-acetylglucosamine (GlcNAc) on epidermal growth factor-like (EGF) repeats located consecutively in the extracellular domain of Notch receptors. Being fine-tuned by glycans is an important property of Notch receptors. In this review article, we summarize the latest findings on the regulation of Notch activation by glycosylation and discuss future challenges.

Notch Signaling in B Cell Immune Responses

The Notch signaling pathway is highly evolutionarily conserved, dictating cell fate decisions and influencing the survival and growth of progenitor cells that give rise to the cells of the immune system. The roles of Notch signaling in hematopoietic stem cell maintenance and in specification of T lineage cells have been well-described. Notch signaling also plays important roles in B cells. In particular, it is required for specification of marginal zone type B cells, but Notch signaling is also important in other stages of B cell development and activation. This review will focus on established and new roles of Notch signaling during B lymphocyte lineage commitment and describe the function of Notch within mature B cells involved in immune responses.

Effect of Site-Specific O-Glycosylation on the Structural Behavior of NOTCH1 Receptor Extracellular EGF-like Domains 11 and 10

Human NOTCH1 receptor contains 36 epidermal growth factor (EGF)-like repeating domains, in which O-glycosylation status of EGF12 domain regulates the interaction with Notch ligands. Our interest is focused on the effect of specific O-glycosylation states on the structural behavior of EGF11 and EGF10, because they appeared to affect molecular mechanism in receptor-ligand interactions by inducing some conformational alterations in these domains and/or the regions connecting two domains. To understand the structural impact of various O-glycosylation patterns on the pivotal EGF-like repeats 10, 11, and 12, we performed chemical synthesis and NMR studies of site-specifically O-glycosylated EGF11 and EGF10. Our strategy enabled us to synthesize four EGF11 and five EGF10 modules. The specific O-glycosylation states affected in vitro folding of EGF10 more than EGF11, while calcium ion had a larger effect on EGF11 folding. Comprehensive NMR studies shed light on the new type "sugar bridges" crosslinking Thr-O-GlcNAc in the consensus sequence C5-X-X-G-X-(T/S)-G-X-X-C6 and an amino acid in the hinge region between the domains, 445Thr-O-GlcNAc-IIe451 in domain 11 and 405Thr-O-GlcNAc-Gln411 in domain 10, respectively.

Recombinant mussel protein Pvfp-5β: A potential tissue bioadhesive

During their lifecycle, many marine organisms rely on natural adhesives to attach to wet surfaces for movement and self-defense in aqueous tidal environments. Adhesive proteins from mussels are biocompatible and elicit only minimal immune responses in humans. Therefore these proteins have received increased attention for their potential applications in medicine, biomaterials, and biotechnology. The Asian green mussel Perna viridis secretes several byssal plaque proteins, molecules that help anchoring the mussel to surfaces. Among these proteins, protein-5β (Pvfp-5β) initiates interactions with the substrate, displacing interfacial water molecules before binding to the surface. Here, we established the first recombinant expression in Escherichia coli of Pvfp-5β. We characterized recombinant Pvfp-5β, finding that despite displaying a CD spectrum consistent with features of a random coil, the protein is correctly folded as indicated by MS and NMR analyses. Pvfp-5β folds as a β-sheet-rich protein as expected for an epidermal growth factor-like module. We examined the effects of Pvfp-5β on cell viability and adhesion capacity in NIH-3T3 and HeLa cell lines, revealing that Pvfp-5β has no cytotoxic effects at the protein concentrations used and provides good cell-adhesion strength on both glass and plastic plates. Our findings suggest that the adhesive properties of recombinant Pvfp-5β make it an efficient surface-coating material, potentially suitable for biomedical applications including regeneration of damaged tissues.

Physical Principles of Membrane Shape Regulation by the Glycocalyx

Cells bend their plasma membranes into highly curved forms to interact with the local environment, but how shape generation is regulated is not fully resolved. Here, we report a synergy between shape-generating processes in the cell interior and the external organization and composition of the cell-surface glycocalyx. Mucin biopolymers and long-chain polysaccharides within the glycocalyx can generate entropic forces that favor or disfavor the projection of spherical and finger-like extensions from the cell surface. A polymer brush model of the glycocalyx successfully predicts the effects of polymer size and cell-surface density on membrane morphologies. Specific glycocalyx compositions can also induce plasma membrane instabilities to generate more exotic undulating and pearled membrane structures and drive secretion of extracellular vesicles. Together, our results suggest a fundamental role for the glycocalyx in regulating curved membrane features that serve in communication between cells and with the extracellular matrix.

Combining genetic and biophysical approaches to probe the structure and function relationships of the notch receptor

Notch is a conserved cell signalling receptor regulating many aspects of development and tissue homeostasis. Notch is activated by ligand-induced proteolytic cleavages that release the Notch intracellular domain, which relocates to the nucleus to regulate gene transcription. Proteolytic activation first requires mechanical force to be applied to the Notch extracellular domain through an endocytic pulling mechanism transmitted through the ligand/receptor interface. This exposes the proteolytic cleavage site allowing the signal to be initiated following removal of the Notch extracellular domain. Ligands can also act, when expressed in the same cell, through non-productive cis-interactions to inhibit Notch activity. Furthermore, ligand selectivity and Notch activation are regulated by numerous post-translational modifications of the extracellular domain. Additional non-canonical trans and cis interactions with other regulatory proteins may modulate alternative mechanisms of Notch activation that depend on endocytic trafficking of the full-length receptor and proteolytic release of the intracellular domain from endo-lysosomal surface. Mutations of Notch, located in different regions of the protein, are associated with a spectrum of different loss and gain of function phenotypes and offer the possibility to dissect distinct regulatory interactions and mechanisms, particularly when combined with detailed structural analysis of Notch in complex with various regulatory partners.

Two novel protein O-glucosyltransferases that modify sites distinct from POGLUT1 and affect Notch trafficking and signaling

The Notch-signaling pathway is normally activated by Notch-ligand interactions. A recent structural analysis suggested that a novel O-linked hexose modification on serine 435 of the mammalian NOTCH1 core ligand-binding domain lies at the interface with its ligands. This serine occurs between conserved cysteines 3 and 4 of Epidermal Growth Factor-like (EGF) repeat 11 of NOTCH1, a site distinct from those modified by protein O-glucosyltransferase 1 (POGLUT1), suggesting that a different enzyme is responsible. Here, we identify two novel protein O-glucosyltransferases, POGLUT2 and POGLUT3 (formerly KDELC1 and KDELC2, respectively), which transfer O-glucose (O-Glc) from UDP-Glc to serine 435. Mass spectrometric analysis of NOTCH1 produced in HEK293T cells lacking POGLUT2, POGLUT3, or both genes showed that either POGLUT2 or POGLUT3 can add this novel O-Glc modification. EGF11 of NOTCH2 does not have a serine residue in the same location for this O-glucosylation, but EGF10 of NOTCH3 (homologous to EGF11 in NOTCH1 and -2) is also modified at the same position. Comparison of the sites suggests a consensus sequence for modification. In vitro assays with POGLUT2 and POGLUT3 showed that both enzymes modified only properly folded EGF repeats and displayed distinct acceptor specificities toward NOTCH1 EGF11 and NOTCH3 EGF10. Mutation of the O-Glc modification site on EGF11 (serine 435) in combination with sensitizing O-fucose mutations in EGF8 or EGF12 affected cell-surface presentation of NOTCH1 or reduced activation of NOTCH1 by Delta-like1, respectively. This study identifies a previously undescribed mechanism for fine-tuning the Notch-signaling pathway in mammals.

Structural Insights into Notch Receptor-Ligand Interactions

Pioneering cell aggregation experiments from the Artavanis-Tsakonas group in the late 1980's localized the core ligand recognition sequence in the Drosophila Notch receptor to epidermal growth factor-like (EGF) domains 11 and 12. Since then, advances in protein expression, structure determination methods and functional assays have enabled us to define the molecular basis of the core receptor/ligand interaction and given new insights into the architecture of the Notch complex at the cell surface. We now know that Notch EGF11 and 12 interact with the Delta/Serrate/LAG-2 (DSL) and C2 domains of ligand and that membrane-binding, together with additional protein-protein interactions outside the core recognition domains, are likely to fine-tune generation of the Notch signal. Furthermore, structure determination of O-glycosylated variants of Notch alone or in complex with receptor fragments, has shown that these sugars contribute directly to the binding interface, as well as to stabilizing intra-molecular domain structure, providing some mechanistic insights into the observed modulatory effects of O-glycosylation on Notch activity.Future challenges lie in determining the complete extracellular architecture of ligand and receptor in order to understand (i) how Notch/ligand complexes may form at the cell surface in response to physiological cues, (ii) the role of lipid binding in stabilizing the Notch/ligand complex, (iii) the impact of O-glycosylation on binding and signalling and (iv) to dissect the different pathologies that arise as a consequence of mutations that affect proteins involved in the Notch pathway.

The Canonical Notch Signaling Pathway: Structural and Biochemical Insights into Shape, Sugar, and Force

The Notch signaling pathway relies on a proteolytic cascade to release its transcriptionally active intracellular domain, on force to unfold a protective domain and permit proteolysis, on extracellular domain glycosylation to tune the forces exerted by endocytosed ligands, and on a motley crew of nuclear proteins, chromatin modifiers, ubiquitin ligases, and a few kinases to regulate activity and half-life. Herein we provide a review of recent molecular insights into how Notch signals are triggered and how cell shape affects these events, and we use the new insights to illuminate a few perplexing observations.

The N-Terminal Region of Fibrillin-1 Mediates a Bipartite Interaction with LTBP1

Fibrillin-1 (FBN1) mutations associated with Marfan syndrome lead to an increase in transforming growth factor β (TGF-β) activation in connective tissues resulting in pathogenic changes including aortic dilatation and dissection. Since FBN1 binds latent TGF-β binding proteins (LTBPs), the major reservoir of TGF-β in the extracellular matrix (ECM), we investigated the structural basis for the FBN1/LTBP1 interaction. We present the structure of a four-domain FBN1 fragment, EGF2-EGF3-Hyb1-cbEGF1 (FBN1E2cbEGF1), which reveals a near-linear domain organization. Binding studies demonstrate a bipartite interaction between a C-terminal LTBP1 fragment and FBN1E2cbEGF1, which lies adjacent to the latency-associated propeptide (LAP)/TGF-β binding site of LTBP1. Modeling of the binding interface suggests that, rather than interacting along the longitudinal axis, LTBP1 anchors itself to FBN1 using two independent epitopes. As part of this mechanism, a flexible pivot adjacent to the FBN1/LTBP1 binding site allows LTBP1 to make contacts with different ECM networks while presumably facilitating a force-induced/traction-based TGF-β activation mechanism.

Structural and functional dissection of the interplay between lipid and Notch binding by human Notch ligands

Recent data have expanded our understanding of Notch signalling by identifying a C2 domain at the N-terminus of Notch ligands, which has both lipid- and receptor-binding properties. We present novel structures of human ligands Jagged2 and Delta-like4 and human Notch2, together with functional assays, which suggest that ligand-mediated coupling of membrane recognition and Notch binding is likely to be critical in establishing the optimal context for Notch signalling. Comparisons between the Jagged and Delta family show a huge diversity in the structures of the loops at the apex of the C2 domain implicated in membrane recognition and Jagged1 missense mutations, which affect these loops and are associated with extrahepatic biliary atresia, lead to a loss of membrane recognition, but do not alter Notch binding. Taken together, these data suggest that C2 domain binding to membranes is an important element in tuning ligand-dependent Notch signalling in different physiological contexts.

Structural and biochemical differences between the Notch and the amyloid precursor protein transmembrane domains

γ-Secretase cleavage of the Notch receptor transmembrane domain is a critical signaling event for various cellular processes. Efforts to develop inhibitors of γ-secretase cleavage of the amyloid-β precursor C99 protein as potential Alzheimer's disease therapeutics have been confounded by toxicity resulting from the inhibition of normal cleavage of Notch. We present biochemical and structural data for the combined transmembrane and juxtamembrane Notch domains (Notch-TMD) that illuminate Notch signaling and that can be compared and contrasted with the corresponding traits of C99. The Notch-TMD and C99 have very different conformations, adapt differently to changes in model membrane hydrophobic span, and exhibit different cholesterol-binding properties. These differences may be exploited in the design of agents that inhibit cleavage of C99 while allowing Notch cleavage.

Notch-Jagged complex structure implicates a catch bond in tuning ligand sensitivity

Notch receptor activation initiates cell fate decisions and is distinctive in its reliance on mechanical force and protein glycosylation. The 2.5-angstrom-resolution crystal structure of the extracellular interacting region of Notch1 complexed with an engineered, high-affinity variant of Jagged1 (Jag1) reveals a binding interface that extends ~120 angstroms along five consecutive domains of each protein. O-Linked fucose modifications on Notch1 epidermal growth factor-like (EGF) domains 8 and 12 engage the EGF3 and C2 domains of Jag1, respectively, and different Notch1 domains are favored in binding to Jag1 than those that bind to the Delta-like 4 ligand. Jag1 undergoes conformational changes upon Notch binding, exhibiting catch bond behavior that prolongs interactions in the range of forces required for Notch activation. This mechanism enables cellular forces to regulate binding, discriminate among Notch ligands, and potentiate Notch signaling.

Notch, lipids, and endothelial cells

PURPOSE OF REVIEW

Notch signaling is an evolutionary conserved pathway critical for cardiovascular development and angiogenesis. More recently, the contribution of Notch signaling to the homeostasis of the adult vasculature has emerged as an important novel paradigm, but much remains to be understood.

RECENT FINDINGS

Recent findings shed light on the impact of Notch in vascular and immune responses to microenvironmental signals as well as on the onset of atherosclerosis. In the past year, studies in human and mice explored the role of Notch in the maintenance of a nonactivated endothelium. Novel pieces of evidence suggest that this pathway is sensitive to environmental factors, including inflammatory mediators and diet-derived by-products.

SUMMARY

An emerging theme is the ability of Notch to respond to changes in the microenvironment, including glucose and lipid metabolites. In turn, alterations in Notch enable an important link between metabolism and transcriptional changes, thus this receptor appears to function as a metabolic sensor with direct implications to gene expression.