Effects of Notch glycosylation on health and diseases

Rational Design of Dual-Domain Binding Inhibitors for N-Acetylgalactosamine Transferase 2 with Improved Selectivity over the T1 and T3 Isoforms

The GalNAc-transferase (GalNAc-T) family, consisting of 20 isoenzymes, regulates the O-glycosylation process of mucin glycopeptides by transferring GalNAc units to serine/threonine residues. Dysregulation of specific GalNAc-Ts is associated with various diseases, making these enzymes attractive targets for drug development. The development of inhibitors is key to understanding the implications of GalNAc-Ts in human diseases. However, developing selective inhibitors for individual GalNAc-Ts represents a major challenge due to shared structural similarities among the isoenzymes and some degree of redundancy among the natural substrates. Herein, we report the development of a GalNAc-T2 inhibitor with higher potency compared to those of the T1 and T3 isoforms. The most promising candidate features bivalent GalNAc and thiophene moieties on a peptide chain, enabling binding to both the lectin and catalytic domains of the enzyme. The binding mode was confirmed by competitive saturation transfer difference NMR experiments and validated through molecular dynamics simulations. The inhibitor demonstrated an IC50 of 21.4 μM for GalNAc-T2, with 8- and 32-fold higher selectivity over the T3 and T1 isoforms, respectively, representing a significant step forward in the synthesis of specific GalNAc-T inhibitors tailored to the unique structural features of the targeted isoform.

Uncovering novel regulatory variants in carbohydrate metabolism: a comprehensive multi-omics study of glycemic traits in the Indian population

Clinical biomarkers such as fasting glucose, HbA1c, and fasting insulin, which gauge glycemic status in the body, are highly influenced by diet. Indians are genetically predisposed to type 2 diabetes and their carbohydrate-centric diet further elevates the disease risk. Despite the combined influence of genetic and environmental risk factors, Indians have been inadequately explored in the studies of glycemic traits. Addressing this gap, we investigate the genetic architecture of glycemic traits at genome-wide level in 4927 Indians (without diabetes). Our analysis revealed numerous variants of sub-genome-wide significance, and their credibility was thoroughly assessed by integrating data from various levels. This identified key effector genes, ZNF470, DPP6, GXYLT2, PITPNM3, BEND7, and LORICRIN-PGLYRP3. While these genes were weakly linked with carbohydrate intake or glycemia earlier in other populations, our findings demonstrated a much stronger association in the Indian population. Associated genetic variants within these genes served as expression quantitative trait loci (eQTLs) in various gut tissues essential for digestion. Additionally, majority of these gut eQTLs functioned as methylation quantitative trait loci (meth-QTLs) observed in peripheral blood samples from 223 Indians, elucidating the underlying mechanism of their regulation of target gene expression. Specific co-localized eQTLs-meth-QTLs altered the binding affinity of transcription factors targeting crucial genes involved in glucose metabolism. Our study identifies previously unreported genetic variants that strongly influence the diet-glycemia relationship. These findings set the stage for future research into personalized lifestyle interventions integrating genetic insights with tailored dietary strategies to mitigate disease risk based on individual genetic profiles.

Glycosylation in aging and neurodegenerative diseases

Aging, a complex biological process, involves the progressive decline of physiological functions across various systems, leading to increased susceptibility to neurodegenerative diseases. In society, demographic aging imposes significant economic and social burdens due to these conditions. This review specifically examines the association of protein glycosylation with aging and neurodegenerative diseases. Glycosylation, a critical post-translational modification, influences numerous aspects of protein function that are pivotal in aging and the pathophysiology of diseases such as Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. We highlight the alterations in glycosylation patterns observed during aging, their implications in the onset and progression of neurodegenerative diseases, and the potential of glycosylation profiles as biomarkers for early detection, prognosis, and monitoring of these age-associated conditions, and delve into the mechanisms of glycosylation. Furthermore, this review explores their role in regulating protein function and mediating critical biological interactions in these diseases. By examining the changes in glycosylation profiles associated with each part, this review underscores the potential of glycosylation research as a tool to enhance our understanding of aging and its related diseases.

Asymmetric and parallel subgenome selection co-shape common carp domestication

BACKGROUND

The common carp (Cyprinus carpio) might best represent the domesticated allopolyploid animals. Although subgenome divergence which is well-known to be a key to allopolyploid domestication has been comprehensively characterized in common carps, the link between genetic architecture underlying agronomic traits and subgenome divergence is unknown in the selective breeding of common carps globally.

RESULTS

We utilized a comprehensive SNP dataset in 13 representative common carp strains worldwide to detect genome-wide genetic variations associated with scale reduction, vibrant skin color, and high growth rate in common carp domestication. We identified numerous novel candidate genes underlie the three agronomically most desirable traits in domesticated common carps, providing potential molecular targets for future genetic improvement in the selective breeding of common carps. We found that independently selective breeding of the same agronomic trait (e.g., fast growing) in common carp domestication could result from completely different genetic variations, indicating the potential advantage of allopolyploid in domestication. We observed that candidate genes associated with scale reduction, vibrant skin color, and/or high growth rate are repeatedly enriched in the immune system, suggesting that domestication of common carps was often accompanied by the disease resistance improvement.

CONCLUSIONS

In common carp domestication, asymmetric subgenome selection is prevalent, while parallel subgenome selection occurs in selective breeding of common carps. This observation is not due to asymmetric gene retention/loss between subgenomes but might be better explained by reduced pleiotropy through transposable element-mediated expression divergence between ohnologs. Our results demonstrate that domestication benefits from polyploidy not only in plants but also in animals.

Single-cell sequencing reveals SATB2/NOTCH1 signaling promotes the progression of malignancy of epithelial cells from papillary thyroid cancer

Although most papillary thyroid cancers (PTCs) are deemed to have a favorable clinical course and outcome, some develop an aggressive biological behavior at diagnosis or during treatment. Single-cell RNA sequencing (scRNA-seq), which is based on quantifying the features of individual cells to resolve tumor tissue heterogeneity, was used to uncover gene regulatory relationships and trace the transcriptional trajectories underlying the malignant transformation. In this study, we performed single-cell sequencing on samples from four PTC patients and one benign thyroid tumor patient. These included two papillary thyroid microcarcinoma cancers (PTMC) patients, two age-matched advanced PTC patients with invading surrounding tissues, and one patient undergoing surgical treatment due to a benign thyroid tumor. We constructed a new PTC RNA spectrum using single-cell sequencing. Single-cell sequencing analysis indicated that there was a highly invasive subgroup in the PTC epithelial cells, the expression of SATB2 (special AT-rich binding protein-2) was related to the prognosis and clinical progress of PTC, and SATB2 could promote the proliferation, migration, and invasion of PTC cells. We found that NOTCH1 was the key target gene of SATB2, and the activation of the SATB2/NOTCH1 pathway was one of the reasons for the high carcinogenicity of this subgroup.

Microglial Galectin3 enhances endothelial metabolism and promotes pathological angiogenesis via Notch inhibition by competitively binding to Jag1

Microglia were considered as immune cells in inflammation until their angiogenic role was widely understood. Although the pro-inflammatory role of microglia in retinal angiogenesis has been explored, little is known about its role in pro-angiogenesis and the microglia-endothelia interaction. Here, we report that galectin-3 (Gal3) released by activated microglia functions as a communicator between microglia and endothelia and competitively binds to Jag1, thus inhibiting the Notch signaling pathway and enhancing endothelial angiogenic metabolism to promote angiogenesis. These results suggest that Gal3 may be a novel and effective target in the treatment of retinal angiogenesis.

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.

Coccomyxa sp.KJ extract affects the fate of T cells stimulated by toxic shock syndrome toxin-1, a superantigen secreted by Staphylococcus aureus

T cell stimulation by bacterial superantigens induces a cytokine storm. After T cell activation and inflammatory cytokine secretion, regulatory T cells (Treg) are produced to suppress the immune response. Coccomyxa sp.KJ (IPOD FERM BP‐22254), a green alga, is reported to regulate immune reactions. Therefore, we examined the effects of Coccomyxa sp.KJ extract (CE) on the superantigen‐induced immune response. When human peripheral blood mononuclear cells (PBMCs) were stimulated with toxic shock syndrome‐1 (TSST‐1) in the presence of CE, the number of activated T cells decreased moderately. Purified T cells stimulated in the presence of CE comprised more non‐proliferating cells than those stimulated in the absence of CE, whereas some T cells proliferated more quickly. The levels of activation markers on the stimulated T cells increased in the presence of CE. Most of the inflammatory cytokines did not change but IL‐1β, IL‐17, IL‐4, and IL‐13 secretion increased, whereas that of IL‐2, TNF‐α, and IL‐18 decreased. IL‐10 secretion was also decreased by CE treatment, suggesting that the immune response was not suppressed by Treg cells. CE enhanced the expression of stem cell‐like memory cell markers in T cells. These results suggest that CE can regulate the fate of T cells and can help to ameliorate superantigen‐induced T cell hyperactivation and immune suppression.

Significant Roles of Notch O-Glycosylation in Cancer

Notch signaling, which was initially identified in Drosophila wing morphogenesis, plays pivotal roles in cell development and differentiation. Optimal Notch pathway activity is essential for normal development and dysregulation of Notch signaling leads to various human diseases, including many types of cancers. In hematopoietic cancers, such as T-cell acute lymphoblastic leukemia, Notch plays an oncogenic role, while in acute myeloid leukemia, it has a tumor-suppressive role. In solid tumors, such as hepatocellular carcinoma and medulloblastoma, Notch may have either an oncogenic or tumor-suppressive role, depending on the context. Aberrant expression of Notch receptors or ligands can alter the ligand-dependent Notch signaling and changes in trafficking can lead to ligand-independent signaling. Defects in any of the two signaling pathways can lead to tumorigenesis and tumor progression. Strikingly, O-glycosylation is one such process that modulates ligand–receptor binding and trafficking. Three types of O-linked modifications on the extracellular epidermal growth factor-like (EGF) repeats of Notch receptors are observed, namely O-glucosylation, O-fucosylation, and O-N-acetylglucosamine (GlcNAc) modifications. In addition, O-GalNAc mucin-type O-glycosylation outside the EGF repeats also appears to occur in Notch receptors. In this review, we first briefly summarize the basics of Notch signaling, describe the latest information on O-glycosylation of Notch receptors classified on a structural basis, and finally describe the regulation of Notch signaling by O-glycosylation in cancer.

Notch Signaling in HSC Emergence: When, Why and How

The hematopoietic stem cell (HSC) sustains blood homeostasis throughout life in vertebrates. During embryonic development, HSCs emerge from the aorta-gonads and mesonephros (AGM) region along with hematopoietic progenitors within hematopoietic clusters which are found in the dorsal aorta, the main arterial vessel. Notch signaling, which is essential for arterial specification of the aorta, is also crucial in hematopoietic development and HSC activity. In this review, we will present and discuss the evidence that we have for Notch activity in hematopoietic cell fate specification and the crosstalk with the endothelial and arterial lineage. The core hematopoietic program is conserved across vertebrates and here we review studies conducted using different models of vertebrate hematopoiesis, including zebrafish, mouse and in vitro differentiated Embryonic stem cells. To fulfill the goal of engineering HSCs in vitro, we need to understand the molecular processes that modulate Notch signaling during HSC emergence in a temporal and spatial context. Here, we review relevant contributions from different model systems that are required to specify precursors of HSC and HSC activity through Notch interactions at different stages of development.

Notch signaling in oral pre-cancer and oral cancer

Notch signaling involves cell to cell contact. It is an ancient signaling mechanism that is conserved throughout the animal kingdom. The basic function of Notch signaling is to decide cell fate and execute asymmetrical division. Notch signaling is indispensable for embryo growth. Aberrant Notch signaling involves in cancer progression by altering cell proliferation rate, tumor micro-environment, stem cell activities. The role of Notch signaling in cancer progression is context-dependent. In breast cancer and T cell lymphoma Notch signaling is highly active, whereas in squamous cell carcinoma (SCC) as oral and skin cancer, the signaling is suppressed. It is believed that in SCC, Notch-mediated tumor growth is due to the cell non-autonomous function. Oral cancer is the 6th most risky cancer worldwide. In many patients, oral cancer is preceded by pre-cancer conditions. In this review, we have summarized the research knowledge related to the role of Notch signaling in oral cancer and pre-cancer conditions and the therapeutic options available targeting different components of Notch pathways.

Modulation of the NOTCH1 Pathway by LUNATIC FRINGE Is Dominant over That of MANIC or RADICAL FRINGE

Fringes are glycosyltransferases that transfer a GlcNAc to O-fucose residues on Epidermal Growth Factor-like (EGF) repeats. Three Fringes exist in mammals: LUNATIC FRINGE (LFNG), MANIC FRINGE (MFNG), and RADICAL FRINGE (RFNG). Fringe modification of O-fucose on EGF repeats in the NOTCH1 (N1) extracellular domain modulates the activation of N1 signaling. Not all O-fucose residues of N1 are modified by all Fringes; some are modified by one or two Fringes and others not modified at all. The distinct effects on N1 activity depend on which Fringe is expressed in a cell. However, little data is available on the effect that more than one Fringe has on the modification of O-fucose residues and the resulting downstream consequence on Notch activation. Using mass spectral glycoproteomic site mapping and cell-based N1 signaling assays, we compared the effect of co-expression of N1 with one or more Fringes on modification of O-fucose and activation of N1 in three cell lines. Individual expression of each Fringe with N1 in the three cell lines revealed differences in modulation of the Notch pathway dependent on the presence of endogenous Fringes. Despite these cell-based differences, co-expression of several Fringes with N1 demonstrated a dominant effect of LFNG over MFNG or RFNG. MFNG and RFNG appeared to be co-dominant but strongly dependent on the ligands used to activate N1 and on the endogenous expression of Fringes. These results show a hierarchy of Fringe activity and indicate that the effect of MFNG and/or RFNG could be small in the presence of LFNG.

Other Types of Glycosylation

O-Linked glycosylation such as O-fucose, O-glucose, and O-N-acetylglucosamine are considered to be unusual. As suggested by the high levels of evolutional conservation, these O-glycans are fundamentally important for life. In the last two decades, our understanding of the importance of these glycans has greatly advanced. In particular, identification of the glycosyltransferases responsible for the biosynthesis of these glycans has accelerated basic research on the functional significance and molecular mechanisms by which these O-glycans regulate protein functions as well as clinical research on human diseases due to changes in these types of O-glycosylation. Notably, Notch receptor signaling is modified with and regulated by these types of O-glycans. Here, we summarize the current view of the structures and the significance of these O-glycans mainly in the context of Notch signaling regulation and human diseases.

The developmental origins of Notch-driven intrahepatic bile duct disorders

The Notch signaling pathway is an evolutionarily conserved mechanism of cell-cell communication that mediates cellular proliferation, cell fate specification, and maintenance of stem and progenitor cell populations. In the vertebrate liver, an absence of Notch signaling results in failure to form bile ducts, a complex tubular network that radiates throughout the liver, which, in healthy individuals, transports bile from the liver into the bowel. Loss of a functional biliary network through congenital malformations during development results in cholestasis and necessitates liver transplantation. Here, we examine to what extent Notch signaling is necessary throughout embryonic life to initiate the proliferation and specification of biliary cells and concentrate on the animal and human models that have been used to define how perturbations in this signaling pathway result in developmental liver disorders.

Narrative review of urinary glycan biomarkers in prostate cancer

Prostate cancer (PC) is the second most common cancer in men worldwide. The application of the prostate-specific antigen (PSA) test has improved the diagnosis and treatment of PC. However, the PSA test has become associated with overdiagnosis and overtreatment. Therefore, there is an unmet need for novel diagnostic, prognostic, and predictive biomarkers of PC. Urinary glycoproteins and exosomes are a potential source of PC glycan biomarkers. Urinary glycan profiling can provide noninvasive monitoring of tumor heterogeneity and aggressiveness throughout a treatment course. However, urinary glycan profiling is not popular due to technical disadvantages, such as complicated structural analysis that requires specialized expertise. The technological development of glycan analysis is a rapidly advancing field. A lectin-based microarray can detect aberrant glycoproteins in urine, including PSA glycoforms and exosomes. Glycan enrichment beads can enrich the concentration of N-linked glycans specifically. Capillary electrophoresis, liquid chromatography-tandem mass spectrometry, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry can detect glycans directory. Many studies suggest potential of urinary glycoproteins, exosomes, and glycosyltransferases as a biomarker of PC. Although further technological challenges remain, urinary glycan analysis is one of the promising approaches for cancer biomarker discovery.

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.

Effect of Notch pathway on lipid accumulation induced by mono-2-ethylhexyl phthalate on 3T3-L1 cells

BACKGROUND

Mono-2-ethylhexyl phthalate (MEHP) is a major metabolite of di (2-ethylhexyl) phthalate (DEHP). Our previous researches have shown that MEHP can induce lipid accumulation in preadipocytes, while, the underlying mechanism is unclear. The present study was undertaken to clarify the effect of Notch pathway on lipid accumulation induced by MEHP.

METHODS

3T3-L1 preadipocytes were exposed to MEHP (0, 10, 50, 250 µM and 0.1%DMSO) for the whole differentiation phase. Then the level of TG and cell cycle were detected. RT-PCR was used to detect the mRNA expression and Western blot was used to detect the expression of protein by Notch pathway genes and lipid metabolic related genes.

RESULTS

In this study, the level of TG in the 250 µM and 250 µM MEHP groups was significantly higher than that in the control, DMSO and 10 µM MEHP groups (P < 0.05). The relative mRNA level of Notch-1, Notch-3, Notch-4, Jagged-2 and Dll-4 in 250 µM group was higher than other groups (P < 0.05). The expression of Notch signal pathway proteins increased in MEHP treated groups, and the expression of Notch-2, Jagged-1, Jagged-2, Dll-1 and Dll-4 in 250 µM group were significantly higher than control group (P < 0.05). The expression of lipid metabolic related gene mRNA and protein increased in MEHP treated groups, and 250 µM MEHP group was higher than other groups (P < 0.05). The intracellular TG content was significantly correlated with the expression levels of Notch-1 and Jagged-2 mRNA (P < 0.05).

CONCLUSION

In this study, we have found that MEHP exposure could increase the TG content in 3T3-L1 cells. The expression of Notch pathway mRNA and proteins were disturbed by the MEHP. Notch-1 and its ligand Jagged-2 play a critical role in the abnormal lipid metabolism in 3T3-L1 cells caused by MEHP.

Structure, function, and pathology of protein O-glucosyltransferases

Protein O-glucosylation is a crucial form of O-glycosylation, which involves glucose (Glc) addition to a serine residue within a consensus sequence of epidermal growth factor epidermal growth factor (EGF)-like repeats found in several proteins, including Notch. Glc provides stability to EGF-like repeats, is required for S2 cleavage of Notch, and serves to regulate the trafficking of Notch, crumbs2, and Eyes shut proteins to the cell surface. Genetic and biochemical studies have shown a link between aberrant protein O-glucosylation and human diseases. The main players of protein O-glucosylation, protein O-glucosyltransferases (POGLUTs), use uridine diphosphate (UDP)-Glc as a substrate to modify EGF repeats and reside in the endoplasmic reticulum via C-terminal KDEL-like signals. In addition to O-glucosylation activity, POGLUTs can also perform protein O-xylosylation function, i.e., adding xylose (Xyl) from UDP-Xyl; however, both activities rely on residues of EGF repeats, active-site conformations of POGLUTs and sugar substrate concentrations in the ER. Impaired expression of POGLUTs has been associated with initiation and progression of human diseases such as limb-girdle muscular dystrophy, Dowling-Degos disease 4, acute myeloid leukemia, and hepatocytes and pancreatic dysfunction. POGLUTs have been found to alter the expression of cyclin-dependent kinase inhibitors (CDKIs), by affecting Notch or transforming growth factor-β1 signaling, and cause cell proliferation inhibition or induction depending on the particular cell types, which characterizes POGLUT's cell-dependent dual role. Except for a few downstream elements, the precise mechanisms whereby aberrant protein O-glucosylation causes diseases are largely unknown, leaving behind many questions that need to be addressed. This systemic review comprehensively covers literature to understand the O-glucosyltransferases with a focus on POGLUT1 structure and function, and their role in health and diseases. Moreover, this study also raises unanswered issues for future research in cancer biology, cell communications, muscular diseases, etc.

Changes in Protein Glycosylation in Head and Neck Squamous Cell Carcinoma

Glycosylation is an important posttranslational modification of proteins, and it has a profound influence on diverse life processes. An abnormal polysaccharide structure and mutation of the glycosylation pathway are closely correlated with human cancer progression. Glycoproteins such as EGFR, E-cadherin, CD44, PD-1/PD-L1, B7-H3 and Muc1 play important roles in the progression of head and neck squamous cell carcinoma (HNSCC), and their levels of glycosylation and changes in glycosyl structure are closely linked to HNSCC progression and malignant transformation. The regulation of protein glycosylation in HNSCC provides potential strategies to control cancer stem cell (CSC) subgroup expansion, epithelial-mesenchymal transition (EMT), tumor-related immunity escape and autophagy. Glycoproteins with altered glycosylation can be used as biomarkers for the early diagnosis, monitoring and prognostication of HNSCC. However, the glycobiology of cancer is still a new field that needs to be deeply studied, especially in HNSCC.

O-glycan recognition and function in mice and human cancers

Protein glycosylation represents a nearly ubiquitous post-translational modification, and altered glycosylation can result in clinically significant pathological consequences. Here we focus on O-glycosylation in tumor cells of mice and humans. O-glycans are those linked to serine and threonine (Ser/Thr) residues via N-acetylgalactosamine (GalNAc), which are oligosaccharides that occur widely in glycoproteins, such as those expressed on the surfaces and in secretions of all cell types. The structure and expression of O-glycans are dependent on the cell type and disease state of the cells. There is a great interest in O-glycosylation of tumor cells, as they typically express many altered types of O-glycans compared with untransformed cells. Such altered expression of glycans, quantitatively and/or qualitatively on different glycoproteins, is used as circulating tumor biomarkers, such as CA19-9 and CA-125. Other tumor-associated carbohydrate antigens (TACAs), such as the Tn antigen and sialyl-Tn antigen (STn), are truncated O-glycans commonly expressed by carcinomas on multiple glycoproteins; they contribute to tumor development and serve as potential biomarkers for tumor presence and stage, both in immunohistochemistry and in serum diagnostics. Here we discuss O-glycosylation in murine and human cells with a focus on colorectal, breast, and pancreatic cancers, centering on the structure, function and recognition of O-glycans. There are enormous opportunities to exploit our knowledge of O-glycosylation in tumor cells to develop new diagnostics and therapeutics.

Isolation and transcriptional characterization of mouse perivascular astrocytes

In the post-natal mammalian brain perivascular astrocytes (PAs) ensheath blood vessels to regulate their unique permeability properties known as the blood-brain barrier (BBB). Very little is known about PA-expressed genes and signaling pathways that mediate contact and communication with endothelial cells (ECs) to regulate BBB physiology. This is due, in part, to lack of suitable models to distinguish PAs from other astrocyte sub-populations in the brain. To decipher the unique biology of PAs, we used in vivo gene knock-in technology to fluorescently label these cells in the adult mouse brain followed by fractionation and quantitative single cell RNA sequencing. In addition, PAs and non-PAs were also distinguished with transgenic fluorescent reporters followed by gene expression comparisons using bulk RNA sequencing. These efforts have identified several genes and pathways in PAs with potential roles in contact and communication with brain ECs. These genes encode various extracellular matrix (ECM) proteins and adhesion receptors, secreted growth factors, and intracellular signaling enzymes. Collectively, our experimental data reveal a set of genes that are expressed in PAs with putative roles in BBB physiology.

Differential Labeling of Glycoproteins with Alkynyl Fucose Analogs

Fucosylated glycans critically regulate the physiological functions of proteins and cells. Alterations in levels of fucosylated glycans are associated with various diseases. For detection and functional modulation of fucosylated glycans, chemical biology approaches using fucose (Fuc) analogs are useful. However, little is known about how efficiently each unnatural Fuc analog is utilized by enzymes in the biosynthetic pathway of fucosylated glycans. We show here that three clickable Fuc analogs with similar but distinct structures labeled cellular glycans with different efficiency and protein specificity. For instance, 6-alkynyl (Alk)-Fuc modified O-Fuc glycans much more efficiently than 7-Alk-Fuc. The level of GDP-6-Alk-Fuc produced in cells was also higher than that of GDP-7-Alk-Fuc. Comprehensive in vitro fucosyltransferase assays revealed that 7-Alk-Fuc is commonly tolerated by most fucosyltransferases. Surprisingly, both protein O-fucosyltransferases (POFUTs) could transfer all Fuc analogs in vitro, likely because POFUT structures have a larger space around their Fuc binding sites. These findings demonstrate that labeling and detection of fucosylated glycans with Fuc analogs depend on multiple cellular steps, including conversion to GDP form, transport into the ER or Golgi, and utilization by each fucosyltransferase, providing insights into design of novel sugar analogs for specific detection of target glycans or inhibition of their functions.

The oncogenic role of Jagged1/Notch signaling in cancer

Aberrant activation of Notch signaling plays an oncogenic role in cancer development. Jagged1 (JAG1) is an important Notch ligand that triggers Notch signaling through cell-cell interactions. JAG1 overexpression has been reported in many different types of cancer and correlates with a poor clinical prognosis. JAG1/Notch signaling controls oncogenic processes in different cell types and cellular contexts. Furthermore, JAG1/Notch signaling cascades activate a number of oncogenic factors that regulate cellular functions such as proliferation, metastasis, drug-resistance, and angiogenesis. To suppress the severe toxicity of pan-Notch inhibitors, JAG1 is attracting increasing attention as a source of therapeutic targets for cancers. In this review, the oncogenic role of JAG1/Notch signaling in cancer is discussed, as well as implications of strategies to inhibit JAG1/Notch signaling activity.

Expression, purification, and glycosylation of epidermal growth factor-like repeat 27 from mouse NOTCH1

Notch receptors have large extracellular domains containing up to 36 tandem epidermal growth factor-like (EGF) repeats, which facilitate cell signaling by binding ligands on neighboring cells. Notch receptors play major roles in a variety of developmental processes by controlling cell fate decisions. Each EGF repeat consists of about 40 amino acids with 3 conserved disulfide bonds. Many of the EGF repeats are modified by O-linked fucose glycans, and more than half have calcium-binding sites, but the sequences of the EGF repeats vary giving distinct roles to each repeat. EGF repeat 27 (EGF27) from mouse NOTCH1 is modified with O-fucose and is 1 of 7 repeats that is differentially modified by specific Fringe enzymes, which are known to regulate NOTCH1 activation and ligand binding. To better understand the role of EGF27 in NOTCH1 function and regulation, the 3-dimensional structures of EGF27 and its glycoforms are being pursued. E. coli cells were used to produce EGF27 in sufficient quantities for nuclear magnetic resonance analysis. Previous attempts to express the repeat alone and refold the repeat under a steady redox environment were unsuccessful due to low yields and extensive mixed-disulfide bond cross-linking. A new strategy using a cleavable maltose binding protein fusion tag increased the solubility and yield of EGF27. With the fusion tag, EGF27 was refolded to produce the correct disulfide bond arrangement, which was verified enzymatically with the glycosyltransferases, Protein O-fucosyltransferase 1 (POFUT1) and Lunatic Fringe (LFNG).

Xylosyl Extension of O-Glucose Glycans on the Extracellular Domain of NOTCH1 and NOTCH2 Regulates Notch Cell Surface Trafficking

Biochemical and genetic studies have indicated that O-linked glycosylation such as O-glucose (Glc), fucose (Fuc), and N-acetylglucosamine (GlcNAc) is critical for Notch signaling; however, it is not fully understood how O-glycans regulate the Notch receptor function. Notch receptors are type-I transmembrane proteins with large extracellular domains (ECD), containing 29–36 epidermal growth factor-like (EGF) repeats. Here, we analyzed O-Glc glycans on NOTCH1 and NOTCH2 expressed in HEK293T cells using an Orbitrap Fusion mass spectrometer and successfully revealed the structures and stoichiometries of all 17 EGF repeats of NOTCH1 with the O-Glc consensus sequence (C1-X-S-X-(P/A)-C2), and 16 out of 17 EGF repeats of NOTCH2 with the same consensus sequence. High levels of O-Glc attachment and xylosyl elongation were detected on most NOTCH1 and NOTCH2 EGF repeats. When both glucoside xylosyltransferases, GXYLT1 and GXYLT2, responsible for the xylosyl elongation of O-glucose, were genetically deleted, the expression of endogenous NOTCH1 and NOTCH2 on the surface of HEK293T cells did not change, but the cell surface expression of overexpressed NOTCH1 and NOTCH2 decreased compared with that in the wild type cells. In vitro secretion assays consistently showed a reduced secretion of both the NOTCH1 and NOTCH2 ECDs in GXYLT1 and GXYLT2 double knockout cells compared with the wild type cells, suggesting a significant role of the elongation of O-Glc glycans on the Notch ECDs in the quality control of Notch receptors.

The cross-talk of NOTCH and GSK-3 signaling in colon and other cancers

The GSK-3 kinases, GSK-3α and GSK-3β, have a central role in regulating multiple cellular processes such as glycogen synthesis, insulin signaling, cell proliferation and apoptosis. GSK-3β is the most well studied, and was originally described for its role in regulating glycogen synthase. GSK-3β has been studied as a participant in the oncogenic process in a variety of cancers due to its intersection with the PTEN/PI3K/AKT and RAS/RAF/MEK/ERK pathways. Dysregulated signaling through the Notch family of receptors can also promote oncogenesis. Normal Notch receptor signaling regulates cell fate determination in stem cell pools. GSK-3β and Notch share similar targets such β-catenin and the WNT pathway. WNT and β-catenin are involved in several oncogenic processes including those of the colon. In addition, GSK-3β may directly regulate aspects of Notch signaling. This review describes how crosstalk between GSK-3β and Notch can promote oncogenesis, using colon cancer as the primary example.