Regulation of Notch signaling by E3 ubiquitin ligases

Notch signalling: multifaceted role in development and disease

Notch pathway is an evolutionarily conserved signalling system that operates to influence an astonishing array of cell fate decisions in different developmental contexts. Notch signalling plays important roles in many developmental processes, making it difficult to name a tissue or a developing organ that does not depend on Notch function at one stage or another. Thus, dysregulation of Notch signalling is associated with many developmental defects and various pathological conditions, including cancer. Although many recent advances have been made to reveal different aspects of the Notch signalling mechanism and its intricate regulation, there are still many unanswered questions related to how the Notch signalling pathway functions in so many developmental events. The same pathway can be deployed in numerous cellular contexts to play varied and critical roles in an organism's development and this is only possible because of the complex regulatory mechanisms of the pathway. In this review, we provide an overview of the mechanism and regulation of the Notch signalling pathway along with its multifaceted functions in different aspects of development and disease.

The First Defined Null Allele of the Notch Regulator, a Suppressor of Deltex: Uncovering Its Novel Roles in Drosophila melanogaster Oogenesis

Suppressor of deltex (Su(dx)) is a Drosophila melanogaster member of the NEDD4 family of the HECT domain E3 ubiquitin ligases. Su(dx) acts as a regulator of Notch endocytic trafficking, promoting Notch lysosomal degradation and the down-regulation of both ligand-dependent and ligand-independent signalling, the latter involving trafficking through the endocytic pathway and activation of the endo/lysosomal membrane. Mutations of Su(dx) result in developmental phenotypes in the Drosophila wing that reflect increased Notch signalling, leading to gaps in the specification of the wing veins, and Su(dx) functions to provide the developmental robustness of Notch activity to environmental temperature shifts. The full developmental functions of Su(dx) are unclear; however, this is due to a lack of a clearly defined null allele. Here we report the first defined null mutation of Su(dx), generated by P-element excision, which removes the complete open reading frame. We show that the mutation is recessive-viable, with the Notch gain of function phenotypes affecting wing vein and leg development. We further uncover new roles for Su(dx) in Drosophila oogenesis, where it regulates interfollicular stalk formation, egg chamber separation and germline cyst enwrapment by the follicle stem cells. Interestingly, while the null allele exhibited a gain in Notch activity during oogenesis, the previously described Su(dx)SP allele, which carries a seven amino acid in-frame deletion, displayed a Notch loss of function phenotypes and an increase in follicle stem cell turnover. This is despite both alleles displaying similar Notch gain of function in wing development. We attribute this unexpected context-dependent outcome of Su(dx)sp being due to the partial retention of function by the intact C2 and WW domain regions of the protein. Our results extend our understanding of the developmental role of Su(dx) in the tissue renewal and homeostasis of the Drosophila ovary and illustrate the importance of examining an allelic series of mutations to fully understand developmental functions.

Exposure to virgin and marine incubated microparticles of biodegradable and conventional polymers modulates the hepatopancreas transcriptome of Mytilus galloprovincialis

Biodegradable polymers have been proposed as an alternative to conventional plastics to mitigate the impact of marine litter, but the research investigating their toxicity is still in its infancy. This study evaluates the potential ecotoxicological effects of both virgin and marine-incubated microparticles (MPs), at environmentally relevant concentration (0.1 mg/l), made of different biodegradable polymers (Polycaprolactone, Mater-Bi, cellulose) and conventional polymers (Polyethylene) on Mytilus galloprovincialis by using transcriptomics. This approach is increasingly being used to assess the effects of pollutants on organisms, obtaining data on numerous biological pathways simultaneously. Whole hepatopancreas de novo transcriptome sequencing was performed, individuating 972 genes differentially expressed across experimental groups compared to the control. Through the comparative transcriptomic profiling emerges that the preponderant effect is attributable to the marine incubation of MPs, especially for incubated polycaprolactone (731 DEGs). Mater-Bi and cellulose alter the smallest number of genes and biological processes in the mussel hepatopancreas. All microparticles, regardless of their polymeric composition, dysregulated innate immunity, and fatty acid metabolism biological processes. These findings highlight the necessity of considering the interactions of MPs with the environmental factors in the marine ecosystem when performing ecotoxicological evaluations. The results obtained contribute to fill current knowledge gaps regarding the potential environmental impacts of biodegradable polymers.

Glycosylation: A new signaling paradigm for the neurovascular diseases

A wide range of life-threatening conditions with complicated pathogenesis involves neurovascular disorders encompassing Neurovascular unit (NVU) damage. The pathophysiology of NVU is characterized by several features including tissue hypoxia, stimulation of inflammatory and angiogenic processes, and the initiation of intricate molecular interactions, collectively leading to an elevation in blood-brain barrier permeability, atherosclerosis and ultimately, neurovascular diseases. The presence of compelling data about the significant involvement of the glycosylation in the development of diseases has sparked a discussion on whether the abnormal glycosylation may serve as a causal factor for neurovascular disorders, rather than being just recruited as a secondary player in regulating the critical events during the development processes like embryo growth and angiogenesis. An essential tool for both developing new anti-ischemic therapies and understanding the processes of ischemic brain damage is undertaking pre-clinical studies of neurovascular disorders. Together with the post-translational modification of proteins, the modulation of glycosylation and its enzymes implicates itself in several abnormal activities which are known to accelerate neuronal vasculopathy. Despite the failure of the majority of glycosylation-based preclinical and clinical studies over the past years, there is a significant probability to provide neuroprotection utilizing modern and advanced approaches to target abnormal glycosylation activity at embryonic stages as well. This article focuses on a variety of experimental evidence to postulate the interconnection between glycosylation and vascular disorders along with possible treatment options.

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.

N4BP1 mediates RAM domain-dependent notch signaling turnover during neocortical development

Notch signaling pathway activity, particularly fluctuations in the biologically active effector fragment NICD, is required for rapid and efficient dynamic regulation of proper fate decisions in stem cells. In this study, we identified NEDD4-binding protein 1 (N4BP1), which is highly expressed in the developing mouse cerebral cortex, as a negative modulator of Notch signaling dynamics in neural progenitor cells. Intriguingly, N4BP1 regulated NICD stability specifically after Notch1 S3 cleavage through ubiquitin-mediated degradation that depended on its RAM domain, not its PEST domain, as had been extensively and previously described. The CoCUN domain in N4BP1, particularly the "Phe-Pro" motif (862/863 amino acid), was indispensable for mediating NICD degradation. The Ring family E3 ligase Trim21 was, in contrast to other NEDD4 family members, required for N4BP1-regulated NICD degradation. Overexpression of N4BP1 in cortical neural progenitors promoted neural stem cell differentiation, whereas neural progenitor cells lacking N4BP1 were sensitized to Notch signaling, resulting in the maintenance of stem-like properties in neural progenitor cells and lower production of cortical neurons.

Unraveling the Complex Web of Mechanistic Regulation of Versatile NEDD4 Family by Non-Coding RNAs in Carcinogenesis and Metastasis: From Cell Culture Studies to Animal Models

Discoveries related to an intriguing feature of ubiquitination have prompted a detailed analysis of the ubiquitination patterns in malignant cells. How the "ubiquitinome" is reshaped during multistage carcinogenesis has garnered significant attention. Seminal studies related to the structural and functional characterization of NEDD4 (Neuronal precursor cell-expressed developmentally downregulated-4) have consolidated our understanding at a new level of maturity. Additionally, regulatory roles of non-coding RNAs have further complicated the complex interplay between non-coding RNAs and the members of NEDD4 family. These mechanisms range from the miRNA-mediated targeting of NEDD4 family members to the regulation of transcriptional factors for a broader range of non-coding RNAs. Additionally, the NEDD4-mediated degradation of different proteins is modulated by lncRNAs and circRNAs. The miRNA-mediated targeting of NEDD4 family members is also regulated by circRNAs. Tremendous advancements have been made in the identification of different substrates of NEDD4 family and in the comprehensive analysis of the molecular mechanisms by which various members of NEDD4 family catalyze the ubiquitination of substrates. In this review, we have attempted to summarize the multifunctional roles of the NEDD4 family in cancer biology, and how different non-coding RNAs modulate these NEDD4 family members in the regulation of cancer. Future molecular studies should focus on the investigation of a broader drug design space and expand the scope of accessible targets for the inhibition/prevention of metastasis.

Notch Partners in the Long Journey of T-ALL Pathogenesis

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological disease that arises from the oncogenic transformation of developing T cells during T-lymphopoiesis. Although T-ALL prognosis has improved markedly in recent years, relapsing and refractory patients with dismal outcomes still represent a major clinical issue. Consequently, understanding the pathological mechanisms that lead to the appearance of this malignancy and developing novel and more effective targeted therapies is an urgent need. Since the discovery in 2004 that a major proportion of T-ALL patients carry activating mutations that turn NOTCH1 into an oncogene, great efforts have been made to decipher the mechanisms underlying constitutive NOTCH1 activation, with the aim of understanding how NOTCH1 dysregulation converts the physiological NOTCH1-dependent T-cell developmental program into a pathological T-cell transformation process. Several molecular players have so far been shown to cooperate with NOTCH1 in this oncogenic process, and different therapeutic strategies have been developed to specifically target NOTCH1-dependent T-ALLs. Here, we comprehensively analyze the molecular bases of the cross-talk between NOTCH1 and cooperating partners critically involved in the generation and/or maintenance and progression of T-ALL and discuss novel opportunities and therapeutic approaches that current knowledge may open for future treatment of T-ALL patients.

Notch signaling pathway: a comprehensive prognostic and gene expression profile analysis in breast cancer

Breast cancer is a complex disease exhibiting a great degree of heterogeneity due to different molecular subtypes. Notch signaling regulates the differentiation of breast epithelial cells during normal development and plays a crucial role in breast cancer progression through the abnormal expression of the Notch up-and down-stream effectors. To date, there are only a few patient-centered clinical studies using datasets characterizing the role of Notch signaling pathway regulators in breast cancer; thus, we investigate the role and functionality of these factors in different subtypes using publicly available databases containing records from large studies. High-throughput genomic data and clinical information extracted from TCGA were analyzed. We performed Kaplan-Meier survival and differential gene expression analyses using the HALLMARK_NOTCH_SIGNALING gene set. To determine if epigenetic regulation of the Notch regulators contributes to their expression, we analyzed methylation levels of these factors using the TCGA HumanMethylation450 Array data. Notch receptors and ligands expression is generally associated with the tumor subtype, grade, and stage. Furthermore, we showed gene expression levels of most Notch factors were associated with DNA methylation rate. Modulating the expression levels of Notch receptors and effectors can be a potential therapeutic approach for breast cancer. As we outline herein, elucidating the novel prognostic and regulatory roles of Notch implicate this pathway as an essential mediator controlling breast cancer progression.

Notch signaling: A possible therapeutic target and its role in diabetic foot ulcers

BACKGROUND & AIM

Diabetic foot ulcers are major cause of lower limb amputations in the diabetic population. The major factors that play a role in causing the delay of the process of healing in diabetic foot ulcers broadly are decreased angiogenesis, reduced proliferation and migration of keratinocytes/fibroblasts. The typical wound healing process has four phases which are overlapping with each other thus making the healing even more complex. Hence it is essential to identify a therapeutic target that involves the regulation of the cellular factors involved in healing and helps to increase angiogenesis and can regulate all four phases accordingly.

METHOD

Literature review involved a search of the databases namely, PubMed, Cochrane, EMBASE, and Web of Science database. Articles were identified and retrieved that specifically dealt with Notch as a target in healing of wounds and its mechanism of action on various cells and phases of healing.

RESULTS

Notch is a cell surface receptor which interacts with transmembrane ligands of the nearby cells and is involved in cell proliferation, differentiation, cell fate and death. It is also involved in cell-to-cell communication, cell signaling, and various phases of development. There exist four known notch genes and five ligands which interact with notch proteins. Hyperglycemia plays a role in the activation of the notch receptor thus causing the release of inflammatory mediators via macrophages. As notch can regulate macrophage-mediated inflammation it can serve as a therapeutic target for diabetic foot ulcers.

CONCLUSION

This review focuses on the effect of notch on various cell mediators and phases of diabetic wound healing and deals with how notch activation or inhibition can serve as a potential therapeutic target for healing diabetic foot ulcers.

"A fly appeared": sable, a classic Drosophila mutation, maps to Yippee, a gene affecting body color, wings, and bristles

Insect body color is an easily assessed and visually engaging trait that is informative on a broad range of topics including speciation, biomaterial science, and ecdysis. Mutants of the fruit fly Drosophila melanogaster have been an integral part of body color research for more than a century. As a result of this long tenure, backlogs of body color mutations have remained unmapped to their genes, all while their strains have been dutifully maintained, used for recombination mapping, and part of genetics education. Stemming from a lesson plan in our undergraduate genetics class, we have mapped sable1, a dark body mutation originally described by Morgan and Bridges, to Yippee, a gene encoding a predicted member of the E3 ubiquitin ligase complex. Deficiency/duplication mapping, genetic rescue, DNA and cDNA sequencing, RT-qPCR, and 2 new CRISPR alleles indicated that sable1 is a hypomorphic Yippee mutation due to an mdg4 element insertion in the Yippee 5'-UTR. Further analysis revealed additional Yippee mutant phenotypes including curved wings, ectopic/missing bristles, delayed development, and failed adult emergence. RNAi of Yippee in the ectoderm phenocopied sable body color and most other Yippee phenotypes. Although Yippee remains functionally uncharacterized, the results presented here suggest possible connections between melanin biosynthesis, copper homeostasis, and Notch/Delta signaling; in addition, they provide insight into past studies of sable cell nonautonomy and of the genetic modifier suppressor of sable.

Cleaved Delta like 1 intracellular domain regulates neural development via Notch signal-dependent and -independent pathways

Notch-Delta signaling regulates many developmental processes, including tissue homeostasis and maintenance of stem cells. Upon interaction of juxtaposed cells via Notch and Delta proteins, intracellular domains of both transmembrane proteins are cleaved and translocate to the nucleus. Notch intracellular domain activates target gene expression; however, the role of the Delta intracellular domain remains elusive. Here, we show the biological function of Delta like 1 intracellular domain (D1ICD) by modulating its production. We find that the sustained production of D1ICD abrogates cell proliferation but enhances neurogenesis in the developing dorsal root ganglia (DRG), whereas inhibition of D1ICD production promotes cell proliferation and gliogenesis. D1ICD acts as an integral component of lateral inhibition mechanism by inhibiting Notch activity. In addition, D1ICD promotes neurogenesis in a Notch signaling-independent manner. We show that D1ICD binds to Erk1/2 in neural crest stem cells and inhibits the phosphorylation of Erk1/2. In summary, our results indicate that D1ICD regulates DRG development by modulating not only Notch signaling but also the MAP kinase pathway.

Targeting Notch4 in Cancer: Molecular Mechanisms and Therapeutic Perspectives

The dysregulation of Notch signaling is found in many cancers and is closely related to cancer progression. As an important Notch receptor, abnormal Notch4 expression affects several tumor-cell behaviors, including stemness, the epithelial-mesenchymal transition, radio/chemoresistance and angiogenesis. In order to inhibit the oncogenic effects of Notch4 activation, several methods for targeting Notch4 signaling have been proposed. In this review, we summarize the known molecular mechanisms through which Notch4 affects cancer progression. Finally, we discuss potential Notch4-targeting therapeutic strategies as a reference for future research.

Revisiting Ehrlichia ruminantium Replication Cycle Using Proteomics: The Host and the Bacterium Perspectives

The Rickettsiales Ehrlichia ruminantium, the causal agent of the fatal tick-borne disease Heartwater, induces severe damage to the vascular endothelium in ruminants. Nevertheless, E. ruminantium-induced pathobiology remains largely unknown. Our work paves the way for understanding this phenomenon by using quantitative proteomic analyses (2D-DIGE-MS/MS, 1DE-nanoLC-MS/MS and biotin-nanoUPLC-MS/MS) of host bovine aorta endothelial cells (BAE) during the in vitro bacterium intracellular replication cycle. We detect 265 bacterial proteins (including virulence factors), at all time-points of the E. ruminantium replication cycle, highlighting a dynamic bacterium–host interaction. We show that E. ruminantium infection modulates the expression of 433 host proteins: 98 being over-expressed, 161 under-expressed, 140 detected only in infected BAE cells and 34 exclusively detected in non-infected cells. Cystoscape integrated data analysis shows that these proteins lead to major changes in host cell immune responses, host cell metabolism and vesicle trafficking, with a clear involvement of inflammation-related proteins in this process. Our findings led to the first model of E. ruminantium infection in host cells in vitro, and we highlight potential biomarkers of E. ruminantium infection in endothelial cells (such as ROCK1, TMEM16K, Albumin and PTPN1), which may be important to further combat Heartwater, namely by developing non-antibiotic-based strategies.