Notch signalling: multifaceted role in development and disease

E3 ubiquitin ligase Deltex facilitates the expansion of Wingless gradient and antagonizes Wingless signaling through a conserved mechanism of transcriptional effector Armadillo/β-catenin degradation

The Wnt/Wg pathway controls myriads of biological phenomena throughout the development and adult life of all organisms across the phyla. Thus, an aberrant Wnt signaling is associated with a wide range of pathologies in humans. Tight regulation of Wnt/Wg signaling is required to maintain proper cellular homeostasis. Here, we report a novel role of E3 ubiquitin ligase Deltex in Wg signaling regulation. Drosophila dx genetically interacts with wg and its pathway components. Furthermore, Dx LOF results in a reduced spreading of Wg while its over-expression expands the diffusion gradient of the morphogen. We attribute this change in Wg gradient to the endocytosis of Wg through Dx which directly affects the short- and long-range Wg targets. We also demonstrate the role of Dx in regulating Wg effector Armadillo where Dx down-regulates Arm through proteasomal degradation. We also showed the conservation of Dx function in the mammalian system where DTX1 is shown to bind with β-catenin and facilitates its proteolytic degradation, spotlighting a novel step that potentially modulates Wnt/Wg signaling cascade.

Cysteine and glycine-rich protein 2 is crucial for maintaining the malignant phenotypes of gliomas through its action on Notch signalling cascade

Cysteine and glycine-rich protein 2 (CSRP2) is expressed differently in numerous cancers and plays a key role in carcinogenesis. However, the role of CSRP2 in glioma is unknown. This study sought to determine the expression profile and clinical significance of CSRP2 in glioma and explore its biological functions and mechanisms via lentivirus-mediated CSRP2 silencing experiments. Increased CSRP2 was frequently observed in gliomas, which was associated with clinicopathological characteristics and an unfavourable prognosis. Decreasing CSRP2 led to the suppression of malignant proliferation, metastasis and stemness in glioma cells while causing hypersensitivity to chemotherapeutic drugs. Mechanistic investigations revealed that CSRP2 plays a role in mediating the Notch signalling cascade. Silencing CSRP2 decreased the levels of Notch1, cleaved Notch1, HES1 and HEY1, suppressing the Notch signalling cascade. Reactivation of Notch markedly diminished the tumour-inhibiting effects of CSRP2 silencing on the malignant phenotypes of glioma cells. Notably, CSRP2-silencing glioma cells exhibited reduced potential in the formation of xenografts in nude mice in vivo, which was associated with an impaired Notch signalling cascade. These results showed that CSRP2 is overexpressed in glioma and has a crucial role in sustaining the malignant phenotypes of glioma, suggesting that targeting CSRP2 could be a promising strategy for glioma treatment.

Novel insight into FCSK-congenital disorder of glycosylation through a CRISPR-generated cell model

BACKGROUND

FCSK-congenital disorder of glycosylation (FCSK-CDG) is a recently discovered rare autosomal recessive genetic disorder with defective fucosylation due to mutations in the fucokinase encoding gene, FCSK. Despite the essential role of fucokinase in the fucose salvage pathway and severe multisystem manifestations of FCSK-CDG patients, it is not elucidated which cells or which types of fucosylation are affected by its deficiency.

METHODS

In this study, CRISPR/Cas9 was employed to construct an FCSK-CDG cell model and explore the molecular mechanisms of the disease by lectin flow cytometry and real-time PCR analyses.

RESULTS

Comparison of cellular fucosylation by lectin flow cytometry in the created CRISPR/Cas9 FCSK knockout and the same unedited cell lines showed no significant change in the amount of cell surface fucosylated glycans, which is consistent with the only documented previous study on different cell types. It suggests a probable effect of this disease on secretory glycoproteins. Investigating O-fucosylation by analysis of the NOTCH3 gene expression as a potential target revealed a significant decrease in the FCSK knockout cells compared with the same unedited ones, proving the effect of fucokinase deficiency on EGF-like repeats O-fucosylation.

CONCLUSION

This study expands insight into the FCSK-CDG molecular mechanism; to the best of our knowledge, it is the first research conducted to reveal a gene whose expression level alters due to this disease.

Neuromesodermal specification during head-to-tail body axis formation

The anterior-to-posterior (head-to-tail) body axis is extraordinarily diverse among vertebrates but conserved within species. Body axis development requires a population of axial progenitors that resides at the posterior of the embryo to sustain elongation and is then eliminated once axis extension is complete. These progenitors occupy distinct domains in the posterior (tail-end) of the embryo and contribute to various lineages along the body axis. The subset of axial progenitors with neuromesodermal competency will generate both the neural tube (the precursor of the spinal cord), and the trunk and tail somites (producing the musculoskeleton) during embryo development. These axial progenitors are called Neuromesodermal Competent cells (NMCs) and Neuromesodermal Progenitors (NMPs). NMCs/NMPs have recently attracted interest beyond the field of developmental biology due to their clinical potential. In the mouse, the maintenance of neuromesodermal competency relies on a fine balance between a trio of known signals: Wnt/β-catenin, FGF signalling activity and suppression of retinoic acid signalling. These signals regulate the relative expression levels of the mesodermal transcription factor Brachyury and the neural transcription factor Sox2, permitting the maintenance of progenitor identity when co-expressed, and either mesoderm or neural lineage commitment when the balance is tilted towards either Brachyury or Sox2, respectively. Despite important advances in understanding key genes and cellular behaviours involved in these fate decisions, how the balance between mesodermal and neural fates is achieved remains largely unknown. In this chapter, we provide an overview of signalling and gene regulatory networks in NMCs/NMPs. We discuss mutant phenotypes associated with axial defects, hinting at the potential significant role of lesser studied proteins in the maintenance and differentiation of the progenitors that fuel axial elongation.

Single-Cell Transcriptomic Analysis of Salivary Gland Endothelial Cells

Vascular endothelial cells have important tissue-specific functions in fibrosis and regeneration. In the salivary gland, endothelial cells are required for proper development, but their roles within adult glands are largely unknown. To identify ligand-receptor interactions between endothelial cells and other cell types that may be important during fibrosis and regeneration, we used a reversible ductal ligation injury. To induce injury, a clip was applied to the primary ducts for 14 d, and to induce a regenerative response, the clip was subsequently removed for 5 d. To identify endothelial cell-produced factors, we used single-cell RNA sequencing of stromal-enriched cells from adult female submandibular and sublingual salivary glands. Transcriptional profiles of homeostatic salivary gland endothelial cells were compared to endothelial cells of other organs. Salivary gland endothelial cells expressed many unique genes and displayed the highest overlap in gene expression with other fenestrated endothelial cells from the colon, small intestine, and kidney. Comparison of the 14-d ligated, mock-ligated, and 5-d deligated stromal-enriched transcripts and lineage tracing revealed that endothelial cells retain their identity following ligation and recovery from injury. CellChat and NATMI were used to predict changes in ligand-receptor interactions from endothelial cells to other cells in response to ligation and deligation. CellChat and NATMI predicted that after ligation, interactions with fibroblasts, epithelial cells, and glial cells were increased, and following deligation, interactions with pericyte, glia, fibroblasts, and immune cells were increased. Some of the highest-ranked interactions predicted in ligated compared to mock endothelial cells were between glial cells via Col4a2-Cd93 and Jag2-Notch1, as well as epithelial cells via Pecam1-Cd38, while in deligated compared to ligated endothelial cells, the top interactions were between fibroblasts via Ntf3-Ntrk2, glial cells via Hspg2-Itgb1, and pericytes via Jam2-F11r. Understanding salivary gland endothelial cell signaling will inform future endothelial cell-based regenerative therapies.

Epigenetically dysregulated NOTCH-Delta-HES signaling cascade can serve as a subtype classifier for acute lymphoblastic leukemia

The NOTCH-Delta-HES signaling cascade is regarded as a double-edged sword owing to its dual tumor-suppressor and oncogenic roles, in different cellular environments. In the T-cells, it supports leukemogenesis by promoting differentiation while in B-cells, it controls leukemogenesis by inhibiting early differentiation/inducing growth arrest in the lead to apoptosis. The present study was undertaken to assess if this bi-faceted behavior of NOTCH family can be exploited as a diagnostic biomarker or subtype classifier of acute lymphoblastic leukemia (ALL). In this pursuit, expression of seven NOTCH cascade genes was analyzed in bone marrow (BM) biopsy and blood plasma (BP) of pediatric ALL patients using quantitative PCR (qPCR). Further, promoter DNA methylation status of the differentially expressed genes (DEGs) was assessed by methylation-specific qMSP and validated through bisulphite amplicon sequencing. Whereas hypermethylation of JAG1, DLL1, and HES-2, HES-4, and HES-5 was observed in all patients, NOTCH3 was found hypermethylated specifically in Pre-B ALL cases while DLL4 in Pre-T ALL cases. Aberrant DNA methylation strongly correlated with downregulated gene expression, which restored at complete remission stage as observed in "follow-up/post-treatment" subjects. The subtype-specific ROC curve analysis and Kaplan-Meier survival analysis predicted a clinically applicable diagnostic and prognostic potential of the panel. Moreover, the logistic regression model (Pre-B vs Pre-T ALL) was found to be the best-fitted model (McFadden's R2 = 0.28, F1 measure = 0.99). Whether analyzed in BM-aspirates or blood plasma, the NOTCH epigenetic signatures displayed comparable results (p < 0.001), advocating the potential of NOTCH-Delta-HES cascade, as a subtype classifier, in minimally invasive diagnosis of ALL.

Metastasis and cancer associated fibroblasts: taking it up a NOTCH

Metastasis is the least understood aspect of cancer biology. 90% of cancer related deaths occur due extensive metastatic burden in patients. Apart from metastasizing cancer cells, the pro-tumorigenic and pro-metastatic role of the tumor stroma plays a crucial part in this complex process often leading to disease relapse and therapy resistance. Cellular signaling processes play a crucial role in the process of tumorigenesis and metastasis when aberrantly turned on, not just in the cancer cells, but also in the cells of the tumor microenvironment (TME). One of the most conserved pathways includes the Notch signaling pathway that plays a crucial role in the development and progression of many cancers. In addition to its well documented role in cancer cells, recent evidence suggests crucial involvement of Notch signaling in the stroma as well. This review aims to highlight the current findings focusing on the oncogenic role of notch signaling in cancer cells and the TME, with a specific focus on cancer associated fibroblasts (CAFs), which constitute a major part of the tumor stroma and are important for tumor progression. Recent efforts have focused on the development of anti-cancer and anti-metastatic therapies targeting TME. Understanding the importance of Notch signaling in the TME would help identify important drivers for stromal reprogramming, metastasis and importantly, drive future research in the effort to develop TME-targeted therapies utilizing Notch.

Regulation of miR-61 and col-19 via TGF-β and Notch signalling in Caenorhabditis elegans against Klebsiella aerogenes infection

Klebsiella aerogenes, previously known as Enterobacter aerogenes, is a gram-negative bacterium typically present in the gastrointestinal tract. While numerous studies reported the pathogenicity and drug resistance of this bacterium there remains a lack of comprehensive research on K. aerogenes induced alterations in the host cellular mechanisms. In this study, we identify a previously uncharacterized C. elegans miR-61 that defines an evolutionarily conserved miRNA important for development and innate immunity regulation through Notch and TGF-β signaling pathway. We employed C. elegans wild-type (N2) as well as mutant strains, such as TGF-β (sma-6) and notch-signaling pathway mutants (adm-4 and mir-61). Our results have demonstrated that the K. aerogenes infected mutants exhibited significantly reduced survival rate, reduced pharyngeal pumping, altered swimming and chemotactic behavior. Moreover, K. aerogenes affects the healthspan by increasing ROS level in the mutants. The gene expression analysis revealed that K. aerogenes upregulated egl-30, tph-1 and sod-1 in adm-4, mir-61 mutants not in sma-6. The in-silico analysis indicated an interaction between mir-61 and col-19, which was confirmed by the upregulation of miR-61 expression and the downregulation of col-19 in sma-6, adm-4, and wild-type strains. These findings suggest that C. elegans activates mir-61 and col-19 regulation through the Notch and TGF-β signaling pathway against K. aerogenes infection.

Lipid environment modulates processivity and kinetics of a presenilin homolog acting on multiple substrates in vitro

Intramembrane proteases (IPs) hydrolyze peptides in the lipid membrane. IPs participate in a number of cellular pathways including immune response and surveillance, and cholesterol biosynthesis, and they are exploited by viruses for replication. Despite their broad importance across biology, how activity is regulated in the cell to control protein maturation and release of specific bioactive peptides at the right place and right time remains largely unanswered, particularly for the intramembrane aspartyl protease (IAP) subtype. At a molecular biochemical level, different IAP homologs can cleave non-biological substrates, and there is no sequence recognition motif among the nearly 150 substrates identified for just one IAP, presenilin-1, the catalytic component of γ-secretase known for its involvement in the production of amyloid-β plaques associated with Alzheimer disease. Here we used gel-based assays combined with quantitative mass spectrometry and FRET-based kinetics assays to probe the cleavage profile of the presenilin homolog from the methanogen Methanoculleus marisnigri JR1 as a function of the surrounding lipid-mimicking environment, either detergent micelles or bicelles. We selected four biological IAP substrates that have not undergone extensive cleavage profiling previously, namely, the viral core protein of Hepatitis C virus, the viral core protein of Classical Swine Fever virus, the transmembrane segment of Notch-1, and the tyrosine receptor kinase ErbB4. Our study demonstrates a proclivity toward cleavage of substrates at positions of low average hydrophobicity and a consistent role for the lipid environment in modulating kinetic properties.

Notch Signaling in Insect Development: A Simple Pathway with Diverse Functions

Notch signaling is an evolutionarily conserved pathway which functions between adjacent cells to establish their distinct identities. Despite operating in a simple mechanism, Notch signaling plays remarkably diverse roles in development to regulate cell fate determination, organ growth and tissue patterning. While initially discovered and characterized in the model insect Drosophila melanogaster, recent studies across various insect species have revealed the broad involvement of Notch signaling in shaping insect tissues. This review focuses on providing a comprehensive picture regarding the roles of the Notch pathway in insect development. The roles of Notch in the formation and patterning of the insect embryo, wing, leg, ovary and several specific structures, as well as in physiological responses, are summarized. These results are discussed within the developmental context, aiming to deepen our understanding of the diversified functions of the Notch signaling pathway in different insect species.