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A model of Notch signalling control of angiogenesis: Evidence of a role for Notch ligand heterodimerization.

The ubiquitous Notch receptor signalling network is essential for tissue growth and maintenance. Operationally, receptor activity is regulated by two principal, counterposed mechanisms: intercellular Notch transactivation triggered by interactions between receptors and ligands expressed in neighbouring cells; intracellular cis inhibition mediated by ligands binding to receptors expressed in the same cell. Moreover, different Notch receptor/ligand combinations are known to elicit distinct molecular and cellular responses, and together, these phenomena determine the strength, the duration and the specificity of Notch receptor signalling. To date, it has been assumed that these processes involve discrete ligand homomers and not heteromeric complexes composed of more than one ligand species. In this study, we explore the molecular basis of the opposing actions of the Notch ligands, DLL4 and JAG1, which control angiogenic sprouting. Through a combination of experimental approaches and mathematical modelling, we provide evidence that two mechanisms could underpin this process: 1) DLL4 rather than JAG1 induces efficient Notch1 receptor transactivation; 2) JAG1 directly blocks DLL4-dependent cis-inhibition of Notch signalling through the formation of a JAG1/DLL4 complex. We propose a new model of Notch signalling that recapitulates the formation of tip and stalk cells, which is necessary for sprouting angiogenesis.

Signal Transduction

Somatic mutations reveal hyperactive Notch signaling in prurigo nodularis.

Prurigo nodularis (PN) is a chronic inflammatory skin disease characterized by pruritic skin nodules of unknown etiology. Little is known about genetic changes in PN pathogenesis, particularly somatic events, which are often implicated in inflammatory conditions. We thus performed whole-exome sequencing on 54 lesional and nonlesional skin biopsies from 17 patients with PN and 10 patients with atopic dermatitis (AD) for comparison. Somatic mutational analysis revealed that PN lesional skin harbors recurrent somatic mutations in fibrotic, neurotropic, and cancer-associated genes that are absent in adjacent PN nonlesional skin. Nonsynonymous mutations were most frequently present in NOTCH1 and the Notch signaling pathway, a key regulator of cellular proliferation and tissue fibrosis. In contrast, NOTCH1 mutations were absent in AD. Somatic copy-number analysis, combined with expression data, identified recurrently deleted and downregulated genes in PN lesional skin, which are associated with axonal guidance and extension. Follow-up immunofluorescence validation demonstrated increased NOTCH1 expression in PN lesional skin fibroblasts and increased Notch signaling in PN lesional dermis. Finally, a multicenter analysis revealed increased risk of NOTCH1-associated diseases in patients with PN. In characterizing the somatic landscape of PN, this study highlights the potential role of Notch pathway dysregulation in PN pathogenesis and fibrosis.

Humans

A case of congenital heart defects and familial exudative vitreoretinopathy caused by activation of a cryptic splice donor in NOTCH1.

BACKGROUND: NOTCH1 is associated with two disorders of vascular development, Adams-Oliver Syndrome 5 (AOS5) and aortic valve disease 1 (AOVD1). Here we report a disease-causing variant in NOTCH1 that has a previously undemonstrated effect on splicing. Additionally, we found that the proband has the optic phenotype of familial exudative vitreoretinopathy (FEVR) which has been reported for probands with pathogenic variants in genes in the notch signaling pathway, but never for NOTCH1. CASE PRESENTATION: The proband presented with a ventricular septal defect, pulmonic stenosis, and ocular findings consistent with familial exudative vitreoretinopathy (FEVR), which NOTCH1 has not been associated with to date. Trio exome sequencing identified a paternally inherited variant of uncertain significance in NOTCH1:c.2153 A > G. We assessed the variant's effect using RT-PCR, finding an increased use of a cryptic donor compared to the control. On this basis, we were able to re-classify this variant as pathogenic. CONCLUSIONS: We expand the phenotypic spectrum of NOTCH1 and contribute to the building evidence that variants in NOTCH1 cause a spectrum of disorders of vascular development.

Humans

NOTCH1 acts as a tumor suppressor that induces early differentiation in head and neck cancer.

Inactivating NOTCH1 mutations in head and neck squamous cell carcinoma (HNSCC) were described over a decade ago, suggesting a tumor suppressor function - unlike its oncogenic role in other tumors. Today, much debate persists regarding a putative oncogenic role in HNSCC as well, with reports that NOTCH1 signaling drives tumor growth and a cancer stem cell (CSC) phenotype. In this work, comprehensive experiments unequivocally demonstrate that NOTCH1 is a tumor suppressor in HNSCC regardless of mutation or activation status and that it reduces CSC frequency. We developed a signature of NOTCH1 activation showing the pathway is associated with very early differentiation, an altered tumor microenvironment, and better prognosis. Clarifying whether NOTCH1 occasionally functions as an oncogenic driver in HNSCC is crucial to prognosis and personalized therapy. The results presented unify the field, reconcile conflicting data, and provide critical insights into the biological and clinical significance of NOTCH1, with broader implications in other squamous carcinomas with NOTCH1 mutations.

Receptor, Notch1

Transcriptional activation of regenerative hematopoiesis via microenvironmental sensing.

Transition between activation and quiescence states in hematopoietic stem and progenitor cells (HSPCs) is tightly governed by cell-intrinsic means and microenvironmental co-adaptation. Although this balance is fundamental for lifelong hematopoiesis and immunity, the underlying molecular mechanisms remain poorly defined. Multimodal analysis divulging differential transcriptional activity between distinct HSPC states indicates the presence of Fli-1 transcription factor binding motif in activated hematopoietic stem cells. We reveal that Fli-1 activity is essential during regenerative hematopoiesis in mice. Fli-1 directs activation programs while priming cellular sensory and output machineries, enabling HSPCs co-adoptability with a stimulated vascular niche through propagation of niche-derived angiocrine Notch1 signaling. Constitutively induced Notch1 signaling is sufficient to recuperate functional hematopoietic stem cells impairments in the absence of Fli-1, without leukemic transformation. Applying FLI-1 transient modified-mRNA transduction into latent adult human mobilized HSPCs, enables their niche-mediated expansion and superior engraftment capacities. Thus, decryption of stem cell activation programs offers valuable insights for immunological regenerative medicine.

Animals

Mechanisms by which carbamoylated high-density lipoprotein (C-HDL) promotes calcific aortic valve disease and exploration of potential targeted therapies.

Calcific aortic valve disease (CAVD) is a progressive fibrocalcific illness for which no effective pharmaceutical treatment exists. This study investigated whether carbamoylated high-density lipoprotein (C-HDL), a defective type of HDL that can develop during inflammation, contributes to CAVD progression and the involved molecular pathways. Male ApoE-/- mice were divided into three groups: CAVD model, cyanate-treated, and inhibitor, and analyzed after 12 weeks. C57BL/6 mice on a regular diet served as blank controls. Serum paraoxonase-1 (PON1), aortic valve calcification, cluster of differentiation 31 (CD31), phosphorylated nuclear factor kappa B p65 (p-p65), NOTCH receptor 1 (NOTCH1), and runt-related transcription factor 2 (RUNX2) were evaluated. In parallel, using RNA sequencing (RNA-seq), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, protein-protein interaction (PPI) network analysis, and quantitative real-time polymerase chain reaction. Cyanate treatment reduced serum PON1 levels, increased von Kossa-positive calcium deposition, and raised CD31, p-p65, NOTCH1, and RUNX2 levels compared with the model group, but Gly partially corrected these effects. Transcriptomic research identified 270 C-HDL-associated differentially expressed genes (DEGs) enriched in pathways associated with inflammatory signaling and NF-κB activity. Five potential hub genes (BIRC6, PIK3R1, ATM, IFIH1, and DDX58) were discovered and verified using qRT-PCR. These data show that C-HDL may accelerate CAVD by disrupting valve endothelial homeostasis and stimulating inflammatory signaling, and they identify potential molecular targets for future functional validation.

bioinformatics

Genomic landscape of hepatocellular carcinoma in Egyptian patients by whole exome sequencing.

BACKGROUND: Hepatocellular carcinoma (HCC) is the most common primary liver cancer. Chronic hepatitis and liver cirrhosis lead to accumulation of genetic alterations driving HCC pathogenesis. This study is designed to explore genomic landscape of HCC in Egyptian patients by whole exome sequencing. METHODS: Whole exome sequencing using Ion Torrent was done on 13 HCC patients, who underwent surgical intervention (7 patients underwent living donor liver transplantation (LDLT) and 6 patients had surgical resection}. RESULTS: Mutational signature was mostly S1, S5, S6, and S12 in HCC. Analysis of highly mutated genes in both HCC and Non-HCC revealed the presence of highly mutated genes in HCC (AHNAK2, MUC6, MUC16, TTN, ZNF17, FLG, MUC12, OBSCN, PDE4DIP, MUC5b, and HYDIN). Among the 26 significantly mutated HCC genes-identified across 10 genome sequencing studies-in addition to TCGA, APOB and RP1L1 showed the highest number of mutations in both HCC and Non-HCC tissues. Tier 1, Tier 2 variants in TCGA SMGs in HCC and Non-HCC (TP53, PIK3CA, CDKN2A, and BAP1). Cancer Genome Landscape analysis revealed Tier 1 and Tier 2 variants in HCC (MSH2) and in Non-HCC (KMT2D and ATM). For KEGG analysis, the significantly annotated clusters in HCC were Notch signaling, Wnt signaling, PI3K-AKT pathway, Hippo signaling, Apelin signaling, Hedgehog (Hh) signaling, and MAPK signaling, in addition to ECM-receptor interaction, focal adhesion, and calcium signaling. Tier 1 and Tier 2 variants KIT, KMT2D, NOTCH1, KMT2C, PIK3CA, KIT, SMARCA4, ATM, PTEN, MSH2, and PTCH1 were low frequency variants in both HCC and Non-HCC. CONCLUSION: Our results are in accordance with previous studies in HCC regarding highly mutated genes, TCGA and specifically enriched pathways in HCC. Analysis for clinical interpretation of variants revealed the presence of Tier 1 and Tier 2 variants that represent potential clinically actionable targets. The use of sequencing techniques to detect structural variants and novel techniques as single cell sequencing together with multiomics transcriptomics, metagenomics will integrate the molecular pathogenesis of HCC in Egyptian patients.

Humans

Transcriptomic insights into the coordinated regulation of signaling, apoptosis, immunity, and metabolism during Sinonovacula constricta larval metamorphosis.

Metamorphosis is a critical ontogenetic transition for marine bivalves, marking the shift from planktonic to benthic lifestyles, where successful transformation dictates survival. The razor clam Sinonovacula constricta is economically important; however, low larval metamorphosis rates remain a major bottleneck in seedling production. To elucidate the mechanisms governing this process, we performed a comparative transcriptome analysis of S. constricta larvae at pre- and post-metamorphosis stages using Illumina sequencing. A total of 3701 differentially expressed genes (DEGs) were identified, including 3254 up-regulated and 447 down-regulated genes. Functional annotation of the respective top 20 significantly up-regulated and down-regulated DEGs indicated their potential pivotal roles in signal transduction (e.g., up-regulated: CAV1, CHRNA2; down-regulated: APP, NOTCH1), cellular proliferation and differentiation (e.g., up-regulated: TUBA, EGF1; down-regulated: KIF23, TTC25), transcriptional and epigenetic regulation (e.g., up-regulated: NFIL3; down-regulated: OVO, HMX1), substance transport (e.g., up-regulated: LRP2, LRP1B; down-regulated: SLC51A, Slc33a1), substance metabolism (e.g., up-regulated: CPK3, CYP26A1; down-regulated: RDMT1, ADAC), immunomodulation (e.g., up-regulated: CPN2, CRISP2), and protein homeostasis (e.g., up-regulated: HSP27, NAS-27). Functional enrichment analysis further revealed that DEGs were significantly enriched in pathways related to signal transduction and developmental regulation (e.g., Ras, TNF), cell death and homeostasis (e.g., apoptosis), immune responses (e.g., Toll-like receptor), energy metabolism (e.g., lipid), cardiovascular related (e.g., Fluid shear stress), cell junction and architecture (e.g., Tight junction), and infectious disease (e.g., measles). These results suggest a synergistic interplay between signaling, apoptosis, immunity, and metabolism during S. constricta metamorphosis. This study advances our understanding of marine bivalve metamorphosis and offers candidate genes for further mechanistic studies.

Animals

Multidimensional Proteomics Reveals the Pro-apoptotic Mechanism of Platycodin D: Targeting RFC4 to Regulate the Notch Signaling Axis in Non-Small Cell Lung Cancer.

Platycodin D (PD), a major bioactive saponin isolated from the traditional Chinese medicine Platycodon grandiflorus, has shown promising therapeutic potential against non-small cell lung cancer (NSCLC). However, the functional mechanisms of PD in NSCLC progression remains unclear. This study aimed to explore the pharmacological mechanism of PD against NSCLC. Thermal proteome profiling approach, molecular docking, cellular thermal shift assay and peptide-centric local stability assay were employed to identify the potential binding target of PD. Subsequent Western Blot and immunoprecipitation-Western Blot experiments were conducted to investigate the downstream signaling pathways of the target. Furthermore, proteomic and ubiquitinomic profiling of PD-treated cells were performed to investigate its functions on global. replication factor C subunit 4 (RFC4) was identified as a potential binding target of PD by thermal proteome profiling and their binding sites were further exposed by peptide-centric local stability assay. PD-RFC4 complex promotes the degradation of Notch1 and Notch3 by reducing nuclear entry of their domains. Compared with control treatment, the differentially expressed proteins induced by PD were found to be primarily involved in ferroptosis, ubiquitination, platinum drug resistance, and ribosome-related processes. The ubiquitin proteome analysis revealed that proteins associated with the Notch pathway underwent ubiquitin modifications. PD binds to RFC4 and inhibits its activity, leading to downregulation of the Notch signaling pathway, ultimately triggering cancer cell apoptosis. PD is a natural product with potential therapeutic value for NSCLC.

Saponins