Regulated proteolysis of NOTCH2 and NOTCH3 receptors by ADAM10 and presenilins

The Abelson kinase and the Nedd4 family E3 ligases co-regulate Notch trafficking to limit signaling

Precise output from the conserved Notch signaling pathway governs a plethora of cellular processes and developmental transitions. Unlike other pathways that use a cytoplasmic relay, the Notch cell surface receptor transduces signaling directly to the nucleus, with endocytic trafficking providing critical regulatory nodes. Here we report that the cytoplasmic tyrosine kinase Abelson (Abl) facilitates Notch internalization into late endosomes/multivesicular bodies (LEs), thereby limiting signaling output in both ligand-dependent and -independent contexts. Abl phosphorylates the PPxY motif within Notch, a molecular target for its degradation via Nedd4 family ubiquitin ligases. We show that Su(dx), a family member, mediates the Abl-directed LE regulation of Notch via the PPxY, while another family member, Nedd4Lo, contributes to Notch internalization into LEs through both PPxY-dependent and -independent mechanisms. Our findings demonstrate how a network of posttranslational modifiers converging at LEs cooperatively modulates Notch signaling to ensure the precision and robustness of its cellular and developmental functions.

Signaling pathways and molecular mechanisms involved in the onset and progression of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL); a focus on Notch3 signaling

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an autosomal-dominantly inherited cerebral small-vessel disease (SVD). CADASIL has diverse clinical features such as migraine with aura, dementia, and recurrent strokes, and is caused by a pathogenic mutation in the NOTCH3 gene which encodes a transmembrane receptor found in smooth muscle cells of small arteries and pericytes of brain capillaries. Pathogenic mutations alter the number of cysteine residues in the extracellular domain of NOTCH3, leading to the abnormal accumulation of granular osmiophilic material in the vessels of affected individuals. In addition, potential signaling pathways, such as transforming growth factor beta (TGF-β), may be involved in pathogenesis of the disease. This review aims to elucidate these mechanisms, particularly NOTCH3, in the context of CADASIL pathogenesis, providing insight into the role of NOTCH3 signaling and discussing the significance of these pathways for potential future therapeutic interventions in CADASIL patients.

Tetraspanins 10 and 15 support Venezuelan equine encephalitis virus replication in astrocytoma cells

Tetraspanins (Tspans) are transmembrane proteins that coordinate life cycle steps of viruses from distinct families. Here, we identify the human Tspan10 and Tspan15, both members of the TspanC8 subfamily, as replication factors for alphavirus Venezuelan equine encephalitis virus (VEEV) in astrocytoma cells. Pharmacological inhibition and small interfering RNA (siRNA)-mediated silencing of TspanC8 interactor a disintegrin and metalloproteinase 10 (ADAM10) reduced VEEV infection. Silencing of Tspan10, Tspan15, and ADAM10 did not affect VEEV entry but diminished viral genome replication. We report that Tspan10 is important for VEEV infection of several cell lines, while silencing of Tspan15 diminishes infection with several alphaviruses, but not flaviviruses, in astrocytoma cells. Conversely, we demonstrate that siRNA-mediated silencing of Tspan14, another member of the TspanC8 family, enhances infection with lentiviral pseudoparticles harbouring the envelope proteins of VEEV, identifying it as a restriction factor for VEEV entry. Silencing of ADAM10/Tspan15 substrate neuronal (N)-cadherin reduced VEEV infectivity, suggesting potential roles of ADAM10 substrates in VEEV infection. In sum, our study identifies three TspanC8s and ADAM10 as important modulators of VEEV infectivity.

Traumatic brain injury causes early aggregation of beta-amyloid peptides and NOTCH3 reduction in vascular smooth muscle cells of leptomeningeal arteries

Traumatic brain injury (TBI) often leads to impaired regulation of cerebral blood flow, which may be caused by pathological changes of the vascular smooth muscle cells (VSMCs) in the arterial wall. Moreover, these cerebrovascular changes may contribute to the development of various neurodegenerative disorders such as Alzheimer's-like pathologies that include amyloid beta aggregation. Despite its importance, the pathophysiological mechanisms responsible for VSMC dysfunction after TBI have rarely been evaluated. Here, we show that acute human TBI resulted in early pathological changes in leptomeningeal arteries, closely associated with a decrease in VSMC markers such as NOTCH3 and alpha smooth muscle actin (α-SMA).These changes coincided with increased aggregation of variable-length amyloid peptides including Aβ1-40/42, Aβ1-16, and β-secretase-derived fragment (βCTF) (C99) caused by altered processing of amyloid precursor protein (APP) in VSMCs. The aggregation of Aβ1-40/42 peptides were also observed in the leptomeningeal arteries of young TBI patients. These pathological changes also included higher β-secretase (BACE1) when compared to α-secretase A Disintegrin And Metalloprotease 10 (ADAM10) expression in the leptomeningeal arteries, plausibly caused by hypoxia and oxidative stress as shown using human VSMCs in vitro. Importantly, BACE1 inhibition not only restored NOTCH3 signalling but also normalized ADAM10 levels in vitro. Furthermore, we found reduced ADAM10 activity and decreased NOTCH3, along with increased βCTF (C99) levels in mice subjected to an experimental model of TBI. This study provides evidence of early post-injury changes in VSMCs of leptomeningeal arteries that can contribute to vascular dysfunction and exacerbate secondary injury mechanisms following TBI.

Diversity in Notch ligand-receptor signaling interactions

The Notch signaling pathway uses families of ligands and receptors to transmit signals to nearby cells. These components are expressed in diverse combinations in different cell types, interact in a many-to-many fashion, both within the same cell (in cis) and between cells (in trans), and their interactions are modulated by Fringe glycosyltransferases. A fundamental question is how the strength of Notch signaling depends on which pathway components are expressed, at what levels, and in which cells. Here, we used a quantitative, bottom-up, cell-based approach to systematically characterize trans-activation, cis-inhibition, and cis-activation signaling efficiencies across a range of ligand and Fringe expression levels in Chinese hamster and mouse cell lines. Each ligand (Dll1, Dll4, Jag1, and Jag2) and receptor variant (Notch1 and Notch2) analyzed here exhibited a unique profile of interactions, Fringe dependence, and signaling outcomes. All four ligands were able to bind receptors in cis and in trans, and all ligands trans-activated both receptors, although Jag1-Notch1 signaling was substantially weaker than other ligand-receptor combinations. Cis-interactions were predominantly inhibitory, with the exception of the Dll1- and Dll4-Notch2 pairs, which exhibited cis-activation stronger than trans-activation. Lfng strengthened Delta-mediated trans-activation and weakened Jagged-mediated trans-activation for both receptors. Finally, cis-ligands showed diverse cis-inhibition strengths, which depended on the identity of the trans-ligand as well as the receptor. The map of receptor-ligand-Fringe interaction outcomes revealed here should help guide rational perturbation and control of the Notch pathway.

A novel lineage-tracing tool reveals that hypoxic tumor cells drive tumor relapse after radiotherapy

PURPOSE

Tumor hypoxia imposes a main obstacle to the efficacy of anti-cancer therapy. Understanding the cellular dynamics of individual hypoxic cells before, during and post-treatment has been hampered by the technical inability to identify and trace these cells over time.

METHODS AND MATERIALS

Here, we present a novel lineage-tracing reporter for hypoxic cells based on the conditional expression of a HIF1a-CreERT2-UnaG biosensor that can visualize hypoxic cells in a time-dependent manner and trace the fate of hypoxic cells over time. We combine this system with multiphoton microscopy, flow cytometry, and immunofluorescence to characterize the role of hypoxic cells in tumor relapse after irradiation in H1299 tumor spheroids and in vivo xenografts.

RESULTS

We validate the reporter in monolayer cultures and we show that tagged cells colocalize in spheroids and human tumor xenografts with the hypoxic marker pimonidazole. We found that irradiation of H1299-HIFcreUnaG spheroids leads to preferential outgrowth of cells from the hypoxic core. Similarly, in xenografts tumors, although initially UnaG-positive-cells coincide with pimonidazole-positive tumor areas and they are merely quiescent, upon irradiation UnaG-positive cells enrich in regrowing tumors and are mainly proliferative.

CONCLUSIONS

Collectively, our data provide clear evidence that the hypoxic cells drive tumor relapse after irradiation.

Diversity in Notch ligand-receptor signaling interactions

The Notch signaling pathway uses families of ligands and receptors to transmit signals to nearby cells. These components are expressed in diverse combinations in different cell types, interact in a many-to-many fashion, both within the same cell (in cis) and between cells (in trans), and their interactions are modulated by Fringe glycosyltransferases. A fundamental question is how the strength of Notch signaling depends on which pathway components are expressed, at what levels, and in which cells. Here, we used a quantitative, bottom-up, cell-based approach to systematically characterize trans-activation, cis-inhibition, and cis-activation signaling efficiencies across a range of ligand and Fringe expression levels in two mammalian cell types. Each ligand (Dll1, Dll4, Jag1, and Jag2) and receptor variant (Notch1 and Notch2) analyzed here exhibited a unique profile of interactions, Fringe-dependence, and signaling outcomes. All four ligands were able to bind receptors in cis and in trans, and all ligands trans-activated both receptors, although Jag1-Notch1 signaling was substantially weaker than other ligand-receptor combinations. Cis-interactions were predominantly inhibitory, with the exception of the Dll1- and Dll4-Notch2 pairs, which exhibited cis-activation stronger than trans-activation. Lfng strengthened Delta-mediated trans-activation and weakened Jagged-mediated trans-activation for both receptors. Finally, cis-ligands showed diverse cis-inhibition strengths, which depended on the identity of the trans-ligand as well as the receptor. The map of receptor-ligand-Fringe interaction outcomes revealed here should help guide rational perturbation and control of the Notch pathway.

Notch signaling regulates UNC5B to suppress endothelial proliferation, migration, junction activity, and retinal plexus branching

Notch signaling guides vascular development and function by regulating diverse endothelial cell behaviors, including migration, proliferation, vascular density, endothelial junctions, and polarization in response to flow. Notch proteins form transcriptional activation complexes that regulate endothelial gene expression, but few of the downstream effectors that enable these phenotypic changes have been characterized in endothelial cells, limiting our understanding of vascular Notch activities. Using an unbiased screen of translated mRNA rapidly regulated by Notch signaling, we identified novel in vivo targets of Notch signaling in neonatal mouse brain endothelium, including UNC5B, a member of the netrin family of angiogenic-regulatory receptors. Endothelial Notch signaling rapidly upregulates UNC5B in multiple endothelial cell types. Loss or gain of UNC5B recapitulated specific Notch-regulated phenotypes. UNC5B expression inhibited endothelial migration and proliferation and was required for stabilization of endothelial junctions in response to shear stress. Loss of UNC5B partially or wholly blocked the ability of Notch activation to regulate these endothelial cell behaviors. In the developing mouse retina, endothelial-specific loss of UNC5B led to excessive vascularization, including increased vascular outgrowth, density, and branchpoint count. These data indicate that Notch signaling upregulates UNC5B as an effector protein to control specific endothelial cell behaviors and inhibit angiogenic growth.

Combinatorial expression motifs in signaling pathways

In animal cells, molecular pathways often comprise families of variant components, such as ligands or receptors. These pathway components are differentially expressed by different cell types, potentially tailoring pathway function to cell context. However, it has remained unclear how pathway expression profiles are distributed across cell types and whether similar profiles can occur in dissimilar cell types. Here, using single-cell gene expression datasets, we identified pathway expression motifs, defined as recurrent expression profiles that are broadly distributed across diverse cell types. Motifs appeared in core pathways, including TGF-β, Notch, Wnt, and the SRSF splice factors, and involved combinatorial co-expression of multiple components. Motif usage was weakly correlated between pathways in adult cell types and during dynamic developmental transitions. Together, these results suggest a mosaic view of cell type organization, in which different cell types operate many of the same pathways in distinct modes.

Iron-responsive element of Divalent metal transporter 1 (Dmt1) controls Notch-mediated cell fates

Notch receptor activation is regulated by the intramembrane protease γ-secretase, which cleaves and liberates the Notch intracellular domain (Nicd) that regulates gene transcription. While γ-secretase cleavage is necessary, we demonstrate it is insufficient for Notch activation and requires vesicular trafficking. Here, we report Divalent metal transporter 1 (Dmt1, Slc11A2) as a novel and essential regulator of Notch signalling. Dmt1-deficient cells are defective in Notch signalling and have perturbed endolysosomal trafficking and function. Dmt1 encodes for two isoforms, with and without an iron response element (ire). We show that isoform-specific silencing of Dmt1-ire and Dmt1+ire has opposite consequences on Notch-dependent cell fates in cell lines and intestinal organoids. Loss of Dmt1-ire suppresses Notch activation and promotes differentiation, whereas loss of Dmt1+ire causes Notch activation and maintains stem-progenitor cell fates. Dmt1 isoform expression correlates with Notch and Wnt signalling in Apc-deficient intestinal organoids and human colorectal cancers. Consistently, Dmt1-ire silencing induces Notch-dependent differentiation in colorectal cancer cells. These data identify Dmt1 isoforms as binary switches controlling Notch cell fate decisions in normal and tumour cells.

DLBCL-associated NOTCH2 mutations escape ubiquitin-dependent degradation and promote chemoresistance

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma. Up to 40% of patients with DLBCL display refractory disease or relapse after standard chemotherapy treatment (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone [R-CHOP]), leading to significant morbidity and mortality. The molecular mechanisms of chemoresistance in DLBCL remain incompletely understood. Using a cullin-really interesting new gene (RING) ligase-based CRISPR-Cas9 library, we identify that inactivation of the E3 ubiquitin ligase KLHL6 promotes DLBCL chemoresistance. Furthermore, proteomic approaches helped identify KLHL6 as a novel master regulator of plasma membrane-associated NOTCH2 via proteasome-dependent degradation. In CHOP-resistant DLBCL tumors, mutations of NOTCH2 result in a protein that escapes the mechanism of ubiquitin-dependent proteolysis, leading to protein stabilization and activation of the oncogenic RAS signaling pathway. Targeting CHOP-resistant DLBCL tumors with the phase 3 clinical trial molecules nirogacestat, a selective γ-secretase inhibitor, and ipatasertib, a pan-AKT inhibitor, synergistically promotes DLBCL destruction. These findings establish the rationale for therapeutic strategies aimed at targeting the oncogenic pathway activated in KLHL6- or NOTCH2-mutated DLBCL.

Update on the Epidemiology, Pathogenesis, and Biomarkers of Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common monogenic disorder of the cerebral small blood vessels. It is caused by mutations in the NOTCH3 gene on chromosome 19, and more than 280 distinct pathogenic mutations have been reported to date. CADASIL was once considered a very rare disease with an estimated prevalence of 1.3-4.1 per 100,000 adults. However, recent large-scale genomic studies have revealed a high prevalence of pathogenic NOTCH3 variants among the general population, with the highest risk being among Asians. The disease severity and age at onset vary significantly even among individuals who carry the same NOTCH3 mutations. It is still unclear whether a significant genotype-phenotype correlation is present in CADASIL. The accumulation of granular osmiophilic material in the vasculature is a characteristic feature of CADASIL. However, the exact pathogenesis of CADASIL remains largely unclear despite various laboratory and clinical observations being made. Major hypotheses proposed so far have included aberrant NOTCH3 signaling, toxic aggregation, and abnormal matrisomes. Several characteristic features have been observed in the brain magnetic resonance images of patients with CADASIL, including subcortical lacunar lesions and white matter hyperintensities in the anterior temporal lobe or external capsule, which were useful in differentiating CADASIL from sporadic stroke in patients. The number of lacunes and the degree of brain atrophy were useful in predicting the clinical outcomes of patients with CADASIL. Several promising blood biomarkers have also recently been discovered for CADASIL, which require further research for validation.

Tetraspanins as Potential Modulators of Glutamatergic Synaptic Function

Tetraspanins (Tspans) comprise a membrane protein family structurally defined by four transmembrane domains and intracellular N and C termini that is found in almost all cell types and tissues of eukaryotes. Moreover, they are involved in a bewildering multitude of diverse biological processes such as cell adhesion, motility, protein trafficking, signaling, proliferation, and regulation of the immune system. Beside their physiological roles, they are linked to many pathophysiological phenomena, including tumor progression regulation, HIV-1 replication, diabetes, and hepatitis. Tetraspanins are involved in the formation of extensive protein networks, through interactions not only with themselves but also with numerous other specific proteins, including regulatory proteins in the central nervous system (CNS). Interestingly, recent studies showed that Tspan7 impacts dendritic spine formation, glutamatergic synaptic transmission and plasticity, and that Tspan6 is correlated with epilepsy and intellectual disability (formerly known as mental retardation), highlighting the importance of particular tetraspanins and their involvement in critical processes in the CNS. In this review, we summarize the current knowledge of tetraspanin functions in the brain, with a particular focus on their impact on glutamatergic neurotransmission. In addition, we compare available resolved structures of tetraspanin family members to those of auxiliary proteins of glutamate receptors that are known for their modulatory effects.

Secretases Related to Amyloid Precursor Protein Processing

Alzheimer’s disease (AD) is a common neurodegenerative disease whose prevalence increases with age. An increasing number of findings suggest that abnormalities in the metabolism of amyloid precursor protein (APP), a single transmembrane aspartic protein that is cleaved by β- and γ-secretases to produce β-amyloid protein (Aβ), are a major pathological feature of AD. In recent years, a large number of studies have been conducted on the APP processing pathways and the role of secretion. This paper provides a summary of the involvement of secretases in the processing of APP and the potential drug targets that could provide new directions for AD therapy.

Protein biomarkers in breast cancer-derived extracellular vesicles for use in liquid biopsies

Breast cancer is the most common malignant disease in women worldwide. Early diagnosis and treatment can greatly improve the management of breast cancer. Liquid biopsies are becoming convenient detection methods for diagnosing and monitoring breast cancer due to their noninvasiveness and ability to provide real-time feedback. A range of liquid biopsy markers, including circulating tumor proteins, circulating tumor cells, and circulating tumor nucleic acids, have been implemented for breast cancer diagnosis and prognosis, with each having its own advantages and limitations. Circulating extracellular vesicles are messengers of intercellular communication that are packed with information from mother cells and are found in a wide variety of bodily fluids; thus, they are emerging as ideal candidates for liquid biopsy biomarkers. In this review, we summarize extracellular vesicle protein markers that can be potentially used for the early diagnosis and prognosis of breast cancer or determining its specific subtypes.

BMP7 reduces the fibrocartilage chondrocyte phenotype

The fibrocartilage chondrocyte phenotype has been recognized to attribute to osteoarthritis (OA) development. These chondrocytes express genes related to unfavorable OA outcomes, emphasizing its importance in OA pathology. BMP7 is being explored as a potential disease-modifying molecule and attenuates the chondrocyte hypertrophic phenotype. On the other hand, BMP7 has been demonstrated to relieve organ fibrosis by counteracting the pro-fibrotic TGFβ-Smad3-PAI1 axis and increasing MMP2-mediated Collagen type I turnover. Whether BMP7 has anti-fibrotic properties in chondrocytes is unknown. Human OA articular chondrocytes (HACs) were isolated from end-stage OA femoral cartilage (total knee arthroplasty; n = 18 individual donors). SW1353 cells and OA HACs were exposed to 1 nM BMP7 for 24 h, after which gene expression of fibrosis-related genes and fibrosis-mediating factors was determined by RT-qPCR. In SW1353, Collagen type I protein levels were determined by immunocytochemistry and western blotting. PAI1 and MMP2 protein levels and activity were measured with an ELISA and activity assays, respectively. MMP2 activity was inhibited with the selective MMP-2 inhibitor OA-Hy. SMAD3 activity was determined by a (CAGA)₁₂-reporter assay, and pSMAD2 levels by western blotting. Following BMP7 exposure, the expression of fibrosis-related genes was reduced in SW1353 cells and OA HACs. BMP7 reduced Collagen type I protein levels in SW1353 cells. Gene expression of MMP2 was increased in SW1353 cells following BMP7 treatment. BMP7 reduced PAI1 protein levels and -activity, while MMP2 protein levels and -activity were increased by BMP7. BMP7-dependent inhibition of Collagen type I protein levels in SW1353 cells was abrogated when MMP2 activity was inhibited. Finally, BMP7 reduced pSMAD2 levels determined by western blotting and reduced SMAD3 transcriptional activity as demonstrated by decreased (CAGA)₁₂ luciferase reporter activity. Our data demonstrate that short-term exposure to BMP7 decreases the fibrocartilage chondrocyte phenotype. The BMP7-dependent reduction of Collagen type I protein expression seems MMP2-dependent and inhibition of Smad2/3-PAI1 activity was identified as a potential pathway via which BMP7 exerts its anti-fibrotic action. This indicates that in chondrocytes BMP7 may have a double mode-of-action by targeting both the hypertrophic as well as the fibrotic chondrocyte phenotype, potentially adding to the clinical relevance of using BMP7 as an OA disease-modifying molecule.

The Role of Intracellular Trafficking of Notch Receptors in Ligand-Independent Notch Activation

Aberrant Notch signaling has been found in a broad range of human malignancies. Consequently, small molecule inhibitors and antibodies targeting Notch signaling in human cancers have been developed and tested; however, these have failed due to limited anti-tumor efficacy because of dose-limiting toxicities in normal tissues. Therefore, there is an unmet need to discover novel regulators of malignant Notch signaling, which do not affect Notch signaling in healthy tissues. This review provides a comprehensive overview of the current knowledge on the role of intracellular trafficking in ligand-independent Notch receptor activation, the possible mechanisms involved, and possible therapeutic opportunities for inhibitors of intracellular trafficking in Notch targeting.

Regulation of ADAM10 by the TspanC8 Family of Tetraspanins and Their Therapeutic Potential

The ubiquitously expressed transmembrane protein a disintegrin and metalloproteinase 10 (ADAM10) functions as a “molecular scissor”, by cleaving the extracellular regions from its membrane protein substrates in a process termed ectodomain shedding. ADAM10 is known to have over 100 substrates including Notch, amyloid precursor protein, cadherins, and growth factors, and is important in health and implicated in diseases such as cancer and Alzheimer’s. The tetraspanins are a superfamily of membrane proteins that interact with specific partner proteins to regulate their intracellular trafficking, lateral mobility, and clustering at the cell surface. We and others have shown that ADAM10 interacts with a subgroup of six tetraspanins, termed the TspanC8 subgroup, which are closely related by protein sequence and comprise Tspan5, Tspan10, Tspan14, Tspan15, Tspan17, and Tspan33. Recent evidence suggests that different TspanC8/ADAM10 complexes have distinct substrates and that ADAM10 should not be regarded as a single scissor, but as six different TspanC8/ADAM10 scissor complexes. This review discusses the published evidence for this “six scissor” hypothesis and the therapeutic potential this offers.

Biological Significance of NOTCH Signaling Strength

The evolutionarily conserved NOTCH signaling displays pleotropic functions in almost every organ system with a simple signaling axis. Different from many other signaling pathways that can be amplified via kinase cascades, NOTCH signaling does not contain any intermediate to amplify signal. Thus, NOTCH signaling can be activated at distinct signaling strength levels, disruption of which leads to various developmental disorders. Here, we reviewed mechanisms establishing different NOTCH signaling strengths, developmental processes sensitive to NOTCH signaling strength perturbation, and transcriptional regulations influenced by NOTCH signaling strength changes. We hope this could add a new layer of diversity to explain the pleotropic functions of NOTCH signaling pathway.

Discovery of bone morphogenetic protein 7-derived peptide sequences that attenuate the human osteoarthritic chondrocyte phenotype

Treatment of osteoarthritis (OA) is mainly symptomatic by alleviating pain to postpone total joint replacement. Bone morphogenetic protein 7 (BMP7) is a candidate morphogen for experimental OA treatment that favorably alters the chondrocyte and cartilage phenotype. Intra-articular delivery and sustained release of a recombinant growth factor for treating OA are challenging, whereas the use of peptide technology potentially circumvents many of these challenges. In this study, we screened a high-resolution BMP7 peptide library and discovered several overlapping peptide sequences from two regions in BMP7 with nanomolar bioactivity that attenuated the pathological OA chondrocyte phenotype. A single exposure of OA chondrocytes to peptides p[63-82] and p[113-132] ameliorated the OA chondrocyte phenotype for up to 8 days, and peptides were bioactive on chondrocytes in OA synovial fluid. Peptides p[63-82] and p[113-132] required NKX3-2 for their bioactivity on chondrocytes and provoke changes in SMAD signaling activity. The bioactivity of p[63-82] depended on specific evolutionary conserved sequence elements common to BMP family members. Intra-articular injection of a rat medial meniscal tear (MMT) model with peptide p[63-82] attenuated cartilage degeneration. Together, this study identified two regions in BMP7 from which bioactive peptides are able to attenuate the OA chondrocyte phenotype. These BMP7-derived peptides provide potential novel disease-modifying treatment options for OA.

Evolution of Human Brain Size-Associated NOTCH2NL Genes Proceeds toward Reduced Protein Levels

Ever since the availability of genomes from Neanderthals, Denisovans, and ancient humans, the field of evolutionary genomics has been searching for protein-coding variants that may hold clues to how our species evolved over the last ∼600,000 years. In this study, we identify such variants in the human-specific NOTCH2NL gene family, which were recently identified as possible contributors to the evolutionary expansion of the human brain. We find evidence for the existence of unique protein-coding NOTCH2NL variants in Neanderthals and Denisovans which could affect their ability to activate Notch signaling. Furthermore, in the Neanderthal and Denisovan genomes, we find unusual NOTCH2NL configurations, not found in any of the modern human genomes analyzed. Finally, genetic analysis of archaic and modern humans reveals ongoing adaptive evolution of modern human NOTCH2NL genes, identifying three structural variants acting complementary to drive our genome to produce a lower dosage of NOTCH2NL protein. Because copy-number variations of the 1q21.1 locus, encompassing NOTCH2NL genes, are associated with severe neurological disorders, this seemingly contradicting drive toward low levels of NOTCH2NL protein indicates that the optimal dosage of NOTCH2NL may have not yet been settled in the human population.

Genetic and polygenic risk score analysis for Alzheimer's disease in the Chinese population

INTRODUCTION

Dozens of Alzheimer's disease (AD)-associated loci have been identified in European-descent populations, but their effects have not been thoroughly investigated in the Hong Kong Chinese population.

METHODS

TaqMan array genotyping was performed for known AD-associated variants in a Hong Kong Chinese cohort. Regression analysis was conducted to study the associations of variants with AD-associated traits and biomarkers. Lasso regression was applied to establish a polygenic risk score (PRS) model for AD risk prediction.

RESULTS

SORL1 is associated with AD in the Hong Kong Chinese population. Meta-analysis corroborates the AD-protective effect of the SORL1 rs11218343 C allele. The PRS is developed and associated with AD risk, cognitive status, and AD-related endophenotypes. TREM2 H157Y might influence the amyloid beta 42/40 ratio and levels of immune-associated proteins in plasma.

DISCUSSION

SORL1 is associated with AD in the Hong Kong Chinese population. The PRS model can predict AD risk and cognitive status in this population.

A lineage-tracing tool to map the fate of hypoxic tumour cells

Intratumoural hypoxia is a common characteristic of malignant treatment-resistant cancers. However, hypoxia-modification strategies for the clinic remain elusive. To date, little is known on the behaviour of individual hypoxic tumour cells in their microenvironment. To explore this issue in a spatial and temporally controlled manner, we developed a genetically encoded sensor by fusing the O2-labile hypoxia-inducible factor 1α (HIF-1α) protein to eGFP and a tamoxifen-regulated Cre recombinase. Under normoxic conditions, HIF-1α is degraded but, under hypoxia, the HIF-1α-GFP-Cre-ERT2 fusion protein is stabilised and in the presence of tamoxifen activates a tdTomato reporter gene that is constitutively expressed in hypoxic progeny. We visualise the random distribution of hypoxic tumour cells from hypoxic or necrotic regions and vascularised areas using immunofluorescence and intravital microscopy. Once tdTomato expression is induced, it is stable for at least 4 weeks. Using this system, we could show in vivo that the post-hypoxic cells were more proliferative than non-labelled cells. Our results demonstrate that single-cell lineage tracing of hypoxic tumour cells can allow visualisation of their behaviour in living tumours using intravital microscopy. This tool should prove valuable for the study of dissemination and treatment response of post-hypoxic tumour cells in vivo at single-cell resolution.This article has an associated First Person interview with the joint first authors of the paper.

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signalling

Amyloid beta peptides (Aβ) proteins play a key role in vascular pathology in Alzheimer’s Disease (AD) including impairment of the blood–brain barrier and aberrant angiogenesis. Although previous work has demonstrated a pro-angiogenic role of Aβ, the exact mechanisms by which amyloid precursor protein (APP) processing and endothelial angiogenic signalling cascades interact in AD remain a largely unsolved problem. Here, we report that increased endothelial sprouting in human-APP transgenic mouse (TgCRND8) tissue is dependent on β-secretase (BACE1) processing of APP. Higher levels of Aβ processing in TgCRND8 tissue coincides with decreased NOTCH3/JAG1 signalling, overproduction of endothelial filopodia and increased numbers of vascular pericytes. Using a novel in vitro approach to study sprouting angiogenesis in TgCRND8 organotypic brain slice cultures (OBSCs), we find that BACE1 inhibition normalises excessive endothelial filopodia formation and restores NOTCH3 signalling. These data present the first evidence for the potential of BACE1 inhibition as an effective therapeutic target for aberrant angiogenesis in AD.

NOTCH3 is non-enzymatically fragmented in inherited cerebral small-vessel disease

The small-vessel disorder cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) arises from mutations in the human gene encoding NOTCH3 and results in vascular smooth muscle cell degeneration, stroke, and dementia. However, the structural changes in NOTCH3 involved in CADASIL etiology are unclear. Here, we discovered site-specific fragmentation of NOTCH3 protein in pathologically affected vessels of human CADASIL-affected brains. EM-based experiments to pinpoint NOTCH3 localization in these brains indicated accumulation of NOTCH3 fragmentation products in the basement membrane, collagen fibers, and granular osmiophilic material within the cerebrovasculature. Using antibodies generated against a disease-linked neo-epitope found in degenerating vascular medium of CADASIL brains, we mapped the site of fragmentation to the NOTCH3 N terminus at the peptide bond joining Asp⁸⁰ and Pro⁸¹ Cleavage at this site was predicted to separate the first epidermal growth factor (EGF)-like domain from the remainder of the protein. We found that the cleavage product from this fragmentation event is released into the conditioned medium of cells expressing recombinant NOTCH3 fragments. Mutagenesis of Pro⁸¹ abolished the fragmentation, and low pH and reducing conditions enhanced NOTCH3 proteolysis. Furthermore, substitution of multiple cysteine residues of the NOTCH3 N terminus activated proteolytic release of the first EGF-like repeat, suggesting that the elimination of multiple disulfide bonds in NOTCH3 accelerates its fragmentation. These characteristics link the signature molecular genetic alterations present in individuals with CADASIL to a post-translational protein alteration in degenerating brain arteries. The cellular consequences of these pathological NOTCH3 fragments are an important area for future investigation.

TspanC8 tetraspanins differentially regulate ADAM10 endocytosis and half-life

ADAM10 is a transmembrane metalloprotease that is essential for development and tissue homeostasis. It cleaves the ectodomain of many proteins, including amyloid precursor protein, and plays an essential role in Notch signaling. ADAM10 associates with six members of the tetraspanin superfamily referred to as TspanC8 (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17, and Tspan33), which regulate its exit from the endoplasmic reticulum and its substrate selectivity. We now show that ADAM10, Tspan5, and Tspan15 influence each other's expression level. Notably, ADAM10 undergoes faster endocytosis in the presence of Tspan5 than in the presence of Tspan15, and Tspan15 stabilizes ADAM10 at the cell surface yielding high expression levels. Reciprocally, ADAM10 stabilizes Tspan15 at the cell surface, indicating that it is the Tspan15/ADAM10 complex that is retained at the plasma membrane. Chimeric molecules indicate that the cytoplasmic domains of these tetraspanins contribute to their opposite action on ADAM10 trafficking and Notch signaling. In contrast, an unusual palmitoylation site at the end of Tspan15 C-terminus is dispensable. Together, these findings uncover a new level of ADAM10 regulation by TspanC8 tetraspanins.

NOTCH signaling promotes the survival of irradiated basal airway stem cells

Radiation-induced lung injury to normal airway epithelium is a frequent side-effect and dose-limiting factor in radiotherapy of tumors in the thoracic cavity. NOTCH signaling plays key roles in self-renewal and differentiation of upper airway basal lung stem cells during development, and the NOTCH pathway is frequently deregulated in lung cancer. In preclinical lung cancer models, NOTCH inhibition was shown to improve the radiotherapy response by targeting tumor stem cells, but the effects in combination with irradiation on normal lung stem cells are unknown. NOTCH/γ-secretase inhibitors are potent clinical candidates to block NOTCH function in tumors, but their clinical implementation has been hampered by normal tissue side-effects. Here we show that NOTCH signaling is active in primary human- and murine-derived airway epithelial stem cell models and when combined with radiation NOTCH inhibition provokes a decrease in S-phase and increase in G1-phase arrest. We show that NOTCH inhibition in irradiated lung basal stem cells leads to a more potent activation of the DNA damage checkpoint kinases pATM and pCHK2 and results in an increased level of residual 53BP1 foci in irradiated lung basal stem cells reducing their capacity for self-renewal. The effects are recapitulated in ex vivo cultured lung basal stem cells after in vivo whole thorax irradiation and NOTCH inhibition. These results highlight the importance of studying normal tissue effects that may counteract the therapeutic benefit in the use of NOTCH/γ-secretase inhibitors in combination with radiation for antitumor treatment.

Novel Notch signaling inhibitor NSI‑1 suppresses nuclear translocation of the Notch intracellular domain

The Notch receptor serves a fundamental role in the regulation of cell fate determination through intracellular signal transmission. Mutation of the Notch receptor results in abnormal active signaling, leading to the development of diseases involving abnormal cell growth, including malignant tumors. Therefore, the Notch signaling pathway is a useful pharmacological target for the treatment of cancer. In the present study, a compound screening system was designed to identify inhibitors of the Notch signaling targeting Notch intracellular domain (NICD). A total of 9,600 compounds were analyzed using the Michigan Cancer Foundation‑7 (MCF7) human breast adenocarcinoma cell line and the SH‑SY5Y human neuroblastoma cell line with the reporter assay system using an artificial protein encoding a partial Notch carboxyl‑terminal fragment fused to the Gal4 DNA‑binding domain. The molecular mechanism underlying the inhibition of Notch signaling by a hit compound was further validated using biochemical and cell biological approaches. Using the screening system, a potential candidate, Notch signaling inhibitor‑1 (NSI‑1), was isolated which showed 50% inhibition at 6.1 µM in an exogenous Notch signaling system. In addition, NSI‑1 suppressed the nuclear translocation of NICD and endogenous gene expression of hairy and enhancer of split‑1, indicating that NSI‑1 specifically targets Notch. Notably, NSI‑1 suppressed the cell viability of MCF7 cells and another human breast adenocarcinoma cell line, MDA‑MB‑231 exhibiting constitutive and high Notch signaling activity, whereas no significant effect was observed in the SH‑SY5Y cells bearing a lower Notch signaling activity. NSI‑1 significantly suppressed the viability of SH‑SY5Y cells expressing exogenous human Notch1. These results indicate that NSI‑1 is a novel Notch signaling inhibitor and suggest its potential as a useful drug for the treatment of diseases induced by constitutively active Notch signaling.

Disruption of NOTCH signaling by a small molecule inhibitor of the transcription factor RBPJ

NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-secretase inhibitors are commonly used to probe NOTCH function, but also block processing of numerous other proteins. We discovered a new class of small molecule inhibitor that disrupts the interaction between NOTCH and RBPJ, which is the main transcriptional effector of NOTCH signaling. RBPJ Inhibitor-1 (RIN1) also blocked the functional interaction of RBPJ with SHARP, a scaffold protein that forms a transcriptional repressor complex with RBPJ in the absence of NOTCH signaling. RIN1 induced changes in gene expression that resembled siRNA silencing of RBPJ rather than inhibition at the level of NOTCH itself. Consistent with disruption of NOTCH signaling, RIN1 inhibited the proliferation of hematologic cancer cell lines and promoted skeletal muscle differentiation from C2C12 myoblasts. Thus, RIN1 inhibits RBPJ in its repressing and activating contexts, and can be exploited for chemical biology and therapeutic applications.

Delta-like 1-mediated cis-inhibition of Jagged1/2 signalling inhibits differentiation of human epidermal cells in culture

Epidermal homeostasis depends on a balance between self-renewal of stem cells and terminal differentiation of their progeny. Notch signalling is known to play a role in epidermal  stem cell patterning and differentiation. However, the molecular mechanisms are incompletely understood. Here we demonstrate dynamic patterns of Notch ligand and receptor expression in cultured human epidermis. Notch2 and 3 act together to promote differentiation, while Notch1 decreases stem cell proliferation. The Notch ligand Jagged1 triggers differentiation when presented on an adhesive substrate or on polystyrene beads and over-rides the differentiation inhibitory effect of cell spreading. In contrast, Delta-like 1 (Dll1) overexpression abrogates the pro-differentiation effect of Jagged1 in a cell autonomous fashion. We conclude that Dll1 expression by stem cells not only stimulates differentiation of neighbouring cells in trans, but also inhibits differentiation cell autonomously. These results highlight the distinct roles of different Notch receptors and ligands in controlling epidermal homeostasis.

Blood-brain barrier and innate immunity in the pathogenesis of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is only partly understood. This is the probable reason why significant efforts to treat or prevent AD have been unsuccessful. In fact, as of April 2019, there have been 2094 studies registered for AD on the clinicaltrials.gov U.S. National Library of Science web page, of which only a few are still ongoing. In AD, abnormal accumulation of amyloid and tau proteins in the brain are thought to begin 10-20 years before the onset of overt symptoms, suggesting that interventions designed to prevent pathological amyloid and tau accumulation may be more effective than attempting to reverse a pathology once it is established. However, to be successful, such early interventions need to be selectively administered to individuals who will likely develop the disease long before the symptoms occur. Therefore, it is critical to identify early biomarkers that are strongly predictive of AD. Currently, patients are diagnosed on the basis of a variety of clinical scales, neuropsychological tests, imaging and laboratory modalities, but definitive diagnosis can be made only by postmortem assessment of underlying neuropathology. People suffering from AD thus may be misdiagnosed clinically with other primary causes of dementia, and vice versa, thereby also reducing the power of clinical trials. The amyloid cascade hypothesis fits well for the familial cases of AD with known mutations, but is not sufficient to explain sporadic, late-onset AD (LOAD) that accounts for over 95% of all cases. Since the earliest descriptions of AD there have been neuropathological features described other than amyloid plaques (AP) and neurofibrillary tangles (NFT), most notably gliosis and neuroinflammation. However, it is only recently that genetic and experimental studies have implicated microglial dysfunction as a causal factor for AD, as opposed to a merely biological response of its accumulation around AP. Additionally, many studies have suggested the importance of changes in blood-brain barrier (BBB) permeability in the pathogenesis of AD. Here we suggest how these less investigated aspects of the disease that have gained increased attention in recent years may contribute mechanistically to the development of lesions and symptoms of AD.

Overexpression of miRNA-25-3p inhibits Notch1 signaling and TGF-β-induced collagen expression in hepatic stellate cells

During chronic liver injury hepatic stellate cells (HSCs), the principal source of extracellular matrix in the fibrotic liver, transdifferentiate into pro-fibrotic myofibroblast-like cells - a process potentially regulated by microRNAs (miRNAs). Recently, we found serum miRNA-25-3p (miR-25) levels were upregulated in children with Cystic Fibrosis (CF) without liver disease, compared to children with CF-associated liver disease and healthy individuals. Here we examine the role of miR-25 in HSC biology. MiR-25 was detected in the human HSC cell line LX-2 and in primary murine HSCs, and increased with culture-induced activation. Transient overexpression of miR-25 inhibited TGF-β and its type 1 receptor (TGFBR1) mRNA expression, TGF-β-induced Smad2 phosphorylation and subsequent collagen1α1 induction in LX-2 cells. Pull-down experiments with biotinylated miR-25 revealed Notch signaling (co-)activators ADAM-17 and FKBP14 as miR-25 targets in HSCs. NanoString analysis confirmed miR-25 regulation of Notch- and Wnt-signaling pathways. Expression of Notch signaling pathway components and endogenous Notch1 signaling was downregulated in miR-25 overexpressing LX-2 cells, as were components of Wnt signaling such as Wnt5a. We propose that miR-25 acts as a negative feedback anti-fibrotic control during HSC activation by reducing the reactivity of HSCs to TGF-β-induced collagen expression and modulating the cross-talk between Notch, Wnt and TGF-β signaling.

The role of oncogenic Notch2 signaling in cancer: a novel therapeutic target

Deregulated Notch signaling is a key factor thought to facilitate the stem-like proliferation of cancer cells, thereby facilitating disease progression. Four subtypes of Notch receptor have been described to date, with each playing a distinct role in cancer development and progression, therefore warranting a careful and comprehensive examination of the targeting of each receptor subtype in the context of oncogenesis. Clinical efforts to translate the DAPT, which blocks Notch signaling, have been unsuccessful due to a combination of serious gastrointestinal side effects and a lack of complete blocking efficacy. There is therefore a clear need to identify better therapeutic strategies for targeting and manipulating Notch signaling. Notch2 is a Notch receptor that is commonly overexpressed in a range of cancers, and which is linked to a unique oncogenic mechanism. Successful efforts to block Notch2 signaling will depend upon doing so both efficiently and specifically in patients. As such, in the present review we will explore the role of Notch2 signaling in the development and progression of cancer, and we will assess agents and strategies with the potential to effectively disrupt Notch2 signaling and thereby yield novel cancer treatment regimens.

The role of ENPP1/PC-1 in osteoinduction by calcium phosphate ceramics

In the past decade, calcium phosphate (CaP) ceramics have emerged as alternatives to autologous bone grafts for the treatment of large, critical-sized bone defects. In order to be effective in the regeneration of such defects, ceramics must show osteoinductive behaviour, defined as the ability to induce de novo heterotopic bone formation. While a set of osteoinductive CaP ceramics has been developed, the exact processes underlying osteoinduction, and the role of the physical and chemical properties of the ceramics, remain largely unknown. Previous studies have focused on the role of the transcriptome to shed light on the mechanism of osteoinduction at the mRNA level. To complement these studies, a proteomic analysis was performed to study the behaviour of hMSCs on osteoinductive and non-osteoinductive CaPs. The results of this analysis suggest that plasma cell glycoprotein 1 (PC-1), encoded by the ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene, plays a key role in the process of osteoinduction by CaP ceramics. Validation experiments have confirmed that indeed, the mRNA expression of ENPP1 and the production of PC-1 are higher on osteoinductive than on non-osteoinductive CaP ceramics, a trend that was also observed for other osteogenic markers such as bone morphogenetic protein 2 (BMP2) and osteopontin (OPN), but not for alkaline phosphatase (ALP). Our results also showed that the expression of PC-1 is restricted to those cells which are in direct contact with the CaP ceramic surface, plausibly due to the localised depletion of calcium and inorganic phosphate ions from the supersaturated cell culture medium as CaP crystallises on the ceramic surface. Replicating the surface of the osteoinductive ceramic in polystyrene resulted in a significant decrease in ENPP1 expression, suggesting that surface structural properties alone are not sufficient to induce ENPP1 expression. Finally, knocking down ENPP1 expression in hMSCs resulted in increased BMP2 expression, both at the mRNA and protein level, suggesting that ENPP1 is a negative regulator of BMP-2 signalling. Taken together, this study shows, for the first time, that ENPP1/PC-1 plays an important role in CaP-induced osteogenic differentiation of hMSCs and thus possibly osteoinduction by CaP ceramics. Furthermore, we have identified a crucial role for the interfacial (chemical) events occurring on the CaP ceramic surface in the process of osteoinduction. This knowledge can contribute to the development of new bone graft substitutes, with improved osteoinductive potential.

Novel Contribution of Secreted Amyloid-β Precursor Protein to White Matter Brain Enlargement in Autism Spectrum Disorder

The most replicated neuroanatomical finding in autism is the tendency toward brain overgrowth, especially in younger children. Research shows that both gray and white matter are enlarged. Proposed mechanisms underlying brain enlargement include abnormal inflammatory and neurotrophic signals that lead to excessive, aberrant dendritic connectivity via disrupted pruning and cell adhesion, and enlargement of white matter due to excessive gliogenesis and increased myelination. Amyloid-β protein precursor (βAPP) and its metabolites, more commonly associated with Alzheimer's disease (AD), are also dysregulated in autism plasma and brain tissue samples. This review highlights findings that demonstrate how one βAPP metabolite, secreted APPα, and the ADAM family α-secretases, may lead to increased brain matter, with emphasis on increased white matter as seen in autism. sAPPα and the ADAM family α-secretases contribute to the anabolic, non-amyloidogenic pathway, which is in contrast to the amyloid (catabolic) pathway known to contribute to Alzheimer disease. The non-amyloidogenic pathway could produce brain enlargement via genetic mechanisms affecting mRNA translation and polygenic factors that converge on molecular pathways (mitogen-activated protein kinase/MAPK and mechanistic target of rapamycin/mTOR), promoting neuroinflammation. A novel mechanism linking the non-amyloidogenic pathway to white matter enlargement is proposed: α-secretase and/or sAPPα, activated by ERK receptor signaling activates P13K/AKt/mTOR and then Rho GTPases favoring myelination via oligodendrocyte progenitor cell (OPC) activation of cofilin. Applying known pathways in AD to autism should allow further understanding and provide options for new drug targets.

The antiviral protein viperin regulates chondrogenic differentiation via CXCL10 protein secretion

Viperin (also known as radical SAM domain–containing 2 (RSAD2)) is an interferon-inducible and evolutionary conserved protein that participates in the cell's innate immune response against a number of viruses. Viperin mRNA is a substrate for endoribonucleolytic cleavage by RNase mitochondrial RNA processing (MRP) and mutations in the RNase MRP small nucleolar RNA (snoRNA) subunit of the RNase MRP complex cause cartilage-hair hypoplasia (CHH), a human developmental condition characterized by metaphyseal chondrodysplasia and severe dwarfism. It is unknown how CHH-pathogenic mutations in RNase MRP snoRNA interfere with skeletal development, and aberrant processing of RNase MRP substrate RNAs is thought to be involved. We hypothesized that viperin plays a role in chondrogenic differentiation. Using immunohistochemistry, real-time quantitative PCR, immunoblotting, ELISA, siRNA-mediated gene silencing, plasmid-mediated gene overexpression, label-free MS proteomics, and promoter reporter bioluminescence assays, we discovered here that viperin is expressed in differentiating chondrocytic cells and regulates their protein secretion and the outcome of chondrogenic differentiation by influencing transforming growth factor β (TGF-β)/SMAD family 2/3 (SMAD2/3) activity via C-X-C motif chemokine ligand 10 (CXCL10). Of note, we observed disturbances in this viperin–CXCL10–TGF-β/SMAD2/3 axis in CHH chondrocytic cells. Our results indicate that the antiviral protein viperin controls chondrogenic differentiation by influencing secretion of soluble proteins and identify a molecular route that may explain impaired chondrogenic differentiation of cells from individuals with CHH.

Intriguing Roles for Endothelial ADAM10/Notch Signaling in the Development of Organ-Specific Vascular Beds

The vasculature is a remarkably interesting, complex, and interconnected organ. It provides a conduit for oxygen and nutrients, filtration of waste products, and rapid communication between organs. Much remains to be learned about the specialized vascular beds that fulfill these diverse, yet vital functions. This review was prompted by the discovery that Notch signaling in mouse endothelial cells is crucial for the development of specialized vascular beds found in the heart, kidneys, liver, intestines, and bone. We will address the intriguing questions raised by the role of Notch signaling and that of its regulator, the metalloprotease ADAM10, in the development of specialized vascular beds. We will cover fundamentals of ADAM10/Notch signaling, the concept of Notch-dependent cell fate decisions, and how these might govern the development of organ-specific vascular beds through angiogenesis or vasculogenesis. We will also consider common features of the affected vessels, including the presence of fenestra or sinusoids and their occurrence in portal systems with two consecutive capillary beds. We hope to stimulate further discussion and study of the role of ADAM10/Notch signaling in the development of specialized vascular structures, which might help uncover new targets for the repair of vascular beds damaged in conditions like coronary artery disease and glomerulonephritis.

Moving Breast Cancer Therapy up a Notch

Breast cancer is the second most common malignancy, worldwide. Treatment decisions are based on tumor stage, histological subtype, and receptor expression and include combinations of surgery, radiotherapy, and systemic treatment. These, together with earlier diagnosis, have resulted in increased survival. However, initial treatment efficacy cannot be guaranteed upfront, and these treatments may come with (long-term) serious adverse effects, negatively affecting a patient's quality of life. Gene expression-based tests can accurately estimate the risk of recurrence in early stage breast cancers. Disease recurrence correlates with treatment resistance, creating a major need to resensitize tumors to treatment. Notch signaling is frequently deregulated in cancer and is involved in treatment resistance. Preclinical research has already identified many combinatory therapeutic options where Notch involvement enhances the effectiveness of radiotherapy, chemotherapy or targeted therapies for breast cancer. However, the benefit of targeting Notch has remained clinically inconclusive. In this review, we summarize the current knowledge on targeting the Notch pathway to enhance current treatments for breast cancer and to combat treatment resistance. Furthermore, we propose mechanisms to further exploit Notch-based therapeutics in the treatment of breast cancer.

Synergistic Effects of NOTCH/γ-Secretase Inhibition and Standard of Care Treatment Modalities in Non-small Cell Lung Cancer Cells

Background: Lung cancer is the leading cause of cancer death worldwide. More effective treatments are needed to increase durable responses and prolong patient survival. Standard of care treatment for patients with non-operable stage III-IV NSCLC is concurrent chemotherapy and radiation. An activated NOTCH signaling pathway is associated with poor outcome and treatment resistance in non-small cell lung cancer (NSCLC). NOTCH/γ-secretase inhibitors have been effective in controlling tumor growth in preclinical models but the therapeutic benefit of these inhibitors as monotherapy in patients has been limited so far. Because NOTCH signaling has been implicated in treatment resistance, we hypothesized that by combining NOTCH inhibitors with chemotherapy and radiotherapy this could result in an increased therapeutic effect. A direct comparison of the effects of NOTCH inhibition when combined with current treatment combinations for NSCLC is lacking.

Methods: Using monolayer growth assays, we screened 101 FDA-approved drugs from the Cancer Therapy Evaluation Program alone, or combined with radiation, in the H1299 and H460 NSCLC cell lines to identify potent treatment interactions. Subsequently, using multicellular three-dimensional tumor spheroid assays, we tested a selection of drugs used in clinical practice for NSCLC patients, and combined these with a small molecule inhibitor, currently being tested in clinical trials, of the NOTCH pathway (BMS-906024) alone, or in combination with radiation, and measured specific spheroid growth delay (SSGD). Statistical significance was determined by one-way ANOVA with post-hoc Bonferroni correction, and synergism was assessed using two-way ANOVA.

Results: Monolayer assays in H1299 and H460 suggest that 21 vs. 5% were synergistic, and 17 vs. 11% were additive chemoradiation interactions, respectively. In H1299 tumor spheroids, significant SSGD was obtained for cisplatin, etoposide, and crizotinib, which increased significantly after the addition of the NOTCH inhibitor BMS-906024 (but not for paclitaxel and pemetrexed), and especially in triple combination with radiation. Synergistic interactions were observed when BMS-906024 was combined with chemoradiation (cisplatin, paclitaxel, docetaxel, and crizotinib). Similar results were observed for H460 spheroids using paclitaxel or crizotinib in dual combination treatment with NOTCH inhibition and triple with radiation.

Conclusions: Our findings point to novel synergistic combinations of NOTCH inhibition and chemoradiation that should be tested in NSCLC in vivo models for their ability to achieve an improved therapeutic ratio.

Ttyh1 regulates embryonic neural stem cell properties by enhancing the Notch signaling pathway

Despite growing evidence linking Drosophila melanogaster tweety-homologue 1 (Ttyh1) to normal mammalian brain development and cell proliferation, its exact role has not yet been determined. Here, we show that Ttyh1 is required for the maintenance of neural stem cell (NSC) properties as assessed by neurosphere formation and in vivo analyses of cell localization after in utero electroporation. We find that enhanced Ttyh1-dependent stemness of NSCs is caused by enhanced γ-secretase activity resulting in increased levels of Notch intracellular domain (NICD) production and activation of Notch targets. This is a unique function of Ttyh1 among all other Ttyh family members. Molecular analyses revealed that Ttyh1 binds to the regulator of γ-secretase activity Rer1 in the endoplasmic reticulum and thereby destabilizes Rer1 protein levels. This is the key step for Ttyh1-dependent enhancement of γ-secretase activity, as Rer1 overexpression completely abolishes the effects of Ttyh1 on NSC maintenance. Taken together, these findings indicate that Ttyh1 plays an important role during mammalian brain development by positively regulating the Notch signaling pathway through the downregulation of Rer1.

Notch3-dependent β-catenin signaling mediates EGFR TKI drug persistence in EGFR mutant NSCLC

EGFR tyrosine kinase inhibitors cause dramatic responses in EGFR-mutant lung cancer, but resistance universally develops. The involvement of β-catenin in EGFR TKI resistance has been previously reported, however, the precise mechanism by which β-catenin activation contributes to EGFR TKI resistance is not clear. Here, we show that EGFR inhibition results in the activation of β-catenin signaling in a Notch3-dependent manner, which facilitates the survival of a subset of cells that we call "adaptive persisters". We previously reported that EGFR-TKI treatment rapidly activates Notch3, and here we describe the physical association of Notch3 with β-catenin, leading to increased stability and activation of β-catenin. We demonstrate that the combination of EGFR-TKI and a β-catenin inhibitor inhibits the development of these adaptive persisters, decreases tumor burden, improves recurrence free survival, and overall survival in xenograft models. These results supports combined EGFR-TKI and β-catenin inhibition in patients with EGFR mutant lung cancer.

The multiple usages of Notch signaling in development, cell differentiation and cancer

Notch is a well-conserved signaling pathway all through evolution that is crucial to specify different cell fates. Although there is a strong context dependent component in each decision, the basic mechanisms that originate from the interplay among ligands and receptors is greatly preserved. In this review we will cover the latest findings on the different mechanisms for Notch activation and signaling. The regulation of this pathway is essential to understand development, cell differentiation and disease.

Human-Specific NOTCH2NL Genes Affect Notch Signaling and Cortical Neurogenesis

Genetic changes causing brain size expansion in human evolution have remained elusive. Notch signaling is essential for radial glia stem cell proliferation and is a determinant of neuronal number in the mammalian cortex. We find that three paralogs of human-specific NOTCH2NL are highly expressed in radial glia. Functional analysis reveals that different alleles of NOTCH2NL have varying potencies to enhance Notch signaling by interacting directly with NOTCH receptors. Consistent with a role in Notch signaling, NOTCH2NL ectopic expression delays differentiation of neuronal progenitors, while deletion accelerates differentiation into cortical neurons. Furthermore, NOTCH2NL genes provide the breakpoints in 1q21.1 distal deletion/duplication syndrome, where duplications are associated with macrocephaly and autism and deletions with microcephaly and schizophrenia. Thus, the emergence of human-specific NOTCH2NL genes may have contributed to the rapid evolution of the larger human neocortex, accompanied by loss of genomic stability at the 1q21.1 locus and resulting recurrent neurodevelopmental disorders.

Gαi Signaling Promotes Marginal Zone B Cell Development by Enabling Transitional B Cell ADAM10 Expression

The follicular (FO) versus marginal zone (MZ) B cell fate decision in the spleen depends upon BCR, BAFF, and Notch2 signaling. Whether or how G_i signaling affects this fate decision is unknown. Here, we show that direct contact with Notch ligand expressing stromal cells (OP9-Delta-like 1) cannot promote normal MZ B cell development when progenitor B cells lack Gα_i proteins, or if Gi signaling is disabled. Consistent with faulty ADAM10-dependent Notch2 processing, Gα_i-deficient transitional B cells had low ADAM10 membrane expression levels and reduced Notch2 target gene expression. Immunoblotting Gα_i-deficient B cell lysates revealed a reduction in mature, processed ADAM10. Suggesting that Gα_i signaling promotes ADAM10 membrane expression, stimulating normal transitional B cells with CXCL12 raised it, while inhibiting Gα_i nucleotide exchange blocked its upregulation. Surprisingly, inhibiting Gα_i nucleotide exchange in transitional B cells also impaired the upregulation of ADAM10 that occurs following antigen receptor crosslinking. These results indicate that Gα_i signaling supports ADAM10 maturation and activity in transitional B cells, and ultimately Notch2 signaling to promote MZ B cell development.

The metalloprotease ADAM10 (a disintegrin and metalloprotease 10) undergoes rapid, postlysis autocatalytic degradation

The transmembrane protein, ADAM10 (a disintegrin and metalloprotease 10), has key physiologic functions-for example, during embryonic development and in the brain. During transit through the secretory pathway, immature ADAM10 (proADAM10) is converted into its proteolytically active, mature form (mADAM10). Increasing or decreasing the abundance and/or activity of mADAM10 is considered to be a therapeutic approach for the treatment of such diseases as Alzheimer's disease and cancer. Yet biochemical detection and characterization of mADAM10 has been difficult. In contrast, proADAM10 is readily detected-for example, in immunoblots-which suggests that mADAM10 is only a fraction of total cellular ADAM10. Here, we demonstrate that mADAM10, but not proADAM10, unexpectedly undergoes rapid, time-dependent degradation upon biochemical cell lysis in different cell lines and in primary neurons, which prevents the detection of the majority of mADAM10 in immunoblots. This degradation required the catalytic activity of ADAM10, was efficiently prevented by adding active site inhibitors to the lysis buffer, and did not affect proADAM10, which suggests that ADAM10 degradation occurred in an intramolecular and autoproteolytic manner. Inhibition of postlysis autoproteolysis demonstrated efficient cellular ADAM10 maturation with higher levels of mADAM10 than proADAM10. Moreover, a cycloheximide chase experiment revealed that mADAM10 is a long-lived protein with a half-life of approximately 12 h. In summary, our study demonstrates that mADAM10 autoproteolysis must be blocked to allow for the proper detection of mADAM10, which is essential for the correct interpretation of biochemical and cellular studies of ADAM10.-Brummer, T., Pigoni, M., Rossello, A., Wang, H., Noy, P. J., Tomlinson, M. G., Blobel, C. P., Lichtenthaler, S. F. The metalloprotease ADAM10 (a disintegrin and metalloprotease 10) undergoes rapid, postlysis autocatalytic degradation.

Blocking 17β-hydroxysteroid dehydrogenase type 1 in endometrial cancer: a potential novel endocrine therapeutic approach

The enzyme type 1 17β-hydroxysteroid dehydrogenase (17β-HSD-1), responsible for generating active 17β-estradiol (E2) from low-active estrone (E1), is overexpressed in endometrial cancer (EC), thus implicating an increased intra-tissue generation of E2 in this estrogen-dependent condition. In this study, we explored the possibility of inhibiting 17β-HSD-1 and impairing the generation of E2 from E1 in EC using in vitro, in vivo, and ex vivo models. We generated EC cell lines derived from the well-differentiated endometrial adenocarcinoma Ishikawa cell line and expressing levels of 17β-HSD-1 similar to human tissues. In these cells, HPLC analysis showed that 17β-HSD-1 activity could be blocked by a specific 17β-HSD-1 inhibitor. In vitro, E1 administration elicited colony formation similar to E2, and this was impaired by 17β-HSD-1 inhibition. In vivo, tumors grafted on the chicken chorioallantoic membrane (CAM) demonstrated that E1 upregulated the expression of the estrogen responsive cyclin A similar to E2, which was impaired by 17β-HSD-1 inhibition. Neither in vitro nor in vivo effects of E1 were observed using 17β-HSD-1-negative cells (negative control). Using a patient cohort of 52 primary ECs, we demonstrated the presence of 17β-HSD-1 enzyme activity (ex vivo in tumor tissues, as measured by HPLC), which was inhibited by over 90% in more than 45% of ECs using the 17β-HSD-1 inhibitor. Since drug treatment is generally indicated for metastatic/recurrent and not primary tumor, we next demonstrated the mRNA expression of the potential drug target, 17β-HSD-1, in metastatic lesions using a second cohort of 37 EC patients. In conclusion, 17β-HSD-1 inhibition efficiently blocks the generation of E2 from E1 using various EC models. Further preclinical investigations and 17β-HSD-1 inhibitor development to make candidate compounds suitable for the first human studies are awaited. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Decitabine, a DNA-demethylating agent, promotes differentiation via NOTCH1 signaling and alters immune-related pathways in muscle-invasive bladder cancer

Aberrant DNA methylation observed in cancer can provide survival benefits to cells by silencing genes essential for anti-tumor activity. DNA-demethylating agents such as Decitabine (DAC)/Azacitidine (AZA) activate otherwise silenced tumor suppressor genes, alter immune response and epigenetically reprogram tumor cells. In this study, we show that non-cytotoxic nanomolar DAC concentrations modify the bladder cancer transcriptome to activate NOTCH1 at the mRNA and protein level, increase double-stranded RNA sensors and CK5-dependent differentiation. Importantly, DAC treatment increases ICN1 expression (the active intracellular domain of NOTCH1) significantly inhibiting cell proliferation and causing changes in cell size inducing morphological alterations reminiscent of senescence. These changes were not associated with β-galactosidase activity or increased p16 levels, but instead were associated with substantial IL-6 release. Increased IL-6 release was observed in both DAC-treated and ICN1 overexpressing cells as compared to control cells. Exogenous IL-6 expression was associated with a similar enlarged cell morphology that was rescued by the addition of a monoclonal antibody against IL-6. Treatment with DAC, overexpression with ICN1 or addition of exogenous IL-6 showed CK5 reduction, a surrogate marker of differentiation. Overall this study suggests that in MIBC cells, DNA hypomethylation increases NOTCH1 expression and IL-6 release to induce CK5-related differentiation.

Role of ADAM10 in intestinal crypt homeostasis and tumorigenesis

A disintegrin and metalloproteinases (ADAMs) are a family of mSultidomain, membrane-anchored proteases that regulate diverse cellular functions, including cell adhesion, migration, proteolysis and other cell signaling events. Catalytically-active ADAMs act as ectodomain sheddases that proteolytically cleave type I and type II transmembrane proteins and some GPI-anchored proteins from the cellular surface. ADAMs can also modulate other cellular signaling events through a process known as regulated intramembrane proteolysis (RIP). Through their proteolytic activity, ADAMs can rapidly modulate key cell signaling pathways in response to changes in the extracellular environment (e.g. inflammation) and play a central role in coordinating intercellular communication. Dysregulation of these processes through aberrant expression, or sustained ADAM activity, is linked to chronic inflammation, inflammation-associated cancer and tumorigenesis. ADAM10 was the first disintegrin-metalloproteinase demonstrated to have proteolytic activity and is the prototypic ADAM associated with RIP activity (e.g. sequential Notch receptor processing). ADAM10 is abundantly expressed throughout the gastrointestinal tract and during normal intestinal homeostasis ADAM10 regulates many cellular processes associated with intestinal development, cell fate specification and maintenance of intestinal stem cell/progenitor populations. In addition, several signaling pathways that undergo ectodomain shedding by ADAM10 (e.g. Notch, EGFR/ErbB, IL-6/sIL-6R) help control intestinal injury/regenerative responses and may drive intestinal inflammation and colon cancer initiation and progression. Here, I review some of the proposed functions of ADAM10 associated with intestinal crypt homeostasis and tumorigenesis within the gastrointestinal tract in vivo. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Scissor sisters: regulation of ADAM10 by the TspanC8 tetraspanins

A disintegrin and metalloprotease 10 (ADAM10) is a ubiquitously expressed transmembrane protein which is essential for embryonic development through activation of Notch proteins. ADAM10 regulates over 40 other transmembrane proteins and acts as a ‘molecular scissor’ by removing their extracellular regions. ADAM10 is also a receptor for α-toxin, a major virulence factor of Staphylococcus aureus. Owing to the importance of its substrates, ADAM10 is a potential therapeutic target for cancer, neurodegenerative diseases such as Alzheimer's and prion diseases, bacterial infection and inflammatory diseases such as heart attack, stroke and asthma. However, targetting ADAM10 is likely to result in toxic side effects. The tetraspanins are a superfamily of 33 four-transmembrane proteins in mammals which interact with and regulate specific partner proteins within membrane nanodomains. Tetraspanins appear to have a cone-shaped structure with a cholesterol-binding cavity, which may enable tetraspanins to undergo cholesterol-regulated conformational change. An emerging paradigm for tetraspanin function is the regulation of ADAM10 by the TspanC8 subgroup of tetraspanins, namely Tspan5, 10, 14, 15, 17 and 33. This review will describe how TspanC8s are required for ADAM10 trafficking from the endoplasmic reticulum and its enzymatic maturation. Moreover, different TspanC8s localise ADAM10 to different subcellular localisations and may cause ADAM10 to adopt distinct conformations and cleavage of distinct substrates. We propose that ADAM10 should now be regarded as six different scissor proteins depending on the interacting TspanC8. Therapeutic targetting of specific TspanC8/ADAM10 complexes could allow ADAM10 targetting in a cell type- or substrate-specific manner, to treat certain diseases while minimising toxicity.