Interactions between NRP1 and VEGFR2 molecules in the plasma membrane

NRP1 interacts with endoglin and VEGFR2 to modulate VEGF signaling and endothelial cell sprouting

Endothelial cells express neuropilin 1 (NRP1), endoglin (ENG) and vascular endothelial growth factor receptor 2 (VEGFR2), which regulate VEGF-A-mediated vascular development and angiogenesis. However, the link between complex formation among these receptors with VEGF-A-induced signaling and biology is yet unclear. Here, we quantify surface receptor interactions by IgG-mediated immobilization of one receptor, and fluorescence recovery after photobleaching (FRAP) measurements of the mobility of another coexpressed receptor. We observe stable ENG/NRP1, ENG/VEGFR2, and NRP1/VEGFR2 complexes, which are enhanced by VEGF-A. ENG augments NRP1/VEGFR2 interactions, suggesting formation of tripartite complexes bridged by ENG. Effects on signaling are measured in murine embryonic endothelial cells expressing (MEEC+/+) or lacking (MEEC-/-) ENG, along with NRP1 and/or ENG overexpression or knockdown. We find that optimal VEGF-A-mediated phosphorylation of VEGFR2 and Erk1/2 requires ENG and NRP1. ENG or NRP1 increase VEGF-A-induced sprouting, becoming optimal in cells expressing all three receptors, and both processes are inhibited by a MEK1/2 inhibitor. We propose a model where the maximal potency of VEGF-A involves a tripartite complex where ENG bridges VEGFR2 and NRP1, providing an attractive therapeutic target for modulation of VEGF-A signaling and biological responses.

Dual targeting of DR5 and VEGFR2 molecular pathways by multivalent fusion protein significantly suppresses tumor growth and angiogenesis

Destroying tumor vasculature is a relevant therapeutic strategy due to its involvement in tumor progression. However, adaptive resistance to approved antiangiogenic drugs targeting VEGF/VEGFR pathway requires the recruitment of additional targets. In this aspect, targeting TRAIL pathway is promising as it is an important component of the immune system involved in tumor immunosurveillance. For dual targeting of malignant cells and tumor vascular microenvironment, we designed a multivalent fusion protein SRH-DR5-B-iRGD with antiangiogenic VEGFR2-specific peptide SRH at the N-terminus and a tumor-targeting and -penetrating peptide iRGD at the C-terminus of receptor-selective TRAIL variant DR5-B. SRH-DR5-B-iRGD obtained high affinity for DR5, VEGFR2 and αvβ3 integrin in nanomolar range. Fusion of DR5-B with effector peptides accelerated DR5 receptor internalization rate upon ligand binding. Antitumor efficacy was evaluated in vitro in human tumor cell lines and primary patient-derived glioblastoma neurospheres, and in vivo in xenograft mouse model of human glioblastoma. Multivalent binding of SRH-DR5-B-iRGD fusion efficiently stimulated DR5-mediated tumor cell death via caspase-dependent mechanism, suppressed xenograft tumor growth by >80 %, doubled the lifespan of xenograft animals, and inhibited tumor vascularization. Therefore, targeting DR5 and VEGFR2 molecular pathways with SRH-DR5-B-iRGD protein may provide a novel therapeutic approach for treatment of solid tumors.

Impaired VEGF-A-Mediated Neurovascular Crosstalk Induced by SARS-CoV-2 Spike Protein: A Potential Hypothesis Explaining Long COVID-19 Symptoms and COVID-19 Vaccine Side Effects?

Long coronavirus disease-19 (COVID-19) is a newly discovered syndrome characterized by multiple organ manifestations that persist for weeks to months, following the recovery from acute disease. Occasionally, neurological and cardiovascular side effects mimicking long COVID-19 have been reported in recipients of COVID-19 vaccines. Hypothetically, the clinical similarity could be due to a shared pathogenic role of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike (S) protein produced by the virus or used for immunization. The S protein can bind to neuropilin (NRP)-1, which normally functions as a coreceptor for the vascular endothelial growth factor (VEGF)-A. By antagonizing the docking of VEGF-A to NRP-1, the S protein could disrupt physiological pathways involved in angiogenesis and nociception. One consequence could be the increase in unbound forms of VEGF-A that could bind to other receptors. SARS-CoV-2-infected individuals may exhibit increased plasma levels of VEGF-A during both acute illness and convalescence, which could be responsible for diffuse microvascular and neurological damage. A few studies suggest that serum VEGF-A may also be a potential biomarker for long COVID-19, whereas evidence for COVID-19 vaccines is lacking and merits further investigation.

From protein-protein interactions to immune modulation: Therapeutic prospects of targeting Neuropilin-1 in high-grade glioma

In the past several years there has been a marked increase in our understanding of the pathophysiological hallmarks of glioblastoma development and progression, with specific respect to the contribution of the glioma tumor microenvironment to the rapid progression and treatment resistance of high-grade gliomas. Despite these strides, standard of care therapy still only targets rapidly dividing tumor cells in the glioma, and does little to curb the pro-tumorigenic functions of non-cancerous cells entrenched in the glioma microenvironment. This tumor promoting environment as well as the heterogeneity of high-grade gliomas contribute to the poor prognosis of this malignancy. The interaction of non-malignant cells in the microenvironment with the tumor cells accentuate phenotypes such as rapid proliferation or immunosuppression, so therapeutically modulating one target expressed on one cell type may be insufficient to restrain these rapidly developing neoplasias. With this in mind, identifying a target expressed on multiple cell types and understanding how it governs tumor-promoting functions in each cell type may have great utility in better managing this disease. Herein, we review the physiology and pathological effects of Neuropilin-1, a transmembrane co-receptor which mediates signal transduction pathways when associated with multiple other receptors. We discuss its effects on the properties of endothelial cells and on immune cell types within gliomas including glioma-associated macrophages, microglia, cytotoxic T cells and T regulatory cells. We also consider its effects when elaborated on the surface of tumor cells with respect to proliferation, stemness and treatment resistance, and review attempts to target Neuroplin-1 in the clinical setting.

Quantitative characterization of tetraspanin 8 homointeractions in the plasma membrane

The spatial distribution of proteins in cell membranes is crucial for signal transduction, cell communication and membrane trafficking. Members of the Tetraspanin family organize functional protein clusters within the plasma membrane into so-called Tetraspanin-enriched microdomains (TEMs). Direct interactions between Tetraspanins are believed to be important for this organization. However, studies thus far have utilized mainly co-immunoprecipitation methods that cannot distinguish between direct and indirect, through common partners, interactions. Here we study Tetraspanin 8 homointeractions in living cells via quantitative fluorescence microscopy. We demonstrate that Tetraspanin 8 exists in a monomer-dimer equilibrium in the plasma membrane. Tetraspanin 8 dimerization is described by a high dissociation constant (Kd = 14 700 ± 1100 Tspan8/µm2), one of the highest dissociation constants measured for membrane proteins in live cells. We propose that this high dissociation constant, and thus the short lifetime of the Tetraspanin 8 dimer, is critical for Tetraspanin 8 functioning as a master regulator of cell signaling.

Interactions between semaphorins and plexin-neuropilin receptor complexes in the membranes of live cells

Signaling of semaphorin ligands via their plexin–neuropilin receptors is involved in tissue patterning in the developing embryo. These proteins play roles in cell migration and adhesion but are also important in disease etiology, including in cancer angiogenesis and metastasis. While some structures of the soluble domains of these receptors have been determined, the conformations of the full-length receptor complexes are just beginning to be elucidated, especially within the context of the plasma membrane. Pulsed-interleaved excitation fluorescence cross-correlation spectroscopy allows direct insight into the formation of protein–protein interactions in the membranes of live cells. Here, we investigated the homodimerization of neuropilin-1 (Nrp1), plexin A2, plexin A4, and plexin D1 using pulsed-interleaved excitation fluorescence cross-correlation spectroscopy. Consistent with previous studies, we found that Nrp1, plexin A2, and plexin A4 are present as dimers in the absence of exogenous ligand. Plexin D1, on the other hand, was monomeric under similar conditions, which had not been previously reported. We also found that plexin A2 and A4 assemble into a heteromeric complex. Stimulation with semaphorin 3A or semaphorin 3C neither disrupts nor enhances the dimerization of the receptors when expressed alone, suggesting that activation involves a conformational change rather than a shift in the monomer–dimer equilibrium. However, upon stimulation with semaphorin 3C, plexin D1 and Nrp1 form a heteromeric complex. This analysis of interactions provides a complementary approach to the existing structural and biochemical data that will aid in the development of new therapeutic strategies to target these receptors in cancer.

Neural network strategies for plasma membrane selection in fluorescence microscopy images

In recent years, there has been an explosion of fluorescence microscopy studies of live cells in the literature. The analysis of the images obtained in these studies often requires labor-intensive manual annotation to extract meaningful information. In this study, we explore the utility of a neural network approach to recognize, classify, and select plasma membranes in high-resolution images, thus greatly speeding up data analysis and reducing the need for personnel training for highly repetitive tasks. Two different strategies are tested: 1) a semantic segmentation strategy, and 2) a sequential application of an object detector followed by a semantic segmentation network. Multiple network architectures are evaluated for each strategy, and the best performing solutions are combined and implemented in the Recognition Of Cellular Membranes software. We show that images annotated manually and with the Recognition Of Cellular Membranes software yield identical results by comparing Förster resonance energy transfer binding curves for the membrane protein fibroblast growth factor receptor 3. The approach that we describe in this work can be applied to other image selection tasks in cell biology.

Use of NanoBiT and NanoBRET to monitor fluorescent VEGF-A binding kinetics to VEGFR2/NRP1 heteromeric complexes in living cells

BACKGROUND AND PURPOSE

VEGF-A is a key mediator of angiogenesis, primarily signalling via VEGF receptor 2 (VEGFR2). Endothelial cells also express the co-receptor neuropilin-1 (NRP1) that potentiates VEGF-A/VEGFR2 signalling. VEGFR2 and NRP1 had distinct real-time ligand binding kinetics when monitored using BRET. We previously characterised fluorescent VEGF-A isoforms tagged at a single site with tetramethylrhodamine (TMR). Here, we explored differences between VEGF-A isoforms in living cells that co-expressed both receptors.

EXPERIMENTAL APPROACH

Receptor localisation was monitored in HEK293T cells expressing both VEGFR2 and NRP1 using membrane-impermeant HaloTag and SnapTag technologies. To isolate ligand binding pharmacology at a defined VEGFR2/NRP1 complex, we developed an assay using NanoBiT complementation technology whereby heteromerisation is required for luminescence emissions. Binding affinities and kinetics of VEGFR2-selective VEGF165 b-TMR and non-selective VEGF165 a-TMR were monitored using BRET from this defined complex.

KEY RESULTS

Cell surface VEGFR2 and NRP1 were co-localised and formed a constitutive heteromeric complex. Despite being selective for VEGFR2, VEGF165 b-TMR had a distinct kinetic ligand binding profile at the complex that largely remained elevated in cells over 90 min. VEGF165 a-TMR bound to the VEGFR2/NRP1 complex with kinetics comparable to those of VEGFR2 alone. Using a binding-dead mutant of NRP1 did not affect the binding kinetics or affinity of VEGF165 a-TMR.

CONCLUSION AND IMPLICATIONS

This NanoBiT approach enabled real-time ligand binding to be quantified in living cells at 37°C from a specified complex between a receptor TK and its co-receptor for the first time.

Pancancer Analysis of Neurovascular-Related NRP Family Genes as Potential Prognostic Biomarkers of Bladder Urothelial Carcinoma

Background

Neurovascular-related genes have been implicated in the development of cancer. Studies have shown that a high expression of neuropilins (NRPs) promotes tumourigenesis and tumour malignancy.

Method

A multidimensional bioinformatics analysis was performed to examine the relationship between NRP genes and prognostic and pathological features, tumour mutational burden (TMB), microsatellite instability (MSI), and immunological features based on public databases and find the potential prognostic value of NRPs in pancancer.

Results

Survival analysis revealed that a low NRP1 expression in adrenocortical carcinoma (ACC), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), low-grade glioma (LGG), and stomach adenocarcinoma (STAD) was associated with poor prognosis. A high NRP2 expression in bladder urothelial carcinoma (BLCA), kidney renal papillary cell carcinoma (KIRP), and mesothelioma (MESO) was associated with poor prognosis. Moreover, NRP1 and NRP2 were associated with TMB and MSI. Subsequent analyses showed that NRP1 and NRP2 were correlated with immune infiltration and immune checkpoints. Genome-wide association analysis revealed that the NRP1 expression was strongly associated with kidney renal clear cell carcinoma (KIRC), whereas the NRP2 expression was closely associated with BLCA. Ultimately, NRP2 was found to be involved in the development of BLCA.

Conclusions

Neurovascular-related NRP family genes are significantly correlated with cancer prognosis, TME, and immune infiltration, particularly in BLCA.

HIF-1α promoted vasculogenic mimicry formation in lung adenocarcinoma through NRP1 upregulation in the hypoxic tumor microenvironment

Neovascularization is a key factor that contributes to tumor metastasis, and vasculogenic mimicry (VM) is an important form of neovascularization found in highly invasive tumors, including lung cancer. Despite the increasing number of studies focusing on VM, the mechanisms underlying VM formation remain unclear. Herein, our study explored the role of the HIF-1α/NRP1 axis in mediating lung adenocarcinoma metastasis and VM formation. HIF-1α, NRP1 expression, and VM in lung adenocarcinoma (LUAD) patient samples were examined by immunohistochemical staining. Quantitative real-time (qRT-PCR), western blot, transwell assay, wound healing assay, and tube formation assay were performed to verify the role of HIF-1α/NRP1 axis in LUAD metastasis and VM formation. ChIP and luciferase reporter assay were used to confirm whether NRP1 is a direct target of HIF-1α. In LUAD tissues, we confirmed a positive relationship between HIF-1α and NRP1 expression. Importantly, high HIF-1α and NRP1 expression and the presence of VM were correlated with poor prognosis. We also found that HIF-1α could induce LUAD cell migration, invasion, and VM formation by regulating NRP1. Moreover, we demonstrated that HIF-1α can directly bind to the NRP1 promoter located between −2009 and −2017 of the promoter. Mechanistically, MMP2, VE-cadherin, and Vimentin expression were affected. HIF-1α plays an important role in inducing lung adenocarcinoma cell metastasis and VM formation via upregulation of NRP1. This study highlights the potential therapeutic value of targeting NRP1 for suppressing lung adenocarcinoma metastasis and progression.

Probing Membrane Protein Association Using Concentration-Dependent Number and Brightness

We introduce concentration-dependent number and brightness (cdN&B), a fluorescence fluctuation technique that can be implemented on a standard confocal microscope and can report on the thermodynamics of membrane protein association in the native plasma membrane. It uses transient transfection to enable measurements of oligomer size as a function of receptor concentration over a broad range, yielding the association constant. We discuss artifacts in cdN&B that are concentration-dependent and can distort the oligomerization curves, and we outline procedures that can correct for them. Using cdN&B, we characterize the association of neuropilin 1 (NRP1), a protein that plays a critical role in the development of the embryonic cardiovascular and nervous systems. We show that NRP1 associates into a tetramer in a concentration-dependent manner, and we quantify the strength of the association. This work demonstrates the utility of cdN&B as a powerful tool in biophysical chemistry.

The Biased Ligands NGF and NT-3 Differentially Stabilize Trk-A Dimers

Trk-A is a receptor tyrosine kinase (RTK) that plays an essential role in the development and functioning of the nervous system. Trk-A is expressed in neurons and signals in response to two ligands, NGF and neurotrophin-3 (NT-3), with very different functional consequences. Thus, NGF and NT-3 are "biased" ligands for Trk-A. Because it has been hypothesized that biased RTK ligands induce differential stabilization of RTK dimers, here, we seek to test this hypothesis for NGF and NT-3. In particular, we use Förster resonance energy transfer (FRET) and fluorescence intensity fluctuation spectroscopy to assess the strength of Trk-A interactions and Trk-A oligomer size in the presence of the two ligands. Although the difference in Trk-A behavior in response to the two ligands has been previously attributed to differences in their binding to Trk-A in the endosomes at low pH, here, we further show differences in the stabilities of the NGF- and NT-3-bound Trk-A dimers in the plasma membrane and at neutral pH. We discuss the biological significance of these new findings and their implications for the design of Trk-A ligands with novel functionalities.

New insights into the role of co-receptor neuropilins in tumour angiogenesis and lymphangiogenesis and targeted therapy strategies

Local tumour sites lead to pathological angiogenesis and lymphangiogenesis due to malignant conditions such as hypoxia. Although VEGF and VEGFR are considered to be the main anti-tumour treatment targets, the problems of limited efficacy and observable side effects of some drugs relevant to this target still remain to be solved. Therefore, it is necessary to identify new therapeutic targets for angiogenesis or lymphangiogenesis. The neuropilin family is a class of single transmembrane glycoprotein receptors, including neuropilin1 (NRP1) and neuropilin2 (NRP2), which could act as co-receptors of VEGFA-165 and VEGFC and play a key role in promoting tumour proliferation, invasion and metastasis. In this review, we introduced the schematic diagram to visually reveal the function of NRP1 and NRP2 in enhancing the binding affinity of VEGFR2 to VEGFA-165 and VEGFR3 to VEGFC, respectively. We also discussed the signalling pathways that depend on the co-receptors NRP1 and NRP2 and some existing targeted therapeutic strategies, such as monoclonal antibodies, targeted peptides, microRNAs and small molecule inhibitors. It will contribute a vital foundation for the future research and development of new drugs targeting NRPs. HIGHLIGHTS NRP1 acts as a co-receptor with VEGFR2 and the pro-angiogenic factor VEGFA-165 to up-regulate tumour angiogenesis by promoting endothelial cells proliferation, survival, migration, invasion and by preventing of apoptosis. NRP2 acts as a co-receptor with VEGFR3 and the pro-lymphogenic factor VEGFC to facilitate tumour metastasis by promoting lymphangiogenesis. Although NRP1 and NRP2 do not have enzymatic signalling activity, the affinity of VEGFR2 for VEGFA-165 and VEGFR3 for VEGFC can increase in a co-receptor manner, as detailed in the schematic. The exclusive roles of NRP1 and NRP2 in signalling pathways are specifically described to emphasise the molecular regulatory mechanisms involved in co-receptors. Various studies have shown that the co-receptors NRP1 and NRP2 can be directly or indirectly targeted by different methods to prevent tumour angiogenesis and lymphangiogenesis. Therapeutic strategies targeting NRPs look promising soon as evidenced by preclinical and clinical studies.

Neuropilin-1 receptor in the rapid and selective estrogen-induced neurovascular remodeling of rat uterus

Sympathetic nerves innervate most organs and regulate organ blood flow. Specifically, in the uterus, estradiol (E2) elicits rapid degeneration of sympathetic axons and stimulates the growth of blood vessels. Both physiological remodeling processes, critical for reproduction, have been extensively studied but as independent events and are still not fully understood. Here, we examine the neuropilin-1 (NRP1), a shared receptor for axon guidance and angiogenic factors. Systemic estradiol or vehicle were chronically injected to prepubertal rats and uterine and sympathetic chain sections immunostained for NRP1. Uterine semaphorin-3A mRNA was evaluated by in situ hybridization. Control sympathetic uterine-projecting neurons (1-month-old) expressed NRP1 in their somas but not in their intrauterine terminal axons. Estradiol did not affect NRP1 in the distal ganglia. However, at the entrance of the organ, some sympathetic NRP1-positive nerves were recognized. Vascular NRP1 was confined to intrauterine small-diameter vessels in both hormonal conditions. Although the overall pattern of NRP1-IR was not affected by E2 treatment, a subpopulation of infiltrated eosinophil leukocytes showed immunoreactivity for NRP1. Sema3A transcripts were detected in this cellular type as well. No NRP1-immunoreactive axons nor infiltrated eosinophils were visualized in other estrogenized pelvic organs. Together, these data suggest the involvement of NRP1/Sema3A signaling in the selective E2-induced uterine neurovascular remodeling. Our data support a model whereby NRP1 could coordinate E2-induced uterine neurovascular remodeling, acting as a positive regulator of growth when expressed in vessels and as a negative regulator of growth when expressed on axons.

Revisiting a controversy: The effect of EGF on EGFR dimer stability

EGFR is a receptor tyrosine kinase that plays a critical role in cell proliferation, differentiation, survival and migration. Its activating ligand, EGF, has long been believed to stabilize the EGFR dimer. Two research studies aimed at quantitative measurements of EGFR dimerization, however, have led to contradicting conclusions and have questioned this view. Given the controversy, here we sought to measure the dimerization of EGFR in the absence and in the presence of saturating EGF concentrations, and to tease out the effect of ligand on dimer stability, using a FRET-based quantitative method. Our measurements show that the dissociation constant is decreased ~150 times due to ligand binding, indicative of significant dimer stabilization. In addition, our measurements demonstrate that EGF binding induces a conformational change in the EGFR dimer.

The RTK Interactome: Overview and Perspective on RTK Heterointeractions

Receptor tyrosine kinases (RTKs) play important roles in cell growth, motility, differentiation, and survival. These single-pass membrane proteins are grouped into subfamilies based on the similarity of their extracellular domains. They are generally thought to be activated by ligand binding, which promotes homodimerization and then autophosphorylation in trans. However, RTK interactions are more complicated, as RTKs can interact in the absence of ligand and heterodimerize within and across subfamilies. Here, we review the known cross-subfamily RTK heterointeractions and their possible biological implications, as well as the methodologies which have been used to study them. Moreover, we demonstrate how thermodynamic models can be used to study RTKs and to explain many of the complicated biological effects which have been described in the literature. Finally, we discuss the concept of the RTK interactome: a putative, extensive network of interactions between the RTKs. This RTK interactome can produce unique signaling outputs; can amplify, inhibit, and modify signaling; and can allow for signaling backups. The existence of the RTK interactome could provide an explanation for the irreproducibility of experimental data from different studies and for the failure of some RTK inhibitors to produce the desired therapeutic effects. We argue that a deeper knowledge of RTK interactome thermodynamics can lead to a better understanding of fundamental RTK signaling processes in health and disease. We further argue that there is a need for quantitative, thermodynamic studies that probe the strengths of the interactions between RTKs and their ligands and between different RTKs.

Tumor and endothelial cells collaborate via transcellular receptor complexes

Many cellular signaling pathways are initiated by cell-surface ligand-sensing complexes that incorporate not just one but multiple receptors. Most studies focus on receptors coexpressed on a single cell (cis interactions), but complexes containing receptors on adjacent cells (trans interactions) are also possible. Recent work by Morin et al published in this journal provides critical evidence for such trans interactions between Neuropilin-1 (NRP1) expressed on human tumor cells and vascular endothelial growth factor receptor 2 (VEGFR2) expressed on adjacent endothelial cells, with the ligand VEGFA binding and bridging the two receptors. They show that the formation of these complexes is correlated with reduced tumor proliferation and increased patient survival. They also observe trans NRP1-VEGFA-VEGFR2 repressing angiogenesis and cis NRP1-VEGFA-VEGFR2 increasing angiogenesis in selected cancers. The distinct molecular signature of each tumor and each patient will determine which type of complexes dominate and will influence prognosis and treatment. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.