Showing papers on "Neuropilins published in 2008"

The semaphorins: versatile regulators of tumour progression and tumour angiogenesis

Abstract: The semaphorins and their receptors, the neuropilins and the plexins, were originally characterized as constituents of the complex regulatory system responsible for the guidance of axons during the development of the central nervous system. However, a growing body of evidence indicates that various semaphorins can either promote or inhibit tumour progression through the promotion or inhibition of processes such as tumour angiogenesis, tumour metastasis and tumour cell survival. This Review focuses on the emerging role of the semaphorins in cancer.

Neuropilins: structure, function and role in disease

Abstract: NRPs (neuropilins) are co-receptors for class 3 semaphorins, polypeptides with key roles in axonal guidance, and for members of the VEGF (vascular endothelial growth factor) family of angiogenic cytokines. They lack a defined signalling role, but are thought to mediate functional responses as a result of complex formation with other receptors, such as plexins in the case of semaphorins and VEGF receptors (e.g. VEGFR2). Mutant mouse studies show that NRP1 is essential for neuronal and cardiovascular development, whereas NRP2 has a more restricted role in neuronal patterning and lymphangiogenesis, but recent findings indicate that NRPs may have additional biological roles in other physiological and disease-related settings. In particular, NRPs are highly expressed in diverse tumour cell lines and human neoplasms and have been implicated in tumour growth and vascularization in vivo. However, despite the wealth of information regarding the probable biological roles of these molecules, many aspects of the regulation of cellular function via NRPs remain uncertain, and little is known concerning the molecular mechanisms through which NRPs mediate the functions of their various ligands in different cell types.

Neuropilin‐1 is a receptor for transforming growth factor β‐1, activates its latent form, and promotes regulatory T cell activity

Abstract: Neuropilin-1 (Nrp1) is a multifunctional protein, identified principally as a receptor for the class 3 semaphorins and members of the vascular endothelial growth factor (VEGF) family, but it is capable of other interactions. It is a marker of regulatory T cells (Tr), which often carry Nrp1 and latency-associated peptide (LAP)-TGF-β1 (the latent form). The signaling TGF-β1 receptors bind only active TGF-β1, and we hypothesized that Nrp1 binds the latent form. Indeed, we found that Nrp1 is a high-affinity receptor for latent and active TGF-β1. Free LAP, LAP-TGF-β1, and active TGF-β1 all competed with VEGF165 for binding to Nrp1. LAP has a basic, arginine-rich C-terminal motif similar to VEGF and peptides that bind to the b1 domain of Nrp1. A C-terminal LAP peptide (QSSRHRR) bound to Nrp1 and inhibited the binding of VEGF and LAP-TGF-β1. We also analyzed the effects of Nrp1/LAP-TGF-β1 coexpression on T cell function. Compared with Nrp1– cells, sorted Nrp1+ T cells had a much greater capacity to capture LAP-TGF-β1. Sorted Nrp1– T cells captured soluble Nrp1-Fc, and this increased their ability to capture LAP-TGF-β1. Conventional CD4+CD25–Nrp1– T cells coated with Nrp1-Fc/LAP-TGF-β1 acquired strong Tr activity. Moreover, LAP-TGF-β was activated by Nrp1-Fc and also by a peptide of the b2 domain of Nrp1 (RKFK; similar to a thrombospondin-1 peptide). Breast cancer cells, which express Nrp1, also captured and activated LAP-TGF-β1 in a Nrp1-dependent manner. Thus, Nrp1 is a receptor for TGF-β1, activates its latent form, and is relevant to Tr activity and tumor biology.

Molecular analysis of neural crest migration

Abstract: The neural crest (NC) cells have been called the ‘explorers of the embryos’ because they migrate all over the embryo where they differentiate into a variety of diverse kinds of cells. In this work, we analyse the role of different molecules controlling the migration of NC cells. First, we describe the strong similarity between the process of NC migration and metastasis in tumour cells. The epithelial–mesenchymal transition process that both kinds of cells undergo is controlled by the same molecular machinery, including cadherins, connexins, Snail and Twist genes and matrix metalloproteases. Second, we analysed the molecular signals that control the patterned migration of the cephalic and trunk NC cells. Most of the factors described so far, such as Eph/ephrins, semaphorins/neuropilins and Slit/Robo, are negative signals that prohibit the migration of NC cells into target areas of the embryo. Finally, we analyse how the direction of migration is controlled by regulation of cell polarity and how the planar cell polarity or non-canonical Wnt signalling is involved in this process.

Neuropilin structure governs VEGF and semaphorin binding and regulates angiogenesis.

Abstract: Neuropilins (NRP) play a central role in neuronal and blood vessel development as receptors for two ligand types, the semaphorin (SEMA) family of axon guidance modulators and the VEGF family of angiogenesis stimulators. The role of NRPs in axon guidance is well documented but a role in blood vessel development is less so. NRPs mediate normal developmental angiogenesis as shown in mouse and zebrafish models, and pathological angiogenesis in tumors and retinal disease. The ability of two disparate ligand families to bind to the same receptor is unusual but may be explainable by analysis of neuropilin structure. There are two NRP genes, nrp1 and nrp2. The NRPs have a relatively large extracellular domain consisting of sub domains, which are ligand binding sites. VEGF(165) binds to the b1b2 subdomain, SEMA3A and SEMA3F also bind to b1b2 but to a1a2 as well. Mutagenesis studies have identified NRP amino acids that bind VEGF(165) but not SEMA3F. These NRP structural elements might dictate differential SEMA and VEGF(165) binding properties, which in turn regulate angiogenesis. This article reviews the latest information of NRP structure and how structure influences angiogenesis. In addition, the role of NRPs in human cancer is addressed.

FAK–MAPK‐dependent adhesion disassembly downstream of L1 contributes to semaphorin3A‐induced collapse

Abstract: Axonal receptors for class 3 semaphorins (Sema3s) are heterocomplexes of neuropilins (Nrps) and Plexin-As signalling coreceptors. In the developing cerebral cortex, the Ig superfamily cell adhesion molecule L1 associates with Nrp1. Intriguingly, the genetic removal of L1 blocks axon responses of cortical neurons to Sema3A in vitro despite the expression of Plexin-As in the cortex, suggesting either that L1 substitutes for Plexin-As or that L1 and Plexin-A are both required and mediate distinct roles. We report that association of Nrp1 with L1 but not Plexin-As mediates the recruitment and activation of a Sema3A-induced focal adhesion kinase-mitogen-activated protein kinase cascade. This signalling downstream of L1 is needed for the disassembly of adherent points formed in growth cones and subsequently their collapse response to Sema3A. Plexin-As and L1 are coexpressed and present in common complexes in cortical neurons and both dominant-negative forms of Plexin-A and L1 impair their response to Sema3A. Consistently, Nrp1-expressing cortical projections are defective in mice lacking Plexin-A3, Plexin-A4 or L1. This reveals that specific signalling activities downstream of L1 and Plexin-As cooperate for mediating the axon guidance effects of Sema3A.

The C. elegans L1CAM homologue LAD-2 functions as a coreceptor in MAB-20/Sema2 mediated axon guidance.

Abstract: The L1 cell adhesion molecule (L1CAM) participates in neuronal development. Mutations in the human L1 gene can cause the neurological disorder CRASH (corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus). This study presents genetic data that shows that L1-like adhesion gene 2 (LAD-2), a Caenorhabditis elegans L1CAM, functions in axon pathfinding. In the SDQL neuron, LAD-2 mediates dorsal axon guidance via the secreted MAB-20/Sema2 and PLX-2 plexin receptor, the functions of which have largely been characterized in epidermal morphogenesis. We use targeted misexpression experiments to provide in vivo evidence that MAB-20/Sema2 acts as a repellent to SDQL. Coimmunoprecipitation assays reveal that MAB-20 weakly interacts with PLX-2; this interaction is increased in the presence of LAD-2, which can interact independently with MAB-20 and PLX-2. These results suggest that LAD-2 functions as a MAB-20 coreceptor to secure MAB-20 coupling to PLX-2. In vertebrates, L1 binds neuropilin1, the obligate receptor to the secreted Sema3A. However, invertebrates lack neuropilins. LAD-2 may thus function in the semaphorin complex by combining the roles of neuropilins and L1CAMs.

Orf virus VEGF-E NZ2 promotes paracellular NRP-1/VEGFR-2 coreceptor assembly via the peptide RPPR

Abstract: Vascular endothelial growth factors (VEGFs) interact with the receptor tyrosine kinases (RTKs) VEGFR-1, -2, and -3; neuropilins (NRPs); and heparan sulfate (HS) proteoglycans. VEGF RTKs signal to downstream targets upon ligand-induced tyrosine phosphorylation, while NRPs and HS act as coreceptors that lack enzymatic activity yet modulate signal output by VEGF RTKs. VEGFs exist in various isoforms with distinct receptor specificity and biological activity. Here, a series of mammalian VEGF-A splice variants and orf virus VEGF-Es, as well as chimeric and mutant VEGF variants, were characterized to determine the motifs required for binding to NRP-1 in the absence (VEGF-E) or presence (VEGF-A(165)) of an HS-binding sequence. We identified the carboxyterminal peptides RPPR and DKPRR as the NRP-1 binding motifs of VEGF-E and VEGF-A, respectively. RPPR had significantly higher affinity for NRP-1 than DKPRR. VEGFs containing an RPPR motif promoted HS-independent coreceptor complex assembly between VEGFR-2 and NRP-1, independent of whether these receptors were expressed on the same or separate cells grown in cocultures. Functional studies showed that stable coreceptor assembly by VEGF correlated with its ability to promote vessel formation in an embryoid body angiogenesis assay.

Neuropilins: a versatile partner of extracellular molecules that regulate development and disease.

Abstract: Neuropilins are a vertebrate-specific family of membrane multidomain proteins. They are crucial for the embryonic development of neural and vascular systems, whereas in the adult organism they are implicated in many processes, such as angiogenesis and the immune response. Additionally, it has been shown that they are overexpressed in numerous types of tumours, which results in higher microvessel density and correlates with poor prognosis. Their functions have been linked to their binding partners: semaphorins/collapsins, vascular endothelial growth factors (VEGFs), fibroblast growth factors (FGFs), hepatocyte growth factor/scatter factor and heparin/heparan sulfate (HS). Multiplicity of ligands alongside complex formation with several membrane receptors makes neuropilins potential 'hub' proteins, which act as a scaffold for multimeric associations. This review focuses on the structural features of neuropilins that underpin their multiple molecular interactions and hence their function.

Semaphorin, neuropilin and VEGF expression in glial tumours: SEMA3G, a prognostic marker?

Abstract: Gliomas are characterised by local infiltration, migration of tumour cells across long distances and sustained angiogenesis; therefore, proteins involved in these processes are most likely important. Such candidates are semaphorins involved in axon guidance and cell migration. In addition, semaphorins regulate tumour progression and angiogenesis. For cell signalling, class-4 semaphorins bind directly to plexins, whereas class-3 semaphorins require additional neuropilin (NRP) receptors that also bind VEGF165. The anti-angiogenic activity of class-3 semaphorins can be explained by competition with VEGF165 for NRP binding. In this study, we analysed the expressions of seven semaphorins of class-3, SEMA4D, VEGF and the NRP1 and NRP2 receptors in 38 adult glial tumours. In these tumours, SEMA3B, SEMA3G and NRP2 expressions were related to prolonged survival. In addition, SEMA3D expression was reduced in high-grade as compared with low-grade gliomas. In contrast, VEGF correlated with higher grade and poor survival. Thus, our data suggest a function for a subset of class-3 semaphorins as inhibitors of tumour progression, and the prognostic value of the VEGF/SEMA3 balance in adult gliomas. Moreover, in multivariate analysis, SEMA3G was found to be the only significant prognostic marker.

Urothelial expression of neuropilins and VEGF receptors in control and interstitial cystitis patients

Abstract: Interstitial cystitis (IC) is a chronic and painful bladder syndrome of unknown cause with no reliable biological marker or effective therapy. Vascular endothelial growth factor (VEGF), which plays a key role in bladder inflammation, is closely associated with the vascular alterations observed in patients with IC. However, our recent findings of VEGF receptors (VEGF-Rs) and VEGF coreceptors on nonendothelial cells in human and mouse urothelium suggest that additional VEGF targets and functions are possible in IC bladders. We report here that VEGF-Rs and coreceptors (neuropilins; NRP) are strongly expressed in both the human bladder urothelium and in the human bladder cancer cell line (J82) and that the expression of NRP2 and VEGF-R1 is significantly downregulated in IC compared with control subjects. In addition, treatment of J82 cells with bacillus Calmette-Guerin (BCG), a novel treatment strategy for IC, upregulates the messages for NRPs and VEGF-Rs. Furthermore, intravesical instillation of an internalizable VEGF fluorescent tracer (scVEGF/Cy5.5) into mouse urinary bladders results in a marked ligand accumulation in the urothelium and bladder parenchyma, indicating that urothelial VEGF-Rs are functionally active and capable of ligand interaction and internalization. Our results suggest that the VEGF pathway is altered in IC, that urinary VEGF may gain access to the bladder wall via these receptors, and that BCG treatment may replenish the missing VEGF-Rs/NRP receptors. Together, these results suggest that levels of NRPs, VEGF-Rs, and VEGF are new putative markers for the diagnosis of IC and that modulating these receptors can be exploited as therapeutic strategies.

VEGF receptors and neuropilins are expressed in the urothelial and neuronal cells in normal mouse urinary bladder and are upregulated in inflammation

Abstract: Recent evidence supports a role for vascular endothelium growth factor (VEGF) signaling in bladder inflammation. However, it is not clear what bladder cells are targeted by VEGF. Therefore, we determined the nature of cells responding to VEGF in normal and inflamed bladders by tagging such cells in vivo with a targeted fluorescent tracer, scVEGF/Cy, an engineered single-chain VEGF labeled with Cy5.5 dye, which identifies cells with accessible and functionally active VEGF receptors. Inflammation was induced by intravesical instillation of PAR-activating peptides or BCG. In vivo NIRF imaging with intravenously injected scVEGF/Cy revealed accumulation of the tracer in the control mouse bladder and established that inflammation increased the steady-state levels of tracer uptake. Ex vivo colocalization of Cy5.5 dye revealed that in normal and at a higher level in inflamed bladder, accumulation of scVEGF/Cy occurs in both urothelial and ganglial cells, expressing VEGF receptors VEGFR-1 and VEGFR-2, as well as VEGF coreceptors neuropilins (NRP) NRP1 and NRP2. PCR results indicate that the messages for VEGF-Rs and NRPs are present in the bladder mucosa and ChIP/QPCR analysis indicated that inflammation induced upregulation of genes encoding VEGFRs and NRPs. Our results strongly suggest new and blossoming VEGF-driven processes in bladder urothelial cells and ganglia in the course of inflammation. We expect that molecular imaging of the VEGF pathway in the urinary tract by receptor-mediated cell tagging in vivo will be useful for clinical diagnosis and therapeutic monitoring, and will help to accelerate the development of bladder-targeting drugs and treatments.

Semaphorin and neuropilin expression during early morphogenesis of Xenopus laevis

Abstract: Semaphorins are major regulators of morphogenesis and are involved in a variety of processes ranging from the guidance of cell migration to the development of cancer. Since semaphorins were first characterized as repulsive neuronal guidance cues, their expression has been best documented in the nervous system. However, broader studies are lacking. Here, we describe the expression of 13 members of the semaphorin family and two neuropilin receptors during early Xenopus laevis development. No particular expression pattern defines any of the semaphorin classes, but many are dynamically expressed in distinct areas undergoing morphogenetic cell movements like the developing mesoderm and the migrating neural crest. Furthermore, the complementary expression patterns of Sema3A/Nrp1 and Sema3F/Nrp2 are maintained across hundreds of millions of years, possibly indicating a conserved role in the guidance of migrating neural crest cells.

Vascular endothelial growth factor in central nervous system injuries - a vascular growth factor getting nervous?

Abstract: Vascular Endothelial Growth Factor ( VEGF) is recognized as a central factor in growth, survival and permeability of blood vessels in both physiological and pathological conditions. It is as such of importance for vascular responses in various central nervous system (CNS) disorders. Accumulating evidence suggest that VEGF may also act as a neuroprotective and neurotrophic factor supporting neuronal survival and neuronal regeneration. Findings of neuropilins as shared co-receptors between molecules with such seemingly different functions as the axon guidance molecules semaphorins and VEGF has further boosted the interest in the role of VEGF in neural tissue injury and repair mechanisms. Thus, VEGF most likely act in parallel or concurrent on cells in both the vascular and nervous system. The present review gives a summary of known or potential aspects of the VEGF system in the healthy and diseased nervous system. The potential benefits but also problems and pitfalls in intervening in the actions of such a multifunctional factor as VEGF in the disordered CNS are also covered.

Bevacizumab resistance in breast cancer: are neuropilins the key?

Abstract: During breast cancer growth and development, angiogenesis is triggered by the interaction between vascular endothelial growth factor (VEGF) and its receptors VEGF-R1 and VEGF-R2. In breast cancer, alternative VEGF receptors, the neuropilins (Np1 and Np2), are often upregulated and serve to augment the effects of VEGF-R1/VEGF-R2 binding and provide alternative signalling pathways. Recently, a humanized antibody, Bevacizumab (Bz), which prevents VEGF binding to VEGF-R1/VEGF-R2, in combination with chemotherapy demonstrated initial efficacy (increased progression-free survival) in breast cancer phase III clinical trials. Eventually, however, the tumours evade treatment control. This may be because neuropilins are not blocked by Bz and provide an alternative VEGF signalling pathway in breast cancer. Therefore the present study aims to evaluate the potential of enhancing efficacy of Bz treatment by simultaneously blocking VEGF–neuropilin binding.

VEGF-C/VEGFR-3 and PDGF-B/PDGFR-b pathways in embryonic lymphangiogenesis

Abstract: 6 REVIEW OF THE LITERATURE 7 1. THE TWO VASCULAR SYSTEMS 7 Blood vascular system 7 Lymphatic vascular system 7 2. DEVELOPMENT OF BLOOD AND LYMPHATIC VASCULAR SYSTEMS 8 Vasculogenesis 8 Angiogenesis 8 Lymphangiogenesis 10 3. VASCULAR ENDOTHELIAL GROWTH FACTORS AND THEIR RECEPTORS 14 VEGF 14 VEGF-B 15 PlGF 15 VEGF-C 15 VEGF-D 16 VEGF-E 17 VEGFR-1 17 VEGFR-2 18 VEGFR-3 18 Neuropilins 19 4. PLATELET-DERIVED GROWTH FACTORS AND THEIR RECEPTORS 20 PDGF-A and PDGF-B 20 PDGF-C and PDGF-D 21 PDGFR-! and PDGFR-s 22 5. LYMPHATIC VESSELS IN DISEASE 22 Lymphedema 22 Tumor metastasis 24 Inflammation 25 AIMS OF THE STUDY 26 MATERIALS AND METHODS 27 RESULTS AND DISCUSSION 29 CONCLUDING REMARKS 36 ACKNOWLEDGEMENTS 37 REFERENCES 38

The Role of the Neuropilins and Their Associated Plexin Receptors in Tumor Angiogenesis and Tumor Progression

Abstract: The neuropilins were described as receptors for the axon guidance factors belonging to the class 3 semaphorins subfamily. They were subsequently found to be expressed in endothelial cells and to function in addition as receptors for specific splice forms of angiogenic factors belonging to the VEGF family. There is increasing evidence indicating that the neuropilins and their associated plexin and tyrosine-kinase VEGF receptors play important roles as regulators of developmental angiogenesis and in the events that initiate tumor angiogenesis. Their VEGF and class 3 semaphorin ligands were found to regulate angiogenesis as a result of their interaction with neuropilins. Furthermore, many types of cancer cells express neuropilins and there is accumulating evidence indicating that class 3 semaphorins and members of the VEGF family of growth factors can affect the behavior of cancer cells as a result of their interaction with neuropilins expressed by cancer cells. This chapter focuses on the role of the neuropilins and of their ligands in tumor angiogenesis and tumor progression.

Vascular Endothelial Growth Factor Family and Its Receptors

Abstract: The vascular endothelial growth factors (VEGFs) are key regulators of blood and lymphatic vessel development during embryogenesis and in promoting new vascular growth during physiological and pathological processes in the adult. The VEGF family of ligands in mammals includes VEGF-A, VEGF-B, VEGF-C, VEGF-D, and placenta growth factor (PlGF). These ligands bind to and activate three receptor tyrosine kinases, designated VEGFR-1, VEGFR-2, and VEGFR-3. VEGF ligands bind to these receptors with overlapping ligand-receptor specificities, and activation may be further modulated through interaction with coreceptors such as the neuropilins (NRP-1 and NRP-2), integrins, or Vascular endothelial-cadherin (VE-cadherin). Ligand activation of VEGFRs triggers a network of distinct downstream-signaling pathways in a cell-type-specific manner that promotes vascular permeability, endothelial cell growth, migration, and survival. VEGF is an important survival factor for hematopoietic stem cells (HSCs) and stimulates the mobilization of endothelial progenitor cells (EPC) from the bone marrow to distant sites of neovascularization. A large body of experimental evidence has established VEGF as an essential molecule in promoting angiogenesis during tumor growth. These findings have led to the development of therapeutic agents that selectively target various VEGF ligands and their receptors. This chapter reviews the biology of VEGF and its receptors, emphasizing their important role for cancerous growth.