Vascular endothelial growth factor (VEGF)-like protein from orf virus NZ2 binds to VEGFR2 and neuropilin-1.
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Orf virus, a member of the poxvirus family, produces a pustular dermatitis in sheep, goats, and humans. The lesions induced after infection with orf virus show extensive proliferation of vascular endothelial cells, dilation of blood vessels and dermal swelling. An explanation for the nature of these lesions may lie in the discovery that orf virus encodes an apparent homolog of the mammalian vascular endothelial growth factor (VEGF) family of molecules. These molecules mediate endothelial cell proliferation, vascular permeability, angiogenesis, and lymphangiogenesis via the endothelial cell receptors VEGFR-1 (Flt1), VEGFR-2 (KDR/Flk1), and VEGFR-3 (Flt4). The VEGF-like protein of orf virus strain NZ2 (ORFV2-VEGF) is most closely related in primary structure to VEGF. In this study we examined the biological activities and receptor specificity of the ORFV2-VEGF protein. ORFV2-VEGF was found to be a disulfide-linked homodimer with a subunit of approximately 25 kDa. ORFV2-VEGF showed mitogenic activity on bovine aortic and human microvascular endothelial cells and induced vascular permeability. ORFV2-VEGF was found to bind and induce autophosphorylation of VEGFR-2 and was unable to bind or activate VEGFR-1 and VEGFR-3, but bound the newly identified VEGF165 receptor neuropilin-1. These results indicate that, from a functional viewpoint, ORFV2-VEGF is indeed a member of the VEGF family of molecules, but is unique, however, in that it utilizes only VEGFR-2 and neuropilin-1. (+info)
Evidence for collapsin-1 functioning in the control of neural crest migration in both trunk and hindbrain regions.
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Collapsin-1 belongs to the Semaphorin family of molecules, several members of which have been implicated in the co-ordination of axon growth and guidance. Collapsin-1 can function as a selective chemorepellent for sensory neurons, however, its early expression within the somites and the cranial neural tube (Shepherd, I., Luo, Y. , Raper, J. A. and Chang, S. (1996) Dev. Biol. 173, 185-199) suggest that it might contribute to the control of additional developmental processes in the chick. We now report a detailed study on the expression of collapsin-1 as well as on the distribution of collapsin-1-binding sites in regions where neural crest cell migration occurs. collapsin-1 expression is detected in regions bordering neural crest migration pathways in both the trunk and hindbrain regions and a receptor for collapsin-1, neuropilin-1, is expressed by migrating crest cells derived from both regions. When added to crest cells in vitro, a collapsin-1-Fc chimeric protein induces morphological changes similar to those seen in neuronal growth cones. In order to test the function of collapsin-1 on the migration of neural crest cells, an in vitro assay was used in which collapsin-1-Fc was immobilised in alternating stripes consisting of collapsin-Fc/fibronectin versus fibronectin alone. Explanted neural crest cells derived from both trunk and hindbrain regions avoided the collapsin-Fc-containing substratum. These results suggest that collapsin-1 signalling can contribute to the patterning of neural crest cell migration in the developing chick. (+info)
Neural development: The semantics of axon guidance.
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Recent studies of the semaphorin family of axon guidance signals and their receptors have revealed a surprising versatility in the ways that they can be used solve problems in neural development, and provided new opportunities for understanding how guidance information is interpreted beneath the cell surface. (+info)
Role of semaphorin III in the developing rodent trigeminal system.
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Semaphorins are a large family of secreted and transmembrane glycoproteins. Sema III, a member of the Class III semaphorins is a potent chemorepulsive signal for subsets of sensory axons and steers them away from tissue regions with high levels of expression. Previous studies in mutant mice lacking sema III gene showed various neural and nonneural abnormalities. In this study, we focused on the developing trigeminal pathway of sema III knockout mice. We show that the peripheral and central trigeminal projections are impaired during initial pathway formation when they develop into distinct nerves or tracts. These axons defasciculate and compromise the normal bundling of nerves and restricted alignment of the central tract. In contrast to trigeminal projections, thalamocortical projections to the barrel cortex appear normal. Furthermore, sema III receptor, neuropilin, is expressed during a short period of development when the tract is laid down, but not in the developing thalamocortical pathway. Peripherally, trigeminal axons express neuropilin for longer duration than their central counterparts. In spite of projection errors, whisker follicle innervation appears normal and whisker-related patterns form in the trigeminal nuclei and upstream thalamic and cortical centers. Our observations suggest that sema III plays a limited role during restriction of developing trigeminal axons to proper pathways and tracts. Other molecular and cellular mechanisms must act in concert with semaphorins in ensuring target recognition, topographic order of projections, and patterning of neural connections. (+info)
Neuropilin-1 mediates collapsin-1/semaphorin III inhibition of endothelial cell motility: functional competition of collapsin-1 and vascular endothelial growth factor-165.
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Neuropilin-1 (NRP1) is a receptor for two unrelated ligands with disparate activities, vascular endothelial growth factor-165 (VEGF165), an angiogenesis factor, and semaphorin/collapsins, mediators of neuronal guidance. To determine whether semaphorin/collapsins could interact with NRP1 in nonneuronal cells, the effects of recombinant collapsin-1 on endothelial cells (EC) were examined. Collapsin-1 inhibited the motility of porcine aortic EC (PAEC) expressing NRP1 alone; coexpressing KDR and NRP1 (PAEC/KDR/NRP1), but not parental PAEC; or PAEC expressing KDR alone. The motility of PAEC expressing NRP1 was inhibited by 65-75% and this inhibition was abrogated by anti-NRP1 antibody. In contrast, VEGF165 stimulated the motility of PAEC/KDR/NRP1. When VEGF165 and collapsin-1 were added simultaneously to PAEC/KDR/NRP1, dorsal root ganglia (DRG), and COS-7/NRP1 cells, they competed with each other in EC motility, DRG collapse, and NRP1-binding assays, respectively, suggesting that the two ligands have overlapping NRP1 binding sites. Collapsin-1 rapidly disrupted the formation of lamellipodia and induced depolymerization of F-actin in an NRP1-dependent manner. In an in vitro angiogenesis assay, collapsin-1 inhibited the capillary sprouting of EC from rat aortic ring segments. These results suggest that collapsin-1 can inhibit EC motility as well as axon motility, that these inhibitory effects on motility are mediated by NRP1, and that VEGF165 and collapsin-1 compete for NRP1-binding sites. (+info)
Differential binding of vascular endothelial growth factor B splice and proteolytic isoforms to neuropilin-1.
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Vascular endothelial growth factor B (VEGF-B) is expressed in various tissues, especially strongly in the heart, and binds selectively to one of the VEGF receptors, VEGFR-1. The two splice isoforms, VEGF-B(167) and VEGF-B(186), have identical NH(2)-terminal cystine knot growth factor domains but differ in their COOH-terminal domains which give these forms their distinct biochemical properties. In this study, we show that both splice isoforms of VEGF-B bind specifically to Neuropilin-1 (NRP1), a receptor for collapsins/semaphorins and for the VEGF(165) isoform. The NRP1 binding of VEGF-B could be competed by an excess of VEGF(165). The binding of VEGF-B(167) was mediated by the heparin binding domain, whereas the binding of VEGF-B(186) to NRP1 was regulated by exposure of a short COOH-terminal proline-rich peptide upon its proteolytic processing. In immunohistochemistry, NRP1 distribution was found to be overlapping or adjacent to known sites of VEGF-B expression in several tissues, in particular in the developing heart, suggesting the involvement of VEGF-B in NRP1-mediated signaling. (+info)
Cloning and characterization of neuropilin-1-interacting protein: a PSD-95/Dlg/ZO-1 domain-containing protein that interacts with the cytoplasmic domain of neuropilin-1.
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Neuropilin-1 (Npn-1), a receptor for semaphorin III, mediates the guidance of growth cones on extending neurites. The molecular mechanism of Npn-1 signaling remains unclear. We have used a yeast two-hybrid system to isolate a protein that interacts with the cytoplasmic domain of Npn-1. This Npn-1-interacting protein (NIP) contains a central PSD-95/Dlg/ZO-1 (PDZ) domain and a C-terminal acyl carrier protein domain. The physiological interaction of Npn-1 and NIP is supported by co-immunoprecipitation of these two proteins in extracts from a heterologous expression system and from a native tissue. The C-terminal three amino acids of Npn-1 (S-E-A-COOH), which is conserved from Xenopus to human, is responsible for interaction with the PDZ domain-containing C-terminal two-thirds of NIP. NIP as well as Npn-1 are broadly expressed in mice as assayed by Northern and Western analysis. Immunohistochemistry and in situ hybridization experiments revealed that NIP expression overlaps with that of Npn-1. NIP has been independently cloned as RGS-GAIP-interacting protein (GIPC), where it was identified by virtue of its interaction with the C terminus of RGS-GAIP and suggested to participate in clathrin-coated vesicular trafficking. We suggest that NIP and GIPC may participate in regulation of Npn-1-mediated signaling as a molecular adapter that couples Npn-1 to membrane trafficking machinery in the dynamic axon growth cone. (+info)
Collapsin-1/semaphorin D is a repellent for chick ganglion of Remak axons.
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Chick collapsin-1/human semaphorin III/mouse semaphorin D is believed to guide the extension of specific axons by a repellent mechanism. Here we examine its role in the guidance of axons of the ganglion of Remak (Remak) in the developing chick intestine. Early in embryogenesis Remak axons extend parallel to, but do not enter, the intestine when collapsin-1 is expressed in the adjacent rectal wall. Remak axons later penetrate the peripheral portions of the rectal wall when collapsin-1 expression retreats from the outer muscle layer to the more internal submucosal and mucosal layers of the rectum. Extension of Remak neurites is repelled in vitro by rectum explants and also by 293T cells expressing collapsin-1. The rectal chemorepellent activity is blocked by anti-collapsin-1 antibodies. Our results suggest that collapsin-1 may help prevent Remak axons from projecting into the intestinal wall at early developmental times and later restricts Remak axon trajectories to the outer part of the intestinal muscle layer. (+info)