Overcoming disease-induced growth factor resistance in therapeutic angiogenesis using recombinant co-receptors delivered by a liposomal system

Current treatment options for ischemia include percutaneous interventions, surgical bypass or pharmacological interventions aimed at slowing the progression of vascular disease. Unfortunately, while each of these treatment modalities provides some benefit for patients in the short-term, many patients have resistant or recurrent disease that is poorly managed by these therapies. A highly appealing strategy for treating ischemic disease is to stimulate the revascularization of the tissue to restore blood flow. While many techniques have been explored in this regard, clinically effective angiogenic therapies remain elusive. Here, we hypothesized that the presence of co-morbid disease states inherently alters the ability of the body to respond to angiogenic therapies. Using a mouse model of diabetes and obesity, we examined alterations in the major components for the signaling pathways for FGF-2, VEGF-A and PDGF under normal and high fat dietary conditions. In skeletal muscle, a high fat diet increased levels of growth factor receptors and co-receptors including syndecan-1, syndecan-4 and PDGFR-α in wild-type mice. These increases did not occur in Ob/Ob mice on a high fat diet and there was a significant decrease in protein levels for neuropilin-1 and heparanase in these mice. With the aim of increasing growth factor effectiveness in the context of disease, we examined whether local treatment with alginate gel-delivered FGF-2 and syndecan-4 proteoliposomes could overcome the growth factor resistance in these mice. This treatment enhanced the formation of new blood vessels in Ob/Ob mice by 6 fold in comparison to FGF-2 delivered alone. Our studies support that disease states cause a profound shift in growth factor signaling pathways and that co-receptor-based therapies have potential to overcome growth factor resistance in the context of disease.

Prognostic implication of neuropilin-1 upregulation in human nasopharyngeal carcinoma

OBJECTIVE

As a receptor for both vascular endothelial growth factors and semaphorin, neuropilin-1 (NRP-1) is reported to be up-regulated in cells of several cancers. However, its roles in human nasopharyngeal carcinoma (NPC) are still unclear. Therefore, the goal of this study was to investigate the expression pattern of NRP-1 in NPC tissues, to clarify the clinical significance of NRP-1 expression in NPC as well as the potential prognostic implication of NRP-1 expression.

METHODS

Immunohistochemistry was performed to detect the expression of NRP-1 in tumor tissue samples from 266 NPC patients. The association of NRP-1 protein expression with the clinicopathological characteristics and the prognosis of NPC were subsequently assessed.

RESULTS

Immunohistochemical analysis showed that 176 of 266 (66.17%) paraffin-embedded archival NPC biopsies showed high expression of NRP-1, but no non-cancerous nasopharyngeal specimens showed positive expression of NRP-1. In addition, high NRP-1 expression was significantly associated with advanced clinical stage (P = 0.02), positive recurrence (P = 0.001) and metastasis status (P = 0.001) of NPC. Moreover, the NPC patients with higher NRP-1 expression had shorter overall survival, whereas patients with lower NRP-1 expression had better survival (P < 0.001). Furthermore, the multivariate analysis indicated that the overexpression of NRP-1 protein was an independent prognostic factor for overall survival (P = 0.001) in NPC patients.

CONCLUSION

These findings suggest for the first time that NRP-1 upregulation may be a novel biomarker for the prediction of advanced tumor progression and unfavorable prognosis in NPC patients who may benefit from alternative treatment strategy and targeted treatment.

VIRTUAL SLIDES

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1507827881105018.

Stability and function of regulatory T cells is maintained by a neuropilin-1-semaphorin-4a axis

Regulatory T cells (Treg cells) have a crucial role in the immune system by preventing autoimmunity, limiting immunopathology, and maintaining immune homeostasis. However, they also represent a major barrier to effective anti-tumour immunity and sterilizing immunity to chronic viral infections. The transcription factor Foxp3 has a major role in the development and programming of Treg cells. The relative stability of Treg cells at inflammatory disease sites has been a highly contentious subject. There is considerable interest in identifying pathways that control the stability of Treg cells as many immune-mediated diseases are characterized by either exacerbated or limited Treg-cell function. Here we show that the immune-cell-expressed ligand semaphorin-4a (Sema4a) and the Treg-cell-expressed receptor neuropilin-1 (Nrp1) interact both in vitro, to potentiate Treg-cell function and survival, and in vivo, at inflammatory sites. Using mice with a Treg-cell-restricted deletion of Nrp1, we show that Nrp1 is dispensable for suppression of autoimmunity and maintenance of immune homeostasis, but is required by Treg cells to limit anti-tumour immune responses and to cure established inflammatory colitis. Sema4a ligation of Nrp1 restrained Akt phosphorylation cellularly and at the immunologic synapse by phosphatase and tensin homologue (PTEN), which increased nuclear localization of the transcription factor Foxo3a. The Nrp1-induced transcriptome promoted Treg-cell stability by enhancing quiescence and survival factors while inhibiting programs that promote differentiation. Importantly, this Nrp1-dependent molecular program is evident in intra-tumoral Treg cells. Our data support a model in which Treg-cell stability can be subverted in certain inflammatory sites, but is maintained by a Sema4a-Nrp1 axis, highlighting this pathway as a potential therapeutic target that could limit Treg-cell-mediated tumour-induced tolerance without inducing autoimmunity.

Tumor-penetrating peptides

Tumor-homing peptides can be used to deliver drugs into tumors. Phage library screening in live mice has recently identified homing peptides that specifically recognize the endothelium of tumor vessels, extravasate, and penetrate deep into the extravascular tumor tissue. The prototypic peptide of this class, iRGD (CRGDKGPDC), contains the integrin-binding RGD motif. RGD mediates tumor-homing through binding to αv integrins, which are selectively expressed on various cells in tumors, including tumor endothelial cells. The tumor-penetrating properties of iRGD are mediated by a second sequence motif, R/KXXR/K. This C-end Rule (or CendR) motif is active only when the second basic residue is exposed at the C-terminus of the peptide. Proteolytic processing of iRGD in tumors activates the cryptic CendR motif, which then binds to neuropilin-1 activating an endocytic bulk transport pathway through tumor tissue. Phage screening has also yielded tumor-penetrating peptides that function like iRGD in activating the CendR pathway, but bind to a different primary receptor. Moreover, novel tumor-homing peptides can be constructed from tumor-homing motifs, CendR elements and protease cleavage sites. Pathologies other than tumors can be targeted with tissue-penetrating peptides, and the primary receptor can also be a vascular "zip code" of a normal tissue. The CendR technology provides a solution to a major problem in tumor therapy, poor penetration of drugs into tumors. The tumor-penetrating peptides are capable of taking a payload deep into tumor tissue in mice, and they also penetrate into human tumors ex vivo. Targeting with these peptides specifically increases the accumulation in tumors of a variety of drugs and contrast agents, such as doxorubicin, antibodies, and nanoparticle-based compounds. Remarkably the drug to be targeted does not have to be coupled to the peptide; the bulk transport system activated by the peptide sweeps along any compound that is present in the blood.

A tumor-penetrating peptide modification enhances the antitumor activity of thymosin alpha 1

A serious limitation of numerous antitumor drugs is the incapacity to penetrate solid tumors. However, addition of an RGD fragment to peptide drugs might solve this problem. In this study, we explored whether the introduction of a permeability-enhancing sequence, such as iRGD (CRGDK/RGPD/EC) fragments, would enhance the activity of thymosin alpha 1 (Tα1). The modified Tα1 (Tα1-iRGD) was successfully expressed and purified, and the in vitro assay showed that Tα1-iRGD presented a similar activity as Tα1 in promoting proliferation of mouse splenocytes. Meanwhile, cell adhesion analysis revealed that Tα1-iRGD exhibited more specific and greater binding with tumor cells compared with Tα1. Furthermore, the iRGD fragment evidently enhanced the basal ability of Tα1 to inhibit proliferation of cancer cells in vitro, particularly of mouse melanoma cell line B16F10 and human lung cancer cell line H460. Our findings indicated that the addition of an iRGD fragment increased the anti-proliferative activity of Tα1 against cancer cells by improving the ability of Tα1 to penetrate the tumor cells. This study highlighted the important roles of an iRGD sequence in the therapeutic strategy of Tα1-iRGD. Thus, Tα1-iRGD could be a novel drug candidate for cancer treatment.

Neuropilin-1 expression promotes invasiveness of melanoma cells through vascular endothelial growth factor receptor-2-dependent and -independent mechanisms

The majority of human melanoma cell lines secretes vascular endothelial growth factor-A (VEGF-A) and expresses its receptors VEGFR-1, VEGFR-2 and neuropilin-1 (NRP‑1), a co-receptor for VEGF-A that amplifies the signalling through VEGFR-2. Since it is known that the VEGF-A/VEGFR-2 autocrine loop promotes melanoma cell invasiveness, the aim of the present study was to investigate the involvement of NPR-1 in melanoma progression. Syngeneic human melanoma cell lines expressing either VEGFR-2 or NRP-1, both or none of them, were analyzed for their in vitro ability to migrate, invade the extracellular matrix (ECM) and secrete active metalloproteinase-2 (MMP-2). The results indicate that NRP-1 cooperates with VEGFR-2 in melanoma cell migration induced by VEGF-A. Moreover, NRP-1 expression is sufficient to promote MMP-2 secretion and melanoma cell invasiveness, as demonstrated by the ability of cells expressing solely NRP-1 to spontaneously invade the ECM. This ability is specifically downregulated by anti-NRP-1 antibodies or by interfering with NRP-1 expression using an shRNA construct. Investigation of the signal transduction pathways triggered by NRP-1 in melanoma cells, indicated that NRP-1-dependent promotion of cell invasiveness involves Akt activation through its phosphorylation on T308. Overall, the results demonstrate that NRP-1 is involved in melanoma progression through VEGFR-2-dependent and -independent mechanisms and suggest NRP-1 as a target for the treatment of the metastatic disease.

Polysialic acid on neuropilin-2 is exclusively synthesized by the polysialyltransferase ST8SiaIV and attached to mucin-type o-glycans located between the b2 and c domain

Neuropilin-2 (NRP2) is well known as a co-receptor for class 3 semaphorins and vascular endothelial growth factors, involved in axon guidance and angiogenesis. Moreover, NRP2 was shown to promote chemotactic migration of human monocyte-derived dendritic cells (DCs) toward the chemokine CCL21, a function that relies on the presence of polysialic acid (polySia). In vertebrates, this posttranslational modification is predominantly found on the neural cell adhesion molecule (NCAM), where it is synthesized on N-glycans by either of the two polysialyltransferases, ST8SiaII or ST8SiaIV. In contrast to NCAM, little is known on the biosynthesis of polySia on NRP2. Here we identified the polySia attachment sites and demonstrate that NRP2 is recognized only by ST8SiaIV. Although polySia-NRP2 was found on bone marrow-derived DCs from wild-type and St8sia2(-/-) mice, polySia was completely lost in DCs from St8sia4(-/-) mice despite normal NRP2 expression. In COS-7 cells, co-expression of NRP2 with ST8SiaIV but not ST8SiaII resulted in the formation of polySia-NRP2, highlighting distinct acceptor specificities of the two polysialyltransferases. Notably, ST8SiaIV synthesized polySia selectively on a NRP2 glycoform that was characterized by the presence of sialylated core 1 and core 2 O-glycans. Based on a comprehensive site-directed mutagenesis study, we localized the polySia attachment sites to an O-glycan cluster located in the linker region between b2 and c domain. Combined alanine exchange of Thr-607, -613, -614, -615, -619, and -624 efficiently blocked polysialylation. Restoration of single sites only partially rescued polysialylation, suggesting that within this cluster, polySia is attached to more than one site.

Functional proteomics, human genetics and cancer biology of GIPC family members

GIPC1, GIPC2 and GIPC3 consist of GIPC homology 1 (GH1) domain, PDZ domain and GH2 domain. The regions around the GH1 and GH2 domains of GIPC1 are involved in dimerization and interaction with myosin VI (MYO6), respectively. The PDZ domain of GIPC1 is involved in interactions with transmembrane proteins [IGF1R, NTRK1, ADRB1, DRD2, TGFβR3 (transforming growth factorβ receptor type III), SDC4, SEMA4C, LRP1, NRP1, GLUT1, integrin α5 and VANGL2], cytosolic signaling regulators (APPL1 and RGS19) and viral proteins (HBc and HPV-18 E6). GIPC1 is an adaptor protein with dimerizing ability that loads PDZ ligands as cargoes for MYO6-dependent endosomal trafficking. GIPC1 is required for cell-surface expression of IGF1R and TGFβR3. GIPC1 is also required for integrin recycling during cell migration, angiogenesis and cytokinesis. On early endosomes, GIPC1 assembles receptor tyrosine kinases (RTKs) and APPL1 for activation of PI3K-AKT signaling, and G protein-coupled receptors (GPCRs) and RGS19 for attenuation of inhibitory Gα signaling. GIPC1 upregulation in breast, ovarian and pancreatic cancers promotes tumor proliferation and invasion, whereas GIPC1 downregulation in cervical cancer with human papillomavirus type 18 infection leads to resistance to cytostatic transforming growth factorβ signaling. GIPC2 is downregulated in acute lymphocytic leukemia owing to epigenetic silencing, while Gipc2 is upregulated in estrogen-induced mammary tumors. Somatic mutations of GIPC2 occur in malignant melanoma, and colorectal and ovarian cancers. Germ-line mutations of the GIPC3 or MYO6 gene cause nonsyndromic hearing loss. As GIPC proteins are involved in trafficking, signaling and recycling of RTKs, GPCRs, integrins and other transmembrane proteins, dysregulation of GIPCs results in human pathologies, such as cancer and hereditary deafness.

Inhibition of tumor cell migration by LD22-4, an N-terminal fragment of 24-kDa FGF2, is mediated by Neuropilin 1

LD22-4, an 86-amino acid fragment of the basic fibroblast growth factor, is an inhibitor of cell migration. LD22-4 inhibits the migration of various tumor cells, endothelial cells, and fibroblasts in vitro and suppresses tumor growth and angiogenesis in vivo. LD22-4 is effective in the presence of multiple growth factors, either alone or in combination, as well as haptotactic factors. LD22-4 inhibits the rate of malignant gliomas prepared from U87MG cells in an orthotopic mouse model by 90% compared with untreated mice. Using U87MG cells, we identified the LD22-4 membrane receptor as neuropilin 1 (NRP1). The identification of NRP1 as the LD22-4 receptor was based upon mass spectrometric analysis of proteins that bind to LD22-4, immunoprecipitation of an NRP1-LD22-4 complex formed during incubation of LD22-4 with U87MG cells, LD22-4-NRP1 coimmunoprecipitation studies, and binding of LD22-4 to HEK293 cells expressing NRP1. In contrast, NRP1 binding of an inactive mutant of LD22-4 was substantially reduced. As is typical of NRP1-binding proteins, LD22-4 itself binds to heparin and requires heparan sulfate for binding to cells. The addition of heparin to migration assays increased the inhibitory activity of LD22-4. In addition to a heparin-binding region, LD22-4 contains a 5-amino acid C-terminus that matches an NRP1 consensus binding sequence. Thus, direct binding experiments, dependence on heparan sulfate, and the presence of a NRP1 consensus binding sequence indicate that NRP1 is the binding site of LD22-4 and mediates inhibition of cell migration.

Peritumoral brain edema in angiomatous supratentorial meningiomas: an investigation of the vascular endothelial growth factor A pathway

The aim of this work was to study the vascular endothelial growth factor A (VEGF-A) pathway and peritumoral brain edema (PTBE) through comparison of non-angiomatous and angiomatous meningiomas. Meningiomas are common intracranial tumors, which often have PTBE. VEGF-A is an integral part of PTBE formation and angiogenesis, and the capillary-rich angiomatous meningiomas are known for their PTBE. The VEGF-A receptor VEGFR-2 is responsible for the angiogenic effect of VEGF-A on endothelial cells, which is enhanced by the co-receptor neuropilin-1. Forty non-angiomatous, 22 angiomatous meningiomas, and 10 control tissue samples were collected for the study. Magnetic resonance images were available for 40 non-angiomatous and 10 angiomatous meningiomas. Tissue sections were immunostained for CD34, MIB-1, estrogen- and progesterone receptors. ELISA, chemiluminescence, and RT-qPCR were used for VEGF-A, VEGFR-2, and neuropilin-1 protein and mRNA quantification. Angiomatous meningiomas had larger PTBE (695 vs 218 cm(3) , p = 0.0045) and longer capillary length (3614 vs 605 mm/mm(3) , p < 0.0001). VEGF-A mRNA, neuropilin-1 mRNA, and VEGFR-2 protein levels were higher in angiomatous meningiomas independently of the capillary length (p < 0.05). Neuropilin-1 protein levels were lower in angiomatous meningiomas (p < 0.0001). The VEGF-A pathway and tumor capillary length may be essential for PTBE-formation in meningiomas. Further investigations of this pathway could lead to earlier therapy and targeted pharmacological treatment options.

Production of soluble human vascular endothelial growth factor VEGF-A165-heparin binding domain in Escherichia coli

We report a method for production of soluble heparin binding domain (HBD) of human vascular endothelial growth factor VEGF-A₁₆₅. Recombinant VEGF-A₁₆₅-HBD that contains four disulphide bridges was expressed in specialised E. coli SHuffle cells and its activity has been confirmed through interactions with neuropilin and heparin. The ability to produce significant quantities of a soluble active form of VEGF-A₁₆₅-HBD will enable further studies addressing the role of VEGF-A in essential processes such as angiogenesis, vasculogenesis and vascular permeability.

Norrin/Frizzled4 signaling in retinal vascular development and blood brain barrier plasticity

Norrin/Frizzled4 (Fz4) signaling activates the canonical Wnt pathway to control retinal vascular development. Using genetically engineered mice, we show that precocious Norrin production leads to premature retinal vascular invasion and delayed Norrin production leads to characteristic defects in intraretinal vascular architecture. In genetic mosaics, wild-type endothelial cells (ECs) instruct neighboring Fz4(-/-) ECs to produce an architecturally normal mosaic vasculature, a cell nonautonomous effect. However, over the ensuing weeks, Fz4(-/-) ECs are selectively eliminated from the mosaic vasculature, implying the existence of a quality control program that targets defective ECs. In the adult retina and cerebellum, gain or loss of Norrin/Fz4 signaling results in a cell-autonomous gain or loss, respectively, of blood retina barrier and blood brain barrier function, indicating an ongoing requirement for Frizzled signaling in barrier maintenance and substantial plasticity in mature CNS vascular structure.

Rhodocetin-αβ-induced neuropilin-1-cMet association triggers restructuring of matrix contacts in endothelial cells

OBJECTIVE

The snake venom component rhodocetin-αβ (RCαβ) stimulates endothelial cell motility in an α2β1 integrin-independent manner. We aimed to elucidate its cellular and molecular mechanisms.

METHODS AND RESULTS

We identified neuropilin-1 (Nrp1) as a novel target of RCαβ by protein-chemical methods. RCαβ and vascular endothelial growth factor (VEGF)-A avidly bind to Nrp1. Instead of acting as VEGF receptor 2 coreceptor, Nrp1 associates upon RCαβ treatment with cMet. Furthermore, cell-based ELISAs and kinase inhibitor studies showed that RCαβ induces phosphorylation of tyrosines 1234/1235 [corrected] and thus activation of cMet. Consequently, paxillin is phosphorylated at Y31, which is redistributed from streak-like focal adhesions to spot-like focal contacts at the cell perimeter, along with α2β1 integrin, thereby regulating cell-matrix interactions. Cortactin is abundant in the cell perimeter, where it is involved in the branching of the cortical actin network of lamellipodia, whereas tensile force-bearing actin stress fibers radiating from focal adhesions disappear together with zyxin, a focal adhesion marker, on RCαβ treatment.

CONCLUSIONS

Our data demonstrate that (1) Nrp1 is a novel target for venom components, such as RCαβ; (2) Nrp1 coupled to cMet regulates the type of cell-matrix interactions in a manner involving paxillin phosphorylation; and (3) altered cell-matrix interactions determine endothelial cell migration and cellular force management.

Plexin structures are coming: opportunities for multilevel investigations of semaphorin guidance receptors, their cell signaling mechanisms, and functions

Plexin transmembrane receptors and their semaphorin ligands, as well as their co-receptors (Neuropilin, Integrin, VEGFR2, ErbB2, and Met kinase) are emerging as key regulatory proteins in a wide variety of developmental, regenerative, but also pathological processes. The diverse arenas of plexin function are surveyed, including roles in the nervous, cardiovascular, bone and skeletal, and immune systems. Such different settings require considerable specificity among the plexin and semaphorin family members which in turn are accompanied by a variety of cell signaling networks. Underlying the latter are the mechanistic details of the interactions and catalytic events at the molecular level. Very recently, dramatic progress has been made in solving the structures of plexins and of their complexes with associated proteins. This molecular level information is now suggesting detailed mechanisms for the function of both the extracellular as well as the intracellular plexin regions. Specifically, several groups have solved structures for extracellular domains for plexin-A2, -B1, and -C1, many in complex with semaphorin ligands. On the intracellular side, the role of small Rho GTPases has been of particular interest. These directly associate with plexin and stimulate a GTPase activating (GAP) function in the plexin catalytic domain to downregulate Ras GTPases. Structures for the Rho GTPase binding domains have been presented for several plexins, some with Rnd1 bound. The entire intracellular domain structure of plexin-A1, -A3, and -B1 have also been solved alone and in complex with Rac1. However, key aspects of the interplay between GTPases and plexins remain far from clear. The structural information is helping the plexin field to focus on key questions at the protein structural, cellular, as well as organism level that collaboratoria of investigations are likely to answer.

TAG1 regulates the endocytic trafficking and signaling of the semaphorin3A receptor complex

Endocytic trafficking of membrane proteins is essential for neuronal structure and function. We show that Transient Axonal Glycoprotein 1 (TAG1 or CNTN2), a contactin-related adhesion molecule, plays a central role in the differential trafficking of components of the semaphorin3A (Sema3A) receptor complex into distinct endosomal compartments in murine spinal sensory neuron growth cones. The semaphorin3A receptor is composed of Neuropilin1 (NRP1), PlexinA4, and L1, with NRP1 being the ligand-binding component. TAG1 interacts with NRP1, causing a change in its association with L1 in the Sema3A response such that L1 is lost from the complex following Sema3A binding. Initially, however, L1 and NRP1 endocytose together and only become separated intracellularly, with NRP1 becoming associated with endosomes enriched in lipid rafts and colocalizing with TAG1 and PlexinA4. When TAG1 is missing, NRP1 and L1 fail to separate and NRP1 does not become raft associated; colocalization with PlexinA4 is reduced and Plexin signaling is not initiated. These observations identify a novel role for TAG1 in modulating the intracellular sorting of signaling receptor complexes.

Interplay of neuropilin-1 and semaphorin 3A after partial hepatectomy in rats

AIM: To elucidate the role of neuropilin-1 (Nrp-1) and semaphorin 3A (Sema3A) in sinusoidal remodeling during liver regeneration in rats.

METHODS: Male Wistar/ST rats at 7 wk of age, weighing about 200 g, were used for all animal experiments. In vivo, at 24, 48, 72, 96, 144 and 192 h after two-thirds partial hepatectomy (PHx), the remnant livers were removed. Liver tissues were immunohistochemically stained for Nrp-1, Sema3A and SE-1, a liver sinusoidal endothelial cell (SEC) marker. Total RNA of the liver tissue was extracted and reversely transcribed into cDNA. The mRNA expression of Sema3A was analyzed by quantitative real-time polymerase chain reaction and normalized to that of ribosomal protein S18. In vitro, SECs were isolated from rat liver and cultured in endothelial growth medium containing 20 ng/mL vascular endothelial cell growth factor. Migration of SECs in primary culture was assessed by cell transwell assay with or without recombinant Sema3A. Apoptotic cells were determined by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling method.

RESULTS: In vitro, immunohistochemistry study revealed that Sema3A and Nrp-1 were constitutively expressed in hepatocytes and SECs, respectively, in normal rat liver tissues. Nrp-1 expression in SECs was quantified by the percentage of immunostained area with anti-Nrp-1 antibody in relation to the area stained with SE-1. Between 24 h and 96 h following resection of liver, Nrp-1 expression in SECs was transiently increased. Compared with the baseline (5.2% ± 0.1%), Nrp-1 expression in SECs significantly increased at 24 h (17.3% ± 0.7%, P < 0.05), 48 h (39.1% ± 0.6%, P < 0.01), 72 h (46.9% ± 4.5%, P < 0.01) and 96 h (29.9% ± 3.8%, P < 0.01) after PHx, then returned to the basal level at termination of liver regeneration. Interestingly, the expression of Sema3A was inversely associated with that of Nrp-1 in liver after PHx. Sema3A mRNA expression was significantly reduced by about 75% over the period 24-144 h after PHx (P < 0.05), and returned to basal levels at 192 h after PHx. In vitro, SECs isolated from rats after PHx (PHx-SECs) were observed to migrate to the lower chamber of the cell transwell system after incubation for 24 h, but not cells from normal rats (CONT-SECs), indicating that mobility of PHx-SECs increases as compared with that of CONT-SECs. Moreover, recombinant Sema3A significantly attenuated migration in PHx-SECs in primary culture (vehicle-treated 100% ± 7.9% vs Sema3A-treated 42.6% ± 5.4%, P < 0.01), but not in CONT-SECs. Compared with CONT-SECs, the apoptotic rate of PHx-SECs decreased by 78.3% (P < 0.05). There was no difference in apoptosis between CONT-SECs that were treated with vehicle and Sema3A. However, in PHx-SECs, apoptosis was induced by the presence of 5 nmol Sema3A for 24 h (vehicle-treated 21.7% ± 7.6% vs Sema3A-treated 104.3% ± 8.9%, P < 0.05). In addition, immunohistochemistry confirmed the increased expression of Nrp-1 in PHx-SECs, while it was noted to a lesser extent in CONT-SECs.

CONCLUSION: The interplay of Nrp-1 and Sema3A shown in our results may lead to a better understanding of interaction between sinusoidal remodeling and SECs during liver regeneration.

Semaphorin signals tweaking the tumor microenvironment

Solid tumors not only comprise malignant cells but also other nonmalignant cell types, forming a unique microenvironment that can strongly influence the behavior of tumor cells. Recent advances in the understanding of cancer biology have highlighted the functional role of semaphorins. In fact, semaphorins form a family of molecular signals known to guide and control cell migration during embryo development and in adults. Tumor cells express semaphorins as well as their receptors, plexins and neuropilins. It has been shown that semaphorin signaling can regulate tumor cell behavior. Moreover, semaphorins are important regulators of tumor angiogenesis. Conversely, very little is known about the functional relevance of semaphorin signals for tumor-infiltrating stromal cells, such as leukocytes. In this chapter, we review the current knowledge on the functional role of semaphorins in cancer progression, and we focus on the emerging role of semaphorins in mediating the cross talk between tumor cells and different tumor stromal cells.

Neuropilin-2 and vascular endothelial growth factor receptor-3 are up-regulated in human vascular malformations

Despite multiple previous studies in the field of vascular anomalies, the mechanism(s) leading to their development, progression and maintenance has remained unclear. In this study, we have characterized the expression levels of vascular endothelial growth factors and their receptors in 33 human vascular anomalies. Analysis with quantitative real-time PCR and gene-specific assays showed higher expression of neuropilin-2 (NRP2) and VEGF-receptor-3 (VEGFR-3) mRNAs in vascular malformations (VascM) as compared to infantile hemangiomas (Hem). In addition, the expression levels of PlGF and VEGF-C mRNA were significantly higher in venous VascM when compared to the other VascM and Hem. Higher expression of NRP2 and VEGFR-3 were confirmed by immunohistochemistry. To further study the importance of NRP2 and VEGFR-3, endothelial cell (EC) cultures were established from vascular anomalies. It was found that NRP2 and VEGFR-3 mRNA levels were significantly higher in some of the VascM ECs as compared to human umbilical vein ECs which were used as control cells in the study. Furthermore, adenoviral delivery of soluble decoy NRP2 prevented the proliferation of ECs isolated from most of the vascular anomalies. Our findings suggest that NRP2 functions as a factor maintaining the pathological vascular network in these anomalies. Thus, NRP2 could become a potential therapeutic target for the diagnosis and treatment of vascular anomalies.

Neuropilins are multifunctional coreceptors involved in tumor initiation, growth, metastasis and immunity

The neuropilins (Nrps) are multifunctional proteins involved in development, immunity and cancer. Neuropilin-1 (Nrp1), or its homologue neuropilin-2 (Nrp2), are coreceptors that enhance responses to several growth factors (GFs) and other mediators. Nrps are coreceptors for the class 3 semaphorins (SEMA3), involved in axonal guidance, and several members of the vascular endothelial growth factor (VEGF) family. However, recent findings reveal they have a much broader spectrum of activity. They bind transforming growth factor β1 (TGF-β1) and its receptors, hepatocyte growth factor (HGF) and its receptor (cMet), platelet derived growth factor (PDGF) and its receptors, fibroblast growth factors (FGFs), and integrins. Nrps also promote Hedgehog signaling. These ligands and pathways are all relevant to angiogenesis and wound healing. In the immune system, the Nrps are expressed primarily by dendritic cells (DCs) and regulatory T cells (Tregs), and exert mainly inhibitory effects. In cancer, Nrps have been linked to a poor prognosis, which is consistent with their numerous interactions with ligands and receptors that promote tumor progression. We hypothesize that Nrps boost responses by capturing ligands, regulating GF receptor expression, endocytosis and recycling, and possibly also by signaling independently. Importantly, they promote epithelial-mesenchymal transition (EMT), and the survival of cancer stem cells. The recent finding that Nrps bind and internalize cell-penetrating peptides (CPPs) with arginine/lysine-rich C-terminal motifs (C-end rule; e.g., RXXR) is of interest. These CPPs can be coupled to large drugs for cancer therapy. Almost all studies have been preclinical, but findings suggest Nrps are excellent targets for anti-cancer drug development.

Receptor complexes for each of the Class 3 Semaphorins

The Class 3 Semaphorins (Sema3s) are a sub-family of proteins whose known biological roles are varied and growing. The mechanism of action of the Sema3s requires binding to transmembrane receptors that comprise heteromeric complexes of Neuropilins, Plexins and cell adhesion molecules (CAMs). However, knowledge of the receptor components of the Sema3s remains incomplete, and there may be receptor components which are as yet undiscovered. The receptor complexes of the Sema3s share receptor components with each other, and it is the specific combination of these components within a heteromeric complex that is thought to give rise to selective binding and signalling for individual Sema3s. This crosstalk makes it experimentally difficult to define a single holoreceptor for each Sema3. Furthermore, the receptor composition for a given Sema3 may differ between cell types, and change as a function of developmental state or pathological situation. Nevertheless, there are at least some known differences in the constitutive structure of the receptors for the Sema3s. For example in neural cells, Sema3a and Sema3f signal through different Neuropilins (Nrp1 and Nrp2 respectively) and L1cam only appears important for Sema3a signaling, while Nrcam forms a complex with Nrp2. Further complexity arises from crosstalk of other families of ligands (e.g., VEGF) with Sema3 receptor components. Thus the Sema3s, which have been shown as antagonists for each other, can also act as antagonists for other families of molecules. This review compiles experimental evidence describing the receptor components for the Sema3s, detailing the current state of knowledge of which components are important for signaling of each Sema3 before going on to consider possible future directions for the field.

Signalling from hindbrain boundaries regulates neuronal clustering that patterns neurogenesis

During central nervous system development, neural progenitors are patterned to form discrete neurogenic and non-neurogenic zones. In the zebrafish hindbrain, neurogenesis is organised by Fgf20a emanating from neurons located at each segment centre that inhibits neuronal differentiation in adjacent progenitors. Here, we have identified a molecular mechanism that clusters fgf20a-expressing neurons in segment centres and uncovered a requirement for this positioning in the regulation of neurogenesis. Disruption of hindbrain boundary cell formation alters the organisation of fgf20a-expressing neurons, consistent with a role of chemorepulsion from boundaries. The semaphorins Sema3fb and Sema3gb, which are expressed by boundary cells, and their receptor Nrp2a are required for clustering of fgf20a-expressing neurons at segment centres. The dispersal of fgf20a-expressing neurons that occurs following the disruption of boundaries or of Sema3fb/Sema3gb signalling leads to reduced FGF target gene expression in progenitors and an increased number of differentiating neurons. Sema3 signalling from boundaries thus links hindbrain segmentation to the positioning of fgf20a-expressing neurons that regulates neurogenesis.

Molecular imaging of vascular endothelial growth factor receptors in graft arteriosclerosis

OBJECTIVE

Vascular endothelial growth factor (VEGF) signaling plays a key role in the pathogenesis of vascular remodeling, including graft arteriosclerosis. Graft arteriosclerosis is the major cause of late organ failure in cardiac transplantation. We used molecular near-infrared fluorescent imaging with an engineered Cy5.5-labeled single-chain VEGF tracer (scVEGF/Cy) to detect VEGF receptors and vascular remodeling in human coronary artery grafts by molecular imaging.

METHODS AND RESULTS

VEGF receptor specificity of probe uptake was shown by flow cytometry in endothelial cells. In severe combined immunodeficiency mice, transplantation of human coronary artery segments into the aorta followed by adoptive transfer of allogeneic human peripheral blood mononuclear cells led to significant neointima formation in the grafts over a period of 4 weeks. Near-infrared fluorescent imaging of transplant recipients at 4 weeks demonstrated focal uptake of scVEGF/Cy in remodeling artery grafts. Uptake specificity was demonstrated using an inactive homolog of scVEGF/Cy. scVEGF/Cy uptake predominantly localized in the neointima of remodeling coronary arteries and correlated with VEGF receptor-1 but not VEGF receptor-2 expression. There was a significant correlation between scVEGF/Cy uptake and transplanted artery neointima area.

CONCLUSIONS

Molecular imaging of VEGF receptors may provide a noninvasive tool for detection of graft arteriosclerosis in solid organ transplantation.

Anti-angiogenic therapy: concept to clinic

It has been 40 years since Folkman hypothesized the use of anti-angiogenic therapy as a strategy in the treatment of cancer. Since then, vascular endothelial growth factor (VEGF) has been identified as the most potent cytokine to induce angiogenesis and drugs targeting VEGF, principally the humanized monoclonal antibody bevacizumab and the tyrosine kinase inhibitors sunitinib and sorafenib, have proven therapeutic benefit. The initial high expectations of tumor vascular targeting agents, however, have yet to be fulfilled. In unselected patient populations, the benefits of these agents is often marginal, they cause harmful side effects, and drug resistance is quickly established. Biomarkers to identify patients suitable for anti-angiogenic therapy will be key to the future development of these drugs.

Neuropilins: expression and roles in the epithelium

Initially found expressed in neuronal and then later in endothelial cells, it is well established that the transmembrane glycoproteins neuropilin-1 (NRP1) and neuropilin-2 (NRP2) play essential roles in axonal growth and guidance and in physiological and pathological angiogenesis. Neuropilin expression and function in epithelial cells has received little attention when compared with neuronal and endothelial cells. Overexpression of NRPs is shown to enhance growth, correlate with invasion and is associated with poor prognosis in various tumour types, especially those of epithelial origin. The contribution of NRP and its ligands to tumour growth and metastasis has spurred a strong interest in NRPs as novel chemotherapy drug targets. Given NRP's role as a multifunctional co-receptor with an ability to bind with disparate ligand families, this has sparked new areas of research implicating NRPs in diverse biological functions. Here, we review the growing body of research demonstrating NRP expression and role in the normal and neoplastic epithelium.

De novo pathogenic SCN8A mutation identified by whole-genome sequencing of a family quartet affected by infantile epileptic encephalopathy and SUDEP

Individuals with severe, sporadic disorders of infantile onset represent an important class of disease for which discovery of the underlying genetic architecture is not amenable to traditional genetic analysis. Full-genome sequencing of affected individuals and their parents provides a powerful alternative strategy for gene discovery. We performed whole-genome sequencing (WGS) on a family quartet containing an affected proband and her unaffected parents and sibling. The 15-year-old female proband had a severe epileptic encephalopathy consisting of early-onset seizures, features of autism, intellectual disability, ataxia, and sudden unexplained death in epilepsy. We discovered a de novo heterozygous missense mutation (c.5302A>G [p.Asn1768Asp]) in the voltage-gated sodium-channel gene SCN8A in the proband. This mutation alters an evolutionarily conserved residue in Nav1.6, one of the most abundant sodium channels in the brain. Analysis of the biophysical properties of the mutant channel demonstrated a dramatic increase in persistent sodium current, incomplete channel inactivation, and a depolarizing shift in the voltage dependence of steady-state fast inactivation. Current-clamp analysis in hippocampal neurons transfected with p.Asn1768Asp channels revealed increased spontaneous firing, paroxysmal-depolarizing-shift-like complexes, and an increased firing frequency, consistent with a dominant gain-of-function phenotype in the heterozygous proband. This work identifies SCN8A as the fifth sodium-channel gene to be mutated in epilepsy and demonstrates the value of WGS for the identification of pathogenic mutations causing severe, sporadic neurological disorders.

Structural basis for selective vascular endothelial growth factor-A (VEGF-A) binding to neuropilin-1

Neuropilin-1 (Nrp1) is an essential receptor for angiogenesis that binds to VEGF-A. Nrp1 binds directly to VEGF-A with high affinity, but the nature of their selective binding has remained unclear. Nrp1 was initially reported to bind to the exon 7-encoded region of VEGF-A and function as an isoform-specific receptor for VEGF-A(164/165). Recent data have implicated exon 8-encoded residues, which are found in all proangiogenic VEGF-A isoforms, in Nrp binding. We have determined the crystal structure of the exon 7/8-encoded VEGF-A heparin binding domain in complex with the Nrp1-b1 domain. This structure clearly demonstrates that residues from both exons 7 and 8 physically contribute to Nrp1 binding. Using an in vitro binding assay, we have determined the relative contributions of exon 7- and 8-encoded residues. We demonstrate that the exon 8-encoded C-terminal arginine is essential for the interaction of VEGF-A with Nrp1 and mediates high affinity Nrp binding. Exon 7-encoded electronegative residues make additional interactions with the L1 loop of Nrp1. Although otherwise conserved, the primary sequences of Nrp1 and Nrp2 differ significantly in this region. We further show that VEGF-A(164) binds 50-fold more strongly to Nrp1 than Nrp2. Direct repulsion between the electronegative exon 7-encoded residues of the heparin binding domain and the electronegative L1 loop found only in Nrp2 is found to significantly contribute to the observed selectivity. The results reveal the basis for the potent and selective binding of VEGF-A(164) to Nrp1.

Sequences prior to conserved catalytic motifs of polysialyltransferase ST8Sia IV are required for substrate recognition

Polysialic acid on the neural cell adhesion molecule (NCAM) modulates cell-cell adhesion and signaling, is required for proper brain development, and plays roles in neuronal regeneration and the growth and invasiveness of tumor cells. Evidence indicates that NCAM polysialylation is highly protein-specific, requiring an initial polysialyltransferase-NCAM protein-protein interaction. Previous work suggested that a polybasic region located prior to the conserved polysialyltransferase catalytic motifs may be involved in NCAM recognition, but not overall enzyme activity (Foley, D. A., Swartzentruber, K. G., and Colley, K. J. (2009) J. Biol. Chem. 284, 15505-15516). Here, we employ a competition assay to evaluate the role of this region in substrate recognition. We find that truncated, catalytically inactive ST8SiaIV/PST proteins that include the polybasic region, but not those that lack this region, compete with endogenous ST8SiaIV/PST and reduce NCAM polysialylation in SW2 small cell lung carcinoma cells. Replacing two polybasic region residues, Arg(82) and Arg(93), eliminates the ability of a full-length, catalytically inactive enzyme (PST H331K) to compete with SW2 cell ST8SiaIV/PST and block NCAM polysialylation. Replacing these residues singly or together in ST8SiaIV/PST substantially reduces or eliminates NCAM polysialylation, respectively. In contrast, replacing Arg(82), but not Arg(93), substantially reduces the ability of ST8SiaIV/PST to polysialylate neuropilin-2 and SynCAM 1, suggesting that Arg(82) plays a general role in substrate recognition, whereas Arg(93) specifically functions in NCAM recognition. Taken together, our results indicate that the ST8SiaIV/PST polybasic region plays a critical role in substrate recognition and suggest that different combinations of basic residues may mediate the recognition of distinct substrates.

Molecular mechanisms of tumor angiogenesis

Tumors have been recently recognized as aberrant organs composed of a complex mixture of highly interactive cells that in addition to the cancer cell include stroma (fibroblasts, adipocytes, and myofibroblasts), inflammatory (innate and adaptive immune cells), and vascular cells (endothelial and mural cells). While initially cancer cells co-opt tissue-resident vessels, the tumor eventually recruits its own vascular supply. The process of tumor neovascularization proceeds through the combined output of inductive signals from the entire cellular constituency of the tumor. During the last two decades, the identification and mechanistic outcome of signaling pathways that mediate tumor angiogenesis have been elucidated. Interestingly, many of the genes and signaling pathways activated in tumor angiogenesis are identical to those operational during developmental vascular growth, but they lack feedback regulatory control and are highly affected by inflammatory cells and hypoxia. Consequently, tumor vessels are abnormal, fragile, and hyperpermeable. The lack of hierarchy and inconsistent investment of mural cells dampen the ability of the vessels to effectively perfuse the tumor, and the resulting hypoxia installs a vicious cycle that continuously perpetuates a state of vascular inefficiency. Pharmacological targeting of blood vessels, mainly through the VEGF signaling pathway, has proven effective in normalizing tumor vessels. This normalization improves perfusion and distribution of chemotherapeutic drugs with resulting tumor suppression and moderate increase in overall survival. However, resistance to antiangiogenic therapy occurs frequently and constitutes a critical barrier in the inhibition of tumor growth. A concrete understanding of the chief signaling pathways that stimulate vascular growth in tumors and their cross-talk will continue to be essential to further refine and effectively abort the angiogenic response in cancer.

How neuropilin-1 regulates receptor tyrosine kinase signalling: the knowns and known unknowns

Essential roles of NRP1 (neuropilin-1) in cardiovascular development and in neuronal axon targeting during embryogenesis are thought to be mediated primarily through binding of NRP1 to two unrelated types of ligands: the VEGF (vascular endothelial growth factor) family of angiogenic cytokines in the endothelium, and the class 3 semaphorins in neurons. A widely accepted mechanism for the role of NRP1 in the endothelium is VEGF binding to NRP1 and VEGFR2 (VEGF receptor 2) and VEGF-dependent formation of complexes or NRP1–VEGFR2 holoreceptors with enhanced signalling activity and biological function. However, although some basic features of this model are solidly based on biochemical and cellular data, others are open to question. Furthermore, a mechanistic account of NRP1 has to accommodate research which emphasizes the diversity of NRP1 functions in different cell types and particularly an emerging role in signalling by other growth factor ligands for RTKs (receptor tyrosine kinases) such as HGF (hepatocyte growth factor) and PDGF (platelet-derived growth factor). It is uncertain, however, whether the model of NRP1–RTK heterocomplex formation applies in all of these situations. In the light of these developments, the need to explain mechanistically the role of NRP1 in signalling is coming increasingly to the fore. The present article focuses on some of the most important unresolved questions concerning the mechanism(s) through which NRP1 acts, and highlights recent findings which are beginning to generate insights into these questions.

Microdeletions and microduplications in patients with congenital heart disease and multiple congenital anomalies

OBJECTIVE

Multiple genetic syndromes are caused by recurrent chromosomal microdeletions or microduplications. The increasing use of high-resolution microarrays in clinical analysis has allowed the identification of previously undetectable submicroscopic copy number variants (CNVs) associated with genetic disorders. We hypothesized that patients with congenital heart disease and additional dysmorphic features or other anomalies would be likely to harbor previously undetected CNVs, which might identify new disease loci or disease-related genes for various cardiac defects.

DESIGN

Copy number analysis with single nucleotide polymorphism-based, oligonucleotide microarrays was performed on 58 patients with congenital heart disease and other dysmorphic features and/or other anomalies. The observed CNVs were validated using independent techniques and validated CNVs were further analyzed using computational algorithms and comparison with available control CNV datasets in order to assess their pathogenic potential.

RESULTS

Potentially pathogenic CNVs were detected in twelve of 58 patients (20.7%), ranging in size from 240 Kb to 9.6 Mb. These CNVs contained between 1 and 55 genes, including NRP1, NTRK3, MESP1, ADAM19, and HAND1, all of which are known to participate in cardiac development.

CONCLUSIONS

Genome-wide analysis in patients with congenital heart disease and additional phenotypes has identified potentially pathogenic CNVs affecting genes involved in cardiac development. The identified variant loci and the genes within them warrant further evaluation in similarly syndromic and nonsyndromic cardiac cohorts.

Neuropilin-1 is upregulated in hepatocellular carcinoma and contributes to tumour growth and vascular remodelling

BACKGROUND & AIMS

Neuropilin-1 (NRP1) is a transmembrane co-receptor for semaphorins and heparin-binding pro-angiogenic cytokines, principally members of the vascular endothelial growth factor family. Recent studies revealed an important role of NRP1 in angiogenesis and malignant progression of many cancers. The role of NRP1 in the development of hepatocellular carcinoma (HCC) is not completely understood.

METHODS

We used human tissue microarrays and a mouse transgenic model of HCC to establish the spatio-temporal patterns of NRP1 expression in HCC. To evaluate the therapeutic potential of targeting NRP1 in HCC, we treated HCC mice with peptide N, an NRP1 binding recombinant protein and competitive inhibitor of the VEGF-A(165)/NRP1 interaction.

RESULTS

We demonstrate that NRP1 is expressed in hepatic endothelial cells of both human healthy biopsies and in HCC samples, but not in normal hepatocytes. We found that increased NRP1 expression in human tumour hepatocytes is significantly associated with primary HCC. Using RT-PCR, Western blot and immunofluorescence analysis we show that NRP1 expression in the liver of transgenic HCC mice is increased with disease progression, in both vascular and tumour compartments. Blocking NRP1 function with peptide N leads to the inhibition of vascular remodelling and tumour liver growth in HCC mice.

CONCLUSIONS

Our results indicate a specific role of NRP1 in HCC growth and vascular remodelling and highlight the possibility of therapeutically targeting NRP1 for the treatment of HCC.

Heparan sulfate proteoglycans mediate the angiogenic activity of the vascular endothelial growth factor receptor-2 agonist gremlin

OBJECTIVE

Heparan sulfate proteoglycans (HSPGs) modulate the interaction of proangiogenic heparin-binding vascular endothelial growth factors (VEGFs) with signaling VEGF receptor-2 (VEGFR2) and neuropilin coreceptors in endothelial cells (ECs). The bone morphogenic protein antagonist gremlin is a proangiogenic ligand of VEGFR2, distinct from canonical VEGFs. Here we investigated the role of HSPGs in VEGFR2 interaction, signaling, and proangiogenic capacity of gremlin in ECs.

METHODS AND RESULTS

Surface plasmon resonance demonstrated that gremlin binds heparin and heparan sulfate, but not other glycosaminoglycans, via N-, 2-O, and 6-O-sulfated groups of the polysaccharide. Accordingly, gremlin binds HSPGs of the EC surface and extracellular matrix. Gremlin/HSPG interaction is prevented by free heparin and heparan sulfate digestion or undersulfation following EC treatment with heparinase II or sodium chlorate. However, at variance with canonical heparin-binding VEGFs, gremlin does not interact with neuropilin-1 coreceptor. On the other hand, HSPGs mediate VEGFR2 engagement and autophosphorylation, extracellular signaling-regulated kinase(1/2) and p38 mitogen-activated protein kinase activation, and consequent proangiogenic responses of ECs to gremlin. On this basis, we evaluated the gremlin-antagonist activity of a panel of chemically sulfated derivatives of the Escherichia coli K5 polysaccharide. The results demonstrate that the highly N,O-sulfated derivative K5-N,OS(H) binds gremlin with high potency, thus inhibiting VEGFR2 interaction and angiogenic activity in vitro and in vivo.

CONCLUSIONS

HSPGs act as functional gremlin coreceptors in ECs, affecting its productive interaction with VEGFR2 and angiogenic activity. This has allowed the identification of the biotechnological K5-N,OS(H) as a novel angiostatic gremlin antagonist.

VEGF binding to NRP1 is essential for VEGF stimulation of endothelial cell migration, complex formation between NRP1 and VEGFR2, and signaling via FAK Tyr407 phosphorylation

In endothelial cells, neuropilin-1 (NRP1) binds vascular endothelial growth factor (VEGF)-A and is thought to act as a coreceptor for kinase insert domain-containing receptor (KDR) by associating with KDR and enhancing VEGF signaling. Here we report mutations in the NRP1 b1 domain (Y297A and D320A), which result in complete loss of VEGF binding. Overexpression of Y297A and D320A NRP1 in human umbilical vein endothelial cells reduced high-affinity VEGF binding and migration toward a VEGF gradient, and markedly inhibited VEGF-induced angiogenesis in a coculture cell model. The Y297A NRP1 mutant also disrupted complexation between NRP1 and KDR and decreased VEGF-dependent phosphorylation of focal adhesion kinase at Tyr407, but had little effect on other signaling pathways. Y297A NRP1, however, heterodimerized with wild-type NRP1 and NRP2 indicating that nonbinding NRP1 mutants can act in a dominant-negative manner through formation of NRP1 dimers with reduced binding affinity for VEGF. These findings indicate that VEGF binding to NRP1 has specific effects on endothelial cell signaling and is important for endothelial cell migration and angiogenesis mediated via complex formation between NRP1 and KDR and increased signaling to focal adhesions. Identification of key residues essential for VEGF binding and biological functions provides the basis for a rational design of antagonists of VEGF binding to NRP1.

Neuropilin-1 mediates PDGF stimulation of vascular smooth muscle cell migration and signalling via p130Cas

NRP1 (neuropilin-1) is a co-receptor for members of the VEGF (vascular endothelial growth factor) family in endothelial cells, but is increasingly implicated in signalling induced by other growth factors. NRP1 is expressed in VSMCs (vascular smooth muscle cells), but its function and the mechanisms involved are poorly understood. The present study aimed to determine the role of NRP1 in the migratory response of HCASMCs (human coronary artery smooth muscle cells) to PDGF (platelet-derived growth factor), and to identify the signalling mechanisms involved. NRP1 is highly expressed in HAoSMCs (human aortic smooth muscle cells) and HCASMCs, and modified in VSMCs by CS (chondroitin sulfate)-rich O-linked glycosylation at Ser⁶¹². HCASMC migration induced by PDGF-BB and PDGF-AA was inhibited by NRP1 siRNA (small interfering RNA), and by adenoviral overexpression of an NRP1 mutant lacking the intracellular domain (Ad.NRP1ΔC). NRP1 co-immunoprecipitated with PDGFRα (PDGF receptor α), and immunofluorescent staining indicated that NRP1 and PDGFRα co-localized in VSMCs. NRP1 siRNA also inhibited PDGF-induced PDGFRα activation. NRP1-specific siRNA, Ad.NRP1ΔC and removal of CS glycans using chondroitinase all inhibited PDGF-BB and -AA stimulation of tyrosine phosphorylation of the adapter protein, p130^Cas (Cas is Crk-associated substrate), with little effect on other major signalling pathways, and p130^Cas knockdown inhibited HCASMC migration. Chemotaxis and p130^Cas phosphorylation induced by PDGF were inhibited by chondroitinase, and, additionally, adenoviral expression of a non-glycosylatable NRP1S612A mutant inhibited chemotaxis, but not p130^Cas phosphorylation. These results indicate a role for NRP1 and NRP1 glycosylation in mediating PDGF-induced VSMC migration, possibly by acting as a co-receptor for PDGFRα and via selective mobilization of a novel p130^Cas tyrosine phosphorylation pathway.

Advanced glycation end products inhibit adhesion ability of differentiated podocytes in a neuropilin-1-dependent manner

Podocyte injury can occur by a number of stimuli. Maintaining of an intact podocyte structure is essential for glomerular filtration; therefore, podocyte damage severely impairs renal function. Recently, we have reported that addition of glycated BSA [advanced glycation end products (AGE)-BSA] to differentiated murine podocytes inhibited neuropilin-1 (NRP1) expression and dramatically influenced podocyte migration ability (Bondeva T, Ruster C, Franke S, Hammerschmid E, Klagsbrun M, Cohen CD, Wolf G. Kidney Int 75: 605-616, 2009; Bondeva T, Wolf G. Am J Nephrol 30: 336-345, 2009). The present study analyzes the influence of AGEs and NRP1 on podocyte adhesion and cytoskeleton reorganization. We show that treatment with AGE-BSA significantly reduced podocyte adhesion to collagen IV, laminin, and fibronectin compared with Co-BSA (nonglycated BSA)-incubated cells, which was further augmented by transient inhibition of NRP1 expression using NRP1 short interference (si) RNA. On the other hand, forced overexpression of NRP1 markedly increased the adhesion ability of podocytes to the ECMs despite the AGE-BSA treatment. No changes were observed when podocyte adhesion to collagen I was assayed. These findings were also manifested with disorganization of podocyte actin stress fibers and decreased lamellipodia formation processes due to AGE-BSA treatment or NRP1 suppression. In addition, AGE-BSA or suppression of NRP1 both reduced the phosphorylation of focal adhesion kinase (FAK) and Erk1/2 in PMA-stimulated differentiated podocytes. Analysis of RhoA family GTPase activity demonstrated that treatment with AGE-BSA or NRP1 depletion inhibited as well the activation of the Rac-1 and Cdc42 but did not affect RhoA activity. All these effects were reversed by forced overexpression of full-length NRP1 cloned into the pcDNA3 vector in differentiated podocytes. Our study demonstrates that AGEs, in part via suppression of NRP1 expression, decreased podocyte adhesion and contribute to reduction of Rac-1 and Cdc42 GTPase activity. These effects may be further responsible for the podocytes damage and loss in diabetic nephropathy. Our findings suggest a role for NRP1 in regulating the podocyte actin cytoskeleton, and therefore reduction of NRP1 expression could be critical for podocyte function.

Molecular aspects of HTLV-1 entry: functional domains of the HTLV-1 surface subunit (SU) and their relationships to the entry receptors

The initial step in retroviral infection involves specific interactions between viral envelope proteins (Env) and specific receptors on the surface of target cells. For many years, little was known about the entry receptors for HTLV-1. During this time, however, functional domains of the HTLV-1 Env were identified by analyzing the effects of neutralizing antibodies and specific mutations in Env on HTLV-1 infectivity. More recent studies have revealed that HTLV-1 infectivity involves interactions with three different molecules: heparan sulfate proteoglycans (HSPG), the VEGF-165 receptor Neuropilin 1 (NRP-1) and glucose transporter type 1 (GLUT1). Here, we revisit previously published data on the functional domains of Env in regard to the recent knowledge acquired about this multi-receptor complex. We also discuss the similarities and differences between HTLV-1 and other deltaretroviruses in regards to receptor usage.

IL-17-producing invariant NKT cells in lymphoid organs are recent thymic emigrants identified by neuropilin-1 expression

Despite increasing knowledge on the mechanisms of invariant natural killer T (iNKT)-cell development in the thymus, the function of recent thymic emigrant (RTE) iNKT cells remains largely unexplored, principally because of a lack of bona fide markers to distinguish RTE from long-lived iNKT cells. Whether the recently described IL-17-producing iNKT cell subset is part of RTE has notably not been addressed. In the present study, we show that neuropilin-1 (Nrp-1), a transmembrane receptor mainly found on T-regulatory (Treg) cells in the murine immune system, is specifically expressed on RTE iNKT cells in naive mice. We used the Nrp-1 marker to discriminate RTE from mature iNKT cells and compare their functions. We show that RTE iNKT cells proliferate more than mature iNKT cells after in vitro activation; that, unlike mature iNKT cells, most RTE iNKT cells fail to rapidly produce IFN-γ and IL-4 after in vivo activation; and, most importantly, that IL-17-producing iNKT cells in lymphoid organs of naive mice are contained within the RTE iNKT cell pool. Our results establish an accurate marker of RTE iNKT cells and reveal that continuous thymic output is required for pro-inflammatory IL-17 secretion, a key function of adult iNKT cells.

Neuropilins: a new target for cancer therapy

Recent investigations highlighted strong similarities between neural crest migration during embryogenesis and metastatic processes. Indeed, some families of axon guidance molecules were also reported to participate in cancer invasion: plexins/semaphorins/neuropilins, ephrins/Eph receptors, netrin/DCC/UNC5. Neuropilins (NRPs) are transmembrane non tyrosine-kinase glycoproteins first identified as receptors for class-3 semaphorins. They are particularly involved in neural crest migration and axonal growth during development of the nervous system. Since many types of tumor and endothelial cells express NRP receptors, various soluble molecules were also found to interact with these receptors to modulate cancer progression. Among them, angiogenic factors belonging to the Vascular Endothelial Growth Factor (VEGF) family seem to be responsible for NRP-related angiogenesis. Because NRPs expression is often upregulated in cancer tissues and correlated with poor prognosis, NRPs expression might be considered as a prognostic factor. While NRP1 was intensively studied for many years and identified as an attractive angiogenesis target for cancer therapy, the NRP2 signaling pathway has just recently been studied. Although NRP genes share 44% homology, differences in their expression patterns, ligands specificities and signaling pathways were observed. Indeed, NRP2 may regulate tumor progression by several concurrent mechanisms, not only angiogenesis but lymphangiogenesis, epithelial-mesenchymal transition and metastasis. In view of their multiples functions in cancer promotion, NRPs fulfill all the criteria of a therapeutic target for innovative anti-tumor therapies. This review focuses on NRP-specific roles in tumor progression.

Differential expression of neuronal genes in Müller glia in two- and three-dimensional cultures

PURPOSE

Müller glia in the mammalian retina have some stem cell-like characteristics, although their capacity for neurogenesis remains limited both in vivo and in vitro. In vitro studies to date have used traditional two-dimensional (2D) cell culture to assess neuronal differentiation of Müller glia. The purpose of this study was to compare the effects of 2D and three-dimensional (3D) environments on Müller glial gene expression after growth factor stimulation.

METHODS

Conditionally immortalized mouse Müller glia cells (ImM10) were cultured under nonimmortalizing conditions with EGF/FGF2 to generate spheres that were differentiated in vitro on uncoated culture dishes (2D) or encapsulated in self-assembling, RADA-16 peptide hydrogels (3D) under identical media and growth factor supplementation conditions. Gene expression was analyzed using quantitative RT-PCR and immunocytochemistry. Cellular morphology was analyzed with light and confocal microscopy; sphere ultrastructure was analyzed with transmission electron microscopy.

RESULTS

ImM10 Müller cells express numerous genes associated with neural stem cells and retinal progenitors in both normal growth conditions and sphere-forming conditions. When encapsulated in the 3D hydrogel, cells can migrate and send processes into the hydrogel. Many genes associated with neurogenesis, as well as retinal neuron-specific genes, are differentially expressed in 2D and 3D differentiation conditions.

CONCLUSIONS

ImM10 Müller glia upregulate genes characteristic of retinal neurons after growth factor stimulation in vitro, and gene expression patterns are altered in 3D hydrogel cultures.

Network-like impact of MicroRNAs on neuronal lineage differentiation of unrestricted somatic stem cells from human cord blood

Unrestricted somatic stem cells (USSCs) represent an intrinsically multipotent CD45-negative fetal population from human cord blood. They show differentiation into neuronal cells of a dopaminergic phenotype, which express neuronal markers such as synaptophysin, neuronal-specific nuclear protein, and neurofilament and release the neurotransmitter dopamine accompanied by expression of dopaminergic key factors tyrosine hydroxylase and Nurr1 (NR4A2). MicroRNA expression analysis highlighted their importance in neural development but their specific functions remain poorly understood. Here, downregulation of a set of 18 microRNAs during neuronal lineage differentiation of unrestricted somatic stem cells, including members of the miR-17-92 family and additional microRNAs such as miR-130a, -138, -218, and -335 as well as their target genes, is described. In silico target gene predictions for this microRNA group uncovered a large set of proteins involved in neuronal differentiation and having a strong impact on differentiation-related pathways such as axon guidance and TGFβ, WNT, and MAPK signaling. Experimental target validations confirmed approximately 35% of predictions tested and revealed a group of proteins with specific impact on neuronal differentiation and function including neurobeachin, neurogenic differentiation 1, cysteine-rich motor neuron protein 1, neuropentraxin 1, and others. These proteins are combined targets for several subgroups from the set of 18 downregulated microRNAs. This finding was further supported by the observed upregulation of a significant amount of predicted and validated target genes based on Illumina Beadstudio microarray data. Confirming the functional relationship of a limited panel of microRNAs and predicted target proteins reveals a clear network-like impact of the group of 18 downregulated microRNAs on proteins involved in neuronal development and function.

Neuropilin-1 signaling through p130Cas tyrosine phosphorylation is essential for growth factor-dependent migration of glioma and endothelial cells

Neuropilin-1 (NRP1) is a receptor for vascular endothelial growth factor (VEGF) and plays an important role in mediating cell motility. However, the NRP1 signaling pathways important for cell motility are poorly understood. Here we report that p130(Cas) tyrosine phosphorylation is stimulated by hepatocyte growth factor and platelet-derived growth factor in U87MG glioma cells and VEGF in endothelial cells and is dependent on NRP1 via its intracellular domain. In endothelial cells, NRP1 silencing reduced, but did not prevent, VEGF receptor 2 (VEGFR2) phosphorylation, while expression of a mutant form of NRP1 lacking the intracellular domain (NRP1ΔC) did not affect receptor phosphorylation in U87MG cells or human umbilical vein endothelial cells (HUVECs). In HUVECs, NRP1 was also required for VEGF-induced phosphorylation of proline-rich tyrosine kinase 2, which was necessary for p130(Cas) phosphorylation. Importantly, knockdown of NRP1 or p130(Cas) or expression of either NRP1ΔC or a non-tyrosine-phosphorylatable substrate domain mutant protein (p130(Cas15F)) was sufficient to inhibit growth factor-mediated migration of glioma and endothelial cells. These data demonstrate for the first time the importance of the NRP1 intracellular domain in mediating a specific signaling pathway downstream of several receptor tyrosine kinases and identify a critical role for a novel NRP1-p130(Cas) pathway in the regulation of chemotaxis.

Polysialic acid is required for neuropilin-2a/b-mediated control of CCL21-driven chemotaxis of mature dendritic cells and for their migration in vivo

Migration of mature dendritic cells (mDCs) to secondary lymphoid organs is required for the development of immunity. Recently, we reported that polysialic acid (PSA) and the transmembrane glycoprotein neuropilin-2 (NRP2) control mDC chemotaxis to CCL21 and that this process is dependent on the C-terminal basic region of the chemokine. Herein, we provide further insight into the molecular components controlling PSA regulated chemotaxis in mDCs. In the present study, we demonstrate that human mDCs express the NRP2 isoforms NRP2a and NRP2b, that both of them are susceptible to polysialylation and that polysialylation is required to specifically enhance chemotaxis toward CCL21 in mDCs. The results presented suggest that PSA attached to NRP2 isoforms acts as a binding module for the CCL21 chemokine, thereby facilitating its presentation to the chemokine receptor CCR7. To investigate the relevance of polysialylation on mDC migration, a xenograft mouse model was used and the migration of human DCs to mouse lymph nodes analyzed. Here, we demonstrate that the depletion of PSA from mDCs results in a drastic reduction in the migration of the cells to draining popliteal lymph nodes. With this finding, we provide first evidence that PSA is a crucial factor for in vivo migration of mDCs to lymph nodes.