Regulation of VEGF signaling by membrane traffic

Epsin Endocytic Adaptor Proteins in Angiogenic and Lymphangiogenic Signaling

Circulating vascular endothelial growth factor (VEGF) ligands and receptors are central regulators of vasculogenesis, angiogenesis, and lymphangiogenesis. In response to VEGF ligand binding, VEGF receptor tyrosine kinases initiate the chain of events that transduce extracellular signals into endothelial cell responses such as survival, proliferation, and migration. These events are controlled by intricate cellular processes that include the regulation of gene expression at multiple levels, interactions of numerous proteins, and intracellular trafficking of receptor-ligand complexes. Endocytic uptake and transport of macromolecular complexes through the endosome-lysosome system helps fine-tune endothelial cell responses to VEGF signals. Clathrin-dependent endocytosis remains the best understood means of macromolecular entry into cells, although the importance of non-clathrin-dependent pathways is increasingly recognized. Many of these endocytic events rely on adaptor proteins that coordinate internalization of activated cell-surface receptors. In the endothelium of both blood and lymphatic vessels, epsins 1 and 2 are functionally redundant adaptors involved in receptor endocytosis and intracellular sorting. These proteins are capable of binding both lipids and proteins and are important for promoting curvature of the plasma membrane as well as binding ubiquitinated cargo. Here, we discuss the role of epsin proteins and other endocytic adaptors in governing VEGF signaling in angiogenesis and lymphangiogenesis and discuss their therapeutic potential as molecular targets.

Dynamic contrast-enhanced MRI to characterize angiogenesis in primary epithelial ovarian cancer: An exploratory study

PURPOSE

Angiogenesis is essential for tumor growth. Currently, there are no established imaging biomarkers to show angiogenesis in tumor tissue. The aim of this prospective study was to evaluate whether semiquantitative and pharmacokinetic DCE-MRI perfusion parameters could be used to assess angiogenesis in epithelial ovarian cancer (EOC).

METHOD

We enrolled 38 patients with primary EOC treated in 2011-2014. DCE-MRI was performed with a 3.0 T imaging system before the surgical treatment. Two different sizes of ROI were used to evaluate semiquantitative and pharmacokinetic DCE perfusion parameters: a large ROI (L-ROI) covering the whole primary lesion on one plane and a small ROI (S-ROI) covering a small solid, highly enhancing focus. Tissue samples from tumors were collected during the surgery. Immunohistochemistry was used to measure the expression of vascular endothelial growth factor (VEGF), its receptors (VEGFRs) and to analyse microvascular density (MVD) and the number of microvessels.

RESULTS

VEGF expression correlated inversely with K^trans (L-ROI, r = -0.395 (p = 0.009), S-ROI, r = -0.390, (p = 0.010)), V_e (L-ROI, r = -0.395 (p = 0.009), S-ROI, r = -0.412 (p = 0.006)) and V_p (L-ROI, r = -0.388 (p = 0.011), S-ROI, r = -0.339 (p = 0.028)) values in EOC. Higher VEGFR-2 correlated with lower DCE parameters K^trans (L-ROI, r = -0.311 (p = 0.040), S-ROI, r = -0.337 (p = 0.025)) and V_e (L-ROI, r = -0.305 (p = 0.044), S-ROI, r = -0.355 (p = 0.018)). We also found that MVD and the number of microvessels correlated positively with AUC, Peak and WashIn values.

CONCLUSIONS

We observed that several DCE-MRI parameters correlated with VEGF and VEGFR-2 expression and MVD. Thus, both semiquantitative and pharmacokinetic perfusion parameters of DCE-MRI represent promising tools for the assessment of angiogenesis in EOC.

YULINK regulates vascular formation in zebrafish and HUVECs

BACKGROUND

The distinct arterial and venous cell fates are dictated by a combination of various genetic factors which form diverse types of blood vessels such as arteries, veins, and capillaries. We report here that YULINK protein is involved in vasculogenesis, especially venous formation.

METHODS

In this manuscript, we employed gene knockdown, yeast two-hybrid, FLIM-FRET, immunoprecipitation, and various imaging technologies to investigate the role of YULINK gene in zebrafish and human umbilical vein endothelial cells (HUVECs).

RESULTS

Knockdown of YULINK during the arterial-venous developmental stage of zebrafish embryos led to the defective venous formation and abnormal vascular plexus formation. Knockdown of YULINK in HUVECs impaired their ability to undergo cell migration and differentiation into a capillary-like tube formation. In addition, the phosphorylated EPHB4 was decreased in YULINK knockdown HUVECs. Yeast two-hybrid, FLIM-FRET, immunoprecipitation, as well as imaging technologies showed that YULINK colocalized with endosome related proteins (EPS15, RAB33B or TICAM2) and markers (Clathrin and RHOB). VEGF-induced VEGFR2 internalization was also compromised in YULINK knockdown HUVECs, demonstrating to the involvement of YULINK.

CONCLUSION

This study suggests that YULINK regulates vasculogenesis, possibly through endocytosis in zebrafish and HUVECs.

Held Up in Traffic-Defects in the Trafficking Machinery in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT), also known as motor and sensory neuropathy, describes a clinically and genetically heterogenous group of disorders affecting the peripheral nervous system. CMT typically arises in early adulthood and is manifested by progressive loss of motor and sensory functions; however, the mechanisms leading to the pathogenesis are not fully understood. In this review, we discuss disrupted intracellular transport as a common denominator in the pathogenesis of different CMT subtypes. Intracellular transport via the endosomal system is essential for the delivery of lipids, proteins, and organelles bidirectionally to synapses and the soma. As neurons of the peripheral nervous system are amongst the longest neurons in the human body, they are particularly susceptible to damage of the intracellular transport system, leading to a loss in axonal integrity and neuronal death. Interestingly, defects in intracellular transport, both in neurons and Schwann cells, have been found to provoke disease. This review explains the mechanisms of trafficking and subsequently summarizes and discusses the latest findings on how defects in trafficking lead to CMT. A deeper understanding of intracellular trafficking defects in CMT will expand our understanding of CMT pathogenesis and will provide novel approaches for therapeutic treatments.

EVL regulates VEGF receptor-2 internalization and signaling in developmental angiogenesis

Endothelial tip cells are essential for VEGF‐induced angiogenesis, but underlying mechanisms are elusive. The Ena/VASP protein family, consisting of EVL, VASP, and Mena, plays a pivotal role in axon guidance. Given that axonal growth cones and endothelial tip cells share many common features, from the morphological to the molecular level, we investigated the role of Ena/VASP proteins in angiogenesis. EVL and VASP, but not Mena, are expressed in endothelial cells of the postnatal mouse retina. Global deletion of EVL (but not VASP) compromises the radial sprouting of the vascular plexus in mice. Similarly, endothelial‐specific EVL deletion compromises the radial sprouting of the vascular plexus and reduces the endothelial tip cell density and filopodia formation. Gene sets involved in blood vessel development and angiogenesis are down‐regulated in EVL‐deficient P5‐retinal endothelial cells. Consistently, EVL deletion impairs VEGF‐induced endothelial cell proliferation and sprouting, and reduces the internalization and phosphorylation of VEGF receptor 2 and its downstream signaling via the MAPK/ERK pathway. Together, we show that endothelial EVL regulates sprouting angiogenesis via VEGF receptor‐2 internalization and signaling.

Microvasculature in hepatocellular carcinoma: An ultrastructural study

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most vascularized tumor types, and is characterized by development of heterogeneous immature vessels with increased permeability. Here, we analyzed morphology and vascular permeability-related structures in endothelial cells of HCC microvessels.

METHODS

Small (Type I) and large (Type II) peritumoral blood microvessels were assessed in HCC-bearing mice. By transmission electron microscopy, endothelial cell cytoplasm area, free transport vesicles, vesiculo-vacuolar organelles and clathrin-coated vesicles were measured.

RESULTS

The phenotypic changes in the HCC microvessels included presence of sinusoidal capillarization, numerous luminal microprocesses and abnormal luminal channels, irregular dilatations of interendothelial junctions, local detachment of basement membranes and widened extracellular space. Endothelial cells Type I microvessels showed increased vesicular trafficking-related structures.

CONCLUSION

Ultrastructural characteristics of microvessels Type I can associate with HCC new-formed microvessels. The morphological changes observed in HCC microvessels might explain the increased transcellular and paracellular permeability in HCC endothelial cells.

The chemical environmental pollutants BPA and BPS induce alterations of the proteomic profile of different phenotypes of human breast cancer cells: A proposed interactome

Breast cancer is one of the most common malignancies and the second leading cause of death in women. Despite efforts for its early detection, its worldwide incidence continues to increase. Thus, identification of risk factors for its development and new targets for its therapy are of vital importance. Environmental pollutants derived from human activity have been associated with predisposition to the development of cancer. Bisphenol A (BPA) is an endocrine disruptor compound (EDC) widely used in the manufacture of polycarbonates, and it has affinity for the estrogen receptor (ER). Scientific evidence has proposed an association between increased incidence of breast cancer and BPA exposure at lower doses. Among worldwide concerns with BPA exposure, different industries proceeded to replace BPA with analogs such as bisphenol S (BPS), which is now employed in products labelled as BPA-free. Nevertheless, recent studies exhibit that its exposure results in altered mammary gland development and morphogenesis; and promotes breast cancer cell proliferation. Of note, most of the effects of both BPA and BPS have been performed in estrogen-dependent breast cancer models. However, gaps in knowledge still exist on the roles and mechanisms that both compounds, specifically BPS, may play in cancer initiation and development in hormone-dependent and other types of breast cancer. Thus, the aim of the present study was to deepen the understanding of biological targets modulated by these ubiquitous pollutants in different breast cancer cell lines, representing two scenarios of this pathology: hormone-dependent and hormone-independent breast cancer. Results point out that both compounds induced proliferation in ER positive cells, not showing this effect in the ER-negative breast cancer cells. Different targets modified at the proteomic level in both breast cancer scenarios were also identified. Stem cell markers (eg. CD44) and invasion proteins (eg. MMP-14) were importantly increased by BPA and BPS in ER-positive breast cancer cells. In contrast, growth factors and associated receptors such as EGFR and TGF-β were induced by BPS in the ER-negative breast cancer cells; both pollutants induced an increase of vascular endothelial growth factor (VEGF) protein secretion. This finding suggests that the use of BPS must be considered with more caution than BPA, since it can act independently of the presence of the hormonal receptor. These findings show new evidence that BPA and BPS exposure can contribute to breast cancer development and progression. Our results suggest that both BPA and BPS must be considered equally as outstanding risk factors for this pathology.

Epsins in vascular development, function and disease

Epsins are a family of adaptor proteins involved in clathrin-dependent endocytosis. In the vasculature, epsins 1 and 2 are functionally redundant members of this family that are expressed in the endothelial cells of blood vessels and the lymphatic system throughout development and adulthood. These proteins contain a number of peptide motifs that allow them to interact with lipid moieties and a variety of proteins. These interactions facilitate the regulation of a wide range of cell signaling pathways. In this review, we focus on the involvement of epsins 1 and 2 in controlling vascular endothelial growth factor receptor signaling in angiogenesis and lymphangiogenesis. We also discuss the therapeutic implications of understanding the molecular mechanisms of epsin-mediated regulation in diseases such as atherosclerosis and diabetes.

Morphological Analysis of Blood Capillaries and Transport Function of Endothelial Cells in Hepatocellular Carcinoma-29

Hepatocellular carcinoma is characterized by the pronounced vascularization, high levels of vascular endothelial growth factors, and intensive angiogenesis. Caveola-mediated endocytosis and clathrin-dependent endocytosis contribute to internalization of various growth factors, thus affecting blood supply to the tumor and neoangiogenesis. We performed a quantitative analysis of blood vessels in the tumor and evaluated the basal levels of endocytosis-associated vesicular structures in the endothelial cells of the hepatocellular carcinoma-29. The numbers of blood vessels and clathrin-coated vesicles in endothelial cells in the tumor tissue were significantly higher than in normal tissue. The association between clathrin-dependent endocytosis in the endotheliocytes of the capillaries and tumor angiogenesis can provide the basis for the development of new molecular targets for antiangiogenic antitumor therapy.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

Synthesis, 3D-structure and stability analyses of NRPa-308, a new promising anti-cancer agent

We report herein the synthesis of a newly described anti-cancer agent, NRPa-308. This compound antagonizes Neuropilin-1, a multi-partners transmembrane receptor overexpressed in numerous tumors, and thereby validated as promising target in oncology. The preparation of NRPa-308 proved challenging because of the orthogonality of the amide and sulphonamide bonds formation. Nevertheless, we succeeded a gram scale synthesis, according to an expeditious three steps route, without intermediate purification. This latter point is of utmost interest in reducing the ecologic impact and production costs in the perspective of further scale-up processes. The purity of NRPa-308 has been attested by means of conventional structural analyses and its crystallisation allowed a structural assessment by X-Ray diffraction. We also reported the remarkable chemical stability of this molecule in acidic, neutral and basic aqueous media. Eventually, we observed for the first time the accumulation of NRPa-308 in two types of human breast cancer cells MDA-MB231 and BT549.

Regulation of VEGFR2 trafficking and signaling by Rab GTPase-activating proteins

Vascular endothelial growth factor receptor-2 (VEGFR2) and its ligands (VEGFs) are crucial players in vasculogenesis and angiogenesis. General blocking of this signaling system with antibodies or small molecule inhibitors is an established strategy to treat cancer and age-related macular degeneration. Nevertheless, the activated receptor can signal to discrete downstream signaling pathways and the equilibrium between these pathways is modulated by coreceptors and distinct isoforms of VEGF. Here we investigated the influence of Rab GTPase activating proteins (RabGAPs) on VEGFR2 signaling, tube formation, and migration of endothelial cells. We demonstrate that members of the TBC1D10 subfamily of RabGAPs have opposite effects. Whereas TBC1D10A leads to increased Erk1/2 signaling, TBC1D10B lowered Erk1/2 and p38 signaling and reduced tube formation in vitro. TBC1D10A is a RabGAP acting on RAB13 that was shown before to play a role in angiogenesis and we could indeed show colocalization of these two proteins with VEGFR2 in activated cells. In addition, we observed that cells expressing TBC1D10B show lower expression of VEGFR2 and NRP1 on filopodia of activated cells. Taken together, our systematic analysis of influence of RabGAPs on VEGFR2 signaling identifies the TBC1D10 subfamily members as modulators of angiogenesis.

Adventitial fibroblast-derived vascular endothelial growth factor promotes vasa vasorum-associated neointima formation and macrophage recruitment

Aims

Adventitial vasa vasorum provides oxygen and nourishment to the vascular wall, but whether it regulates vascular disease remains unclear. We have previously shown that an increased expression of VEGF (vascular endothelial growth factor) is associated with macrophage infiltration. This study aims to determine whether adventitial fibroblast (AF)-derived VEGF increases the number of vasa vasorum contributing to neointima formation through macrophage recruitment.

Methods and results

In rat balloon injury model, vasa vasorum count was increased particularly in the adventitia accompanied by cell proliferation and VEGF expression. Both endogenous and PKH26-labelled exogenous macrophages were mainly distributed in adventitia around vasa vasorum. Interestingly, perivascular delivery of Ranibizumab preferentially concentrated in adventitia resulted in a decrease of neointima formation with concurrent reduction of vasa vasorum count and macrophage infiltration. AFs with adenovirus-mediated VEGF over-expression delivered to the adventitia significantly enhanced these pathological changes after injury. In Tie2-cre/Rosa-LoxP-RFP mice, endothelial cells were increased in the adventitia after wire injury. By using multiphoton laser scanning microscopy, macrophage rolling, adhesion and transmigration were observed in vasa vasorum. Moreover, adoptive transfer of macrophages accelerated injury-induced neointima formation. VEGF-neutralizing antibody administration also attenuated wire injury-induced neointima formation and macrophage infiltration. In primary cultured AFs, exogenous VEGF increased VEGF expression and secretion in a time- and dose-dependent manner. AF-conditioned medium promoted endothelial cell angiogenesis, vascular cell adhesion molecule-1 expression and macrophage adhesion was blocked by VEGF-neutralizing antibody and VEGFR2 inhibitor ZM323881, which also inhibited activation of VEGFR2/ERK1/2 pathway.

Conclusion

These results demonstrate that AF-derived VEGF plays a significant role in the increase of vasa vasorum count which is involved in macrophage recruitment and neointima formation.

GIPC proteins negatively modulate Plexind1 signaling during vascular development

Semaphorins (SEMAs) and their Plexin (PLXN) receptors are central regulators of metazoan cellular communication. SEMA-PLXND1 signaling plays important roles in cardiovascular, nervous, and immune system development, and cancer biology. However, little is known about the molecular mechanisms that modulate SEMA-PLXND1 signaling. As PLXND1 associates with GIPC family endocytic adaptors, we evaluated the requirement for the molecular determinants of their association and PLXND1's vascular role. Zebrafish that endogenously express a Plxnd1 receptor with a predicted impairment in GIPC binding exhibit low penetrance angiogenesis deficits and antiangiogenic drug hypersensitivity. Moreover, gipc mutant fish show angiogenic impairments that are ameliorated by reducing Plxnd1 signaling. Finally, GIPC depletion potentiates SEMA-PLXND1 signaling in cultured endothelial cells. These findings expand the vascular roles of GIPCs beyond those of the Vascular Endothelial Growth Factor (VEGF)-dependent, proangiogenic GIPC1-Neuropilin 1 complex, recasting GIPCs as negative modulators of antiangiogenic PLXND1 signaling and suggest that PLXND1 trafficking shapes vascular development.

Sec14l3 potentiates VEGFR2 signaling to regulate zebrafish vasculogenesis

Vascular endothelial growth factor (VEGF) regulates vasculogenesis by using its tyrosine kinase receptors. However, little is known about whether Sec14-like phosphatidylinositol transfer proteins (PTP) are involved in this process. Here, we show that zebrafish sec14l3, one of the family members, specifically participates in artery and vein formation via regulating angioblasts and subsequent venous progenitors’ migration during vasculogenesis. Vascular defects caused by sec14l3 depletion are partially rescued by restoration of VEGFR2 signaling at the receptor or downstream effector level. Biochemical analyses show that Sec14l3/SEC14L2 physically bind to VEGFR2 and prevent it from dephosphorylation specifically at the Y¹¹⁷⁵ site by peri-membrane tyrosine phosphatase PTP1B, therefore potentiating VEGFR2 signaling activation. Meanwhile, Sec14l3 and SEC14L2 interact with RAB5A/4A and facilitate the formation of their GTP-bound states, which might be critical for VEGFR2 endocytic trafficking. Thus, we conclude that Sec14l3 controls vasculogenesis in zebrafish via the regulation of VEGFR2 activation.

The growth factor VEGF is known to regulate vasculogenesis but the downstream pathways activated are unclear. Here, the authors report that Sec14l3, a member of the PITP (phosphatidyl inositol transfer proteins) family regulates the formation of zebrafish vasculature by promoting VEGFR2 endocytic trafficking.

SNX9 determines the surface levels of integrin β1 in vascular endothelial cells: Implication in poor prognosis of human colorectal cancers overexpressing SNX9

Angiogenesis, the formation of new blood vessels, is involved in a variety of diseases including the tumor growth. In response to various angiogenic stimulations, a number of proteins on the surface of vascular endothelial cells are activated to coordinate cell proliferation, migration, and spreading processes to form new blood vessels. Plasma membrane localization of these angiogenic proteins, which include vascular endothelial growth factor receptors and integrins, are warranted by intracellular membrane trafficking. Here, by using a siRNA library, we screened for the sorting nexin family that regulates intracellular trafficking and identified sorting nexin 9 (SNX9) as a novel angiogenic factor in human umbilical vein endothelial cells (HUVECs). SNX9 was essential for cell spreading on the Matrigel, and tube formation that mimics in vivo angiogenesis in HUVECs. SNX9 depletion significantly delayed the recycling of integrin β1, an essential adhesion molecule for angiogenesis, and reduced the surface levels of integrin β1 in HUVECs. Clinically, we showed that SNX9 protein was highly expressed in tumor endothelial cells of human colorectal cancer tissues. High-level expression of SNX9 messenger RNA significantly correlated with poor prognosis of the patients with colorectal cancer. These results suggest that SNX9 is an angiogenic factor and provide a novel target for the development of new antiangiogenic drugs.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

The Rab-effector protein RABEP2 regulates endosomal trafficking to mediate vascular endothelial growth factor receptor-2 (VEGFR2)-dependent signaling

As a master regulator of endothelial cell function, vascular endothelial growth factor receptor-2 (VEGFR2) activates multiple downstream signaling pathways that are critical for vascular development and normal vessel function. VEGFR2 trafficking through various endosomal compartments modulates its signaling output. Accordingly, proteins that regulate the speed and direction by which VEGFR2 traffics through endosomes have been demonstrated to be particularly important for arteriogenesis. However, little is known about how these proteins control VEGFR2 trafficking and about the implications of this control for endothelial cell function. Here, we show that Rab GTPase-binding effector protein 2 (RABEP2), a Rab-effector protein implicated in arteriogenesis, modulates VEGFR2 trafficking. By employing high-resolution microscopy and biochemical assays, we demonstrate that RABEP2 interacts with the small GTPase Rab4 and regulates VEGFR2 endosomal trafficking to maintain cell-surface expression of VEGFR2 and VEGF signaling. Lack of RABEP2 also led to prolonged retention of VEGFR2 in Rab5-positive sorting endosomes, which increased VEGFR2's exposure to phosphotyrosine phosphatase 1b (PTP1b), causing diminished VEGFR2 signaling. Finally, the loss of RABEP2 increased VEGFR2 degradation by diverting VEGFR2 to Rab7-positive endosomes destined for the lysosome. These results implicate RABEP2 as a key modulator of VEGFR2 endosomal trafficking, and demonstrate the importance of RABEP2 and Rab4 for VEGFR2 signaling in endothelial cells.

Blood-brain barrier dysfunction and recovery after ischemic stroke

The blood-brain barrier (BBB) plays a vital role in regulating the trafficking of fluid, solutes and cells at the blood-brain interface and maintaining the homeostatic microenvironment of the CNS. Under pathological conditions, such as ischemic stroke, the BBB can be disrupted, followed by the extravasation of blood components into the brain and compromise of normal neuronal function. This article reviews recent advances in our knowledge of the mechanisms underlying BBB dysfunction and recovery after ischemic stroke. CNS cells in the neurovascular unit, as well as blood-borne peripheral cells constantly modulate the BBB and influence its breakdown and repair after ischemic stroke. The involvement of stroke risk factors and comorbid conditions further complicate the pathogenesis of neurovascular injury by predisposing the BBB to anatomical and functional changes that can exacerbate BBB dysfunction. Emphasis is also given to the process of long-term structural and functional restoration of the BBB after ischemic injury. With the development of novel research tools, future research on the BBB is likely to reveal promising potential therapeutic targets for protecting the BBB and improving patient outcome after ischemic stroke.

The Different Effects of VEGFA121 and VEGFA165 on Regulating Angiogenesis Depend on Phosphorylation Sites of VEGFR2

The effects of VEGFA isoforms on the vascular permeability and structure are still unclear. In this study, we found that VEGFA121 and VEGFA165, 2 isoforms of VEGFA, exerted the opposing effects of antiangiogenesis and proangiogenesis on regulating vascular endothelia cells proliferation and tube formation. The 2 isoforms affected the protein expression of Ras-related protein 1-GTPase-activating protein 1 (Rap1GAP) and thrombospondin 1, 2 important signal molecules of Rap1GAP/thrombospondin 1 signal pathway in primary human umbilical vein endothelial cells by regulating 2 different phosphorylating sites of VEGFR2, Tyr(1175) and Tyr(1214). We also found that VEGFA121 and VEGFA165 regulating angiogenesis was related to their regulating VEGFR2 and Rap1GAP/thrombospondin 1 signal pathway with the technology of RNA intervening the gene expression of VEGFR2 and Rap1GAP. Meanwhile, 2 inhibitors of VEGFR2, cabozantinib malate and ZM 323881 HCl (ZM), were used to investigate the relationship among VEGFA(121 and 165), VEGFR2, and angiogenesis. It was demonstrated that cabozantinib malate blocked VEGFA121 and VEGFA165 binding to VEGFR2 and inhibited angiogenesis by specifically binding to VEGFR2 rather than changing VEGFR2 phosphorylation or regulating the expression of VEGFR2. However, ZM antagonized the effect of VEGFA on angiogenesis by specifically reversing the phosphorylation induced by VEGFA121 and VEGFA165. The experiments in vivo also demonstrated that obvious abnormality of VEGFA121 and VEGFA165 presented in the serum of ulcerative colitis (UC) rats compared with that of the normal rats. ZM could promote the repairation of the injuries of the vessels and tissues of colonic mucosa of UC rats and caused mild inflammation in colonic mucosa of normal rats. On the contrary, cabozantinib malate caused injury of vessels and inflammation in the colonic mucosa of normal rats and aggravated the injuries of the vessels and inflammation in the colonic mucosa of UC rats. Hence, our data indicated that the activation of different phosphorylation sites of VEGFR2 leaded to VEGFA121 and VEGFA165 exerting opposing effects on angiogenesis, and it might be an underlying pathogenesis of UC and a potential target for UC treatment.

RCAN1.4 regulates VEGFR-2 internalisation, cell polarity and migration in human microvascular endothelial cells

Regulator of calcineurin 1 (RCAN1) is an endogenous inhibitor of the calcineurin pathway in cells. It is expressed as two isoforms in vertebrates: RCAN1.1 is constitutively expressed in most tissues, whereas transcription of RCAN1.4 is induced by several stimuli that activate the calcineurin-NFAT pathway. RCAN1.4 is highly upregulated in response to VEGF in human endothelial cells in contrast to RCAN1.1 and is essential for efficient endothelial cell migration and tubular morphogenesis. Here, we show that RCAN1.4 has a role in the regulation of agonist-stimulated VEGFR-2 internalisation and establishment of endothelial cell polarity. siRNA-mediated gene silencing revealed that RCAN1 plays a vital role in regulating VEGF-mediated cytoskeletal reorganisation and directed cell migration and sprouting angiogenesis. Adenoviral-mediated overexpression of RCAN1.4 resulted in increased endothelial cell migration. Antisense-mediated morpholino silencing of the zebrafish RCAN1.4 orthologue revealed a disrupted vascular development further confirming a role for the RCAN1.4 isoform in regulating vascular endothelial cell physiology. Our data suggest that RCAN1.4 plays a novel role in regulating endothelial cell migration by establishing endothelial cell polarity in response to VEGF.

Endocytosis and membrane receptor internalization: implication of F-BAR protein Carom

Endocytosis is a cellular process mostly responsible for membrane receptor internalization. Cell membrane receptors bind to their ligands and form a complex which can be internalized. We previously proposed that F-BAR protein initiates membrane curvature and mediates endocytosis via its binding partners. However, F-BAR protein partners involved in membrane receptor endocytosis and the regulatory mechanism remain unknown. In this study, we established database mining strategies to explore mechanisms underlying receptor-related endocytosis. We identified 34 endocytic membrane receptors and 10 regulating proteins in clathrin-dependent endocytosis (CDE), a major process of membrane receptor internalization. We found that F-BAR protein FCHSD2 (Carom) may facilitate endocytosis via 9 endocytic partners. Carom is highly expressed, along with highly expressed endocytic membrane receptors and partners, in endothelial cells and macrophages. We established 3 models of Carom-receptor complexes and their intracellular trafficking based on protein interaction and subcellular localization. We conclude that Carom may mediate receptor endocytosis and transport endocytic receptors to the cytoplasm for receptor signaling and lysosome/proteasome degradation, or to the nucleus for RNA processing, gene transcription and DNA repair.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Asymmetric division coordinates collective cell migration in angiogenesis

The asymmetric division of stem or progenitor cells generates daughters with distinct fates and regulates cell diversity during tissue morphogenesis. However, roles for asymmetric division in other more dynamic morphogenetic processes, such as cell migration, have not previously been described. Here we combine zebrafish in vivo experimental and computational approaches to reveal that heterogeneity introduced by asymmetric division generates multicellular polarity that drives coordinated collective cell migration in angiogenesis. We find that asymmetric positioning of the mitotic spindle during endothelial tip cell division generates daughters of distinct size with discrete 'tip' or 'stalk' thresholds of pro-migratory Vegfr signalling. Consequently, post-mitotic Vegfr asymmetry drives Dll4/Notch-independent self-organization of daughters into leading tip or trailing stalk cells, and disruption of asymmetry randomizes daughter tip/stalk selection. Thus, asymmetric division seamlessly integrates cell proliferation with collective migration, and, as such, may facilitate growth of other collectively migrating tissues during development, regeneration and cancer invasion.

Adenosine triphosphate is a critical determinant for VEGFR signal during hypoxia

Hypoxia induces angiogenesis through the VEGF signaling pathway; however, signal propagation of VEGF in hypoxia is not fully understood. In this study, we examined alterations in VEGF signaling during hypoxia conditions and its determinant in endothelial cells. To analyze VEGF signaling during hypoxia, human umbilical vein endothelial cells (HUVECs) were exposed to 3 h of hypoxia (1% O₂) followed by 3 h of reoxygenation or 12 h of hypoxia. Hypoxia induced expression of VEGF mRNA, but it was not associated with an increase in tube formation by HUVECs. During 3 h of hypoxia, VEGF-induced phosphorylation of VEGF receptor-2 (VEGFR-2) and downstream molecules were significantly inhibited without a change in VEGFR-2 expression, but it was completely restored after reoxygenation. VEGF-mediated VEGFR-2 phosphorylation is associated with a reduction in cellular ATP in hypoxia conditions (65.93 ± 8.32% of normoxia, means ± SE, P < 0.01). Interestingly, attenuation of VEGFR-2 phosphorylation was restored by addition of ATP to prepared membranes from cells that underwent 3 h of hypoxia. In contrast to 3 h of hypoxia, exposure of cells to 12 h of hypoxia decreased VEGFR-2 expression and VEGF-mediated VEGFR-2 phosphorylation. The magnitude of VEGFR-2 phosphorylation was not fully restored by addition of ATP to prepared membranes from cells exposed to 12 h of hypoxia. These data indicate that ATP is an important determinant of VEGF signaling in hypoxia and suggest that the activation process of VEGFR-2 was modified by sustained hypoxia. These observations contribute to our understanding of signal alterations in VEGF in endothelial cells during hypoxia.

Role of BMP receptor traffic in synaptic growth defects in an ALS model

In a Drosophila model of ALS, neuronal defects are associated with altered endosomal traffic of growth factor receptors and loss of growth-promoting signals. Manipulation of an endosomal recycling pathway suppresses these neuronal defects. The findings suggest that rerouting membrane traffic could be therapeutic in ALS.

TAR DNA-binding protein 43 (TDP-43) is genetically and functionally linked to amyotrophic lateral sclerosis (ALS) and regulates transcription, splicing, and transport of thousands of RNA targets that function in diverse cellular pathways. In ALS, pathologically altered TDP-43 is believed to lead to disease by toxic gain-of-function effects on RNA metabolism, as well as by sequestering endogenous TDP-43 and causing its loss of function. However, it is unclear which of the numerous cellular processes disrupted downstream of TDP-43 dysfunction lead to neurodegeneration. Here we found that both loss and gain of function of TDP-43 in Drosophila cause a reduction of synaptic growth–promoting bone morphogenic protein (BMP) signaling at the neuromuscular junction (NMJ). Further, we observed a shift of BMP receptors from early to recycling endosomes and increased mobility of BMP receptor–containing compartments at the NMJ. Inhibition of the recycling endosome GTPase Rab11 partially rescued TDP-43–induced defects in BMP receptor dynamics and distribution and suppressed BMP signaling, synaptic growth, and larval crawling defects. Our results indicate that defects in receptor traffic lead to neuronal dysfunction downstream of TDP-43 misregulation and that rerouting receptor traffic may be a viable strategy for rescuing neurological impairment.

VEGF-A isoforms program differential VEGFR2 signal transduction, trafficking and proteolysis

Vascular endothelial growth factor A (VEGF-A) binding to the receptor tyrosine kinase VEGFR2 triggers multiple signal transduction pathways, which regulate endothelial cell responses that control vascular development. Multiple isoforms of VEGF-A can elicit differential signal transduction and endothelial responses. However, it is unclear how such cellular responses are controlled by isoform-specific VEGF-A-VEGFR2 complexes. Increasingly, there is the realization that the membrane trafficking of receptor-ligand complexes influences signal transduction and protein turnover. By building on these concepts, our study shows for the first time that three different VEGF-A isoforms (VEGF-A165, VEGF-A121 and VEGF-A145) promote distinct patterns of VEGFR2 endocytosis for delivery into early endosomes. This differential VEGFR2 endocytosis and trafficking is linked to VEGF-A isoform-specific signal transduction events. Disruption of clathrin-dependent endocytosis blocked VEGF-A isoform-specific VEGFR2 activation, signal transduction and caused substantial depletion in membrane-bound VEGFR1 and VEGFR2 levels. Furthermore, such VEGF-A isoforms promoted differential patterns of VEGFR2 ubiquitylation, proteolysis and terminal degradation. Our study now provides novel insights into how different VEGF-A isoforms can bind the same receptor tyrosine kinase and elicit diverse cellular outcomes.

A Review of the Mechanisms of Blood-Brain Barrier Permeability by Tissue-Type Plasminogen Activator Treatment for Cerebral Ischemia

Cerebrovascular homeostasis is maintained by the blood-brain barrier (BBB), which forms a mechanical and functional barrier between systemic circulation and the central nervous system (CNS). In patients with ischemic stroke, the recombinant tissue-type plasminogen activator (rt-PA) is used to accelerate recanalization of the occluded vessels. However, rt-PA is associated with a risk of increasing intracranial bleeding (ICB). This effect is thought to be caused by the increase in cerebrovascular permeability though various factors such as ischemic reperfusion injury and the activation of matrix metalloproteinases (MMPs), but the detailed mechanisms are unknown. It was recently found that rt-PA treatment enhances BBB permeability not by disrupting the BBB, but by activating the vascular endothelial growth factor (VEGF) system. The VEGF regulates both the dissociation of endothelial cell (EC) junctions and endothelial endocytosis, and causes a subsequent increase in vessel permeability through the VEGF receptor-2 (VEGFR-2) activation in ECs. Here, we review the possibility that rt-PA increases the penetration of toxic molecules derived from the bloodstream including rt-PA itself, without disrupting the BBB, and contributes to these detrimental processes in the cerebral parenchyma.

Targeting angiogenesis in endometrial cancer - new agents for tailored treatments

INTRODUCTION

Endometrial carcinoma represents the most frequent gynecologic tumor in developed countries. The majority of women presents with low-grade tumors but a significant subset of women experience recurrence and do not survive their disease. Patients with stage III/ IV or recurrent endometrial cancer have a poor prognosis. Identification of active and tolerable new targeted agents versus specific molecular targets is a priority objective. Angiogenesis is a complex process that plays a crucial role in the development of many types of cancer and in particular endometrial cancer.

AREAS COVERED

In this review, the authors highlight the main angiogenetic molecular pathways and the anti-angiogenic agents in Phase II clinical trials for endometrial cancer treatment. The authors focus on reports from recent years on angiogenesis inhibitors used in endometrial cancer, including anti- vascular endothelial growth factor (VEGF) monoclonal antibodies (bevacizumab and aflibercept), mammalian target of rapamycin inhibitors (mTORi) (everolimus, temsirolimus and ridaforolimus), PI3 K inhibitors (BKM120), tyrosine kinase inhibitors (brivanib, sunitinib, dovitinib and nintedanib) and thalidomide.

EXPERT OPINION

These anti-angiogenic drugs, while used either alone or in combination with chemotherapy, have presented mixed results in treating endometrial cancer patients. Challenges for the future include the identification of new pathways, early identification and overcoming resistance and the use of these molecules in combination with old and new chemotherapeutic and targeted agents.

VEGFR2 Trafficking, Signaling and Proteolysis is Regulated by the Ubiquitin Isopeptidase USP8

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular function. VEGF-A binding to vascular endothelial growth factor receptor 2 (VEGFR2) stimulates endothelial signal transduction and regulates multiple cellular responses. Activated VEGFR2 undergoes ubiquitination but the enzymes that regulate this post-translational modification are unclear. In this study, the de-ubiquitinating enzyme, USP8, is shown to regulate VEGFR2 trafficking, de-ubiquitination, proteolysis and signal transduction. USP8-depleted endothelial cells displayed altered VEGFR2 ubiquitination and production of a unique VEGFR2 extracellular domain proteolytic fragment caused by VEGFR2 accumulation in the endosome-lysosome system. In addition, perturbed VEGFR2 trafficking impaired VEGF-A-stimulated signal transduction in USP8-depleted cells. Thus, regulation of VEGFR2 ubiquitination and de-ubiquitination has important consequences for the endothelial cell response and vascular physiology.

Recombinant tissue-type plasminogen activator transiently enhances blood-brain barrier permeability during cerebral ischemia through vascular endothelial growth factor-mediated endothelial endocytosis in mice

Recombinant tissue-type plasminogen activator (rt-PA) modulates cerebrovascular permeability and exacerbates brain injury in ischemic stroke, but its mechanisms remain unclear. We studied the involvement of vascular endothelial growth factor (VEGF)-mediated endocytosis in the increase of blood-brain barrier (BBB) permeability potentiated by rt-PA after ischemic stroke. The rt-PA treatment at 4 hours after middle cerebral artery occlusion induced a transient increase in BBB permeability after ischemic stroke in mice, which was suppressed by antagonists of either low-density lipoprotein receptor families (LDLRs) or VEGF receptor-2 (VEGFR-2). In immortalized bEnd.3 endothelial cells, rt-PA treatment upregulated VEGF expression and VEGFR-2 phosphorylation under ischemic conditions in an LDLR-dependent manner. In addition, rt-PA treatment increased endocytosis and transcellular transport in bEnd.3 monolayers under ischemic conditions, which were suppressed by the inhibition of LDLRs, VEGF, or VEGFR-2. The rt-PA treatment also increased the endocytosis of endothelial cells in the ischemic brain region after stroke in mice. These findings indicate that rt-PA increased BBB permeability via induction of VEGF, which at least partially mediates subsequent increase in endothelial endocytosis. Therefore, inhibition of VEGF induction may have beneficial effects after thrombolytic therapy with rt-PA treatment after stroke.

Procyanidin B2 3,3″-di-O-gallate inhibits endothelial cells growth and motility by targeting VEGFR2 and integrin signaling pathways

Targeting angiogenesis, one of the hallmarks of carcinogenesis, using non-toxic phytochemicals has emerged as a translational opportunity for angioprevention and to control advanced stages of malignancy. Herein, we investigated the inhibitory effects and associated mechanism/s of action of Procyanidin B2-3,3″-di- O-gallate (B2G2), a major component of grape seed extract, on human umbilical vein endothelial cells (HUVECs) and human prostate microvascular endothelial cells (HPMECs). Our results showed that B2G2 (10-40 μM) inhibits growth and induces death in both HUVECs and HPMECs. Additional studies revealed that B2G2 causes a G1 arrest in cell cycle progression of HUVECs by down-regulating cyclins (D1 and A), CDKs (Cdk2 and Cdc2) and Cdc25c phosphatase and up-regulating CDK inhibitors (p21 and p27) expression. B2G2 also induced strong apoptotic death in HUVECs through increasing p53, Bax and Smac/Diablo expression while decreasing Bcl-2 and survivin levels. Additionally, B2G2 inhibited the growth factors-induced capillary tube formation in HUVECs and HPMECs. Interestingly, conditioned media (CCM) from prostate cancer (PCA) cells (LNCaP and PC3) grown under normoxic (~21% O2) and hypoxic (1% O2) conditions significantly enhanced the tube formation in HUVECs, which was compromised in presence of conditioned media from B2G2-treated PCA cells. B2G2 also inhibited the motility and invasiveness of both HUVECs and HPMECs. Mechanistic studies showed that B2G2 targets VEGFR2/PI3K/Akt and integrin signaling molecules which are important for endothelial cells survival, proliferation, tube formation and motility. Overall, we report that B2G2 inhibits several attributes of angiogenesis in cell culture; therefore, it warrants further investigation for efficacy for angioprevention and cancer control.

Regulation of signaling interactions and receptor endocytosis in growing blood vessels

Blood vessels and the lymphatic vasculature are extensive tubular networks formed by endothelial cells that have several indispensable functions in the developing and adult organism. During growth and tissue regeneration but also in many pathological settings, these vascular networks expand, which is critically controlled by the receptor EphB4 and the ligand ephrin-B2. An increasing body of evidence links Eph/ephrin molecules to the function of other receptor tyrosine kinases and cell surface receptors. In the endothelium, ephrin-B2 is required for clathrin-dependent internalization and full signaling activity of VEGFR2, the main receptor for vascular endothelial growth factor. In vascular smooth muscle cells, ephrin-B2 antagonizes clathrin-dependent endocytosis of PDGFRβ and controls the balanced activation of different signal transduction processes after stimulation with platelet-derived growth factor. This review summarizes the important roles of Eph/ephrin molecules in vascular morphogenesis and explains the function of ephrin-B2 as a molecular hub for receptor endocytosis in the vasculature.

Role of microRNA-520h in 20(R)-ginsenoside-Rg3-mediated angiosuppression

Background

Ginsenoside-Rg3, the pharmacologically active component of red ginseng, has been found to inhibit tumor growth, invasion, metastasis, and angiogenesis in various cancer models. Previously, we found that 20(R)-ginsenoside-Rg3 (Rg3) could inhibit angiogenesis. Since microRNAs (miRNAs) have been shown to affect many biological processes, they might play an important role in ginsenoside-mediated angiomodulation.

Methods

In this study, we examined the underlying mechanisms of Rg3-induced angiosuppression through modulating the miRNA expression. In the miRNA-expression profiling analysis, six miRNAs and three miRNAs were found to be up- or down-regulated in vascular-endothelial-growth-factor-induced human-umbilical-vein endothelial cells (HUVECs) after Rg3 treatment, respectively.

Results

A computational prediction suggested that mature hsa-miR-520h (miR-520h) targets ephrin receptor (Eph) B2 and EphB4, and hence, affecting angiogenesis. The up-regulation of miR-520h after Rg3 treatment was validated by quantitative real-time polymerase chain reaction, while the protein expressions of EphB2 and EphB4 were found to decrease, respectively. The mimics and inhibitors of miR-520h were transfected into HUVECs and injected into zebra-fish embryos. The results showed that overexpression of miR-520h could significantly suppress the EphB2 and EphB4 protein expression, proliferation, and tubulogenesis of HUVECs, and the subintestinal-vessel formation of the zebra fish.

Conclusion

These results might provide further information on the mechanism of Rg3-induced angiosuppression and the involvement of miRNAs in angiogenesis.

The Plant-Specific RAB5 GTPase ARA6 is Required for Starch and Sugar Homeostasis in Arabidopsis thaliana

Endosomal trafficking plays integral roles in various eukaryotic cell activities. In animal cells, a member of the RAB GTPase family, RAB5, is a key regulator of various endosomal functions. In addition to orthologs of animal RAB5, plants harbor the plant-specific RAB5 group, the ARA6 group, which is conserved in land plant lineages. In Arabidopsis thaliana, ARA6 and conventional RAB5 act in distinct endosomal trafficking pathways; ARA6 mediates trafficking from endosomes to the plasma membrane, whereas conventional RAB5 acts in endocytic and vacuolar trafficking pathways. ARA6 is also required for normal salt and osmotic stress tolerance, although the functional link between ARA6 and stress tolerance remains unclear. In this study, we investigated ARA6 function in stress tolerance by monitoring broad-scale changes in gene expression in the ara6 mutant. A comparison of the expression profiles between wild-type and ara6-1 plants revealed that the expression of the Qua-Quine Starch (QQS) gene was significantly affected by the ara6-1 mutation. QQS is involved in starch homeostasis, consistent with the starch content decreasing in the ara6 mutants to approximately 60% of that of the wild-type plant. In contrast, the free and total glucose content increased in the ara6 mutants. Moreover, the proliferation of Pseudomonas syringae pv. tomato DC3000 was repressed in ara6 mutants, which could be attributed to the elevated sugar content. These results suggest that ARA6 is responsible for starch and sugar homeostasis, most probably through the function of QQS.

VEGF-A isoform-specific regulation of calcium ion flux, transcriptional activation and endothelial cell migration

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology such as cell migration, proliferation, tubulogenesis and cell-cell interactions. Numerous isoforms of VEGF-A exist but their physiological significance is unclear. Here we evaluated two different VEGF-A isoforms and discovered differential regulation of cytosolic calcium ion flux, transcription factor localisation and endothelial cell response. Analysis of VEGF-A isoform-specific stimulation of VEGFR2-dependent signal transduction revealed differential capabilities for isoform activation of multiple signal transduction pathways. VEGF-A₁₆₅ treatment promoted increased phospholipase Cγ1 phosphorylation, which was proportional to the subsequent rise in cytosolic calcium ions, in comparison to cells treated with VEGF-A₁₂₁. A major consequence of this VEGF-A isoform-specific calcium ion flux in endothelial cells is differential dephosphorylation and subsequent nuclear translocation of the transcription factor NFATc2. Using reverse genetics, we discovered that NFATc2 is functionally required for VEGF-A-stimulated endothelial cell migration but not tubulogenesis. This work presents a new mechanism for understanding how VEGF-A isoforms program complex cellular outputs by converting signal transduction pathways into transcription factor redistribution to the nucleus, as well as defining a novel role for NFATc2 in regulating the endothelial cell response.

Angiogenesis versus arteriogenesis: neuropilin 1 modulation of VEGF signaling

In development and disease, vascular endothelial growth factor (VEGF) regulates the expansion of the vascular tree. In response to hypoxia, VEGF promotes new capillary formation through the process of angiogenesis by inducing endothelial cell sprouting, proliferation, and migration. Wound healing, tissue regeneration, and tumor growth depend on angiogenesis for adequate nutrient and oxygen delivery. Under different conditions, VEGF promotes arterial growth, modulates lumen expansion, and induces collateral vessel formation, events collectively referred to as arteriogenesis. Induction of arteriogenesis after cardiac or cerebral arterial occlusion can reduce ischemia and improve disease outcome. Endothelial VEGF receptor 2 (VEGFR2) signaling governs both processes. However, modulation of downstream VEGF signaling effectors, such as extracellular-signal-regulated kinase (ERK) activation, differs in order to achieve angiogenic versus arteriogenic outcomes. Recent reports show that neuropilin 1 (NRP1), a VEGF receptor, can instill VEGF signaling outcomes that specifically regulate either angiogenesis or arteriogenesis. Here, we discuss how NRP1 functions as a VEGFR2 co-receptor in angiogenesis and a modulator of VEGFR2 trafficking in arteriogenesis. The unique role played by neuropilin in different endothelial processes makes it an exciting therapeutic target to specifically enhance angiogenesis or arteriogenesis in disease settings.

Combined therapy with thrombospondin-1 type I repeats (3TSR) and chemotherapy induces regression and significantly improves survival in a preclinical model of advanced stage epithelial ovarian cancer

Most women are diagnosed with epithelial ovarian cancer (EOC) at advanced stage, where therapies have limited effectiveness and the long-term survival rate is low. We evaluated the effects of combined antiangiogenic and chemotherapy treatments on advanced stage EOC. Treatment of EOC cells with a recombinant version of the thrombospondin-1 type I repeats (3TSR) induced more apoptotic cell death (36.5 ± 9.6%) in vitro compared to untreated controls (4.1 ± 1.4). In vivo, tumors were induced in an orthotopic, syngeneic mouse model of advanced stage EOC. Mice were treated with 3TSR (4 mg/kg per day) alone or in combination with chemotherapy drugs delivered with maximum tolerated dose or metronomic scheduling. Pretreatment with 3TSR induced tumor regression, normalized tumor vasculature, and improved uptake of chemotherapy drugs. Combination 3TSR and metronomic chemotherapy induced the greatest tumor regression (6.2-fold reduction in size compared to PBS-treated controls) and highest survival when treatment was initiated at advanced stage. 3TSR binding to its receptor, CD36 (cluster of differentiation 36), increased binding of CD36 and SHP-1, which significantly inhibited phosphorylation of the VEGF receptor. In this study, we describe a novel treatment approach and mechanism of action with 3TSR and chemotherapy that induces regression of advanced stage EOC and significantly improves survival.-Russell, S., Duquette, M., Liu, J., Drapkin, R., Lawler, J., Petrik, J. Combined therapy with thrombospondin-1 type I repeats (3TSR) and chemotherapy induces regression and significantly improves survival in a preclinical model of advanced stage epithelial ovarian cancer.

Prednisolone-induced predisposition to femoral head separation and the accompanying plasma protein changes in chickens

Femoral head separation (FHS) is an idiopathic bone problem that causes lameness and production losses in commercial poultry. In a model of prednisolone-induced susceptibility to FHS, the changes in plasma proteins and peptides were analyzed to find possible biomarkers. Plasma samples from control and FHS-susceptible birds were depleted of their high abundance proteins by acetonitrile precipitation and were then subjected to cation exchange and reverse-phase (RP) fractionations. Analysis with matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) showed several differentially expressed peptides, two of which were isolated by RP-HPLC and identified as the fragments of apolipoprotein A-I. The acetonitrile fractionated plasma proteins were subjected to reduction/alkylation and trypsin digestion followed by liquid chromatography and tandem mass spectrometry, which showed the absence of protocadherin 15, vascular endothelial growth factor-C, and certain transcription and ubiquitin-mediated proteolytic factors in FHS-prone birds. It appears that prednisolone-induced dyslipidemia, vascular, and tissue adhesion problems may be consequential to FHS. Validity of these biomarkers in our model and the natural disease must be verified in future using traditional approaches.

BIOMARKER INSIGHTS

Lameness because of femoral head separation (FHS) is a production and welfare problem in the poultry industry. Selection against FHS requires identification of the birds with subclinical disease with biomarkers from a source such as blood. Prednisolone can induce femoral head problems and predisposition to FHS. Using this experimental model, we analyzed the plasma peptides and proteins from normal and FHS-prone chickens by mass spectrometry to identify differentially expressed peptides and proteins. We found two peptides, both derived from apolipoprotein A-I, quantitatively elevated and two proteins, protocadherin 15 and VEGF-C, that were conspicuously absent in FHS-susceptible birds.

Impaired Cav-1 expression in SSc mesenchymal cells upregulates VEGF signaling: a link between vascular involvement and fibrosis

BACKGROUND

Systemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast. It is well known that vascular endothelial growth factor A (VEGF-A, hereafter referred to as VEGF) may induce a profibrotic phenotype on perivascular cells. Caveolin-1 (Cav-1) is involved in the regulation of VEGF signaling, playing a role in the transport of internalized VEGF receptor 2 (VEGFR2) toward degradation, thus decreasing VEGF signaling. In this work, we assessed the levels of Cav-1 in SSc bone marrow mesenchymal stem cells (SSc-MSCs), a pericyte surrogate, and correlate these results with VEGF signaling, focusing onpotential pathogenic pathways leading to fibrosis.

RESULTS

WE EXPLORED THE VEGF SIGNALING ASSESSING: (1) Cav-1 expression; (2) its co-localization with VEGFR2; (3) the activity of VEGFR2, by IF, immunoprecipitation, and western blot. In SSc-MSCs, Cav-1 levels were lower when compared to healthy controls (HC)-MSCs. Furthermore, the Cav-1/VEGFR2 co-localization and the ubiquitination of VEGFR2 were impaired in SSc-MSCs, suggesting a decreased degradation of the receptor and, as a consequence, the tyrosine phosphorylation of VEGFR2 and the PI3-kinase-Akt pathways were significantly increased when compared to HC. Furthermore, an increased connective tissue growth factor (CTGF) expression was observed in SSc-MSCs. Taken together, these data suggested the upregulation of VEGF signaling in SSc-MSCs. Furthermore, after silencing Cav-1 expression in HC-MSCs, an increased CTGF expression in HC-MSCs was observed, mirroring the results obtained in SSc-MSCs, and confirming the potential role that the lack of Cav-1 may play in the persistent VEGF signaling .

CONCLUSIONS

During SSc, the lower levels of Cav-1 may contribute to the pathogenesis of fibrosis via an upregulation of the VEGF signaling in perivascular cells which are shifted to a profibrotic phenotype.

Nucleoside diphosphate kinase B regulates angiogenesis through modulation of vascular endothelial growth factor receptor type 2 and endothelial adherens junction proteins

OBJECTIVE

Nucleoside diphosphate kinase B (NDPKB) participates in the activation of heterotrimeric and monomeric G proteins, which are pivotal mediators in angiogenic signaling. The role of NDPKB in angiogenesis has to date not been defined. Therefore, we analyzed the contribution of NDPKB to angiogenesis and its underlying mechanisms in well-characterized in vivo and in vitro models.

APPROACH AND RESULTS

Zebrafish embryos were depleted of NDPKB by morpholino-mediated knockdown. These larvae displayed severe malformations specifically in vessels formed by angiogenesis. NDPKB-deficient (NDPKB(-/-)) mice were subjected to oxygen-induced retinopathy. In this model, the number of preretinal neovascularizations in NDPKB(-/-) mice was strongly reduced in comparison with wild-type littermates. In accordance, a delayed blood flow recovery was detected in the NDPKB(-/-) mice after hindlimb ligation. In in vitro studies, a small interfering RNA-mediated knockdown of NDPKB was performed in human umbilical endothelial cells. NDPKB depletion impaired vascular endothelial growth factor (VEGF)-induced sprouting and hampered the VEGF-induced spatial redistributions of the VEGF receptor type 2 and VE-cadherin at the plasma membrane. Concomitantly, NDPKB depletion increased the permeability of the human umbilical endothelial cell monolayer.

CONCLUSIONS

This is the first report to show that NDPKB is required for VEGF-induced angiogenesis and contributes to the correct localization of VEGF receptor type 2 and VE-cadherin at the endothelial adherens junctions. Therefore, our data identify NDPKB as a novel molecular target to modulate VEGF-dependent angiogenesis.

VEGF-A isoforms differentially regulate ATF-2-dependent VCAM-1 gene expression and endothelial-leukocyte interactions

VEGF-A isoforms differentially stimulate endothelial VCAM-1 gene expression via an ERK1/2 protein kinase and ATF-2 transcription factor–dependent mechanism. Such signal transduction enables VEGF-A isoform–specific stimulation of leukocyte binding to endothelial cells, explaining how inflammation could be differentially regulated.

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology. VEGF-A stimulates signal transduction pathways that modulate endothelial outputs such as cell migration, proliferation, tubulogenesis, and cell–cell interactions. Multiple VEGF-A isoforms exist, but the biological significance of this is unclear. Here we analyzed VEGF-A isoform–specific stimulation of VCAM-1 gene expression, which controls endothelial–leukocyte interactions, and show that this is dependent on both ERK1/2 and activating transcription factor-2 (ATF-2). VEGF-A isoforms showed differential ERK1/2 and p38 MAPK phosphorylation kinetics. A key feature of VEGF-A isoform–specific ERK1/2 activation and nuclear translocation was increased phosphorylation of ATF-2 on threonine residue 71 (T71). Using reverse genetics, we showed ATF-2 to be functionally required for VEGF-A–stimulated endothelial VCAM-1 gene expression. ATF-2 knockdown blocked VEGF-A–stimulated VCAM-1 expression and endothelial–leukocyte interactions. ATF-2 was also required for other endothelial cell outputs, such as cell migration and tubulogenesis. In contrast, VCAM-1 was essential only for promoting endothelial–leukocyte interactions. This work presents a new paradigm for understanding how soluble growth factor isoforms program complex cellular outputs and responses by modulating signal transduction pathways.

Receptor tyrosine kinases endocytosis in endothelium: biology and signaling

Receptor tyrosine kinases are involved in regulation of key processes in endothelial biology, including proliferation, migration, and angiogenesis. It is now generally accepted that receptor tyrosine kinase signaling occurs intracellularly and on the plasma membrane, although many important details remain to be worked out. Endocytosis and subsequent intracellular trafficking spatiotemporally regulate receptor tyrosine kinase signaling, whereas signaling endosomes provide a platform for the compartmentalization of signaling events. This review summarizes recent advances in our understanding of endothelial receptor tyrosine kinase endocytosis and signaling using vascular endothelial growth factor receptor-2 as a paradigm.

Expression profiling and significance of VEGF-A, VEGFR2, VEGFR3 and related proteins in endometrial carcinoma

BACKGROUND

Angiogenesis plays a key role in the progression of various tumors, including endometrial carcinomas. Several cytokines and their associated receptors are shown to be involved, particularly VEGF-A with VEGFR1, -2 and -3.

METHODS

The expressions of VEGF-A, VEGFR2 and VEGFR3 were studied in by immunohistochemistry in 76 endometrial carcinoma specimens. VEGFR2 and VEGFR3 receptor expression were also studied by qRT-PCR in 17 tumors in comparison to normal endometrium. The expression profiles were correlated with tumor type, grade, stage, lymphovascular invasion, disease free survival, and the expressions of other cytokine receptors (EGFR, CXCR1 and CXCR2).

RESULTS

Immunohistochemically, 63% of endometrial cancers expressed VEGF-A, 55% VEGFR2 and 26% VEGFR3. VEGFR3 was significantly correlated with tumor stage (p=0.02), with a trend towards poorer disease free survival (p=0.09). VEGF-A was significantly correlated with microvessel density (p<0.01). Using qRT-PCR, increased expression of VEGFR2 (17.2-fold) and VEGFR3 (21.9-fold) was seen in endometrial carcinomas compared with normal endometrium, with significant correlations among the expression levels of VEGFR2, VEGFR3, EGFR, CXCR1 and CXCR2.

CONCLUSION

Our study suggests that evaluation of VEGFR3 expression in tumors may provide prognostic data, and help identify patients who would best benefit from anti-angiogenic therapeutic agents. This is the first report showing correlations between the expressions levels of the different receptors.

Endosome-to-Plasma Membrane Recycling of VEGFR2 Receptor Tyrosine Kinase Regulates Endothelial Function and Blood Vessel Formation

Rab GTPases are implicated in endosome-to-plasma membrane recycling, but how such membrane traffic regulators control vascular endothelial growth factor receptor 2 (VEGFR2/KDR) dynamics and function are not well understood. Here, we evaluated two different recycling Rab GTPases, Rab4a and Rab11a, in regulating endothelial VEGFR2 trafficking and signalling with implications for endothelial cell migration, proliferation and angiogenesis. In primary endothelial cells, VEGFR2 displays co-localisation with Rab4a, but not Rab11a GTPase, on early endosomes. Expression of a guanosine diphosphate (GDP)-bound Rab4a S22N mutant caused increased VEGFR2 accumulation in endosomes. TfR and VEGFR2 exhibited differences in endosome-to-plasma membrane recycling in the presence of chloroquine. Depletion of Rab4a, but not Rab11a, levels stimulated VEGF-A-dependent intracellular signalling. However, depletion of either Rab4a or Rab11a levels inhibited VEGF-A-stimulated endothelial cell migration. Interestingly, depletion of Rab4a levels stimulated VEGF-A-regulated endothelial cell proliferation. Rab4a and Rab11a were also both required for endothelial tubulogenesis. Evaluation of a transgenic zebrafish model showed that both Rab4 and Rab11a are functionally required for blood vessel formation and animal viability. Rab-dependent endosome-to-plasma membrane recycling of VEGFR2 is important for intracellular signalling, cell migration and proliferation during angiogenesis.

NRP1 presented in trans to the endothelium arrests VEGFR2 endocytosis, preventing angiogenic signaling and tumor initiation

Neuropilin 1 (NRP1) modulates angiogenesis by binding vascular endothelial growth factor (VEGF) and its receptor, VEGFR2. We examined the consequences when VEGFR2 and NRP1 were expressed on the same cell (cis) or on different cells (trans). In cis, VEGF induced rapid VEGFR2/NRP1 complex formation and internalization. In trans, complex formation was delayed and phosphorylation of phospholipase Cγ (PLCγ) and extracellular regulated kinase 2 (ERK2) was prolonged, whereas ERK1 phosphorylation was reduced. Trans complex formation suppressed initiation and vascularization of NRP1-expressing mouse fibrosarcoma and melanoma. Suppression in trans required high-affinity, steady-state binding of VEGF to NRP1, which was dependent on the NRP1 C-terminal domain. Compatible with a trans effect of NRP1, quiescent vasculature in the developing retina showed continuous high NRP1 expression, whereas angiogenic sprouting occurred where NRP1 levels fluctuated between adjacent endothelial cells. Therefore, through communication in trans, NRP1 can modulate VEGFR2 signaling and suppress angiogenesis.