Microvesicle-delivery miR-150 promotes tumorigenesis by up-regulating VEGF,and the neutralization of miR-150 attenuate tumor development

Tumor-associated macrophages (TAMs) mostly exhibit M2-like (alternatively activated) properties and play positive roles in angiogenesis and tumorigenesis. Vascular endothelial growth factor (VEGF) is a key angiogenic factor. During tumor development, TAMs secrete VEGF and other factors to promote angiogenesis; thus, anti-treatment against TAMs and VEGF can repress cancer development, which has been demonstrated in clinical trials and on an experimental level. In the present work, we show that miR-150 is an oncomir because of its promotional effect on VEGF. MiR-150 targets TAMs to up-regulate their secretion of VEGF in vitro. With the utilization of cell-derived vesicles, named microvesicles (MVs), we transferred antisense RNA targeted to miR-150 into mice and found that the neutralization of miR-150 down-regulates miR-150 and VEGF levels in vivo and attenuates angiogenesis. Therefore, we proposed the therapeutic potential of neutralizing miR-150 to treat cancer and demonstrated a novel, natural, microvesicle-based method for the transfer of nucleic acids.     

Abnormally enhanced blood concentrations of vascular endothelial growth factor (VEGF) in metastatic cancer patients and their relation to circulating dendritic cells, IL-12 and endothelin-1

Elevated VEGF blood concentrations have been proven to be associated with poor prognosis in human neoplasms. This finding is generally explained as a consequence of the potential angiogenic properties of VEGF itself. However, preliminary experimental studies suggest that VEGF, in addition to its angiogenic activity, may also play an immunosuppressant role by inhibiting dendritic cell (DC) maturation. The present study was performed to analyze blood levels of VEGF in cancer patients in relation to those of another potentially angiogenic tumor growth factor, endothelin-1 (ET-1), and to the absolute number of circulating immature and mature DC, and serum levels of the best known antitumor cytokine, IL-12. The study was performed in 100 healthy controls and in 80 solid tumor patients (colorectal cancer: 24; gastric cancer: 17; cancer of pancreas: 4; lung cancer: 13; breast cancer: 11; renal cell cancer: 6; gynecologic tumors: 5), 48 of whom showed distant organ metastases. In each patient, we have evaluated serum concentrations of VEGF-165, total VEGF, ET-1, IL-12 and the circulating number of immature (CD123+) and mature (CD11c+) DC. Mean serum levels of VEGF-165 were significantly higher in metastatic patients than in controls or in non-metastatic patients, whereas the total amounts of VEGF were not significantly higher. Moreover, it has been observed that patients with abnormally elevated blood concentrations of VEGF-165 showed significantly lower mean values of immature DC, mature DC and IL-12 and significantly higher mean levels of ET-1 than those with normal concentrations. This study, by confirming that advanced neoplastic disease may be associated with increased endogenous secretion of VEGF, seems to suggest that the association between high blood levels of VEGF and poor prognosis in cancer does not depend only on VEGF-induced stimulation of the neovascularization, but also on VEGF-related immunosuppression.     

Eicosanoid regulation of vascular endothelial growth factor expression and angiogenesis in microvessel endothelial cells

12(R)-Hydroxy-5,8,14-eicosatrienoic acid (HETrE) is a potent inflammatory and angiogenic eicosanoid in ocular and dermal tissues. Previous studies suggested that 12(R)-HETrE activates microvessel endothelial cells via a high affinity binding site; however, the cellular mechanisms underlying 12(R)-HETrE angiogenic activity are unexplored. Because the synthesis of 12(R)-HETrE is induced in response to hypoxic injury, we examined its interactions with vascular endothelial growth factor (VEGF) in rabbit limbal microvessel endothelial cells. Addition of 12(R)-HETrE (0.1 nm) to the cells increased VEGF mRNA levels with maximum 5-fold increase at 45 min. The increase in VEGF mRNA was followed by an increase in immunoreactive VEGF protein. 12(R)-HETrE (0.1 nm) rapidly activated the extracellular signal-regulated kinases (ERKs) ERK1 and ERK2. Moreover, preincubation of cells with PD98059, a selective inhibitor of MEK-1, inhibited 12(R)-HETrE-induced VEGF mRNA. Addition of VEGF antibody to cells grown in Matrigel-coated culture plates inhibited 12(R)-HETrE-induced capillary tube-like formation, suggesting that VEGF mediates, at least in part, the angiogenic response to 12(R)-HETrE. The results indicate that in microvessel endothelial cells, 12(R)-HETrE induces VEGF expression via activation of ERK1/2 and that VEGF mediates, at least in part, the angiogenic activity of 12(R)-HETrE. Given the fact that both VEGF and 12(R)-HETrE are produced in the cornea after hypoxic injury, their interaction may be an important determinant in the development of neovascularized tissues.     

Semaphorin-PlexinD1 signaling limits angiogenic potential via the VEGF decoy receptor sFlt1

Sprouting angiogenesis expands the embryonic vasculature enabling survival and homeostasis. Yet how the angiogenic capacity to form sprouts is allocated among endothelial cells (ECs) to guarantee the reproducible anatomy of stereotypical vascular beds remains unclear. Here we show that Sema-PlxnD1 signaling, previously implicated in sprout guidance, represses angiogenic potential to ensure the proper abundance and stereotypical distribution of the trunk's segmental arteries (SeAs). We find that Sema-PlxnD1 signaling exerts this effect by antagonizing the proangiogenic activity of vascular endothelial growth factor (VEGF). Specifically, Sema-PlxnD1 signaling ensures the proper endothelial abundance of soluble flt1 (sflt1), an alternatively spliced form of the VEGF receptor Flt1 encoding a potent secreted decoy. Hence, Sema-PlxnD1 signaling regulates distinct but related aspects of angiogenesis: the spatial allocation of angiogenic capacity within a primary vessel and sprout guidance.     

Matrix metalloproteinases cleave connective tissue growth factor and reactivate angiogenic activity of vascular endothelial growth factor 165

Vascular endothelial growth factor (VEGF), a potent angiogenic mitogen, plays a crucial role in angiogenesis under various pathophysiological conditions. We have recently demonstrated that VEGF(165), one of the VEGF isoforms, binds connective tissue growth factor (CTGF) and that its angiogenic activity is inhibited in the VEGF(165).CTGF complex form (Inoki, I., Shiomi, T., Hashimoto, G., Enomoto, H., Nakamura, H., Makino, K., Ikeda, E., Takata, S., Kobayashi, K. and Okada, Y. (2002) FASEB J. 16, 219-221). In the present study, we further examined the susceptibility of the VEGF(165).CTGF complex to matrix metalloproteinases (MMP-1, -2, -3, -7, -9, and -13), ADAMTS4 (aggrecanase-1), and serine proteinases, and evaluated the recovery of the angiogenic activity of VEGF(165) after the treatment. Among the MMPs, MMP-1, -3, -7, and -13 processed CTGF of the complex into the major NH(2)- and COOH-terminal fragments, whereas VEGF(165) was completely resistant to the MMPs. On the other hand, elastase and plasmin cleaved both CTGF and VEGF(165) of the complex, but they were completely resistant to ADAMTS4. By digestion of the immobilized VEGF(165).CTGF complex with MMP-3 or MMP-7, both NH(2)- and COOH-terminal fragments of CTGF were dissociated and released from the complex into the liquid phase. The in vitro angiogenic activity of VEGF(165) blocked in the VEGF(165).CTGF complex was reactivated to original levels after CTGF digestion of the complex with MMP-1, -3, and -13. Recovery of angiogenic activity was further confirmed by in vivo angiogenesis assay using a Matrigel injection model in mice. These results demonstrate for the first time that CTGF is a substrate of MMPs and that the angiogenic activity of VEGF(165) suppressed by the complex formation with CTGF is recovered through the selective degradation of CTGF by MMPs. MMPs may play a novel role through CTGF degradation in VEGF-induced angiogenesis during embryonic development, tissue maintenance, and/or pathological processes of various diseases.     

Vascular endothelial growth factor induces heat shock protein (HSP) 27 serine 82 phosphorylation and endothelial tubulogenesis via protein kinase D and independent of p38 kinase

Proteomic analysis identified HSP27 phosphorylation as a major change in protein phosphorylation stimulated by Vascular Endothelial Growth Factor (VEGF) in Human Umbilical Vein Endothelial Cells (HUVEC). VEGF-induced HSP27 phosphorylation at serines 15, 78 and 82, but whereas HSP27 phosphorylation induced by H2O2 and TNFalpha was completely blocked by the p38 kinase inhibitor, SB203580, VEGF-stimulated serine 82 phosphorylation was resistant to SB203580 and small interfering(si)RNA-mediated knockdown of p38 kinase and MAPKAPK2. The PKC inhibitor, GF109203X, partially reduced VEGF-induced HSP27 serine 82 phosphorylation, and SB203580 plus GF109203X abolished phosphorylation. VEGF activated Protein Kinase D (PKD) via PKC, and siRNAs targeted to PKD1 and PKD2 inhibited VEGF-induced HSP27 serine 82 phosphorylation. Furthermore recombinant PKD selectively phosphorylated HSP27 at serine 82 in vitro, and PKD2 activated by VEGF in HUVECs also phosphorylated HSP27 selectively at this site. Knockdown of HSP27 and PKDs markedly inhibited VEGF-induced HUVEC migration and tubulogenesis, whereas inhibition of the p38 kinase pathway using either SB203580 or siRNAs against p38alpha or MAPKAPK2, had no significant effect on the chemotactic response to VEGF. These findings identify a novel pathway for VEGF-induced HSP27 serine 82 phosphorylation via PKC-mediated PKD activation and direct phosphorylation of HSP27 by PKD, and show that PKDs and HSP27 play major roles in the angiogenic response to VEGF.     

Angiogenic activity of bFGF and VEGF suppressed by proteolytic cleavage by neutrophil elastase

Neutrophil elastase (NE), a serine protease released from the azurophil granules of activated neutrophil, proteolytically cleaves multiple cytokines, and cell surface proteins. In the present study, we examined whether NE affects the biological abilities of angiogenic growth factors such as basic-fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). NE degraded bFGF and VEGF in a time- and concentration-dependent manner, and these degradations were suppressed by sivelestat, a synthetic inhibitor of NE. The bFGF- or VEGF-mediated proliferative activity of human umbilical vein endothelial cells was inhibited by NE, and the activity was recovered by sivelestat. Furthermore, NE reduced the bFGF- or VEGF-induced tubulogenic response of the mice aortas, ex vivo angiogenesis assay, and these effects were also recovered by sivelestat. Neutrophil-derived NE degraded potent angiogenic factors, resulting in loss of their angiogenic activity. These findings provide additional insight into the role played by neutrophils in the angiogenesis process at sites of inflammation.     

Exercise training improves aging-induced downregulation of VEGF angiogenic signaling cascade in hearts

Exercise training improves aging-induced deterioration of angiogenesis in the heart. However, the mechanisms underlying exercise-induced improvement of capillary density in the aged heart are unclear. Vascular endothelial growth factor (VEGF) is implicated in angiogenesis, which activated angiogenic signaling cascade through Akt and endothelial nitric oxide synthase (eNOS)-related pathway. We hypothesized that VEGF angiogenic signaling cascade in the heart contributes to a molecular mechanism of exercise training-induced improvement of capillary density in old age. With the use of hearts of sedentary young rats (4 mo old), sedentary aged rats (23 mo old), and exercise-trained aged rats (23 mo old, swim training for 8 wk), the present study investigated whether VEGF and VEGF-related angiogenic molecular expression in the aged heart is affected by exercise training. Total capillary density in the heart was significantly lower in the sedentary aged rats compared with the sedentary young rats, whereas that in the exercise-trained rat was significantly higher than the sedentary aged rats. The mRNA and protein expressions of VEGF and of fms-like tyrosine kinase-1 (Flt-1) and fetal liver kinase-1 (Flk-1), which are main VEGF receptors, in the heart were significantly lower in the sedentary aged rats compared with the sedentary young rats, whereas those in the exercise-trained rats were significantly higher than those in the sedentary aged rats. The phosphorylation of Akt protein and eNOS protein in the heart corresponded to the changes in the VEGF protein levels. These findings suggest that exercise training improves aging-induced downregulation of cardiac VEGF angiogenic signaling cascade, thereby contributing to the exercise training-induced improvement of angiogenesis in old age.     

Integrin affinity modulation in angiogenesis

Integrins, transmembrane glycoprotein receptors, play vital roles in pathological angiogenesis, but their precise regulatory functions are not completely understood and remain controversial. This study aims to assess the regulatory functions of individual beta subunits of endothelial integrins in angiogenic responses induced by vascular endothelial growth factor (VEGF). Inhibition of expression of β1, β3, or β5 integrins in endothelial cells resulted in down regulation of EC adhesion and migration on the primary ligand for the corresponding integrin receptor, while no effects on the recognition of other ligands were detected. Although inhibition of expression of each subunit substantially affected capillary growth stimulated by VEGF, the loss of β3 integrin was the most inhibitory. EC stimulation by VEGF induced formation of the high affinity (activated) state of αVβ3 in a monolayer and activated αVβ3 was co-localized with VEGF receptor-2 (VEGFR-2). Inhibition of expression of β1, β3, or β5 did not affect expression levels of VEGFR-2 in EC. However, inhibition of β3, but not β1 or β5, resulted in substantial inhibition of VEGFR-2 phosphorylation stimulated by VEGF. Exogenous stimulation of αVβ3 integrin with activating antibodies augmented VEGF-dependent phosphorylation of VEGFR-2, whereas integrin blockade suppressed this response. Most importantly, activated αVβ3 was detected on endothelial cells of tumor vasculature. Activation of αVβ3 was substantially increased in highly-vascularized tumors as compared to normal tissues. Moreover, activated αVβ3 was co-localized with VEGFR-2 on endothelial cells of proliferating blood vessels. Together, these results show the unique role of αVβ3 integrin in cross-talk with VEGFR-2 in the context of pathological angiogenesis.     

Enhanced platelet adhesion induces angiogenesis in intestinal inflammation and inflammatory bowel disease microvasculature

Although angiogenesis is viewed as a fundamental component of inflammatory bowel disease (IBD) pathogenesis, we presently lack a thorough knowledge of the cell type(s) involved in its induction and maintenance in the inflamed intestinal mucosa. This study aimed to determine whether platelet (PLT) adhesion to inflamed intestinal endothelial cells of human origin may favour angiogenesis. Unstimulated or thrombin‐activated human PLT were overlaid on resting or tumour necrosis factor (TNF)‐α‐treated human intestinal microvascular endothelial cells (HIMEC), in the presence or absence of blocking antibodies to either vascular cell adhesion molecule (VCAM)‐1, intercellular adhesion molecule (ICAM)‐1, integrin α_vβ₃, tissue factor (TF) or fractalkine (FKN). PLT adhesion to HIMEC was evaluated by fluorescence microscopy, and release of angiogenic factors (VEGF and soluble CD40L) was measured by ELISA. A matrigel tubule formation assay was used to estimate PLT capacity to induce angiogenesis after co‐culturing with HIMEC. TNF‐α up‐regulated ICAM‐1, α_vβ₃ and FKN expression on HIMEC. When thrombin‐activated PLT were co‐cultured with unstimulated HIMEC, PLT adhesion increased significantly, and this response was further enhanced by HIMEC activation with TNF‐α. PLT adhesion to HIMEC was VCAM‐1 and TF independent but ICAM‐1, FKN and integrin α_vβ₃ dependent. VEGF and sCD40L were undetectable in HIMEC cultures either before or after TNF‐α stimulation. By contrast, VEGF and sCD40L release significantly increased when resting or activated PLT were co‐cultured with TNF‐α‐pre‐treated HIMEC. These effects were much more pronounced when PLT were derived from IBD patients. Importantly, thrombin‐activated PLT promoted tubule formation in HIMEC, a functional estimate of their angiogenic potential. In conclusion, PLT adhesion to TNF‐α‐pre‐treated HIMEC is mediated by ICAM‐1, FKN and α_vβ₃, and is associated with VEGF and sCD40L release. These findings suggest that inflamed HIMEC may recruit PLT which, upon release of pro‐angiogenic factors, actively contribute to inflammation‐induced angiogenesis.     

Modulation of expression of LDH isoenzymes in endothelial cells by laminin: implications for angiogenesis

Endothelial cell (EC) matrix interaction is critical in angiogenesis. Although matrix components can regulate the process of angiogenesis by acting as a reservoir of various cytokines, it is not clear if extracellular matrix (ECM) can modulate the production and activity of angiogenic cytokines. Investigations were therefore carried out to study the influence of the basement membrane (BM) protein, laminin (Ln) on the activity of vascular endothelial growth factor (VEGF), the major angiogenic cytokine, using isolated human umbilical vein ECs (HUVECs) in culture. Analysis of the biochemical markers of angiogenesis confirmed proangiogenic effect of Ln. The levels of VEGF protein and mRNA were not different in cells maintained on Ln, collagen I or polylysine substrata. Chorioallantoic membrane assay using VEGF isolated from cell extracts however revealed that Ln increased its angiogenic potency. Immunoblotting and HPLC analysis showed considerable reduction in poly adenosyl ribosylation of VEGF associated with a significant decrease in the levels of NAD+, in cells maintained on Ln substrata. Further, a shift in the isoenzymic pattern of LDH towards the B rich forms and an upregulation of LDH B gene were observed in cells maintained on Ln. Ln modulates expression of LDH gene through alpha(6)beta(4) integrin mediated downstream signaling involving p38 mitogen activated protein kinases (MAPK) pathway. It thus appears that Ln can affect aerobic metabolism of ECs by modulating the expression of LDH isoenzymes resulting in a decrease in the level of NAD+ that can cause a reduction in the poly adenosyl ribosylation of VEGF altering its angiogenic potency.     

Vascular endothelial growth factor (VEGF) stimulates monocyte migration through endothelial monolayers via increased integrin expression

Monocytes play an important role in collateral vessel formation (arteriogenesis) by attaching to activated endothelium and by invading the walls of innate collateral vessels where they produce growth factors. Previous studies have demonstrated that this process can be promoted by several chemokines and growth factors. In this study we examined the interaction between monocytes and endothelium under stimulation of the angiogenic agent vascular endothelial growth factor (VEGF). We report here the novel finding that VEGF stimulates the expression of the alphaL-, alphaM- and beta2-integrin monomers. In functional assays and by using neutralizing antibodies it was shown that VEGF stimulates adhesion of monocytes to human umbilical vein endothelial cells (HUVEC), and increased transmigration through endothelial monolayers is dependent on interaction of monocyte beta2-integrins with its endothelial counter ligand ICAM-1. Based on these in vitro data we hypothesize that the positive effect of VEGF on arteriogenesis may involve monocyte activation.     

Control of Angiogenesis by Galectins Involves the Release of Platelet-Derived Proangiogenic Factors

Platelets contribute to vessel formation through the release of angiogenesis-modulating factors stored in their α-granules. Galectins, a family of lectins that bind β-galactoside residues, are up-regulated in inflammatory and cancerous tissues, trigger platelet activation and mediate vascularization processes. Here we aimed to elucidate whether the release of platelet-derived proangiogenic molecules could represent an alternative mechanism through which galectins promote neovascularization. We show that different members of the galectin family can selectively regulate the release of angiogenic molecules by human platelets. Whereas Galectin (Gal)-1, -3, and -8 triggered vascular endothelial growth factor (VEGF) release, only Gal-8 induced endostatin secretion. Release of VEGF induced by Gal-8 was partially prevented by COX-1, PKC, p38 and Src kinases inhibitors, whereas Gal-1-induced VEGF secretion was inhibited by PKC and ERK blockade, and Gal-3 triggered VEGF release selectively through a PKC-dependent pathway. Regarding endostatin, Gal-8 failed to stimulate its release in the presence of PKC, Src and ERK inhibitors, whereas aspirin or p38 inhibitor had no effect on endostatin release. Despite VEGF or endostatin secretion, platelet releasates generated by stimulation with each galectin stimulated angiogenic responses in vitro including endothelial cell proliferation and tubulogenesis. The platelet angiogenic activity was independent of VEGF and was attributed to the concerted action of other proangiogenic molecules distinctly released by each galectin. Thus, secretion of platelet-derived angiogenic molecules may represent an alternative mechanism by which galectins promote angiogenic responses and its selective blockade may lead to the development of therapeutic strategies for angiogenesis-related diseases.     

Distinct regulation of vascular endothelial growth factor in intact human conduit vessels exposed to laminar fluid shear stress and pressure

VEGF is a potent angiogenic factor. We tested the hypothesis that biomechanical forces may regulate VEGF expression. By using a computerized perfusion system, human umbilical veins were exposed to high/low shear stress or intraluminal pressure (25/4 dyn/cm(2) or 40/20 mmHg) for 1.5, 3, or 6 h. Quantification of VEGF gene expression was performed with real-time RT-PCR. VEGF protein was characterized by quantitative immunohistochemistry. All perfusion experiments were performed under identical pH, PO(2), and temperature. Shear stress induced significant biphasic regulation pattern of VEGF (P = 0.0044) with significant downregulation by 45 and 40% after 1.5 and 6 h perfusion, respectively (P = 0.006 and P = 0.0002). The temporal changes of the gene expression were accompanied by synchronal changes at the protein level. High pressure induced transient 25% downregulation of VEGF gene expression after 1.5 h perfusion (P = 0.031). These data provide the first evidence on modulating effects of biomechanical forces on the vascular angiogenic property.     

Vascular endothelial growth factor up-regulates expression of receptor activator of NF-kappa B (RANK) in endothelial cells. Concomitant increase of angiogenic responses to RANK ligand

Vascular endothelial growth factor (VEGF) is known as a key regulator of angiogenesis during endochondral bone formation. Recently, we demonstrated that TNF-related activation-induced cytokine (TRANCE or RANKL), which is essential for bone remodeling, also had an angiogenic activity. Here we report that VEGF up-regulates expression of receptor activator of NF-kappa B (RANK) and increases angiogenic responses of endothelial cells to TRANCE. Treatment of human umbilical vein endothelial cells (HUVECs) with VEGF increased both RANK mRNA and surface protein expression. Although placenta growth factor specific to VEGF receptor-1 had no significant effect on RANK expression, inhibition of downstream signaling molecules of the VEGF receptor-2 (Flk-1/KDR) such as Src, phospholipase C, protein kinase C, and phosphatidylinositol 3'-kinase suppressed VEGF-stimulated RANK expression in HUVECs. Moreover, the MEK inhibitor PD98059 or expression of dominant negative MEK1 inhibited induction of RANK by VEGF but not the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). VEGF potentiated TRANCE-induced ERK activation and tube formation via RANK up-regulation in HUVECs. Together, these results show that VEGF enhances RANK expression in endothelial cells through Flk-1/KDR-protein kinase C-ERK signaling pathway, suggesting that VEGF plays an important role in modulating the angiogenic action of TRANCE under physiological or pathological conditions.     

Induction of cysteine-rich motor neuron 1 mRNA expression in vascular endothelial cells

Cysteine-rich motor neuron 1 (CRIM1) is expressed in vascular endothelial cells and plays a crucial role in angiogenesis. In this study, we investigated the expression of CRIM1 mRNA in human umbilical vein endothelial cells (HUVECs). CRIM1 mRNA levels were not altered in vascular endothelial growth factor (VEGF)-stimulated monolayer HUVECs or in cells in collagen gels without VEGF. In contrast, the expression of CRIM1 mRNA was elevated in VEGF-stimulated cells in collagen gels. The increase in CRIM1 mRNA expression was observed even at 2 h when HUVECs did not form tubular structures in collagen gels. Extracellular signal-regulated kinase (Erk) 1/2, Akt and focal adhesion kinase (FAK) were activated by VEGF in HUVECs. The VEGF-induced expression of CRIM1 mRNA was significantly abrogated by PD98059 or PF562271, but was not affected by LY294002. These results demonstrate that CRIM1 is an early response gene in the presence of both angiogenic stimulation (VEGF) and environmental (extracellular matrix) factors, and Erk and FAK might be involved in the upregulation of CRIM1 mRNA expression in vascular endothelial cells.