Sialic acid associated with αvß3 integrin mediates HIV-1 Tat protein interaction and endothelial cell proangiogenic activation.

Sialic acid (NeuAc) is a major anion on endothelial cells (ECs) that regulates different biological processes including angiogenesis. NeuAc is present in the oligosaccharidic portion of integrins, receptors that interact with extracellular matrix components and growth factors regulating cell adhesion, migration, and proliferation. Tat is a cationic polypeptide that, once released by HIV-1(+) cells, accumulates in the extracellular matrix, promoting EC adhesion and proangiogenic activation by engaging α(v)ß(3). By using two complementary approaches (NeuAc removal by neuraminidase or its masking by NeuAc-binding lectin from Maackia amurensis, MAA), we investigated the presence of NeuAc on endothelial α(v)ß(3) and its role in Tat interaction, EC adhesion, and proangiogenic activation. α(v)ß(3) immunoprecipitation with biotinylated MAA or Western blot analysis of neuraminidase-treated ECs demonstrated that NeuAc is associated with both the α(v) and the ß(3) subunits. Surface plasmon resonance analysis demonstrated that the masking of α(v)ß(3)-associated NeuAc by MAA prevents Tat/α(v)ß(3) interaction. MAA and neuraminidase prevent α(v)ß(3)-dependent EC adhesion to Tat, the consequent FAK and ERK1/2 phosphorylation, and EC proliferation, migration, and regeneration in a wound-healing assay. Finally, MAA inhibits Tat-induced neovascularization in the ex vivo human artery ring sprouting assay. The inhibitions are specific because the NeuAc-unrelated lectin from Ulex europaeus is ineffective on Tat. Also, MAA and neuraminidase affect only weakly integrin-dependent EC adhesion and proangiogenic activation by fibronectin. In conclusion, NeuAc is associated with endothelial α(v)ß(3) and mediates Tat-dependent EC adhesion and proangiogenic activation. These data point to the possibility to target integrin glycosylation for the treatment of angiogenesis/AIDS-associated pathologies.

Substrate-immobilized HIV-1 Tat drives VEGFR2/α(v)ß(3)-integrin complex formation and polarization in endothelial cells.

OBJECTIVE: The HIV-1 transactivating factor (Tat) possesses features typical of both cell-adhesive and angiogenic growth factor (AGF) proteins, inducing endothelial cell (EC) adhesion and proangiogenic activation. Tat was exploited to investigate the events triggered by EC adhesion to substrate-bound AGF that lead to proangiogenic activation. METHODS AND RESULTS: Immobilized Tat induces actin cytoskeleton organization, formation of α(v)ß(3) integrin(+)focal adhesion plaques, and recruitment of vascular endothelial growth factor receptor-2 (VEGFR2) in the ventral plasma membrane of adherent ECs. Also, acceptor photobleaching fluorescence resonance energy transfer demonstrated that VEGFR2/α(v)ß(3) coupling occurs at the basal aspect of Tat-adherent ECs. Cell membrane fractionation showed that a limited fraction of α(v)ß(3) integrin and VEGFR2 does colocalize in lipid rafts at the basal aspect of Tat-adherent ECs. VEGFR2 undergoes phosphorylation and triggers pp60src/ERK(1/2) activation. The use of lipid raft disrupting agents and second messenger inhibitors demonstrated that intact lipid rafts and the VEGFR2/pp60src/ERK(1/2) pathway are both required for cytoskeleton organization and proangiogenic activation of Tat-adherent ECs. CONCLUSIONS: Substrate-immobilized Tat causes VEGFR2/α(v)ß(3) complex formation and polarization at the basal aspect of adherent ECs, VEGFR2/pp60src/ERK(1/2) phosphorylation, cytoskeleton organization, and proangiogenic activation. These results provide novel insights in the AGF/tyrosine kinase receptor/integrin cross-talk.

alphavbeta3 Integrin-dependent antiangiogenic activity of resveratrol stereoisomers.

Angiogenesis is target for antineoplastic and chemopreventive therapies. The natural phytoalexin resveratrol is found in grapes and red wine as cis and trans stereoisomers. trans-Resveratrol shows antiangiogenic activity, but its mechanism of action is not fully elucidated. Recently, trans-resveratrol has been shown to interact with the beta3 integrin subunit, raising the possibility that inhibition of endothelial alphavbeta3 integrin function may concur to its angiosuppressive activity. To get novel insights about the antiangiogenic activity of resveratrol, we compared cis- and trans-resveratrol stereoisomers for their effect on the angiogenesis process and endothelial alphavbeta3 integrin function. trans-Resveratrol inhibits endothelial cell proliferation and the repair of mechanically wounded endothelial cell monolayers. Also, it prevents endothelial cell sprouting in fibrin gel, collagen gel invasion, and morphogenesis on Matrigel. In vivo, trans-resveratrol inhibits vascularization of the chick embryo area vasculosa and murine melanoma B16 tumor growth and neovascularization. In all the assays, cis-resveratrol exerts a limited, if any, effect. In keeping with these observations, trans-resveratrol, but not cis-resveratrol, inhibits alphavbeta3 integrin-dependent endothelial cell adhesion and the recruitment of enhanced green fluorescent protein-tagged beta3 integrin in focal adhesion contacts. In conclusion, stereoisomery affects the antiangiogenic activity of resveratrol, the trans isomer being significantly more potent than the cis isoform. The different antiangiogenic potential of resveratrol stereoisomers is related, at least in part, to their different capacity to affect alphavbeta3 integrin function. This may have profound implications for the design of synthetic antiangiogenic/angiopreventive phytoalexin derivatives.

The combination of Ezetimibe and Statin: a new treatment for hypercholesterolemia.

The combination of Simvastatin and Ezetimibe allows dual inhibition of both cholesterol production and absorption. This treatment approach allows achieving same low serum cholesterol levels with the administration of much lower doses of statins. This should reduce side effects, compared to statin only therapy, enabling more patients to achieve their LDL cholesterol treatment goals. With ezetimibe/simvastatin therapy, reductions of about 60% from baseline in LDL cholesterol have been shown. Concomitant improvement in other lipid fractions have also been demonstrated. The ezetimibe/simvastatin combination has been well tolerated, with a safety profile similar to that of statin therapy. This article will review clinical experience with ezetimibe/simvastatin combination, commenting upon its place and potential value in the prevention of cardiovascular disease.

Integrin alphavbeta3 as a target for blocking HIV-1 Tat-induced endothelial cell activation in vitro and angiogenesis in vivo.

OBJECTIVE: The transactivating factor (Tat) of HIV-1 binds to alphavbeta3 integrin present on endothelial cells contributing to neovascularization. Here, we investigated the biological consequences of Tat/alphavbeta3 interaction and the antagonist effect of an Arg-Gly-Asp (RGD)-based peptidomimetic. METHODS AND RESULTS: Binding of Tat to endothelial alphavbeta3 triggers focal adhesion kinase and nuclear factor-kappaB activation, leading to endothelial cell proliferation, membrane ruffling, and motility in vitro and neovascularization in vivo. The RGD-peptidomimetic SCH221153 inhibits Tat/alphavbeta3 interaction in a solid phase binding assay and endothelial cell adhesion to immobilized Tat with a potency higher than that of RGD-containing peptides. Accordingly, SCH221153 inhibits Tat/alphavbeta3-dependent focal adhesion kinase and nuclear factor-kappaB activation, proliferation, membrane ruffling, and motility in endothelial cells. Finally, SCH221153 inhibits the angiogenic response triggered by Tat in the chick-embryo chorioallantoic membrane without affecting physiological vascularization. SCH221153 exerts these inhibitory effects without affecting the interaction of Tat with endothelial heparan sulfate proteoglycans or with the vascular endothelial growth factor receptor-2/kinase domain-containing receptor. In all the assays the negative control SCH216687 was ineffective. CONCLUSIONS: These data provide new insights on the mechanism of endothelial cell activation by Tat and point to RGD peptidomimetics as prototypes for the development of novel Tat antagonists.

Antiangiogenic activity of semisynthetic biotechnological heparins: low-molecular-weight-sulfated Escherichia coli K5 polysaccharide derivatives as fibroblast growth factor antagonists.

OBJECTIVE: Low-molecular-weight heparin (LMWH) exerts antitumor activity in clinical trials. The K5 polysaccharide from Escherichia coli has the same structure as the heparin precursor. Chemical and enzymatic modifications of K5 polysaccharide lead to the production of biotechnological heparin-like compounds. We investigated the fibroblast growth factor-2 (FGF2) antagonist and antiangiogenic activity of a series of LMW N,O-sulfated K5 derivatives. METHODS AND RESULTS: Surface plasmon resonance analysis showed that LMW-K5 derivatives bind FGF2, thus inhibiting its interaction with heparin immobilized to a BIAcore sensor chip. Interaction of FGF2 with tyrosine-kinase receptors (FGFRs), heparan sulfate proteoglycans (HSPGs), and alpha(v)beta3 integrin is required for biological response in endothelial cells. Similar to LMWH, LMW-K5 derivatives abrogate the formation of HSPG/FGF2/FGFR ternary complexes by preventing FGF2-mediated attachment of FGFR1-overexpressing cells to HSPG-bearing cells and inhibit FGF2-mediated endothelial cell proliferation. However, LMW-K5 derivatives, but not LMWH, also inhibit FGF2/alpha(v)beta3 integrin interaction and consequent FGF2-mediated endothelial cell sprouting in vitro and angiogenesis in vivo in the chick embryo chorioallantoic membrane. CONCLUSIONS: LMW N,O-sulfated K5 derivatives affect both HSPG/FGF2/FGFR and FGF2/alpha(v)beta3 interactions and are endowed with FGF2 antagonist and antiangiogenic activity. These compounds may provide the basis for the design of novel LMW heparin-like angiostatic compounds.

CXCL1/macrophage inflammatory protein-2-induced angiogenesis in vivo is mediated by neutrophil-derived vascular endothelial growth factor-A.

The angiogenic activity of CXC-ELR(+) chemokines, including CXCL8/IL-8, CXCL1/macrophage inflammatory protein-2 (MIP-2), and CXCL1/growth-related oncogene-alpha in the Matrigel sponge angiogenesis assay in vivo, is strictly neutrophil dependent, as neutrophil depletion of the animals completely abrogates the angiogenic response. In this study, we demonstrate that mice deficient in the src family kinases, Hck and Fgr (hck(-/-)fgr(-/-)), are unable to develop an angiogenic response to CXCL1/MIP-2, although they respond normally to vascular endothelial growth factor-A (VEGF-A). Histological examination of the CXCL1/MIP-2-containing Matrigel implants isolated from wild-type or hck(-/-)fgr(-/-) mice showed the presence of an extensive neutrophil infiltrate, excluding a defective neutrophil recruitment into the Matrigel sponges. Accordingly, neutrophils from hck(-/-)fgr(-/-) mice normally migrated and released gelatinase B in response to CXCL1/MIP-2 in vitro, similarly to wild-type neutrophils. However, unlike wild-type neutrophils, those from hck(-/-)fgr(-/-) mice were completely unable to release VEGF-A upon stimulation with CXCL1/MIP-2. Furthermore, neutralizing anti-VEGF-A Abs abrogated the angiogenic response to CXCL1/MIP-2 in wild-type mice and CXCL1/MIP-2 induced angiogenesis in the chick embryo chorioallantoic membrane assay, indicating that neutrophil-derived VEGF-A is a major mediator of CXCL1/MIP-2-induced angiogenesis. Finally, in vitro kinase assays confirmed that CXCL1/MIP-2 activates Hck and Fgr in murine neutrophils. Taken together, these data demonstrate that CXCL1/MIP-2 leads to recruitment of neutrophils that, in turn, release biologically active VEGF-A, resulting in angiogenesis in vivo. Our observations delineate a novel mechanism by which CXCL1/MIP-2 induces neutrophil-dependent angiogenesis in vivo.

Generation of biologically active angiostatin kringle 1-3 by activated human neutrophils.

The contribution of polymorphonuclear neutrophils (PMN) to host defense and natural immunity extends well beyond their traditional role as professional phagocytes. In this study, we demonstrate that upon stimulation with proinflammatory stimuli, human PMN release enzymatic activities that, in vitro, generate bioactive angiostatin fragments from purified plasminogen. We also provide evidence that these angiostatin-like fragments, comprising kringle domain 1 to kringle domain 3 (kringle 1-3) of plasminogen, are generated as a byproduct of the selective proteolytic activity of neutrophil-secreted elastase. Remarkably, affinity-purified angiostatin kringle 1-3 fragments generated by neutrophils inhibited basic fibroblast growth factor plus vascular endothelial growth factor-induced endothelial cell proliferation in vitro, and both vascular endothelial growth factor-induced angiogenesis in the matrigel plug assay and fibroblast growth factor-induced angiogenesis in the chick embryo chorioallantoic membrane assay, in vivo. These results represent the first demonstration that biologically active angiostatin-like fragments can be generated by inflammatory human neutrophils. Because angiostatin is a potent inhibitor of angiogenesis, tumor growth, and metastasis, the data suggest that activated PMN not only act as potent effectors of inflammation, but might also play a critical role in the inhibition of angiogenesis in inflammatory diseases and tumors, by generation of a potent anti-angiogenic molecule.

Biological activity of substrate-bound basic fibroblast growth factor (FGF2): recruitment of FGF receptor-1 in endothelial cell adhesion contacts.

Substrate-bound FGF2 promotes endothelial cell adhesion by interacting with alpha(v)beta(3) integrin. Here, endothelial GM7373 cells spread and organize focal adhesion plaques on immobilized FGF2, fibronectin (FN), and vitronectin (VN). alpha(v)beta(3) integrin, paxillin, focal adhesion kinase, vinculin and pp60(src) localize in cell-substratum contact sites on FGF2, FN or VN. However, only immobilized FGF2 induces a long-lasting activation of extracellular signal-regulated kinases(1/2) (ERK(1/2)) and cell proliferation that was inhibited by the ERK(1/2) inhibitor PD 098059 and the tyrosine kinase (TK) inhibitor tyrphostin 23, pointing to the engagement of FGF receptor (FGFR) at the basal side of the cell. To assess this hypothesis, GM7373 cells were transfected with a dominant negative TK(-)-DeltaFGFR1 mutant (GM7373-DeltaFGFR1 cells) or with the full-length receptor (GM7373-FGFR1 cells). Both transfectants adhere and spread on FGF2 but GM7373-DeltaFGFR1 cells do not proliferate. Also, parental and GM7373-FGFR1 cells, but not GM7373-DeltaFGFR1 cells, undergo morphological changes and increased motility on FGF2-coated plastic. Finally, FGFR1, but not TK(-)-DeltaFGFR1, localizes in cell adhesion contacts on immobilized FGF2. In conclusion, substrate-bound FGF2 induces endothelial cell proliferation, motility, and the recruitment of FGFR1 in cell-substratum contacts. This may contribute to the cross talk among intracellular signaling pathways activated by FGFR1 and alpha(v)beta(3) integrin in endothelial cells.

Cell membrane GM1 ganglioside is a functional coreceptor for fibroblast growth factor 2.

Free gangliosides bind fibroblast growth factor 2 (FGF2), thus preventing cell interaction and biological activity of the growth factor in endothelial cells. Here we investigated the role of cell-associated gangliosides in mediating the biological activity of FGF2. Treatment of endothelial cells of different origin with the ganglioside biosynthesis inhibitors fumonisin B1, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol or D-1-threo-1-phenyl-2-hexa-decanoylamino-3-pyrrolidino-1-propanol-HCl, impairs their capacity to proliferate when exposed to FGF2. Also, the mitogenic activity of FGF2 is inhibited by the GM1-binding cholera toxin B subunit (CTB). Conversely, overloading of endothelial GM 7373 cell membranes with exogenous GM1 causes a 10-fold increase of the mitogenic potency of FGF2. 125I-FGF2 binds to cell membrane GM1 (K(d) = 3 nM) in complex ganglioside/heparan sulfate-deficient Chinese hamster ovary (CHO)-K1-pgsA745 cell mutants that were overloaded with exogenous GM1. Moreover, FGF2 competes with FITC-CTB for the binding to cell membrane GM1 in different CHO cell lines independently of their capacity to express heparan sulfate proteoglycans. Conversely, CTB inhibits cell proliferation triggered by FGF2 in CHO cells overexpressing the tyrosine kinase FGF receptor 1. Finally, GM1-overloading confers to FGF receptor 1-transfected, complex ganglioside-deficient CHO-K1 cell mutants the capacity to proliferate when stimulated by FGF2. This proliferation is inhibited by CTB. Cell proliferation triggered by serum or by phorbol 12-myristate 13-acetate is instead independent of the cell membrane ganglioside milieu. In conclusion, cell membrane GM1 binds FGF2 and is required for the mitogenic activity of the growth factor. Our data indicate that cell-associated gangliosides may act as functional FGF2 co-receptors in different cell types.