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

Far beyond anti-angiogenesis: Benefits for anti-basicFGF therapy in cancer

Basic FGF (bFGF) was discovered as a typical inducer of angiogenesis and has already been studied for 3 decades. Recent evidence indicates that bFGF plays different roles and controls signaling pathways that participate in the hallmarks of cancer, underscoring bFGF an appealing target for anti-cancer therapy. However, the early clinical trials designed to block bFGF signaling showed safety without satisfiable benefits for cancer patients. In this review, we firstly discuss bFGF's canonical signaling pathways and later review newly identified bFGF's functions that contribute to the cancer hallmarks besides its typical role in angiogenesis. After, we summarize the role of bFGF as a therapeutic target in response to different cancer therapies including radiotherapy, chemotherapy, targeted therapy, immunotherapy, and highlight the difficulties we must solve regarding the design of drugs targeting specifically bFGF. We also emphasize the need, especially for natural bFGF traps, to deepen their molecular mechanisms of action considering the specific context of cancer with different FGFR status, as well as the urgence of stratifying patients for both anti-bFGF first line and second line anti-cancer therapy. Finally, a perspective on potential feed-forward oncogenic signaling pathways mediated by bFGF is made. We discuss the importance of developing additional robust biomarkers to select patients who will benefit from bFGF-targeted therapy, as well as the rationale of developing combinatory therapies targeting either bFGF and/or its intracellular (co)effectors. This would ultimately provide novel therapeutic strategies to fight cancer.

Multifaceted Interplay between Hormones, Growth Factors and Hypoxia in the Tumor Microenvironment

Simple Summary

Hormones and growth factors impact many processes in the cell. Moreover, these molecules influence tumor growth, as does a lack of oxygen (hypoxia) that characterizes cancer progression. Proteins that are stabilized by low oxygen tension, known as hypoxia-inducible factors (HIFs), help tumor cells to adapt to their environment. Of note, hormones and growth factors regulate the activity of HIFs toward malignant aggressiveness, including the resistance to therapy. In this review, we summarize the current knowledge regarding the role of hormones and growth factors in cancer development with a particular focus on their interplay with hypoxia and HIFs and comment on how these factors influence the response to cancer immunotherapy.

Abstract

Hormones and growth factors (GFs) are signaling molecules implicated in the regulation of a variety of cellular processes. They play important roles in both healthy and tumor cells, where they function by binding to specific receptors on target cells and activating downstream signaling cascades. The stages of tumor progression are influenced by hormones and GF signaling. Hypoxia, a hallmark of cancer progression, contributes to tumor plasticity and heterogeneity. Most solid tumors contain a hypoxic core due to rapid cellular proliferation that outgrows the blood supply. In these circumstances, hypoxia-inducible factors (HIFs) play a central role in the adaptation of tumor cells to their new environment, dramatically reshaping their transcriptional profile. HIF signaling is modulated by a variety of factors including hormones and GFs, which activate signaling pathways that enhance tumor growth and metastatic potential and impair responses to therapy. In this review, we summarize the role of hormones and GFs during cancer onset and progression with a particular focus on hypoxia and the interplay with HIF proteins. We also discuss how hypoxia influences the efficacy of cancer immunotherapy, considering that a hypoxic environment may act as a determinant of the immune-excluded phenotype and a major hindrance to the success of adoptive cell therapies.

The canonical FGF-FGFR signaling system at the molecular level

Extracellular signaling molecules, among them the fibroblast growth factors (FGFs), enable cells to communicate with neighboring cells. Such signaling molecules that receive and transmit a signal require specific tyrosine kinase receptors located at the cell surface (fibroblast growth factor receptors, FGFRs). The binding of a signaling molecule to its specific receptor results in receptor dimerization and conformational changes in the cytoplasmic part of the receptor. The conformational changes lead to trans-autophosphorylation of the tyrosine kinase domains of the receptors and subsequently to induction of several downstream signaling pathways and expression of appropriate genes. The signaling pathways activated by FGFs control and coordinate cell behaviors such as cell division, migration, differentiation, and cell death. FGFs and their transmembrane receptors are widely distributed in different tissues and participate in fundamental processes during embryonic, fetal, and adult human life. The human FGF/FGFR family comprises 22 ligands and 4 high affinity receptors. In addition, FGFs bind to low affinity receptors, heparan sulfate proteoglycans at the cell surface. The availability of appropriate ligand/receptor pair, combined with the co-receptor, initiates signaling. Inappropriate FGF/FGFR signaling can cause skeletal disorders, primarily dwarfism, craniofacial malformation syndromes, mood disorders, metabolic disorders, and Kallman syndrome. In addition, aberrations in FGF/FGFR signaling have already been reported in several types of malignant diseases. Knowledge about the molecular mechanisms of FGF/FGFR activation and signaling is necessary to understand the basis of these diseases.

HIV-1 Tat and Heparan Sulfate Proteoglycans Orchestrate the Setup of in Cis and in Trans Cell-Surface Interactions Functional to Lymphocyte Trans-Endothelial Migration

HIV-1 transactivating factor Tat is released by infected cells. Extracellular Tat homodimerizes and engages several receptors, including integrins, vascular endothelial growth factor receptor 2 (VEGFR2) and heparan sulfate proteoglycan (HSPG) syndecan-1 expressed on various cells. By means of experimental cell models recapitulating the processes of lymphocyte trans-endothelial migration, here, we demonstrate that upon association with syndecan-1 expressed on lymphocytes, Tat triggers simultaneously the in cis activation of lymphocytes themselves and the in trans activation of endothelial cells (ECs). This "two-way" activation eventually induces lymphocyte adhesion and spreading onto the substrate and vascular endothelial (VE)-cadherin reorganization at the EC junctions, with consequent endothelial permeabilization, leading to an increased extravasation of Tat-presenting lymphocytes. By means of a panel of biochemical activation assays and specific synthetic inhibitors, we demonstrate that during the above-mentioned processes, syndecan-1, integrins, FAK, src and ERK_1/2 engagement and activation are needed in the lymphocytes, while VEGFR2, integrin, src and ERK_1/2 are needed in the endothelium. In conclusion, the Tat/syndecan-1 complex plays a central role in orchestrating the setup of the various in cis and in trans multimeric complexes at the EC/lymphocyte interface. Thus, by means of computational molecular modelling, docking and dynamics, we also provide a characterization at an atomic level of the binding modes of the Tat/heparin interaction, with heparin herein used as a structural analogue of the heparan sulfate chains of syndecan-1.

Tumor Microenvironment in Prostate Cancer: Toward Identification of Novel Molecular Biomarkers for Diagnosis, Prognosis, and Therapy Development

Prostate cancer (PCa) is by far the most commonly diagnosed cancer in men worldwide. Despite sensitivity to androgen deprivation, patients with advanced disease eventually develop resistance to therapy and may die of metastatic castration-resistant prostate cancer (mCRPC). A key challenge in the management of PCa is the clinical heterogeneity that is hard to predict using existing biomarkers. Defining molecular biomarkers for PCa that can reliably aid in diagnosis and distinguishing patients who require aggressive therapy from those who should avoid overtreatment is a significant unmet need. Mechanisms underlying the development of PCa are not confined to cancer epithelial cells, but also involve the tumor microenvironment. The crosstalk between epithelial cells and stroma in PCa has been shown to play an integral role in disease progression and metastasis. A number of key markers of reactive stroma has been identified including stem/progenitor cell markers, stromal-derived mediators of inflammation, regulators of angiogenesis, connective tissue growth factors, wingless homologs (Wnts), and integrins. Here, we provide a synopsis of the stromal-epithelial crosstalk in PCa focusing on the relevant molecular biomarkers pertaining to the tumor microenvironment and their role in diagnosis, prognosis, and therapy development.

Growth Factors VEGF-A165 and FGF-2 as Multifunctional Biomolecules Governing Cell Adhesion and Proliferation

Vascular endothelial growth factor-A165 (VEGF-A165) and fibroblast growth factor-2 (FGF-2) are currently used for the functionalization of biomaterials designed for tissue engineering. We have developed a new simple method for heterologous expression and purification of VEGF-A165 and FGF-2 in the yeast expression system of Pichia pastoris. The biological activity of the growth factors was assessed in cultures of human and porcine adipose tissue-derived stem cells (ADSCs) and human umbilical vein endothelial cells (HUVECs). When added into the culture medium, VEGF-A165 stimulated proliferation only in HUVECs, while FGF-2 stimulated the proliferation of both cell types. A similar effect was achieved when the growth factors were pre-adsorbed to polystyrene wells. The effect of our recombinant growth factors was slightly lower than that of commercially available factors, which was attributed to the presence of some impurities. The stimulatory effect of the VEGF-A165 on cell adhesion was rather weak, especially in ADSCs. FGF-2 was a potent stimulator of the adhesion of ADSCs but had no to negative effect on the adhesion of HUVECs. In sum, FGF-2 and VEGF-A165 have diverse effects on the behavior of different cell types, which maybe utilized in tissue engineering.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

Establishment of a three-dimensional model to study human uterine angiogenesis

STUDY QUESTION

Can primary human uterine microvascular endothelial cells (UtMVECs) be used as a model to study uterine angiogenic responses in vitro that are relevant in pregnancy?

SUMMARY ANSWER

UtMVECs demonstrated angiogenic responses when stimulated with proangiogenic factors, including sphingosine 1-phosphate (S1P), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), physiological levels of wall shear stress (WSS), human chorionic gonadotropin (hCG) and various combinations of estrogen and progesterone.

WHAT IS KNOWN ALREADY

During sprouting angiogenesis, signaling from growth factors and cytokines induces a monolayer of quiescent endothelial cells (ECs) lining the vasculature to degrade the extracellular matrix and invade the surrounding tissue to form new capillaries. During pregnancy and the female reproductive cycle, the uterine endothelium becomes activated and undergoes sprouting angiogenesis to increase the size and number of blood vessels in the endometrium.

STUDY DESIGN, SIZE, DURATION

The study was designed to examine the angiogenic potential of primary human UtMVECs using the well-characterized human umbilical vein EC (HUVEC) line as a control to compare angiogenic potential. ECs were seeded onto three-dimensional (3D) collagen matrices, supplemented with known proangiogenic stimuli relevant to pregnancy and allowed to invade for 24 h. Sprouting responses were analyzed using manual and automated methods for quantification.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RT-PCR, Western blot analysis and immunostaining were used to characterize UtMVECs. Angiogenic responses were examined using 3D invasion assays. Western blotting was used to confirm signaling responses after proangiogenic lipid, pharmacological inhibitor, and recombinant lentiviral treatments. All experiments were repeated at least three times.

MAIN RESULTS AND THE ROLE OF CHANCE

After ensuring that UtMVECs expressed the proper endothelial markers, we found that UtMVECs invade 3D collagen matrices dose-dependently in response to known proangiogenic stimuli (e.g. S1P, VEGF, bFGF, hCG, estrogen, progesterone and WSS) present during early pregnancy. Invasion responses were positively correlated with phosphorylation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and p42/p44 mitogen-activated protein kinase (ERK). Inhibition of these second messengers significantly impaired sprouting (P < 0.01). Gene silencing of membrane type 1-matrix metalloproteinase using multiple approaches completely abrogated sprouting (P < 0.001). Finally, UtMVECs displayed a unique ability to undergo sprouting in response to hCG, and combined estrogen and progesterone treatment.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The study of uterine angiogenesis in vitro has limitations and any findings many not fully represent the in vivo state. However, these experiments do provide evidence for the ability of UtMVECs to be used in functional sprouting assays in a 3D environment, stimulated by physiological factors that are produced locally within the uterus during early pregnancy.

WIDER IMPLICATIONS OF THE FINDINGS

We show that UtMVECs can be used reliably to investigate how growth factors, hormones, lipids and other factors, such as flow, affect angiogenesis in the uterus.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by NIH award HL095786 to K.J.B. The authors have no conflicts of interest.

N-tert-butyloxycarbonyl-Phe-Leu-Phe-Leu-Phe (BOC2) inhibits the angiogenic activity of heparin-binding growth factors

The peptides N-tert-butyloxycarbonyl-Phe-Leu-Phe-Leu-Phe (BOC2) and BOC-Met-Leu-Phe (BOC1) are widely used antagonists of formyl peptide receptors (FPRs), BOC2 acting as an FPR1/FPR2 antagonist whereas BOC1 inhibits FPR1 only. Extensive investigations have been performed by using these FPR antagonists as a tool to assess the role of FPRs in physiological and pathological conditions. Based on previous observations from our laboratory, we assessed the possibility that BOC2 may exert also a direct inhibitory effect on the angiogenic activity of vascular endothelial growth factor-A (VEGF-A). Our data demonstrate that BOC2, but not BOC1, inhibits the angiogenic activity of heparin-binding VEGF-A₁₆₅ with no effect on the activity of the non-heparin-binding VEGF-A₁₂₁ isoform. Endothelial cell-based bioassays, surface plasmon resonance analysis, and computer modeling indicate that BOC2 may interact with the heparin-binding domain of VEGF-A₁₆₅, thus competing for heparin interaction and preventing the binding of VEGF-A₁₆₅ to tyrosine kinase receptor VEGFR2, its phosphorylation and downstream signaling. In addition, BOC2 inhibits the interaction of a variety of heparin-binding angiogenic growth factors with heparin, including fibroblast growth factor 2 (FGF2) whose angiogenic activity is blocked by the compound. Accordingly, BOC2 suppresses the angiogenic potential of human tumor cell lines that co-express VEGF-A and FGF2. Thus, BOC2 appears to act as a novel multi-heparin-binding growth factor antagonist. These findings caution about the interpretation of FPR-focusing experimental data obtained with this compound and set the basis for the design of novel BOC2-derived, FPR independent multi-target angiogenesis inhibitors.

Molecular and clinical significance of fibroblast growth factor 2 (FGF2 /bFGF) in malignancies of solid and hematological cancers for personalized therapies

Fibroblast growth factor (FGF) signaling is essential for normal and cancer biology. Mammalian FGF family members participate in multiple signaling pathways by binding to heparan sulfate and FGF receptors (FGFR) with varying affinities. FGF2 is the prototype member of the FGF family and interacts with its receptor to mediate receptor dimerization, phosphorylation, and activation of signaling pathways, such as Ras-MAPK and PI3K pathways. Excessive mitogenic signaling through the FGF/FGFR axis may induce carcinogenic effects by promoting cancer progression and increasing the angiogenic potential, which can lead to metastatic tumor phenotypes. Dysregulated FGF/FGFR signaling is associated with aggressive cancer phenotypes, enhanced chemotherapy resistance and poor clinical outcomes. In vitro experimental settings have indicated that extracellular FGF2 affects proliferation, drug sensitivity, and apoptosis of cancer cells. Therapeutically targeting FGF2 and FGFR has been extensively assessed in multiple preclinical studies and numerous drugs and treatment options have been tested in clinical trials. Diagnostic assays are used to quantify FGF2, FGFRs, and downstream signaling molecules to better select a target patient population for higher efficacy of cancer therapies. This review focuses on the prognostic significance of FGF2 in cancer with emphasis on therapeutic intervention strategies for solid and hematological malignancies.

Membrane-Type 1 Matrix Metalloproteinase Downregulates Fibroblast Growth Factor-2 Binding to the Cell Surface and Intracellular Signaling

Membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14), a transmembrane proteinase with an extracellular catalytic domain and a short cytoplasmic tail, degrades extracellular matrix components and controls diverse cell functions through proteolytic and non-proteolytic interactions with extracellular, intracellular, and transmembrane proteins. Here we show that in tumor cells MT1-MMP downregulates fibroblast growth factor-2 (FGF-2) signaling by reducing the amount of FGF-2 bound to the cell surface with high and low affinity. FGF-2 induces weaker activation of ERK1/2 MAP kinase in MT1-MMP expressing cells than in cells devoid of MT1-MMP. This effect is abolished in cells that express proteolytically inactive MT1-MMP but persists in cells expressing MT1-MMP mutants devoid of hemopexin-like or cytoplasmic domain, showing that FGF-2 signaling is downregulated by MT1-MMP proteolytic activity. MT1-MMP expression results in downregulation of FGFR-1 and -4, and in decreased amount of cell surface-associated FGF-2. In addition, MT1-MMP strongly reduces the amount of FGF-2 bound to the cell surface with low affinity. Because FGF-2 association with low-affinity binding sites is a prerequisite for binding to its high-affinity receptors, downregulation of low-affinity binding to the cell surface results in decreased FGF-2 signaling. Consistent with this conclusion, FGF-2 induction of tumor cell migration and invasion in vitro is stronger in cells devoid of MT1- MMP than in MT1-MMP expressing cells. Thus, MT1-MMP controls FGF-2 signaling by a proteolytic mechanism that decreases the cell's biological response to FGF-2.

β3 Integrin Promotes Long-Lasting Activation and Polarization of Vascular Endothelial Growth Factor Receptor 2 by Immobilized Ligand

Supplemental Digital Content is available in the text.

Objective—

During neovessel formation, angiogenic growth factors associate with the extracellular matrix. These immobilized factors represent a persistent stimulus for the otherwise quiescent endothelial cells (ECs), driving directional EC migration and proliferation and leading to new blood vessel growth. Vascular endothelial growth factor receptor 2 (VEGFR2) is the main mediator of angiogenesis. Although VEGFR2 signaling has been deeply characterized, little is known about its subcellular localization during neovessel formation. Aim of this study was the characterization and molecular determinants of activated VEGFR2 localization in ECs during neovessel formation in response to matrix-immobilized ligand.

Approach and Results—

Here we demonstrate that ECs stimulated by extracellular matrix–associated gremlin, a noncanonical VEGFR2 ligand, are polarized and relocate the receptor in close contact with the angiogenic factor–enriched matrix both in vitro and in vivo. GM1 (monosialotetrahexosylganglioside)-positive planar lipid rafts, β₃ integrin receptors, and the intracellular signaling transducers focal adhesion kinase and RhoA (Ras homolog gene family, member A) cooperate to promote VEGFR2 long-term polarization and activation.

Conclusions—

A ligand anchored to the extracellular matrix induces VEGFR2 polarization in ECs. Long-lasting VEGFR2 relocation is closely dependent on lipid raft integrity and activation of β₃ integrin pathway. The study of the endothelial responses to immobilized growth factors may offer insights into the angiogenic process in physiological and pathological conditions, including cancer, and for a better engineering of synthetic tissue scaffolds to blend with the host vasculature.

Cellular Responses Modulated by FGF-2 Adsorbed on Albumin/Heparin Layer-by-Layer Assemblies

In a typical cell culture system, growth factors immobilized on the cell culture surfaces can serve as a reservoir of bio-signaling molecules, without the need to supplement them additionally into the culture medium. In this paper, we report on the fabrication of albumin/heparin (Alb/Hep) assemblies for controlled binding of basic fibroblast growth factor (FGF-2). The surfaces were constructed by layer-by-layer adsorption of polyelectrolytes albumin and heparin and were subsequently stabilized by covalent crosslinking with glutaraldehyde. An analysis of the surface morphology by atomic force microscopy showed that two Alb/Hep bilayers are required to cover the surface of substrate. The formation of the Alb/Hep assemblies was monitored by the surface plasmon resonance (SPR), the infrared multiinternal reflection spectroscopy (FTIR MIRS) and UV/VIS spectroscopy. The adsorption of FGF-2 on the cross-linked Alb/Hep was followed by SPR. The results revealed that FGF-2 binds to the Alb/Hep assembly in a dose and time-dependent manner up to the surface concentration of 120 ng/cm². The bioactivity of the adsorbed FGF-2 was assessed in experiments in vitro, using calf pulmonary arterial endothelial cells (CPAE). CPAE cells could attach and proliferate on Alb/Hep surfaces. The adsorbed FGF-2 was bioactive and stimulated both the proliferation and the differentiation of CPAE cells. The improvement was more pronounced at a lower FGF-2 surface concentration (30 ng/cm²) than on surfaces with a higher concentration of FGF-2 (120 ng/cm²).

Microfluidic analysis of extracellular matrix-bFGF crosstalk on primary human myoblast chemoproliferation, chemokinesis, and chemotaxis

Exposing myoblasts to basic fibroblast growth factor (bFGF), which is released after muscle injury, results in receptor phosphorylation, faster migration, and increased proliferation. These effects occur on time scales that extend across three orders of magnitude (10(0)-10(3) minutes). Finite element modeling of Transwell assays, which are traditionally used to assess chemotaxis, revealed that the bFGF gradient formed across the membrane pore is short-lived and diminishes 45% within the first minute. Thus, to evaluate bFGF-induced migration over 10(2) minutes, we employed a microfluidic assay capable of producing a stable, linear concentration gradient to perform single-cell analyses of chemokinesis and chemotaxis. We hypothesized that the composition of the underlying extracellular matrix (ECM) may affect the behavioral response of myoblasts to soluble bFGF, as previous work with other cell types has suggested crosstalk between integrin and fibroblast growth factor (FGF) receptors. Consistent with this notion, we found that bFGF significantly reduced the doubling time of myoblasts cultured on laminin but not fibronectin or collagen. Laminin also promoted significantly faster migration speeds (13.4 μm h(-1)) than either fibronectin (10.6 μm h(-1)) or collagen (7.6 μm h(-1)) without bFGF stimulation. Chemokinesis driven by bFGF further increased migration speed in a strictly additive manner, resulting in an average increase of 2.3 μm h(-1) across all ECMs tested. We observed relatively mild chemoattraction (∼67% of myoblast population) in response to bFGF gradients of 3.2 ng mL(-1) mm(-1) regardless of ECM identity. Thus, while ECM-bFGF crosstalk did impact chemoproliferation, it did not have a significant effect on chemokinesis or chemotaxis. These data suggest that the main physiological effect of bFGF on myoblast migration is chemokinesis and that changes in the surrounding ECM, resulting from aging and/or disease may impact muscle regeneration by altering myoblast migration and proliferation.

Anti-proliferative and angio-suppressive effect of Stoechospermum marginatum (C. Agardh) Kutzing extract using various experimental models

BACKGROUND/OBJECTIVES

Abundant consumption of seaweeds in the diet is epidemiologically linked to the reduction in risk of developing cancer. In larger cases, however, identification of particular seaweeds that are accountable for these effects is still lacking, hindering the recognition of competent dietary-based chemo preventive approaches. The aim of this research was to establish the antiproliferative potency and angiosuppressive mode of action of Stoechospermum marginatum seaweed methanolic extract using various experimental models.

MATERIALS/METHODS

Among the 15 seaweeds screened for antiproliferative activity against Ehrlich ascites tumor (EAT) cell line, Stoechospermum marginatum extract (SME) was found to be the most promising. Therefore, it was further investigated for its anti-proliferative activity in-vitro against choriocarcinoma (BeWo) and non-transformed Human embryonic kidney (HEK 293) cells, and for its anti-migratory/tube formation activity against HUVEC cells in-vitro. Subsequently, the angiosuppressive activity of S. marginatum was established by inhibition of angiogenesis in in-vivo (peritoneal angiogenesis and chorioallantoic membrane assay) and ex-vivo (rat cornea assay) models.

RESULTS

Most brown seaweed extracts inhibited the proliferation of EAT cells, while green and red seaweed extracts were much less effective. According to the results, SME selectively inhibited proliferation of BeWo cells in-vitro in a dose-dependent manner, but had a lesser effect on HEK 293 cells. SME also suppressed the migration and tube formation of HUVEC cells in-vitro. In addition, SME was able to suppress VEGF-induced angiogenesis in the chorio allantoic membrane, rat cornea, and tumor induced angiogenesis in the peritoneum of EAT bearing mice. A decrease in the microvessel density count and CD31 antigen staining of treated mice peritoneum provided further evidence of its angiosuppressive activity.

CONCLUSIONS

Altogether, the data underline that VEGF mediated angiogenesis is the target for the angiosuppressive action of SME and could potentially be useful in cancer prevention or treatment involving stimulated angiogenesis.

Initial contact of glioblastoma cells with existing normal brain endothelial cells strengthen the barrier function via fibroblast growth factor 2 secretion: a new in vitro blood-brain barrier model

Glioblastoma multiforme (GBM) cells invade along the existing normal capillaries in brain. Normal capillary endothelial cells function as the blood-brain barrier (BBB) that limits permeability of chemicals into the brain. To investigate whether GBM cells modulate the BBB function of normal endothelial cells, we developed a new in vitro BBB model with primary cultures of rat brain endothelial cells (RBECs), pericytes, and astrocytes. Cells were plated on a membrane with 8 μm pores, either as a monolayer or as a BBB model with triple layer culture. The BBB model consisted of RBEC on the luminal side as a bottom, and pericytes and astrocytes on the abluminal side as a top of the chamber. Human GBM cell line, LN-18 cells, or lung cancer cell line, NCI-H1299 cells, placed on either the RBEC monolayer or the BBB model increased the transendothelial electrical resistance (TEER) values against the model, which peaked within 72 h after the tumor cell application. The TEER value gradually returned to baseline with LN-18 cells, whereas the value quickly dropped to the baseline in 24 h with NCI-H1299 cells. NCI-H1299 cells invaded into the RBEC layer through the membrane, but LN-18 cells did not. Fibroblast growth factor 2 (FGF-2) strengthens the endothelial cell BBB function by increased occludin and ZO-1 expression. In our model, LN-18 and NCI-H1299 cells secreted FGF-2, and a neutralization antibody to FGF-2 inhibited LN-18 cells enhanced BBB function. These results suggest that FGF-2 would be a novel therapeutic target for GBM in the perivascular invasive front.

Indolinones and anilinophthalazines differentially target VEGF-A- and basic fibroblast growth factor-mediated responses in primary human endothelial cells

BACKGROUND AND PURPOSE

The potent pro-angiogenic growth factors VEGF-A and basic fibroblast growth factor (bFGF) exert their effects by binding VEGF receptor 2 and FGF receptor tyrosine kinases, respectively. Indolinones (e.g. SU5416 and Sutent) and anilinophthalazines (e.g. PTK787) are potent small molecule inhibitors of VEGFR2 and other tyrosine kinases, but their effects on VEGF-A- and bFGF-stimulated endothelial responses are unclear. Here we assess the ability of these compounds to inhibit pro-angiogenic responses through perturbation of receptor activity and endothelial function(s).

EXPERIMENTAL APPROACH

We used in silico modelling, in vitro tyrosine kinase assays, biochemistry and microscopy to evaluate the effects of small molecules on receptor tyrosine kinase activation and intracellular signalling. Primary human endothelial cells were used to assess intracellular signalling, cell migration, proliferation and tubulogenesis.

KEY RESULTS

We predicted that the anilinophthalazine PTK787 binds the tyrosine kinase activation loop whereas indolinones are predicted to bind within the hinge region of the split kinase domain. Sutent is a potent inhibitor of both VEGFR2 and FGFR1 tyrosine kinase activity in vitro. The compounds inhibit both ligand-dependent and -independent VEGFR2 trafficking events, are not selective for endothelial cell responses and inhibit both VEGF-A- and bFGF-mediated migration, wound healing and tubulogenesis at low concentrations. CONCLUSIONS AND IMPLICATIONS; We propose that these compounds have novel properties including inhibition of bFGF-mediated endothelial responses and perturbation of VEGFR2 trafficking. Differential inhibitor binding to receptor tyrosine kinases translates into more potent inhibition of bFGF- and VEGF-A-mediated intracellular signalling, cell migration and tubulogenesis. Indolinones and anilinophthalazines thus belong to a class of multi-kinase inhibitors that show clinical efficacy in disease therapy.

Integrin-α5 coordinates assembly of posterior cranial placodes in zebrafish and enhances Fgf-dependent regulation of otic/epibranchial cells

Vertebrate sensory organs develop in part from cranial placodes, a series of ectodermal thickenings that coalesce from a common domain of preplacodal ectoderm. Mechanisms coordinating morphogenesis and differentiation of discrete placodes are still poorly understood. We have investigated whether placodal assembly in zebrafish requires Integrin- α5 (itga5), an extracellular matrix receptor initially expressed throughout the preplacodal ectoderm. Morpholino knockdown of itga5 had no detectable effect on anterior placodes (pituitary, nasal and lens), but posterior placodes developed abnormally, resulting in disorganization of trigeminal and epibranchial ganglia and reduction of the otic vesicle. Cell motion analysis in GFP-transgenic embryos showed that cell migration in itga5 morphants was highly erratic and unfocused, impairing convergence and blocking successive recruitment of new cells into these placodes. Further studies revealed genetic interactions between itga5 and Fgf signaling. First, itga5 morphants showed changes in gene expression mimicking modest reduction in Fgf signaling. Second, itga5 morphants showed elevated apoptosis in the otic/epibranchial domain, which was rescued by misexpression of Fgf8. Third, knockdown of the Fgf effector erm had no effect by itself but strongly enhanced defects in itga5 morphants. Finally, proper regulation of itga5 requires dlx3b/4b and pax8, which are themselves regulated by Fgf. These findings support a model in which itga5 coordinates cell migration into posterior placodes and augments Fgf signaling required for patterning of these tissues and cell survival in otic/epibranchial placodes.

A pro-inflammatory signature mediates FGF2-induced angiogenesis

Fibroblast growth factor-2 (FGF2) is a potent angiogenic growth factor. Here, gene expression profiling of FGF2-stimulated microvascular endothelial cells revealed, together with a prominent pro-angiogenic profile, a pro-inflammatory signature characterized by the upregulation of pro-inflammatory cytokine/chemokines and their receptors, endothelial cell adhesion molecules and members of the eicosanoid pathway. Real-time quantitative PCR demonstrated early induction of most of the FGF2-induced, inflammation-related genes. Accordingly, chick embryo chorioallantoic membrane (CAM) and murine Matrigel plug angiogenesis assays demonstrated a significant monocyte/macrophage infiltrate in the areas of FGF2-driven neovascularization. Similar results were obtained when the conditioned medium (CM) of FGF2-stimulated endothelial cells was delivered onto the CAM, suggesting that FGF2-upregulated chemoattractants mediate the inflammatory response. Importantly, FGF2-triggered new blood vessel formation was significantly reduced in phosphatidylinositol 3-kinase-gamma null mice exhibiting defective leucocyte migration or in clodronate liposome-treated, macrophage-depleted mice. Furthermore, the viral pan-chemokine antagonist M3 inhibited the angiogenic and inflammatory responses induced by the CM of FGF2-stimulated endothelial cells and impaired FGF2-driven neovascularization in the CAM assay. These findings point to inflammatory chemokines as early mediators of FGF2-driven angiogenesis and indicate a non-redundant role for inflammatory cells in the neovascularization process elicited by the growth factor.

Differential interactions of FGFs with heparan sulfate control gradient formation and branching morphogenesis

The developmental activities of morphogens depend on the gradients that they form in the extracellular matrix. Here, we show that differences in the binding of fibroblast growth factor 7 (FGF7) and FGF10 to heparan sulfate (HS) underlie the formation of different gradients that dictate distinct activities during branching morphogenesis. Reducing the binding affinity of FGF10 for HS by mutating a single residue in its HS-binding pocket converted FGF10 into a functional mimic of FGF7 with respect to gradient formation and regulation of branching morphogenesis. In particular, the mutant form of FGF10 caused lacrimal and salivary gland epithelium buds to branch rather than to elongate. In contrast, mutations that reduced the affinity of the FGF10 for its receptor affected the extent, but not the nature, of the response. Our data may provide a general model for understanding how binding to HS regulates other morphogenetic gradients.

Extracellular interactome of the FGF receptor-ligand system: complexities and the relative simplicity of the worm

Fibroblast growth factors (FGFs) and their receptors (FGFRs) regulate a multitude of biological functions in embryonic development and in adult. A major question is how does one family of growth factors and their receptors control such a variety of functions? Classically, specificity was thought to be imparted by alternative splicing of the FGFRs, resulting in isoforms that bind specifically to a subset of the FGFs, and by different saccharide sequences in the heparan sulfate proteoglycan (HSPG) co-receptor. A growing number of noncanonical co-receptors such as integrins and neural cell adhesion molecule (NCAM) are now recognized as imparting additional complexity to classic FGFR signaling. This review will discuss the noncanonical FGFR ligands and speculate on the possibility that they provide additional and alternative means to determining the functional specificity of FGFR signaling. We will also discuss how invertebrate models such as C. elegans may advance our understanding of noncanonical FGFR signaling.

Neural stem cell differentiation is mediated by integrin beta4 in vitro

Neural stem cells are capable of differentiating into three major neural cell types, but the underlying molecular mechanisms remain unclear. Here, we investigated the mechanism by which integrin beta4 modulates mouse neural stem cell differentiation in vitro. Inhibition of endogenous integrin beta4 by RNA interference inhibited the cell differentiation and the expression of fibroblast growth factor receptor 2 but not fibroblast growth factor receptor 1 or fibroblast growth factor receptor 3. Overexpression of integrin beta4 in neural stem cells promoted neural stem cell differentiation. Furthermore, integrin beta4-induced differentiation of neural stem cells was attenuated by SU5402, the inhibitor of fibroblast growth factor receptors. Finally, we investigated the role of integrin beta4 in neural stem cell survival: knockdown of integrin beta4 did not affect survival or apoptosis of neural stem cells. These data provide evidence that integrin beta4 promotes differentiation of mouse neural stem cells in vitro possibly through fibroblast growth factor receptor 2.

Direct binding of integrin alphavbeta3 to FGF1 plays a role in FGF1 signaling

Integrins play a role in fibroblast growth factor (FGF) signaling through cross-talk with FGF receptors (FGFRs), but the mechanism underlying the cross-talk is unknown. We discovered that FGF1 directly bound to soluble and cell-surface integrin alphavbeta3 (K(D) about 1 microm). Antagonists to alphavbeta3 (monoclonal antibody 7E3 and cyclic RGDfV) blocked this interaction. alphavbeta3 was the predominant, if not the only, integrin that bound to FGF1, because FGF1 bound only weakly to several beta1 integrins tested. We presented evidence that the CYDMKTTC sequence (the specificity loop) within the ligand-binding site of beta3 plays a role in FGF1 binding. We found that the integrin-binding site of FGF1 overlaps with the heparin-binding site but is distinct from the FGFR-binding site using docking simulation and mutagenesis. We identified an FGF1 mutant (R50E) that was defective in integrin binding but still bound to heparin and FGFR. R50E was defective in inducing DNA synthesis, cell proliferation, cell migration, and chemotaxis, suggesting that the direct integrin binding to FGF1 is critical for FGF signaling. Nevertheless, R50E induced phosphorylation of FGFR1 and FRS2alpha and activation of AKT and ERK1/2. These results suggest that the defect in R50E in FGF signaling is not in the initial activation of FGF signaling pathway components, but in the later steps in FGF signaling. We propose that R50E is a useful tool to identify the role of integrins in FGF signaling.

Pathophysiology of tumor neovascularization

Neovascularization is essential to the process of development and differentiation of tissues in the vertebrate embryo, and is also involved in a wide variety of physiological and pathological conditions in adults, including wound repair, metabolic diseases, inflammation, cardiovascular disorders, and tumor progression. Thanks to cumulative studies on vasculature, new therapeutic approaches have been opened for us to some life-threatening diseases by controlling angiogenesis in the affected organs. In cancer therapy, for example, modulation of factors responsible for tumor angiogenesis may be beneficial in inhibiting of tumor progression. Several antiangiogenic approaches are currently under preclinical trial. However, the mechanisms of neovascularization in tumors are complicated and each tumor shows unique features in its vasculature, depending on tissue specificity, angiogenic micromilieu, grades and stages, host immunity, and so on. For better understanding and effective therapeutic approaches, it is important to clarify both the general mechanism of angiogenic events and the disease-specific mechanism of neovascularization. This review discusses the general features of angiogenesis under physiological and pathological conditions, mainly in tumor progression. In addition, recent topics such as contribution of the endothelial progenitor cells, tumor vasculogenic mimicry, markers for tumor-derived endothelial cells and pericytes, and angiogenic/angiostatic chemokines are summarized.

Dobesilate diminishes activation of the mitogen-activated protein kinase ERK1/2 in glioma cells

Fibroblast growth factors (FGFs) and their receptors, regularly expressed at high levels in gliomas, are further upregulated during the transition of the tumor from low- to high-grade malignancy, and are essential for glioma progression. FGFs induce upregulation of the mitogen-activated protein kinase (MAPK) signaling cascade in cultured glioma cells, which suggests that MAPK pathway participates in the FGF-dependent glioma development. Recently, it has been shown that dobesilate, an inhibitor of FGF mitogenic activity, shows antiproliferative and proapoptotic activities in glioma cell cultures. Accordingly, it should be expected this new synthetic FGF inhibitor to affect the activation levels of MAPK. Here we report that immunocytochemical and Western blot data unequivocally show that treatment of cell cultures with dobesilate causes a significant decrease of the intracellular levels of ERK1/2 activation, one of the components of the MAPK signalling cascade. This finding supports an important role for dobesilate in glioma growth, suggesting that dobesilate should be a treatment to be born in mind for glioma management.

Extracellular angiogenic growth factor interactions: an angiogenesis interactome survey

Angiogenesis plays a key role in various physiological and pathological processes, including inflammation and tumor growth. Numerous angiogenic growth factors (AGFs) have been identified. Usually, the angiogenic process is assumed to represent the outcome of a straightforward interaction of AGFs with specific signalling receptors of the endothelial cell (EC) surface. Actually, the mechanisms by which AGFs induce neovascularization are much more complex. Indeed, angiogenesis is the result of the simultaneous actions of various AGFs and angiogenesis modulators; multiple EC surface receptors with different structure and biological properties are engaged by AGFs to exert a full angiogenic response; AGFs bind a variety of free and immobilized proteins, polysaccharides, and complex lipids of the extracellular milieu that affect AGF integrity, stability, and bioavailability; some of the AGF-binding molecules interact also with AGF receptors. In this review the authors summarize literature data and discuss the current knowledge about the extracellular molecules able to interact with AGFs, thus representing possible key regulators of the angiogenesis process and targets/templates for the development of novel antiangiogenic drugs. This work represents an attempt to highlight common theme in the AGF interactome that occurs at the extracellular level during neovascularization.

Inhibition of fibroblast growth factor receptor signaling attenuates atherosclerosis in apolipoprotein E-deficient mice

OBJECTIVE

To determine the significance of fibroblast growth factor receptor (FGFR) expression for the development of atherosclerotic lesions in apoE-deficient (apoE-/-) mice.

METHODS AND RESULTS

ApoE-/- mice fed a high-fat diet were administered the FGFR tyrosine kinase inhibitor SU5402 (25 mg/kg/d sc), which inhibited neointima growth by 85%. We measured its effects on lesion size at the aortic sinus, macrophage and smooth muscle cell (SMC) accumulation, the expression of monocyte chemotactic and retention factors, as well as its effects on FGFR expression/phosphorylation. FGFR tyrosine kinase inhibition reduced phosphorylated FGFRs in lesions by 90%, associated with a 65% reduction in lesion size measured using Oil Red O. Macrophages and SMCs within lesions were reduced by 58% and 78%, respectively. Monocyte chemotactic protein-1 (MCP-1) expression was also reduced, as was the expression of hyaluronan synthase, cyclooxygenase-2, CD36, and endothelial monocyte-activating polypeptide-II. Although 3 FGFR types were expressed in lesions, the effects of SU5402 could be attributed largely to inhibition of FGFR-1 phosphorylation.

CONCLUSIONS

Atherosclerotic lesions in apoE-/- mice express multiple FGFRs and an active FGF:FGFR-1 signaling system that promotes atherosclerosis development via increased SMC proliferation, and by augmenting macrophage accumulation via increased expression of MCP-1 and factors promoting macrophage retention in lesions.

Regulated expression of FLRT genes implies a functional role in the regulation of FGF signalling during mouse development

Within the mammalian genome, there are many multimember gene families that encode membrane proteins with extracellular leucine rich repeats which are thought to act as cell adhesion or signalling molecules. We previously showed that the members of the NLRR gene family are expressed in a developmentally restricted manner in the mouse with NLRR-1 being expressed in the developing myotome. The FLRT gene family shows a similar genomic layout and predicted protein secondary structure to the NLRRs so we analysed expression of the three FLRT genes during mouse development. FLRTs are glycosylated membrane proteins expressed at the cell surface which localise in a homophilic manner to cell-cell contacts expressing the focal adhesion marker vinculin. Each member of the FLRT family has a distinct, highly regulated expression pattern, as was seen for the NLRR family. FLRT3 has a provocative expression pattern during somite development being expressed in regions of the somite where muscle precursor cells migrate from the dermomyotome and move into the myotome, and later in myotomal precursors destined to migrate towards their final destination, for example, those that form the ventral body wall. FLRT3 is also expressed at the midbrain/hindbrain boundary and in the apical ectodermal ridge, regions where FGF signalling is known to be important, suggesting that the role for FLRT3 in FGF signalling identified in Xenopus is conserved in mammals. FLRT1 is expressed at brain compartmental boundaries and FLRT2 is expressed in a subset of the sclerotome, adjacent to the region that forms the syndetome, suggesting that interaction with FGF signalling may be a general property of FLRT proteins. We confirmed this by showing that all FLRTs can interact with FGFR1 and FLRTs can be induced by the activation of FGF signalling by FGF-2. We conclude that FLRT proteins act as regulators of FGF signalling, being induced by the signal and then able to interact with the signalling receptor, in many tissues during mouse embryogenesis. This process may, in part, be dependent on homophilic intercellular interactions between FLRT molecules.

Ectopic activity of fibroblast growth factor receptor 1 in hepatocytes accelerates hepatocarcinogenesis by driving proliferation and vascular endothelial growth factor-induced angiogenesis

Fibroblast growth factor (FGF) signaling mediates cell-to-cell communication in development and organ homeostasis in adults. Of the four FGF receptor (FGFR) tyrosine kinases, only FGFR4 is expressed in mature hepatocytes. Although FGFR1 is expressed by hepatic cell progenitors and adult nonparenchymal cells, ectopic expression is commonly observed in hepatoma cells. Here, we determined whether ectopic FGFR1 is a cause or consequence of hepatocellular carcinoma by targeting a constitutively active human FGFR1 to mouse hepatocytes. Livers of transgenic mice exhibited accelerated regeneration after partial hepatectomy but no signs of neoplastic or preneoplastic abnormalities for up to 18 months. However, in diethylnitrosamine-treated mice, the chronic FGFR1 activity promoted an incidence of 44% adenomas at 4 months and 38% hepatocellular carcinoma at 8 months. No adenoma or hepatocellular carcinoma was observed in diethylnitrosamine-treated wild-type (WT) livers at 4 or 8 months, respectively. At 10 and 12 months, tumor-bearing livers in transgenic mice were twice the size of those in WT animals. Isolated hepatoma cells from the transgenic tumors exhibited a growth advantage in culture. Advanced hepatocellular carcinoma in the transgenic livers exhibited a reduced rate of necrosis. This was accompanied by a mean microvessel density of 2.7 times that of WT tumors and a markedly higher level of vascular endothelial growth factor. In cooperation with an initiator, the persistent activity of ectopic FGFR1 in hepatocytes is a strong promoter of hepatocellular carcinoma by driving cell proliferation at early stages and promoting neoangiogenesis at late stages of progression.

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.

FGF-2 binding to fibrin(ogen) is required for augmented angiogenesis

We have shown previously that fibrin(ogen) binds fibroblast growth factor 2 (FGF-2) and potentiates stimulation of endothelial-cell (EC) proliferation. We have now used 2 FGF-2 mutants differing only in the 5 residues constituting the binding site to characterize the importance of this interaction in angiogenesis. The nonbinding (2212) and binding (221*2) mutants stimulated EC proliferation by 2.2 +/- 0.4-fold and 2.9 +/- 0.3-fold over control, respectively, and both were similar to wild-type (wt) FGF-2 (2.5 +/- 0.3-fold). Proliferation was augmented by fibrinogen to 5.3 +/- 1.2-fold and 4.8 +/- 0.8-fold with wtFGF-2 and 221*2, whereas no augmentation occurred with 2212 and fibrinogen. Using a placental explant model in a fibrin matrix, wtFGF-2 resulted in 2.6 +/- 0.9-fold more growth over control, and 221*2 increased growth 3.3 plus or minus 0.9-fold. Vessel outgrowth with 2212 was minimal and comparable to control. Similarly, fibrinogen potentiated wtFGF-2 or 221*2-mediated angiogenesis in the chicken chorioallantoic membrane model. In a mouse Matrigel implant model, fibrinogen significantly increased angiogenesis with either wtFGF-2 or 221*2, whereas there was no augmentation with 2212. These results demonstrate that binding of FGF-2 to fibrin(ogen) mediated by the 5-residue FGF-2-fibrin(ogen) interactive site is required for augmented angiogenesis.

αvβ3-integrin-dependent activation of focal adhesion kinase mediates NF-κB activation and motogenic activity by HIV-1 Tat in endothelial cells

Once in the extracellular environment, the transactivator protein HIV-1 Tat exerts several pleiotropic effects by interacting with different cellular receptors, including integrin αvβ3. Real-time surface plasmon resonance analysis reveals that Tat/αVβ3 interaction occurs with rapid kinetics (association and dissociation rates equal to 1.16×107 M-1 s-1 and 3.78×10-1 s-1, respectively) and high affinity (dissociation constant = 32 nM). Through this interaction, substratum-immobilized Tat promotes adhesion and motogenic activity in endothelial cells. Also, αvβ3/Tat interaction triggers the activation of focal adhesion kinase, RhoA and pp60src. Overexpression of the dominant negative form of focal adhesion kinase, but not of an inactive Leu1034Ser substitution mutant isoform, impairs the activation of focal adhesion kinase and RhoA, but not that of pp60src, without affecting endothelial cell adhesion and spreading. αvβ3/Tat interaction triggers the activation of NF-κB in endothelial cells in a focal adhesion kinase-, RhoA- and pp60src-dependent manner, as shown in dominant negative focal adhesion kinase transfectants or using specific pharmacological inhibitors. Finally, the activation of focal adhesion kinase, RhoA, NF-κB and pp60src are required to mediate the motogenic activity of Tat in endothelial cells.

Since Tat accumulates in an immobilized form in the extracellular matrix, these results provide new biochemical and biological insights about αvβ3/Tat interaction exploitable for the design of anti-Tat strategies.

Endothelial cell activation by IL-1beta in the presence of fibrinogen requires alphavbeta3

OBJECTIVE

The purpose of this study was to investigate the receptor requirements for enhanced IL-1beta-induced secretion of nitric oxide (NO) by endothelial cells (ECs) in the presence of fibrinogen.

METHODS AND RESULTS

ECs were exposed to IL-1beta with or without fibrinogen and NO was measured as nitrite. NO production by EC exposed to fibrinogen (0.3+/-0.1 micromol/L) was comparable concentration to control (0.2+/-0.1 micromol/L), but IL-1beta significantly increased NO production (0.8+/-0.1 micromol/L), and the combination of both fibrinogen and IL-1beta resulted in a further increase to 2.2+/-0.2 micromol/L (P<0.002). 7E3 or LM609, antibodies to alphavbeta3, inhibited NO production stimulated by fibrinogen-bound IL-1beta to 0.2+/-0.1 micromol/L (P<0.001) or 0.2+/-0.03 micromol/L (P<0.0001), respectively. These levels were comparable to control and significantly less than with IL-1beta (P<0.002). EC or fibroblasts exposed to both fibrinogen and IL-1beta, but not vitronectin and IL-1beta, demonstrated positive Western blotting for alphavbeta3 after immunopurification with anti- IL-1R, indicating specific association between alphavbeta3 and IL-1R. Dual immunofluorescence also revealed colocalization of alphavbeta3 and IL-1R only when the cells were exposed to both fibrinogen and IL-1beta.

CONCLUSIONS

The enhanced NO production by ECs in the presence of fibrinogen-bound IL-1beta requires the coordinated effects of colocalized alphavbeta3 and IL-1R.

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

Fibroblast growth factors (FGFs) are a family of heparin-binding growth factors. FGFs exert their pro-angiogenic activity by interacting with various endothelial cell surface receptors, including tyrosine kinase receptors, heparan-sulfate proteoglycans, and integrins. Their activity is modulated by a variety of free and extracellular matrix-associated molecules. Also, the cross-talk among FGFs, vascular endothelial growth factors (VEGFs), and inflammatory cytokines/chemokines may play a role in the modulation of blood vessel growth in different pathological conditions, including cancer. Indeed, several experimental evidences point to a role for FGFs in tumor growth and angiogenesis. This review will focus on the relevance of the FGF/FGF receptor system in adult angiogenesis and its contribution to tumor vascularization.

Antiangiogenic Activity of Semisynthetic Biotechnological Heparins

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.

Stimulation of endothelial cell proliferation by FGF-2 in the presence of fibrinogen requires αvβ3

We have shown previously that fibrin(ogen) binding potentiates the capacity of fibroblast growth factor 2 (FGF-2) to stimulate endothelial cell (EC) proliferation. We have now investigated the receptor requirement for EC proliferation by fibrinogen-bound FGF-2. ECs were cultured with 25 ng/mL FGF-2 with or without 10 μg/mL fibrinogen, and proliferation was measured as 3H-thymidine incorporation. Proliferation was increased 2.4 ± 0.5-fold over medium alone with FGF-2 and increased significantly more to 4.0 ± 0.7-fold with fibrinogen and FGF-2 (P &lt; .005). Addition of 7E3 or LM609, antibodies to αvβ3, inhibited EC proliferation with fibrinogen-bound FGF-2 by 80% ± 8% (P &lt; .001) or 67% ± 14% (P &lt; .002), respectively, to levels significantly less than that observed with FGF-2 alone (P &lt; .001). Neither LM609 nor 7E3 exhibited any inhibition of activity with FGF-2 alone. Peptide GRGDS caused dose-dependent inhibition of proliferation by fibrinogen-bound FGF-2 of 31% ± 8%, 45% ± 9%, and 68% ± 11% at 0.25, 0.5, and 1 mM, respectively. Coimmunoprecipitation and immunofluorescence studies demonstrated a direct specific association between αvβ3 and FGF receptor 1 (FGFR1) in ECs and fibroblasts when exposed to both FGF-2 and fibrinogen but not with vitronectin. We conclude that fibrinogen binding of FGF-2 enhances EC proliferation through the coordinated effects of colocalized αvβ3 and FGFR1.

Fibrinogen binding potentiates FGF-2 but not VEGF induced expression of u-PA, u-PAR, and PAI-1 in endothelial cells

Endothelial cell responses at sites of injury occur in a fibrin matrix and are regulated by growth factors including those of the FGF and VEGF families. The pericellular proteolytic balance is important in these responses, and FGF-2 and VEGF up-regulate endothelial cell u-PA, u-PAR and PAI-1. Because both VEGF and FGF-2 bind to fibrinogen, we have examined the capacity of fibrinogen to modulate the up-regulation of these proteins by FGF-2 and VEGF. Confluent cultures of endothelial cells were exposed to FGF-2, VEGF, and fibrinogen or to combinations of growth factors with fibrinogen. Changes in mRNA levels of u-PA, u-PAR and PAI-1 were measured by Northern blot. FGF-2 increased u-PA, u-PAR, and PAI-1 mRNA, but there was a significantly greater induction when fibrinogen was added to FGF-2 at all concentrations. The potentiation by fibrinogen was particularly evident at an FGF-2 concentration of 0.1 ng mL(-1), which resulted in non-significant change in transcript levels by itself, but significantly increased up to 2.6-fold with fibrinogen. VEGF also increased endothelial cell expression of u-PA, u-PAR and PAI-1, but this effect was not potentiated by fibrinogen. Addition of LM609, a monoclonal antibody to alphaVbeta3, significantly inhibited induction of u-PA mRNA and activity by fibrinogen-bound FGF-2 compared to FGF-2. A monoclonal antibody to FGFR1 also inhibited u-PA mRNA expression induced by fibrinogen-bound FGF-2. We conclude that fibrinogen increases the capacity of FGF-2, but not of VEGF, to up-regulate u-PA, u-PAR, and PAI-1 in endothelial cells and that fibrinogen-bound FGF-2 requires alphaVbeta3 binding to up-regulate endothelial cell u-PA.

Interleukin-1beta but not IL-1alpha binds to fibrinogen and fibrin and has enhanced activity in the bound form

Fibrin is formed at sites of injury or inflammation and provides the temporary matrix to support vascular cell responses that are also mediated by cytokines including interleukin-1 (IL-1). We have shown previously that fibroblast growth factor 2 (FGF-2) binds with high affinity to fibrin(ogen). Because IL-1 has a structure similar to FGF-2, we have investigated the possible binding of IL-1 to fibrin(ogen). Experiments using IL-1 immobilized on Sepharose beads and soluble iodine 125 ((125)I)-labeled fibrinogen demonstrated no specific interaction of IL-1alpha with fibrinogen, but IL-1beta showed saturable and specific binding. Scatchard analysis indicated a single binding site with an apparent K(d) = 1.5 nM and a maximum molar binding ratio of IL-1beta to fibrinogen of 1.8:1. Binding of (125)I-IL-1beta to Sepharose-immobilized fibrinogen also demonstrated a single binding site with an apparent K(d) of 3.5 nM. IL-1beta also bound specifically to fibrin monomer and polymerized fibrin with apparent K(d)s of 3.4 nM and 2.3 nM, respectively. IL-1beta displaced FGF-2 for binding to fibrin, indicating an interaction with the same or a closely related site. Compared with free form, fibrinogen-bound IL-1beta stimulated increased activation of endothelial cell nuclear factor kappaB (NF-kappaB), monocyte chemoattractant protein-1 (MCP-1) secretion, and nitric oxide (NO) synthesis. We conclude that IL-1beta binds with high affinity to fibrin(ogen) and demonstrates increased activity in the bound form.

Thrombospondin 1 as a scavenger for matrix-associated fibroblast growth factor 2

The antiangiogenic factor thrombospondin 1 (TSP-1) binds with high affinity to several heparin-binding angiogenic factors, including fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), and hepatocyte growth factor/scatter factor (HGF/SF). The aim of this study was to investigate whether TSP-1 affects FGF-2 association with the extracellular matrix (ECM) and its bioavailability. TSP-1 prevented the binding of free FGF-2 to endothelial cell ECM. It also promoted the mobilization of matrix-bound FGF-2, generating a TSP-1/FGF-2 complex. The region of TSP-1 responsible for these activities was located within the 140-kDa antiangiogenic and FGF-2 binding fragment, whereas the 25-kDa heparin-binding fragment was inactive. Matrix-released FGF-2/TSP-1 complex had a reduced ability to bind to and induce proliferation of endothelial cells. TSP-1 depleted the ECM laid by FGF-2-overproducing tumor cells of its FGF-2-dependent mitogenic activity for endothelial cells. Besides FGF-2, TSP-1 also inhibited VEGF and HGF/SF binding to the ECM and mobilized them from the ECM. Our study shows that TSP-1 acts as a scavenger for matrix-associated angiogenic factors, affecting their location, bioavailability, and function.

Thrombospondin signaling through the calreticulin/LDL receptor-related protein co-complex stimulates random and directed cell migration

The matricellular extracellular matrix protein thrombospondin-1 (TSP1) stimulates focal adhesion disassembly through a sequence (known as the hep I peptide) in its heparin-binding domain. This mediates signaling through a receptor co-complex involving calreticulin and low-density lipoprotein (LDL) receptor-related protein (LRP). We postulate that this transition to an intermediate adhesive state enhances cellular responses to dynamic environmental conditions. Since cell adhesion dynamics affect cell motility, we asked whether TSP1/hep I-induced intermediate adhesion alters cell migration. Using both transwell and Dunn chamber assays, we demonstrate that TSP1 and hep I gradients stimulate endothelial cell chemotaxis. Treatment with focal adhesion-labilizing concentrations of TSP1/hep I in the absence of a gradient enhances endothelial cell random migration, or chemokinesis, associated with an increase in cells migrating, migration speed, and total cellular displacement. Calreticulin-null and LRP-null fibroblasts do not migrate in response to TSP1/hep I, nor do endothelial cells treated with the LRP inhibitor receptor-associated protein (RAP). Furthermore, TSP1/hep I-induced focal adhesion disassembly is associated with reduced chemotaxis to basic fibroblast growth factor (bFGF) but enhanced chemotaxis to acidic (a)FGF, suggesting differential modulation of growth factor-induced migration. Thus, TSP1/hep I stimulation of intermediate adhesion regulates the migratory phenotype of endothelial cells and fibroblasts, suggesting a role for TSP1 in remodeling responses.