Sulfate moieties in the subendothelial extracellular matrix are involved in basic fibroblast growth factor sequestration, dimerization, and stimulation of cell proliferation

Sulfated and Phosphorylated Agarose as Biomaterials for a Biomimetic Paradigm for FGF-2 Release

Cardiovascular diseases such as myocardial infarction or limb ischemia are characterized by regression of blood vessels. Local delivery of growth factors (GFs) involved in angiogenesis such as fibroblast blast growth factor-2 (FGF-2) has been shown to trigger collateral neovasculature and might lead to a therapeutic strategy. In vivo, heparin, a sulfated polysaccharide present in abundance in the extracellular matrix (ECM), has been shown to function as a local reservoir for FGF-2 by binding FGF-2 and other morphogens and it plays a role in the evolution of GF gradients. To access injectable biomaterials that can mimic such natural electrostatic interactions between soluble signals and macromolecules and mechanically tunable environments, the backbone of agarose, a thermogelling marine-algae-derived polysaccharide, was modified with sulfate, phosphate, and carboxylic moieties and the interaction and release of FGF-2 from these functionalized hydrogels was assessed by ELISA in vitro and CAM assay in ovo. Our findings show that FGF-2 remains active after release, and FGF-2 release profiles can be influenced by sulfated and phosphorylated agarose, and in turn, promote varied blood vessel formation kinetics. These modified agaroses offer a simple approach to mimicking electrostatic interactions experienced by GFs in the extracellular environment and provide a platform to probe the role of these interactions in the modulation of growth factor activity and may find utility as an injectable gel for promoting angiogenesis and as bioinks in 3D bioprinting.

Aqueous humour-induced lens epithelial cell proliferation requires FGF-signalling

The eye lens grows by systematic proliferation of its epithelial cells and their differentiation into fibre cells. The anterior aqueous humour regulates lens epithelial cell proliferation whereas posteriorly, the vitreous stimulates lens fibre differentiation. Vitreous-derived members of the fibroblast growth factor (FGF) family induce fibre differentiation, with added support for FGFs as putative regulators of aqueous-induced lens cell proliferation. To further characterize this, given FGFs' known affinity for proteoglycans, we compared the effect of proteoglycan sulphation in growth factor- and aqueous-induced lens cell proliferation. Disruption of proteoglycan sulphation in lens cells specifically impacted on aqueous- and FGF-induced MAPK/ERK1/2-signalling, but not on that induced by other mitogens such as PDGF; however, cell proliferation was reduced in all treatment groups, regardless of the mitogen. Overall, by disrupting proteoglycan activity, we further highlight the significant role of FGFs in aqueous-induced ERK1/2 phosphorylation leading to lens cell proliferation.

The potential of fibroblast growth factor/fibroblast growth factor receptor signaling as a therapeutic target in tumor angiogenesis

INTRODUCTION

Fibroblast growth factors (FGFs) are endowed with a potent pro-angiogenic activity. Activation of the FGF/FGF receptor (FGFR) system occurs in a variety of human tumors. This may lead to neovascularization, supporting tumor progression and metastatic dissemination. Thus, a compelling biologic rationale exists for the development of anti-FGF/FGFR agents for the inhibition of tumor angiogenesis in cancer therapy.

AREAS COVERED

A comprehensive search on PubMed was performed to identify studies on the role of the FGF/FGFR system in angiogenesis. Endothelial FGFR signaling, the pro-angiogenic function of canonical FGFs, and their role in human tumors are described. In addition, experimental approaches aimed at the identification and characterization of nonselective and selective FGF/FGFR inhibitors and their evaluation in clinical trials are summarized.

EXPERT OPINION

Different approaches can be envisaged to inhibit the FGF/FGFR system, a target for the development of 'two-compartment' anti-angiogenic/anti-tumor agents, including FGFR selective and nonselective small-molecule tyrosine kinase inhibitors, anti-FGFR antibodies, and FGF ligand traps. Further studies are required to define the correlation between tumor vascularization and activation of the FGF/FGFR system and for the identification of cancer patients more likely to benefit from anti-FGF/FGFR treatments. In addition, advantages and disadvantages about the use of selective versus non-selective FGF inhibitors remain to be elucidated.

Heparin/Heparan sulfate proteoglycans glycomic interactome in angiogenesis: biological implications and therapeutical use

Angiogenesis, the process of formation of new blood vessel from pre-existing ones, is involved in various intertwined pathological processes including virus infection, inflammation and oncogenesis, making it a promising target for the development of novel strategies for various interventions. To induce angiogenesis, angiogenic growth factors (AGFs) must interact with pro-angiogenic receptors to induce proliferation, protease production and migration of endothelial cells (ECs). The action of AGFs is counteracted by antiangiogenic modulators whose main mechanism of action is to bind (thus sequestering or masking) AGFs or their receptors. Many sugars, either free or associated to proteins, are involved in these interactions, thus exerting a tight regulation of the neovascularization process. Heparin and heparan sulfate proteoglycans undoubtedly play a pivotal role in this context since they bind to almost all the known AGFs, to several pro-angiogenic receptors and even to angiogenic inhibitors, originating an intricate network of interaction, the so called "angiogenesis glycomic interactome". The decoding of the angiogenesis glycomic interactome, achievable by a systematic study of the interactions occurring among angiogenic modulators and sugars, may help to design novel antiangiogenic therapies with implications in the cure of angiogenesis-dependent diseases.

A prospective comparison of 3 approved systems for autologous bone marrow concentration demonstrated nonequivalency in progenitor cell number and concentration

OBJECTIVES

To evaluate the efficacy of 3 commercially available systems: the Harvest SmartPReP 2 BMAC, Biomet BioCUE, and Arteriocyte Magellan systems. We compared the number and concentration of progenitor cells achieved both before and after centrifugation and the percentage of progenitor cells salvaged after centrifugation.

METHODS

Forty patients, mean age 47 ± 18 years (range: 18-92 years, 19 male/21 female) were prospectively consented for bilateral iliac crest aspiration. The first 20 aspirations compared the Harvest and Biomet systems, and based on those results, the second 20 compared the Harvest and Arteriocyte systems. One system was randomly assigned to each iliac crest. Each system's unique marrow acquisition process and centrifugation mechanism was followed. Samples for analysis were taken both immediately before the marrow was put into the centrifugation system (after acquisition), and after centrifugation. The number of progenitor cells in each sample was estimated by counting the connective tissue progenitors (CTPs).

RESULTS

The Harvest system achieved a significantly greater number and concentration of CTPs both before and after centrifugation when compared to the Biomet system. There was no difference in the percent yield of CTPs after centrifugation. There was no significant difference in the number and concentration of CTPs between the Harvest and Arteriocyte systems before centrifugation, but the Harvest system had a significantly greater number and concentration of CTPs after centrifugation. The Harvest system also had a significantly higher percent yield of CTPs after centrifugation compared with the Arteriocyte system.

CONCLUSIONS

The Harvest system resulted in a greater CTP number and concentration after centrifugation when compared with the Biomet and Arteriocyte systems and may thus provide increased osteogenic and chondrogenic capacity.

The adipogenic potential of various extracellular matrices under the influence of an angiogenic growth factor combination in a mouse tissue engineering chamber

The extracellular matrix (ECM) Matrigel™ has frequently and successfully been used to generate new adipose tissue experimentally, but is unsuitable for human application. This study sought to compare the adipogenic potential of a number of alternative, biologically derived or synthetic ECMs with potential for human application, with and without growth factors and a small fat autograft. Eight groups, with six severe combined immunodeficient (SCID) mice per group, were created with bilateral chambers (silicone tubes) implanted around the epigastric vascular pedicle, with one chamber/animal containing a 5mg fat autograft. Two animal groups were created for each of four ECMs (Matrigel™, Myogel, Cymetra® and PuraMatrix™) which filled the bilateral chambers. One group/ECM had no growth factors added to chambers whilst the other group had growth factors (GFs) (vascular endothelial growth factor-A (VEGF-A) plus fibroblast growth factor-2 (FGF-2) plus platelet-derived growth factor-BB (PDGF-BB)) added to both chambers. At 6weeks, chamber tissue was morphometrically assessed for percent and absolute adipose tissue volume. Overall, the triple GF regime significantly increased percent(∗) and absolute(#) adipose tissue volume (p<0.0005(∗#)) compared to chambers without triple GF treatment. The fat autograft also significantly increased percent (p<0.0005) and absolute (p<0.011) adipose tissue volume. Cymetra® (human collagen) constructs yielded the largest total tissue and absolute adipose tissue volume. We found that the pro-angiogenic FGF-2, VEGF-A and PDGF-BB combination in ECMs of synthetic and biological origin produced an overall significantly increased adipose tissue volume at 6weeks and may have clinical application, particularly with Cymetra.

Organization of the neuroepithelial actin cytoskeleton is regulated by heparan sulfation during neurulation

Heparan sulfate and cytoskeletal actin microfilaments have both been shown to be important regulators of neural tube closure during embryonic development. To determine the functional relationship of these two molecules in formation of the spinal neural tube, we cultured ARC mouse embryos at embryonic day E8.5 in the presence of chlorate, a competitive inhibitor of glycosaminoglycan sulfation, and examined the effects on organization of actin microfilaments in the neuroepithelium. Compared against embryos cultured under control conditions, chlorate-treated embryos had shortened posterior neuropore, a loss of median hinge point formation and increased bending at the paired dorsolateral hinge points. Furthermore, apical organization of actin microfilaments in the neuroepithelial cells was absent, and this was associated with convex bending of the neuroepithelium. The results suggest that heparan sulfate is an important determinant of cytoskeletal actin organization during spinal neurulation, and that its biological action is dependent on sulfation of the heparan molecule.

HSULF-1 inhibits ERK and AKT signaling and decreases cell viability in vitro in human lung epithelial cells

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) modulate the binding and activation of signaling pathways of specific growth factors, such as fibroblast growth factor-2 (FGF-2). Human endosulfatase 1 (HSULF-1) is an enzyme that selectively removes 6-O sulfate groups from HS side chains and alter their level and pattern of sulfation and thus biological activity. It is known that HSULF-1 is expressed at low levels in some cancer cell lines and its enhanced expression can inhibit cancer cell growth or induce apoptosis, but the mechanism(s) involved has not been identified.

METHODS

HSULF-1 mRNA expression was assessed in five normal cells (primary human lung alveolar type 2 (hAT2) cells, adult lung fibroblasts (16Lu), fetal lung fibroblasts (HFL), human bronchial epithelial cells (HBE), and primary human lung fibroblasts (HLF)) and five lung cancer cell lines (A549, H292, H1975, H661, and H1703) using quantitative real time polymerase chain reaction (qRT-PCR). H292 and hAT2 cells over-expressing HSULF-1 were analyzed for cell viability, apoptosis, and ERK/Akt signaling, by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) assay, and Western Blot, respectively. Apoptosis pathway activation was confirmed by PCR array in hAT2, H292, and A549 cells.

RESULTS

HSULF-1 was expressed at a significantly lower level in epithelial cancer cell lines compared to normal cells. Infection with recombinant adenovirus for HSULF-1 over-expression resulted in decreased cell viability in H292 cells, but not in normal hAT2 cells. HSULF-1 over-expression induced apoptosis in H292 cells, but not in hAT2 cells. In addition, apoptosis pathways were activated in both H292 and A549 cells, but not in hAT2 cells. HSULF-1 over-expression reduced ERK and Akt signaling activation in H292 cells, which further demonstrated its inhibitory effects on signaling related to proliferation.

CONCLUSIONS

These results indicate that HSULF-1 is expressed at lower levels in H292 lung cancer cells than in normal human alveolar cells and that its over-expression reduced cell viability in H292 cells by inducing apoptotic pathways, at least in part by inhibiting ERK/Akt signaling. We hypothesize that HSULF-1 plays important roles in cancer cells and functions to modify cell signaling, inhibit cancer proliferation, and promote cancer cell death.

Protein and mineral composition of osteogenic extracellular matrix constructs generated with a flow perfusion bioreactor

This study investigated the temporal composition of an osteogenic extracellular matrix construct generated by culturing mesenchymal stem cells in an electrospun biodegradable poly(ε-caprolactone) fiber mesh scaffold within a flow perfusion bioreactor. Constructs of different extracellular matrix maturities were analyzed for their protein and mineral composition at several culture durations by liquid chromatography-tandem mass spectrometry, scanning electron microscopy, energy-dispersive X-ray diffraction, X-ray diffraction, and calcium and phosphate assays. The analysis revealed that at short culture durations the cells deposited cellular adhesion proteins as a prerequisite protein network for further bone formation. At the later culture durations, the extracellular matrix was composed of collagen 1, hydroxyapatite, matrix remodeling proteins, and regulatory proteins. These results suggest that the later culture duration constructs would allow for improved bone regeneration due to the ability to mineralize and the capabilities for future remodeling.

Mid-term effect of stem cells combined with transmyocardial degradable stent on swine model of acute myocardial infarction

BACKGROUND

We aimed to confirm the mid-term results of the new method combined with bone marrow-derived mesenchymal stem cells (MSCs) transplantation and transmyocardial drilling revascularization (TMDR) with degradable stent incorporated with basic fibroblast growth factor and heparin.

METHODS

The miniswine underwent acute myocardial infarction by ligation of the left anterior descending coronary artery. Transmyocardial channels with 3.5 mm diameter (TMDR) were made by mechanical drilling in the infarction territory and basic fibroblast growth factor stents were implanted into the channels. Animals were randomly divided into the following four groups (n=6 in each): control; II: MSCs implantation; III: TMDR+stent implantation; IV: TMDR+stent implantation+MSCs implantation. Three months postoperatively, ECG-gated single photon emission computed tomography, histopathological examination, and reverse transcription-polymerase chain reaction were carried out.

RESULTS

Left ventricular ejection fraction and myocardial perfusion were significantly improved in group IV than that in other groups (P<0.05). Compared with other groups, vessel density was augmented and cell apoptosis was reduced in group IV (P<0.01). Reverse transcription-polymerase chain reaction results showed that the expression levels of von Willebrand factor, transforming growth factor-beta3, vascular endothelial growth factor, and interleukin-1beta were much higher in group IV than that in other groups (P<0.05).

CONCLUSION

Three months after operation, MSCs transplantation combined with TMDR and degradable stent significantly improved cardiac function, enhanced neovascular density, reduced infarcted size, improved ventricular remodeling, and reduced cardiac myocyte apoptosis, and therefore provides strong information for clinical trial.

Proteomic analysis of potential keratan sulfate, chondroitin sulfate A, and hyaluronic acid molecular interactions

PURPOSE

Corneal stroma extracellular matrix (ECM) glycosaminoglycans (GAGs) include keratan sulfate (KS), chondroitin sulfate A (CSA), and hyaluronic acid (HA). Embryonic corneal keratocytes and sensory nerve fibers grow and differentiate according to chemical cues they receive from the ECM. This study asked which of the proteins that may regulate keratocytes or corneal nerve growth cone immigration interact with corneal GAGs.

METHODS

Biotinylated KS (bKS), CSA (bCSA), and HA (bHA) were prepared and used in microarray protocols to assess their interactions with 8268 proteins and a custom microarray of 85 extracellular epitopes of nerve growth-related proteins. Surface plasmon resonance (SPR) was performed with bKS and SLIT2, and their ka, kd, and KD were determined.

RESULTS

Highly sulfated KS interacted with 217 microarray proteins, including 75 kinases, several membrane or secreted proteins, many cytoskeletal proteins, and many nerve function proteins. CSA interacted with 24 proteins, including 10 kinases and 2 cell surface proteins. HA interacted with 6 proteins, including several ECM-related structural proteins. Of 85 ECM nerve-related epitopes, KS bound 40 proteins, including SLIT, 2 ROBOs, 9 EPHs, 8 Ephrins (EFNs), 8 semaphorins (SEMAs), and 2 nerve growth factor receptors. CSA bound nine proteins, including ROBO2, 2 EPHs, 1 EFN, two SEMAs, and netrin 4. HA bound no ECM nerve-related epitopes. SPR confirmed that KS binds SLIT2 strongly. The KS core protein mimecan/osteoglycin bound 15 proteins.

CONCLUSIONS

Corneal stromal GAGs bind, and thus could alter the availability or conformation of, many proteins that may influence keratocyte and nerve growth cone behavior in the cornea.

A new transmyocardial degradable stent combined with growth factor, heparin, and stem cells in acute myocardial infarction

AIMS

We developed a new method-transmyocardial drilling revascularization (TMDR) with absorbable stent incorporated with basic fibroblast growth factor (bFGF) and heparin. The present study tested the effect of this method with transplantation of bone marrow-derived stem cells (BMSCs) in acute myocardial infarction.

METHODS AND RESULTS

Infarction was produced in mini-swine by ligating the left anterior descending (LAD) coronary artery. TMDR of 3.0 mm in diameter was made by mechanical drilling in the infarcted area. The animals that had LAD ligation were divided into six groups according to the procedures followed (n = 6 in each): control; T (TMDR); C (cell implantation); TS (TMDR+stent implantation); TC (TMDR+cell implantation); TSC (TMDR+stent implantation+cell implantation). Left ventricular (LV) function, myocardial perfusion, vascular density, and histological and morphological analyses were evaluated pre-operatively and at 30 min and 6 weeks post-operatively. Six weeks after operation, the above indices were significantly better in the TSC group than in other groups (P < 0.001 compared with the control group, and P < 0.05 or 0.01 compared with the TS and TC groups), although TS and TC also showed better results than the control group (P < 0.05).

CONCLUSION

We have demonstrated in a pig model that an intramyocardial stent implanted with slow release of bFGF, heparin, and BMSC transplantation may significantly increase LV function, cardiac blood flow, and vascular density. Therefore, the present study may provide a new method for the surgical treatment of myocardial infarction.

Nonviral delivery of basic fibroblast growth factor gene to bone marrow stromal cells

Basic fibroblast growth factor (bFGF) is capable of stimulating osteogenic differentiation of preosteoblast cells in vitro and new bone tissue deposition in vivo. Delivering the gene for the protein, rather than the protein itself, is considered advantageous for bone repair since gene delivery obviates the need to produce the protein in pharmaceutical quantities. To explore the feasibility of bFGF gene delivery by nonviral methods, we transfected primary rat bone marrow stromal cells (BMSC) using cationic polymers (polyethylenimine and poly(L-lysine)-palmitic acid) in vitro. After delivering a bFGF-expression plasmid (pFGF2-IRES-AcGFP) to BMSC, the presence of bFGF in culture supernatants was detected by a commercial ELISA. As much as 0.3 ng bFGF/10(6) cells/day was obtained from the BMSC under optimal conditions. This secretion rate was approximately 100-fold lower than the secretion obtained from immortal, and easy-to-transfect, human 293T cells. These data suggest the feasibility of modifying BMSC with nonviral delivery systems for bFGF expression, but also highlight the need for substantial improvement in transfection rate for an effective therapy.

DSD-1-Proteoglycan/Phosphacan and Receptor Protein Tyrosine Phosphatase-Beta Isoforms during Development and Regeneration of Neural Tissues

Interactions between neurons and glial cells play important roles in regulating key events of development and regeneration of the CNS. Thus, migrating neurons are partly guided by radial glia to their target, and glial scaffolds direct the growth and directional choice of advancing axons, e.g., at the midline. In the adult, reactive astrocytes and myelin components play a pivotal role in the inhibition of regeneration. The past years have shown that astrocytic functions are mediated on the molecular level by extracellular matrix components, which include various glycoproteins and proteoglycans. One important, developmentally regulated chondroitin sulfate proteoglycan is DSD-1-PG/phosphacan, a glial derived proteoglycan which represents a splice variant of the receptor protein tyrosine phosphatase (RPTP)-beta (also known as PTP-zeta). Current evidence suggests that this proteoglycan influences axon growth in development and regeneration, displaying inhibitory or stimulatory effects dependent on the mode of presentation, and the neuronal lineage. These effects seem to be mediated by neuronal receptors of the Ig-CAM superfamily.

Glucose modulates basement membrane fibroblast growth factor-2 via alterations in endothelial cell permeability

The effects of glucose extremes on vascular physiology and endothelial cell function have been examined across a range of time scales. Not unexpectedly, chronic glucose exposure induces long term tissue effects. Yet short term exposure can also impose lasting consequences. The persistence of vascular pathology after euglycemic restoration further suggests a glucose exposure memory. Slow turnover reservoirs such as basement membrane are candidates for prolongation of acute events. We hypothesized that glucose-induced vascular dysfunction is related to altered vasoactive compound handling within the endothelial cell-basement membrane co-regulatory unit. Endothelial cell basement membrane-associated fibroblast growth factor-2 increased linearly with culture glucose within days of elevated glucose exposure. Surprisingly, basement membrane fibroblast growth factor-2 binding kinetics remained unchanged. The glucose-induced increase in basement membrane fibroblast growth factor-2 was instead related to enhanced endothelial cell fibroblast growth factor-2 release and permeability. Cellular fibroblast growth factor-2 release occurred concomitant with apoptosis but was not blocked by caspase inhibitors. These data suggest that release was associated with sub-lethal early apoptotic cell membrane damage, perhaps related to reactive oxygen species formation. High glucose basement membrane in turn enhanced endothelial cell proliferation in a fibroblast growth factor-2-dependent manner. We now show that glucose-induced alterations in endothelial cell function promote changes in basement membrane composition, and these changes further affect endothelial cell function. These data highlight the interrelationship of cell and basement membrane in pathological conditions such as hyperglycemia. These phenomena may explain long term effects on the endothelium of short term exposure to glucose extremes.

Basic fibroblast growth factor controls migration in human mesenchymal stem cells

Little is known about the migration of mesenchymal stem cells (MSCs). Some therapeutic approaches had demonstrated that MSCs were able to regenerate injured tissues when applied from different sites of application. This implies that MSCs are not only able to migrate but also that the direction of migration is controlled. Factors that are involved in the control of the migration of MSCs are widely unknown. The migratory ability of isolated MSCs was tested in different conditions. The migratory capability was examined using Boyden chamber assay in the presence or absence of basic fibroblast growth factor (bFGF), erythropoietin, interleukin-6, stromal cell-derived factor-beta, and vascular endothelial growth factor. bFGF in particular was able to increase the migratory activity of MSCs through activation of the Akt/protein kinase B (PKB) pathway. The results were supported by analyzing the orientation of the cytoskeleton. In the presence of a bFGF gradient, the actin filaments developed a parallelized pattern that was strongly related to the gradient. Surprisingly, the influence of bFGF was not only an attraction but also routing of MSCs. The bFGF gradient experiment showed that low concentrations of bFGF lead to an attraction of the cells, whereas higher concentrations resulted in repulsion. This ambivalent effect of bFGF provides the possibility to a purposeful routing of MSCs.

Regulation, function and clinical significance of heparanase in cancer metastasis and angiogenesis

Heparanase is an endoglycosidase which cleaves heparan sulfate (HS) and hence participates in degradation and remodeling of the extracellular matrix (ECM). Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an invasive phenotype in experimental animals. The enzyme also releases angiogenic factors from the ECM and thereby induces an angiogenic response in vivo. Heparanase upregulation correlates with increased tumor vascularity and poor post-operative survival of cancer patients. Heparanase is synthesized as a 65 kDa inactive precursor that undergoes proteolytic cleavage, yielding 8 and 50 kDa protein subunits that heterodimerize to form an active enzyme. Human heparanase is localized primarily within late endosomes and lysosomes and occasionally on the cell surface and within the cell nucleus. Transcriptional activity of the heparanase promoter is stimulated by demethylation, early growth response 1 (EGR1) transcription factor, estrogen, inflammatory cytokines and inactivation of p53. N-acetylated glycol-split species of heparin as well as siRNA heparanase gene silencing inhibit tumor metastasis and angiogenesis in experimental models. These observations and the unexpected identification of a single functional heparanase, suggest that the enzyme is a promising target for anti-cancer and anti-inflammatory drug development. Heparanase exhibits also non-enzymatic activities, independent of its involvement in ECM degradation and changes in the extracellular microenvironment. For example, cell surface expression of heparanase elicits a firm cell adhesion, reflecting an involvement in cell-ECM interaction. Heparanase enhances Akt signaling and stimulates PI3K- and p38-dependent endothelial cell migration and invasion. It also promotes VEGF expression via the Src pathway. The enzyme may thus activate endothelial cells and elicits angiogenic and survival responses. Studies with heparanase over-expressing transgenic mice revealed that the enzyme functions in normal processes involving cell mobilization, HS turnover, tissue vascularization and remodeling. In this review, we summarize the current status of heparanase research, emphasizing molecular and cellular aspects of the enzyme, including its mode of processing and activation, control of heparanase gene expression, enzymatic and non-enzymatic functions, and causal involvement in cancer metastasis and angiogenesis. We also discuss clinical aspects and strategies for the development of heparanase inhibitors.

pH-specific sequestration of phosphoglucose isomerase/autocrine motility factor by fibronectin and heparan sulphate

Phosphoglucose isomerase (PGI) is a glycolytic enzyme that moonlights as a cytokine under the aliases autocrine motility factor (AMF), neuroleukin and maturation factor. The cytokine function of PGI/AMF targets multiple cell types however mechanisms that regulate and sequester this ubiquitous, circulating cytokine remain largely unidentified. PGI/AMF is shown here to exhibit fibronectin (FN)-dependent cell surface association at both neutral and acid pH. Direct PGI/AMF binding to FN and fluorescence resonance energy transfer (FRET) between PGI/AMF and FN were detected only at pH 5. At neutral pH, the interaction of PGI/AMF with FN is receptor-mediated requiring prior clathrin-dependent endocytosis. PGI/AMF and FN do not co-internalize and PGI/AMF undergoes a second round of endocytosis upon recycling to the plasma membrane indicating that recycling PGI/AMF receptor complexes associate with FN fibrils. Heparan sulphate does not affect cell association of PGI/AMF at neutral pH but enhances the FN-independent cell surface association of PGI/AMF at acid pH identifying two distinct mechanisms for PGI/AMF sequestration under acidic conditions. However, only PGI/AMF sequestration by FN at acid pH was able to stimulate cell motility upon pH neutralization identifying FN as a pH-dependent cytokine trap for PGI/AMF. The multiple ways of cellular association of PGI/AMF may represent acquired mechanisms to regulate and harness the cytokine function of PGI/AMF.

Structurally different RGTAs modulate collagen-type expression by cultured aortic smooth muscle cells via different pathways involving fibroblast growth factor-2 or transforming growth factor-beta1

We have engineered polymers called ReGeneraTing Agents (RGTAs), which mimic the protecting and potentiating properties of heparan sulfates toward heparin-binding growth factors (HBGF). RGTAs have been shown to optimize cell growth and regulate collagen production in vitro. Here, we studied relationships between RGTA structure and collagen-type expression in aortic smooth muscle cells by using two RGTAs, the carboxylmethylsulfate dextran RG-1503 and the carboxylmethylsulfate dextran with added benzylamide RG-1192. RG-1192 specifically induced a fivefold decrease in collagen III synthesis. This effect was abolished by FGF-2 neutralizing antibody. RG-1192 and FGF-2 acted synergistically to decrease collagen III. RG-1192 was more effective than heparin in this process. RG-1192 increased the pericellular localization of FGF-2 and protected FGF-2 from proteolysis. Surface plasmon resonance analysis indicated a Kd of 15.7 nM for the RG-1192/FGF-2 interaction (10.6 nM for the heparin/FGF-2 interaction). The structurally different RG-1503 (without benzylamide) did not interact with FGF-2 and worked synergistically with TGF-beta1 to specifically induce a twofold increase in collagen V. RGTAs with different structures exert different modulating effects on the collagen phenotype. Selection of appropriate RGTAs, which had been shown to enhance in vivo tissue repair, may provide a mean of correcting collagen abnormalities in vascular disorders and more generally in fibrotic diseases.

A glycopolymer chaperone for fibroblast growth factor-2

Mono- and disaccharide-containing glycopolymers were synthesized by cyanoxyl-mediated polymerization of acrylamide with acrylate-derivatized mono- and disaccharides. We demonstrate that a glycopolymer bearing pendant, fully sulfated lactose units effectively replaces heparin and heparan sulfate as a molecular chaperone for fibroblast growth factor-2 (FGF-2). Specifically, a compound was identified that protects FGF-2 from proteolytic, acid, and heat-induced degradation, while selectively promoting growth factor and receptor dimerization. Significantly, the capacity of this heparin-mimic to promote an FGF-2 specific proliferative cell response was confirmed and suggests potential applications for this compound and related derivatives in areas related to therapeutic angiogenesis.

Heparin affects signaling pathways stimulated by fibroblast growth factor-1 and -2 in type II cells

Undersulfation of the basement membrane matrix of alveolar type II (AT2) cells compared with that of neighboring type I cells is believed to account for some of the known morphological and functional differences between these pneumocytes. Heparin, a model for sulfated components of basement membrane matrices, is known to inhibit fibroblast growth factor (FGF)-2-stimulated DNA synthesis as well as gene expression of FGF-2 and its receptor in AT2 cells. To determine whether these end points result from specific effects of heparin on FGF-related signaling pathways, isolated rat AT2 cells were treated with 100 ng/ml FGF-1 or FGF-2 in the presence of up to 500 microg/ml heparin. In addition, experiments were done on cells grown in the presence of 20 mM sodium chlorate (sulfation inhibitor). High-dose heparin reduced FGF-1- or FGF-2-stimulated phosphorylation of mitogen-activated protein kinase kinases (MEK1/2), p44/42 mitogen-activated protein kinases (MAPK/ERK1/2), stress-activated protein kinase/c-Jun NH(2)-terminal kinase, Akt/protein kinase B, and p90(RSK). FGF-2-stimulated signaling was more sensitive to heparin's effects than was signaling stimulated by FGF-1. Heparin had an additive effect on the reduced [(3)H]thymidine incorporation in FGF-2-treated AT2 cells caused by inhibition of the MEK/ERK pathway by the MEK inhibitor PD-98059. The data suggest that heparin's known capacity to alter DNA synthesis and, possibly, other biological end points is realized via cross talk between multiple signaling pathways.

Heparin inhibits DNA synthesis and gene expression in alveolar type II cells

Responses of isolated type II alveolar cells to fibroblast growth factors (FGF) have been shown to be sensitive to the level of sulfation in extracellular matrix (ECM) substrata. These observations may reflect the specific in situ distribution and level of sulfation of ECM within the alveolar basement membranes (ABM) associated with type II cells. The goal of this study was to determine if the model sulfated ECM heparin modified DNA synthesis and gene expression by type II cells in a concentration dependent-manner. Isolated rat type II cells were exposed to different concentrations of heparin (0.005-500 micro g/ml) in serum-free medium for 1-3 d with or without FGF-1 or FGF-2. The effects of heparin were examined by [(3)H]thymidine incorporation into DNA, total cell protein, cell number, and selected gene expression. Results indicated that heparin inhibited [(3)H]thymidine uptake in a concentration-dependent manner. Total protein, cell number, and FGF-2 protein expression and mRNA of FGF-1, -2, and FGF receptor-2 detected by reverse transcriptase-polymerase chain reaction were decreased by heparin. These results demonstrate that sulfated molecules in the ABM may play important regulatory role(s) in selected type II cell activities during normal cell homeostasis, turnover, and repair after lung injury.

Phosphorylation of STAT-3 in response to basic fibroblast growth factor occurs through a mechanism involving platelet-activating factor, JAK-2, and Src in human umbilical vein endothelial cells. Evidence for a dual kinase mechanism

Platelet-activating factor (PAF) is a potent proinflammatory phospholipid with multiple pathological and physiological effects. We have shown that basic fibroblast growth factor (bFGF) supplementation induces rapid proliferation of human umbilical vein endothelial cells (HUVEC), which is reduced upon removal of bFGF or by bFGF immunoneutralization. The PAF receptor antagonist LAU-8080 inhibited bFGF-stimulated HUVEC proliferation, indicating the involvement of PAF in the bFGF-mediated signaling of HUVEC. Although FGF receptor phosphorylation was not affected by LAU-8080, the bFGF-mediated prolonged phosphorylation, and activation of Erk-1 and -2 were attenuated. Phosphorylation of STAT-3 was observed in the presence of PAF or bFGF, which was attenuated by PAFR antagonists. PAF-induced STAT-3 phosphorylation observed in HUVEC pretreated with either Src inhibitor PP1 or JAK-2 inhibitor AG-490 indicated (i) immediate (1 min) phosphorylation of STAT-3 is dependent on Src, (ii) JAK-2-dependent STAT-3 phosphorylation occurs after the delayed (30 min) PAF exposure, and (iii) prolonged (60 min) STAT-3 phosphorylation may be either through Src and/or JAK-2. Attenuation of the STAT-3 phosphorylation by the PAFR antagonists indicated signaling through the PAF receptor. Taken together, these findings suggest the production of PAF is important for bFGF-mediated signaling and that a dual kinase mechanism is involved in the PAF-mediated signal transduction cascade.

Heparan sulphate proteoglycans and spinal neurulation in the mouse embryo

Heparan sulphate proteoglycans have been implicated in the binding and presentation of several growth factors to their receptors, thereby regulating cellular growth and differentiation. To investigate the role of heparan sulphate proteoglycans in mouse spinal neurulation, we administered chlorate, a competitive inhibitor of glycosaminoglycan sulphation, to cultured E8.5 embryos. Treated embryos exhibit accelerated posterior neuropore closure, accompanied by suppression of neuroepithelial bending at the median hinge point and accentuated bending at the paired dorsolateral hinge points of the posterior neuropore. These effects appear specific, as they can be prevented by addition of heparan sulphate to the culture medium, whereas heparitinase-treated heparan sulphate and chondroitin sulphate are ineffective. Both N- and O-sulphate groups appear to be necessary for the action of heparan sulphate. In situ hybridisation analysis demonstrates a normal distribution of sonic hedgehog mRNA in chlorate-treated embryos. By contrast, patched 1 transcripts are abnormally abundant in the notochord, and diminished in the overlying neuroepithelium, suggesting that sonic hedgehog signalling from the notochord may be perturbed by inhibition of heparan sulphation. Together, these results demonstrate a regulatory role for heparan sulphate in mouse spinal neurulation.

Neural stem cells and regulation of cell number

Normal CNS development involves the sequential differentiation of multipotent stem cells. Alteration of the numbers of stem cells, their self-renewal ability, or their proliferative capacity will have major effects on the appropriate development of the nervous system. In this review, we discuss different mechanisms that regulate neural stem cell differentiation. Proliferation signals and cell cycle regulators may regulate cell kinetics or total number of cell divisions. Loss of trophic support and cytokine receptor activation may differentially contribute to the induction of cell death at specific stages of development. Signaling from differentiated progeny or asymmetric distribution of specific molecules may alter the self-renewal characteristics of stem cells. We conclude that the final decision of a cell to self-renew, differentiate or remain quiescent is dependent on an integration of multiple signaling pathways and at each instant will depend on cell density, metabolic state, ligand availability, type and levels of receptor expression, and downstream cross-talk between distinct signaling pathways.

Kinase insert domain receptor (KDR) extracellular immunoglobulin-like domains 4-7 contain structural features that block receptor dimerization and vascular endothelial growth factor-induced signaling

The vascular endothelial growth factor (VEGF) receptor tyrosine kinase subtype kinase insert domain receptor (KDR) contains seven extracellular Ig-like domains, of which the three most amino-terminal contain the necessary structural features required for VEGF binding. To clarify the functional role of KDR Ig-like domains 4-7, we compared VEGF-induced signaling in human embryonic kidney and porcine aortic endothelial cells expressing native versus mutant receptor proteins in which Ig-like domains 4-7, 4-6, or 7 had been deleted. Western blotting using an anti-receptor antibody indicated equivalent expression levels for each of the recombinant proteins. As expected, VEGF treatment robustly augmented native receptor autophosphorylation. In contrast, receptor autophosphorylation, as well as downstream signaling events, were VEGF-independent for cells expressing mutant receptors. (125)I-VEGF(165) bound with equal or better affinity to mutant versus native receptor, although the number of radioligand binding sites was significantly reduced because a significant percentage of mutant, but not native, receptors were localized to the cell interior. As was the case for native KDR, (125)I-VEGF(165) binding to the mutant receptors was dependent upon cell surface heparan sulfate proteoglycans, and (125)I-VEGF(121) bound with an affinity equal to that of (125)I-VEGF(165) to the native and mutant receptors. It is concluded that KDR Ig-like domains 4-7 contain structural features that inhibit receptor signaling by a mechanism that is independent of neuropilin-1 and heparan sulfate proteoglycans. We speculate that this provides a cellular mechanism for blocking unwanted signaling events in the absence of VEGF.

Regulation of urokinase/urokinase receptor interaction by heparin-like glycosaminoglycans

We show here that the interaction between the urokinase-type plasminogen activator and its receptor, which plays a critical role in cell invasion, is regulated by heparan sulfate present on the cell surface and in the extracellular matrix. Heparan sulfate oligomers showing a composition close to the dimeric repeats of heparin (glucosamine-NSO(3)(6-OSO(3))-iduronic acid(2-OSO(3))) n = 5 and n > 5, where iduronic acid may alternate with glucuronic acid, exhibit affinity for urokinase plasminogen activator and confer specificity on urokinase/urokinase receptor interaction. Cell surface clearance of heparan sulfate reduces the affinity of such interaction with a parallel decrease of specific urokinase binding in the presence of an unaltered expression of receptor. Transfection of human urokinase plasminogen activator receptor in normal Chinese hamster ovary fibroblasts and in Chinese hamster ovary cells defective for the synthesis of sulfated glycosaminoglycans results in specific urokinase/receptor interaction only in nondefective cells. Heparan sulfate/urokinase and receptor/urokinase interactions exhibit similar K(d) values. We concluded that heparan sulfate functions as an adaptor molecule that confers specificity on urokinase/receptor binding.

Inhibition of cell migration by 24-kDa fibroblast growth factor-2 is dependent upon the estrogen receptor

The single-copy gene for fibroblast growth factor-2 (FGF-2) encodes for multiple forms of the protein with molecular masses of 24, 22.5, 22, and 18 kDa. We reported previously that the 24-22-kDa FGF-2 forms inhibit the migration of endothelial and MCF-7 cells by 50% and 70%, respectively. Here we show that this inhibition of migration is mediated by the estrogen receptor (ER). We have found that depletion of the receptor in either cell line abrogates the inhibitory activity of 24-kDa FGF-2 while re-introduction of the ER into deficient cells once again promotes the inhibitory response. To determine whether exposure to 24-kDa FGF-2 resulted in the activation of the estrogen receptor, 3T3 cells were cotransfected with estrogen receptor cDNA and an estrogen regulatory element-luciferase gene reporter construct and treated with 24- and 18-kDa FGF-2. The high molecular weight form stimulated luciferase activity 5-fold while 18-kDa FGF-2 at the same concentration had no effect. Treatment of ER-positive MCF-7 cells transfected with the reporter construct only showed the same results. Inclusion of the pure estrogen antagonist ICI 182,780 blocked the increase in luciferase activity by 24-kDa FGF-2, further indicating that the response was estrogen receptor dependent. Expression of dominant negative FGF receptor 1 inhibited ER activation, indicating that this was the cell surface receptor mediating the effect. Although growth factor-dependent activation of the ER was reported to require mitogen-activated protein kinase-induced phosphorylation at Ser(118) in COS and HeLa cells, this mechanism is not involved with the activation by 24-kDa FGF-2. These results suggest that the addition of 55 amino acids to the amino-terminal end of 18-kDa FGF-2 by alternative translation alters FGF-2 function and allows for the activation of a second signaling pathway involving the estrogen receptor.

Matrix localization of tissue factor pathway inhibitor-2/matrix-associated serine protease inhibitor (TFPI-2/MSPI) involves arginine-mediated ionic interactions with heparin and dermatan sulfate: heparin accelerates the activity of TFPI-2/MSPI toward plasmin

Human tissue factor pathway inhibitor-2 (TFPI-2)/matrix-associated serine protease inhibitor (MSPI), a Kunitz-type serine protease inhibitor, inhibits plasmin, trypsin, chymotrypsin, plasma kallikrein, cathepsin G, and factor VIIa-tissue factor complex. The mature protein has a molecular mass of 32-33 kDa, but exists in vivo as two smaller, underglycosylated species of 31 and 27 kDa. TFPI-2/MSPI triplet is synthesized and secreted by a variety of cell types that include epithelial, endothelial, and mesenchymal cells. Because the majority (75-90%) of TFPI-2/MSPI is associated with the extracellular matrix (ECM), we examined which components of the ECM bind TFPI-2/MSPI. We found that TFPI-2/MSPI bound specifically to heparin and dermatan sulfate. Interaction of these two glycosaminoglycans (GAGs) with TFPI-2/MSPI involved one or more common protein domains, as evidenced by cross-competition experiments. However, binding affinity for TFPI-2/MSPI with heparin was 250-300 times greater than that for TFPI-2/MSPI with dermatan sulfate. Binding of TFPI-2/MSPI to GAGs was inhibited by NaCl or arginine but not by glucose, mannose, galactose, 6-aminohexanoic acid, or urea, suggesting that arginine-mediated ionic interactions participate in the GAG binding of TFPI-2/MSPI. This supposition was supported by the observation that only NaCl or arginine could elute the TFPI-2/MSPI protein triplet from an ECM derived from human dermal fibroblasts. Reduced TFPI-2/MSPI did not bind to heparin, suggesting that proper disulfide pairings and conformation are essential for matrix binding. To determine whether heparin modulates the activity of TFPI-2/MSPI, we determined the rate of inhibition of plasmin by the inhibitor with and without heparin and found that TFPI-2/MSPI is more active in the presence of heparin. Collectively, our results demonstrate that conformation-dependent arginine-mediated ionic interactions are responsible for the TFPI-2/MSPI triplet binding to fibroblast ECM, heparin, and dermatan sulfate and that heparin augmented the rate of inhibition of plasmin by TFPI-2/MSPI.

Inducible expression of the cell surface heparan sulfate proteoglycan syndecan-2 (fibroglycan) on human activated macrophages can regulate fibroblast growth factor action

Monocyte/macrophages play important roles in regulating tissue growth and angiogenesis through the controlled release of heparin-binding growth factors such as fibroblast growth factor (FGF), vascular endothelial growth factor, and heparin binding epidermal growth factor. The action of these potent growth mediators is known to be regulated by adsorption to heparan sulfate proteoglycans (HSPGs) on the surface and within the extracellular matrix of other neighboring cells, which respectively promote or restrict interactions with their signal-transducing receptors on target cells. Here we report on the nature of HSPGs inducibly expressed on the surface of macrophages that confer these cells with the capacity to regulate endogenous growth factor activity. We reveal that activated human macrophages express only a single major 48-kDa cell surface HSPG, syndecan-2 (fibroglycan) as the result of de novo RNA and protein synthesis. In addition, we demonstrate this macrophage HSPG selectively binds the macrophage-derived growth factors FGF-2, vascular endothelial growth factor and heparin binding EGF and can present FGF-2 in a form that transactivates receptor-bearing BaF32 cells. These results define a novel and unique proteoglycan profile for macrophages and imply a key role for syndecan-2 in the delivery of sequestered growth factors by inflammatory macrophages for productive binding to their appropriate target cells in vivo.

Monomer complexes of basic fibroblast growth factor and heparan sulfate oligosaccharides are the minimal functional unit for cell activation

The interaction of basic fibroblast growth factor (bFGF) with heparan sulfate (HS)/heparin has been shown to strongly enhance the activity of the growth factor although the mechanism of activation is unclear. We have addressed the issue of the minimal stoichiometry of an active HS oligosaccharide.bFGF complex by chemically cross-linking the two components to form novel covalent conjugates. The cross-linking procedure produced both monomeric and dimeric bFGF. oligosaccharide complexes, which were purified to homogeneity. Dimer conjugates were shown to have been formed as a result of disulfide bridging of monomer conjugates. These monomer conjugates were subsequently found to be biologically active in a mitogenesis assay. We therefore conclude that a monomeric bFGF.oligosaccharide complex is the minimal functional unit required for mitogenic stimulation.

Heparan sulfate mediates bFGF transport through basement membrane by diffusion with rapid reversible binding

Basic fibroblast growth factor (bFGF) is a pluripotent cytokine with a wide range of target cells. Heparan sulfate binds bFGF, and this interaction has been demonstrated to protect bFGF against physical denaturation and protease degradation. The high concentrations of heparan sulfate in basement membranes have implicated these matrices as storage sites for bFGF in vivo. However, the mechanisms by which basement membranes modulate bFGF storage and release is unknown. To gain insight into these mechanisms, we have developed experimental and mathematical models of extracellular growth factor transport through basement membrane. Intact Descemet's membranes isolated from bovine corneas were mounted within customized diffusion cells and growth factor transport was measured under a variety of conditions that decoupled the diffusion process from the heparan sulfate binding phenomenon. Transport experiments were conducted with bFGF and interleukin 1beta. In addition, bFGF-heparan sulfate binding was disrupted in diffusion studies with high ionic strength buffer and buffers containing protamine sulfate. Transport of bFGF was enhanced dramatically when heparan sulfate binding was inhibited. This process was modeled as a problem of diffusion with fast reversible binding. Experimental parameters were incorporated into a mathematical model and independent simulations were run that showed that the experimental data were accurately predicted by the mathematical model. Thus, this study indicated that basement membranes function as dynamic regulators of growth factor transport, allowing for rapid response to changing environmental conditions. The fundamental principles controlling bFGF transport through basement membrane that have been identified here might have applications in understanding how growth factor distribution is regulated throughout an organism during development and in the adult state.

Dual activities of 22-24 kDA basic fibroblast growth factor: inhibition of migration and stimulation of proliferation

Basic fibroblast growth factor (FGF2) is synthesized as four isoforms with molecular weights of 24, 22.5, 22, and 18 kDa, with each of the three higher molecular weight forms (hmwFGF2) produced by the initiation of translation at one of three upstream CUG codons. We have shown that bovine arterial endothelial cells export the high molecular weight forms of FGF2 (hmwFGF2) in a 17beta-estradiol-dependent manner (Piotrowicz et al., 1997, J Biol Chem 272:7042-7047). To determine whether the hmwFGF2 forms affected cell behavior after release, we evaluated the effect of recombinant hmwFGF2 on the growth and migration of endothelial cells and mammary carcinoma cells (MCF-7). Treatment with the recombinant protein resulted in the inhibition of endothelial cell migration by 45% and MCF-7 cell migration by 70%. HmwFGF2-dependent inhibition was observed when endothelial cell migration was stimulated by 18 kDa FGF2 or vascular endothelial growth, and MCF cell migration was stimulated with insulin-like growth factor. In each case, inclusion of an antibody against the 55 amino acid amino terminal end of 24 kDa FGF2 abrogated the inhibition of migration, while antibodies to the 18 kDa FGF2 domain had no effect. When endothelial cells were cultured under conditions which promoted export of hmwFGF2, a 40% decrease in motility was observed which was reversed by the antibodies to the 24 kDa FGF2. Thus, both recombinant and endogenously produced hmw-FGF2 are capable of inhibiting migration. In contrast to the ubiquitous effect on migration, hmwFGF2 had no effect on endothelial cell growth but stimulated MCF-7 growth equally as well as the 18 kDa FGF2 (threefold). Antibodies to the 18 kDa domain of 24 kDa FGF2 blocked the growth-promoting activity of hmwFGF2, but those to the amino terminal end were ineffective. These data suggest that hmwFGF2 has dual activities, an inhibitory effect on cell migration and a growth-stimulating effect. The two activities can be localized to different parts of hmwFGF2: inhibitory activity to the amino terminal 55 amino acids (which are absent from the 18 kDa FGF2) and growth-promoting activity to the 18 kDa domain. Therefore, the ratio of hmwFGF2 and 18 kDa FGF2 in the extracellular space may provide a mechanism of control for angiogenesis and mammary tumor development.

Role of heparan sulphate proteoglycans in the regulation of human lactoferrin binding and activity in the MDA-MB-231 breast cancer cell line

We previously demonstrated that lactoferrin increases breast cell sensitivity to natural killer cell cytotoxicity whereas haematopoietic cells are unaffected by lactoferrin. It has been described that lactoferrin binds to various glycosaminoglycans. Compared to haematopoietic cells, breast cancer cells and particularly the breast cell line MDA-MB-231, possess a high level of proteoglycans. Scatchard analysis of 125I-lactoferrin binding to MDA-MB-231 cells revealed the presence of two classes of binding sites: a low affinity site with a Kd of about 700 nM and 3.9 x 10(6) sites and a higher affinity class with a Kd of 45 nM and 2.9 x 10(5) sites per cell. To investigate the potential regulation of lactoferrin activity by proteoglycans expressed on the MDA-MB-231 cells, we treated these cells with glycosaminoglycan-degrading enzymes or sodium chlorate, a metabolic inhibitor of proteoglycan sulphation. We showed that chondroitinase treatment has no effect, while heparinase or chlorate treatment significantly reduces both the binding of lactoferrin to cell surface sulphated molecules such as heparan sulphate proteoglycans (HSPG) and the affinity of lactoferrin for the higher affinity binding sites. The modulation of the lactoferrin binding was correlated with a decrease in lactoferrin activities on both MDA-MB-231 cell sensitisation to lysis and proliferation. Taken together, these results suggest that the presence of adequately sulphated molecules, in particular HSPG, is important for lactoferrin interaction and activity on the breast cancer cells MDA-MB-231.

The DSD-1 carbohydrate epitope depends on sulfation, correlates with chondroitin sulfate D motifs, and is sufficient to promote neurite outgrowth

The neural chondroitin sulfate (CS) proteoglycan (PG) DSD-1-PG was originally identified with the monoclonal antibody (mAb) 473HD. It promotes neurite outgrowth of hippocampal neurons when coated as a substrate in the presence of polycations. This effect is inhibited by mAb 473HD that specifically recognizes the DSD-1 epitope. The DSD-1 epitope is also detectable in CS-C and CS-D preparations from shark cartilage but not in other chondroitin sulfates that are structurally related and differ in their sulfation patterns. Non-sulfated DSD-1-PG and chemically desulfated CS-D were not recognized by mAb 473HD, suggesting that the DSD-1 epitope depends on sulfation. It was possible to enrich DSD-1 epitope-bearing carbohydrates and D disaccharide units from CS-C and CS-D preparations on a mAb 473HD affinity matrix. This indicates that the DSD-1 epitope represents a distinct glycosaminoglycan structure containing D units. The analysis of glycosaminoglycan digestion products by high pressure liquid chromatography revealed that DSD-1-PG preparations contain a unique D disaccharide unit as well as an A, a C, and a non-sulfated disaccharide unit. In neurite outgrowth assays with hippocampal neurons, substrate-bound CS-D promoted neurite outgrowth, whereas CS-A, CS-B, or CS-C did not. This effect of CS-D was inhibited by mAb 473HD. DSD-1 epitope-enriched fractions obtained from CS-D and CS-C promoted neurite outgrowth, whereas CS-C had no such effect prior to enrichment on the mAb 473HD matrix. Based on these findings we conclude that the DSD-1 epitope by itself is sufficient to promote neurite outgrowth and that this activity is possibly associated with D motifs.

Heparan sulfate oligosaccharides require 6-O-sulfation for promotion of basic fibroblast growth factor mitogenic activity

The interaction of heparan sulfate (HS) with basic fibroblast growth factor (bFGF) is influential in enabling the growth factor to bind to its cell surface tyrosine kinase receptor. In this study, we have investigated further the structural properties of HS required to mediate the activity of bFGF in a mitogenic assay. We have prepared a library of heparinase III-generated HS oligosaccharides fractionated by both their size (dp6-dp12) and sulfate content. The ability of these oligosaccharides to activate bFGF in a mitogenic assay was then correlated with their length and disaccharide composition. All octa- and hexasaccharide fractions tested were unable to activate bFGF. Dodeca- and decasaccharide fractions were found to contain both activating and non-activating oligosaccharides, and showed a clear correlation between total sulfate content and the level of activatory activity. Disaccharide analysis of a range of dodeca- and decasaccharide fractions showed that both activating and non-activating oligosaccharides were composed mainly of N-sulfated and IdoA(2S)-containing disaccharides. The only significant difference between activating and non-activating oligosaccharides was the content of 6-O-sulfated disaccharides, in particular the disaccharide IdoA(2S)alpha1,4GlcNSO3(6S). These results show that there is a requirement for 6-O-sulfation of N-sulfated glucosamine residues, in addition to the 2-O-sulfation of IdoA, for the promotion of bFGF mitogenic activity by naturally occurring HS oligosaccharides. Analysis of the structure-activity relationships in the dodecasaccharide fractions in particular, suggests that a minimum bFGF activation sequence exists which is dependent on the positioning of at least one 6-O-sulfate group.

New strategies for chemokine inhibition and modulation: you take the high road and I'll take the low road

Chemokines are low molecular weight cytokines that induce extravasation, chemotaxis, and activation of a wide variety of leukocytes. Members of the different chemokine families are defined by the orientation of specific critical cysteine residues, and are designated as C-X-C (e.g. interleukin-8), C-C (e.g. regulated upon activation normally T cell expressed and secreted, RANTES), or C (lymphotactin). All chemokines bind to members of a G-protein coupled serpentine receptor superfamily that span the leukocyte cell surface membrane seven times and mediate the biological activities of the individual ligands. Most chemokines possess two major binding surfaces: a high affinity site responsible for specific ligand/receptor interactions and a lower affinity site, also called the heparin-binding or glycosaminoglycan-binding domain, believed to be responsible for the establishment and presentation of chemokine gradients on the surface of endothelial cells and within the extracellular matrix. Although chemokines are clearly beneficial in wound healing, hemopoiesis, and the clearance of infectious organisms, the continued expression of chemokines is associated with chronic inflammation. Therefore, this class of cytokines are attractive targets for the creation of antagonists that abrogate one or more chemokine functions. It is envisioned that such antagonists could serve as a new class of anti-inflammatory drugs. In this commentary, we will discuss two different but related strategies for antagonizing chemokine-induced functions, namely, disruption of the low and high affinity binding sites.

The N-terminal Arg2, Arg3 and Arg4 of human lactoferrin interact with sulphated molecules but not with the receptor present on Jurkat human lymphoblastic T-cells

We previously characterized a 105 kDa receptor for human lactoferrin (hLf) on Jurkat human lymphoblastic T-cells. To delineate the role of the basic cluster Arg2-Arg3-Arg4-Arg5 of hLf in the interaction with Jurkat cells, we isolated N-terminally deleted hLf species of molecular mass 80 kDa lacking two, three or four N-terminal residues (hLf-2N, hLf-3N and hLf-4N) from native hLf that had been treated with trypsin. Native hLf bound to 102000 sites on Jurkat cells with a dissociation constant (Kd) of 70 nM. Consecutive removal of N-terminal arginine residues from hLf progressively increased the binding affinity but decreased the number of binding sites on the cells. A recombinant hLF mutant lacking the first five N-terminal residues (rhLf-5N) bound to 17000 sites with a Kd of 12 nM. The binding parameters of bovine lactoferrin (Lf) and native hLf did not significantly differ, whereas the binding parameters of murine Lf (8000 sites; Kd 30 nM) resembled those of rhLf-5N. Culture of Jurkat cells in the presence of chlorate, which inhibits sulphation, decreased the number of binding sites for both native hLf and hLf-3N but not for rhLf-5N, indicating that the hLf-binding sites include sulphated molecules. We propose that the interaction of hLf with a large number of binding sites (approx. 80000 per cell) on Jurkat cells is dependent on Arg2-Arg3-Arg4, but not on Arg5. Interaction with approx. 20000 binding sites per cell, presumably the hLf receptor, does not require the first N-terminal basic cluster of hLf. Moreover, the affinity of hLf for the latter binding site is enhanced approx. 6-fold after removal of the first basic cluster. Thus N-terminal proteolysis of hLf in vivo might serve to modulate the nature of its binding to cells and thereby its effects on cellular physiology.

Modulation of fibroblast growth factor-2 receptor binding, dimerization, signaling, and angiogenic activity by a synthetic heparin-mimicking polyanionic compound

Heparan sulfate (HS) proteoglycans play a key role in cell proliferation induced by basic fibroblast growth factor (FGF-2) and other heparin-binding growth factors. To modulate the involvement of HS, we have used a synthetic, nonsulfated polyanionic aromatic compound (RG-13577) that mimics functional features of heparin/HS. FGF-2-stimulated proliferation of vascular endothelial cells was markedly inhibited in the presence of 5-10 microg/ml compound RG-13577 (poly-4-hydroxyphenoxy acetic acid; Mr approximately 5 kD). Direct interaction between RG-13577 and FGF-2 was demonstrated by the ability of the former to compete with heparin on binding to FGF-2. RG-13577 inhibited FGF-2 binding to soluble- and cell surface-FGF receptor 1 (FGFR1). Unlike heparin, RG-13577 alone failed to mediate dimerization of FGF-2. Moreover, it abrogated heparin-mediated dimerization of FGF-2 and FGFR1, as well as FGF-2 mitogenic activity in HS-deficient F32 lymphoid cells. The antiproliferative effect of compound RG-13577 was associated with abrogation of FGF-2-induced tyrosine phosphorylation of FGFR1 and of cytoplasmic proteins involved in FGF-2 signal transduction, such as p90 and mitogen-activated protein kinase. A more effective inhibition of tyrosine phosphorylation was obtained after removal of the cell surface HS by heparinase. In contrast, tyrosine phosphorylation of an approximately 200-kD protein was stimulated by RG-13577, but not by heparin or FGF-2. RG-13577 prevented microvessel outgrowth from rat aortic rings embedded in a collagen gel. Development of nontoxic polyanionic compounds may provide an effective strategy to inhibit FGF-2-induced cell proliferation associated with angiogenesis, arteriosclerosis, and restenosis.

VEGF145, a secreted vascular endothelial growth factor isoform that binds to extracellular matrix

A vascular endothelial growth factor (VEGF) mRNA species containing exons 1-6 and 8 of the VEGF gene was found to be expressed as a major VEGF mRNA form in several cell lines derived from carcinomas of the female reproductive system. This mRNA is predicted to encode a VEGF form of 145 amino acids (VEGF145). Recombinant VEGF145 induced the proliferation of vascular endothelial cells and promoted angiogenesis in vivo. VEGF145 was compared with previously characterized VEGF species with respect to interaction with heparin-like molecules, cellular distribution, VEGF receptor recognition, and extracellular matrix (ECM) binding ability. VEGF145 shares with VEGF165 the ability to bind to the KDR/flk-1 receptor of endothelial cells. It also binds to heparin with an affinity similar to that of VEGF165. However, VEGF145 does not bind to two additional endothelial cell surface receptors that are recognized by VEGF165 but not by VEGF121. VEGF145 is secreted from producing cells as are VEGF121 and VEGF165. However, VEGF121 and VEGF165 do not bind to the ECM produced by corneal endothelial cells, whereas VEGF145 binds efficiently to this ECM. Basic fibroblast growth factor (bFGF)-depleted ECM containing bound VEGF145 induces proliferation of endothelial cells, indicating that the bound VEGF145 is active. The mechanism by which VEGF145 binds to the ECM differs from that of bFGF. Digestion of the ECM by heparinase inhibited the binding of bFGF to the ECM and released prebound bFGF, whereas the binding of VEGF145 was not affected by heparinase digestion. It therefore seems that VEGF145 possesses a unique combination of biological properties distinct from those of previously characterized VEGF species.

The biochemistry of cancer dissemination

The progression of a tumor cell from one of benign delimited proliferation to invasive and metastatic growth is the major cause of poor clinical outcome of cancer patients. Recent research has revealed that this complex process requires many components for successful dissemination and growth of the tumor cell at secondary sites. These include angiogenesis, enhanced extracellular matrix degradation via tumor and host-secreted proteases, tumor cell migration, and modulation of tumor cell adhesion. Each individual component is multifaceted and is discussed within this review with respect to historical and recent findings. The identification of components and their interrelationship have yielded new therapeutic targets leading to the development of agents that may prove effective in the treatment of cancer and its metastatic progression.

Involvement of heparan sulfate and related molecules in sequestration and growth promoting activity of fibroblast growth factor

Heparan sulfate proteoglycans (HSPGs) are ubiquitous macromolecules associated with the cell surface and extracellular matrix (ECM) of a wide range of cells of vertebrate and invertebrate tissues [1, 2]. The basic HSPG structure consists of a protein core to which several linear heparan sulfate (HS) chains are covalently attached. The polysaccharide chains are typically composed of repeating hexuronic and D-glucosamine disaccharide units that are substituted to a varying extent with N- and O-linked sulfate moieties and N-linked acetyl groups [1, 2]. Beside serving as a scaffold for the attachment of various ECM components (e.g., collagen, laminin, fibronectin), the binding of HS to certain proteins has been suggested to induce a conformational change which may lead to the exposure of novel reactive determinants or conversely stabilize an inert protein configuration [1-4]. Of particular significance is the interaction of HS with fibroblast growth factors (FGFs), mediating their sequestration, stabilization and high affinity receptor binding and signaling [3-7]. Cellular responses to FGFs may hence be modulated by metabolic inhibitors of HS synthesis and sulfation, HS-degrading enzymes, and synthetic mimetics of heparin/HS. In the present review we focus on the involvement of HS in basic FGF (bFGF) receptor binding and mitogenic activity and its modulation by species of heparin, HS, and synthetic polyanionic 'heparin-mimicking' compounds. The results are discussed in relation to the current thoughts on the dual involvement of low and high affinity receptor sites in the growth promoting and angiogenic activities of bFGF and other heparin-binding growth factors.