Quantitative proteomic analysis of fibroblast nuclear proteins after stimulation with mitogen activated protein kinase inhibiting heparan sulfate

Certain structures of heparan sulfate (HS) inhibit cell proliferation of fibroblasts. Whether this inhibition is dependent on inhibition of mitogenic signaling pathways or nuclear translocation of HS is unknown. In this study we investigated possible mechanism(s) and structural requirements by which antiproliferative glycosaminoglycans exert their effects on mitogen-activated protein kinase (MAP kinase) phosphorylation, a key intermediate in cell signaling, followed by quantitative proteomic analysis of nuclear proteins by stable isotope coded affinity tags, multidimensional chromatography and tandem mass spectrometry. Serum starved human lung fibroblasts were stimulated with serum, platelet derived growth factor (PDGF-BB) or epidermal growth factor (EGF) in the presence of structurally different glycosaminoglycans. Antiproliferative heparan sulfate with a high content of 2-O-sulfated iduronic acid (IdoA-2SO4) and heavily sulfated glucosamine, and the structurally related glycosaminoglycan heparin inhibited significantly serum stimulated MAP kinase phosphorylation, by at least 80% when stimulated by serum and HS6. We hypothesized that the inhibition of the MAP kinase pathway will have effect in the nuclear proteome. Therefore an isotope coded affinity tag (ICAT) reagent labeling of nuclear proteins and tandem mass spectrometry was applied, resulting in the identification and quantification of 206 proteins. Several nuclear proteins were found to be induced or repressed due to HS stimulation, where the repression EBNA-2 co-activator and the induction of PML protein were of special interest. These results show that heparan sulfate with high content of (IdoA-2SO4) and heavily sulfated glucosamine specifically inhibits MAP kinase activation with a subsequent change in the nuclear proteome of the fibroblast.

Antiviral activity of human lactoferrin: inhibition of alphavirus interaction with heparan sulfate

Human lactoferrin is a component of the non-specific immune system with distinct antiviral properties. We used alphaviruses, adapted to interaction with heparan sulfate (HS), as a tool to investigate the mechanism of lactoferrin's antiviral activity. Lactoferrin inhibited infection of BHK-21 cells by HS-adapted, but not by non-adapted, Sindbis virus (SIN) or Semliki Forest virus (SFV). Lactoferrin also inhibited binding of radiolabeled HS-adapted viruses to BHK-21 cells or liposomes containing lipid-conjugated heparin as a receptor analog. On the other hand, low-pH-induced fusion of the viruses with liposomes, which occurs independently of virus-receptor interaction, was unaffected. Studies involving preincubation of virus or cells with lactoferrin suggested that the protein does not bind to the virus, but rather blocks HS-moieties on the cell surface. Charge-modified human serum albumin, with a net positive charge, had a similar antiviral effect against HS-adapted SIN and SFV, suggesting that the antiviral activity of lactoferrin is related to its positive charge. It is concluded that human lactoferrin inhibits viral infection by interfering with virus-receptor interaction rather than by affecting subsequent steps in the viral cell entry or replication processes.

Heparan sulfate targets the HIV-1 envelope glycoprotein gp120 coreceptor binding site

Human immunodeficiency virus (HIV) attachment to host cells is a multi-step process that involves interaction of the viral envelope gp120 with the primary receptor CD4 and coreceptors. HIV gp120 also binds to other cell surface components, including heparan sulfate (HS), a sulfated polysaccharide whose wide interactive properties are exploited by many pathogens for attachment and concentration at the cell surface. To analyze the structural features of gp120 binding to HS, we used soluble CD4 to constrain gp120 in a specific conformation. We first found that CD4 induced conformational change of gp120, dramatically increasing binding to HS. We then showed that HS binding interface on gp120 comprised, in addition to the well characterized V3 loop, a CD4-induced epitope. This epitope is efficiently targeted by nanomolar concentrations of size-defined heparin/HS-derived oligosaccharides. Because this domain of the protein also constitutes the binding site for the viral coreceptors, these results support an implication of HS at late stages of the virus-cell attachment process and suggest potential therapeutic applications.

Structural Basis of Citrate-dependent and Heparan Sulfate-mediated Cell Surface Retention of Cobra Cardiotoxin A3

Anionic citrate is a major component of venom, but the role of venom citrate in toxicity other than its inhibitory effect on the cation-dependent action of venom toxins is poorly understood. By immobilizing Chinese hamster ovary cells in microcapillary tubes and heparin on sensor chips, we demonstrated that heparan sulfate-mediated cell retention of the major cardiotoxin (CTX) from the Taiwan cobra, CTX A3, near membrane surfaces is citrate-dependent. X-ray determination of a CTX A3-heparin hexasaccharide complex structure at 2.4 A resolution revealed a molecular mechanism for toxin retention in which heparin-induced conformational changes of CTX A3 lead to citrate-mediated dimerization. A citrate ion bound to Lys-23 and Lys-31 near the tip of loop II stabilizes hydrophobic contact of the CTX A3 homodimer at the functionally important loop I and II regions. Additionally, the heparin hexasaccharide interacts with five CTX A3 molecules in the crystal structure, providing another mechanism whereby the toxin establishes a complex network of interactions that result in a strong interaction with cell surfaces presenting heparan sulfate. Our results suggest a novel role for venom citrate in biological activity and reveal a structural model that explains cell retention of cobra CTX A3 through heparan sulfate-CTX interactions.

Human xylosyltransferase I: functional and biochemical characterization of cysteine residues required for enzymic activity

XT-I (xylosyltransferase I) is the initial enzyme in the post-translational biosynthesis of glycosaminoglycan chains in proteoglycans. To gain insight into the structure-function relationship of the enzyme, a soluble active form of human XT-I was expressed in High Five insect cells with an apparent molecular mass of 90 kDa. Analysis of the electrophoretic mobility of the protein under non-reducing and reducing conditions indicated that soluble XT-I does not form homodimers through disulphide bridges. In addition, the role of the cysteine residues was investigated by site-directed mutagenesis combined with chemical modifications of XT-I by N-phenylmaleimide. Replacement of Cys471 or Cys574 with alanine led to a complete loss of catalytic activity, indicating the necessity of these residues for maintaining an active conformation of soluble recombinant XT-I by forming disulphide bonds. On the other hand, N-phenylmaleimide treatment showed no effect on wild-type XT-I but strongly inactivated the cysteine mutants in a dose-dependant manner, indicating that seven intramolecular disulphide bridges are formed in wild-type XT-I. The inhibitory effect of UDP on the XT-I activity of C561A (Cys561-->Ala) mutant enzyme was significantly reduced compared with all other tested cysteine mutants. In addition, we tested for binding to UDP-agarose beads. The inactive mutants revealed no significantly different nucleotide-binding properties. Our study demonstrates that recombinant XT-I is organized as a monomer with no free thiol groups and strongly suggests that the catalytic activity does not depend on the presence of free thiol groups, furthermore, we identified five cysteine residues which are critical for enzyme activity.

Conditional signaling by Toll-like receptor 4

Signaling through Toll-like receptor 4 (TLR4) is thought to initiate innate and adaptive immune responses. Signaling of TLR4 is usually studied using isolated cells, which are activated by sub-nanomolar concentrations of lipopolysaccharide (LPS). However, in normal tissues, cells bearing TLR4 reside in microenvironments containing large amounts of endogenous substances that can stimulate the receptor. We developed an in vitro model system using the human cell line HEK 293 and an in vivo model using mice that have normal or that lack TLR4 receptors to study how TLR4 functions in such microenvironments. Here we report that signaling through TLR4 is strongly inhibited by intact extracellular matrix and that inhibition is abrogated and endogenous agonist(s) are liberated when the matrix is degraded. Thus, release from inhibition rather than direct stimulation by agonists such as LPS is the critical first event by which TLR4 initiates immune responses.

Protamine sulfate reduces the susceptibility of thermally injured mice to Pseudomonas aeruginosa infection

BACKGROUND

In this study, we investigated the ability of protamine sulfate, at sub-bactericidal dosing, to interfere with the in vivo virulence of Pseudomonas aeruginosa (PAO1) during burn wound infection.

MATERIALS AND METHODS

The study was conducted using the murine model of thermal injury. Preliminary experiments determined a protocol for administration of protamine sulfate that had no in vivo bactericidal effects. Based on this, the effect of local injection of protamine sulfate on the in vivo virulence of PAO1 was assessed using these parameters: (1) the percent mortality among PAO1-infected, thermally injured mice; (2) the local proliferation and spread of PAO1 within the infected burned tissue; (3) the systemic spread of PAO1 within thermally injured/infected mice; and (4) the local cytokine response elicited by PAO1 thermally injured/infected mice.

RESULTS

Injection of protamine sulfate into the thermally injured tissue of PAO1-infected/thermally injured mice significantly decreased the percent mortality and inhibited the systemic dissemination of PAO1 microorganisms to the liver and spleen. It had no effect, however, on the ability of the bacteria to proliferate and spread within the thermally injured tissue. It also was determined that protamine sulfate was ineffective at preventing mouse death at the dose administered if injected intramuscularly instead of directly into burned tissue. Protamine sulfate reduced the expression of the proinflammatory cytokines IL-6 and LIF in the injured/infected tissue. Heparan sulfate given in conjunction with protamine sulfate returned mortality levels to those of untreated mice.

CONCLUSIONS

Our results suggest that: (1) local injection of sub-bactericidal doses of protamine sulfate reduces the virulence of P. aeruginosa; (2) this effect is due to interference with the systemic rather than local spread of P. aeruginosa; and (3) local application of protamine sulfate may have potential as supportive therapy for prevention of systemic P. aeruginosa infection in severely burned patients.

Stimulation of Fas agonistic antibody-mediated apoptosis by heparin-like agents suppresses Hsp27 but not Bcl-2 protective activity

We report that in Jurkat T cells or freshly isolated T lymphocytes, physiological concentrations of high-molecular weight sulfated polysaccharides such as heparin, heparan sulfate, and dextran sulfate significantly increased the percentage of cell death induced by Fas IgM agonistic antibody. The phenomenon was caspase dependent and P53 independent and correlated with an increased accessibility of cell surface Fas receptors. We also observed that the Fas IgM agonistic antibody-dependent formation of sodium dodecyl sulfate (SDS)-resistant large structures containing Fas receptor was decreased in the presence of heparin-like agents. In contrast, the different agents had no effect when cell death was triggered by FasL, the natural ligand of Fas that does not generate SDS-resistant forms of Fas. Interestingly, the synergistic effect of heparin-like agents toward Fas IgM agonistic antibody-mediated cell death abolished Hsp27 antiapoptotic activity but did not alter much the protection generated by Bcl-2 expression.

Heparan Sulfate Regulates the Antiangiogenic Activity of Endothelial Monocyte-Activating Polypeptide-II at Acidic pH

Endothelial monocyte-activating polypeptide-II (EMAP II) is an antiangiogenic factor for rapidly growing endothelial cells that is released from tumor cells under physiological stress such as hypoxia. We have previously shown that the interaction between EMAP II and the alpha-subunit of ATP synthase, alpha-ATP synthase, can play a regulatory function in the growth of endothelial cells. In the current study, we found that EMAP II-alpha-ATP synthase interaction could be inhibited by excess heparin, whereas the interaction could be enhanced by a low concentration of heparin. Both EMAP II and alpha-ATP synthase could specifically interact with heparin, and this interaction was increased under acidic conditions. In addition, EMAP II and alpha-ATP synthase were found to contain the heparin binding motifs determined by analysis using site-directed mutant forms. In endothelial cells, binding of EMAP II to cells was dramatically enhanced, and alpha-ATP synthase could associate with heparan sulfate at acidic pH. The inhibitory effect of EMAP II on the growth of cultured endothelial cells was also significantly enhanced at acidic pH. Analysis using mutant EMAP II proteins demonstrated that heparan sulfate was essential for the enhanced binding and EMAP II function to endothelial cells at acidic pH. Furthermore, the enhanced inhibitory effects of EMAP II could be abrogated by excess heparin or heparinase treatment. In the endothelial cell, heparan sulfate may regulate the function of EMAP II released from the tumor cell in hypoxic condition.

Inhibition of antithrombin by hyaluronic acid may be involved in the pathogenesis of rheumatoid arthritis

Thrombin is a key factor in the stimulation of fibrin deposition, angiogenesis, proinflammatory processes, and proliferation of fibroblast-like cells. Abnormalities in these processes are primary features of rheumatoid arthritis (RA) in synovial tissues. Tissue destruction in joints causes the accumulation of large quantities of free hyaluronic acid (HA) in RA synovial fluid. The present study was conducted to investigate the effects of HA and several other glycosaminoglycans on antithrombin, a plasma inhibitor of thrombin. Various glycosaminoglycans, including HA, chondroitin sulfate, keratan sulfate, heparin, and heparan, were incubated with human antithrombin III in vitro. The residual activity of antithrombin was determined using a thrombin-specific chromogenic assay. HA concentrations ranging from 250 to 1000 μg/ml significantly blocked the ability of antithrombin to inhibit thrombin in the presence of Ca²⁺ or Fe³⁺, and chondroitin A, B and C also reduced this ability under the same conditions but to a lesser extent. Our study suggests that the high concentration of free HA in RA synovium may block antithrombin locally, thereby deregulating thrombin activity to drive the pathogenic process of RA under physiological conditions. The study also helps to explain why RA occurs and develops in joint tissue, because the inflamed RA synovium is uniquely rich in free HA along with extracellular matrix degeneration. Our findings are consistent with those of others regarding increased coagulation activity in RA synovium.

Investigation of penetratin peptides. Part 2.In vitro uptake of penetratin and two of its derivatives

As endocytic uptake of the Antennapedia homeodomain-derived penetratin peptide (RQIKIWFQNRRMKWKK) is finally being revealed, some of the early views about penetratin need to be reconsidered. Endocytic uptake seems to contradict the indispensability of tryptophans and also the minimum length of 16 amino acid residues for efficient internalization. To revise the membrane translocation of penetratin, two penetratin analogs were designed and synthesized: a peptide in which tryptophans were replaced by phenylalanines (Phe(6,14)-penetratin, RQIKIFFQNRRMKFKK) and a shortened analog (dodeca-penetratin, RQIKIWF-R-KWKK) made up of only 12 residues. The peptides were fluorescently labeled and applied to live, unfixed cells from various lines. Cellular uptake was analysed by confocal microscopy and flow cytometry. Low temperature or ATP-depletion blocked the intracellular entry of all three penetratin peptides. A decrease in membrane fluidity or cholesterol depletion with methyl-beta-cyclodextrin greatly inhibited peptide uptake, showing the involvement of cholesterol-rich lipid rafts in internalization. Exogenous heparan sulfate also diminished the internalization of penetratin and its derivatives, reflecting the paramount importance of electrostatic interactions with polyanionic cell-surface proteoglycans. The beneficial presence of tryptophans is supported by observations on the decreased cellular uptake of Phe(6, 14)-penetratin. The maintained translocational efficiency of dodeca-penetratin demonstrates that a thorough understanding of penetratin internalization can yield new penetratin analogs with unaltered translocational abilities. This study provides evidence on the energy-dependent and lipid raft-mediated endocytic uptake of penetratin and highlights the necessity of revealing those pathways that cationic cell-penetrating peptides employ to enter live cells.

Glycosaminoglycans and the regulation of allergic inflammation

Glycosaminoglycans (GAGs) are large, polyanionic molecules expressed throughout the body. The GAG heparin, co-released with histamine, is synthesised by and stored exclusively in mast cells, whereas the closely related molecule heparan sulphate is expressed, as part of a proteoglycan, on cell surfaces and throughout tissue matrices. These molecules are increasingly thought to play a role in regulation of the inflammatory response and heparin like molecules are now being seriously considered to hold potential in the treatment of inflammatory diseases such as asthma. Heparin and related molecules have been found to exert anti-inflammatory effects in a wide range of in vitro assays, animal models and in human disease. The anti-inflammatory activities of heparin are independent of the well-established anticoagulant activity of heparin, suggesting that the separation of these properties could yield novel anti-inflammatory drugs, which may be useful in the future treatment of inflammatory diseases.

Syndecan-dependent binding of Drosophila hemocytes to laminin alpha3/5 chain LG4-5 modules: potential role in sessile hemocyte islets formation

Heparin-column chromatography and elastase-digestion of medium from hemocyte Kc167 gave Drosophila laminin alpha3/5betagamma trimer, alpha3/5LG2-3 and alpha3/5LG4-5 modules with eluting NaCl concentrations of 450, 280 and 450 mM, respectively. Kc167 cells bound dish surface with alpha3/5betagamma trimer or alpha3/5LG4-5, but not with alpha3/5LG2-3 modules. Cell binding was counteracted by treating with heparin or heparan sulfate. RNA interference of syndecan in Kc167 cells impaired the binding, but that of dally or dally-like did not. Green fluorescent protein-expressing hemocytes also bound surface with alpha3/5betagamma trimer or alpha3/5LG4-5 module. Thus, syndecan-dependent binding of hemocytes to laminin may have a potential role in sessile hemocytes islets formation in T2-A8 segments of Drosophila.

Novel heparan sulfate mimetic compounds as antitumor agents

Heparan sulfate glycosaminoglycans (HSGAGs) are involved in tumor cell growth, adhesion, invasion, and migration, due to their interactions with various proteins. In this study, novel HSGAG-mimetic compounds (KI compounds) were designed and synthesized. As a result of cell-based assays, KI-105 was found to exert potent inhibitory activities against migration and invasion of human fibrosarcoma HT1080 cells. The present results indicate that a novel invasion/migration inhibitor, KI-105, can increase the adherence of HT1080 cells. It was conceivable that this cellular effect was caused by an increase in the amount of cell-surface HSGAGs and focal adhesions. Although further investigations are needed to decipher the molecular mechanism of KI-105, it is suggested that heparanase and Cdc42 are involved in its biological effects.

Bone marrow stromal proteoglycans regulate megakaryocytic differentiation of human progenitor cells

Adherence of hematopoietic progenitor cells (HPCs) to stroma is an important regulatory step in megakaryocytic differentiation. However, the mechanisms through which megakaryocytic progenitors are inhibited by stroma are poorly understood. We examined the role of sulfated glycoconjugates, such as proteoglycans (PGs), on human bone marrow stroma (hBMS). To this end, PG structure was altered by desulfation or enzymatic cleavage. PGs participated in adhesion of human HPC, as desulfation resulted in about 50% decline in adhesion to hBMS. Heparan sulfate proteoglycans (HSPGs) were found to be responsible by showing about 25% decline in adhesion after pre-incubation of HPC with heparin and about 15% decline in adhesion after enzymatic removal of HSPGs from hBMS. Furthermore, PGs were involved in binding cytokines. Both desulfation and enzymatic removal of stromal HSPGs increased release of megakaryocytopoiesis-inhibiting cytokines, that is, interleukin-8 (IL-8, 1.9-fold increase) and macrophage inflammatory protein-1alpha (MIP-1alpha, 1.4-fold increase). The megakaryocytic output of HPC grown in conditioned medium of desulfated stroma was decreased to 50% of the megakaryocytic output in CM of sulfated stroma. From these studies, it can be concluded that PGs in bone marrow, in particular HSPGs, are involved in binding HPC and megakaryocytopoiesis-inhibiting cytokines. Bone marrow stromal PGs thus reduce differentiation of HPC toward megakaryocytes.

A new peptide with membrane-permeable function derived from human circadian proteins

Basic peptides such as human immunodeficiency virus type 1 (HIV-1) Tat-(48-60) and Drosophila Antennapedia-(43-58) have been reported to have a membrane permeability and a carrier function for intracellular protein delivery. Based on the fluorescence microscopic observations of the vascular endothelial cells (ECV-304) and the primary cultured neuroglial cells, we found that human Clock protein DNA-binding peptide [residue 35-47, hClock-(35-47)] had a translocation activity very similar to Tat-(48-60). The cellular uptake of hClock-(35-47) increases with the increase of incubation time and concentration. The internalization effect at 4 degrees was same as that at 37 degrees C. Internalization of hClock-(35-47) was saturable and could be inhibited by the excess of the other MPPs. Moreover, the uptake of these peptides were significantly inhibited in the presence of heparan sulfate. These results strongly suggested that the hClock-(35-47) shared a common or very similar internalization pathway with other MPPs. Furthermore, we injected rat through the common carotid artery with hClock-(35-47)-FITC peptide, and cryostat sections of the brain were prepared and observed using a fluorescence microscope. Result showed that the peptide had the ability to translocate through the blood-brain barrier. It is promising to provide a new safe carrier for the intracellular and encephalic treatment.

The low molecular weight heparan sulfate-mimetic, PI-88, inhibits cell-to-cell spread of herpes simplex virus

Although a number of sulfated polysaccharides have been shown to inhibit infection of cells by herpes simplex virus (HSV), little is known about their effects on the cell-to-cell spread of the virus. These compounds act by inhibiting the virus binding to cells, and their antiviral potencies usually increase with increasing molecular weight and sulfation density. We report that the low molecular weight HS-mimetic, PI-88, which is a mixture of highly sulfated mannose-containing di- to hexa-saccharides, inhibited HSV infection of cells and cell-to-cell spread of HSV-1 and HSV-2. Compared to a relatively large heparin polysaccharide, PI-88 demonstrated weaker inhibition of HSV infectivity but more efficient reduction of cell-to-cell spread of HSV. A tetrasaccharide fraction of PI-88 was the minimum fragment necessary to inhibit HSV-1 infectivity, while a trisaccharide was sufficient to reduce cell-to-cell spread. A reduction in HSV lateral spread was also observed in cells incubated with another low molecular weight compound, pentosan polysulfate but not with much larger polysaccharide chondroitin sulfate E. Some differences as regards the effects of PI-88, heparin, protamine, poly-L-lysine and sodium chlorate on intercellular spread of HSV-1 and HSV-2 were found. We conclude that structurally different sulfated oligosaccharides are preferred for inhibition of HSV infectivity and the cell-to-cell spread. The latter was efficiently inhibited by a relatively small but densely sulfated PI-88 oligosaccharide, very likely due to the capability of the compound to access the narrow intercellular space.

Chemokines promote quiescence and survival of human neural progenitor cells

Many cell types in the brain express chemokines and chemokine receptors under homeostatic conditions, arguing for a role of these proteins in normal brain processes. Because chemokines have been shown to regulate hematopoietic progenitor cell proliferation, we hypothesized that chemokines would regulate neural progenitor cell (NPC) proliferation as well. Here we show that chemokines activating CXCR4 or CCR3 reversibly inhibit NPC proliferation in isolated cells, neurospheres, and in hippocampal slice cultures. Cells induced into quiescence by chemokines maintain their multipotential ability to form both neurons and astrocytes. The mechanism of chemokine action appears to be a reduction of extracellular signal-related kinase phosphorylation as well as an increase in Reelin expression. The inhibitory effects of chemokines are blocked by heparan sulfate and apolipoprotein E3 but not apolipoprotein E4, suggesting a regulatory role of these molecules on the effects of chemokines. Additionally, we found that the chemokine fractalkine promotes survival of NPCs. In addition to their role in chemotaxis, chemokines affect both the survival and proliferation of human NPCs in vitro. The presence of constitutively expressed chemokines in the brain argues that under homeostatic conditions, chemokines promote survival but maintain NPCs in a quiescent state. Our studies also suggest a link between inflammatory chemokine production and the inhibition of neurogenesis.

Heparan sulfate/heparin oligosaccharides protect stromal cell-derived factor-1 (SDF-1)/CXCL12 against proteolysis induced by CD26/dipeptidyl peptidase IV

Stromal cell-derived factor-1 (SDF-1) is a CXC chemokine that is constitutively expressed in most tissues and displayed on the cell surface in association with heparan sulfate (HS). Its numerous biological effects are mediated by a specific G protein-coupled receptor, CXCR4. A number of cells inactivate SDF-1 by specific processing of the N-terminal domain of the chemokine. In particular, CD26/dipeptidyl peptidase IV (DPP IV), a serine protease that co-distributes with CXCR4 at the cell surface, mediates the selective removal of the N-terminal dipeptide of SDF-1. We report here that heparin and HS specifically prevent the processing of SDF-1 by DPP IV expressed by Caco-2 cells. The level of processing increases with the level of differentiation of these cells, which correlates with an increase of DPP IV activity. A mutant SDF-1 that does not interact with HS is readily cleaved by DPP IV, a process that is not inhibited by HS, demonstrating that a productive interaction between HS and SDF-1 is required for the protection to take place. Moreover, we found that protection depends on the degree of polymerization of the HS sulfated S-domains. Finally a structural model of SDF-1, in complex with HS oligosaccharides of defined length, rationalizes the experimental data. The mechanisms by which HS regulates SDF-1 may thus include, in addition to its ability to locally concentrate the chemokine at the cell surface, a control of selective protease cleavage events that directly affect the chemokine activity.

Heparan sulfate and control of endothelial cell proliferation: increased synthesis during the S phase of the cell cycle and inhibition of thymidine incorporation induced by ortho-nitrophenyl-β-d-xylose

The effect of xylosides on the synthesis of [35S]-sulfated glycosaminoglycans by endothelial cells in culture was investigated. Ortho-nitrophenyl-beta-D-xylose (10(-3)M) produces a dramatic enhancement on the synthesis of heparan sulfate and chondroitin sulfate secreted to the medium (20- and 100-fold, respectively). Para-nitrophenylxyloside, at the same concentration, produces an enhancement of only 37- and 3-fold of chondroitin sulfate and heparan sulfate, respectively. These differences of action seem to be related with the higher lipophilic character of ortho-nitrophenyl-xyloside. A lower enhancement of the synthesis of the two glycosaminoglycans is also observed with 2-naphtol beta-D-xylose and cis/trans-decahydro-2-naphtol beta-D-xylose. Besides stimulating the synthesis, O-nitrophenyl-beta-D-xylose as PMA [J. Cell. Biochem. 70 (1998) 563] also inhibits [3H]-thymidine incorporation by quiescent endothelial cells stimulated for growth by fetal calf serum (FCS). The combination of xylosides with PMA produced some cumulative effect. PMA stimulates the synthesis of heparan sulfate mainly at G1 phase whereas the highest enhancement of synthesis produced by the xylosides is in the S phase of the endothelial cell cycle.

Heparanase uptake is mediated by cell membrane heparan sulfate proteoglycans

Heparanase is a mammalian endoglycosidase that degrades heparan sulfate (HS) at specific intrachain sites, an activity that is strongly implicated in cell dissemination associated with metastasis and inflammation. In addition to its structural role in extracellular matrix assembly and integrity, HS sequesters a multitude of polypeptides that reside in the extracellular matrix as a reservoir. A variety of growth factors, cytokines, chemokines, and enzymes can be released by heparanase activity and profoundly affect cell and tissue function. Thus, heparanase bioavailability, accessibility, and activity should be kept tightly regulated. We provide evidence that HS is not only a substrate for, but also a regulator of, heparanase. Addition of heparin or xylosides to cell cultures resulted in a pronounced accumulation of, heparanase in the culture medium, whereas sodium chlorate had no such effect. Moreover, cellular uptake of heparanase was markedly reduced in HS-deficient CHO-745 mutant cells, heparan sulfate proteoglycan-deficient HT-29 colon cancer cells, and heparinase-treated cells. We also studied the heparanase biosynthetic route and found that the half-life of the active enzyme is approximately 30 h. This and previous localization studies suggest that heparanase resides in the endosomal/lysosomal compartment for a relatively long period of time and is likely to play a role in the normal turnover of HS. Co-localization studies and cell fractionation following heparanase addition have identified syndecan family members as candidate molecules responsible for heparanase uptake, providing an efficient mechanism that limits extracellular accumulation and function of heparanase.

Angiotensin II type 1-receptor mediated changes in heparan sulfate proteoglycans in human SV40 transformed podocytes

In patients with diabetic nephropathy, glomerular staining for heparan sulfate proteoglycans (HSPG) side chains and for agrin is decreased. In the present study, the influence of angiotensin II (AngII) on the production of HSPG in SV40 transformed podocytes was investigated. SV40 transformed human podocytes were cultivated with or without 1 microM AngII, and HSPG production was measured by sequential DEAE-anion exchange chromatography and HPLC-DEAE separation. Expression of agrin was studied by indirect immunofluorescence and Western blot analysis using specific mono- and polyclonal antibodies. DEAE separation of total glycosaminoglycans (GAG) revealed a significant increase of GAG in the culture supernatant and decrease in the cell and matrix layer when podocytes were cultured for 72 h in the presence of AngII. This was particularly found for HS-GAG. Qualitative analysis of HSPG, using gel filtration of HNO(2)-treated fractions, showed that AngII treatment decreased N-sulfation of HS-GAG side chains. Indirect immunofluorescence staining with anti-agrin polyclonal antibody was strongly decreased after AngII stimulation. A reduction in agrin expression in cell extracts could also be detected in Western blot analysis using an mAb. No changes in agrin mRNA were found after AngII stimulation. It is concluded from this study that AngII decreases the amount of HSPG on the cell surface and in the extracellular matrix of podocytes. Because HSPG play a fundamental role in the permselectivity of the glomerular basement membrane, these results thus may explain at least partially the antiproteinuric effects of angiotensin-converting enzyme inhibition in patients with diabetic nephropathy.

Rational design and synthesis of novel heparan sulfate mimetic compounds as antiadhesive agents

A biological evaluation of the antiadhesive activity of novel heparan sulfate glycosaminoglycans mimetic compounds (KI-compounds) is described. In an adhesion assay, KI-111 [2-(4-fluoro-3-nitrobenzoyl)benzoic acetic anhydride] was found to exert potent inhibitory activities against the adhesion of human fibrosarcoma HT1080 cells and HeLa cells to fibronectin. Cell growth, migration, and invasion of HT1080 cells were also inhibited by KI-111 at almost equal concentrations.

Heparan sulphate mediates swine vesicular disease virus attachment to the host cell

Heparan sulphate (HS) has been found to serve as receptor for initial cell binding of numerous viruses. Different glycosaminoglycans (GAGs), including heparin and HS, were analysed for their ability to bind swine vesicular disease virus (SVDV), a picornavirus with close homology to human coxsackie B5 virus. Binding of SVDV was established by heparin-affinity chromatography. In addition, infection of IB-RS-2 epithelial porcine cells was inhibited by treating the virus with soluble HS, heparin, and chondroitin sulphate B (CS-B), as well as by enzymic digestion of cell surface GAGs. Analysis of the infection course showed that SVDV uses cellular HS for its binding to the cell surface and that this interaction occurs during attachment of the virus, prior to its internalization into the cell. Sequence analysis of SVDV variants selected for their lack of sensitivity to heparin inhibition in vitro led to the identification of two residues (A2135V and I1266K) potentially involved in heparin/HS interaction. The location of these residues in a three-dimensional model shows that they are clustered in a well-exposed region of the capsid, providing a physical mechanism that could account for the heparin-binding phenotype.