Interaction of heparin with human angiogenin

How good are comparative models in the understanding of protein dynamics?

The 3D structure of a protein is essential to understand protein dynamics. If experimentally determined structure is unavailable, comparative models could be used to infer dynamics. However, the effectiveness of comparative models, compared to experimental structures, in inferring dynamics is not clear. To address this, we compared dynamics features of ~800 comparative models with their crystal structures using normal mode analysis. Average similarity in magnitude, direction, and correlation of residue motions is >0.8 (where value 1 is identical) indicating that the dynamics of models and crystal structures are highly similar. Accuracy of 3D structure and dynamics is significantly higher for models built on multiple and/or high sequence identity templates (>40%). Three-dimensional (3D) structure and residue fluctuations of models are closer to that of crystal structures than to templates (TM score 0.9 vs 0.7 and square inner product 0.92 vs 0.88). Furthermore, long-range molecular dynamics simulations on comparative models of RNase 1 and Angiogenin showed significant differences in the conformational sampling of conserved active-site residues that characterize differences in their activity levels. Similar analyses on two EGFR kinase variant models highlight the effect of mutations on the functional state-specific αC helix motions and these results corroborate with the previous experimental observations. Thus, our study adds confidence to the use of comparative models in understanding protein dynamics.

Heparan Sulfate in the Tumor Microenvironment

The biology of tumor cells strictly depends on their microenvironment architecture and composition, which controls the availability of growth factors and signaling molecules. Thus, the network of glycosaminoglycans, proteoglycans, and proteins known as extracellular matrix (ECM) that surrounds the cells plays a central role in the regulation of tumor fate. Heparan sulfate (HS) and heparan sulfate proteoglycans (HSPGs) are highly versatile ECM components that bind and regulate the activity of growth factors, cell membrane receptors, and other ECM molecules. These HS binding partners modulate cell adhesion, motility, and proliferation that are processes altered during tumor progression. Modification in the expression and activity of HS, HSPGs, and the respective metabolic enzymes results unavoidably in alteration of tumor cell microenvironment. In this light, the targeting of HS structure and metabolism is potentially a new tool in the treatment of different cancer types.

Heparin: An essential drug for modern medicine

Heparin is a life-saving drug, which belongs to few clinically used drugs without defined molecular structures in modern medicine. Heparin is the mostly negatively charged biopolymer with a broad distributions in molecular weight, charge density, and biological activities. Heparin is mainly composed of repeating trisulfated disaccharide units, which is made by mast cells that are enriched in the intestines, lungs or livers of animals. Porcine intestines and bovine lungs are two mostly used sources for heparin isolation. Heparin is well known for its anticoagulant and antithrombotic pharmacological effects. The anticoagulant activity of heparin is attributable to a 3-O-sulfate and 6-O-sulfate containing pentasaccharide sequence or a minimum eight-repeating disaccharide units containing the pentasaccharide sequence that catalyzes the suicidal inactivation of factor Xa or thrombin by a serpin or serine protease inhibitor named antithrombin III, respectively. Thus, heparin is responsible for the simultaneous inhibition of both thrombin generation and thrombin activity in the blood circulation. Moreover, heparin has many pharmacological properties such as anti-inflammatory, anti-viral, anti-angiogenesis, anti-neoplastic, and anti-metastatic effects though high affinity interactions with a variety of proteases, protease inhibitors, chemokines, cytokines, growth factors, and their respective receptors. The one drug multiple molecular targeting properties make heparin a very special drug in that various clinical trials are still conducting worldwide even 100 years after its discovery. In this review, we will summarize the structure-function relationship and the molecular mechanisms of heparin. We will also provide an overview of different clinical and potential clinical applications of heparin.

The cellular uptake of angiogenin, an angiogenic and neurotrophic factor is through multiple pathways and largely dynamin independent

Angiogenin (ANG), a member of the RNase superfamily (also known as RNase 5) has neurotrophic, neuroprotective and angiogenic activities. Recently it has also been shown to be important in stem cell homeostasis. Mutations in ANG are associated with neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS) and Fronto-temporal dementia (FTD). ANG is a secreted protein which is taken up by cells and translocated to the nucleus. However, the import pathway/s through which ANG is taken up is/are still largely unclear. We have characterised the uptake of ANG in neuronal, astrocytic and microglial cell lines as well as primary neurons and astrocytes using pharmacological agents as well as dominant negative dynamin and Rab5 to perturb uptake and intracellular trafficking. We find that uptake of ANG is largely clathrin/dynamin independent and microtubule depolymerisation has a marginal effect. Perturbation of membrane ruffling and macropinocytosis significantly inhibited ANG uptake suggesting an uptake mechanism similar to RNase A. Our findings shed light on why mutations which do not overtly affect RNase activity but cause impaired localization are associated with neurodegenerative disease.

Interaction between human angiogenin and the p53 TAD2 domain and its implication for inhibitor discovery

Interaction between angiogenin and the p53 TAD2 domain in cancer cells can inhibit the function of the p53 tumor suppressor and promote cell survival. Based on a model structure using NMR and mutational analysis, positively charged ³¹ RRR³³ and ⁵⁰ KRSIK⁵⁴ motifs of human angiogenin were identified as p53-binding sites that could interact with negatively charged D48/E51 and E56 residues of the p53 TAD2 domain, respectively. These results suggest that ³¹ RRR³³ and ⁵⁰ KRSIK⁵⁴ motifs of human angiogenin might play a critical role in the regulation of p53-mediated apoptosis and angiogenesis in cancer cells. This study identifies potential target sites for screening angiogenin-specific inhibitors that could not only inhibit p53 binding but could also simultaneously inhibit cell binding, internalization, DNA binding, and nuclear translocation of human angiogenin.

The role of the KRSIK motif of human angiogenin in heparin and DNA binding

The ⁵⁰KRSIK⁵⁴ motif is the main interaction site of hAng for heparin and DNA binding, providing an insight into the potential role of the motif for the internalization and DNA binding of hAng, which is essential for the regulation of angiogenesis.

The dual binding site of angiogenin and its inhibition mechanism: the crystal structure of the rat angiogenin-heparin complex

The heparin complex of rat angiogenin revealed that a heparin strand is fitted into a positively charged groove formed by the dual binding site of rat angiogenin, suggesting that cell adhesion to angiogenin is facilitated by its interaction with substrates on the cell surface and can be inhibited by heparin.

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.

Angiogenin expression during early human placental development; association with blood vessel formation

The placenta is a transient organ essential for fetal development. During human placental development, chorionic villi grow in coordination with a large capillary network resulting from both vasculogenesis and angiogenesis. Angiogenin is one of the most potent inducers of neovascularisation in experimental models in vivo. We and others have previously mapped angiogenin expression in the human term placenta. Here, we explored angiogenin involvement in early human placental development. We studied, angiogenin expression by in situ hybridisation and/or by RT-PCR in tissues and primary cultured trophoblastic cells and angiogenin cellular distribution by coimmunolabelling with cell markers: CD31 (PECAM-1), vascular endothelial cadherin (VE-cadherin), vascular endothelial growth factor receptor-2 (VEGF-R2), Tie-2, von Willebrand factor, CD34, erythropoeitin receptor (Epo-R), alpha-smooth muscle actin, CD45, cytokeratin 7, and Ki-67. Extravillous and villous cytotrophoblasts, isolated and differentiated in vitro, expressed and secreted angiogenin. Angiogenin was detected in villous trophoblastic layers, and structured and nascent fetal vessels. In decidua, it was expressed by glandular epithelial cells, vascular cells and macrophages. The observed pattern of angiogenin expression is compatible with a role in blood vessel formation and in cross-talk between trophoblasts and endothelial cells. In view of angiogenin properties, we suggest that angiogenin may participate in placental vasculogenesis and organogenesis.

Characterization of biometal profiles in neurological disorders

This review summarizes the findings on dysregulation of metal ions in neurological diseases and tries to develop and predict specific biometal profiles.

In silico prediction and in vitro characterization of multifunctional human RNase3

Human ribonucleases A (hRNaseA) superfamily consists of thirteen members with high-structure similarities but exhibits divergent physiological functions other than RNase activity. Evolution of hRNaseA superfamily has gained novel functions which may be preserved in a unique region or domain to account for additional molecular interactions. hRNase3 has multiple functions including ribonucleolytic, heparan sulfate (HS) binding, cellular binding, endocytic, lipid destabilization, cytotoxic, and antimicrobial activities. In this study, three putative multifunctional regions, ³⁴RWRCK³⁸ (HBR1), ⁷⁵RSRFR⁷⁹ (HBR2), and ¹⁰¹RPGRR¹⁰⁵ (HBR3), of hRNase3 have been identified employing in silico sequence analysis and validated employing in vitro activity assays. A heparin binding peptide containing HBR1 is characterized to act as a key element associated with HS binding, cellular binding, and lipid binding activities. In this study, we provide novel insights to identify functional regions of hRNase3 that may have implications for all hRNaseA superfamily members.

Crystal structures of murine angiogenin-2 and -3-probing 'structure--function' relationships amongst angiogenin homologues

Angiogenin (Ang) is a potent inducer of neovascularization. Point mutations in human Ang have been linked to cancer progression and two neurodegenerative diseases: amyotrophic lateral sclerosis and Parkinson's disease. Intensive structural and functional analyses of Ang have been paramount in assigning functions to this novel homologue of bovine pancreatic RNase A. However, inhibitor-binding studies with crystalline Ang (for designing potential anti-cancer drugs) have been hampered as a result of the inaccessibility of the active site. Experiments with the murine homologues of Ang have not only overcome the obvious practical limitations encountered when studying the role of a human protein in healthy individuals, but also the crystal structures of murine angiogenins (mAng and mAng-4) have revealed themselves to have greater potential for the visualization of small-molecule inhibitor binding at the active site. In the present study, we report the crystal structures of two more murine Ang paralogues, mAng-2 and mAng-3, at 1.6 and 1.8 Å resolution, respectively. These constitute the first crystal structures of an Ang with a zinc ion bound at the active site and provide some insight into the possible mode of inhibition of the ribonucleolytic activity of the enzyme by these divalent cations. Both structures show that the residues forming the putative P₁, B₁ and B₂ subsites occupy positions similar to their counterparts in human Ang and are likely to have conserved roles. However, a less obtrusive conformation of the C-terminal segment in mAng-3 and the presence of a sulfate ion in the B₁ subsite of mAng-2 suggest that these proteins have the potential to be used for inhibitor-binding studies. We also discuss the biological relevance of the structural similarities and differences between the different Ang homologues.

Motoneurons secrete angiogenin to induce RNA cleavage in astroglia

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disorder affecting motoneurons. Mutations in angiogenin, encoding a member of the pancreatic RNase A superfamily, segregate with ALS. We previously demonstrated that angiogenin administration shows promise as a neuroprotective therapeutic in studies using transgenic ALS mice and primary motoneuron cultures. Its mechanism of action and target cells in the spinal cord, however, are largely unknown. Using mixed motoneuron cultures, motoneuron-like NSC34 cells, and primary astroglia cultures as model systems, we here demonstrate that angiogenin is a neuronally secreted factor that is endocytosed by astroglia and mediates neuroprotection in paracrine. We show that wild-type angiogenin acts unidirectionally to induce RNA cleavage in astroglia, while the ALS-associated K40I mutant is also secreted and endocytosed, but fails to induce RNA cleavage. Angiogenin uptake into astroglia requires heparan sulfate proteoglycans, and engages clathrin-mediated endocytosis. We show that this uptake mechanism exists for mouse and human angiogenin, and delivers a functional RNase output. Moreover, we identify syndecan 4 as the angiogenin receptor mediating the selective uptake of angiogenin into astroglia. Our data provide new insights into the paracrine activities of angiogenin in the nervous system, and further highlight the critical role of non-neuronal cells in the pathogenesis of ALS.

Site-specific PEGylation endows a mammalian ribonuclease with antitumor activity

Mammalian ribonucleases are emerging as cancer chemotherapeutic agents. Their cationicity engenders cell permeability, and their enzymatic activity destroys the biochemical information encoded by RNA. The pharmacologic potential of ribonucleases is, however, obviated by their high sensitivity to a cytosolic inhibitor protein (RI) and their small size, which limits their residence in serum. We reasoned that site specific conjugation of a poly(ethylene glycol) (PEG) chain could both reduce sensitivity to RI and increase serum half-life. We found that appending a PEG moiety can enable bovine pancreatic ribonuclease (RNase A) to evade RI, depending on the site of conjugation and the length and branching of the chain. Although a pendant PEG moiety decreases antiproliferative activity in vitro, PEGylation discourages renal clearance in vivo and leads to nearly complete tumor growth inhibition in a mouse xenograft model. These data demonstrate that a pendant PEG moiety can be beneficial to the action of proteins that act within the cytosol, and that strategic site-specific PEGylation can endow a mammalian ribonuclease with potent antitumor activity.

Heparin impairs angiogenesis through inhibition of microRNA-10b

Heparin, which has been used as an anticoagulant drug for decades, inhibits angiogenesis, whereas thrombin promotes tumor-associated angiogenesis. However, the mechanisms underlying the regulation of angiogenesis by heparin and thrombin are not well understood. Here, we show that microRNA-10b (miR-10b) is down-regulated by heparin and up-regulated by thrombin in human microvascular endothelial cells (HMEC-1). Overexpression of miR-10b induces HMEC-1 cell migration, tube formation, and angiogenesis, and down-regulates homeobox D10 (HoxD10) expression via direct binding of miR-10b to the putative 3' UTR of HoxD10. In addition, HMEC-1 cell migration and tube formation are induced by HoxD10 knockdown, whereas angiogenesis is arrested when HoxD10 expression is increased after anti-miR-10b or heparin treatments. Furthermore, expression of miR-10b and its transcription factor Twist are up-regulated by thrombin, whereas HoxD10 expression is impaired by thrombin. Using quartz crystal microbalance analysis, we show that heparin binds to thrombin, thereby inhibiting thrombin-induced expression of Twist and miR-10b. However, the expression of miR-10b is not attenuated by heparin any more after thrombin expression is silenced by its siRNA. Interestingly, we find that heparin attenuates miR-10b expression and induces HoxD10 expression in vivo to inhibit angiogenesis and impair the growth of MDA-MB-231 tumor xenografts. These results provide insight into the molecular mechanism by which heparin and thrombin regulate angiogenesis.

Rat recombinant β-defensin 22 is a heparin-binding protein with antimicrobial activity

Approximately 40-50 β-defensins are predominantly expressed in the male reproductive system of mammals. This selective expression raises the question as to the roles of these molecules in innate immunity and fertility in the male reproductive tract. Rat β-defensin 22 is an epididymis-specific β-defensin expressed in segments 12-14 of the epididymis. This protein contains both β-defensin and lectin signature sequences, yet its antimicrobial activity and carbohydrate-binding ability have not been shown. We herein demonstrated the antimicrobial activity of recombinant rat β-defensin 22 against Escherichia coli and Candida albicans. Its lectin-like activity was also investigated by demonstrating its binding ability with heparin beads. This heparin-binding activity implies some potential roles for this defensin in determining the fertilisation capabilities of sperm.

Heparan sulfate proteoglycans: structure, protein interactions and cell signaling

Heparan sulfate proteoglycans are ubiquitously found at the cell surface and extracellular matrix in all the animal species. This review will focus on the structural characteristics of the heparan sulfate proteoglycans related to protein interactions leading to cell signaling. The heparan sulfate chains due to their vast structural diversity are able to bind and interact with a wide variety of proteins, such as growth factors, chemokines, morphogens, extracellular matrix components, enzymes, among others. There is a specificity directing the interactions of heparan sulfates and target proteins, regarding both the fine structure of the polysaccharide chain as well precise protein motifs. Heparan sulfates play a role in cellular signaling either as receptor or co-receptor for different ligands, and the activation of downstream pathways is related to phosphorylation of different cytosolic proteins either directly or involving cytoskeleton interactions leading to gene regulation. The role of the heparan sulfate proteoglycans in cellular signaling and endocytic uptake pathways is also discussed.

Enhanced angiogenesis in porous collagen-chitosan scaffolds loaded with angiogenin

Artificial dermis lacks a vascular network, and angiogenesis is slow in vivo. Controlled delivery of angiogenin (ANG), a potent inducer of angiogenesis, should promote angiogenesis in artificial dermis. In this study, a porous collagen-chitosan scaffold was fabricated and heparinized using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) with a freeze-drying method. Using radioiodine labeling, the effect of heparin on the binding of ANG to the scaffold was studied. The release of ANG from the heparinized scaffold was investigated using a radioiodine labeling method or an enzyme-linked immunosorbent assay method. In vivo angiogenesis of the scaffold was studied for 28 days. All scaffolds possess three-dimensional porous structures, and their mean pore sizes increase upon EDC-NHS cross-linking. The binding of ANG to the scaffold showed a linear correlation with ANG concentration. With ANG concentrations of 160 ng/mL, the binding of ANG to the heparinized scaffold was 36.5%. In vitro, ANG was released from the heparinized scaffold in a controlled manner. The presence of ANG enhanced the angiogenesis of the heparinized scaffold after subcutaneous implantation into rabbits. The results of this study indicate that a porous collagen-chitosan scaffold loaded with ANG may be valuable in the development of artificial dermis requiring enhanced angiogenesis.

Polyanionic drugs and viral oncogenesis: a novel approach to control infection, tumor-associated inflammation and angiogenesis

Polyanionic macromolecules are extremely abundant both in the extracellular environment and inside the cell, where they are readily accessible to many proteins for interactions that play a variety of biological roles. Among polyanions, heparin, heparan sulfate proteoglycans (HSPGs) and glycosphingolipids (GSLs) are widely distributed in biological fluids, at the cell membrane and inside the cell, where they are implicated in several physiological and/or pathological processes such as infectious diseases, angiogenesis and tumor growth. At a molecular level, these processes are mainly mediated by microbial proteins, cytokines and receptors that exert their functions by binding to HSPGs and/or GSLs, suggesting the possibility to use polyanionic antagonists as efficient drugs for the treatment of infectious diseases and cancer. Polysulfated (PS) or polysulfonated (PSN) compounds are a heterogeneous group of natural, semi-synthetic or synthetic molecules whose prototypes are heparin and suramin. Different structural features confer to PS/PSN compounds the capacity to bind and inhibit the biological activities of those same heparin-binding proteins implicated in infectious diseases and cancer. In this review we will discuss the state of the art and the possible future development of polyanionic drugs in the treatment of infectious diseases and cancer.

The solution structure and dynamics of human pancreatic ribonuclease determined by NMR spectroscopy provide insight into its remarkable biological activities and inhibition

Human pancreatic ribonuclease (RNase 1) is expressed in many tissues; has several important enzymatic and biological activities, including efficient cleavage of single-stranded RNA, double-stranded RNA and double-stranded RNA-DNA hybrids, digestion of dietary RNA, regulation of vascular homeostasis, inactivation of the HIV, activation of immature dendritic cells and induction of cytokine production; and furthermore shows potential as an anti-tumor agent. The solution structure and dynamics of uncomplexed, wild-type RNase 1 have been determined by NMR spectroscopy methods to better understand these activities. The family of 20 structures determined on the basis of 6115 unambiguous nuclear Overhauser enhancements is well resolved (pairwise backbone RMSD=1.07 A) and has the classic RNase A type of tertiary structure. Important structural differences compared with previously determined crystal structures of RNase 1 variants or inhibitor-bound complexes are observed in the conformation of loop regions and side chains implicated in the enzymatic as well as biological activities and binding to the cytoplasmic RNase inhibitor. Multiple side chain conformations observed for key surface residues are proposed to be crucial for membrane binding as well as translocation and efficient RNA hydrolysis. (15)N-(1)H relaxation measurements interpreted with the standard and our extended Lipari-Szabo formalism reveal rigid regions and identify more dynamic loop regions. Some of the most dynamic areas are key for binding to the cytoplasmic RNase inhibitor. This finding and the important differences observed between the structure in solution and that bound to the inhibitor are indications that RNase 1 to inhibitor binding can be better described by the "induced fit" model rather than the rigid "lock-into-key" mechanism. Translational diffusion measurements reveal that RNase 1 is predominantly dimeric above 1 mM concentration; the possible implications of this dimeric state for the remarkable biological properties of RNase 1 are discussed.

Cytotoxic ribonucleases: the dichotomy of Coulombic forces

Cells tightly regulate their contents. Still, nonspecific Coulombic interactions between cationic molecules and anionic membrane components can lead to adventitious endocytosis. Here, we characterize this process in a natural system. To do so, we create variants of human pancreatic ribonuclease (RNase 1) that differ in net molecular charge. By conjugating a small-molecule latent fluorophore to these variants and using flow cytometry, we are able to determine the kinetic mechanism for RNase 1 internalization into live human cells. We find that internalization increases with solution concentration and is not saturable. Internalization also increases with time to a steady-state level, which varies linearly with molecular charge. In contrast, the rate constant for internalization (t1/2 = 2 h) is independent of charge. We conclude that internalization involves an extracellular equilibrium complex between the cationic proteins and abundant anionic cell-surface molecules, followed by rate-limiting internalization. The enhanced internalization of more cationic variants of RNase 1 is, however, countered by their increased affinity for the cytosolic ribonuclease inhibitor protein, which is anionic. Thus, Coulombic forces mediate extracellular and intracellular equilibria in a dichotomous manner that both endangers cells and defends them from the potentially lethal enzymatic activity of ribonucleases.

Extracellular angiogenic growth factor interactions: an angiogenesis interactome survey

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

Internalization of cationic peptides: the road less (or more?) traveled

Facilitating the entry of molecules into mammalian cells is of great interest to fields as diverse as cell biology and drug delivery. The discovery of natural protein transduction domains and the development of artificial ones, including polyarginine, provides a means to achieve this goal. Here, we comment on key chemical and biological aspects of cationic peptide internalization, including the physiological relevance of this process.

Alpha-actinin-2, a cytoskeletal protein, binds to angiogenin

Angiogenin is an angiogenic factor which is involved in tumorigenesis. However, no particular intracellular protein is known to interact directly with angiogenin. In the present study, we reported the identification of alpha-actinin-2, an actin-crosslinking protein, as a potential angiogenin-interacting partner by yeast two-hybrid screening. This interaction was confirmed by different approaches. First, angiogenin was pulled down together with His-tagged alpha-actinin-2 by Ni(2+)-agarose resins. Second, alpha-actinin-2 was coimmunoprecipitated with angiogenin by anti-angiogenin monoclonal antibody. Third, the in vivo interaction of these two proteins was revealed by fluorescence resonance energy transfer analysis. Since members of alpha-actinin family play pivotal roles in cell proliferation, migration, and invasion, the interaction between alpha-actinin-2 and angiogenin may underline one possible mechanism of angiogenin in angiogenesis. Our finding presents the first evidence of an interaction of a cytosolic protein with angiogenin, which might be a novel interference target for anti-angiogenesis and anti-tumor therapy.

Angiogenin distribution in human term placenta, and expression by cultured trophoblastic cells

Human angiogenin is a 14-kDa secreted protein with angiogenic and ribonucleolytic activities. Angiogenin is associated with tumour development but is also present in normal biological fluids and tissues. To further address the physiological role of angiogenin, we studied its expression in situ and in vitro, using the human term placenta as a model of physiological angiogenesis. Angiogenin was immunodetected by light and transmission electron microscopy, and its cellular distribution was established by double immunolabelling with cell markers including von Willebrand factor, platelet/endothelial cell adhesion molecule-1 (PECAM-1), CD34, Tie-2, vascular endothelial cadherin (VE-cadherin), vascular endothelial growth factor receptor-2 (VEGF-R2), erythropoeitin receptor (Epo-R), alpha-smooth muscle actin, CD45, cytokeratin 7, and Ki-67. Angiogenin immunoreactivity was detected in villous and extravillous trophoblasts, the trophoblast basement membrane, the endothelial basal lamina, foetal blood vessels, foetal and maternal red blood cells, and amnionic cells. Its expression was confirmed by in situ hybridisation with a digoxygenin-labelled cDNA probe and reverse transcriptase-polymerase chain reaction amplification. Villous cytotrophoblasts, isolated and differentiated in vitro into a functional syncytiotrophoblast, expressed and secreted angiogenin. Given its known biological activities in vitro and its observed pattern of expression, these data suggest that, in human placenta, angiogenin has a role not only in angiogenesis but also in vascular and tissue homeostasis, maternal immune tolerance of the foetus, and host defences.

Combination antiangiogenesis therapy with marimastat, captopril and fragmin in patients with advanced cancer

Marimastat, low molecular weight heparins and captopril have antiangiogenic activity in vitro and in animal models. We studied the safety and efficacy of the combination of these drugs in patients with advanced cancer. In all, 50 patients were enrolled. Captopril was given orally at a dose of 50 mg bd daily. Fragmin was administered as a daily subcutaneous injection of 200 units kg⁻¹ for the first 28 days and 5000 units thereafter. Marimastat was given at 10 mg bd orally. Serum, plasma and urinary angiogenic factors were measured at baseline and after 1 month of treatment. Inhibition of release of tumour necrosis factor alpha (TNF-alpha) from peripheral lymphocytes was used as a surrogate pharmacodynamic end point. There was one case of haemorrhagic stroke and one upper gastrointestinal haemorrhage. The commonest toxicity was myalgia. One of 10 patients with renal cancer had a partial response, and three patients had a prolonged period of stable disease. The treatment significantly inhibited phytohaemagglutinin (PHA)-stimulated TNF-alpha release from patient's lymphocytes. The combination of marimastat, fragmin and captopril is well tolerated and has in vivo activity. Inhibition of PHA-stimulated TNF-alpha release from lymphocytes is a surrogate pharmacodynamic marker of metalloprotease inhibition.

Antimicrobial activities of heparin-binding peptides

Antimicrobial peptides are effector molecules of the innate immune system. We recently showed that the human antimicrobial peptides alpha-defensin and LL-37 bind to glycosaminoglycans (heparin and dermatan sulphate). Here we demonstrate the obverse, i.e. structural motifs associated with heparin affinity (cationicity, amphipaticity, and consensus regions) may confer antimicrobial properties to a given peptide. Thus, heparin-binding peptides derived from laminin isoforms, von Willebrand factor, vitronectin, protein C inhibitor, and fibronectin, exerted antimicrobial activities against Gram-positive and Gram-negative bacteria. Similar results were obtained using heparin-binding peptides derived from complement factor C3 as well as consensus sequences for heparin-binding (Cardin and Weintraub motifs). These sequence motifs, and additional peptides, also killed the fungus Candida albicans. These data will have implications for the search for novel antimicrobial peptides and utilization of heparin-protein interactions should be helpful in the identification and purification of novel antimicrobial peptides from complex biological mixtures. Finally, consensus regions may serve as templates for de novo synthesis of novel antimicrobial molecules.

Angiogenin: a novel inhibitor of neutrophil lactoferrin release during extracorporeal circulation

Degranulation of polymorphonuclear leukocytes (PMNL) occurs during extracorporeal circulation. A degranulation-inhibiting protein identical to angiogenin was recently isolated from high-flux dialyzer ultrafiltrate. This protein inhibits the release of lactoferrin and metalloproteinases from PMNL in vitro. In the present study, we investigated end-stage renal disease patients undergoing regular hemodialysis treatment with either high-flux dialyzers (n = 51) or low-flux dialyzers (n = 44), and chronically uremic patients undergoing hemodiafiltration (n = 30). Hemodialysis therapy with low-flux polysulfone or cellulose triacetate membranes caused no or only minimal reduction (</=8%) of plasma angiogenin levels within 2 h of dialysis treatment associated with a 1.6-fold lactoferrin release from PMNL. Hemodialysis therapy with high-flux membranes (e.g. cellulose triacetate, polymethylmethacrylate) or hemodiafiltration resulted in a reduction of plasma angiogenin levels by 20-40% after 2 h associated with a nearly 4-fold PMNL lactoferrin release. The release of PMNL elastase was not affected by the different treatment modalities used. We conclude that high angiogenin plasma levels protect against lactoferrin release from PMNL during extracorporeal circulation in chronically uremic patients. A decrease of plasma angiogenin between 20 and 40% during extracorporeal circulation, however, results in marked PMNL lactoferrin release. This novel mechanism may explain, at least in part, PMNL degranulation also in non complement activating high-flux membranes.

Elevated angiogenin levels in synovial fluid from patients with inflammatory arthritis and secretion of angiogenin by cultured synovial fibroblasts

Angiogenesis is a key process in the pathogenesis of inflammatory arthritis. Angiogenin is one of the most potent inducers of neovascularization in experimental models in vivo. To look for evidence that angiogenin is involved in inflammatory joint disease, we examined plasma and synovial fluid (SF) samples from rheumatology patients and synovial fibroblast cell culture supernatants. Angiogenin levels were determined by radioimmunoassay and ELISA. Plasma angiogenin concentrations ranged from 96 to 478 ng/ml, with no significant difference between patients and normal controls. In SF, angiogenin concentrations were significantly higher in patients with acute or chronic synovitis (rheumatoid arthritis (RA): median, 104 ng/ml; range 13-748, n = 14; crystal-induced arthritis (CIA): median, 149 ng/ml; range, 37-616, n = 14, and other chronic inflammatory arthritis: median, 42 ng/ml; range, 15-205; n = 9) than in the 18 patients with osteoarthritis (OA) (median, 20 ng/ml; range 8-116) (P < 0.0001, anova). Angiogenin levels in SF from RA patients in remission with secondary OA were similar to those achieved in primary OA, and decreased in parallel with the resolution of acute gout. Angiogenin protein was released by cultured synovial fibroblasts from OA and RA patients, and reached 1.18 ng/106 cells/day. These data suggest that angiogenin may mediate local inflammation in arthritis via effects on angiogenesis and leucocyte regulation.

Increased in vitro cytotoxicity of TNF-alpha analog LK-805 is based on the interaction with cell surface heparan sulfate proteoglycan

Our tumor necrosis factor-alpha (TNF-alpha) analog LK-805 (E107K) exhibited twofold higher specific cytotoxicity on the mouse fibroblast L-929 cell line than its native counterpart. In addition, significantly lowered systemic toxicity was observed in tumor-bearing mouse models treated with this analog. Due to a charge reversal and clustering of three lysines in the exposed tip region of LK-805, we assumed that additional ionic interactions between the positively charged TNF analog and the negatively charged components of the cell surface were created, which might contribute to improved properties of LK-805. To prove this hypothesis, we designed truncated forms of TNF-alpha and analog LK-805 and performed three independent sets of experiments: measurement of cytotoxic activity in the presence of excess heparan sulfate, determination of cytotoxic activity on heparinase-treated L-929 cells, and binding of various TNF-alpha proteins onto the heparin-sepharose affinity column. Cytotoxicity studies of both kinds confirmed the pivotal role of the E107K mutation for interaction with heparan sulfate proteoglycans on the cell surface of L-929 cells. However, heparin-binding studies revealed that intact, full-length N-termini of TNF-alpha or its analogs were necessary for high retention on the heparin affinity column, whereas the three-lysine containing tip of LK-805 by itself was not enough for binding. Obviously, immobilized heparin does not represent an adequate model for membrane-bound heparan sulfate proteoglycans of L-929 cells.

A small-molecule inhibitor of the ribonucleolytic activity of human angiogenin that possesses antitumor activity

The results of previous preclinical and clinical studies have identified angiogenin (ANG) as a potentially important target for anticancer therapy. Here we report the design and implementation of a high-throughput screening assay to identify small molecules that bind to the ribonucleolytic active site of ANG, which is critically involved in the induction of angiogenesis by this protein. Screening of 18,310 compounds from the National Cancer Institute (NCI) Diversity Set and ChemBridge DIVERSet yielded 15 hits that inhibit the enzymatic activity of ANG with K(i) values <100 microM. One of these, NCI compound 65828 [8-amino-5-(4'-hydroxybiphenyl-4-ylazo)naphthalene-2-sulfonate; K(i) = 81 microM], was selected for more detailed studies. Minor changes in ANG or ligand structure markedly reduced potency, demonstrating that inhibition reflects active-site rather than nonspecific binding; these observations are consistent with a computationally generated model of the ANG.65828 complex. Local treatment with modest doses of 65828 significantly delayed the formation of s.c. tumors from two distinct human cancer cell types in athymic mice. ANG is the likely target involved because (i) a 65828 analogue with much lower potency against the enzymatic activity of ANG failed to exert any antitumor effect, (ii) tumors from 65828-treated mice had fewer interior blood vessels than those from control mice, and (iii) 65828 appears to have no direct effect on the tumor cells. Our findings provide considerable support for the targeting of the enzymatic active site of ANG as a strategy for developing new anticancer drugs.

Human single chain antibodies against heparin: selection, characterization, and effect on coagulation

Heparin, located in mast cells and basophilic granulocytes, is widely used as an anticoagulant. It belongs to a class of linear polysaccharides called glycosaminoglycans (GAGs). Using phage display technology, we have selected 19 unique human antiheparin antibodies. Some antibodies react almost exclusively with heparin, others also react with the structurally related heparan sulfate, and some with chondroitin sulfate. In all cases, sulfate groups are essential for binding. For activity of some antibodies, O-sulfation is more important than N-sulfation. Antibodies are reactive with heparin in mast cells. Each antibody showed a defined staining pattern on cryosections of rat kidney, pancreas, and testis. Enzymatic digestion with glycosidases on tissue sections further indicated that the antibodies are specific for GAGs. All antibodies recognize a unique epitope. The effect of the antibodies on heparin as an anticoagulant was also studied. There were 3 antibodies that were very effective inhibitors of heparin action in the activated partial thromboplastin time (APTT) clotting assay, and their effect was related to the amount of heparin bound. Some antibodies reacted strongly with the pentasaccharide, which interacts with antithrombin III. The human antibodies selected represent unique tools to study the structure, location, and function of heparin and related GAGs, and some may be used as blocking agents.

Fibroblast growth factors are translocated to the nucleus of human endothelial cells in a microtubule- and lysosome-independent pathway

Exogenous acidic and basic fibroblast growth factors undergo rapid nuclear translocation in human umbilical vein endothelial cells. When nuclear translocation reaches saturation, more than 70% of the internalized growth factors are in the nuclear fraction. Lysosomal inhibitors, such as leupeptin and chloroquine, and microtubule inhibitors including colchicine and 2-methoxyl-beta-estradiol neither increase nor decrease nuclear translocation. The results suggest that nuclear translocation of fibroblast growth factors does not require cytosolic accumulation or lysosomal processing and that the transportation of exogenous growth factors across the cytoplasm is independent of microtubules.

Human angiogenin is rapidly translocated to the nucleus of human umbilical vein endothelial cells and binds to DNA

Human angiogenin is translocated to the nucleus of human umbilical vein endothelial cells in a time-dependent manner. Exogenous angiogenin appears in the nucleus in 2 min, reaches saturation in 15 min when 85% of the internalized angiogenin is in the nuclei, and remains associated with the nucleus for at least 4 h. Endothelial cells cultured at low density have a much higher capacity to translocate angiogenin to the nucleus than do those cultured at high density. This observation is consistent with previous findings that both the ability of endothelial cells to proliferate in response to angiogenin and the expression of an angiogenin receptor on the cell surface depend on cell density. Nuclear (125)I-angiogenin is not degraded and is neither spontaneously dissociated nor replaced by unlabeled angiogenin. It is, however, released by deoxyribonuclease I, but not by ribonuclease A, suggesting that angiogenin binds to DNA in the nucleus. These results suggest that in addition to acting as a ribonuclease, angiogenin may play a role in regulating gene expression by direct binding to DNA.

Expression of receptors for human angiogenin in vascular smooth muscle cells

Human angiogenin is a plasma protein with angiogenic and ribonucleolytic activities. Angiogenin inhibited both DNA replication and proliferation of aortic smooth muscle cells. Binding of 125I-angiogenin to bovine aortic smooth muscle cells at 4 degrees C was specific, saturable, reversible and involved two families of interactions. High-affinity binding sites with an apparent dissociation constant of 0.2 nm bound 1 x 104 molecules per cell grown at a density of 3 x 104.cm-2. Low-affinity binding sites with an apparent dissociation constant of 0.1 micrometer bound 4 x 106 molecules.cell-1. High-affinity binding sites decreased as cell density increased and were not detected at confluence. 125I-angiogenin bound specifically to cells routinely grown in serum-free conditions, indicating that the angiogenin-binding components were cell-derived. Affinity labelling of sparse bovine smooth muscle cells yielded seven major specific complexes of 45, 52, 70, 87, 98, 210 and 250-260 kDa. The same pattern was obtained with human cells. Potential modulators of angiogenesis such as protamine, heparin and the placental ribonuclease inhibitor competed for angiogenin binding to the cells. Together these data suggest that cultured bovine and human aortic smooth muscle cells express specific receptors for human angiogenin.

Heparin interferes with translocation of Yop proteins into HeLa cells and binds to LcrG, a regulatory component of the Yersinia Yop apparatus

Yersiniae are equipped with the Yop virulon, an apparatus that allows extracellular bacteria to deliver toxic Yop proteins inside the host cell cytosol in order to sabotage the communication networks of the host cell or even to cause cell death. LcrG is a component of the Yop virulon involved in the regulation of secretion of the Yops. In this paper, we show that LcrG can bind HeLa cells, and we analyse the role of proteoglycans in this phenomenon. Treatment of the HeLa cells with heparinase I, but not chondroitinase ABC, led to inhibition of binding. Competition assays indicated that heparin and dextran sulphate strongly inhibited binding, but that other glycosaminoglycans did not. This demonstrated that binding of HeLa cells to purified LcrG is caused by heparan sulphate proteoglycans. LcrG could bind directly to heparin-agarose beads and, in agreement with these results, analysis of the protein sequence of Yersinia enterocolitica LcrG revealed heparin-binding motifs. In vitro production and secretion by Y. enterocolitica of the Yops was unaffected by the addition of heparin. However, the addition of exogenous heparin decreased the level of YopE-Cya translocation into HeLa cells. A similar decrease was seen with dextran sulphate, whereas the other glycosaminoglycans tested had no significant effect. Translocation was also decreased by treatment of HeLa cells with heparinitase, but not with chondroitinase. Thus, heparan sulphate proteoglycans have an important role to play in translocation. The interaction between LcrG and heparan sulphate anchored at the surface of HeLa cells could be a signal triggering deployment of the Yop translocation machinery. This is the first report of a eukaryotic receptor interacting with the type III secretion and associated translocation machinery of Yersinia or of other bacteria.