Heparin-binding Sites in Granulocyte-Macrophage Colony-stimulating Factor

Amphiphilic cytokine traps remodel marrow adipose tissue for hematopoietic microenvironment amelioration

Hematopoietic stem cell transplantation (HSCT) is extensively employed in the treatment of hematological malignancies but is markedly constrained by the paucity of hematopoietic stem/progenitor cells (HSPCs). Recent studies have found that marrow adipose tissue (MAT) acts on hematopoiesis through complicated mechanisms. Therefore, the osteo-organoids fabricated in vivo using biomaterials loaded with recombinant human bone morphogenetic protein 2 (rhBMP-2) have been used as models of MAT for our research. To obtain sufficient amounts of therapeutic HSPCs and healthy MAT, we have developed amphiphilic chitosan (AC)-gelatin as carriers of rhBMP-2 to the regulate type conversion of adipose tissue and trap hematopoietic growth factors. Unlike medicine interventions or cell therapies, the traps based on AC not only attenuate the occupancy of adipocytes within the hematopoietic microenvironment while preserving stem cell factor concentrations, but also improve marrow metabolism by promoting MAT browning. In conclusion, this approach increases the proportion of HSPCs in osteo-organoids, and optimizes the composition and metabolic status of MAT. These findings furnish an experimental basis for regulating hematopoiesis in vivo through materials that promote the development of autologous HSPCs. Additionally, this approach presents a theoretical model of rapid adipogenesis for the study of adipose-related pathologies and potential pharmacological targets.

Recognition of granulocyte-macrophage colony-stimulating factor by specific S100 proteins

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic myelopoietic growth factor and proinflammatory cytokine, clinically used for multiple indications and serving as a promising target for treatment of many disorders, including cancer, multiple sclerosis, rheumatoid arthritis, psoriasis, asthma, COVID-19. We have previously shown that dimeric Ca2+-bound forms of S100A6 and S100P proteins, members of the multifunctional S100 protein family, are specific to GM-CSF. To probe selectivity of these interactions, the affinity of recombinant human GM-CSF to dimeric Ca2+-loaded forms of 18 recombinant human S100 proteins was studied by surface plasmon resonance spectroscopy. Of them, only S100A4 protein specifically binds to GM-CSF with equilibrium dissociation constant, Kd, values of 0.3-2 μM, as confirmed by intrinsic fluorescence and chemical crosslinking data. Calcium removal prevents S100A4 binding to GM-CSF, whereas monomerization of S100A4/A6/P proteins disrupts S100A4/A6 interaction with GM-CSF and induces a slight decrease in S100P affinity for GM-CSF. Structural modelling indicates the presence in the GM-CSF molecule of a conserved S100A4/A6/P-binding site, consisting of the residues from its termini, helices I and III, some of which are involved in the interaction with GM-CSF receptors. The predicted involvement of the 'hinge' region and F89 residue of S100P in GM-CSF recognition was confirmed by mutagenesis. Examination of S100A4/A6/P ability to affect GM-CSF signaling showed that S100A4/A6 inhibit GM-CSF-induced suppression of viability of monocytic THP-1 cells. The ability of the S100 proteins to modulate GM-CSF activity is relevant to progression of various neoplasms and other diseases, according to bioinformatics analysis. The direct regulation of GM-CSF signaling by extracellular forms of the S100 proteins should be taken into account in the clinical use of GM-CSF and development of the therapeutic interventions targeting GM-CSF or its receptors.

A glycan-based approach to cell characterization and isolation: Hematopoiesis as a paradigm

Cell surfaces display a wide array of molecules that confer identity. While flow cytometry and cluster of differentiation (CD) markers have revolutionized cell characterization and purification, functionally heterogeneous cellular subtypes remain unresolvable by the CD marker system alone. Using hematopoietic lineages as a paradigm, we leverage the extraordinary molecular diversity of heparan sulfate (HS) glycans to establish cellular "glycotypes" by utilizing a panel of anti-HS single-chain variable fragment antibodies (scFvs). Prospective sorting with anti-HS scFvs identifies functionally distinct glycotypes within heterogeneous pools of mouse and human hematopoietic progenitor cells and enables further stratification of immunophenotypically pure megakaryocyte-erythrocyte progenitors. This stratification correlates with expression of a heptad of HS-related genes that is reflective of the HS epitope recognized by specific anti-HS scFvs. While we show that HS glycotyping provides an orthogonal set of tools for resolution of hematopoietic lineages, we anticipate broad utility of this approach in defining and isolating novel, viable cell types across diverse tissues and species.

Current Development of Nano-Drug Delivery to Target Macrophages

Macrophages are the most important innate immune cells that participate in various inflammation-related diseases. Therefore, macrophage-related pathological processes are essential targets in the diagnosis and treatment of diseases. Since nanoparticles (NPs) can be preferentially taken up by macrophages, NPs have attracted most attention for specific macrophage-targeting. In this review, the interactions between NPs and the immune system are introduced to help understand the pharmacokinetics and biodistribution of NPs in immune cells. The current design and strategy of NPs modification for specific macrophage-targeting are investigated and summarized.

Heparinoid Complex-Based Heparin-Binding Cytokines and Cell Delivery Carriers

Heparinoid is the generic term that is used for heparin, heparan sulfate (HS), and heparin-like molecules of animal or plant origin and synthetic derivatives of sulfated polysaccharides. Various biological activities of heparin/HS are attributed to their specific interaction and regulation with various heparin-binding cytokines, antithrombin (AT), and extracellular matrix (ECM) biomolecules. Specific domains with distinct saccharide sequences in heparin/HS mediate these interactions are mediated and require different highly sulfated saccharide sequences with different combinations of sulfated groups. Multivalent and cluster effects of the specific sulfated sequences in heparinoids are also important factors that control their interactions and biological activities. This review provides an overview of heparinoid-based biomaterials that offer novel means of engineering of various heparin-binding cytokine-delivery systems for biomedical applications and it focuses on our original studies on non-anticoagulant heparin-carrying polystyrene (NAC-HCPS) and polyelectrolyte complex-nano/microparticles (N/MPs), in addition to heparin-coating devices.

Immunomodulation as Rescue for Chronic Atonic Skin Wounds

Chronic skin wounds, caused by arterial or venous insufficiency or by physical pressure, constitute an increasing medical problem as populations age. Whereas typical wounds are characterized by local inflammation that participates in the healing process, atonic wounds lack inflammatory markers, such as neutrophil infiltration, and generally do not heal. Recently, prominent roles in the immunopathology of chronic wounds were attributed to dysregulations in specific cytokines, chemokines, matrix metalloproteinases (MMPs), and their substrates. Together with the complement system, these molecular players provide necessary defense against infections, initiate angiogenesis, and prepare tissue reconstitution. Here, we review the current state of the field and include the concept that, aside from surgery and stem cell therapy, healing may be enhanced by immunomodulating agents.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Distinguishing autocrine and paracrine signals in hematopoietic stem cell culture using a biofunctional microcavity platform

Homeostasis of hematopoietic stem cells (HSC) in the mammalian bone marrow stem cell niche is regulated by signals of the local microenvironment. Besides juxtacrine, endocrine and metabolic cues, paracrine and autocrine signals are involved in controlling quiescence, proliferation and differentiation of HSC with strong implications on expansion and differentiation ex vivo as well as in vivo transplantation. Towards this aim, a cell culture analysis on a polymer microcavity carrier platform was combined with a partial least square analysis of a mechanistic model of cell proliferation. We could demonstrate the discrimination of specific autocrine and paracrine signals from soluble factors as stimulating and inhibitory effectors in hematopoietic stem and progenitor cell culture. From that we hypothesize autocrine signals to be predominantly involved in maintaining the quiescent state of HSC in single-cell niches and advocate our analysis platform as an unprecedented option for untangling convoluted signaling mechanisms in complex cell systems being it of juxtacrine, paracrine or autocrine origin.

Interaction of the Heparin-Binding Consensus Sequence of β-Amyloid Peptides with Heparin and Heparin-Derived Oligosaccharides

Alzheimer's disease (AD) is characterized by the presence of amyloid plaques in the AD brain. Comprised primarily of the 40- and 42-residue β-amyloid (Aβ) peptides, there is evidence that the heparan sulfate (HS) of heparan sulfate proteoglycans (HSPGs) plays a role in amyloid plaque formation and stability; however, details of the interaction of Aβ peptides with HS are not known. We have characterized the interaction of heparin and heparin-derived oligosaccharides with a model peptide for the heparin- and HS-binding domain of Aβ peptides (Ac-VHHQKLV-NH2; Aβ(12-18)), with mutants of Aβ(12-18), and with additional histidine-containing peptides. The nature of the binding interaction was characterized by NMR, binding constants and other thermodynamic parameters were determined by isothermal titration calorimetry (ITC), and relative binding affinities were determined by heparin affinity chromatography. The binding of Aβ(12-18) by heparin and heparin-derived oligosaccharides is pH-dependent, with the imidazolium groups of the histidine side chains interacting site-specifically within a cleft created by a trisaccharide sequence of heparin, the binding is mediated by electrostatic interactions, and there is a significant entropic contribution to the binding free energy as a result of displacement of Na(+) ions from heparin upon binding of cationic Aβ(12-18). The binding constant decreases as the size of the heparin-derived oligosaccharide decreases and as the concentration of Na(+) ion in the bulk solution increases. Structure-binding relationships characterized in this study are analyzed and discussed in terms of the counterion condensation theory of the binding of cationic peptides by anionic polyelectrolytes.

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.

Effect of systemic heparan sulfate haploinsufficiency on steady state hematopoiesis and engraftment of hematopoietic stem cells

Heparan sulfate (HS) proteoglycans on stromal and hematopoietic stem/progenitor cells (HSPC) help form the stem cell niche, co-localize molecules that direct stem cell fate, and modulate HSPC homing and retention. Inhibition of HS function mobilizes marrow HSPC. In vitro, HSPC maintenance is influenced by stromal HS structure and concentration. Because inhibition of HS activity or synthesis may be developed for HSPC transplantation, it is important to examine if systemic HS deficiency influences hematopoiesis in vivo. In a transgenic mouse model of HS haploinsufficiency, we examined endogenous hematopoiesis and engraftment of allogeneic bone marrow. Endogenous hematopoiesis was normal except gender-specific alterations in peripheral blood monocyte and platelet counts. Donor engraftment was achieved in all mice following myeloablative irradiation, but HS deficiency in the stromal microenvironment, on HSPC, or both (the 3 test conditions), was associated with a trend towards lower donor engraftment percentage in the bone marrow. Following non-myeloablative irradiation, competitive engraftment was achieved in 22% of mice in the test conditions, vs 50% of control animals (P = 0.03). HS deficiency did not re-direct donor engraftment from bone marrow to spleen or liver. Normal HS levels in the stromal microenvironment and HSPC are required for HSPC engraftment following non-myeloablative conditioning.

Modulation of cellular stress response via the erythropoietin/CD131 heteroreceptor complex in mouse mesenchymal-derived cells

Tissue-protective properties of erythropoietin (EPO) have let to the discovery of an alternative EPO signaling via an EPO-R/CD131 receptor complex which can now be specifically targeted through pharmaceutically designed short sequence peptides such as ARA290. However, little is still known about specific functions of alternative EPO signaling in defined cell populations. In this study, we investigated effects of signaling through EPO-R/CD131 complex on cellular stress responses and pro-inflammatory activation in different mesenchymal-derived phenotypes. We show that anti-apoptotic, anti-inflammatory effects of ARA290 and EPO coincide with the externalization of CD131 receptor component as an immediate response to cellular stress. In addition, alternative EPO signaling strongly modulated transcriptional, translational, or metabolic responses after stressor removal. Specifically, we saw that ARA290 was able to overcome a TNFα-mediated inhibition of transcription factor activation related to cell stress responses, most notably of serum response factor (SRF), heat shock transcription factor protein 1 (HSF1), and activator protein 1 (AP1). We conclude that alternative EPO signaling acts as a modulator of pro-inflammatory signaling pathways and likely plays a role in restoring tissue homeostasis. Key message: Erythropoietin (EPO) triggers an alternative pathway via heteroreceptor EPO/CD131. ARA290 peptide specifically binds EPO/CD131 but not the canonical EPO/EPO receptor. Oxidative stress and inflammation promote cell surface expression of CD131. ARA290 prevents tumor necrosis factor-mediated inhibition of stress-related genes. Alternative EPO signaling modulates inflammation and promotes tissue homeostasis.

Deletion of plant-specific sugar residues in plant N-glycans by repression of GDP-D-mannose 4,6-dehydratase and β-1,2-xylosyltransferase genes

Production of pharmaceutical glycoproteins, such as therapeutic antibodies and cytokines, in plants has many advantages in safety and reduced costs. However, plant-made glycoproteins have N-glycans with plant-specific sugar residues (core β-1,2-xylose and α-1,3-fucose) and a Lewis a (Le(a)) epitope, Galβ(1-3)[Fucα(1-4)]GlcNAc. Because it is likely that these sugar residues and glycan structures are immunogenic, many attempts have been made to delete them. Previously, we reported the simultaneous deletion of the plant-specific core α-1,3-fucose and α-1,4-fucose residues in Le(a) epitopes by repressing the GDP-D-mannose 4,6-dehydratase (GMD) gene, which is associated with GDP-L-fucose biosynthesis, in Nicotiana benthamiana plants (rGMD plants, renamed to ΔGMD plants) (Matsuo and Matsumura, Plant Biotechnol. J., 9, 264-281, 2011). In the present study, we generated a core β-1,2-xylose residue-repressed transgenic N. benthamiana plant by co-suppression of β-1,2-xylosyltransferase (ΔXylT plant). By crossing ΔGMD and ΔXylT plants, we successfully generated plants in which plant-specific sugar residues were repressed (ΔGMDΔXylT plants). The proportion of N-glycans with deleted plant-specific sugar residues found in total soluble protein from ΔGMDΔXylT plants increased by 82.41%. Recombinant mouse granulocyte/macrophage-colony stimulating factor (mGM-CSF) and human monoclonal immunoglobulin G (hIgG) harboring N-glycans with deleted plant-specific sugar residues were successfully produced in ΔGMDΔXylT plants. Simultaneous repression of the GMD and XylT genes in N. benthamiana is thus very useful for deleting plant-specific sugar residues.

Association between cytokine removal by polymyxin B hemoperfusion and improved pulmonary oxygenation in patients with acute exacerbation of idiopathic pulmonary fibrosis

Acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) is characterized by severe worsening dyspnea of unknown etiology and high mortality without effective treatment. Recently, direct hemoperfusion with polymyxin B (PMX)-immobilized fiber cartridge (PMX-DHP) has been reported to improve pulmonary oxygenation and survival in patients with AE-IPF although its mechanism of action remains unknown. To gain insights into the pathobiology of AE-IPF through the beneficial effects of PMX-DHP, we analyzed the profile of cytokines adsorbed onto PMX-fibers used in 9 AE-IPF patients. In addition, the sera of these AE-IPF patients collected immediately before and after PMX-DHP, 9 stable IPF patients and 8 healthy individuals were also analyzed. The serum levels of cytokines including IL-9, IL-12, IL-17, PDGF and VEGF were significantly decreased immediately after PMX-DHP (P<0.02), and VEGF and IL-12 were most prominently reduced. In addition to PDGF and VEGF, IL-1β, IL-1ra, IL-8, IL-23, FGF basic, GM-CSF, IP-10, RANTES and TGF-β were eluted from used PMX-fibers. Interestingly, improved pulmonary oxygenation after PMX-DHP was correlated well with the quantities of eluted VEGF. These results suggest that adsorption of proinflammatory, profibrotic and proangiogenic cytokines onto PMX-fibers is one of the mechanisms of action of PMX-DHP in AE-IPF. Notably, removal of VEGF by PMX-DHP may contribute to the rapid improvement in oxygenation by suppressing vascular permeability in the lung.

Mast cell proteoglycans

Mast cells are versatile effector cells of the immune system, contributing to both innate and adaptive immunity toward pathogens but also having profound detrimental activities in the context of inflammatory disease. A hallmark morphological feature of mast cells is their large content of cytoplasmic secretory granules, filled with numerous secretory compounds, including highly negatively charged heparin or chondroitin sulfate proteoglycans of serglycin type. These anionic proteoglycans provide the basis for the strong metachromatic staining properties of mast cells seen when applying various cationic dyes. Functionally, the mast cell proteoglycans have been shown to have an essential role in promoting the storage of other granule-contained compounds, including bioactive monoamines and different mast cell-specific proteases. Moreover, granule proteoglycans have been shown to regulate the enzymatic activities of mast cell proteases and to promote apoptosis. Here, the current knowledge of mast cell proteoglycans is reviewed.

Promotion of angiogenesis by sustained release of rhGM-CSF from heparinized collagen/chitosan scaffolds

A novel dermal substitute of combining recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) with a porous heparinized collagen/chitosan scaffolds was developed, considering the inadequate angiogenesis during repair of full-thickness skin defects. The physicochemical properties of heparinized collagen/chitosan scaffolds were examined and in vitro release pattern of rhGM-CSF from scaffolds was measured by ELISA. Four groups of composite scaffolds (heparinized or unheparinized scaffolds loaded with or without rhGM-CSF) were fabricated for subcutaneous implantation in young adult male Sprague-Dawley (SD) rats. Tissue specimens were harvested at different time points after implantation for histopathological, immunohistochemical observation, and Western blotting analysis. The heparinized scaffolds (H(1)E) showed slower biodegradation and sustained release of rhGM-CSF in vitro, although no significantly different release pattern was observed between the H(1)E and unheparinized scaffolds (H(0)E). In vivo investigation revealed that the heparinized scaffolds loaded with rhGM-CSF (H(1)E/rhGM-CSF) had the best cellular adhesion and migration, new vessel formation, and highest expression of VEGF and TGF-β1, indicating promoted angiogenesis. This study demonstrated that composite dermal substitute of combining rhGM-CSF with a porous heparinized collagen/chitosan scaffolds could be a potential therapeutic agent for full-thickness skin defects because of its sustained delivery of rhGM-CSF.

Human apolipoprotein A-I-derived amyloid: its association with atherosclerosis

Amyloidoses constitute a group of diseases in which soluble proteins aggregate and deposit extracellularly in tissues. Nonhereditary apolipoprotein A-I (apoA-I) amyloid is characterized by deposits of nonvariant protein in atherosclerotic arteries. Despite being common, little is known about the pathogenesis and significance of apoA-I deposition. In this work we investigated by fluorescence and biochemical approaches the impact of a cellular microenvironment associated with chronic inflammation on the folding and pro-amyloidogenic processing of apoA-I. Results showed that mildly acidic pH promotes misfolding, aggregation, and increased binding of apoA-I to extracellular matrix elements, thus favoring protein deposition as amyloid like-complexes. In addition, activated neutrophils and oxidative/proteolytic cleavage of the protein give rise to pro amyloidogenic products. We conclude that, even though apoA-I is not inherently amyloidogenic, it may produce non hereditary amyloidosis as a consequence of the pro-inflammatory microenvironment associated to atherogenesis.

Determination of the primary structure and carboxyl pK (A)s of heparin-derived oligosaccharides by band-selective homonuclear-decoupled two-dimensional (1)H NMR

Determination of the structure of heparin-derived oligosaccharides by ¹H NMR is challenging because resonances for all but the anomeric protons cover less than 2 ppm. By taking advantage of increased dispersion of resonances for the anomeric H¹ protons at low pD and the superior resolution of band-selective, homonuclear-decoupled (BASHD) two-dimensional ¹H NMR, the primary structure of the heparin-derived octasaccharide ∆UA(2S)-[(1 → 4)-GlcNS(6S)-(1 → 4)-IdoA(2S)-]₃-(1 → 4)-GlcNS(6S) has been determined, where ∆UA(2S) is 2-O-sulfated ∆^4,5-unsaturated uronic acid, GlcNS(6S) is 6-O-sulfated, N-sulfated β-d-glucosamine and IdoA(2S) is 2-O-sulfated α-l-iduronic acid. The spectrum was assigned, and the sites of N- and O-sulfation and the conformation of each uronic acid residue were established, with chemical shift data obtained from BASHD-TOCSY spectra, while the sequence of the monosaccharide residues in the octasaccharide was determined from inter-residue NOEs in BASHD-NOESY spectra. Acid dissociation constants were determined for each carboxylic acid group of the octasaccharide, as well as for related tetra- and hexasaccharides, from chemical shift–pD titration curves. Chemical shift–pD titration curves were obtained for each carboxylic acid group from sub-spectra taken from BASHD-TOCSY spectra that were measured as a function of pD. The pK_As of the carboxylic acid groups of the ∆UA(2S) residues are less than those of the IdoA(2S) residues, and the pK_As of the carboxylic acid groups of the IdoA(2S) residues for a given oligosaccharide are similar in magnitude. Relative acidities of the carboxylic acid groups of each oligosaccharide were calculated from chemical shift data by a pH-independent method.

Granulocyte-macrophage colony-stimulating factor gene based therapy for acute limb ischemia in a mouse model

BACKGROUND

Granulocyte-colony-stimulating factor (GM-CSF) is a pleiotropic factor for hematopoiesis that stimulates myeloblasts, monoblasts and mobilization of bone marrow stem cells. Therefore, the GM-CSF gene is a potential candidate for vessel formation and tissue remodeling in the treatment of ischemic diseases.

METHODS

A new mouse limb ischemia was established by surgery and gene transfer was performed by injection of 100 microg of a plasmid carrying GM-CSF. Muscle force and weight, histology, capillary density, circulating stem cells and monocytes were determined after 3-4 weeks.

RESULTS

More than 60% of nontreated ischemic animals showed gangrene below the heel after 4 weeks, whereas the GM-CSF gene-treated animals showed only darkening of nails or toes. These animals demonstrated a full recovery of the affected muscles in terms of weight, force and muscle fiber structure, but the muscles of nontreated ischemic animals lost approximately 50% weight, 86% force and their regular structure. When the GM-CSF gene was injected into the contralateral limb, only partial loss was observed, demonstrating a distant effect of GM-CSF. The capillary density in the GM-CSF-treated group was 52% higher in relation to the nontreated group. Blood analysis by flow cytometry showed that the GM-CSF-treated group had 10-20% higher levels of circulating monocytes and Sca-1(+).

CONCLUSIONS

We conclude that the direct administration of GM-CSF gene in limb ischemia had a strong therapeutic effect because it promoted the recovery of muscle mass, force and structure by mobilizing therapeutic cells and augmenting the number of vessels.

Tumor-induced tolerance and immune suppression by myeloid derived suppressor cells

Emerging evidence indicates that the Achilles' heel of cancer immunotherapies is often the complex interplay of tumor-derived factors and deviant host properties, which involve a wide range of immune elements in the lymphoid and myeloid compartments. Regulatory lymphocytes, tumor-conditioned myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages, and dysfunctional and immature dendritic cells take part in a complex immunoregulatory network. Despite the fact that some mechanisms governing tumor-induced immune tolerance and suppression are starting to be better understood and their complexity dissected, little is known about the diachronic picture of immune tolerance. Based on observations of MDSCs, we present a time-structured and topologically consistent idea of tumor-dependent tolerance progression in tumor-bearing hosts.

Biological implications of glycosaminoglycan interactions with haemopoietic cytokines

Heparan sulphate (HS) glycosaminoglycans (GAGs) are an integral part of the signalling complex of fibroblast derived growth factor (FGF) family members, HS being regarded as a coreceptor. FGFs are also retained in the tissues by binding to HS structures. Early studies on the contribution of the bone marrow stroma to haemopoiesis suggested that cytokines with a role in haemopoiesis were similarly retained in the stroma through interactions with HS. However, the functional outcomes of these cytokines binding HS were poorly understood. Here the GAG-binding properties of cytokines of the four alpha-helical bundle family and the biological consequences of such binding are reviewed. From this analysis it is apparent that although many of these cytokines do bind GAGs, GAG binding is not a consistent feature, nor is the site of GAG binding conserved among these cytokines. The biological outcome of GAG binding depends, in part, on the location of the GAG-binding site on the cytokine. In some cases GAG binding appears to block signalling, whereas in others signalling is likely to be facilitated by binding. It is postulated that the interactions of these cytokines with their receptor complexes evolved independently of GAG binding, with GAG binding being an additional feature for a subset of this cytokine family. Nevertheless, because GAG binding localizes cytokines to sites within tissues, these interactions are likely to be critically important for the biology of these cytokines.

Evidence for NL1-independent nuclear translocation of the mineralocorticoid receptor

In the absence of hormone, corticosteroid receptors are primarily located in the cytoplasm, and they rapidly accumulate in the nucleus (t0.5 = 5 min) upon ligand binding. It is generally believed that the dissociation of hsp90 from the receptor is an absolute requirement for allowing its nuclear translocation. However, recent evidence suggests that hsp90 may remain associated with the glucocorticoid receptor during this process, and thus, the receptor nuclear localization signal (NLS) is not obscured by its presence. To determine the requirements for mineralocorticoid receptor (MR) nuclear transport, it was first shown that in rat kidney collecting duct cells, nuclear localization of MR in the presence of aldosterone was complete in 10 min. Although the hsp90 inhibitor radicicol delayed nuclear translocation, it did not prevent complete nuclear accumulation of MR at longer incubation times (t0.5 = 30-40 min). MR carbamylation generates a non-steroid-transformed receptor that, in contrast to native MR, is very stable in cell-free systems. In contrast to the full nuclear translocation of aldosterone-transformed MR, only a fraction of the carbamylated MR became nuclear in digitonin-permeabilized cells even though its NLS is exposed. Furthermore, while preincubation of permeabilized cells with NL1 peptide or anti-NL1 antibody fully inhibited the nuclear translocation of NL1-tagged albumin, neither treatment fully inhibited MR nuclear translocation. We postulate that there are at least two possible mechanisms for MR nuclear translocation. One of them is hsp90- and NL1-dependent, and the other functions in a manner that is independent of the classical pathway.

Leukocyte infiltration in cancer creates an unfavorable environment for antitumor immune responses: a novel target for therapeutic intervention

The interaction between tumor cells and the nearby environment is being actively investigated to explore how this interplay affects the initiation and progression of cancer. Host-tumor relationship results in the production of pro-inflammatory cytokines and chemokines that promote the recruitment of leukocytes within and around developing neoplasms. Cancer cells, together with newly recruited tumor-infiltrating cells, can also activate fibroblast and vascular responses, thus resulting in a chronic microenvironment perturbation. In this complex scenario, interactions between innate and adaptive immune cells can be disturbed, leading to a failure of immune-mediated tumor recognition and destruction. On the basis of the recent awareness about tumor promotion and immune deregulation by immune/inflammatory cells, novel anti-cancer strategies can be exploited.

Structure, dynamics and heparin binding of the C-terminal domain of insulin-like growth factor-binding protein-2 (IGFBP-2)

Insulin-like growth factor-binding protein-2 (IGFBP-2) is the largest member of a family of six proteins (IGFBP-1 to 6) that bind insulin-like growth factors I and II (IGF-I/II) with high affinity. In addition to regulating IGF actions, IGFBPs have IGF-independent functions. The C-terminal domains of IGFBPs contribute to high-affinity IGF binding, and confer binding specificity and have overlapping but variable interactions with many other molecules. Using nuclear magnetic resonance (NMR) spectroscopy, we have determined the solution structure of the C-terminal domain of IGFBP-2 (C-BP-2) and analysed its backbone dynamics based on 15N relaxation parameters. C-BP-2 has a thyroglobulin type 1 fold consisting of an alpha-helix, a three-stranded anti-parallel beta-sheet and three flexible loops. Compared to C-BP-6 and C-BP-1, structural differences that may affect IGF binding and underlie other functional differences were found. C-BP-2 has a longer disordered loop I, and an extended C-terminal tail, which is unstructured and very mobile. The length of the helix is identical with that of C-BP-6 but shorter than that of C-BP-1. Reduced spectral density mapping analysis showed that C-BP-2 possesses significant rapid motion in the loops and termini, and may undergo slower conformational or chemical exchange in the structured core and loop II. An RGD motif is located in a solvent-exposed turn. A pH-dependent heparin-binding site on C-BP-2 has been identified. Protonation of two histidine residues, His271 and His228, seems to be important for this binding, which occurs at slightly acidic pH (6.0) and is more significant at pH 5.5, but is largely suppressed at pH 7.4. Possible preferential binding of IGFBP-2 and its C- domain fragments to glycosaminoglycans in the acidic extracellular matrix (ECM) of tumours may be related to their roles in cancer.