Insights into the role of heparan sulphate in fibroblast growth factor signalling

Experimental study of a heparin-coated venous stent fabricated by atomic layer deposition

OBJECTIVE

To evaluate the safety and efficacy of heparin-coated venous stents in animals.

METHODS

We used atomic layer deposition technology to obtain a heparin coating with good stability and then prepared a heparin-coated venous stent based on this technology. The experimental stents were prepared according to the diameter of the rabbit inferior vena cava and were divided into Ni-Ti alloy stent group, Ni-Ti-Al₂O₃ stent group and Ni-Ti-Al₂O₃-Heparin stent group. 3 days, 7 days and 14 days after stent implantation, the materials were collected, and the three groups of stents were observed by hard tissue section pathology, immunohistochemistry and scanning electron microscope to observe the differences in vascular wall inflammation, thrombosis, lumen stenosis and vascular intima regeneration.

RESULT AND CONCLUSION

The experiment confirmed the safety of the heparin-coated stent in vivo. Compared with the control group, the experimental group showed a high degree of vascular endothelialization and an intact neointimal structure 14 days after implantation. The long-term safety and biological effects of heparin-coated venous stents in animals require further study.

Phenol-Grafted Alginate Sulfate Hydrogel as an Injectable FGF-2 Carrier

In the field of tissue engineering, fibroblast growth factor-2 (FGF-2) effectively regenerates damaged tissue and restores its biological function. However, FGF-2 readily diffuses and degrades under physiological conditions. Therefore, methods for the sustained and localized delivery of FGF-2 are needed. Drug delivery systems using hydrogels as carriers have attracted significant interest. Injectable hydrogels with an affinity for FGF-2 are candidates for FGF-2 delivery systems. In this study, we fabricated a hydrogel from phenol-grafted alginate sulfate (AlgS-Ph) and investigated its application to the delivery of FGF-2. The hydrogel was prepared under mild conditions via horseradish peroxidase (HRP)-mediated cross-linking. Surface plasmon resonance (SPR) measurements show that the AlgS-Ph hydrogel has an affinity for FGF-2 in accordance with its degree of sulfation. Conditions for the preparation of the AlgS-Ph hydrogel, including HRP and H₂O₂ concentrations, are optimized so that the hydrogel can be used as an injectable drug carrier. The hydrogel shows no cytotoxicity when using 10T1/2 cells as a model cell line. The angiogenesis assay shows that FGF-2 released from the AlgS-Ph hydrogel promotes the formation of blood vessels. These results indicate that the AlgS-Ph hydrogel is a suitable candidate for the FGF-2 carrier.

Development of a Chemically Defined Medium for in vitro Expansion of Primary Bovine Satellite Cells

The use of fetal bovine serum (FBS) in animal cell culture media is widely spread since it provides a broad spectrum of molecules that are known to support cell attachment and growth. However, the harvest and collection procedures of FBS raise ethical concerns and serum is an ill-defined and expensive component. This is especially problematic when it comes to regulatory approval for food applications like cultured meat. The aim of this study is to develop a chemically defined, cost efficient serum-free and animal-free medium that supports the attachment and expansion of bovine myoblasts while maintaining their differentiation capacity. Bovine satellite cells were harvested and isolated from a fresh sample of skeletal muscle tissue and cultured in planar systems. The efficacy of the tested formulations was assessed with metabolic assays and cell counting techniques. Optical microscopy was used to observe cellular morphology and statistical analysis was applied. Based on a comprehensive literature analysis, a defined serum-free medium (SFM) composition was developed consisting of DMEM/F12 as basal medium, supplemented with L-ascorbic acid 2-phosphate, fibronectin, hydrocortisone, GlutaMAX^™, albumin, ITS-X, hIL-6, α-linolenic acid, and growth factors such as FGF-2, VEGF, IGF-1, HGF, and PDGF-BB. To our knowledge, this is the first defined serum-free and animal free medium formulation specific for bovine myoblasts to date. We conclude that the SFM formulation supported exponential cell growth up to 97% of the serum—containing golden standard growth medium. All reagents used in this study are chemically defined.

Growth factor dependence of the proliferation and survival of cultured lacrimal gland epithelial cells isolated from late-embryonic mice

Epidermal growth factor (EGF) and hepatocyte growth factor (HGF) regulate the growth and morphogenesis of various exocrine glands with branched morphologies. Their roles in lacrimal gland (LG) development remain unknown, but fibroblast growth factor (FGF) 10 is crucial for early LG organogenesis. To clarify the roles of EGF, HGF, and FGF10 in LG development, LG epithelial cells were isolated from late-embryonic and neonatal mice; cultured; and treated with EGF, HGF, or FGF10 and their respective receptor tyrosine kinase (RTK) inhibitors AG1478, PHA665752, or SU5402. EGF and HGF increased the number of viable cells by enhancing DNA synthesis, FGF10 and SU5402 showed no such effect, and RTK inhibitors exhibited the opposite effect. EGF and HGF receptors were immunostained in cultured late-embryonic LG epithelial cells and terminal LG acini from late embryos and adult mice. HGF was detected in neonatal LG epithelial cell culture supernatants by western blotting. In the absence of EGF and HGF RTK inhibitors, growth factor addition increased the number of viable cells and suppressed cell death. However, when one RTK was inhibited and a growth factor targeting an intact RTK was added, the number of dead cells increased as the number of viable cells increased. No cells survived when both RTKs were inhibited. In explant cultures of LGs from embryos, AG1478 or PHA665752 decreased the number of Ki67-positive proliferating epithelial cells in terminal acini. Thus, EGF and HGF may function in a cooperative autocrine manner, supporting cell proliferation and survival during LG development in late-embryonic and neonatal mice.

The canonical FGF-FGFR signaling system at the molecular level

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

Expression of Syndecan-1 in Chronic Liver Diseases: Correlation With Hepatic Fibrosis

BACKGROUND/AIM

The mechanisms underlying the contribution of the heparan sulfate proteoglycan syndecan-1 to liver tissue injury and to crucial biological processes, such as fibrogenesis, remain to be elucidated. Therefore, we investigated the immunohistochemical expression of syndecan-1 in chronic liver diseases (CLDs) and its probable role in hepatic fibrosis.

MATERIALS AND METHODS

Immunohistochemistry was performed on formalin-fixed, paraffin-embedded tissue sections of biopsy material obtained from 128 patients diagnosed with CLDs. The correlation between syndecan-1 expression and the stage of fibrosis was investigated.

RESULTS

According to the severity of fibrosis, cases were categorized into three groups: early fibrosis; intermediate fibrosis; advanced fibrosis. Syndecan-1 expression was significantly enhanced in advanced fibrosis compared to early (p<0.012) and intermediate (p<0.003) fibrosis.

CONCLUSION

In CLDs, syndecan-1 immunohisto-chemical overexpression was found to be positively correlated with the severity of fibrosis, suggesting its probable role in hepatic fibrogenesis.

What Are the Potential Roles of Nuclear Perlecan and Other Heparan Sulphate Proteoglycans in the Normal and Malignant Phenotype

The recent discovery of nuclear and perinuclear perlecan in annulus fibrosus and nucleus pulposus cells and its known matrix stabilizing properties in tissues introduces the possibility that perlecan may also have intracellular stabilizing or regulatory roles through interactions with nuclear envelope or cytoskeletal proteins or roles in nucleosomal-chromatin organization that may regulate transcriptional factors and modulate gene expression. The nucleus is a mechano-sensor organelle, and sophisticated dynamic mechanoresponsive cytoskeletal and nuclear envelope components support and protect the nucleus, allowing it to perceive and respond to mechano-stimulation. This review speculates on the potential roles of perlecan in the nucleus based on what is already known about nuclear heparan sulphate proteoglycans. Perlecan is frequently found in the nuclei of tumour cells; however, its specific role in these diseased tissues is largely unknown. The aim of this review is to highlight probable roles for this intriguing interactive regulatory proteoglycan in the nucleus of normal and malignant cell types.

Role of Fibroblast Growth Factors Receptors (FGFRs) in Brain Tumors, Focus on Astrocytoma and Glioblastoma

Despite pharmacological treatments and surgical practice options, the mortality rate of astrocytomas and glioblastomas remains high, thus representing a medical emergency for which it is necessary to find new therapeutic strategies. Fibroblast growth factors (FGFs) act through their associated receptors (FGFRs), a family of tyrosine kinase receptors consisting of four members (FGFR1-4), regulators of tissue development and repair. In particular, FGFRs play an important role in cell proliferation, survival, and migration, as well as angiogenesis, thus their gene alteration is certainly related to the development of the most common diseases, including cancer. FGFRs are subjected to multiple somatic aberrations such as chromosomal amplification of FGFR1; mutations and multiple dysregulations of FGFR2; and mutations, translocations, and significant amplifications of FGFR3 and FGFR4 that correlate to oncogenesis process. Therefore, the in-depth study of these receptor systems could help to understand the etiology of both astrocytoma and glioblastoma so as to achieve notable advances in more effective target therapies. Furthermore, the discovery of FGFR inhibitors revealed how these biological compounds improve the neoplastic condition by demonstrating efficacy and safety. On this basis, this review focuses on the role and involvement of FGFRs in brain tumors such as astrocytoma and glioblastoma.

Bi-allelic Pathogenic Variants in HS2ST1 Cause a Syndrome Characterized by Developmental Delay and Corpus Callosum, Skeletal, and Renal Abnormalities

Heparan sulfate belongs to the group of glycosaminoglycans (GAGs), highly sulfated linear polysaccharides. Heparan sulfate 2-O-sulfotransferase 1 (HS2ST1) is one of several specialized enzymes required for heparan sulfate synthesis and catalyzes the transfer of the sulfate groups to the sugar moiety of heparan sulfate. We report bi-allelic pathogenic variants in HS2ST1 in four individuals from three unrelated families. Affected individuals showed facial dysmorphism with coarse face, upslanted palpebral fissures, broad nasal tip, and wide mouth, developmental delay and/or intellectual disability, corpus callosum agenesis or hypoplasia, flexion contractures, brachydactyly of hands and feet with broad fingertips and toes, and uni- or bilateral renal agenesis in three individuals. HS2ST1 variants cause a reduction in HS2ST1 mRNA and decreased or absent heparan sulfate 2-O-sulfotransferase 1 in two of three fibroblast cell lines derived from affected individuals. The heparan sulfate synthesized by the individual 1 cell line lacks 2-O-sulfated domains but had an increase in N- and 6-O-sulfated domains demonstrating functional impairment of the HS2ST1. As heparan sulfate modulates FGF-mediated signaling, we found a significantly decreased activation of the MAP kinases ERK1/2 in FGF-2-stimulated cell lines of affected individuals that could be restored by addition of heparin, a GAG similar to heparan sulfate. Focal adhesions in FGF-2-stimulated fibroblasts of affected individuals concentrated at the cell periphery. Our data demonstrate that a heparan sulfate synthesis deficit causes a recognizable syndrome and emphasize a role for 2-O-sulfated heparan sulfate in human neuronal, skeletal, and renal development.

Receptor tyrosine kinase ligands and inflammatory cytokines cooperatively suppress the fibrogenic activity in temporomandibular-joint-derived fibroblast-like synoviocytes via mitogen-activated protein kinase kinase/extracellular signal-regulated kinase

Osteoarthritis (OA)-related fibrosis is a possible cause of temporomandibular joint (TMJ) stiffness. However, the molecular mechanisms underlying the fibrogenic activity in fibroblast-like synoviocytes (FLSs) remain to be clarified. The present study examined the effects of receptor tyrosine kinase (RTK) ligands, such as fibroblast growth factor (FGF)-1 and epidermal growth factor (EGF), on myofibroblastic differentiation of the FLS cell line FLS1, which is derived from the mouse TMJ. The present study revealed that both FGF-1 and EGF dose-dependently suppressed the expression of the myofibroblast (MF) markers, including α-smooth muscle actin (α-SMA) and type I collagen, in FLS1 cells. Additionally, both FGF-1 and EGF activated extracellular signal-regulated kinase (ERK) in FLS1 cells. In addition, the mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126 abrogated the FGF-1- and EGF-mediated suppression of MF marker expression. On the other hand, inflammatory cytokines, such as interleukin-1β and tumor necrosis factor-α, also suppressed the expression of MF markers in FLS1 cells. Importantly, U0126 abrogated the inflammatory cytokine-mediated suppression of MF marker expression. Interestingly, RTK ligands and inflammatory cytokines additively suppressed the expression of type I collagen. These results suggested that RTK ligands and inflammatory cytokines cooperatively inhibited the fibrogenic activity in FLSs derived from the TMJ in a MEK/ERK-dependent manner. The present findings partially clarify the molecular mechanisms underlying the development of OA-related fibrosis in the TMJ and may aid in identifying therapeutic targets for this condition. Additionally, FGF-1 and EGF could be therapeutically utilized to prevent OA-related fibrosis around the inflammatory TMJ.

HS2ST1-dependent signaling pathways determine breast cancer cell viability, matrix interactions, and invasive behavior

Heparan sulfate proteoglycans (HSPGs) act as signaling co‐receptors by interaction of their sulfated glycosaminoglycan chains with numerous signaling molecules. In breast cancer, the function of heparan sulfate 2‐O‐sulfotransferase (HS2ST1), the enzyme mediating 2‐O‐sulfation of HS, is largely unknown. Hence, a comparative study on the functional consequences of HS2ST1 overexpression and siRNA knockdown was performed in the breast cancer cell lines MCF‐7 and MDA‐MB‐231. HS2ST1 overexpression inhibited Matrigel invasion, while its knockdown reversed the phenotype. Likewise, cell motility and adhesion to fibronectin and laminin were affected by altered HS2ST1 expression. Phosphokinase array screening revealed a general decrease in signaling via multiple pathways. Fluorescent ligand binding studies revealed altered binding of fibroblast growth factor 2 (FGF‐2) to HS2ST1‐expressing cells compared with control cells. HS2ST1‐overexpressing cells showed reduced MAPK signaling responses to FGF‐2, and altered expression of epidermal growth factor receptor (EGFR), E‐cadherin, Wnt‐7a, and Tcf4. The increased viability of HS2ST1‐depleted cells was reduced to control levels by pharmacological MAPK pathway inhibition. Moreover, MAPK inhibitors generated a phenocopy of the HS2ST1‐dependent delay in scratch wound repair. In conclusion, HS2ST1 modulation of breast cancer cell invasiveness is a compound effect of altered E‐cadherin and EGFR expression, leading to altered signaling via MAPK and additional pathways.

Peptide growth factors and their receptors in the vein wall

The varicose vein wall remodeling is a very complex process, which is controlled by numerous factors, including peptide growth factors. The aim of the study was to assess a/b FGF, IGF-1, TGF-β1, VEGF-A and their receptors in the vein wall. Varicose vein samples were taken from 24 patients undergoing varicose vein surgery. The control material consisted of vein specimens collected from 12 patients with chronic limb ischemia. Contents of aFGF, bFGF, IGF-I, TGF-β1, VEGF, IGF-1R, VEGF R1 and VEGF R2 were assessed with ELISA method. Protein expression of FGF R1 and TGF-β RII were evaluated with western blot. Increased contents of aFGF, IGF-1 and VEGF-A were found in varicose veins in comparison with normal ones (p<0.05). In contrast, a significant decrease in TGF-β content was demonstrated in varicose veins (p<0.05). Furthermore, there was no difference in bFGF content in both groups (p>0.05). IGF-1 R content was significantly increased in varicose veins (p<0.05). There was no difference in VEGF R1 content between varicose and normal veins (p>0.05), whereas VEGF R2 content was significantly increased in varicose veins (p<0.05). Western blot demonstrated increased expression of TGF-β RII in varicose veins (p<0.05) and similar expression of FGF R1 in both groups (p>0.05). Demonstrated changes in peptide growth factors and their receptors may disturb metabolism of extracellular matrix in the varicose vein wall and contribute to the development of the disease to its more advanced stages.

Probing the role of proline -135 on the structure, stability, and cell proliferation activity of human acidic fibroblast growth factor

Human acidic fibroblast growth factor 1 (hFGF1) is a protein intricately involved in cell growth and tissue repair. In this study, we investigate the effect(s) of understanding the role of a conserved proline (P135), located in the heparin binding pocket, on the structure, stability, heparin binding affinity, and cell proliferation activity of hFGF1. Substitution of proline-135 with a positively charged lysine (P135K) resulted in partial destabilization of the protein; however, the overall structural integrity of the protein was maintained upon substitution of proline-135 with either a negative charge (P135E) or a polar amino acid (P135Q). Interestingly, upon heparin binding, an increase in thermal stability equivalent to that of wt-hFGF1 was observed when P135 was replaced with a positive (P135K) or a negative charge (P135E), or with a polar amino acid (P135Q). Surprisingly, introduction of negative charge in the heparin-binding pocket at position 135 (P135E) increased hFGF1's affinity for heparin by 3-fold, while the P135K mutation, did not alter the heparin-binding affinity. However, the enhanced heparin-binding affinity of mutant P135E did not translate to an increase in cell proliferation activity. Interestingly, the P135K and P135E double mutations, P135K/R136E and P135/R136E, reduced the heparin binding affinity by ∼3-fold. Furthermore, the cell proliferation activity was increased when the charge reversal mutation R136E was paired with both P135E (P135E/R136E) and P135K (P135K/R136E). Overall, the results of this study suggest that while heparin is useful for stabilizing hFGF1 on the cell surface, this interaction is not mandatory for activation of the FGF receptor.

Effect of extension of the heparin binding pocket on the structure, stability, and cell proliferation activity of the human acidic fibroblast growth factor

Acidic human fibroblast growth factor (hFGF1) plays a key role in cell growth and proliferation. Activation of the cell surface FGF receptor is believed to involve the glycosaminoglycan, heparin. However, the exact role of heparin is a subject of considerable debate. In this context, in this study, the correlation between heparin binding affinity and cell proliferation activity of hFGF1 is examined by extending the heparin binding pocket through selective engineering via charge reversal mutations (D82R, D84R and D82R/D84R). Results of biophysical experiments such as intrinsic tryptophan fluorescence and far UV circular dichroism spectroscopy suggest that the gross native structure of hFGF1 is not significantly perturbed by the engineered mutations. However, results of limited trypsin digestion and ANS binding experiments show that the backbone structure of the D82R variant is more flexible than that of the wild type hFGF1. Results of the temperature and urea-induced equilibrium unfolding experiments suggest that the stability of the charge-reversal mutations increases in the presence of heparin. Isothermal titration calorimetry (ITC) data reveal that the heparin binding affinity is significantly increased when the charge on D82 is reversed but not when the negative charge is reversed at both positions D82 and D84 (D82R/D84R). However, despite the increased affinity of D82R for heparin, the cell proliferation activity of the D82R variant is observed to be reduced compared to the wild type hFGF1. The results of this study clearly demonstrate that heparin binding affinity of hFGF1 is not strongly correlated to its cell proliferation activity.

Osteoblast Differentiation and Bone Matrix Formation In Vivo and In Vitro

We review the characteristics of osteoblast differentiation and bone matrix synthesis. Bone in air breathing vertebrates is a specialized tissue that developmentally replaces simpler solid tissues, usually cartilage. Bone is a living organ bounded by a layer of osteoblasts that, because of transport and compartmentalization requirements, produce bone matrix exclusively as an organized tight epithelium. With matrix growth, osteoblasts are reorganized and incorporated into the matrix as living cells, osteocytes, which communicate with each other and surface epithelium by cell processes within canaliculi in the matrix. The osteoblasts secrete the organic matrix, which are dense collagen layers that alternate parallel and orthogonal to the axis of stress loading. Into this matrix is deposited extremely dense hydroxyapatite-based mineral driven by both active and passive transport and pH control. As the matrix matures, hydroxyapatite microcrystals are organized into a sophisticated composite in the collagen layer by nucleation in the protein lattice. Recent studies on differentiating osteoblast precursors revealed a sophisticated proton export network driving mineralization, a gene expression program organized with the compartmentalization of the osteoblast epithelium that produces the mature bone matrix composite, despite varying serum calcium and phosphate. Key issues not well defined include how new osteoblasts are incorporated in the epithelial layer, replacing those incorporated in the accumulating matrix. Development of bone in vitro is the subject of numerous projects using various matrices and mesenchymal stem cell-derived preparations in bioreactors. These preparations reflect the structure of bone to variable extents, and include cells at many different stages of differentiation. Major challenges are production of bone matrix approaching the in vivo density and support for trabecular bone formation. In vitro differentiation is limited by the organization and density of osteoblasts and by endogenous and exogenous inhibitors.

The "in and out" of glucosamine 6-O-sulfation: the 6th sense of heparan sulfate

The biological properties of Heparan sulfate (HS) polysaccharides essentially rely on their ability to bind and modulate a multitude of protein ligands. These interactions involve internal oligosaccharide sequences defined by their sulfation patterns. Amongst these, the 6-O-sulfation of HS contributes significantly to the polysaccharide structural diversity and is critically involved in the binding of many proteins. HS 6-O-sulfation is catalyzed by 6-O-sulfotransferases (6OSTs) during biosynthesis, and it is further modified by the post-synthetic action of 6-O-endosulfatases (Sulfs), two enzyme families that remain poorly characterized. The aim of the present review is to summarize the contribution of 6-O-sulfates in HS structure/function relationships and to discuss the present knowledge on the complex mechanisms regulating HS 6-O-sulfation.

Syndecan-1 in Cancer: Implications for Cell Signaling, Differentiation, and Prognostication

Syndecan-1, a cell surface heparan sulfate proteoglycan, is critically involved in the differentiation and prognosis of various tumors. In this review, we highlight the synthesis, cellular interactions, and the signalling pathways regulated by syndecan-1. The basal syndecan-1 level is also crucial for understanding the sequential changes involving malignant transformation, tumor progression, and advanced or disseminated cancer stages. Moreover, we focus on the cellular localization of this proteoglycan as cell membrane anchored and/or shed, soluble syndecan-1 with stromal or nuclear accumulation and how this may carry different, highly tissue specific prognostic information for individual tumor types.

Characterization of membrane protein interactions in plasma membrane derived vesicles with quantitative imaging Förster resonance energy transfer

Here we describe an experimental tool, termed quantitative imaging Förster resonance energy transfer (QI-FRET), that enables the quantitative characterization of membrane protein interactions. The QI-FRET methodology allows us to acquire binding curves and calculate association constants for complex membrane proteins in the native plasma membrane environment. The method utilizes FRET detection, and thus requires that the proteins of interest are labeled with florescent proteins, either FRET donors or FRET acceptors. Since plasma membranes of cells have complex topologies precluding the acquisition of two-dimensional binding curves, the FRET measurements are performed in plasma membrane derived vesicles that bud off cells as a result of chemical or osmotic stress. The results overviewed here are acquired in vesicles produced with an osmotic vesiculation buffer developed in our laboratory, which does not utilize harsh chemicals. The concentrations of the donor-labeled and the acceptor-labeled proteins are determined, along with the FRET efficiencies, in each vesicle. The experiments utilize transient transfection, such that a wide variety of concentrations is sampled. Then, data from hundreds of vesicles are combined to yield dimerization curves. Here we discuss recent findings about the dimerization of receptor tyrosine kinases (RTKs), membrane proteins that control cell growth and differentiation via lateral dimerization in the plasma membrane. We focus on the dimerization of fibroblast growth factor receptor 3 (FGFR3), a RTK that plays a critically important role in skeletal development. We study the role of different FGFR3 domains in FGFR3 dimerization in the absence of ligand, and we show that FGFR3 extracellular domains inhibit unliganded dimerization, while contacts between the juxtamembrane domains, which connect the transmembrane domains to the kinase domains, stabilize the unliganded FGFR3 dimers. Since FGFR3 has been documented to harbor many pathogenic single amino acid mutations that cause skeletal and cranial dysplasias, as well as cancer, we also study the effects of these mutations on dimerization. First, we show that the A391E mutation, linked to Crouzon syndrome with acanthosis nigricans and to bladder cancer, significantly enhances FGFR3 dimerization in the absence of ligand and thus induces aberrant receptor interactions. Second, we present results about the effect of three cysteine mutations that cause thanatophoric dysplasia, a lethal phenotype. Such cysteine mutations have been hypothesized previously to cause constitutive dimerization, but we find instead that they have a surprisingly modest effect on dimerization. Most of the studied pathogenic mutations also altered FGFR3 dimer structure, suggesting that both increases in dimerization propensities and changes in dimer structure contribute to the pathological phenotypes. The results acquired with the QI-FRET method further our understanding of the interactions between FGFR3 molecules and RTK molecules in general. Since RTK dimerization regulates RTK signaling, our findings advance our knowledge of RTK activity in health and disease. The utility of the QI-FRET method is not restricted to RTKs, and we thus hope that in the future the QI-FRET method will be applied to other classes of membrane proteins, such as channels and G protein-coupled receptors.

Hepatoprotective and anti-tumor effects of targeting MMP-9 in hepatocellular carcinoma and its relation to vascular invasion markers

The current study aims to evaluate the hepatoprotective and antitumor efficacy of doxycycline, as an matrix metalloproteases-9 (MMP-9) inhibitor, in an in vivo model of hepatocellular carcinoma (HCC). HCC was induced experimentally by thiocetamide (200 mg/kg) in rats that were treated with doxycycline (5 mg/kg for 16 weeks). Tumor severity was evaluated by measuring α-fetoprotein (AFP) levels, histopathologically by investigating liver sections stained with hematoxylin/eosin and assessing the survival rate. Liver homogenates were used for the measurements of MMP-9, fascin and hepatic heparan sulfate proteoglycan (HSPG) levels. Oxidative stress markers [malonaldehyde (MDA) and glutathione] as well as fibroblast growth factor-2 (FGF-2) gene expression were also among the assessed indicators. HCC in human and animal samples showed significant elevation in the levels of MMP-9 (231.7, 90 %), fascin (33.17, 140 %), as well as FGF-2 gene expression (342 % in animal samples; all respectively), associated with a significant decrease in hepatic HSPG level. Treatment of rats with doxycycline increased the animal survival rate (90 %) and decreased serum AFP level. Moreover, doxycycline ameliorated fibrosis and the induced massive hepatic tissue breakdown. It also restored the integrity of hepatic HSPGs and showed a magnificent inhibitory effect of tumor invasion cascade by significantly reducing the activities of MMP-9 (42 %) and fascin (50 %), as well as reducing the gene expression of FGF-2 (85.7 %). Furthermore, the antioxidant impact of doxycycline was evidenced by the significant elevation in glutathione level and depressing MDA level. To this end, doxycycline, proved promising hepatoprotective and antitumor activity and opens, thereby, a new horizon against vascular migration ability of the tumor cells.

Achieving high signal-to-noise in cell regulatory systems: Spatial organization of multiprotein transmembrane assemblies of FGFR and MET receptors

How is information communicated both within and between cells of living systems with high signal to noise? We discuss transmembrane signaling models involving two receptor tyrosine kinases: the fibroblast growth factor receptor (FGFR) and the MET receptor. We suggest that simple dimerization models might occur opportunistically giving rise to noise but cooperative clustering of the receptor tyrosine kinases observed in these systems is likely to be important for signal transduction. We propose that this may be a more general prerequisite for high signal to noise in transmembrane receptor signaling.

[Endothelial glycocalyx of blood circulation. II. Biological functions, state at norm and pathology, bioengineering application]

In normal state, a complex multicomponent system called glycocalyx is present on the surface of endothelial vascular system. Due to complexity of its composition and location on the border between vessel wall and blood circulation, glycocalyx participates in a number of functions supporting the metabolism of the vascular wall. In pathological conditions undergo complete or partial loss of this structure, which leads to inconsistencies in the vascular wall and change its functions. The functions of endothelial glycocalyx are its involvement in the regulation of vascular permeability, transduction and transformation by the shear stress of blood flow on endothelium, the molecular regulation of glycocalyx microenvironment and its interaction with circulating blood cells. Also briefly be considered participation of glycocalyx in the implementation of cardiovascular diseases, their correction, bioengineering application of glycocalyx and its components.

Back to the future with phenotypic screening

There are no disease-modifying drugs for any old age associated neurodegenerative disease or stroke. This is at least in part due to the failure of drug developers to recognize that the vast majority of neurodegenerative diseases arise from a confluence of multiple toxic insults that accumulate during normal aging and interact with genetic and environmental risk factors. Thus, it is unlikely that the current single target approach based upon rare dominant mutations or even a few preselected targets is going to yield useful drugs for these conditions. Therefore, the identification of drug candidates for neurodegeneration should be based upon their efficacy in phenotypic screening assays that reflect the biology of the aging brain, not a single, preselected target. It is argued here that this approach to drug discovery is the most likely to produce safe and effective drugs for neurodegenerative diseases.

Caveolae-mediated endocytosis of the glucosaminoglycan-interacting adipokine tartrate resistant acid phosphatase 5a in adipocyte progenitor lineage cells

Adipogenesis depends on growth factors controlling proliferation/differentiation of mesenchymal stem cells (MSCs). Membrane binding and endocytosis of growth factors are often coupled to receptor activation and downstream signaling leading to specific cellular responses. The novel adipokine tartrate-resistant acid phosphatase (TRAP) 5a exhibits a growth factor-like effect on MSCs and pre-adipocytes and induces hyperplastic obesity in vivo. However its molecular interaction with pre-adipocytes remains unknown. Therefore, this study aimed to investigate membrane interaction of TRAP and its endocytosis routes in pre-adipocytes. Confocal and/or electron microscopy were used to detect TRAP in untreated or TRAP 5a/b treated pre-adipocytes under conditions that allow or inhibit endocytosis in combination with co-staining of endocytotic vesicles. TRAP interaction with heparin/heparan sulfate was verified by gel filtration. It could be shown that TRAP 5a, but not 5b, binds to the membrane of pre-adipocytes where it co-localizes with heparin-sulfate proteoglycan glypican-4. Also in vitro, TRAP 5a exhibited affinity for both heparin and heparan sulfate with heparin inhibiting its enzyme activity. Upon caveolae-mediated endocytosis of saturating levels of TRAP 5a, TRAP 5a co-localized intracellularly with glypican-4 and late endosomal marker Rab-7 positive vesicles. The protein was also located in multivesicular bodies (MVBs) but did not co-localize with lysosomal marker LAMP-1. TRAP 5a endocytosis was also detectable in pre-osteoblasts, but not fibroblasts, embryonic MSCs or mature adipocytes. These results indicate that TRAP 5a exhibits binding to cell surface, endocytosis and affinity to glucosaminoglycans (GAGs) in pre-adipocyte and pre-osteoblast lineage cells in a manner similar to other heparin-binding growth factors.

A Network Map of FGF-1/FGFR Signaling System

Fibroblast growth factor-1 (FGF-1) is a well characterized growth factor among the 22 members of the FGF superfamily in humans. It binds to all the four known FGF receptors and regulates a plethora of functions including cell growth, proliferation, migration, differentiation, and survival in different cell types. FGF-1 is involved in the regulation of diverse physiological processes such as development, angiogenesis, wound healing, adipogenesis, and neurogenesis. Deregulation of FGF-1 signaling is not only implicated in tumorigenesis but also is associated with tumor invasion and metastasis. Given the biomedical significance of FGFs and the fact that individual FGFs have different roles in diverse physiological processes, the analysis of signaling pathways induced by the binding of specific FGFs to their cognate receptors demands more focused efforts. Currently, there are no resources in the public domain that facilitate the analysis of signaling pathways induced by individual FGFs in the FGF/FGFR signaling system. Towards this, we have developed a resource of signaling reactions triggered by FGF-1/FGFR system in various cell types/tissues. The pathway data and the reaction map are made available for download in different community standard data exchange formats through NetPath and NetSlim signaling pathway resources.

Heparan sulfotransferases Hs6st1 and Hs2st keep Erk in check for mouse corpus callosum development

The corpus callosum (CC) connects the left and right cerebral hemispheres in mammals and its development requires intercellular communication at the telencephalic midline mediated by signaling proteins. Heparan sulfate (HS) is a sulfated polysaccharide that decorates cell surface and extracellular matrix proteins and regulates the biological activity of numerous signaling proteins via sugar-protein interactions. HS is subject to regulated enzymatic sulfation and desulfation and an attractive, although not proven, hypothesis is that the biological activity of HS is regulated by a sugar sulfate code. Mutant mouse embryos lacking the heparan sulfotransferases Hs2st or Hs6st1 have severe CC phenotypes and form Probst bundles of noncrossing axons flanking large tangles of midline glial processes. Here, we identify a precocious accumulation of Sox9-expressing glial cells in the indusium griseum region and a corresponding depletion at the glial wedge associated with the formation of Probst bundles along the rostrocaudal axis in both mutants. Molecularly, we found a surprising hyperactivation of Erk signaling in Hs2st(-/-) (2-fold) and Hs6st1(-/-) (6-fold) embryonic telencephalon that was most striking at the midline, where Erk signaling is lowest in wild-types, and a 2-fold increase in Fgf8 protein levels in Hs6st1(-/-) embryos that could underpin Erk hyperactivation and excessive glial movement to the indusium griseum. The tightly linked Hs6st1(-/-) CC glial and axonal phenotypes can be rescued by genetic or pharmacological suppression of Fgf8/Erk axis components. Overall, our data fit a model in which Hs2st and Hs6st1 normally generate conditions conducive to CC development by generating an HS-containing environment that keeps Erk signaling in check.

Chemopreventive and hepatoprotective effects of Epigallocatechin-gallate against hepatocellular carcinoma: role of heparan sulfate proteoglycans pathway

Objective

Epigallocatechin-gallate (EGCG) claims a plethora of health benefits including protection against neoplastic diseases. Meanwhile, heparan-sulfate proteoglycans (HSPGs) have defensive role against tumour cell invasion. Therefore, the chemopreventive and hepatoprotective effects of EGCG were studied in hepatocellular carcinoma (HCC) in vivo and in vitro and compared with strong water soluble antioxidant, sodium ascorbate.

Methods

HCC was induced in SD rats by thioacetamide (200 mg/Kg). Some rats were treated with EGCG (20 mg/Kg) or sodium ascorbate (100 mg/Kg). Liver impairment was assessed by measuring serum α-fetoprotein and investigating liver sections stained with H/E. Hepatic HSPGs, syndecan-1 and matrix metalloproteinase-9 (MMP-9) were measured by ELISA. Gene expression of fibroblast growth factor (FGF)-2 was measured. Cell death was assessed by caspase-3 activity. In addition, all markers were measured in human hepatocellular carcinoma cell line (HepG2).

Key findings

EGCG increased the animal survival and decreased both α-fetoprotein and HepG2 viability. In addition, EGCG ameliorated fibrosis and massive hepatic tissue breakdown. EGCG restored HSPGs and reduced expression of MMP-9, syndecan-1 and FGF-2 in-vivo and in-vitro. Sodium ascorbate showed significantly lower results than EGCG.

Conclusions

Besides antioxidant activity, other mechanisms are involved in the chemopreventive and hepatoprotective effects of EGCG including restoration of HSPGs receptors and inhibition of vascular invasion.

Role of fibroblast growth factors in elicitation of cell responses

Fibroblast growth factors (FGFs) are signalling peptides that control important cell processes such as proliferation, differentiation, migration, adhesion and survival. Through binding to different types of receptor on the cell surface, these peptides can have different effects on a target cell, the effect achieved depending on many features. Thus, each of the known FGFs elicits specific biological responses. FGF receptors (FGFR 1-5) initiate diverse intracellular pathways, which in turn lead to a variety of results. FGFs also bind the range of FGFRs with a series of affinities and each type of cells expresses FGFRs in different qualitative and quantitative patterns, which also affect responses. To summarize, cell response to binding of an FGF ligand depends on type of FGF, FGF receptor and target cell, all interacting in concert. This review aims to examine properties of the FGF family and its members receptors. It also aims to summarize features of intracellular signalling and highlight differential effects of the various FGFs in different circumstances.

New targets for glycosaminoglycans and glycosaminoglycans as novel targets

Biological functions of a variety of proteins are mediated via their interaction with glycosaminoglycans (GAGs). The structural diversity within the wide GAG landscape provides individual interaction sites for a multitude of proteins involved in several pathophysiological processes. This 'GAG angle' of such proteins as well as their specific GAG ligands give rise to novel therapeutic concepts for drug development. Current glycomic technologies to elucidate the glycan structure-function relationships, methods to investigate the selectivity and specificity of glycan-protein interactions and existing therapeutic approaches to interfere with GAG-protein interactions are discussed.

Biological function of nuclear receptor tyrosine kinase action

Receptor tyrosine kinases (RTKs) were believed until recently to act at the cell membrane in a singular fashion (i.e., binding of ligands on the extracellular domain would activate the intrinsic tyrosine kinase activity in the intracellular domain), which would then start a cascade involving other intracellular signaling molecules that would act as effectors. However, new evidence indicates that some RTKs can signal through a different modality; they can move into the nucleus where they directly exert their actions. Although some studies have showed that the proteolytically released intracellular domain of several RTKs can move to the nucleus where they influence gene expression and cell function, others suggest that RTKs can also move to the nucleus as holoproteins. The identification of this novel signaling mechanism calls for a critical reevaluation of the mechanisms of action of RTKs and their biological roles.

Fucoidan inhibits the growth of hepatocellular carcinoma independent of angiogenesis

Some sulphated polysaccharides can bind bFGF but are unable to present bFGF to its high-affinity receptors. Fucoidan, a sulphated polysaccharide purified from brown algae, which has been used as an anticancer drug in traditional Chinese medicine for hundreds of years, exhibits a variety of anticancer effects, including the induction of the apoptosis and autophagy of cancer cells, the inhibition of the growth of cancer cells, the induction of angiogenesis, and the improvement of antitumour immunity. Our research shows that fucoidan dose not inhibit the expressions of VEGF, bFGF, IL-8, and heparanase in HCC cells and/or tumour tissues. Moreover, fucoidan exhibited low affinity for bFGF and could not block the binding of bFGF to heparan sulphated. Although fucoidan had no effect on angiogenesis and apoptosis in vivo, this drug significantly inhibited the tumour growth and the expression of PCNA. These results suggest that fucoidan exhibits an anticancer effect in vivo at least partly through inhibition of the proliferation of HCC cells, although it is unable to suppress the angiogenesis induced by HCC.

Structure-based design of decoy chemokines as a way to explore the pharmacological potential of glycosaminoglycans

Glycosaminoglycans (GAGs) are a class of highly negatively charged, unbranched, O-linked polysaccharides that are involved in many diseases. Their role as a protein-binding matrix on cell surfaces has long been recognized, but therapeutic approaches to interfere with protein-GAG interactions have been limited due to the complex chemistry of GAGs, on one hand, and due to the lack of specific antibodies against GAGs, on the other hand. We have developed a protein engineering platform (the so-called CellJammer(®) technology), which enables us to introduce higher GAG-binding affinity into wild-type GAG-binding proteins and to combine this with impaired biological, receptor-binding function. Chemokines are among the prototypic GAG-binding proteins and here we present selected results of our CellJammer technology applied to several of these proinflammatory proteins. An overview is given of our lead decoy protein, PA401, which is a CXCL8-based mutant protein with increased GAG-binding affinity and decreased CXCR1/2 binding and activation. Major results from our CCL2 and CCL5 programmes are also summarized and the potential for clinical application of these decoy proteins is presented.

Multiple consequences of a single amino acid pathogenic RTK mutation: the A391E mutation in FGFR3

The A391E mutation in fibroblast growth factor receptor 3 (FGFR3) is the genetic cause for Crouzon syndrome with Acanthosis Nigricans. Here we investigate the effect of this mutation on FGFR3 activation in HEK 293 T cells over a wide range of fibroblast growth factor 1 concentrations using a physical-chemical approach that deconvolutes the effects of the mutation on dimerization, ligand binding, and efficiency of phosphorylation. It is believed that the mutation increases FGFR3 dimerization, and our results verify this. However, our results also demonstrate that the increase in dimerization is not the sole effect of the mutation, as the mutation also facilitates the phosphorylation of critical tyrosines in the activation loop of FGFR3. The activation of mutant FGFR3 is substantially increased due to a combination of these two effects. The low expression of the mutant, however, attenuates its signaling and may explain the mild phenotype in Crouzon syndrome with Acanthosis Nigricans. The results presented here provide new knowledge about the physical basis behind growth disorders and highlight the fact that a single RTK mutation may affect multiple steps in RTK activation.

An alternative approach to drug discovery for Alzheimer's disease dementia

There are no drugs that halt the progression of any age-associated neurodegenerative disease. This may be due to the failure of drug developers to recognize that while there are mutations that predispose individuals to disease as they get older, the vast majority of neurodegenerative diseases arise from a confluence of multiple toxic insults. Thus, it is unlikely that the current single-target approach is going to yield useful drugs for these conditions. The identification of multi-target lead compounds is needed and their selection should be based upon a requirement for their efficacy in phenotypic screening assays that reflect the biology of the aging brain. This approach to neurodegenerative disease drug discovery is likely to produce safe and effective drugs.

Divergent synthesis of 48 heparan sulfate-based disaccharides and probing the specific sugar-fibroblast growth factor-1 interaction

Several biological processes involve glycans, yet understanding their ligand specificities is impeded by their inherent diversity and difficult acquisition. Generating broad synthetic sugar libraries for bioevaluations is a powerful tool in unraveling glycan structural information. In the case of the widely distributed heparan sulfate (HS), however, the 48 theoretical possibilities for its repeating disaccharide call for synthetic approaches that should minimize the effort in an undoubtedly huge undertaking. Here we employed a divergent strategy to afford all 48 HS-based disaccharides from just two orthogonally protected disaccharide precursors. Different combinations and sequence of transformation steps were applied with many downstream intermediates leading up to multiple target products. With the full disaccharide library in hand, affinity screening with fibroblast growth factor-1 (FGF-1) revealed that four of the synthetic sugars bind to FGF-1. The molecular details of the interaction were further clarified through X-ray analysis of the sugar-protein cocrystals. The capability of comprehensive sugar libraries in providing key insights in glycan-ligand interaction is, thus, highlighted.

Immobilization of heparan sulfate on electrospun meshes to support embryonic stem cell culture and differentiation

As our understanding of what guides the behavior of multi- and pluripotent stem cells deepens, so too does our ability to utilize certain cues to manipulate their behavior and maximize their therapeutic potential. Engineered, biologically functionalized materials have the capacity to influence stem cell behavior through a powerful combination of biological, mechanical, and topographical cues. Here, we present the development of a novel electrospun scaffold, functionalized with glycosaminoglycans (GAGs) ionically immobilized onto the fiber surface. Bound GAGs retained the ability to interact with GAG-binding molecules and, crucially, presented GAG sulfation motifs fundamental to mediating stem cell behavior. Bound GAG proved to be biologically active, rescuing the neural differentiation capacity of heparan sulfate-deficient mouse embryonic stem cells and functioning in concert with FGF4 to facilitate the formation of extensive neural processes across the scaffold surface. The combination of GAGs with electrospun scaffolds creates a biomaterial with potent applicability for the propagation and effective differentiation of pluripotent stem cells.

Structural basis of heparan sulfate-specific degradation by heparinase III

Heparinase III (HepIII) is a 73-kDa polysaccharide lyase (PL) that degrades the heparan sulfate (HS) polysaccharides at sulfate-rare regions, which are important co-factors for a vast array of functional distinct proteins including the well-characterized antithrombin and the FGF/FGFR signal transduction system. It functions in cleaving metazoan heparan sulfate (HS) and providing carbon, nitrogen and sulfate sources for host microorganisms. It has long been used to deduce the structure of HS and heparin motifs; however, the structure of its own is unknown. Here we report the crystal structure of the HepIII from Bacteroides thetaiotaomicron at a resolution of 1.6 Å. The overall architecture of HepIII belongs to the (α/α)₅ toroid subclass with an N-terminal toroid-like domain and a C-terminal β-sandwich domain. Analysis of this high-resolution structure allows us to identify a potential HS substrate binding site in a tunnel between the two domains. A tetrasaccharide substrate bound model suggests an elimination mechanism in the HS degradation. Asn260 and His464 neutralize the carboxylic group, whereas Tyr314 serves both as a general base in C-5 proton abstraction, and a general acid in a proton donation to reconstitute the terminal hydroxyl group, respectively. The structure of HepIII and the proposed reaction model provide a molecular basis for its potential practical utilization and the mechanism of its eliminative degradation for HS polysaccarides.

Adeno-associated viral vectors based on serotype 3b use components of the fibroblast growth factor receptor signaling complex for efficient transduction

Adeno-associated virus type 3b (AAV3b) has been largely ignored by gene therapists because of the inability of vectors based on this serotype to transduce target tissues efficiently. Here we describe a phenomenon unique to AAV3b in that vectors based on this serotype mediate enhanced transduction in the presence of heparin. Among the many biological functions attributed to heparin, its interaction with, and ability to regulate, several growth factors (GFs) and growth factor receptors (GFRs) has been well characterized. Using GFR-overexpressing cell lines, soluble GFs and heparins, as well as specific GFR inhibitors, we have demonstrated a requirement for fibroblast growth factor receptor-2 (FGFR2) and FGF1 in the heparin-mediated augmentation of AAV3b vector transduction. In contrast to AAV2, we establish that heparin can be used as an adjunct with AAV3b to further increase transduction in a variety of cells and target tissues, additionally suggesting that AAV3b may be an attractive viral vector for clinical use during procedures in which heparin is used. In summary, AAV3b exhibits FGFR2-dependent, markedly enhanced transduction efficiency in the presence of heparin and FGFs, which could make it a useful vector for gene therapy in a variety of human diseases.

TGF-β-operated growth inhibition and translineage commitment into smooth muscle cells of periodontal ligament-derived endothelial progenitor cells through Smad- and p38 MAPK-dependent signals

The periodontal ligament (PDL) is a fibrous connective tissue that attaches the tooth to the alveolar bone. We previously demonstrated the ability of PDL fibroblast-like cells to construct an endothelial cell (EC) marker-positive blood vessel-like structure, indicating the potential of fibroblastic lineage cells in PDL tissue as precursors of endothelial progenitor cells (EPCs) to facilitate the construction of a vascular system around damaged PDL tissue. A vascular regeneration around PDL tissue needs proliferation of vascular progenitor cells and the subsequent differentiation of the cells. Transforming growth factor-β (TGF-β) is known as an inducer of endothelial-mesenchymal transition (EndMT), however, it remains to be clarified what kinds of TGF-β signals affect growth and mesenchymal differentiation of PDL-derived EPC-like fibroblastic cells. Here, we demonstrated that TGF-β1 not only suppressed the proliferation of the PDL-derived EPC-like fibroblastic cells, but also induced smooth muscle cell (SMC) markers expression in the cells. On the other hand, TGF-β1 stimulation suppressed EC marker expression. Intriguingly, overexpression of Smad7, an inhibitor for TGF-β-induced Smad-dependent signaling, suppressed the TGF-β1-induced growth inhibition and SMC markers expression, but did not the TGF-β1-induced downregulation of EC marker expression. In contrast, p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 suppressed the TGF-β1-induced downregulation of EC marker expression. In addition, the TGF-β1-induced SMC markers expression of the PDL-derived cells was reversed upon stimulation with fibroblast growth factor (FGF), suggesting that the TGF-β1 might not induce terminal SMC differentiation of the EPC-like fibroblastic cells. Thus, TGF-β1 not only negatively controls the growth of PDL-derived EPC-like fibroblastic cells via a Smad-dependent manner but also positively controls the SMC-differentiation of the cells possibly at the early stage of the translineage commitment via Smad- and p38 MAPK-dependent manners.

The mutual impact of syndecan-1 and its glycosaminoglycan chains--a multivariable puzzle

Proteoglycans, with their core proteins and attached glycosaminoglycan chains, are recognized as important partners in many biological processes, yet often experimental analysis of their molecular action is considered for only part of these molecules: either the protein or the carbohydrate unit. In this article, we have tried to summarize, with an example of the syndecan family in general and more specifically with syndecan-1, what is known considering the mutual influence of these different components, and we follow whether the nature of the glycosaminoglycan chains matters for these effects.

Bio-functionalization of ligand-free upconverting lanthanide doped nanoparticles for bio-imaging and cell targeting

We report on the functionalization of ligand-free NaGdF(4):Er(3+), Yb(3+) upconverting nanoparticles with heparin and basic fibroblast growth factor (bFGF). These upconverting nanoparticles are used to obtain high-contrast images of HeLa cells. These images reveal that the heparin-bFGF functionalized nanoparticles show specific binding to the cell membrane.

Gekko-sulfated glycopeptide inhibits tumor angiogenesis by targeting basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) is a therapeutic target of anti-angiogenesis. Here, we report that a novel sulfated glycopeptide derived from Gekko swinhonis Guenther (GSPP), an anticancer drug in traditional Chinese medicine, inhibits tumor angiogenesis by targeting bFGF. GSPP significantly decreased the production of bFGF in hepatoma cells by suppressing early growth response-1. GSPP inhibited the release of bFGF from extracellular matrix by blocking heparanase enzymatic activity. Moreover, GSPP competitively inhibited bFGF binding to heparin/heparan sulfate via direct binding to bFGF. Importantly, GSPP abrogated the bFGF-stimulated proliferation and migration of endothelial cells, whereas it had no inhibitory effect on endothelial cells in the absence of bFGF. Further study revealed that GSPP prevented bFGF-induced neovascularization and inhibited tumor angiogenesis and tumor growth in a xenograft mouse model. These results demonstrate that GSPP inhibits tumor angiogenesis by blocking bFGF production, release from the extracellular matrix, and binding to its low affinity receptor, heparin/heparan sulfate.

Essential roles for soluble virion-associated heparan sulfonated proteoglycans and growth factors in human papillomavirus infections

A subset of human papillomavirus (HPV) infections is causally related to the development of human epithelial tumors and cancers. Like a number of pathogens, HPV entry into target cells is initiated by first binding to heparan sulfonated proteoglycan (HSPG) cell surface attachment factors. The virus must then move to distinct secondary receptors, which are responsible for particle internalization. Despite intensive investigation, the mechanism of HPV movement to and the nature of the secondary receptors have been unclear. We report that HPV16 particles are not liberated from bound HSPG attachment factors by dissociation, but rather are released by a process previously unreported for pathogen-host cell interactions. Virus particles reside in infectious soluble high molecular weight complexes with HSPG, including syndecan-1 and bioactive compounds, like growth factors. Matrix mellatoproteinase inhibitors that block HSPG and virus release from cells interfere with virus infection. Employing a co-culture assay, we demonstrate HPV associated with soluble HSPG-growth factor complexes can infect cells lacking HSPG. Interaction of HPV-HSPG-growth factor complexes with growth factor receptors leads to rapid activation of signaling pathways important for infection, whereas a variety of growth factor receptor inhibitors impede virus-induced signaling and infection. Depletion of syndecan-1 or epidermal growth factor and removal of serum factors reduce infection, while replenishment of growth factors restores infection. Our findings support an infection model whereby HPV usurps normal host mechanisms for presenting growth factors to cells via soluble HSPG complexes as a novel method for interacting with entry receptors independent of direct virus-cell receptor interactions.

A subset of the >120 different types of human papillomaviruses (HPVs) are the most common cause of sexually transmitted infections. Certain HPVs are also associated with approximately 5% of all cancers worldwide. Like many pathogens, HPVs bind first to heparan sulfate proteoglycans (HSPGs) on cells before moving to more specific uptake receptors. However, relatively little is known about the mechanism(s) that triggers the translocation of HPV from HSPGs to the receptors that facilitate entry. As obligate parasites, viruses have evolved numerous means to hijack host cell functions to cause infection. We report two novel mechanisms of pathogen-host interactions. First, bound HPV particles are liberated from cells in an active complex with HSPGs and growth factors rather than dissociating from the sugars to engage secondary receptors. Second, HPV uses the specificity of the associated growth factors to bridge to their cognate receptors as opposed to direct binding to a cell internalization receptor. Signals transduced during these interactions are important for HPV infection. Our study provides new insights into the transmission of a significant viral pathogen and reveals novel means whereby microbes may repurpose normal cell functions during infection of their hosts. Likewise, this work uncovers new targets for HPV prophylaxis.

Glycosaminoglycan and chemokine/growth factor interactions

Heparin and glycosaminoglycans (GAGs) related structurally to heparin, notably heparan sulphate, bind to most, if not all, chemokines and many growth factors. The chemokine and growth factor interactions with GAGs localise the peptide mediators to specific sites in tissues and influence their stability and function. This chapter discusses the nature of these interactions and the effect on the function of a number of chemokines (PF-4, interleukin-8, RANTES and SDF-1) and growth factors (FGF, HGF, VEGF) in normal physiology and the disease setting. Novel therapeutic interventions that target chemokine and growth factor interactions with GAGs are also discussed.

GM130 gain-of-function induces cell pathology in a model of lysosomal storage disease

Cell pathology in lysosomal storage diseases is characterized by the formation of distended vacuoles with characteristics of lysosomes. Our previous studies in mucopolysaccharidosis type IIIB (MPSIIIB), a disease in which a genetic defect induces the accumulation of undigested heparan sulfate (HS) fragments, led to the hypothesis that abnormal lysosome formation was related to events occurring at the Golgi level. We reproduced the enzyme defect of MPSIIIB in HeLa cells using tetracycline-inducible expression of shRNAs directed against α-N-acetylglucosaminidase (NAGLU) and addressed this hypothesis. HeLa cells deprived of NAGLU accumulated abnormal lysosomes. The Golgi matrix protein GM130 was over-expressed. The cis- and medial-Golgi compartments were distended, elongated and formed circularized ribbons. The Golgi microtubule network was enlarged with increased amounts of AKAP450, a partner of GM130 controlling this network. GM130 down-regulation prevented pathology in HeLa cells deprived of NAGLU, whereas GM130 over-expression in control HeLa cells mimicked the pathology of deprived cells. We concluded that abnormal lysosomes forming in cells accumulating HS fragments were the consequence of GM130 gain-of-function and subsequent alterations of the Golgi ribbon architecture. These results indicate that GM130 functions are modulated by HS glycosaminoglycans and therefore possibly controlled by extracellular cues.

The physical basis of FGFR3 response to fgf1 and fgf2

Fibroblast growth factors (fgfs) play important roles in embryonic development and in adult life by controlling cell proliferation, differentiation, and migration. There are 18 known fgfs which activate four fibroblast growth factor receptors (FGFRs), with different isoforms due to alternative splicing. The physical basis behind the specificity of the biological responses mediated by different fgf-FGFR pairs is currently unknown. To gain insight into the specificity of FGFR3c, a membrane receptor which is critical for bone development, we studied, analyzed, and compared the activation of FGFR3c over a wide range of fgf1 and fgf2 concentrations. We found that while the strength of fgf2 binding to FGFR3c is lower than the strength of fgf1 binding, the fgf2-bound dimers exhibit higher phosphorylation of the critical tyrosines in the activation loop. As a result, fgf1 and fgf2 elicit a similar FGFR3c response at low, but not at high, concentrations. The results demonstrate the versatility of FGFR3c response to fgf1 and fgf2 and highlight the complexity in fgf signaling.