Syndecans promote integrin-mediated adhesion of mesenchymal cells in two distinct pathways

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Syndecan-4 is the key proteoglycan involved in mediating sepsis-associated lung injury

Vascular endothelial cell dysfunction involving syndecan (SDC) proteoglycans contributes to acute sepsis-associated lung injury (ALI), but the exact SDC isoform involved is unclear. We aimed to clarify which SDCs are involved in ALI. A relevant gene expression dataset (GSE5883) was analysed for differentially expressed genes (DEGs) between lipopolysaccharide (LPS)-treated and control lung endothelial cells and for SDC isoform expression. Bioinformatic analyses to predict DEG function were conducted using R language, Gene Ontology, and the Kyoto Encyclopedia of Genes and Genomes. SDC2 and SDC4 expression profiles were examined under inflammatory conditions in human lung vascular endothelial cell and mouse sepsis-associated ALI models. Transcription factors regulating SDC2/4 were predicted to indirectly assess SDC involvement in septic inflammation. Of the DEGs, 224 and 102 genes were up- and downregulated, respectively. Functional analysis indicated that DEGs were involved in modulating receptor ligand and signalling receptor activator activities, cytokine receptor binding, responses to LPS and molecules of bacterial origin, regulation of cell adhesion, tumour necrosis factor signalling, and other functions. DEGs were also enriched for cytoplasmic ribonucleoprotein granules, transcription regulator complexes, and membrane raft cellular components. SDC4 gene expression was 4.5-fold higher in the LPS group than in the control group, while SDC2 levels were similar in both groups. SDC4 mRNA and protein expression was markedly upregulated in response to inflammatory injury, and SDC4 downregulation severely exacerbated inflammatory responses in both in vivo and in vitro models. Overall, our data demonstrate that SDC4, rather than SDC2, is involved in LPS-induced sepsis-associated ALI.

The INSR/AKT/mTOR pathway regulates the pace of myogenesis in a syndecan-3-dependent manner

Muscle stem cells (MuSCs) are indispensable for muscle regeneration. A multitude of extracellular stimuli direct MuSC fate decisions from quiescent progenitors to differentiated myocytes. The activity of these signals is modulated by coreceptors such as syndecan-3 (SDC3). We investigated the global landscape of SDC3-mediated regulation of myogenesis using a phosphoproteomics approach which revealed, with the precision level of individual phosphosites, the large-scale extent of SDC3-mediated regulation of signal transduction in MuSCs. We then focused on INSR/AKT/mTOR as a key pathway regulated by SDC3 during myogenesis and mechanistically dissected SDC3-mediated inhibition of insulin receptor signaling in MuSCs. SDC3 interacts with INSR ultimately limiting signal transduction via AKT/mTOR. Both knockdown of INSR and inhibition of AKT rescue Sdc3^-/- MuSC differentiation to wild type levels. Since SDC3 is rapidly downregulated at the onset of differentiation, our study suggests that SDC3 acts a timekeeper to restrain proliferating MuSC response and prevent premature differentiation.

Ubiquitin-modified proteome analysis of Eriocheir sinensis hemocytes during Spiroplasma eriocheiris infection

Spiroplasma eriocheiris, the pathogen of Eriocheir sinensis tremor disease (TD), has bring a huge economic loss to China aquaculture. The hemocytes of crab as the first target cells of S. eriocheiris, but the interactive relationship between the E. sinensis and this pathogen not particularly clear. The present study is the first time to analysis the role of protein ubiquitination in the process of E. sinensis hemocytes response S. eriocheiris infection. By applying label-free quantitative liquid chromatography with tandem mass spectrometry proteomics, 950 lysine ubiquitination sites and 803 ubiquitination peptides on 458 proteins were identified, of which 48 ubiquitination sites on 40 proteins were quantified as significantly changed after the S. eriocheiris infection. Bioinformatics analysis of ubiquitination different proteins suggested many biological process and pathways were participated in the interaction between S. eriocheiris and host cell, such as ubiquitin system, endocytosis, prophenoloxidase system (proPO system), cell apoptosis, glycolysis. Our study can enhance our understanding of interaction between the crab and S. eriocheiris, and also provides basis to study the role of protein ubiquitination in other crustacean innate immune system.

Roles of Syndecan-4 in cardiac injury and repair

The heparan sulphate proteoglycan Syndecan-4 belongs to a 4-member family of transmembrane receptors. Genetic deletion of Syndecan-4 in mice causes negligible developmental abnormalities however when challenged these animals show distinct phenotypes. Synedcan-4 is expressed in many cell types in the heart and its expression is elevated in response to cardiac injury and recent studies have suggested roles for Syndecan-4 in repair mechanisms within the damaged heart. The purpose of this review is to explore these biological insights into the role of Syndecan-4 in both the injured heart and later during cardiac repair and remodeling.

Syndecans and Pancreatic Ductal Adenocarcinoma

Pancreatic Ductal Adenocarcinoma (PDAC) is a fatal disease with poor prognosis because patients rarely express symptoms in initial stages, which prevents early detection and diagnosis. Syndecans, a subfamily of proteoglycans, are involved in many physiological processes including cell proliferation, adhesion, and migration. Syndecans are physiologically found in many cell types and their interactions with other macromolecules enhance many pathways. In particular, extracellular matrix components, growth factors, and integrins collect the majority of syndecans associations acting as biochemical, physical, and mechanical transducers. Syndecans are transmembrane glycoproteins, but occasionally their extracellular domain can be released from the cell surface by the action of matrix metalloproteinases, converting them into soluble molecules that are capable of binding distant molecules such as extracellular matrix (ECM) components, growth factor receptors, and integrins from other cells. In this review, we explore the role of syndecans in tumorigenesis as well as their potential as therapeutic targets. Finally, this work reviews the contribution of syndecan-1 and syndecan-2 in PDAC progression and illustrates its potential to be targeted in future treatments for this devastating disease.

The Cardiac Syndecan-2 Interactome

The extracellular matrix (ECM) is important in cardiac remodeling and syndecans have gained increased interest in this process due to their ability to convert changes in the ECM to cell signaling. In particular, syndecan-4 has been shown to be important for cardiac remodeling, whereas the role of its close relative syndecan-2 is largely unknown in the heart. To get more insight into the role of syndecan-2, we here sought to identify interaction partners of syndecan-2 in rat left ventricle. By using three different affinity purification methods combined with mass spectrometry (MS) analysis, we identified 30 novel partners and 9 partners previously described in the literature, which together make up the first cardiac syndecan-2 interactome. Eleven of the novel partners were also verified in HEK293 cells (i.e., AP2A2, CAVIN2, DDX19A, EIF4E, JPH2, MYL12A, NSF, PFDN2, PSMC5, PSMD11, and RRAD). The cardiac syndecan-2 interactome partners formed connections to each other and grouped into clusters mainly involved in cytoskeletal remodeling and protein metabolism, but also into a cluster consisting of a family of novel syndecan-2 interaction partners, the CAVINs. MS analyses revealed that although syndecan-2 was significantly enriched in fibroblast fractions, most of its partners were present in both cardiomyocytes and fibroblasts. Finally, a comparison of the cardiac syndecan-2 and -4 interactomes revealed surprisingly few protein partners in common.

Adhesion and growth factor receptor crosstalk mechanisms controlling cell migration

Cell migration requires cells to sense and interpret an array of extracellular signals to precisely co-ordinate adhesion dynamics, local application of mechanical force, polarity signalling and cytoskeletal dynamics. Adhesion receptors and growth factor receptors (GFRs) exhibit functional and signalling characteristics that individually contribute to cell migration. Integrins transmit bidirectional mechanical forces and transduce long-range intracellular signals. GFRs are fast acting and highly sensitive signalling machines that initiate signalling cascades to co-ordinate global cellular processes. Syndecans are microenvironment sensors that regulate GTPases to control receptor trafficking, cytoskeletal remodelling and adhesion dynamics. However, an array of crosstalk mechanisms exists, which co-ordinate and integrate the functions of the different receptor families. Here we discuss the nature of adhesion receptor and GFR crosstalk mechanisms. The unifying theme is that efficient cell migration requires precise spatial and temporal co-ordination of receptor crosstalk. However, a higher order of complexity emerges; whereby multiple crosstalk mechanisms are integrated and subject to both positive and negative feedbacks. Exquisite and sensitive control of these mechanisms ensures that mechanical forces and pro-migratory signals are triggered in the right place and at the right time during cell migration. Finally, we discuss the challenges, and potential therapeutic benefits, associated with deciphering this complexity.

New SDC function prediction based on protein-protein interaction using bioinformatics tools

The precise roles for SDC have been complex to specify. Assigning and reanalyzing protein and peptide identification to novel protein functions is one of the most important challenges in postgenomic era. Here, we provide SDC molecular description to support, contextualize and reanalyze the corresponding protein-protein interaction (PPI). From SDC-1 data mining, we discuss the potential of bioinformatics tools to predict new biological rules of SDC. Using these methods, we have assembled new possibilities for SDC biology from PPI data, once, the understanding of biology complexity cannot be capture from one simple question.

Thrombin-cleaved syndecan-3/-4 ectodomain fragments mediate endothelial barrier dysfunction

Objective

The endothelial glycocalyx constitutes part of the endothelial barrier but its degradation leaves endothelial cells exposed to transmigrating cells and circulating mediators that can damage the barrier or promote intercellular gaps. Syndecan proteins are key components of the endothelial glycocalyx and are shed during disease states where expression and activity of proteases such as thrombin are elevated. We tested the ability of thrombin to cleave the ectodomains of syndecans and whether the products could act directly on endothelial cells to alter barrier function.

Approach and results

Using transmission electron microscopy, we illustrated the presence of glycocalyx in human lung microvasculature. We confirmed expression of all syndecan subtypes on the endothelial surface of agarose-inflated human lungs. ELISA and western blot analysis suggested that thrombin can cleave syndecan-3/-4 ectodomains to produce fragments. In vivo, syndecan-3 ectodomain fragments increased extravasation of albumin-bound Evans blue in mouse lung, indicative of plasma protein leakage into the surrounding tissue. Syndecan-3/-4 ectodomain fragments decreased transendothelial electrical resistance, a measure of cell-cell adhesive barrier integrity, in a manner sensitive to a Rho kinase inhibitor. These effects were independent of glycosylation and thrombin receptor PAR1. Moreover, these cleavage products caused rapid VE-cadherin-based adherens junction disorganization and increased F-actin stress fibers, supporting their direct effect on endothelial paracellular permeability.

Conclusions

We suggest that thrombin can cleave syndecan-3/4 ectodomain into fragments which interact with endothelial cells causing paracellular hyperpermeability. This may have important implications in the pathogenesis of vascular dysfunction during sepsis or thrombotic disease states where thrombin is activated.

N-terminal syndecan-2 domain selectively enhances 6-O heparan sulfate chains sulfation and promotes VEGFA165-dependent neovascularization

The proteoglycan Syndecan-2 (Sdc2) has been implicated in regulation of cytoskeleton organization, integrin signaling and developmental angiogenesis in zebrafish. Here we report that mice with global and inducible endothelial-specific deletion of Sdc2 display marked angiogenic and arteriogenic defects and impaired VEGFA₁₆₅ signaling. No such abnormalities are observed in mice with deletion of the closely related Syndecan-4 (Sdc4) gene. These differences are due to a significantly higher 6-O sulfation level in Sdc2 versus Sdc4 heparan sulfate (HS) chains, leading to an increase in VEGFA₁₆₅ binding sites and formation of a ternary Sdc2-VEGFA₁₆₅-VEGFR2 complex which enhances VEGFR2 activation. The increased Sdc2 HS chains 6-O sulfation is driven by a specific N-terminal domain sequence; the insertion of this sequence in Sdc4 N-terminal domain increases 6-O sulfation of its HS chains and promotes Sdc2-VEGFA₁₆₅-VEGFR2 complex formation. This demonstrates the existence of core protein-determined HS sulfation patterns that regulate specific biological activities.

Proteoglycans are glycosylated proteins that play a number of structural and signalling functions. Here, Corti, Wang et al. show that the N-terminal sequence of proteoglycan Syndecan-2 selectively increases 6-O sulfation of its heparan sulfate chains, and that this promotes formation of a ternary Sdc2/VEGFA/VEGFR2 complex leading to increased angiogenesis.

Coacervation-Mediated Combinatorial Synthesis of Biomatrices for Stem Cell Culture and Directed Differentiation

Combinatorial screening represents a promising strategy to discover biomaterials for tailored cell culture applications. Although libraries incorporating different biochemical cues have been investigated, few simultaneously recapitulate relevant biochemical, physical, and dynamic features of the extracellular matrix (ECM). Here, a noncovalent system based on liquid-liquid phase separation (coacervation) and gelation mediated by glycosaminoglycan (GAG)-peptide interactions is reported. Multiple biomaterial libraries are generated using combinations of sulfated glycosaminoglycans and poly(ethylene glycol)-conjugated peptides. Screening these biomaterials reveals preferred biomatrices for the attachment of six cell types, including primary mesenchymal stromal cells (MSCs) and primary neural precursor cells (NPCs). Incorporation of GAGs sustains the expansion of all tested cell types comparable to standard cell culture surfaces, while osteogenic differentiation of MSC and neuronal differentiation of NPC are promoted on chondroitin and heparan biomatrices, respectively. The presented noncovalent system provides a powerful tool for developing tissue-specific ECM mimics.

IGF-I regulates HT1080 fibrosarcoma cell migration through a syndecan-2/Erk/ezrin signaling axis

Fibrosarcoma is a tumor of mesenchymal origin, originating from fibroblasts. IGF-I is an anabolic growth factor which exhibits significant involvement in cancer progression. In this study, we investigated the possible participation of syndecan-2 (SDC-2), a cell membrane heparan sulfate (HS) proteoglycan on IGF-I dependent fibrosarcoma cell motility. Our results demonstrate that SDC-2-deficient HT1080 cells exhibit attenuated IGF-I-dependent chemotactic migration (p < 0.001). SDC-2 was found to co-localize to IGF-I receptor (IGF-IR) in a manner dependent on IGF-I activity (P ≤ 0.01). In parallel, the downregulation of SDC-2 significantly inhibited both basal and due to IGF-I action ERK1/2 activation, (p < 0.001). The phosphorylation levels of ezrin (Thr567), which is suggested to act as a signaling bridge between the cellular membrane receptors and actin cytoskeleton, were strongly enhanced by IGF-I at both 1h and 24h (p < 0.05; p < 0.01). The formation of an immunoprecipitative complex revealed an association between SDC2 and ezrin which was enhanced through IGF-I action (p < 0.05). Immunoflourescence demonstrated a co-localization of IGF-IR, SDC2 and ezrin upregulated by IGF-I action. IGF-I enhanced actin polymerization and ezrin/actin specific localization to cell membranes. Finally, treatment with IGF-I strongly increased SDC2 expression at both the mRNA and protein level (p < 0.001). Therefore, we propose a novel SDC2-dependent mechanism, where SDC2 is co-localized with IGF-IR and enhances its' IGFI-dependent downstream signaling. SDC2 mediates directly IGFI-induced ERK1/2 activation, it recruits ezrin, contributes to actin polymerization and ezrin/actin specific localization to cell membranes, ultimately facilitating the progression of IGFI-dependent fibrosarcoma cell migration.

Emerging roles of syndecan 2 in epithelial and mesenchymal cancer progression

Syndecan 2 (SDC2) belongs to a four-member family of evolutionary conserved small type I transmembrane proteoglycans consisting of a protein core to which glycosaminoglycan chains are covalently attached. SDC2 is a cell surface heparan sulfate proteoglycan, which is increasingly drawing attention for its distinct characteristics and its participation in numerous cell functions, including those related to carcinogenesis. Increasing evidence suggests that the role of SDC2 in cancer pathogenesis is dependent on cancer tissue origin rendering its use as a biomarker/therapeutic target feasible. This mini review discusses the mechanisms, through which SDC2, in a distinct manner, modulates complex signalling networks to affect cancer progression. © 2017 IUBMB Life, 69(11):824-833, 2017.

The Soft- and Hard-Heartedness of Cardiac Fibroblasts: Mechanotransduction Signaling Pathways in Fibrosis of the Heart

Cardiac fibrosis, the excessive accumulation of extracellular matrix (ECM), remains an unresolved problem in most forms of heart disease. In order to be successful in preventing, attenuating or reversing cardiac fibrosis, it is essential to understand the processes leading to ECM production and accumulation. Cardiac fibroblasts are the main producers of cardiac ECM, and harbor great phenotypic plasticity. They are activated by the disease-associated changes in mechanical properties of the heart, including stretch and increased tissue stiffness. Despite much remaining unknown, an interesting body of evidence exists on how mechanical forces are translated into transcriptional responses important for determination of fibroblast phenotype and production of ECM constituents. Such mechanotransduction can occur at multiple cellular locations including the plasma membrane, cytoskeleton and nucleus. Moreover, the ECM functions as a reservoir of pro-fibrotic signaling molecules that can be released upon mechanical stress. We here review the current status of knowledge of mechanotransduction signaling pathways in cardiac fibroblasts that culminate in pro-fibrotic gene expression.

Induction of Syndecan-4 by Organic-Inorganic Hybrid Molecules with a 1,10-Phenanthroline Structure in Cultured Vascular Endothelial Cells

Organic-inorganic hybrid molecules constitute analytical tools used in biological systems. Vascular endothelial cells synthesize and secrete proteoglycans, which are macromolecules consisting of a core protein and glycosaminoglycan side chains. Although the expression of endothelial proteoglycans is regulated by several cytokines/growth factors, there may be alternative pathways for proteoglycan synthesis aside from downstream pathways activated by these cytokines/growth factors. Here, we investigated organic-inorganic hybrid molecules to determine a variant capable of analyzing the expression of syndecan-4, a transmembrane heparan-sulfate proteoglycan, and identified 1,10-phenanthroline (o-Phen) with or without zinc (Zn-Phen) or rhodium (Rh-Phen). Bovine aortic endothelial cells in culture were treated with these compounds, and the expression of syndecan-4 mRNA and core proteins was determined by real-time reverse transcription polymerase chain reaction and Western blot analysis, respectively. Our findings indicated that o-Phen and Zn-Phen specifically and strongly induced syndecan-4 expression in cultured vascular endothelial cells through activation of the hypoxia-inducible factor-1α/β pathway via inhibition of prolyl hydroxylase-domain-containing protein 2. These results demonstrated an alternative pathway involved in mediating induction of endothelial syndecan-4 expression and revealed organic-inorganic hybrid molecules as effective tools for analyzing biological systems.

Syndecan-1 increases B-lymphoid cell extravasation in response to HIV-1 Tat via αvβ3/pp60src/pp125FAK pathway

Syndecan-1 is a heparan sulfate proteoglycan (HSPG) commonly upregulated in AIDS-related B lymphoid malignancies. Tat is the main HIV-1 transactivating factor that has a major role in the pathogenesis of AIDS-related lymphomas (ARL) by engaging heparan sulfate proteoglycans (HSPGs), chemokine receptors and integrins at the lymphoid cell (LC) surface. Here B-lymphoid Namalwa cell clones that do not express or overexpress syndecan-1 (EV-Ncs and SYN-Ncs, respectively) were compared for their responsiveness with Tat: in the absence of syndecan-1, Tat induces a limited EV-Nc migration via C-X-C motif chemokine receptor 4 (CXCR4), G-proteins and Rac. Syndecan-1 overexpression increases SYN-Nc responsiveness to Tat and makes this response independent from CXCR4 and G-protein and dependent instead on pp60src phosphorylation. Tat-induced SYN-Nc migration and pp60src phosphorylation require the engagement of α_vβ₃ integrin and consequent pp125FAK phosphorylation. This complex set of Tat-driven activations is orchestrated by the direct interaction of syndecan-1 with pp60src and its simultaneous coupling with α_vβ₃. The Tat/syndecan-1/α_vβ₃ interplay is retained in vivo and is shared also by other syndecan-1⁺ B-LCs, including BJAB cells, whose responsiveness to Tat is inhibited by syndecan-1 knockdown. In conclusion, overexpression of syndecan-1 confers to B-LCs an increased capacity to migrate in response to Tat, owing to a switch from a CXCR4/G-protein/Rac to a syndecan-1/α_vβ₃/pp60src/pp125FAK signal transduction pathway that depends on the formation of a complex in which syndecan-1 interacts with Tat via its HS-chains, with α_vβ₃ via its core protein ectodomain and with pp60src via its intracellular tail. These findings have implications in ARL progression and may help in identifying new therapeutical targets for the treatment of AIDS-associated neoplasia.

Heparanase-induced shedding of syndecan-1/CD138 in myeloma and endothelial cells activates VEGFR2 and an invasive phenotype: prevention by novel synstatins

Multiple myeloma arises when malignant plasma cells invade and form multiple tumors in the bone marrow. High levels of heparanase (HPSE) correlate with poor prognosis in myeloma patients. A likely target of the enzyme is the heparan sulfate (HS) proteoglycan syndecan-1 (Sdc1, CD138), which is highly expressed on myeloma cells and contributes to poor prognosis in this disease. We find that HPSE promotes an invasive phenotype mediated by the very late antigen-4 (VLA-4, or α4β1 integrin) in myeloma cells plated on either fibronectin (FN) or vascular endothelial cell adhesion molecule-1 (VCAM-1), ligands that are prevalent in the bone marrow. The phenotype depends on vascular endothelial cell growth factor receptor-2 (VEGFR2), which is aberrantly expressed in myeloma, and is characterized by a highly protrusive lamellipodium and cell invasion. HPSE-mediated trimming of the HS on Sdc1 and subsequent matrix metalloproteinase-9-mediated shedding of the syndecan exposes a juxtamembrane site in Sdc1 that binds VEGFR2 and VLA-4, thereby coupling VEGFR2 to the integrin. Shed Sdc1 can be mimicked by recombinant Sdc1 ectodomain or by a peptide based on its binding motif, which causes VLA-4 to re-orient from the lagging edge (uropod) to the leading edge of migrating cells, couple with and activate VEGFR2. Peptides (called 'synstatins') containing only the VLA-4 or VEGFR2 binding sites competitively inhibit invasion, as they block coupling of the receptors. This mechanism is also utilized by vascular endothelial cells, in which it is also activated by HPSE, during endothelial cell tube formation. Collectively, our findings reveal for the first time the mechanism through which HPSE modulates Sdc1 function to promote both tumor cell invasion and angiogenesis, thereby driving multiple myeloma progression. The inhibitory synstatins, or inhibitors of HPSE enzyme activity, are likely to show promise as therapeutics against myeloma extravasation and spread.

Extracellular matrix component signaling in cancer

Cell responses to the extracellular matrix depend on specific signaling events. These are important from early development, through differentiation and tissue homeostasis, immune surveillance, and disease pathogenesis. Signaling not only regulates cell adhesion cytoskeletal organization and motility but also provides survival and proliferation cues. The major classes of cell surface receptors for matrix macromolecules are the integrins, discoidin domain receptors, and transmembrane proteoglycans such as syndecans and CD44. Cells respond not only to specific ligands, such as collagen, fibronectin, or basement membrane glycoproteins, but also in terms of matrix rigidity. This can regulate the release and subsequent biological activity of matrix-bound growth factors, for example, transforming growth factor-β. In the environment of tumors, there may be changes in cell populations and their receptor profiles as well as matrix constitution and protein cross-linking. Here we summarize roles of the three major matrix receptor types, with emphasis on how they function in tumor progression.

Heparan Sulfate Proteoglycans May Promote or Inhibit Cancer Progression by Interacting with Integrins and Affecting Cell Migration

The metastatic disease is one of the main consequences of tumor progression, being responsible for most cancer-related deaths worldwide. This review intends to present and discuss data on the relationship between integrins and heparan sulfate proteoglycans in health and cancer progression. Integrins are a family of cell surface transmembrane receptors, responsible for cell-matrix and cell-cell adhesion. Integrins' main functions include cell adhesion, migration, and survival. Heparan sulfate proteoglycans (HSPGs) are cell surface molecules that play important roles as cell receptors, cofactors, and overall direct or indirect contributors to cell organization. Both molecules can act in conjunction to modulate cell behavior and affect malignancy. In this review, we will discuss the different contexts in which various integrins, such as α5, αV, β1, and β3, interact with HSPGs species, such as syndecans and perlecans, affecting tissue homeostasis.

Shed syndecan-2 inhibits angiogenesis

Angiogenesis is essential for the development of a normal vasculature, tissue repair and reproduction, and also has roles in the progression of diseases such as cancer and rheumatoid arthritis. The heparan sulphate proteoglycan syndecan-2 is expressed on mesenchymal cells in the vasculature and, like the other members of its family, can be shed from the cell surface resulting in the release of its extracellular core protein. The purpose of this study was to establish whether shed syndecan-2 affects angiogenesis. We demonstrate that shed syndecan-2 regulates angiogenesis by inhibiting endothelial cell migration in human and rodent models and, as a result, reduces tumour growth. Furthermore, our findings show that these effects are mediated by the protein tyrosine phosphatase receptor CD148 (also known as PTPRJ) and this interaction corresponds with a decrease in active β1 integrin. Collectively, these data demonstrate an unexplored pathway for the regulation of new blood vessel formation and identify syndecan-2 as a therapeutic target in pathologies characterised by angiogenesis.

Gene expression profiles in Rana pirica tadpoles following exposure to a predation threat

Background

Rana pirica tadpoles show morphological changes in response to a predation threat: larvae of the dragonfly Aeshna nigroflava induce heightened tail depth, whereas larval salamander Hynobius retardatus induce a bulgy morphology with heightened tail depth. Although both predators induce similar tail morphologies, it is possible that there are functional differences between these tail morphs.

Results

Here, we performed a discriminant microarray analysis using Xenopus laevis genome arrays to compare tail tissues of control and predator-exposed tadpoles. We identified 9 genes showing large-scale changes in their expression profile: ELAV-like1, methyltransferase like 7A, dolichyl-phosphate mannosyltransferase, laminin subunit beta-1, gremlin 1, BCL6 corepressor-like 1, and three genes of unknown identity. A further 80 genes showed greater than 5 fold differences in expression after exposure to dragonfly larvae and 81 genes showed altered expression after exposure to larval salamanders. Predation-threat responsive genes were identified by selecting genes that reverted to control levels of expression following removal of the predator. Thirteen genes were induced specifically by dragonfly larvae, nine others were salamander-specific, and sixteen were induced by both. Functional analyses indicated that some of the genes induced by dragonfly larvae caused an increase in laminins necessary for cell adhesion in the extracellular matrix. The higher expression of gremlin 1 and HIF1a genes after exposure to dragonfly larvae indicated an in vivo hypoxic reaction, while down-regulation of syndecan-2 may indicate impairment of angiogenesis. Exposure to larval salamanders caused down-regulation of XCIRP-1, which is known to inhibit expression of adhesion molecules; the tadpoles showed reduced expression of cα(E)-catenin, small muscle protein, dystrophin, and myosin light chain genes.

Conclusion

The connective tissue of tadpoles exposed to larval salamanders may be looser. The differences in gene expression profiles induced by the two predators suggest that there are functional differences between the altered tail tissues of the two groups of tadpoles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1389-4) contains supplementary material, which is available to authorized users.

A novel role for syndecan-3 in angiogenesis

Syndecan-3 is one of the four members of the syndecan family of heparan sulphate proteoglycans and has been shown to interact with numerous growth factors via its heparan sulphate chains. The extracellular core proteins of syndecan-1,-2 and -4 all possess adhesion regulatory motifs and we hypothesized that syndecan-3 may also possess such characteristics. Here we show that a bacterially expressed GST fusion protein consisting of the entire mature syndecan-3 ectodomain has anti-angiogenic properties and acts via modulating endothelial cell migration. This work identifies syndecan-3 as a possible therapeutic target for anti-angiogenic therapy.

Novel insight into the biological functions of syndecan ectodomain core proteins

Syndecans are a four member family of multifunctional transmembrane heparan sulphate bearing cell surface receptors. Each family member has common molecular architecture but a distinct expression profile. Numerous molecular interactions between syndecan heparan sulphate chains, growth factors, cytokines, and extracellular matrix molecules have been reported and syndecans are intimately associated with cell adhesion and migration. Here, we describe the important emerging concept that contained within syndecan extracellular core proteins are "adhesion regulatory domains." Cell adhesion is driven by the integrins and syndecan ectodomain adhesion regulatory domains can alter integrin driven cellular responses. Cell adhesion and migration is central to numerous pathologies and an understanding of how syndecan ectodomains influence integrins will lead to novel therapeutic strategies.

Targeting of heparanase-modified syndecan-1 by prosecretory mitogen lacritin requires conserved core GAGAL plus heparan and chondroitin sulfate as a novel hybrid binding site that enhances selectivity

Cell surface heparan sulfate (HS) proteoglycans shape organogenesis and homeostasis by capture and release of morphogens through mechanisms largely thought to exclude the core protein domain. Nevertheless, heparanase deglycanation of the N-terminal HS-rich domain of syndecan-1 (SDC1), but not SDC2 or -4, is a prerequisite for binding of the prosecretory mitogen lacritin (Ma, P., Beck, S. L., Raab, R. W., McKown, R. L., Coffman, G. L., Utani, A., Chirico, W. J., Rapraeger, A. C., and Laurie, G. W. (2006) Heparanase deglycanation of syndecan-1 is required for binding of the epithelial-restricted prosecretory mitogen lacritin. J. Cell Biol. 174, 1097-1106). We now report that the conserved and hydrophobic GAGAL domain in SDC1, adjacent to predicted HS substitution sites, is necessary to ligate and substantially enhance the α-helicity of the amphipathic C terminus of lacritin. Swapping out GAGAL for GADED in SDC2 or for GDLDD in SDC4 (both less hydrophobic) abrogated binding. HS and chondroitin sulfate are also essential. Both are detected in the N terminus, and when incubated with antibodies HS4C3 (anti-HS) or IO3H10 (anti-chondroitin sulfate), binding was absent, as occurred when all three N-terminal glycosaminoglycan substitution sites were mutated to alanine or when cells were treated with 4-methylumbelliferyl-β-d-xylopyranoside or chlorate to suppress glycosaminoglycan substitution or sulfation, respectively. SDC1 interacts with the hydrophobic face of lacritin via Leu-108/Leu-109/Phe-112 as well as with Glu-103/Lys-107 and Lys-111 of the largely cationic face. Carving a hybrid hydrophobic/electrostatic docking site out of SDC1 in a manner dependent on endogenous heparanase is a dynamic process appropriate for subtle or broad epithelial regulation in morphogenesis, health, and disease.

Synstatin: a selective inhibitor of the syndecan-1-coupled IGF1R-αvβ3 integrin complex in tumorigenesis and angiogenesis

The syndecans are a family of heparan sulfate-decorated cell-surface proteoglycans: matrix receptors with roles in cell adhesion and growth factor signaling. Their heparan sulfate chains recognize 'heparin-binding' motifs that are ubiquitously present in the extracellular matrix, providing the means for syndecans to constitutively bind and cluster to sites of cell-matrix adhesion. Emerging evidence suggests that specialized docking sites in the syndecan extracellular domains may serve to localize other receptors to these sites as well, including integrins and growth factor receptor tyrosine kinases. A prototype of this mechanism is capture of the αvβ3 integrin and insulin-like growth factor 1 receptor (IGF1R) by syndecan-1 (Sdc1), forming a ternary receptor complex in which signaling downstream of IGF1R activates the integrin. This Sdc1-coupled ternary receptor complex is especially prevalent on tumor cells and activated endothelial cells undergoing angiogenesis, reflecting the up-regulated expression of αvβ3 integrin in such cells. As such, much effort has focused on developing therapeutic agents that target this integrin in various cancers. Along these lines, the site in the Sdc1 ectodomain that is responsible for capture and activation of the αvβ3 or αvβ5 integrins by IGF1R can be mimicked by a short peptide called 'synstatin', which competitively displaces the integrin and IGF1R kinase from the syndecan and inactivates the complex. This review summarizes our current knowledge of the Sdc1-coupled ternary receptor complex and the efficacy of synstatin as an emerging therapeutic agent to target this signaling mechanism.

Syndecan-2 is a novel target of insulin-like growth factor binding protein-3 and is over-expressed in fibrosis

Extracellular matrix deposition and tissue scarring characterize the process of fibrosis. Transforming growth factor beta (TGFβ) and Insulin-like growth factor binding protein-3 (IGFBP-3) have been implicated in the pathogenesis of fibrosis in various tissues by inducing mesenchymal cell proliferation and extracellular matrix deposition. We identified Syndecan-2 (SDC2) as a gene induced by TGFβ in an IGFBP-3-dependent manner. TGFβ induction of SDC2 mRNA and protein required IGFBP-3. IGFBP-3 independently induced production of SDC2 in primary fibroblasts. Using an ex-vivo model of human skin in organ culture expressing IGFBP-3, we demonstrate that IGFBP-3 induces SDC2 ex vivo in human tissue. We also identified Mitogen-activated protein kinase-interacting kinase (Mknk2) as a gene induced by IGFBP-3. IGFBP-3 triggered Mknk2 phosphorylation resulting in its activation. Mknk2 independently induced SDC2 in human skin. Since IGFBP-3 is over-expressed in fibrotic tissues, we examined SDC2 levels in skin and lung tissues of patients with systemic sclerosis (SSc) and lung tissues of patients with idiopathic pulmonary fibrosis (IPF). SDC2 levels were increased in fibrotic dermal and lung tissues of patients with SSc and in lung tissues of patients with IPF. This is the first report describing elevated levels of SDC2 in fibrosis. Increased SDC2 expression is due, at least in part, to the activity of two pro-fibrotic factors, TGFβ and IGFBP-3.

Antithetic roles of proteoglycans in cancer

Proteoglycans (PGs), a family of complex post-translationally sculptured macromolecules, are fundamental regulators of most normal and aberrant cellular functions. The unparalleled structural-functional diversity of PGs endows them with the ability to serve as critical mediators of the tumor cells' interaction with the host microenvironment, while directly contributing to the organization and dynamic remodeling of this milieu. Despite their indisputable importance during embryonic development and in the adult organism, and their frequent dysregulation in tumor lesions, their precise involvement in tumorigenesis awaits a more decisive demonstration. Particularly challenging is to ascertain to what extent selected PGs may catalyze tumor progression and to what extent they may inhibit it, implying antithetic functions of individual PGs. Integrated efforts are needed to consolidate the routine use of PGs in the clinical monitoring of cancer patients and to broaden the exploitation of these macromolecules as therapeutic targets. Several PGs have the required attributes to be contemplated as effective antigens for immunotherapeutic approaches, while the tangible results obtained in recent clinical trials targeting the NG2/CSPG4 transmembrane PG urge further development of PG-based cancer treatment modalities.

Stem cell microenvironments--unveiling the secret of how stem cell fate is defined

Stem cells are defined as unspecialized cells that are capable of long term self-renewal and differentiation into specialized cell types. These unique properties make them an attractive cell source for regenerative medicine applications. Although the functions of various stem cells have been extensively studied in the development of organisms and in diseases, the specific factors and conditions that control stem cell fate, specifically the conditions that allow them to remain unspecialized, are not well studied. It has been suggested that adult stem cell survival and maintenance, as well as proliferation and differentiation, are controlled by the three-dimensional (3D) microenvironment, the so-called niche. Major functional niche components include supporting niche cells, growth-modulating soluble factors stored within the niches, and the extracellular matrix (ECM). In this article, we review work highlighting the growing complexity of stem cell-ECM interactions and their impact on the fields of biomaterials research and regenerative medicine.

Syndecan-2 is a novel ligand for the protein tyrosine phosphatase receptor CD148

The proteoglycan syndecan-2 is a novel ligand for the tyrosine phosphatase receptor CD148, an interaction that stimulates a signaling pathway leading to integrin-mediated cell adhesion. The pathway involves SRC and PI3 kinases and is an example of cell surface receptor cross-talk influencing integrin-mediated cellular processes.

Syndecan-2 is a heparan sulfate proteoglycan that has a cell adhesion regulatory domain contained within its extracellular core protein. Cell adhesion to the syndecan-2 extracellular domain (S2ED) is β1 integrin dependent; however, syndecan-2 is not an integrin ligand. Here the protein tyrosine phosphatase receptor CD148 is shown to be a key intermediary in cell adhesion to S2ED, with downstream β1 integrin–mediated adhesion and cytoskeletal organization. We show that S2ED is a novel ligand for CD148 and identify the region proximal to the transmembrane domain of syndecan-2 as the site of interaction with CD148. A mechanism for the transduction of the signal from CD148 to β1 integrins is elucidated requiring Src kinase and potential implication of the C2β isoform of phosphatidylinositol 3 kinase. Our data uncover a novel pathway for β1 integrin–mediated adhesion of importance in cellular processes such as angiogenesis and inflammation.

Specific syndecan-1 domains regulate mesenchymal tumor cell adhesion, motility and migration

Background

Syndecans are proteoglycans whose core proteins have a short cytoplasmic domain, a transmembrane domain and a large N-terminal extracellular domain possessing glycosaminoglycan chains. Syndecans are involved in many important cellular processes. Our recent publications have demonstrated that syndecan-1 translocates into the nucleus and hampers tumor cell proliferation. In the present study, we aimed to investigate the role of syndecan-1 in tumor cell adhesion and migration, with special focus on the importance of its distinct protein domains, to better understand the structure-function relationship of syndecan-1 in tumor progression.

Methodology/Principal Findings

We utilized two mesenchymal tumor cell lines which were transfected to stably overexpress full-length syndecan-1 or truncated variants: the 78 which lacks the extracellular domain except the DRKE sequence proposed to be essential for oligomerization, the 77 which lacks the whole extracellular domain, and the RMKKK which serves as a nuclear localization signal. The deletion of the RMKKK motif from full-length syndecan-1 abolished the nuclear translocation of this proteoglycan. Various bioassays for cell adhesion, chemotaxis, random movement and wound healing were studied. Furthermore, we performed gene microarray to analyze the global gene expression pattern influenced by syndecan-1. Both full-length and truncated syndecan-1 constructs decrease tumor cell migration and motility, and affect cell adhesion. Distinct protein domains have differential effects, the extracellular domain is more important for promoting cell adhesion, while the transmembrane and cytoplasmic domains are sufficient for inhibition of cell migration. Cell behavior seems to depend also on the nuclear translocation of syndecan-1. Many genes are differentially regulated by syndecan-1 and a number of genes are actually involved in cell adhesion and migration.

Conclusions/Significance

Our results demonstrate that syndecan-1 regulates mesenchymal tumor cell adhesion and migration, and different domains have differential effects. Our study provides new insights into better understanding of the role of syndecans in tumor progression.

Syndecans as cell surface receptors: Unique structure equates with functional diversity

An increasing number of functions for syndecan cell surface heparan sulfate proteoglycans have been proposed over the last decade. Moreover, aberrant syndecan regulation has been found to play a critical role in multiple pathologies, including cancers, as well as wound healing and inflammation. As receptors, they have much in common with other molecules on the cell surface. Syndecans are type I transmembrane molecules with cytoplasmic domains that link to the actin cytoskeleton and can interact with a number of regulators. However, they are also highly complex by virtue of their external glycosaminoglycan chains, especially heparan sulfate. This heterodisperse polysaccharide has the potential to interact with many ligands from diverse protein families. Here, we relate the structural features of syndecans to some of their known functions.

Importance of syndecan-4 and syndecan -2 in osteoblast cell adhesion and survival mediated by a tissue transglutaminase-fibronectin complex

Tissue transglutaminase (TG2) has been identified as an important extracellular crosslinking enzyme involved in matrix turnover and in bone differentiation. Here we report a novel cell adhesion/survival mechanism in human osteoblasts (HOB) which requires association of FN bound TG2 with the cell surface heparan sulphates in a transamidase independent manner. This novel pathway not only enhances cell adhesion on FN but also mediates cell adhesion and survival in the presence of integrin competing RGD peptides. We investigate the involvement of cell surface receptors and their intracellular signalling molecules to further explore the pathway mediated by this novel TG-FN heterocomplex. We demonstrate by siRNA silencing the crucial importance of the cell surface heparan sulphate proteoglycans syndecan-2 and syndecan-4 in regulating the compensatory effect of TG-FN on osteoblast cell adhesion and actin cytoskeletal formation in the presence of RGD peptides. By use of immunoprecipitation and inhibitory peptides we show that syndecan-4 interacts with TG2 and demonstrate that syndecan-2 and the α5β1 integrins, but not α4β1 function as downstream modulators in this pathway. Using function blocking antibodies, we show activation of α5β1 occurs by an inside out signalling mechanism involving activation and binding of protein kinase PKCα and phosphorylation of focal adhesion kinase (FAK) at Tyr(861) and activation of ERK1/2.

RGD-independent cell adhesion via a tissue transglutaminase-fibronectin matrix promotes fibronectin fibril deposition and requires syndecan-4/2 α5β1 integrin co-signaling

Fibronectin (FN) deposition mediated by fibroblasts is an important process in matrix remodeling and wound healing. By monitoring the deposition of soluble biotinylated FN, we show that the stress-induced TG-FN matrix, a matrix complex of tissue transglutaminase (TG2) with its high affinity binding partner FN, can increase both exogenous and cellular FN deposition and also restore it when cell adhesion is interrupted via the presence of RGD-containing peptides. This mechanism does not require the transamidase activity of TG2 but is activated through an RGD-independent adhesion process requiring a heterocomplex of TG2 and FN and is mediated by a syndecan-4 and β1 integrin co-signaling pathway. By using α5 null cells, β1 integrin functional blocking antibody, and a α5β1 integrin targeting peptide A5-1, we demonstrate that the α5 and β1 integrins are essential for TG-FN to compensate RGD-induced loss of cell adhesion and FN deposition. The importance of syndecan-2 in this process was shown using targeting siRNAs, which abolished the compensation effect of TG-FN on the RGD-induced loss of cell adhesion, resulting in disruption of actin skeleton formation and FN deposition. Unlike syndecan-4, syndecan-2 does not interact directly with TG2 but acts as a downstream effector in regulating actin cytoskeleton organization through the ROCK pathway. We demonstrate that PKCα is likely to be the important link between syndecan-4 and syndecan-2 signaling and that TG2 is the functional component of the TG-FN heterocomplex in mediating cell adhesion via its direct interaction with heparan sulfate chains.

Syndecan- and integrin-binding peptides synergistically accelerate cell adhesion

Integrins and syndecans mediate cell adhesion to extracellular matrix and their synergistic cooperation is implicated in cell adhesion processes. We previously identified two active peptides, AG73 and EF1, from the laminin alpha1 chain LG4 module, that promote cell attachment through syndecan- and alpha2beta1 integrin-binding, respectively. Here, we examined time-dependent cell attachment on the mixed peptides AG73/EF1. The AG73/EF1 promoted stronger and more rapid cell attachment, spreading, FAK phosphorylation that reached a maximum at 20 min than that on AG73 (40 min) or EF1 (90 min) supplied singly. Thus, the syndecan- and alpha2beta1 integrin-binding peptides synergistically affect cells and accelerate cell adhesion.

Interaction of syndecan and alpha6beta4 integrin cytoplasmic domains: regulation of ErbB2-mediated integrin activation

The alpha6beta4 integrin is a laminin 332 (LN332) receptor central to the formation of hemidesmosomes in epithelial layers. However, the integrin becomes phosphorylated by keratinocytes responding to epidermal growth factor in skin wounds or by squamous cell carcinomas that overexpress/hyperactivate the tyrosine kinase ErbB2, epidermal growth factor receptor, or c-Met. We show here that the beta4-dependent signaling in A431 human squamous carcinoma cells is dependent on the syndecan family of matrix receptors. Yeast two-hybrid analysis identifies an interaction within the distal third (amino acids 1473-1752) of the beta4 cytoplasmic domain and the conserved C2 region of the syndecan cytoplasmic domain. Via its C2 region, Sdc1 forms a complex with the alpha6beta4 integrin along with the receptor tyrosine kinase ErbB2 and the cytoplasmic kinase Fyn in A431 cells. Engagement of LN332 or clustering of the alpha6beta4 integrin with integrin-specific antibodies causes phosphorylation of ErbB2, Fyn, and the beta4 subunit as well as activation of phosphatidylinositol 3-kinase and Akt and their assimilation into this complex. This leads to phosphatidylinositol 3-kinase-dependent cell spreading and Akt-dependent protection from apoptosis. This is disrupted by RNA interference silencing of Sdc1 but can be rescued by mouse Sdc1 or Sdc4 but not by syndecan mutants lacking their C-terminal C2 region. This disruption does not prevent the phosphorylation of ErbB2 or Fyn but blocks the Fyn-mediated phosphorylation of the beta4 tail. We propose that syndecans engage the distal region of the beta4 cytoplasmic domain and bring it to the plasma membrane, where it can be acted upon by Src family kinases.

Heparan sulfate chain valency controls syndecan-4 function in cell adhesion

Fibroblasts null for the transmembrane proteoglycan, syndecan-4, have an altered actin cytoskeleton, compared with matching wild-type cells. They do not organize α-smooth muscle actin into bundles, but will do so when full-length syndecan-4 is re-expressed. This requires the central V region of the core protein cytoplasmic domain, though not interactions with PDZ proteins. A second key requirement is multiple heparan sulfate chains. Mutant syndecan-4 with no chains, or only one chain, failed to restore the wild-type phenotype, whereas those expressing two or three were competent. However, clustering of one-chain syndecan-4 forms with antibodies overcame the block, indicating that valency of interactions with ligands is a key component of syndecan-4 function. Measurements of focal contact/adhesion size and focal adhesion kinase phosphorylation correlated with syndecan-4 status and α-smooth muscle actin organization, being reduced where syndecan-4 function was compromised by a lack of multiple heparan sulfate chains.

Extra-embryonic syndecan 2 regulates organ primordia migration and fibrillogenesis throughout the zebrafish embryo

One of the first steps in zebrafish heart and gut organogenesis is the migration of bilateral primordia to the midline to form cardiac and gut tubes. The mechanisms that regulate this process are poorly understood. Here we show that the proteoglycan syndecan 2 (Sdc2) expressed in the extra-embryonic yolk syncytial layer (YSL) acts locally at the YSL-embryo interface to direct organ primordia migration, and is required for fibronectin and laminin matrix assembly throughout the embryo. Surprisingly, neither endogenous nor exogenous sdc2 expressed in embryonic cells can compensate for knockdown of sdc2 in the YSL, indicating that Sdc2 expressed in extra-embryonic tissues is functionally distinct from Sdc2 in embryonic cells. The effects of sdc2 knockdown in the YSL can be rescued by extra-embryonic Sdc2 lacking an extracellular proteolytic cleavage (shedding) site, but not by extra-embryonic Sdc2 lacking extracellular glycosaminoglycan (GAG) addition sites, suggesting that distinct GAG chains on extra-embryonic Sdc2 regulate extracellular matrix assembly, cell migration and epithelial morphogenesis of multiple organ systems throughout the embryo.

Mutation in the heparan sulfate biosynthesis enzyme EXT1 influences growth factor signaling and fibroblast interactions with the extracellular matrix

Heparan sulfate (HS) chains bind and modulate the signaling efficiency of many ligands, including members of the fibroblast growth factor (FGF) and platelet-derived growth factor families. We previously reported the structure of HS synthesized by embryonic fibroblasts from mice with a gene trap mutation of Ext1 that encodes a glycosyltransferase involved in HS chain elongation. The gene trap mutation results in low expression of Ext1, and, as a consequence, HS chain length is substantially reduced. In the present study, Ext1 mutant and wild-type mouse embryonic fibroblasts were analyzed for the functional consequences of the Ext1 mutation for growth factor signaling and interaction with the extracellular matrix. Here, we show that the phosphorylation of ERK1/2 in response to FGF2 stimulation was markedly decreased in the Ext1 mutant fibroblasts, whereas neither PDGF-BB nor FGF10 signaling was significantly affected. Furthermore, Ext1 mutants displayed reduced ability to attach to collagen I and to contract collagen lattices, even though no differences in the expression of collagen-binding integrins were observed. Reintroduction of Ext1in the Ext1 mutant fibroblasts rescued HS chain length, FGF2 signaling, and the ability of the fibroblasts to contract collagen. These data suggest that the length of the HS chains is a critical determinant of HS-protein interactions and emphasize the essential role of EXT1 in providing specific binding sites for growth factors and extracellular matrix proteins.

Syndecan proteoglycan contributions to cytoskeletal organization and contractility

Cells exert tension on the extracellular matrix through specific receptors that link to the actin cytoskeleton. The best characterized are the integrins, which, when activated and clustered, can link to the extracellular matrix at specialized adhesion zones, known as focal contacts or focal adhesions. However, other transmembrane receptors can also localize there, including one transmembrane proteoglycan, syndecan-4. This heparan sulfate proteoglycan can also link directly to the cytoskeleton through alpha-actinin, and can signal through protein kinase C. In turn, the pathway leads to RhoA and Rho kinases that control actomyosin contractility. Syndecan-4 may, therefore, be a sensor of tension exerted on the matrix. These processes are described here, their significance being potential roles in wound contraction, tumor-stroma interactions, fibrosis and the regulation of motility.

Primary dermal fibroblasts derived from sdc-1 deficient mice migrate faster and have altered alphav integrin function

ABSTRACT The goal of this study is to determine whether dermal fibroblasts lacking syndecan-1 (sdc1) show differences in integrin expression and function that could contribute to the delayed skin and corneal wound healing phenotypes seen in sdc-1 null mice. Using primary dermal fibroblasts, we show that after 3 days in culture no differences in alpha-smooth muscle actin were detected but sdc-1 null cells expressed significantly more alphav and beta1 integrin than wildtype (wt) cells. Transforming growth factor beta1 (TGFbeta1) treatment at day 3 increased alphav- and beta1-integrin expression in sdc-1 null cells at day 5 whereas wt cells showed increased expression only of alphav-integrin. Using time-lapse studies, we showed that the sdc-1 null fibroblasts migrate faster than wt fibroblasts, treatment with TGFbeta1 increased these migration differences, and treatment with a TGFbeta1 antagonist caused sdc-1 null fibroblasts to slow down and migrate at the same rate as untreated wt cells. Cell spreading studies on replated fibroblasts showed altered cell spreading and focal adhesion formation on vitronectin and fibronectin-coated surfaces. Additional time lapse studies with beta1- and alphav-integrin antibody antagonists, showed that wt fibroblasts expressing sdc-1 had activated integrins on their surface that impeded their migration whereas the null cells expressed alphav-containing integrins which were less adhesive and enhanced cell migration. Surface expression studies showed increased surface expression of alpha2beta1 and alpha3beta1 on the sdc-1 null fibroblasts compared with wt fibroblasts but no significant differences in surface expression of alpha5beta1, alphavbeta3, or alphavbeta5. Taken together, our data indicates that sdc-1 functions in the activation of alphav-containing integrins and support the hypothesis that impaired wound healing phenotypes seen in sdc-1 null mice could be due to integrin-mediated defects in fibroblast migration after injury.

Syndecan-2 overexpression regulates adhesion and migration through cooperation with integrin alpha2

Syndecan-2, a transmembrane heparan sulfate proteoglycan, is known to serve as an adhesion receptor, but details of the regulatory mechanism governing syndecan-2 cell adhesion and migration remain unclear. Here, we examined this regulatory mechanism, showing that overexpression of syndecan-2 enhanced collagen adhesion, cell migration and invasion of normal rat intestinal epithelial cells (RIE1), and increased integrin alpha2 expression levels. Interestingly, RIE1 cells transfected with either syndecan-2 or integrin alpha2 showed similar adhesion and migration patterns, and a function-blocking anti-integrin alpha2 antibody abolished syndecan-2-mediated adhesion and migration. Consistent with these findings, transfection of integrin alpha2 siRNA diminished syndecan-2-induced cell migration in HCT116 human colon cancer cells. Taken together, these results demonstrate a novel cooperation between syndecan-2 and integrin alpha2beta1 in adhesion-mediated cell migration and invasion. This interactive dynamic might be a possible mechanism underlying the tumorigenic activities of colon cancer cells.