Trimeric assembly of the C-terminal region of Thrombospondin-1 or Thrombospondin-2 is necessary for cell spreading and fascin spike organisation

Thrombospondins: Conserved mediators and modulators of metazoan extracellular matrix

This review provides a personal overview of significant scientific developments in the thrombospondin field during the course of my career. Thrombospondins are multidomain, multimeric, calcium-binding extracellular glycoproteins with context-specific roles in tissue organisation. They act at cell surfaces and within ECM to regulate cell phenotype and signalling, differentiation and assembly of collagenous ECM, along with tissue-specific roles in cartilage, angiogenesis and synaptic function. More recently, intracellular, homeostatic roles have also been identified. Resolution of structures for the major domains of mammalian thrombospondins has facilitated major advances in understanding thrombospondin biology from molecule to tissue; for example, in illuminating molecular consequences of disease-causing coding mutations in human pseudoachrondroplasia. Although principally studied in vertebrates, thrombospondins are amongst the most ancient of animal ECM proteins, with many invertebrates encoding a single thrombospondin and the thrombospondin gene family of vertebrates originating through gene duplications. Moreover, thrombospondins form one branch of a thrombospondin superfamily that debuted at the origin of metazoans. The super-family includes additional sub-groups, present only in invertebrates, that differ in N-terminal domain organisation, share the distinctive TSP C-terminal region domain architecture and, to the limited extent studied to date, apparently contribute to tissue development and organisation. Finally, major lines of translational research are discussed, related to fibrosis; TSP1, TSP2 and inhibition of angiogenesis; and the alleviation of chronic cartilage tissue pathologies in pseudoachrondroplasia.

Controlled extracellular proteolysis of thrombospondins

Limited proteolysis of thrombospondins is a powerful mechanism to ensure dynamic tuning of their activities in the extracellular space. Thrombospondins are multifunctional matricellular proteins composed of multiple domains, each with a specific pattern of interactions with cell receptors, matrix components and soluble factors (growth factors, cytokines and proteases), thus with different effects on cell behavior and responses to changes in the microenvironment. Therefore, the proteolytic degradation of thrombospondins has multiple functional consequences, reflecting the local release of active fragments and isolated domains, exposure or disruption of active sequences, altered protein location, and changes in the composition and function of TSP-based pericellular interaction networks. In this review current data from the literature and databases is employed to provide an overview of cleavage of mammalian thrombospondins by different proteases. The roles of the fragments generated in specific pathological settings, with particular focus on cancer and the tumor microenvironment, are discussed.

Wiring the ocular surface: A focus on the comparative anatomy and molecular regulation of sensory innervation of the cornea

The cornea is richly innervated with sensory nerves that function to detect and clear harmful debris from the surface of the eye, promote growth and survival of the corneal epithelium and hasten wound healing following ocular disease or trauma. Given their importance to eye health, the neuroanatomy of the cornea has for many years been a source of intense investigation. Resultantly, complete nerve architecture maps exist for adult human and many animal models and these maps reveal few major differences across species. Interestingly, recent work has revealed considerable variation across species in how sensory nerves are acquired during developmental innervation of the cornea. Highlighting such species-distinct key differences, but also similarities, this review provides a full, comparative anatomy analysis of sensory innervation of the cornea for all species studied to date. Further, this article comprehensively describes the molecules that have been shown to guide and direct nerves toward, into and through developing corneal tissue as the final architectural pattern of the cornea's neuroanatomy is established. Such knowledge is useful for researchers and clinicians seeking to better understand the anatomical and molecular basis of corneal nerve pathologies and to hasten neuro-regeneration following infection, trauma or surgery that damage the ocular surface and its corneal nerves.

Therapeutic effect on Alveolar echinococcosis by targeting EM-Leucine aminopeptidase

Alveolar echinococcosis (AE) is a parasitic disease caused by E. multilocularis metacestodes and it is highly prevalent in the northern hemisphere. We have previously found that vaccination with E. multilocularis Leucine aminopeptidase (EM-LAP) induced specific immune response and had an inhibiting effect on the parasites. In this study, the therapeutic effect of recombinant EM-LAP (rEM-LAP) on AE was evaluated and verified using Ubenimex, a broad-spectrum inhibitor of LAP. The results reveal that rEM-LAP could inhibit cyst growth and invasion and induce specific immunity response in BALB/c mice infected with E. multilocularis protoscoleces. The ultrasonic, MRI, and morphological results show that treatment with rEM-LAP inhibits E. multilocularis infection and reduces cyst weight, number, fibrosis and invasion. The same effect is observed for the treatment with Ubenimex by inhibiting LAP activity. The indirect ELISA shows that rEM-LAP could induce specific immunity response and produce high levels of IgG, IgG1, IgG2a, IgM, and IgA, and the serum levels of IFN-γ and IL-4 are significantly increased compared to the control groups, indicating that treatment with rEM-LAP leads to a Th1 and Th2 mixed-type immune response. This study suggests that EM-LAP could be a potential therapeutic target of E. multilocularis infection.

Thrombospondin-1 CD47 Signalling: From Mechanisms to Medicine

Recent advances provide evidence that the cellular signalling pathway comprising the ligand-receptor duo of thrombospondin-1 (TSP1) and CD47 is involved in mediating a range of diseases affecting renal, vascular, and metabolic function, as well as cancer. In several instances, research has barely progressed past pre-clinical animal models of disease and early phase 1 clinical trials, while for cancers, anti-CD47 therapy has emerged from phase 2 clinical trials in humans as a crucial adjuvant therapeutic agent. This has important implications for interventions that seek to capitalize on targeting this pathway in diseases where TSP1 and/or CD47 play a role. Despite substantial progress made in our understanding of this pathway in malignant and cardiovascular disease, knowledge and translational gaps remain regarding the role of this pathway in kidney and metabolic diseases, limiting identification of putative drug targets and development of effective treatments. This review considers recent advances reported in the field of TSP1-CD47 signalling, focusing on several aspects including enzymatic production, receptor function, interacting partners, localization of signalling, matrix-cellular and cell-to-cell cross talk. The potential impact that these newly described mechanisms have on health, with a particular focus on renal and metabolic disease, is also discussed.

Homotrimerization Approach in the Design of Thrombospondin-1 Mimetic Peptides with Improved Potency in Triggering Regulated Cell Death of Cancer Cells

In order to optimize the potency of the first serum-stable peptide agonist of CD47 (PKHB1) in triggering regulated cell death of cancer cells, we designed a maturation process aimed to mimic the trimeric structure of the thrombospondin-1/CD47 binding epitope. For that purpose, an N-methylation scan of the PKHB1 sequence was realized to prevent peptide aggregation. Structural and pharmacological analyses were conducted in order to assess the conformational impact of these chemical modifications on the backbone structure and the biological activity. This structure-activity relationship study led to the discovery of a highly soluble N-methylated peptide that we termed PKT16. Afterward, this monomer was used for the design of a homotrimeric peptide mimic that we termed [PKT16]₃, which proved to be 10-fold more potent than its monomeric counterpart. A pharmacological evaluation of [PKT16]₃ in inducing cell death of adherent (A549) and nonadherent (MEC-1) cancer cell lines was also performed.

Thrombospondin-1 Mediates Axon Regeneration in Retinal Ganglion Cells

Neuronal subtypes show diverse injury responses, but the molecular underpinnings remain elusive. Using transgenic mice that allow reliable visualization of axonal fate, we demonstrate that intrinsically photosensitive retinal ganglion cells (ipRGCs) are both resilient to cell death and highly regenerative. Using RNA sequencing (RNA-seq), we show genes that are differentially expressed in ipRGCs and that associate with their survival and axon regeneration. Strikingly, thrombospondin-1 (Thbs1) ranked as the most differentially expressed gene, along with the well-documented injury-response genes Atf3 and Jun. THBS1 knockdown in RGCs eliminated axon regeneration. Conversely, RGC overexpression of THBS1 enhanced regeneration in both ipRGCs and non-ipRGCs, an effect that was dependent on syndecan-1, a known THBS1-binding protein. All structural domains of the THBS1 were not equally effective; the trimerization and C-terminal domains promoted regeneration, while the THBS type-1 repeats were dispensable. Our results identify cell-type-specific induction of Thbs1 as a novel gene conferring high regenerative capacity.

CD47-independent effects mediated by the TSP-derived 4N1K peptide

4N1K is a peptide fragment derived from the C-terminal, globular domain of thrombospondin which has been shown to mediate integrin-dependent cell adhesion and promote integrin activation acting via the cell-surface receptor, CD47. However, some studies found that 4N1K could act independently of CD47, putting in question the specificity of 4N1K for CD47. This led us to characterize the cellular and non-cellular effects of 4N1K. We found that 4N1K stimulated a potent increase in binding of a variety of non-specific IgG antibodies to cells in suspension. We also found that these same antibodies, as well as CD47-deficient cells, could bind substrate-immobilized 4N1K significantly better than a control peptide, 4NGG. Furthermore, we found that cells treated with 4N1K at higher concentrations inhibited, while lower concentrations promoted cell adhesion to immobilized fibronectin as an integrin substrate. Importantly, both the stimulatory and the inhibitory activity of 4N1K occurred as efficiently in the CD47-deficient JinB8 cells, as it did in the CD47-expressing parental or in JinB8 cells reconstituted with CD47 expression. Given these results, we suggest that 4N1K interacts non-specifically with epitopes commonly found on the cell surface, and conclude that it is not a suitable peptide for use to study the consequences of CD47 receptor ligation.

Oligomerization-induced conformational change in the C-terminal region of Nel-like molecule 1 (NELL1) protein is necessary for the efficient mediation of murine MC3T3-E1 cell adhesion and spreading

NELL1 is a large oligomeric secretory glycoprotein that functions as an osteoinductive factor. NELL1 contains several conserved domains, has structural similarities to thrombospondin 1, and supports osteoblastic cell adhesion through integrins. To define the structural requirements for NELL1-mediated cell adhesion, we prepared a series of recombinant NELL1 proteins (intact, deleted, and cysteine-mutant) from a mammalian expression system and tested their activities. A deletion analysis demonstrated that the C-terminal cysteine-rich region of NELL1 is critical for the cell adhesion activity of NELL1. Reducing agent treatment decreased the cell adhesion activity of full-length NELL1 but not of its C-terminal fragments, suggesting that the intramolecular disulfide bonds within this region are not functionally necessary but that other disulfide linkages in the N-terminal region of NELL1 may be involved in cell adhesion activity. By replacing cysteine residues with serines around the coiled-coil domain of NELL1, which is responsible for oligomerization, we created a mutant NELL1 protein that was unable to form homo-oligomers, and this monomeric mutant showed substantially lower cell adhesion activity than intact NELL1. These results suggest that an oligomerization-induced conformational change in the C-terminal region of NELL1 is important for the efficient mediation of cell adhesion and spreading by NELL1.

sFRP-1 binds via its netrin-related motif to the N-module of thrombospondin-1 and blocks thrombospondin-1 stimulation of MDA-MB-231 breast carcinoma cell adhesion and migration

Secreted frizzled-related protein (sFRP)-1 is a Wnt antagonist that inhibits breast carcinoma cell motility, whereas the secreted glycoprotein thrombospondin-1 stimulates adhesion and motility of the same cells. We examined whether thrombospondin-1 and sFRP-1 interact directly or indirectly to modulate cell behavior. Thrombospondin-1 bound sFRP-1 with an apparent K(d)=48nM and the related sFRP-2 with a K(d)=95nM. Thrombospondin-1 did not bind to the more distantly related sFRP-3. The association of thrombospondin-1 and sFRP-1 is primarily mediated by the amino-terminal N-module of thrombospondin-1 and the netrin domain of sFRP-1. sFRP-1 inhibited α3β1 integrin-mediated adhesion of MDA-MB-231 breast carcinoma cells to a surface coated with thrombospondin-1 or recombinant N-module, but not adhesion of the cells on immobilized fibronectin or type I collagen. sFRP-1 also inhibited thrombospondin-1-mediated migration of MDA-MB-231 and MDA-MB-468 breast carcinoma cells. Although sFRP-2 binds similarly to thrombospondin-1, it did not inhibit thrombospondin-1-stimulated adhesion. Thus, sFRP-1 binds to thrombospondin-1 and antagonizes stimulatory effects of thrombospondin-1 on breast carcinoma cell adhesion and motility. These results demonstrate that sFRP-1 can modulate breast cancer cell responses by interacting with thrombospondin-1 in addition to its known effects on Wnt signaling.

Identification of extracellular matrix and cell adhesion molecule genes associated with muscle development in pigs

Extracellular matrix (ECM) and cell adhesion molecule (CAM) genes are involved in the regulation of skeletal muscle development; however, their roles in skeletal muscle development in pigs are still poorly understood. 65 days postcopulation (dpc) is a critical time point in pig development. Therefore, we analyzed expression of ECM and CAM genes in the longissimus dorsi muscles at 65 dpc from Landrace (lean-type: L65), Tongcheng (obese-type: T65), and Wuzhishan pigs (miniature-type: W65) using microarray technology. A total of 35 genes were differently expressed between the breeds, and of them, 18, 18, and 20 genes, were observed in the comparisons of L65 versus T65, L65 versus W65, and T65 versus W65 (L65/T65, L65/W65, and T65/W65), respectively. In L65/T65, differently expressed genes were widely distributed, whereas in L65/W65 and T65/W65, they mostly focused on the genes encoding CAMs and ECMs proteins. Moreover, the largest number of up-regulated genes involved in skeletal muscle development was detected in L65, a moderate number in W65, and the smallest number was in T65. Cluster analysis suggested that T65 showed a more similar expression pattern to L65 than W65. In addition, we validated that five genes from microarray data were more highly expressed in the prenatal as compared to postnatal periods in Landrace and Tongcheng pigs and showed a greater range of high-level expression during gestation in Landrace than Tongcheng pigs. Our data indicated that ECM and CAM genes are differently expressed among the three breeds, and more complicated molecular events involving CAMs and ECMs were observed in Wuzhishan pigs. This study advances our knowledge of the molecular basis of phenotypic variation and provides a helpful resource for the identification of candidate genes associated with meat production traits in pigs.

The evolution of thrombospondins and their ligand-binding activities

The extracellular matrix (ECM) is a complex, multiprotein network that has essential roles in tissue integrity and intercellular signaling in the metazoa. Thrombospondins (TSPs) are extracellular, calcium-binding glycoproteins that have biologically important roles in mammals in angiogenesis, vascular biology, connective tissues, immune response, and synaptogenesis. The evolution of these complex functional properties is poorly understood. We report here on the evolution of TSPs and their ligand-binding capacities, from comparative genomics of species representing the major phyla of metazoa and experimental analyses of the oligomerization properties of noncanonical TSPs of basal deuterostomes. Monomeric, dimeric, trimeric, and pentameric TSPs have arisen through separate evolutionary events involving gain, loss, or modification of a coiled-coil domain or distinct domains at the amino-terminus. The relative transience of monomeric forms under evolution implicates a biological importance for multivalency of the C-terminal region of TSPs. Most protostomes have a single TSP gene encoding a pentameric TSP. The pentameric form is also present in deuterostomes, and gene duplications at the origin of deuterostomes and gene loss and further gene duplication events in the vertebrate lineage gave rise to distinct forms and novel domain architectures. Parallel analysis of the major ligands of mammalian TSPs revealed that many binding activities are neofunctions representing either coevolutionary innovations in the deuterostome lineage or neofunctions of ancient molecules such as CD36. Contrasting widely conserved capacities include binding to heparan glycosaminoglycans, fibrillar collagen, or RGD-dependent integrins. These findings identify TSPs as fundamental components of the extracellular interaction systems of metazoa and thus impact understanding of the evolution of ECM networks. The widely conserved activities of TSPs in binding to ECM components or PS2 clade integrins will be relevant to use of TSPs in synthetic extracellular matrices or tissue engineering. In contrast, the neofunctions of vertebrate TSPs likely include interactions suitable for therapeutic targeting without general disruption of ECM.

Fascin expression in progression and prognosis of hepatocellular carcinoma

BACKGROUND AND OBJECTIVES

Fascin is an actin-bundling protein and induces membrane protrusions and cell motility after the formation of lamellipodia or filopodia. Fascin expression has been reported to be associated with progression or prognosis in various neoplasms, but the role of fascin in hepatocellular carcinoma (HCC) remains unknown. The aim of this study was to investigate the clinicopathological and prognostic relevance of fascin by immunohistochemistry.

METHODS

A total of 137 patients with HCC were stained with anti-fascin antibody. The tumor cells having unequivocal cytoplasmic and/or membranous fascin immunoreactivity were defined as fascin-positive.

RESULTS

Immunohistochemically, 23 (16.8%) HCCs having unequivocal fascin immunoreactivity were found. Tumors showing fascin expression were larger and less differentiated than those showing no fascin expression (P = 0.0239 and 0.0018, respectively). Portal venous invasion, bile duct invasion, and intrahepatic metastasis were detected significantly more frequently in fascin-positive group (P = 0.0029, 0.0333, and 0.0403, respectively). In addition, high alpha-fetoprotein (AFP) levels were significantly associated with the fascin expression in HCC (P = 0.0116). Fascin-positive group had significantly poorer outcomes than fascin-negative group and was an independent prognostic factor for disease-free survival.

CONCLUSIONS

Fascin might become a novel marker of progression in HCC and a significant indicator of a poor prognosis for patients with HCC.

Fascin overexpression is involved in carcinogenesis and prognosis of human intrahepatic cholangiocarcinoma: immunohistochemical and molecular analysis

Fascin is an actin-bundling protein that induces membrane protrusions and cell motility after the formation of lamellipodia or filopodia. Fascin expression has been associated with progression or prognosis in various neoplasms; however, its role in intrahepatic cholangiocarcinoma is unknown. Tumor sections from 84 patients with intrahepatic cholangiocarcinoma and 16 patients with intrahepatic biliary dysplasia were stained with antifascin antibody. Fascin mRNA expression, measured by real-time reverse transcription-polymerase chain reaction in 20 frozen samples, was compared with the immunohistochemical results. Furthermore, the expression of cyclin D1 was compared with that of fascin. Immunohistochemically, fascin expression was absent or sporadic in normal biliary epithelium, whereas high expression (>70% of tumor cells) was found in 2 (12.5%) dysplasias and 30 (35.7%) intrahepatic cholangiocarcinomas. The difference between the fascin mRNA concentrations in the high-expression and low-expression groups was significant (P = .0082). Tumors showing high expression were poorly differentiated (P = .0019), and among poorly differentiated intrahepatic cholangiocarcinoma, larger tumors (>5 cm) were more likely than smaller lesions to have high fascin expression (P = .0205). A significant correlation was observed between fascin and cyclin D1 immunoreactivity (P = .0289). Patients whose tumors expressed fascin abundantly had a poorer outcome (P = .0085), and fascin overexpression was an independent prognostic factor (P = .0477). Fascin is expressed early in biliary carcinogenesis and might contribute to poor differentiation and to growth of intrahepatic cholangiocarcinoma. It is a significant indicator of a poor prognosis for patients with intrahepatic cholangiocarcinoma.

Thrombospondin 1 promotes tumor macrophage recruitment and enhances tumor cell cytotoxicity of differentiated U937 cells

Inhibition of tumor growth by thrombospondin (TSP) 1 is generally attributed to its antiangiogenic activity, but effects on tumor immunity should also be considered. We show that overexpression of TSP1 in melanoma cells increases macrophage recruitment into xenograft tumors grown in nude or beige/nude mice. In vitro, TSP1 acutely induces expression of plasminogen activator inhibitor-1 (PAI-1) by monocytic cells, suggesting that TSP1-induced macrophage recruitment is at least partially mediated by PAI-1. Tumor-associated macrophages (TAM) can either promote or limit tumor progression. The percentage of M1-polarized macrophages expressing inducible nitric oxide synthase is increased in TSP1-expressing tumors. Furthermore, soluble TSP1 stimulates killing of breast carcinoma and melanoma cells by IFN-gamma-differentiated U937 cells in vitro via release of reactive oxygen species. TSP1 causes a significant increase in phorbol ester-mediated superoxide generation from differentiated monocytes by interaction with alpha(6)beta(1) integrin through its NH(2)-terminal region. The NH(2)-terminal domain of TSP2 also stimulates monocyte superoxide production. Extracellular calcium is required for the TSP1-induced macrophage respiratory burst. Thus, TSP1 may play an important role in antitumor immunity by enhancing recruitment and activation of M1 TAMs, which provides an additional selective pressure for loss of TSP1 and TSP2 expression during tumor progression.

Thrombospondin 1 binding to calreticulin-LRP1 signals resistance to anoikis

Anoikis, apoptotic cell death due to loss of cell adhesion, is critical for regulation of tissue homeostasis in tissue remodeling. Fibrogenesis is associated with reduced fibroblast apoptosis. The matricellular protein thrombospondin 1 (TSP1) regulates cell adhesion and motility during tissue remodeling and in fibrogenesis. The N-terminal domain of TSP1 binds to the calreticulin-LRP1 receptor co-complex to signal down-regulation of cell adhesion and increased cell motility through focal adhesion disassembly. TSP1 signaling through calreticulin-LRP1 activates cell survival signals such as PI3-kinase. Therefore, we tested the hypothesis that TSP1 supports cell survival under adhesion-independent conditions to facilitate tissue remodeling. Here, we show that platelet TSP1, its N-terminal domain (NoC1) as a recombinant protein, or a peptide comprising the calreticulin-LRP1 binding site [amino acids 17-35 (hep I)] in the N-terminal domain promotes fibroblast survival under anchorage-independent conditions. TSP1 activates Akt and decreases apoptotic signaling through caspase 3 and PARP1 in suspended fibroblasts. Inhibition of PI3K/Akt activity blocks TSP1-mediated anchorage-independent survival. Fibroblasts lacking LRP1 or expressing calreticulin lacking the TSP1 binding site do not respond to TSP1 with anchorage-independent survival. These data define a novel role for TSP1 signaling through the calreticulin/LRP1 co-complex in tissue remodeling and fibrotic responses through stimulation of anoikis resistance.-Pallero, M. A., Elzie, C. A., Chen, J., Mosher, D. F., Murphy-Ullrich, J. E. Thrombospondin 1 binding to calreticulin-LRP1 signals resistance to anoikis.

Growth compensatory role of sulindac sulfide-induced thrombospondin-1 linked with ERK1/2 and RhoA GTPase signaling pathways

Previously, we reported that non-steroidal anti-inflammatory drugs (NSAIDs) suppress cellular invasion which was mediated by thrombospondin-1 (TSP-1). As the extending study of the previous observation, we investigated the effect of NSAID-induced TSP-1 on the cellular growth and its related signaling transduction of the TSP-1 production. Among diverse NSAIDs, sulindac sulfide was most potent of inducing the human TSP-1 protein expression. Functionally, induced TSP-1 expression was associated with the growth-compensatory action of NSAID. TSP-1 expression was also elevated by mitogenic signals of ERK1/2 and RhoA GTPase pathway which had also growth-promotive capability after sulindac sulfide treatment. These findings suggest the possible mechanism through which tumor cells can survive the chemopreventive action of NSAIDs or the normal epithelium can reconstitute after NSAID-mediated ulceration in a compensatory way.

Dual actin-bundling and protein kinase C-binding activities of fascin regulate carcinoma cell migration downstream of Rac and contribute to metastasis

Recurrence of carcinomas due to cells that migrate away from the primary tumor is a major problem in cancer treatment. Immunohistochemical analyses of human carcinomas have consistently correlated up-regulation of the actin-bundling protein fascin with a clinically aggressive phenotype and poor prognosis. To understand the functional and mechanistic contributions of fascin, we undertook inducible short hairpin RNA (shRNA) knockdown of fascin in human colon carcinoma cells derived from an aggressive primary tumor. Fascin-depletion led to decreased numbers of filopodia and altered morphology of cell protrusions, decreased Rac-dependent migration on laminin, decreased turnover of focal adhesions, and, in vivo, decreased xenograft tumor development and metastasis. cDNA rescue of fascin shRNA-knockdown cells with wild-type green fluorescent protein-fascin or fascins mutated at the protein kinase C (PKC) phosphorylation site revealed that both the actin-bundling and active PKC-binding activities of fascin are required for the organization of filopodial protrusions, Rac-dependent migration, and tumor metastasis. Thus, fascin contributes to carcinoma migration and metastasis through dual pathways that impact on multiple subcellular structures needed for cell migration.

Fibroblast growth factor-2 binding to the thrombospondin-1 type III repeats, a novel antiangiogenic domain

Thrombospondin-1, an antiangiogenic matricellular protein, binds with high affinity to the angiogenic fibroblast growth factor-2, affecting its bioavailability and activity. The present work aimed at further locating the fibroblast growth factor-2 binding site of thrombospondin-1 and investigating its activity, using recombinant thrombospondin-1 proteins. Only recombinant constructs containing the thrombospondin-1 type III repeats bound fibroblast growth factor-2, whereas other domains, including the known anti-angiogenic type I repeats, were inactive. Binding was specific and inhibited by the anti thrombospondin-1 monoclonal antibody B5.2. Surface plasmon resonance analysis on BIAcore revealed a binding affinity (K(d)) of 310nM for the type III repeats and 11nM for intact thrombospondin-1. Since the type III repeats bind calcium, the effect of calcium on thrombospondin-1 binding to fibroblast growth factor-2 was investigated. Binding was modulated by calcium, as thrombospondin-1 or the type III repeats bound to fibroblast growth factor-2 only in calcium concentrations <0.3mM. The type III repeats inhibited binding of fibroblast growth factor-2 to endothelial cells, fibroblast growth factor-2-induced endothelial cell proliferation in vitro and angiogenesis in the chorioallantoic membrane assay in vivo, thus indicating the antiangiogenic activity of the domain. In conclusion, this study demonstrates that the fibroblast growth factor-2 binding site of thrombospondin-1 is located in the type III repeats. The finding that this domain is active in inhibiting angiogenesis indicates that the type III repeats represent a novel antiangiogenic domain of thrombospondin-1.

Thrombospondins, their polymorphisms, and cardiovascular disease

The thrombospondins are a 5-member gene family that mediate cell-cell and cell-matrix interactions. The thrombospondins are either trimers or pentamers, and their functions depend on their abilities to interact with numerous extracellular ligands and cell surface receptors through the multiple domains that compose each subunit. Recent genetic studies have indicated associations of particular single nucleotide polymorphisms in 3 of the 5 thrombospondins with cardiovascular disease. This observation has stimulated efforts to understand how the thrombospondins influence cardiovascular pathology, to dissect how the individual polymorphisms alter the structure and function of the parent thrombospondin molecules, and to replicate the genetic data in different patient populations. This review seeks to summarize current information that has emerged on each of these fronts.

Thrombospondin-4 and matrix three-dimensionality in axon outgrowth and adhesion in the developing retina

Thrombospondin-4 (TSP-4), a large pentameric glycoprotein of the extracellular matrix, has been described as a neurite outgrowth-promoting molecule. However, the means by which TSP-4 promotes neurite outgrowth in the developing eye is unclear. Here we show that TSP-4 is present at the appropriate time in development and displays a localization pattern within the developing mouse retina consistent with a role in retinal ganglion cell (RGC) neurite outgrowth. Furthermore, results indicate that while TSP-4 alone does not support adhesion or neurite extension, it enhances the ability of laminins to promote adhesion and neurite outgrowth of embryonic retinal cells. The mechanism of enhancement is, in part, based on the ability of TSP-4 to enhance the three-dimensionality and/or clustering of laminins within the substrate matrix. These results support a model where TSP-4 acts as an organizer of adhesive and axon outgrowth-promoting molecules in the ECM to optimize retinal ganglion cell responses.

Versican-thrombospondin-1 binding in vitro and colocalization in microfibrils induced by inflammation on vascular smooth muscle cells

We identified a specific interaction between two secreted proteins, thrombospondin-1 and versican, that is induced during a toll-like receptor-3-dependent inflammatory response in vascular smooth muscle cells. Thrombospondin-1 binding to versican is modulated by divalent cations. This interaction is mediated by interaction of the G1 domain of versican with the N-module of thrombospondin-1 but only weakly with the corresponding N-terminal region of thrombospondin-2. The G1 domain of versican contains two Link modules, which are known to mediate TNFalpha-stimulated gene-6 protein binding to thrombospondin-1, and the related G1 domain of aggrecan is also recognized by thrombospondin-1. Therefore, thrombospondin-1 interacts with three members of the Link-containing hyaladherin family. On the surface of poly-I:C-stimulated vascular smooth muscle cells, versican organizes into fibrillar structures that contain elastin but are largely distinct from those formed by hyaluronan. Endogenous and exogenously added thrombospondin-1 incorporates into these structures. Binding of exogenous thrombospondin-1 to these structures, to purified versican and to its G1 domain is potently inhibited by heparin. At higher concentrations, exogenous thrombospondin-1 delays the poly-I:C induced formation of structures containing versican and elastin, suggesting that thrombospondin-1 negatively modulates this component of a vascular smooth muscle inflammatory response.

NOV/CCN3 induces adhesion of muscle skeletal cells and cooperates with FGF2 and IGF-1 to promote proliferation and survival

During mammalian development, expression of the Nephroblastoma overexpressed gene (NOV/CCN3) is tightly regulated in skeletal muscles. Ex vivo, ectopic expression of NOV blocks myogenic differentiation. NOV also supports endothelial cell adhesion and angiogenesis through interactions with integrins. Integrins play fundamental roles during myogenesis. In this study, we show that NOV mediates adhesion and spreading of myoblasts. Myoblasts adhesion to NOV does not require proteoglycans and is dependent on integrin beta1, whereas spreading involves another RGD-sensitive integrin. The C-Terminal part of NOV as well as full-length is able to support adhesion of myoblasts; in addition, both increase focal-adhesion kinase (FAK) phosphorylation. Furthermore, NOV is an adhesive substrate that, combined with FGF2 or IGF-1, promotes cell specific proliferation and survival, respectively, in a better way than fibronectin. Taken together, these results identify NOV as an adhesion substrate for myoblasts which, in concert with growth factors, could play a role in the physiology of muscle cells.

Roles of fascin in human carcinoma motility and signaling: prospects for a novel biomarker?

Fascin is a globular actin cross-linking protein that has a major function in forming parallel actin bundles in cell protrusions that are key specialisations of the plasma membrane for environmental guidance and cell migration. Fascin is widely expressed in mesenchymal tissues and the nervous system and is low or absent in adult epithelia. Recent data from a number of laboratories have highlighted that fascin is up-regulated in many human carcinomas and, in individual tissues, correlates with the clinical aggressiveness of tumours and poor patient survival. In cell culture, over-expression or depletion of fascin modulates cell migration and alters cytoskeletal organisation. The identification of biomarkers to provide more effective early diagnosis of potentially aggressive tumours, or identify tumours susceptible to targeted therapies, is an important goal in clinical research. Here, we discuss the evidence that fascin is upregulated in carcinomas, its contributions to carcinoma cell behaviour and its potential as a candidate novel biomarker or therapeutic target.

The N-terminal module of thrombospondin-1 interacts with the link domain of TSG-6 and enhances its covalent association with the heavy chains of inter-alpha-trypsin inhibitor

We recently found that leukocytes from thrombospondin-1 (TSP1)-deficient mice exhibit significant reductions in cell surface CD44 relative to those from wild type mice. Because TSG-6 modulates CD44-mediated cellular interactions with hyaluronan, we examined the possibility that TSP1 interacts with TSG-6. We showed that recombinant full-length human TSG-6 (TSG-6Q) and the Link module of TSG-6 (Link_TSG6) bind 125I-TSP1 with comparable affinities. Trimeric recombinant constructs containing the N-modules of TSP1 or TSP2 inhibit binding of TSP1 to TSG-6Q and Link_TSG6, but other recombinant regions of TSP1 do not. Therefore, the N-modules of both TSP1 and TSP2 specifically recognize the Link module of TSG-6. Heparin, which binds to these domains of both proteins, strongly inhibits binding of TSP1 to Link_TSG6 and TSG-6Q, but hyaluronan does not. Inhibition by heparin results from its binding to TSP1, because heparin also inhibits TSP1 binding to Link_TSG6 mutants deficient in heparin binding. Removal of bound Ca2+ from TSP1 reduces its binding to full-length TSG-6. Binding of TSP1 to Link_TSG6, however, is enhanced by chelating divalent cations. In contrast, divalent cations do not influence binding of the N-terminal region of TSP1 to TSG-6Q. This implies that divalent cation dependence is due to conformational effects of calcium-binding to the C-terminal domains of TSP1. TSP1 enhances covalent modification of the inter-alpha-trypsin inhibitor by TSG-6 and transfer of its heavy chains to hyaluronan, suggesting a physiological function of TSP1 binding to TSG-6 in regulation of hyaluronan metabolism at sites of inflammation.

Endostatin inhibits nitric oxide and diminishes VEGF and collagen XVIII in squamous carcinoma cells

Low pO(2) values are a common finding among oral squamous cell carcinomas (SCC). Our objective was to determine the role that oxygen tension plays on the direct tumor effect of endostatin (ES). Squamous carcinoma cell lines were grown under normoxic or hypoxic conditions and treated with endostatin (ES), nitric oxide (NO) donors, NO scavengers, NO synthase inhibitors, or transduced with AdenoVec-hEndo or AdenoVec Null vectors. The expression of vascular endothelial growth factor (VEGF) and collagen XVIII were determined by RT-PCR and protein levels assessed by Western blot analyses. Our studies demonstrated that collagen XVIII and VEGF are expressed and responsive to ES in a limited number of SCC cell lines during normoxia but were most responsive when grown under hypoxic conditions. VEGF and collagen XVIII were downregulated by both ES and transduction of cells with AdenoVec-hEndo. The effects of ES on SCC cells were enhanced by aminoguanidine (Ag), L-NAME, and diphenyleneiodonium chloride (DPI). Endostatin and transduced with ES vectors diminished the levels of NO whereas NO donors enhanced VEGF expression and collagen XVIII expression. In conclusion, the direct effect of endostatins on tumor cells is most effective under conditions of low oxygen tension and can be potentiated by the use of nitric oxide synthase inhibitors or NO scavengers.

Endogenous thrombospondin-1 is not necessary for proliferation but is permissive for vascular smooth muscle cell responses to platelet-derived growth factor

We have reexamined the role of endogenous thrombospondin-1 (TSP1) in growth and motility of vascular smooth muscle cells (SMCs). Based on the ability of aortic-derived SMCs isolated from TSP1 null mice and grown in the absence of exogenous TSP1 to grow at comparable rates and to a slightly higher density than equivalent cells from wild-type mice, TSP1 is not necessary for their growth. Low concentrations of exogenous TSP1 stimulate growth of TSP1 null SMCs, but higher doses of TSP1 or its C-terminal domain are inhibitory. However, SMCs from TSP1 null mice are selectively deficient in chemotactic and proliferative responses to platelet-derived growth factor and in outgrowth in three-dimensional cultures. Recombinant portions of the N- and C-terminal domains of TSP1 stimulate SMC chemotaxis through different integrin receptors. Based on these data, the relative deficiency in SMC outgrowth during an ex vivo angiogenic response of muscle tissue from TSP1 null mice is probably due to restriction of platelet-derived growth factor dependent SMC migration and/or proliferation.

Roles of fascin in cell adhesion and motility

Many cell interactions depend on the assembly of cell protrusions; these include cell attachment and migration in the extracellular matrix, cell-cell communication, and the ability of cells to sense their local environment. Cell protrusions are extensions of the plasma membrane that are supported internally by actin-based structures that impart mechanical stiffness. Fascin is a small, globular actin-bundling protein that has emerging roles in diverse forms of cell protrusions and in cytoplasmic actin bundles. The fascin-actin interaction is under complex regulation from the extracellular matrix, peptide factors and other actin-binding proteins. Recent developments advance our understanding of the multifaceted regulation of fascin and the roles of fascin-containing structures in cell adhesion, motility and invasion in the life of vertebrate organisms.

Fascin protrusions in cell interactions

Cell protrusions are outward extensions of the plasma membrane of individual cells that function in sensing the cell environment and in making initial, dynamic adhesions to extracellular matrix and other cells. Cell protrusions can be grouped into two major categories on the basis of morphology: localized, finger-like structures of highly defined shape and various lengths; or broad, irregular extensions of the plasma membrane. A key requirement of all cell protrusions is the need for a rigid cytoskeleton to support the localized extension of the plasma membrane. This is achieved either by a core unipolar bundle of actin microfilaments in finger-like protrusions, or by a combination of radial, rib-like, actin bundles integrated with a dendritic meshwork of microfilaments in the broad, lamellipodial protrusions. From studies of multiple cell types in vertebrates and invertebrates, fascin-1 has emerged as an actin-bundling protein of general importance for a diverse set of cell protrusions with functions in cell adhesion, cell interactions, and cell migration. This review discusses current knowledge of the molecular and cellular properties and functions of fascin, the roles of fascin-based protrusions in the cardiovascular system in health and disease, and areas of future interest.

Functions of the conserved thrombospondin carboxy-terminal cassette in cell-extracellular matrix interactions and signaling

Thrombospondins (TSPs) are extracellular, multidomain, calcium-binding glycoproteins that function at cell surfaces, in extracellular matrix (ECM) and as bridging molecules in cell-cell interactions. TSPs are multifunctional and modulate cell behavior during development, wound-healing, immune response, tumor growth and in the homeostasis of adult tissues. TSPs are assembled as oligomers that are composed of homologous polypeptides. In all the TSP polypeptides, the most highly-conserved region is the carboxyl-region, which contains a characteristic set of domains comprising EGF domains, TSP type 3 repeats and a globular carboxy-terminal domain. This large region is termed here the thrombospondin carboxy-terminal cassette (TSP-CTC). The strong conservation of the TSP-CTC suggests that it may mediate ancestral functions that are shared by all TSPs. This review summarizes the current knowledge of the TSP-CTC and areas of future interest.

Thrombospondin 1: a multifunctional protein implicated in the regulation of tumor growth

Thrombospondins belong to a family of extracellular matrix (ECM) proteins widely found from embryonic to adult tissues. The modular structure of thrombospondins contains a series of peptide sequences implicated in a multiplicity of biological functions. Extracellular matrix undergoes important alterations under proteolysis that occurs in pathological processes like tumorigenesis. An elevated secretion of thrombospondin 1 (TSP1) is often observed in tumors and is sometimes considered as a predictive factor. However, the role of TSP1 in cancer progression remains controversial and must be carefully apprehended. The regulation of cell adhesion, proliferation, apoptosis by TSP1 is examined in the present review and it is clear from the literature and from our investigations that TSP1 presents both stimulatory and inhibitory effects. The exposition of cryptic sites upon conformational changes can partially explain this contradiction. More interestingly, the analysis of TSP1-directed intracellular signaling pathways activated through specific receptors or supramolecular receptors docking systems may be useful to discriminate the precise function of TSP1 in tumor progression. The central role played by TSP1 in the control of matrix-degrading enzyme activation and catabolism reveals attractive tracks of research and highlights the involvement of the lipoprotein receptor-related protein (LRP) receptor in these events. Therefore, TSP1-derived peptides constitute a source of potentially active matrikins which could provide essential tools in cancer therapy.

Identification of novel beta1 integrin binding sites in the type 1 and type 2 repeats of thrombospondin-1

In addition to the three known beta(1) integrin recognition sites in the N-module of thrombospondin-1 (TSP1), we found that beta(1) integrins mediate cell adhesion to the type 1 and type 2 repeats. The type 1 repeats of TSP1 differ from typical integrin ligands in that recognition is pan-beta(1)-specific. Adhesion of cells that express one dominant beta(1) integrin on immobilized type 1 repeats is specifically inhibited by antagonists of that integrin, whereas adhesion of cells that express several beta(1) integrins is partially inhibited by each alpha-subunit-specific antagonist and completely inhibited by combining the antagonists. beta(1) integrins recognize both the second and third type 1 repeats, and each type 1 repeat shows pan-beta(1) specificity and divalent cation dependence for promoting cell adhesion. Adhesion to the type 2 repeats is less sensitive to alpha-subunit antagonists, but a beta(1) blocking antibody and two disintegrins inhibit adhesion to immobilized type 2 repeats. beta(1) integrin expression is necessary for cell adhesion to the type 1 or type 2 repeats, and beta(1) integrins bind in a divalent cation-dependent manner to a type 1 repeat affinity column. The widely used TSP1 function blocking antibody A4.1 binds to a site in the third type 2 repeat. A4.1 proximally inhibits beta(1) integrin-dependent adhesion to the type 2 repeats and indirectly inhibits integrin-dependent adhesion mediated by the TSP1 type 1 repeats. Although antibody A4.1 is also an antagonist of CD36 binding to TSP1, these data suggest that some biological activities of A4.1 result from antagonism of these novel beta(1) integrin binding sites.

Role of oligomerization domains in thrombospondins and other extracellular matrix proteins

Coiled coils, collagen triple helices and globular oligomerization domains mediate the subunit assembly of many proteins in vertebrates and invertebrates. Oligomerization offers functional advantages including multivalency, increased binding strength and the combined function of different domains. These features are seen in natural proteins and may be introduced by protein engineering. The special focus of this review is on oligomerization domain of extracellular matrix proteins. For thrombospondins, initial interesting results on the functional role of oligomerization have been published. Other features remain to be explored. For example, it is not clear why thrombospondin-1 and thrombospondin-2 are trimers whereas thrombospondins-3 to -5 are pentamers. To stimulate this type of research, this review makes a survey of oligomerization domains and their functional role in extracellular matrix proteins.

A C-terminal EGF-like domain governs BAD1 localization to the yeast surface and fungal adherence to phagocytes, but is dispensable in immune modulation and pathogenicity of Blastomyces dermatitidis

BAD1, an adhesin and immune modulator of Blastomyces dermatitidis, is an essential virulence factor that is released extracellularly before association with the yeast surface. Here, deletion of the C-terminal EGF-like domain profoundly affected BAD1 function, leading to non-association with yeast, extracellular accumulation and impaired yeast adherence to macrophages. In equilibrium binding assays, DeltaC-term BAD1, lacking an EGF-like domain, bound poorly to BAD1 null yeast, yielding a low affinity (Kd, 3 x 10(-7) M versus 5 x 10(-8) M) and Bmax (1.9 x 10(5) versus 7.9 x 10(5)) compared with BAD1. Similar protein binding profiles were observed using chitin particles, reinforcing the notion that chitin fibrils are a receptor for BAD1, and that the EGF-like domain is critical for BAD1 interactions with chitin on yeast. DeltaC-term strains bound poorly to macrophages, compared with parental or BAD1-reconstituted null strains. However, DeltaC-term strains and the purified protein itself sharply suppressed tumour necrosis factor (TNF)-alpha release by phagocytes in vitro and in lung in vivo, and the strains retained pathogenicity in a murine model of blastomycosis. Our results illustrate the previously undefined role of the EGF-like domain for BAD1 localization to yeast surfaces during cell wall biogenesis. They also demonstrate that the requirements for host cell binding and immune modulation by BAD1 can be dissociated from one another, and that the former is unexpectedly dispensable in the requisite role of BAD1 in pathogenesis.

Independent prognostic value of fascin immunoreactivity in stage I nonsmall cell lung cancer

Fascin-1, the most expressed form of fascin in vertebrate tissues, is an actin-bundling protein that induces cell membrane protrusions and increases motility of normal and transformed epithelial cells. Very few data are available on the role of this protein in nonsmall cell lung cancer (NSCLC). Two hundred and twenty patients with stage I NSCLC and long-term follow-up were evaluated immunocytochemically for fascin expression. Overall, variable fascin immunoreactivity was detected in 98% of 116 squamous cell carcinomas, in 78% of 96 adenocarcinomas, in 83% of six large cell carcinomas, and in the two adenosquamous carcinomas under study. Neoplastic emboli were commonly decorated by the antifascin antibody (P<0.001), also when the surrounding invasive carcinoma was unreactive. Fascin immunoreactivity correlated with high tumour grade (P=0.017) and, in adenocarcinomas, with high Ki-67 labelling index (P=0.021). Adenocarcinomas with a prevalent bronchiolo-alveolar in situ component were less commonly immunoreactive for fascin than invasive tumours (P=0.005). Contralateral thoracic or distant metastases were associated significantly with diffuse (>60% immunoreactive tumour cells) fascin expression in adenocarcinomas (P=0.043), and marginally with strong fascin immunostaining in squamous cell carcinomas (P=0.13). No associations were noted with any other clinicopathological variables tested. Patients with tumours showing diffuse (>60% immunoreactive neoplastic cells) and/or strong immunoreactivity for fascin had a shorter survival (P=0.006 for adenocarcinomas and P=0.026 for squamous cell carcinomas), even after multivariate analysis (P=0.014 and 0.050, respectively). The current study documents for the first time that fascin is upregulated in invasive and more aggressive NSCLC, being an independent prognostic predictor of unfavourable clinical course of the disease. Targetting the fascin pathway could be a novel therapeutic strategy of NSCLC.