Reduced Thrombospondin-1 at presentation predicts disease progression in superficial bladder cancer

Objectives: Superficial bladder cancer (SBC) presents a difficult clinical dilemma at diagnosis as only a small subgroup of patients will subsequently develop invasive disease. Study of cancer biology has found that angiogenesis is central to growth and spread. This study examines the relationship between the angiogenic inhibitory factor Thrombospondin-1 (TSP-1) at initial presentation and subsequent progression of SBC. Methods: Using immunohistochemistry, 220 cases of SBC were examined for pattern and extent of expression of TSP-1 at initial presentation. Results: TSP-1 was detected in perivascular tissue, at the epithelial-stromal junction, in the stroma and in tumour cells and reduced perivascular TSP-1 staining at presentation was an independent predictive factor for the subsequent development of muscle invasive or metastatic disease. Conclusion: This adds further weight to the theory that TSP-1 plays a major part in the biology of bladder cancer possibly through the control of angiogenesis. © 2002 Elsevier Science B.V. All rights reserved.

Expression of thrombospondin-1 in resected colorectal liver metastases predicts poor prognosis

Purpose The aim of this study was to examine the expression and prognostic relevance of thrombospondin-1 (TSP-1) in tumor biopsies taken from a consecutive series of liver resections done at the University Hospitals of Leicester and the Royal Liverpool Hospital. Experimental Design Patients having undergone a liver resection for colorectal liver metastases at our institutions between 1993 and 1999 inclusive were eligible. Inclusion criteria were curative intent, sufficient tumor biopsy, and patient follow-up data. One hundred eighty-two patients were considered in this study. Standard immunohistochemical techniques were used to study the expression of TSP-1 in 5-μm tumor sections from paraffin-embedded tissue blocks. TSP-1 was correlated with survival using the Kaplan-Meier method and log-rank test for univariate analysis and the Cox proportional hazard model for multivariate analysis. Results One hundred eighty-two patients (male, n = 122 and female, n = 60) ages between 25 and 81 years (mean, 61 years) were included. TSP-1 was expressed around blood vessels (n = 45, 25%) or in the stroma (n = 59, 33%). No expression was detected in the remaining tumors. TSP-1 significantly correlated with poor survival on univariate (P = 0.01 for perivascular expression and P = 0.03 for stromal expression) and multivariate analysis (P = 0.01 for perivascular expression). Conclusion TSP-1 is a negatively prognostic factor for survival in resected colorectal liver metastases. © 2005 American Association for Cancer Research.

Elongation Factor ELL (Eleven-Nineteen Lysine-rich Leukemia) Acts as a Transcription Factor for Direct Thrombospondin-1 Regulation

The eleven-nineteen lysine-rich leukemia (ELL) gene undergoes translocation and fuses in-frame to the multiple lineage leukemia gene in a substantial proportion of patients suffering from acute forms of leukemia. Studies show that ELL indirectly modulates transcription by serving as a regulator for transcriptional elongation as well as for p53, U19/Eaf2, and steroid receptor activities. Our in vitro and in vivo data demonstrate that ELL could also serve as a transcriptional factor to directly induce transcription of the thrombospondin-1 (TSP-1) gene. Experiments using ELL deletion mutants established that full-length ELL is required for the TSP-1 up-regulation and that the trans-activation domain likely resides in the carboxyl terminus. Moreover, the DNA binding domain may localize to the first 45 amino acids of ELL. Not surprisingly, multiple lineage leukemia-ELL, which lacks these amino acids, did not induce expression from the TSP-1 promoter. In addition, the ELL core-response element appears to localize in the -1426 to -1418 region of the TSP-1 promoter. Finally, studies using zebrafish confirmed that ELL regulates TSP-1 mRNA expression in vivo, and ELL could inhibit zebrafish vasculogenesis, at least in part, through up-regulating TSP-1. Given the importance of TSP-1 as an anti-angiogenic protein, our findings may have important ramifications for better understanding cancer.

Persistent Inflammation Subverts Thrombospondin-1–Induced Regulation of Retinal Angiogenesis and Is Driven by CCR2 Ligation

Neovascular retinal disease is a leading cause of blindness orchestrated by inflammatory responses. Although noninfectious uveoretinitis is mediated by CD4(+) T cells, in the persistent phase of disease, angiogenic responses are observed, along with degeneration of the retina. Full clinical manifestation relies on myeloid-derived cells, which are phenotypically distinct from, but potentially sharing common effector responses to age-related macular degeneration. To interrogate inflammation-mediated angiogenesis, we investigated experimental autoimmune uveoretinitis, an animal model for human uveitis. After the initial acute phase of severe inflammation, the retina sustains a persistent low-grade inflammation with tissue-infiltrating leukocytes for over 4 months. During this persistent phase, angiogenesis is observed as retinal neovascular membranes that arise from inflamed venules and postcapillary venules, increase in size as the disease progresses, and are associated with infiltrating arginase-1(+) macrophages. In the absence of thrombospondin-1, retinal neovascular membranes are markedly increased and are associated with arginase-1(-) CD68(+) macrophages, whereas deletion of the chemokine receptor CCR2 resulted in reduced retinal neovascular membranes in association with a predominant neutrophil infiltrate. CCR2 is important for macrophage recruitment to the retina in experimental autoimmune uveoretinitis and promotes chronicity in the form of a persistent angiogenesis response, which in turn is regulated by constitutive expression of angiogenic inhibitors like thrombospondin-1. This model offers a new platform to dissect the molecular and cellular pathology of inflammation-induced ocular angiogenesis.

Deficiency of thrombospondin-1 reduces Th17 differentiation and attenuates experimental autoimmune encephalomyelitis

Transforming growth factor beta (TGF-beta) plays a role both in the induction of Treg and in the differentiation of the IL-17-secreting T cells (Th17) which drive inflammation in experimental autoimmune encephalomyelitis (EAE). We investigated the role that thrombospondin-1 (TSP-1) dependent activation of TGF-beta played in the generation of an encephalitic Th17 response in EAE. Upon immunization with myelin oligodendrocyte glycoprotein peptide (MOG(35-55)), TSP-1 deficient (TSP-1(null)) mice and MOG(35-55) TCR transgenic mice that lack of TSP-1 (2D2.TSP-1(null)) exhibited an attenuated form of EAE, and secreted lower levels of IL-17. Adoptive transfer of in vitro-activated 2D2.TSP-1(null) T cells induced a milder form of EAE, independent of TSP-1 expression in the recipient mice. Furthermore, in vitro studies demonstrated that anti-CD3/anti-CD28 pre-activated CD4+ T cells transiently upregulated latent TGF-beta in a TSP-1 dependent way, and such activation of latent TGF-beta was required for the differentiation of Th17 cells. These results demonstrate that TSP-1 participates in the differentiation of Th17 cells through its ability to activate latent TGF-beta, and enhances the inflammatory response in EAE. (C) 2009 Elsevier Ltd. All rights reserved.

Versican processing by a disintegrin-like and metalloproteinase domain with thrombospondin-1 repeats proteinases-5 and -15 facilitates myoblast fusion

Skeletal muscle development and regeneration requires the fusion of myoblasts into multinucleated myotubes. Because the enzymatic proteolysis of a hyaluronan and versican-rich matrix by ADAMTS versicanases is required for developmental morphogenesis, we hypothesized that the clearance of versican may facilitate the fusion of myoblasts during myogenesis. Here, we used transgenic mice and an in vitro model of myoblast fusion, C2C12 cells, to determine a potential role for ADAMTS versicanases. Versican processing was observed during in vivo myogenesis at the time when myoblasts were fusing to form multinucleated myotubes. Relevant ADAMTS genes, chief among them Adamts5 and Adamts15, were expressed both in developing embryonic muscle and differentiating C2C12 cells. Reducing the levels of Adamts5 mRNA in vitro impaired myoblast fusion, which could be rescued with catalytically active but not the inactive forms of ADAMTS5 or ADAMTS15. The addition of inactive ADAMTS5, ADAMTS15, or full-length V1 versican effectively impaired myoblast fusion. Finally, the expansion of a hyaluronan and versican-rich matrix was observed upon reducing the levels of Adamts5 mRNA in myoblasts. These data indicate that these ADAMTS proteinases contribute to the formation of multinucleated myotubes such as is necessary for both skeletal muscle development and during regeneration, by remodeling a versican-rich pericellular matrix of myoblasts. Our study identifies a possible pathway to target for the improvement of myogenesis in a plethora of diseases including cancer cachexia, sarcopenia, and muscular dystrophy.

Biosynthesis and expression of a disintegrin-like and metalloproteinase domain with thrombospondin-1 repeats-15

Background
ADAMTS proteoglycanases show proteolytic activity toward versican and other proteoglycans.

Results
ADAMTS15, which cleaves versican, is expressed during early cardiac development and during musculoskeletal development.

Conclusion
With unique and overlapping biological properties, ADAMTS15 is likely to have cooperative roles with other members of the ADAMTS proteoglycanase clade.

Significance
Versican cleavage has profound effects on developmental morphogenesis and regulates cancer cell behavior.

Shear stress modulates the expression of thrombospondin-1 and CD36 in endothelial cells in vitro and during shear stress-induced angiogenesis in vivo

Binding of thrombospondin-1 (TSP-1) to the CD36 receptor inhibits angiogenesis and induces apoptosis in endothelial cells (EC). Conversely, matrix-bound TSP-1 supports vessel formation. In this study we analyzed the shear stress-dependent expression of TSP-1 and CD36 in endothelial cells in vitro and in vivo to reveal its putative role in the blood flow-induced remodelling of vascular networks. Shear stress was applied to EC using a cone-and-plate apparatus and gene expression was analyzed by RT-PCR, Northern and Western blot. Angiogenesis in skeletal muscles of prazosin-fed (50 mg/l drinking water; 4 d) mice was assessed by measuring capillary-to-fiber (C/F) ratios. Protein expression in whole muscle homogenates (WMH) or BS-1 lectin-enriched EC fractions (ECF) was analyzed by Western blot. Shear stress downregulated TSP-1 and CD36 expression in vitro in a force- and time-dependent manner sustained for at least 72 h and reversible by restoration of no-flow conditions. In vivo, shear stress-driven increase of C/F in prazosin-fed mice was associated with reduced expression of TSP-1 and CD36 in ECF, while TSP-1 expression in WMH was increased. Down-regulation of endothelial TSP-1/CD36 by shear stress suggests a mechanism for inhibition of apoptosis in perfused vessels and pruning in the absence of flow. The increase of extra-endothelial (e.g. matrix-bound) TSP-1 could support a splitting type of vessel growth.

Multiple B-cell clones producing antibodies directed to the spacer and disintegrin/thrombospondin type-1 repeat 1 (TSP1) of ADAMTS13 in a patient with acquired thrombotic thrombocytopenic purpura

BACKGROUND: The cysteine-rich/spacer domains of ADAMTS13 contain a major binding site for antibodies in patients with acquired thrombotic thrombocytopenic purpura (TTP). OBJECTIVE: To study the heterogeneity of the antibody response towards these domains an immunoglobulin V-gene phage-display library was constructed to isolate monoclonal anti-ADAMTS13 antibodies from the immunoglobulin repertoire of a patient with acquired TTP. METHODS: Combined variable heavy chain (VH) and variable light chain (VL) segments, expressed as single-chain Fv fragments (scFv), were selected for binding to an ADAMTS13 fragment consisting of the disintegrin/thrombospondin type-1 repeat 1 (TSP1)/cysteine-rich/spacer domains. RESULTS: Seven different scFv antibody clones were identified that were assigned to four groups based on their homology to VH germline gene segments. Epitope-mapping revealed that scFv I-9 (VH1-69), I-26 (VH1-02), and I-41 (VH3-09) bind to an overlapping binding site in the ADAMTS13 spacer domain, whereas scFv I-16 (VH3-07) binds to the disintegrin/TSP1 domains. The affinity of scFv for the disintegrin/TSP1/cysteine-rich/spacer domain was determined by surface plasmon resonance analysis and the dissociation constants ranged from 3 to 254 nM. The scFv partially inhibited ADAMTS13 activity. However, full-length IgG prepared from the variable domains of scFv I-9 inhibited ADAMTS13 activity more profoundly. Plasma of six patients with acquired TTP competed for binding of scFv I-9 to ADAMTS13. CONCLUSION: Our data indicate that multiple B-cell clones producing antibodies directed against the spacer domain are present in the patient analyzed in this study. Our findings also suggest that antibodies with a similar epitope specificity as scFv I-9 are present in plasma of other patients with acquired TTP.

Thrombospondin-1 mediates platelet adhesion at high shear via glycoprotein Ib (GPIb): an alternative/backup mechanism to von Willebrand factor

Acute thrombotic arterial occlusion is the leading cause of morbidity and mortality in the Western world. Von Willebrand factor is thought to be the only indispensable adhesive substrate to promote thrombus formation in high shear environments. We found that thrombospondin-1, a glycoprotein enriched in arteriosclerotic plaques, might function as an alternative substrate for thrombus formation. Platelets adhered to thrombospondin-1 in a shear dependent manner with an optimum shear as found in stenosed arteries. Adhesion is extremely firm, with no detachment of platelets up to a shear rate of 4000 s(-1). Experiments using platelets from a patient completely lacking von Willebrand factor showed that von Willebrand factor is not involved in platelet binding to thrombospondin-1. Platelet adhesion to thrombospondin-1 is not mediated via beta3-integrins or GPIa. CD36 partially mediates the adhesion of pre-activated platelets. We identified GPIb as high shear adhesion-receptor for thrombospondin-1. Soluble GPIb, as well as antibodies against the GPIb, blocked platelet adhesion almost completely. The new discovered thrombospondin-1-GPIb adhesion axis under arterial shear conditions might be important, not only during thrombus formation but also for pathological processes where other cells bind to the endothelium or subendothelium, including arteriosclerosis, inflammation and tumor metastasis, and a promising therapeutic target.

Skeletal abnormalities in mice lacking extracellular matrix proteins, thrombospondin-1, thrombospondin-3, thrombospondin-5, and type IX collagen.

Thrombospondin-5 (TSP5) is a large extracellular matrix glycoprotein found in musculoskeletal tissues. TSP5 mutations cause two skeletal dysplasias, pseudoachondroplasia and multiple epiphyseal dysplasia; both show a characteristic growth plate phenotype with retention of TSP5, type IX collagen (Col9), and matrillin-3 in the rough endoplasmic reticulum. Whereas most studies focus on defining the disease process, few functional studies have been performed. TSP5 knockout mice have no obvious skeletal abnormalities, suggesting that TSP5 is not essential in the growth plate and/or that other TSPs may compensate. In contrast, Col9 knockout mice have diminished matrillin-3 levels in the extracellular matrix and early-onset osteoarthritis. To define the roles of TSP1, TSP3, TSP5, and Col9 in the growth plate, all knockout and combinatorial strains were analyzed using histomorphometric techniques. While significant alterations in growth plate organization were found in certain single knockout mouse strains, skeletal growth was only mildly disturbed. In contrast, dramatic changes in growth plate organization in TSP3/5/Col9 knockout mice resulted in a 20% reduction in limb length, corresponding to similar short stature in humans. These studies show that type IX collagen may regulate growth plate width; TSP3, TSP5, and Col9 appear to contribute to growth plate organization; and TSP1 may help define the timing of growth plate closure when other extracellular proteins are absent.

Thrombospondin-2: A potent endogenous inhibitor of tumor growth and angiogenesis

Recent evidence suggests a potential role for thrombospondin-2 (TSP-2), a matricellular glycoprotein, in the regulation of primary angiogenesis. To directly examine the biological effect of TSP-2 expression on tumor growth and angiogenesis, human A431 squamous cell carcinoma cells, which do not express TSP-2, were stably transfected with a murine TSP-2 expression vector or with vector alone. A431 cells expressing TSP-2 did not show an altered growth rate, colony-forming ability, or susceptibility to induction of apoptosis in vitro. However, injection of TSP-2-transfected clones into the dermis of nude mice resulted in pronounced inhibition of tumor growth that was significantly stronger than the inhibition observed in A431 clones stably transfected with a thrombospondin-1 (TSP-1) expression vector, and combined overexpression of TSP-1 and TSP-2 completely prevented tumor formation. Extensive areas of necrosis were observed in TSP-2-expressing tumors, and both the density and the size of tumor vessels were significantly reduced, although tumor cell expression of the major tumor angiogenesis factor, vascular endothelial growth factor, was maintained at high levels. These findings establish TSP-2 as a potent endogenous inhibitor of tumor growth and angiogenesis.

Down-Regulation of Platelet Endothelial Cell Adhesion Molecule-1 Results in Thrombospondin-1 Expression and Concerted Regulation of Endothelial Cell Phenotype

bEND.3 cells are polyoma middle T-transformed mouse brain endothelial cells that express very little or no thrombospondin-1, a natural inhibitor of angiogenesis, but express high levels of platelet endothelial cell adhesion molecule-1 (PECAM-1) that localizes to sites of cell–cell contact. Here, we have examined the role of PECAM-1 in regulation of bEND.3 cell proliferation, migration, morphogenesis, and hemangioma formation. We show that down-regulating PECAM-1 expression by antisense transfection of bEND.3 cells has a dramatic effect on their morphology, proliferation, and morphogenesis on Matrigel. There is an optimal level for PECAM-1 expression such that high levels of PECAM-1 inhibit, whereas moderate levels of PECAM-1 stimulate, endothelial cell morphogenesis. The down-regulation of PECAM-1 in bEND.3 cells resulted in reexpression of endogenous thrombospondin-1 and its antiangiogenic receptor CD36. The expression of the vascular endothelial growth factor receptors flk-1 and flt-1, as well as integrins and metalloproteinases (which are involved in angiogenesis), were also affected. These observations are consistent with the changes observed in proliferation, migration, and adhesion characteristics of the antisense-transfected bEND.3 cells as well as with their lack of ability to form hemangiomas in mice. Thus, a reciprocal relationship exists between thrombospondin-1 and PECAM-1 expression, such that these two molecules appear to be constituents of a “switch” that regulates in concert many components of the angiogenic and differentiated phenotypes of endothelial cells.