ADAMTS1 mediates the release of antiangiogenic polypeptides from TSP1 and 2

Two molecular weight species of thrombospondin-2 are present in bone and differentially modulated in fractured and nonfractured tibiae in a murine model of bone healing

We report two immuoreactive species of thrombospondin-2 (TSP2), sized approximately 200 and 125 kDa, in the long bones of growing, but not skeletally mature, mice. In vitro osteoblasts secrete a 200-kDa species into the culture medium as early as day 3, and it appears in the cell-matrix layer by day 7. A 125-kDa species appears in the cell-matrix layer in parallel with mineralization; it is not detected in cell-conditioned medium. Unilateral tibial fracture induced a time-dependent upregulation of the 200-kDa species at the site of trauma. By contrast, relative levels of the 125-kDa species at the fracture site were lower than in bones from naive control animals. In the contralateral untouched control tibia, the 200-kDa species was rapidly and substantially reduced compared to bone harvested from naive control mice. Levels of the 125-kDa species in the untouched tibia declined gradually with time postfracture. TSP2 gene expression in uninjured control bone decreased modestly by 21 days postfracture. On the day of fracture, the osteoblast differentiation potential of MSCs harvested from uninjured bones decreased compared to those harvested from naive control animals. The presence of two isoforms suggests that TSP2 may undergo posttranscriptional or posttranslational processing in skeletal tissue. Our data also suggest that, in the context of trauma, the two TSP2 isforms are differentially modulated at injured and noninjured skeletal sites in an animal undergoing fracture healing.

Anti-angiogenic properties of ADAMTS-4 in vitro

Angiogenesis is an indispensable mechanism in development and in many pathologies, including cancer, synovitis and aberrant wound healing. Many angiogenic stimulators and inhibitors have been investigated, and some have progressed to the clinic. A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) is a group of multifunctional proteinases. ADAMTS-1 and ADAMTS-8 have been reported to be anti-angiogenic. Here, we provide evidence that ADAMTS-4, like ADAMTS-1, is expressed by endothelial cells and binds to vascular endothelial groth factor (VEGF). Moreover, ADAMTS-4 inhibited human dermal microvascular endothelial cells (HuDMEC) VEGF-stimulated VEGF receptor (R) R2 phosphorylation, differentiation and migration, suggesting that ADAMTS-4 may be a novel anti-angiogenic molecule.

An essential requirement for β1 integrin in the assembly of extracellular matrix proteins within the vascular wall

β1 integrin has been shown to contribute to vascular smooth muscle cell differentiation, adhesion and mechanosensation in vitro. Here we showed that deletion of β1 integrin at the onset of smooth muscle differentiation resulted in interrupted aortic arch, aneurysms and failure to assemble extracellular matrix proteins. These defects result in lethality prior to birth. Our data indicates that β1 integrin is not required for the acquisition, but it is essential for the maintenance of the smooth muscle cell phenotype, as levels of critical smooth muscle proteins are gradually reduced in mutant mice. Furthermore, while deposition of extracellular matrix was not affected, its structure was disrupted. Interestingly, defects in extracellular matrix and vascular wall assembly, were restricted to the aortic arch and its branches, compromising the brachiocephalic and carotid arteries and to the exclusion of the descending aorta. Additional analysis of β1 integrin in the pharyngeal arch smooth muscle progenitors was performed using wnt1Cre. Neural crest cells deleted for β1 integrin were able to migrate to the pharyngeal arches and associate with endothelial lined arteries; but exhibited vascular remodeling defects and early lethality. This work demonstrates that β1 integrin is dispensable for migration and initiation of the smooth muscle differentiation program, however, it is essential for remodeling of the pharyngeal arch arteries and for the assembly of the vessel wall of their derivatives. It further establishes a critical role of β1 integrin in the protection against aneurysms that is particularly confined to the ascending aorta and its branches.

Thrombospondin1 in tissue repair and fibrosis: TGF-β-dependent and independent mechanisms

Thrombospondin 1 (TSP1) plays major roles in both physiologic and pathologic tissue repair. TSP1 through its type 1 repeats is a known regulator of latent TGF-β activation and plays a role in wound healing and fibrosis. Binding of the TSP N-terminal domain to cell surface calreticulin in complex with LDL-receptor related protein 1 stimulates intermediate cell adhesion, cell migration, anoikis resistance, collagen expression and matrix deposition in an in vivo model of the foreign body response. There is also emerging evidence that TSP EGF-like repeats alter endothelial cell-cell interactions and stimulate epithelial migration through transactivation of EGF receptors. The mechanisms underlying these functions of TSP1 and the implications for physiologic and pathologic wound repair and fibrosis will be discussed.

Synergistic Regulation of Angiogenic Sprouting by Biochemical Factors and Wall Shear Stress

The process of sprouting angiogenesis involves activating endothelial cells in a quiescent monolayer of an existing vessel to degrade and migrate into the underlying matrix to form new blood vessels. While the roles of biochemical factors in angiogenic sprouting have been well characterized, the roles of fluid forces have received much less attention. This review summarizes results that support a role for wall shear stress in post-capillary venules as a mechanical factor capable of synergizing with biochemical factors to stimulate pro-angiogenic signaling in endothelial cells and promote sprout formation.

The thrombospondins

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate cell-dependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.

Altered versican cleavage in ADAMTS5 deficient mice; a novel etiology of myxomatous valve disease

In fetal valve maturation the mechanisms by which the relatively homogeneous proteoglycan-rich extracellular matrix (ECM) of endocardial cushions is replaced by a specialized and stratified ECM found in mature valves are not understood. Therefore, we reasoned that uncovering proteases critical for 'remodeling' the proteoglycan rich (extracellular matrix) ECM may elucidate novel mechanisms of valve development. We have determined that mice deficient in ADAMTS5, (A Disintegrin-like And Metalloprotease domain with ThromboSpondin-type 1 motifs) which we demonstrated is expressed predominantly by valvular endocardium during cardiac valve maturation, exhibited enlarged valves. ADAMTS5 deficient valves displayed a reduction in cleavage of its substrate versican, a critical cardiac proteoglycan. In vivo reduction of versican, in Adamts5(-/-) mice, achieved through Vcan heterozygosity, substantially rescued the valve anomalies. An increase in BMP2 immunolocalization, Sox9 expression and mesenchymal cell proliferation were observed in Adamts5(-/-) valve mesenchyme and correlated with expansion of the spongiosa (proteoglycan-rich) region in Adamts5(-/-) valve cusps. Furthermore, these data suggest that ECM remodeling via ADAMTS5 is required for endocardial to mesenchymal signaling in late fetal valve development. Although adult Adamts5(-/-) mice are viable they do not recover from developmental valve anomalies and have myxomatous cardiac valves with 100% penetrance. Since the accumulation of proteoglycans is a hallmark of myxomatous valve disease, based on these data we hypothesize that a lack of versican cleavage during fetal valve development may be a potential etiology of adult myxomatous valve disease.

Targeting tumor angiogenesis with TSP-1-based compounds: rational design of antiangiogenic mimetics of endogenous inhibitors

Inhibitors of angiogenesis are an important addition to conventional chemotherapy. Among different "druggable" angiogenic factors, fibroblast growth factor-2 (FGF-2) is an attractive target for novel therapies because of its intricated involvement in tumor neovascularization, tumor cell proliferation and migration, and the acquisition of resistance to antiangiogenic therapies. FGF-2 bioavailability and activity is affected by several natural ligands, including the endogenous inhibitor of angiogenesis thrombospondin-1 (TSP-1). We hypothesized that the FGF-2-binding sequence of TSP-1 might serve as a template for the development of non-peptide inhibitors of angiogenesis. Computational biology and nuclear magnetic resonance spectroscopy approaches, major investigative tools in the characterizations of protein-protein interaction (PPI), were used to map the residues at the TSP-1/FGF-2 interface. The translation of this three-dimensional information into a pharmacophore model allowed screening a small molecule databases, identifying three FGF-2-binding, antiangiogenic small molecules, mimetic of TSP-1. Pharmacophore-based approaches are thus feasible tools to exploit naturally occurring PPI, by generating a set of lead compounds mimetic of endogenous proteins, as a starting point for the development of novel therapeutic agents.

ADAMTS-2 functions as anti-angiogenic and anti-tumoral molecule independently of its catalytic activity

ADAMTS-2 is a metalloproteinase that plays a key role in the processing of fibrillar procollagen precursors into mature collagen molecules by excising the amino-propeptide. We demonstrate that recombinant ADAMTS-2 is also able to reduce proliferation of endothelial cells, and to induce their retraction and detachment from the substrate resulting in apoptosis. Dephosphorylation of Erk1/2 and MLC largely precedes the ADAMTS-2 induced morphological alterations. In 3-D culture models, ADAMTS-2 strongly reduced branching of capillary-like structures formed by endothelial cells and their long-term maintenance and inhibited vessels formation in embryoid bodies (EB). Growth and vascularization of tumors formed in nude mice by HEK 293-EBNA cells expressing ADAMTS-2 were drastically reduced. A similar anti-tumoral activity was observed when using cells expressing recombinant deleted forms of ADAMTS-2, including catalytically inactive enzyme. Nucleolin, a nuclear protein also found to be associated with the cell membrane, was identified as a potential receptor mediating the antiangiogenic properties of ADAMTS-2.

Targeting tumor angiogenesis with TSP-1-based compounds: rational design of antiangiogenic mimetics of endogenous inhibitors

Inhibitors of angiogenesis are an important addition to conventional chemotherapy. Among different "druggable" angiogenic factors, fibroblast growth factor-2 (FGF-2) is an attractive target for novel therapies because of its intricated involvement in tumor neovascularization, tumor cell proliferation and migration, and the acquisition of resistance to antiangiogenic therapies. FGF-2 bioavailability and activity is affected by several natural ligands, including the endogenous inhibitor of angiogenesis thrombospondin-1 (TSP-1). We hypothesized that the FGF-2-binding sequence of TSP-1 might serve as a template for the development of non-peptide inhibitors of angiogenesis. Computational biology and nuclear magnetic resonance spectroscopy approaches, major investigative tools in the characterizations of protein-protein interaction (PPI), were used to map the residues at the TSP-1/FGF-2 interface. The translation of this three-dimensional information into a pharmacophore model allowed screening a small molecule databases, identifying three FGF-2-binding, antiangiogenic small molecules, mimetic of TSP-1. Pharmacophore-based approaches are thus feasible tools to exploit naturally occurring PPI, by generating a set of lead compounds mimetic of endogenous proteins, as a starting point for the development of novel therapeutic agents.

PGF2α-F-prostanoid receptor signalling via ADAMTS1 modulates epithelial cell invasion and endothelial cell function in endometrial cancer

Background

An increase in cancer cell invasion and microvascular density is associated with a poorer prognosis for patients with endometrial cancer. In endometrial adenocarcinoma F-prostanoid (FP) receptor expression is elevated, along with its ligand prostaglandin (PG)F_2α, where it regulates expression and secretion of a host of growth factors and chemokines involved in tumorigenesis. This study investigates the expression, regulation and role of a disintegrin and metalloproteinase with thrombospondin repeat 1 (ADAMTS1) in endometrial adenocarcinoma cells by PGF_2α via the FP receptor.

Methods

Human endometrium and adenocarcinoma tissues were obtained in accordance with Lothian Research Ethics Committee guidance with informed patient consent. Expression of ADAMTS1 mRNA and protein in tissues was determined by quantitative RT-PCR analysis and immunohistochemistry. Signal transduction pathways regulating ADAMTS1 expression in Ishikawa cells stably expressing the FP receptor to levels seen in endometrial cancer (FPS cells) were determined by quantitative RT-PCR analysis. In vitro invasion and proliferation assays were performed with FPS cells and human umbilical vein endothelial cells (HUVECs) using conditioned medium (CM) from PGF_2α-treated FPS cells from which ADAMTS1 was immunoneutralised and/or recombinant ADAMTS1. The role of endothelial ADAMTS1 in endothelial cell proliferation was confirmed with RNA interference. The data in this study were analysed by T-test or ANOVA.

Results

ADAMTS1 mRNA and protein expression is elevated in endometrial adenocarcinoma tissues compared with normal proliferative phase endometrium and is localised to the glandular and vascular cells. Using FPS cells, we show that PGF2α-FP signalling upregulates ADAMTS1 expression via a calmodulin-NFAT-dependent pathway and this promotes epithelial cell invasion through ECM and inhibits endothelial cell proliferation. Furthermore, we show that CM from FPS cells regulates endothelial cell ADAMTS1 expression in a rapid biphasic manner. Using RNA interference we show that endothelial cell ADAMTS1 also negatively regulates cellular proliferation.

Conclusions

These data demonstrate elevated ADAMTS1 expression in endometrial adenocarcinoma. Furthermore we have highlighted a mechanism whereby FP receptor signalling regulates epithelial cell invasion and endothelial cell function via the PGF_2α-FP receptor mediated induction of ADAMTS1.

When Cre-mediated recombination in mice does not result in protein loss

Cre/loxP recombination enables cellular specificity and, in the case of inducible systems, temporal control of genomic deletions. Here we used a SM22α tamoxifen-inducible Cre line to inactivate β1 integrin in adult smooth muscle. Interestingly, analysis of two distinct β1 loxP transgenic mice revealed vastly different outcomes after β1 integrin deletion. Lethality occurred 4 weeks postinduction in one Cre/loxP line, while no apparent phenotype was seen in the other line. Genetic analysis revealed appropriate DNA excision in both cases; however, differences were found in the degree of protein loss with absolutely no change in protein levels in the model that lacked a phenotype. Seeking to understand protein persistence despite appropriate recombination, we first validated the flox allele using a constitutive Cre line and demonstrated its ability to mediate effective protein inactivation. We then examined the possibility of heterozygous cell selection, protein turnover, and deletion efficiency with no success for explaining the phenotype. Finally, we documented the presence of the Cre-recombination episomal product, which persisted in tissue samples with no protein loss. The product was only noted in cells with low proliferative capacity. These findings highlight the potential for protein expression from the products of Cre-recombinase excised genes, particularly when deletion occurs in low turnover populations.

The calreticulin-binding sequence of thrombospondin 1 regulates collagen expression and organization during tissue remodeling

Amino acids 17-35 of the thrombospondin1 (TSP1) N-terminal domain (NTD) bind cell surface calreticulin to signal focal adhesion disassembly, cell migration, and anoikis resistance in vitro. However, the in vivo relevance of this signaling pathway has not been previously determined. We engineered local in vivo expression of the TSP1 calreticulin-binding sequence to determine the role of TSP1 in tissue remodeling. Surgical sponges impregnated with a plasmid encoding the secreted calreticulin-binding sequence [NTD (1-35)-EGFP] or a control sequence [mod NTD (1-35)-EGFP] tagged with enhanced green fluorescent protein were implanted subcutaneously in mice. Sponges expressing NTD (1-35)-EFGP formed a highly organized capsule despite no differences in cellular composition, suggesting stimulation of collagen deposition by the calreticulin-binding sequence of TSP1. TSP1, recombinant NTD, or a peptide of the TSP1 calreticulin-binding sequence (hep I) increased both collagen expression and matrix deposition by fibroblasts in vitro. TSP1 stimulation of collagen was inhibited by a peptide that blocks TSP1 binding to calreticulin, demonstrating the requirement for cell surface calreticulin. Collagen stimulation was independent of TGF-β activity and Smad phosphorylation but was blocked by an Akt inhibitor, suggesting that signaling through the Akt pathway is important for regulation of collagen through TSP1 binding to calreticulin. These studies identify a novel function for the NTD of TSP1 as a mediator of collagen expression and deposition during tissue remodeling.

The ADAMTS13 metalloprotease domain: roles of subsites in enzyme activity and specificity

ADAMTS13 modulates von Willebrand factor (VWF) platelet-tethering function by proteolysis of the Tyr1605-Met1606 bond in the VWF A2 domain. To examine the role of the metalloprotease domain of ADAMTS13 in scissile bond specificity, we identified 3 variable regions (VR1, -2, and -3) in the ADAMTS family metalloprotease domain that flank the active site, which might be important for specificity. Eight composite sequence swaps (to residues in ADAMTS1 or ADAMTS2) and 18 single-point mutants were generated in these VRs and expressed. Swapping VR1 (E184-R193) of ADAMTS13 with that of ADAMTS1 or ADAMTS2 abolished/severely impaired ADAMTS13 function. Kinetic analysis of VR1 point mutants using VWF115 as a short substrate revealed reduced proteolytic function (k(cat)/K(m) reduced by 2- to 10-fold) as a result of D187A, R190A, and R193A substitutions. Analysis of VR2 (F216-V220) revealed a minor importance of this region. Mutants of VR3 (G236-A261) proteolysed wild-type VWF115 normally. However, using either short or full-length VWF substrates containing the P1' M1606A mutation, we identified residues within VR3 (D252-P256) that influence P1' amino acid specificity, we hypothesize, by shaping the S1' pocket. It is concluded that 2 subsites, D187-R193 and D252-P256, in the metalloprotease domain play an important role in cleavage efficiency and site specificity.

Type IV collagen induces expression of thrombospondin-1 that is mediated by integrin alpha1beta1 in astrocytes

Following brain injury, thrombospondin-1 (TSP-1) is involved in angiogenesis and synaptic recovery. In this study, we used a cold injury-model and found that TSP-1 mRNA was markedly upregulated after brain injury. Immunohistochemistry showed that TSP-1 was upregulated in both the core of the lesion and in the perilesional area of injured brain tissue. Numerous astrocytes immunopositive for glial fibrillary acidic protein (GFAP) were found in the perilesional area, and TSP-1 was also expressed in almost all astrocytes surrounding blood vessels at 4 days after injury. Next, we examined the influence of vascular basement membrane components on TSP-1 expression. When astrocytes were cultured on type IV collagen, TSP-1 was significantly upregulated compared with the expression when cells were grown on laminin, fibronectin, or poly-L-lysine. This increase occurred exclusively when astrocytes were grown on the native form of type IV collagen but not on the heat-denatured form or the non-collagenous 1 domain. Further, integrin alpha1 and beta1 mRNAs were upregulated concomitantly with GFAP mRNA, and integrin alpha1 protein was localized to the endfeet of astrocytes that surrounded blood vessels in the injured brain. Using function-blocking antibodies, we found that the effect of type IV collagen was attributed to integrin alpha1beta1 in primary astrocytes. Collectively, our results suggest that vascular basement membrane components substantially impact gene expression in astrocytes during brain tissue repair.

C-Mannosylated peptides derived from the thrombospondin type 1 repeat interact with Hsc70 to modulate its signaling in RAW264.7 cells

The thrombospondin type 1 repeat (TSR) is a functional module of proteins called TSR superfamily proteins (e.g., thrombospondin, F-spondin, mindin, etc.) and includes a conserved Trp-x-x-Trp (W-x-x-W) motif, in which the first Trp residue is preferably modified by C-mannosylation. We previously reported that synthesized C-mannosylated TSR-derived peptides (e.g., C-Man-WSPW) specifically enhanced lipopolysaccharide-induced signaling in macrophage-like RAW264.7 cells. In this study, we searched for the proteins that bind to C-mannosylated TSR-derived peptides in RAW264.7 cells and identified heat shock cognate protein 70 (Hsc70). The binding affinity of Hsc70 for C-mannosylated peptides in solution was higher than that for the peptides without C-mannose. The binding was influenced by a nucleotide-induced conformational change of Hsc70, and C-mannosylated peptides preferred the substrate-binding domain of Hsc70. Furthermore, in RAW264.7 cells, addition of Hsc70 stimulated cellular signaling to produce tumor necrosis factor-alpha, via transforming growth factor-beta-activated kinase 1, and the Hsc70-induced signaling was enhanced more in the presence of the peptides with C-mannose than that without C-mannose, suggesting functional interaction between Hsc70 and the C-mannosylated peptides in the cells. Together, these results demonstrate a novel function of the C-mannosylation of TSR-derived peptides in terms of interaction with Hsc70 to regulate cellular signaling.

ADAMTS1 alters blood vessel morphology and TSP1 levels in LNCaP and LNCaP-19 prostate tumors

Background

Decreased expression of the angiogenesis inhibitor ADAMTS1 (ADAM metallopeptidase with thrombospondin type 1 motif, 1) has previously been reported during prostate cancer progression. The aim of this study was to investigate the function of ADAMTS1 in prostate tumors.

Methods

ADAMTS1 was downregulated by shRNA technology in the human prostate cancer cell line LNCaP (androgen-dependent), originally expressing ADAMTS1, and was upregulated by transfection in its subline LNCaP-19 (androgen-independent), expressing low levels of ADAMTS1. Cells were implanted subcutaneously in nude mice and tumor growth, microvessel density (MVD), blood vessel morphology, pericyte coverage and thrombospondin 1 (TSP1) were studied in the tumor xenografts.

Results

Modified expression of ADAMTS1 resulted in altered blood vessel morphology in the tumors. Low expression levels of ADAMTS1 were associated with small diameter blood vessels both in LNCaP and LNCaP-19 tumors, while high levels of ADAMTS1 were associated with larger vessels. In addition, TSP1 levels in the tumor xenografts were inversely related to ADAMTS1 expression. MVD and pericyte coverage were not affected. Moreover, upregulation of ADAMTS1 inhibited tumor growth of LNCaP-19, as evidenced by delayed tumor establishment. In contrast, downregulation of ADAMTS1 in LNCaP resulted in reduced tumor growth rate.

Conclusions

The present study demonstrates that ADAMTS1 is an important regulatory factor of angiogenesis and tumor growth in prostate tumors, where modified ADAMTS1 expression resulted in markedly changed blood vessel morphology, possibly related to altered TSP1 levels.

Tumour angiogenesis is reduced in the Tc1 mouse model of Down's syndrome

Down's syndrome (DS) is a genetic disorder caused by full or partial trisomy of human chromosome 21 and presents with many clinical phenotypes including a reduced incidence of solid tumours. Recent work with the Ts65Dn model of DS, which has orthologues of about 50% of the genes on chromosome 21 (Hsa21), has indicated that three copies of the ETS2 (ref. 3) or DS candidate region 1 (DSCR1) genes (a previously known suppressor of angiogenesis) is sufficient to inhibit tumour growth. Here we use the Tc1 transchromosomic mouse model of DS to dissect the contribution of extra copies of genes on Hsa21 to tumour angiogenesis. This mouse expresses roughly 81% of Hsa21 genes but not the human DSCR1 region. We transplanted B16F0 and Lewis lung carcinoma tumour cells into Tc1 mice and showed that growth of these tumours was substantially reduced compared with wild-type littermate controls. Furthermore, tumour angiogenesis was significantly repressed in Tc1 mice. In particular, in vitro and in vivo angiogenic responses to vascular endothelial growth factor (VEGF) were inhibited. Examination of the genes on the segment of Hsa21 in Tc1 mice identified putative anti-angiogenic genes (ADAMTS1and ERG) and novel endothelial cell-specific genes, never previously shown to be involved in angiogenesis (JAM-B and PTTG1IP), that, when overexpressed, are responsible for inhibiting angiogenic responses to VEGF. Three copies of these genes within the stromal compartment reduced tumour angiogenesis, explaining the reduced tumour growth in DS. Furthermore, we expect that, in addition to the candidate genes that we show to be involved in the repression of angiogenesis, the Tc1 mouse model of DS will permit the identification of other endothelium-specific anti-angiogenic targets relevant to a broad spectrum of cancer patients.

Tasquinimod (ABR-215050), a quinoline-3-carboxamide anti-angiogenic agent, modulates the expression of thrombospondin-1 in human prostate tumors

Background

The orally active quinoline-3-carboxamide tasquinimod [ABR-215050; CAS number 254964-60-8), which currently is in a phase II-clinical trial in patients against metastatic prostate cancer, exhibits anti-tumor activity via inhibition of tumor angiogenesis in human and rodent tumors. To further explore the mode of action of tasquinimod, in vitro and in vivo experiments with gene microarray analysis were performed using LNCaP prostate tumor cells. The array data were validated by real-time semiquantitative reversed transcriptase polymerase chain reaction (sqRT-PCR) and protein expression techniques.

Results

One of the most significant differentially expressed genes both in vitro and in vivo after exposure to tasquinimod, was thrombospondin-1 (TSP1). The up-regulation of TSP1 mRNA in LNCaP tumor cells both in vitro and in vivo correlated with an increased expression and extra cellular secretion of TSP1 protein. When nude mice bearing CWR-22RH human prostate tumors were treated with oral tasquinimod, there was a profound growth inhibition, associated with an up-regulation of TSP1 and a down- regulation of HIF-1 alpha protein, androgen receptor protein (AR) and glucose transporter-1 protein within the tumor tissue. Changes in TSP1 expression were paralleled by an anti-angiogenic response, as documented by decreased or unchanged tumor tissue levels of VEGF (a HIF-1 alpha down stream target) in the tumors from tasquinimod treated mice.

Conclusions

We conclude that tasquinimod-induced up-regulation of TSP1 is part of a mechanism involving down-regulation of HIF1α and VEGF, which in turn leads to reduced angiogenesis via inhibition of the "angiogenic switch", that could explain tasquinimods therapeutic potential.

Thrombospondin-1 as a Paradigm for the Development of Antiangiogenic Agents Endowed with Multiple Mechanisms of Action

Uncontrolled neovascularization occurs in several angiogenesis-dependent diseases, including cancer. Neovascularization is tightly controlled by the balance between angiogenic growth factors and antiangiogenic agents. The various natural angiogenesis inhibitors identified so far affect neovascularization by different mechanisms of action. Thrombospondin-1 (TSP-1) is a matricellular modular glycoprotein that acts as a powerful endogenous inhibitor of angiogenesis. It acts both indirectly, by sequestering angiogenic growth factors and effectors in the extracellular environment, and directly, by inducing an antiangiogenic program in endothelial cells following engagement of specific receptors including CD36, CD47, integrins and proteoglycans (all involved in angiogenesis ). In view of its central, multifaceted role in angiogenesis, TSP-1 has served as a source of antiangiogenic tools, including TSP-1 fragments, synthetic peptides and peptidomimetics, gene therapy strategies, and agents that up-regulate TSP-1 expression. This review discusses TSP-1-based inhibitors of angiogenesis, their mechanisms of action and therapeutic potential, drawing our experience with angiogenic growth factor-interacting TSP-1 peptides, and the possibility of exploiting them to design novel antiangiogenic agents.

Extracellular matrix, inflammation, and the angiogenic response

Inflammation and angiogenesis are frequently coupled in pathological situations such as atherosclerosis, diabetes, and arthritis. The inflammatory response increases capillary permeability and induces endothelial activation, which, when persistent, results in capillary sprouting. This inflammation-induced angiogenesis and the subsequent remodelling steps are in large part mediated by extracellular matrix (ECM) proteins and proteases. The focal increase in capillary permeability is an early consequence of inflammation, and results in the deposition of a provisional fibrin matrix. Subsequently, ECM turnover by proteases permits an invasive program by specialized endothelial cells whose phenotype can be regulated by inflammatory stimuli. ECM activity also provides specific mechanical forces, exposes cryptic adhesion sites, and releases biologically active fragments (matrikines) and matrix-sequestered growth factors, all of which are critical for vascular morphogenesis. Further matrix remodelling and vascular regression contribute to the resolution of the inflammatory response and facilitate tissue repair.

Variable inhibition of thrombospondin 1 against liver and lung metastases through differential activation of metalloproteinase ADAMTS1

Metastasis relies on angiogenesis for tumor expansion. Tumor angiogenesis is restrained by a variety of endogenous inhibitors, including thrombospondin 1 (TSP1). The principal antiangiogenic activity of TSP1 resides in a domain containing three TSP1 repeats (3TSR), and TSP1 cleavage is regulated, in part, by the metalloproteinase ADAMTS1. In this study, we examined the role of TSP1 and ADAMTS1 in controlling metastatic disease in the liver and lung. TSP1 overexpression inhibited metastatic growth of colon or renal carcinoma cells in liver but not lung. Metastatic melanoma in liver grew more rapidly in Tsp1-null mice compared with controls, whereas in lung grew similarly in Tsp1-null mice or controls. Recombinant TSP1 was cleaved more efficiently in lysates from liver than lung. ADAMTS1 inhibition by neutralizing antibody, small interfering RNA, or genetic deletion abrogated cleavage activity. To confirm that lack of cleavage of TSP1 ablated its antiangiogenic function in the lung, we generated colon cancer cells stably secreting only the 3TSR domain and found that they inhibited formation of both liver and lung metastases. Collectively, our results indicate that the antiangiogenic activity of TSP1 is differentially regulated by ADAMTS1 in the liver and lung, emphasizing the concept that regulation of angiogenesis is varied in different tissue environments.

ADAMTS9 is a cell-autonomously acting, anti-angiogenic metalloprotease expressed by microvascular endothelial cells

The metalloprotease ADAMTS9 participates in melanoblast development and is a tumor suppressor in esophageal and nasopharyngeal cancer. ADAMTS9 null mice die before gastrulation, but, ADAMTS9+/- mice were initially thought to be normal. However, when congenic with the C57Bl/6 strain, 80% of ADAMTS9+/- mice developed spontaneous corneal neovascularization. beta-Galactosidase staining enabled by a lacZ cassette targeted to the ADAMTS9 locus showed that capillary endothelial cells (ECs) in embryonic and adult tissues and in capillaries growing into heterotopic tumors expressed ADAMTS9. Heterotopic B.16-F10 melanomas elicited greater vascular induction in ADAMTS9+/- mice than in wild-type littermates, suggesting a potential inhibitory role in tumor angiogenesis. Treatment of cultured human microvascular ECs with ADAMTS9 small-interfering RNA resulted in enhanced filopodial extension, decreased cell adhesion, increased cell migration, and enhanced formation of tube-like structures on Matrigel. Conversely, overexpression of catalytically active, but not inactive, ADAMTS9 in ECs led to fewer tube-like structures, demonstrating that the proteolytic activity of ADAMTS9 was essential. However, unlike the related metalloprotease ADAMTS1, which exerts anti-angiogenic effects by cleavage of thrombospondins and sequestration of vascular endothelial growth factor165, ADAMTS9 neither cleaved thrombospondins 1 and 2, nor bound vascular endothelial growth factor165. Taken together, these data identify ADAMTS9 as a novel, constitutive, endogenous angiogenesis inhibitor that operates cell-autonomously in ECs via molecular mechanisms that are distinct from those used by ADAMTS1.

The cleavage of semaphorin 3C induced by ADAMTS1 promotes cell migration

Metastasis is a sequential process that allows cells to move from the primary tumor and grow elsewhere. Because of their ability to cleave a variety of extracellular signaling and adhesion molecules, metalloproteases have been long considered key components of the metastatic program. However, the function of certain metalloproteases, such as ADAMTS1, is not clear and seems to depend on the cellular environment and/or the stage of tumor progression. To characterize the function of ADAMTS1, we performed two alternative proteomic approaches, difference gel electrophoresis and stable isotope labeling by amino acids in cell culture, to identify novel substrates of the metalloprotease. Both techniques showed that overexpression of ADAMTS1 leads to the release of semaphorin 3C from the extracellular matrix. Although semaphorins are well known regulators of axon guidance, accumulating evidence shows that they may also participate in tumor progression. Here, we show that the cleavage of semaphorin 3C induced by ADAMTS1 promotes the migration of breast cancer cells, indicating that the co-expression of these molecules in tumors may contribute to the metastatic program.

Thrombospondins function as regulators of angiogenesis

Thrombospondins (TSPs) -1 and -2 were among the first protein inhibitors of angiogenesis to be identified, a property that was subsequently attributed to the interactions of sequences in their type I repeats with endothelial cell-surface receptors. The interactions of TSPs-1 and -2 with cell-surface receptors, proteases, growth factors, and other bioactive molecules, coupled with the absence of direct structural functions that can be attributed to these matrix proteins, qualify them for inclusion in the category of ‘matricellular proteins’. The phenotypes of TSP-1, TSP-2, and double TSP-1/2-null mice confirm the roles that these proteins play in the regulation of angiogenesis, and provide clues to some of the other important functions of these multi-domain proteins. One of these functions is the ability of TSP-1 to activate the latent TGFβ1 complex, a property that is not shared by TSP-2. A major pathway by which TSP1 or TSP2 inhibits angiogenesis involves an interaction with CD 36 on endothelial cells, which leads to apoptosis of both the liganded and adjacent cells. However a homeostatic mechanism, which inhibits endothelial cell proliferation, and may be physiologically preferable under some circumstances, has also been elucidated, and involves interaction with the very low density lipoprotein receptor (VLDLR). The interaction of TSP1with its receptor, CD47, further inhibits angiogenesis by antagonizing nitric oxide signaling in endothelial and vascular smooth muscle cells. Paradoxically, there is also evidence that TSP-1 can function to promote angiogenesis. This apparent contradiction can be explained by the presence of sequences in different domains of the protein that interact with different receptors on endothelial cells. The anti-angiogenic function of TSPs has spurred interest in their use as anti-tumor agents. Currently, peptide mimetics, based on sequences in the type I repeats of TSPs that have been shown to have anti-angiogenic properties, are undergoing clinical testing.

FOS proliferating network construction in early colorectal cancer (CRC) based on integrative significant function cluster and inferring analysis

The aim is to setup single distinguished molecular network. We constructed FOS proliferating network from 22 colorectal samples of the same GEO dataset by GRNInfer tool and DAVID based on linear programming and a decomposition procedure with integrated Kappa statistics and fuzzy heuristic clustering. In the control, we found no proliferating subnetwork. In CRC, we identified one FOS proliferating module (SFRP2, ADAMTS1, SYNPO2, VIP, ADAM33 inhibition to FOS and MGP, FOSB activation to FOS. FOS activation to IGFBP5, LGI1, GAS1 and FOS inhibition to VIP). These results may be useful for developing novel prognostic markers and therapeutic targets in CRC.

A disintegrin-like and metalloprotease (reprolysin-type) with thrombospondin type 1 motif (ADAMTS) superfamily: functions and mechanisms

Together with seven ADAMTS-like proteins, the 19 mammalian ADAMTS proteases constitute a superfamily. ADAMTS proteases are secreted zinc metalloproteases whose hallmark is an ancillary domain containing one or more thrombospondin type 1 repeats. ADAMTS-like proteins resemble ADAMTS ancillary domains and lack proteolytic activity. Vertebrate expansion of the superfamily reflects emergence of new substrates, duplication of proteolytic activities in new contexts, and cooperative functions of the duplicated genes. ADAMTS proteases are involved in maturation of procollagen and von Willebrand factor, as well as in extracellular matrix proteolysis relating to morphogenesis, angiogenesis, ovulation, cancer, and arthritis. New insights into ADAMTS mechanisms indicate significant regulatory roles for ADAMTS ancillary domains, propeptide processing, and glycosylation. ADAMTS-like proteins appear to have regulatory roles in the extracellular matrix.

Interactions among stalk modules of thrombospondin-1

Thrombospondin-1 is a trimeric, modular calcium-binding glycoprotein. The subunit is composed of an N-terminal module; oligomerization domain; stalk modules including a von Willebrand factor type C module, three properdin or thrombospondin type 1 repeat (TSR) modules, and two thrombospondin-type EGF-like modules; and a C-terminal signature domain comprising single copies of the epidermal growth factor (EGF)-like, wire, and lectin-like modules. Conformational changes in the signature domain influence ligand binding to the N-terminal modules. Interactions have been demonstrated among the modules of the signature domain and the thrombospondin-type EGF-like modules. We have extended this analysis to the rest of the stalk modules. Differential scanning calorimetry revealed interactions between the most C-terminal TSR module and the EGF-like modules. Calorimetry and differences in expression levels of single versus tandem modules indicated that the three TSRs interact with each other as well. No evidence of interactions between the von Willebrand factor type C and TSR modules were detected by differential scanning calorimetry, circular dichroism, or intrinsic fluorescence. These results indicate that the TSR and thrombospondin-type EGF-like stalk modules act as a unit that may relay conformational information between the N-terminal and C-terminal parts of the protein.

The ADAMTS12 metalloprotease gene is epigenetically silenced in tumor cells and transcriptionally activated in the stroma during progression of colon cancer

Proteases have long been associated with tumor progression, given their ability to degrade extracellular matrix components and facilitate invasion and metastasis. However, recent findings indicate that different proteases can also act as tumor-suppressor enzymes. We have recently reported that lung carcinoma cells expressing the ADAMTS-12 metalloprotease show a remarkable impairment of growth in immunodeficient mice as compared with parental cells. Here, we show that ADAMTS12 promoter is hypermethylated in cancer cell lines and tumor tissues. Interestingly, ADAMTS12 expression in the stromal cells surrounding epithelial malignant cells is higher than in the paired normal tissues. Moreover, the expression of this metalloprotease in colon fibroblasts co-cultured with colon cancer cell lines is higher than in those cultured alone. Furthermore, the expression of ADAMTS-12 by these fibroblasts is linked with an anti-proliferative effect on tumor cells. Based on these findings, we hypothesize that ADAMTS-12 is a novel anti-tumor protease that can reduce the proliferative properties of tumor cells. This function is lost by epigenetic silencing in tumor cells, but concurrently induced in stromal cells, probably as part of a response of the normal tissue aimed at controlling the progression of cancer.

Differential expression of pancreatitis-associated protein and thrombospondins in arterial versus venous tissues

BACKGROUND/AIMS

Arteries and veins modulate cardiovascular homeostasis and contribute to hypertension pathogenesis. Functional differences between arteries and veins are based upon differences in gene expression. To better characterize these expression patterns, and to identify candidate genes that could be manipulated selectively in the venous system, we performed whole genome expression profiling of arteries and veins.

METHODS

We used the CodeLink platform and the major artery (thoracic aorta) and vein (caudal vena cava) of the rat.

RESULTS

The most prominent difference was pancreatitis-associated protein (PAP1), expressed 64-fold higher in vena cava versus aorta. Expression of mRNA for thrombospondins (TSP-1, TSP-4) was greater than 5-fold higher in veins versus arteries. Higher mRNA expression of TSP-1, TSP-2, TSP-4 and PAP1 in vena cava versus aorta was confirmed by PCR. Immunohistochemical analysis of tissue sections qualitatively confirmed a higher expression of these proteins in vena cava versus aorta.

CONCLUSION

This is the first gene array study of adult rat arterial and venous tissues, and also the first study to report differences in inflammatory genes between arteries and veins. Data from these studies may provide novel insights into the genetic basis for functional differences between arteries and veins in health and disease.

ADAMTS1, a putative anti-angiogenic factor, is decreased in human prostate cancer

OBJECTIVE

To investigate the expression of 'ADAM metallopeptidase with thrombospondin type I motif, 1' (ADAMTS1) in human prostate cancer, and to study its relationship to microvessel density (MVD) and metastasis. ADAMTS1 has been described as an anti-angiogenic and antitumour factor, but its function in prostate cancer is unknown.

PATIENTS AND METHODS

ADAMTS1 expression was evaluated by immunohistochemistry in specimens obtained by transurethral resection of the prostate from patients with hormone-naïve and hormone-refractory prostate tumours, including adjacent benign tissue. A semiquantitative scoring system was used for evaluating the staining. MVD was quantified by counting the number of CD34-positive blood vessels.

RESULTS

ADAMTS1 was strongly expressed in the luminal epithelial cells in benign prostate glands, whereas expression was significantly lower in prostate cancer cells. There was no obvious difference between hormone-naïve and hormone-refractory tumours, and ADAMTS1 expression did not correlate with Gleason score. However, in hormone-refractory tumours from patients with metastatic disease, the expression of ADAMTS1 was significantly lower than in tumours from patients without metastases. Furthermore, the MVD was higher in hormone-refractory than in hormone-naïve tumours and benign tissue, and MVD correlated with Gleason score. There was no association between ADAMTS1 and MVD in the hormone-naïve tumours, while hormone-refractory tumours with low ADAMTS1 expression had a higher MVD than those with moderate/high expression.

CONCLUSION

ADAMTS1 expression is decreased in prostate cancer, and might be involved in the early steps of prostate cancer development. Further, ADAMTS1 might have an anti-angiogenic and antimetastatic role in hormone-refractory prostate cancer, where low ADAMTS1 expression is associated with a high MVD and metastasis.

Oligomeric procyanidins inhibit cell migration and modulate the expression of migration and proliferation associated genes in human umbilical vascular endothelial cells

The consumption of flavan-3-ols has been associated with reduced risk of cardiovascular diseases and improvements in vascular function. However, the nature of the flavan-3-ols responsible and the mechanisms underlying the vascular responses are not fully understood. We used microarrays to search for molecular changes in response to the exposure to (-)-epicatechin (EC), procyanidin dimer B2, and a mixture of oligomeric procyanidins in human umbilical vein endothelial cells (HUVECs). No gene expression changes were detected in HUVECs exposed to EC or dimer B2, however, the oligomeric procyanidins induced significant gene expression changes in both resting and TNF-alpha-stimulated cells. In particular, the expression of genes such as ADAMTS1, THBS1, ANGPT2, CYR61, ET-1, EDG3, and PDE4B involved in endothelial cell migration and proliferation, were substantially over-represented. Also, exposure to the oligomers arrested the cells at the G(0)/G(1 )phase and inhibited cell migration. These data show that human endothelial cells respond to oligomeric procyanidins by exhibiting a less migratory phenotype and by a general modulation of the expression of genes that are associated with key events in the angiogenic process. The molecular changes associated with procyanidin treatment identified in this study are consistent with the beneficial effects of flavan-3-ols on vascular function.

HDAC inhibition upregulates the expression of angiostatic ADAMTS1

HDAC inhibitors are promising anticancer agents that induce cell cycle arrest and apoptosis. However, the role of HDACs in cancer progression, such as angiogenesis and metastasis, remains largely unexplored. Among various HDAC inhibitors, we demonstrate that TSA and SAHA upregulated the expression of angiostatic ADAMTS1 in A549 cells. HDAC6 inhibitor tubacin, and knockdown of HDAC6, also lead to ADAMTS1 upregulation. By reporter, DAPA, and ChIP assays, the proximal GC boxes were demonstrated to be essential for ADAMTS1 induction. Decreased binding of SP1 and HDAC6 to the ADAMTS1 promoter after TSA treatment was also seen. These data suggest the involvement of HDAC6 and SP1 in the HDACi-induced expression of angiostatic ADAMTS1.

Role of unusual O-glycans in intercellular signaling

In the last two decades, our knowledge of the role of glycans in development and signal transduction has expanded enormously. While most work has focused on the importance of N-linked or mucin-type O-linked glycosylation, recent work has highlighted the importance of several more unusual forms of glycosylation that are the focus of this review. In particular, the ability of O-fucose glycans on the epidermal growth factor-like (EGF) repeats of Notch to modulate signaling places glycosylation alongside phosphorylation as a means to modulate protein-protein interactions and their resultant downstream signals. The recent discovery that O-glucose modification of Notch EGF repeats is also required for Notch function has further expanded the range of glycosylation events capable of modulating Notch signaling. The prominent role of Notch during development and in later cell-fate decisions underscores the importance of these modifications in human biology. The role of glycans in intercellular signaling events is only beginning to be understood and appears ready to expand into new areas with the discovery that thrombospondin type 1 repeats are also modified with O-fucose glycans. Finally, a rare form of glycosylation called C-mannosylation modifies tryptophans in some signaling competent molecules and may be a further layer of complexity in the field. We will review each of these areas focusing on the glycan structures produced, the consequence of their presence, and the enzymes responsible.

Regulation of thrombospondin1 by extracellular proteases

The contribution of proteases to developmental, physiological and pathological processes has been well accepted. Cleavage of matrix proteins is a key requirement for cell migration and remodeling of the extracellular environment. The constant process of matrix turnover is dependent on the delicate balance between degradation and synthesis. In addition, regulated proteolysis also allows for the release and activation of growth factors and cytokines. Similarly to other extracellular matrix proteins, thrombospondins are also targets of proteolysis. While in some cases enzymatic activity is associated with degradation of the protein; in other situations, targeted and selective cleavage offers the means to release polypeptides with either alternative or enhanced function. Here, we provide a summary of the published information related to thrombospondin proteolysis within the context of how proteolysis of extracellular matrix proteins impacts diversification of protein function. We also discuss its biological relevance and potential therapeutic value of thrombospondin proteolysis with particular emphasis on angiogenesis.

Regulating the angiogenic balance in tissues

A balance between angiogenesis inducers and inhibitors in the microenvironment controls the rate of new blood vessel formation. We hypothesized that fibroblasts, an important cellular constituent of the tissue stroma, secrete molecules that contribute to this balance. We further hypothesized that fibroblasts secrete molecules that promote angiogenesis when they are in a proliferative state and molecules that inhibit angiogenesis when they are not actively cycling (quiescent). Microarray analysis revealed that angiogenesis inducers and inhibitors are regulated as fibroblasts transition into a quiescent state and reenter the cell cycle in response to changes in serum. To assess whether changes in transcript levels result in changes in the levels of secreted proteins, we collected conditioned medium from proliferating and quiescent fibroblasts and performed immunoblotting for selected proteins. Secreted protein levels of the angiogenesis inhibitor pigment epithelium derived factor (PEDF) were higher in quiescent than proliferating fibroblasts. Conversely, proliferating fibroblasts secreted increased levels of the angiogenesis inducer vascular endothelial growth factor-C (VEGF-C). For the angiogenesis inhibitor thrombospondin-2, quiescent cells secreted a prominent 160 kDa form in addition to the 200 kDa form secreted by proliferating and restimulated fibroblasts. Using immunohistochemistry we discovered that fibroblasts surround blood vessels and that the angiogenesis inhibitor PEDF is expressed by quiescent fibroblasts in uterine tissue, supporting a role for PEDF in maintaining quiescence of the vasculature. This work takes a new approach to the study of angiogenesis by examining the expression of multiple angiogenesis regulators secreted from a key stromal cell, the fibroblast.

LDL receptor-related protein 1: unique tissue-specific functions revealed by selective gene knockout studies

The LDL receptor-related protein (originally called LRP, but now referred to as LRP1) is a large endocytic receptor that is widely expressed in several tissues. LRP1 is a member of the LDL receptor family that plays diverse roles in various biological processes including lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes, and cellular entry of bacterial toxins and viruses. Deletion of the LRP1 gene leads to lethality in mice, revealing a critical, but as of yet, undefined role in development. Tissue-specific gene deletion studies reveal an important contribution of LRP1 in the vasculature, central nervous system, macrophages, and adipocytes. Three important properties of LRP1 dictate its diverse role in physiology: 1) its ability to recognize more than 30 distinct ligands, 2) its ability to bind a large number of cytoplasmic adaptor proteins via determinants located on its cytoplasmic domain in a phosphorylation-specific manner, and 3) its ability to associate with and modulate the activity of other transmembrane receptors such as integrins and receptor tyrosine kinases.

Cleavage of syndecan-4 by ADAMTS1 provokes defects in adhesion

Syndecan-4 is a membrane-bound heparan sulfate proteoglycan that participates in cell-cell and cell-matrix interactions and modulates adhesion and migration of many cell types. Through its extracellular domain, syndecan-4 cooperates with adhesion molecules and binds matrix components relevant for cell migration. Importantly, syndecan-4 is a substrate of extracellular proteases, however the biological significance of this cleavage has not been elucidated. Here, we show that the secreted metalloprotease ADAMTS1, involved in angiogenesis and inflammatory processes, cleaves the ectodomain of syndecan-4. We further showed that this cleavage results in altered distribution of cytoskeleton components, functional loss of adhesion, and gain of migratory capacities. Using syndecan-4 null cells, we observed that ADAMTS1 proteolytic action mimics the outcome of genetic deletion of this proteoglycan with regards to focal adhesion. Our findings suggest that the shedding of syndecan-4 by ADAMTS1 disrupts cell adhesion and promotes cell migration.

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.

Protective roles of the fractalkine/CX3CL1-CX3CR1 interactions in alkali-induced corneal neovascularization through enhanced antiangiogenic factor expression

Macrophages accumulate during the course of corneal neovascularization, but its mechanisms and roles still remain elusive. To address these points, we herein examined corneal neovascularization after alkali injury in mice deficient in fractalkine receptor/CX3CR1, which is normally expressed by macrophages. After alkali injury, the mRNA expression of CX3CR1 was augmented along with accumulation of F4/80-positive macrophages and Gr-1-positive neutrophils in the corneas. Compared with wild-type mice, CX3CR1-deficient mice exhibited enhanced corneal neovascularization 2 wk after injury, as evidenced by enlarged CD31-positive areas. Concomitantly, the accumulation of F4/80-positive macrophages, but not Gr-1-positive neutrophils, was markedly attenuated in CX3CR1-deficient mice compared with wild-type mice. The intraocular mRNA expression of vascular endothelial growth factor (VEGF) was enhanced to similar extents in wild-type and CX3CR1-deifient mice after the injury. However, the mRNA expression of antiangiogenic factors, thrombospondin (TSP) 1, TSP-2, and a disintegrin and metalloprotease with thrombospondin (ADAMTS) 1, was enhanced to a greater extent in wild-type than CX3CR1-deificient mice. A double-color immunofluorescence analysis demonstrated that F4/80-positive cells also expressed CX3CR1 and ADAMTS-1 and that TSP-1 and ADAMTS-1 were detected in CX3CR1-positive cells. CX3CL1 enhanced TSP-1 and ADAMTS-1, but not VEGF, expression by peritoneal macrophages. Moreover, topical application of CX3CL1 inhibited corneal neovascularization at 2 wk, along with enhanced intraocular expression of TSP-1 and ADAMTS-1 but not VEGF. Thus, these observations indicate that accumulation of CX3CR1-positive macrophages intraocularly can dampen alkali-induced corneal neovascularization by producing antiangiogenic factors such as TSP-1 and ADAMTS-1 and suggest the potential therapeutic efficacy of using CX3CL1 against alkali-induced corneal neovascularization.

Endocardial Brg1 represses ADAMTS1 to maintain the microenvironment for myocardial morphogenesis

Developing myocardial cells respond to signals from the endocardial layer to form a network of trabeculae that characterize the ventricles of the vertebrate heart. Abnormal myocardial trabeculation results in specific cardiomyopathies in humans and yet trabecular development is poorly understood. We show that trabeculation requires Brg1, a chromatin remodeling protein, to repress ADAMTS1 expression in the endocardium that overlies the developing trabeculae. Repression of ADAMTS1, a secreted matrix metalloproteinase, allows the establishment of an extracellular environment in the cardiac jelly that supports trabecular growth. Later during embryogenesis, ADAMTS1 expression initiates in the endocardium to degrade the cardiac jelly and prevent excessive trabeculation. Thus, the composition of cardiac jelly essential for myocardial morphogenesis is dynamically controlled by ADAMTS1 and its chromatin-based transcriptional regulation. Modification of the intervening microenvironment provides a mechanism by which chromatin regulation within one tissue layer coordinates the morphogenesis of an adjacent layer.

Structures of thrombospondins

Thrombospondins are large secreted, multimodular, calcium-binding glycoproteins that have complex roles in mediating cellular processes. Determination of high-resolution structures of thrombospondins has revealed unique and interesting protein motifs. Here, we review this progress and discuss implications for function. By combining structures of modules from thrombospondins and related extracellular proteins it is now possible to prepare an overall model of the structure of thrombospondin-1 and thrombospondin-2 and discern features of other thrombospondins. (Part of a multi-author Review).

Extracellular matrix retention of thrombospondin 1 is controlled by its conserved C-terminal region

Thrombospondins (TSPs) are an evolutionarily ancient family of extracellular calcium-binding glycoproteins. The five mammalian TSPs collectively have important roles in angiogenesis and vascular biology, synaptogenesis, wound repair and connective tissue organisation. Their complex functions relate to the multiple postsecretion fates of TSPs that can involve endocytic uptake, proteolysis or retention within the extracellular matrix (ECM). Surprisingly, the molecular and cellular mechanisms by which TSPs become retained within the ECM are poorly understood. We hypothesised that the highly conserved TSP C-terminal domain mediates ECM retention. We report that ECM incorporation as insoluble punctate deposits is an evolutionarily conserved property of TSPs. ECM retention of TSP1 is mediated by the C-terminal region in trimeric form, and not by C-terminal monomer or trimers of the N-terminal domain or type 1 repeats. Using a novel mRFP-tagged TSP1 C-terminal trimer, we demonstrate that ECM retention involves the RGD site and a novel site in the L-lectin domain with structural similarity to the ligand-binding site of cargo transport proteins. CD47 and beta1 integrins are dispensable for ECM retention, but beta1 integrins enhance activity. These novel data advance concepts of the molecular processes that lead to ECM retention of TSP1.

Renal ischemia reperfusion inhibits VEGF expression and induces ADAMTS-1, a novel VEGF inhibitor

Reductions in vascular density occur following acute ischemia-reperfusion (I/R) injury that may predispose the development of chronic kidney disease. The mechanisms mediating vascular loss are not clear but may relate to the lack of effective vascular repair responses. To determine the regulation of the VEGF/VEGFR pathway following I/R injury, male Sprague-Dawley rats were subjected to bilateral renal ischemia (45 min) and allowed to recover for 1, 3, 7, and 35 days. VEGF mRNA expression was repressed by greater than 50% of control values up to 3 days postischemia, while VEGF protein was repressed for up to 7 days postischemia. The renal mRNA expression of receptors was not altered postischemia; however, VEGFR1 (flt-1) protein was transiently reduced in kidney while soluble flt-1 was elevated in plasma at 7 days following injury. Microarray analysis of angiogenesis-related genes identified the enhanced expression of a number of genes, among these was ADAMTS-1 (a disintegrin and metalloproteinase with thrombospondin motif-1), a secreted VEGF inhibitor. The altered expression of ADAMTS-1 was confirmed using RT-PCR and Western blot analysis; immunofluorescence localized its expression to proximal tubules following I/R injury. Other genes identified using microarray included aminopeptidase N, Smad-1, and Id-3 and their localization was also examined using immunohistochemistry. In summary, the data indicate no clear pattern of anti-angiogenic gene expression following renal I/R injury. However, the studies do suggest an overall inhibition of the VEGF pathway during the early injury and repair phase of renal ischemia that may contribute to an overall reduction in renal microvascular density.

Altered expression of genes regulating angiogenesis in experimental androgen-independent prostate cancer

BACKGROUND

The aim of this study was to investigate how the expression of genes regulating angiogenesis is altered when prostate cancer cells progress into androgen-independency.

METHODS

A gene array specific for angiogenesis was used to compare the human prostate cancer cell line LNCaP (androgen-dependent) with its more angiogenic and tumorigenic subline LNCaP-19 (androgen-independent). Results were verified with real-time RT-PCR, and further investigations were focused on the angiogenesis inhibitor a disintegrin and metalloproteinase with thrombospondin motifs 1 (ADAMTS1). Expression of ADAMTS1 was investigated in vitro as well as in subcutaneous tumors with real-time RT-PCR and Western blotting. Microvessel density (MVD), versican proteolysis and protein levels of TIMP-2 and TIMP-3, known as ADAMTS1 inhibitors, were also analyzed in tumor xenografts.

RESULTS

The gene array revealed decreased expression of ADAMTS1, ephrin-A5, fibronectin 1, and neuropilin 1 in LNCaP-19 compared to LNCaP, while expression of midkine and VEGF were increased. Further studies showed that mRNA and protein levels of ADAMTS1 were significantly lower in LNCaP-19 compared to LNCaP, both in vitro and in subcutaneous tumors. The amount of ADAMTS1 correlated negatively with MVD, but no relation was found between ADAMTS1 and versican proteolysis.

CONCLUSIONS

Expression of several genes associated with angiogenesis was altered during transition into androgen-independency. Among these, a significant decrease was found for ADAMTS1, whose expression inversely correlated with MVD. Its role in progression of prostate cancer needs further investigation, but this inhibitor of angiogenesis could be an interesting candidate for future anti-angiogenic therapy.

Emerging roles of proteases in tumour suppression

Proteases have long been associated with cancer progression because of their ability to degrade extracellular matrices, which facilitates invasion and metastasis. However, recent studies have shown that these enzymes target a diversity of substrates and favour all steps of tumour evolution. Unexpectedly, the post-trial studies have also revealed proteases with tumour-suppressive effects. These effects are associated with more than 30 different enzymes that belong to three distinct protease classes. What are the clinical implications of these findings?