Pieces of eight: bioactive fragments of extracellular proteins as regulators of angiogenesis

Structural insights into regulation of CCN protein activities and functions

CCN proteins play important functions during development, in repair mechanisms following tissue injury, as well as in pathophysiologic mechanisms of metastasis of cancer. CCNs are secreted proteins that have a multimodular structure and are categorized as matricellular proteins. Although the prevailing view is that CCN proteins regulate biologic processes by interacting with a wide array of other proteins in the microenvironment of the extracellular matrix, the molecular mechanisms of action of CCN proteins are still poorly understood. Not dissuading the current view, however, the recent appreciation that these proteins are signaling proteins in their own right and may even be considered preproproteins controlled by endopeptidases to release a C-terminal bioactive peptide has opened new avenues of research. Also, the recent resolution of the crystal structure of two of the domains of CCN3 have provided new knowledge with implications for the entire CCN family. These resolved structures in combination with structural predictions based upon the AlphaFold artificial intelligence tool provide means to shed new light on CCN functions in context of the notable literature in the field. CCN proteins have emerged as important therapeutic targets in several disease conditions, and clinical trials are currently ongoing. Thus, a review that critically discusses structure - function relationship of CCN proteins, in particular as it relates to interactions with other proteins in the extracellular milieu and on the cell surface, as well as to cell signaling activities of these proteins, is very timely. Suggested mechanism for activation and inhibition of signaling by the CCN protein family (graphics generated with BioRender.com ).

Preparation and Use of Decellularized Extracellular Matrix for Tissue Engineering

The multidisciplinary fields of tissue engineering and regenerative medicine have the potential to revolutionize the practise of medicine through the abilities to repair, regenerate, or replace tissues and organs with functional engineered constructs. To this end, tissue engineering combines scaffolding materials with cells and biologically active molecules into constructs with the appropriate structures and properties for tissue/organ regeneration, where scaffolding materials and biomolecules are the keys to mimic the native extracellular matrix (ECM). For this, one emerging way is to decellularize the native ECM into the materials suitable for, directly or in combination with other materials, creating functional constructs. Over the past decade, decellularized ECM (or dECM) has greatly facilitated the advance of tissue engineering and regenerative medicine, while being challenged in many ways. This article reviews the recent development of dECM for tissue engineering and regenerative medicine, with a focus on the preparation of dECM along with its influence on cell culture, the modification of dECM for use as a scaffolding material, and the novel techniques and emerging trends in processing dECM into functional constructs. We highlight the success of dECM and constructs in the in vitro, in vivo, and clinical applications and further identify the key issues and challenges involved, along with a discussion of future research directions.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Developing Extracellular Matrix Technology to Treat Retinal or Optic Nerve Injury(1,2,3)

Adult mammalian CNS neurons often degenerate after injury, leading to lost neurologic functions. In the visual system, retinal or optic nerve injury often leads to retinal ganglion cell axon degeneration and irreversible vision loss. CNS axon degeneration is increasingly linked to the innate immune response to injury, which leads to tissue-destructive inflammation and scarring. Extracellular matrix (ECM) technology can reduce inflammation, while increasing functional tissue remodeling, over scarring, in various tissues and organs, including the peripheral nervous system. However, applying ECM technology to CNS injuries has been limited and virtually unstudied in the visual system. Here we discuss advances in deriving fetal CNS-specific ECMs, like fetal porcine brain, retina, and optic nerve, and fetal non-CNS-specific ECMs, like fetal urinary bladder, and the potential for using tissue-specific ECMs to treat retinal or optic nerve injuries in two platforms. The first platform is an ECM hydrogel that can be administered as a retrobulbar, periocular, or even intraocular injection. The second platform is an ECM hydrogel and polymer "biohybrid" sheet that can be readily shaped and wrapped around a nerve. Both platforms can be tuned mechanically and biochemically to deliver factors like neurotrophins, immunotherapeutics, or stem cells. Since clinical CNS therapies often use general anti-inflammatory agents, which can reduce tissue-destructive inflammation but also suppress tissue-reparative immune system functions, tissue-specific, ECM-based devices may fill an important need by providing naturally derived, biocompatible, and highly translatable platforms that can modulate the innate immune response to promote a positive functional outcome.

ADAMTS-7 Inhibits Re-endothelialization of Injured Arteries and Promotes Vascular Remodeling Through Cleavage of Thrombospondin-1

Background—

ADAMTS-7, a member of the disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family, was recently identified to be significantly associated genomewide with coronary artery disease. However, the mechanisms that link ADAMTS-7 and coronary artery disease risk remain elusive. We have previously demonstrated that ADAMTS-7 promotes vascular smooth muscle cell migration and postinjury neointima formation via degradation of a matrix protein cartilage oligomeric matrix protein. Because delayed endothelium repair renders neointima and atherosclerosis plaque formation after vessel injury, we examined whether ADAMTS-7 also inhibits re-endothelialization.

Methods and Results—

Wire injury of the carotid artery and Evans blue staining were performed in Adamts7 –/– and wild-type mice. Adamts-7 deficiency greatly promoted re-endothelialization at 3, 5, and 7 days after injury. Consequently, Adamts-7 deficiency substantially ameliorated neointima formation in mice at days 14 and 28 after injury in comparison with the wild type. In vitro studies further indicated that ADAMTS-7 inhibited both endothelial cell proliferation and migration. Surprisingly, cartilage oligomeric matrix protein deficiency did not affect endothelial cell proliferation/migration and re-endothelialization in mice. In a further examination of other potential vascular substrates of ADAMTS-7, a label-free liquid chromatography-tandem mass spectrometry secretome analysis revealed thrombospondin-1 as a potential ADAMTS-7 target. The subsequent studies showed that ADAMTS-7 was directly associated with thrombospondin-1 by its C terminus and degraded thrombospondin-1 in vivo and in vitro. The inhibitory effect of ADAMTS-7 on postinjury endothelium recovery was circumvented in Tsp1 –/– mice.

Conclusions—

Our study revealed a novel mechanism by which ADAMTS-7 affects neointima formation. Thus, ADAMTS-7 is a promising treatment target for postinjury vascular intima hyperplasia.

Revisiting the matricellular concept

The concept of a matricellular protein was first proposed by Paul Bornstein in the mid-1990s to account for the non-lethal phenotypes of mice with inactivated genes encoding thrombospondin-1, tenascin-C, or SPARC. It was also recognized that these extracellular matrix proteins were primarily counter or de-adhesive. This review reappraises the matricellular concept after nearly two decades of continuous investigation. The expanded matricellular family as well as the diverse and often unexpected functions, cellular location, and interacting partners/receptors of matricellular proteins are considered. Development of therapeutic strategies that target matricellular proteins are discussed in the context of pathology and regenerative medicine.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Proteolysis of the matricellular protein hevin by matrix metalloproteinase-3 produces a SPARC-like fragment (SLF) associated with neovasculature in a murine glioma model

The matricellular SPARC-family member hevin (Sparc-like 1/SPARCL-1/SC1/Mast9) contributes to neural development and alters tumor progression in a range of mammalian models. Based on sequence similarity, we hypothesized that proteolytic digestion of hevin would result in SPARC-like fragments (SLF) that affect the activity and/or location of these proteins. Incubation of hevin with matrix metalloproteinase-3 (MMP-3), a protease known to cleave SPARC, produced a limited number of peptides. Sequencing revealed the major proteolytic products to be SPARC-like in primary structure. In gliomas implanted into murine brain, a SLF was associated with SPARC in the neovasculature but not with hevin, the latter prominent in the astrocytes encompassed by infiltrating tumor. In this model of invasive glioma that involves MMP-3 activity, host-derived SLF was not observed in the extracellular matrix adjacent to tumor cells. In contrast, it occurred with its homolog SPARC in the angiogenic response to the tumor. We conclude that MMP-3-derived SLF is a marker of neovessels in glioma, where it could influence the activity of SPARC.

Modulation of Tumor Cell Survival, Proliferation, and Differentiation by the Peptide Derived from Tenascin-C: Implication of β1-Integrin Activation

Cell adhesion to extracellular matrix (ECM) participates in various biological processes, such as cell survival, proliferation, differentiation, and migration. Since these processes are essential for keeping homeostasis, aberration of these processes leads to a variety of diseases including cancer. Previously, we found that a peptide derived from tenascin- (TN-) C, termed TNIIIA2, stimulates cell adhesion to ECM through activation of β1-integrin. It has been shown that TNIIIA2 can modulate cell proliferation and differentiation. Interestingly, TNIIIA2 could not only enhance cell proliferation but also induce apoptotic cell death, depending on cellular context. In this review, we show the function of the peptide TNIIIA2 in cell survival, proliferation, and differentiation and refer to the possibility of new strategy for tumor suppression by regulating cell adhesion status using the ECM-derived functional peptides.

Recombinant kringle 5 from plasminogen antagonises hepatocyte growth factor-mediated signalling

The blood protein plasminogen is proteolytically cleaved to produce angiostatin and kringle 5 (K5), both of which are known angiogenesis inhibitors. A common structural element between K5, angiostatin and other endogenous angiogenesis inhibitors is the presence of the kringle protein-interacting domain. Another kringle domain-containing protein, hepatocyte growth factor (HGF), promotes angiogenesis by binding to and stimulating the tyrosine kinase receptor Met. HGF binding to Met is dependent on the kringle domains of HGF. Because both K5 and HGF contain kringle motifs and because these proteins have opposite effects on angiogenesis, we hypothesised that K5 can antagonise HGF-mediated signalling in a Met-dependent manner. We determined that K5 binding to H1299 cells is competed by HGF suggesting that these two proteins bind to the same protein. Purified K5 immunoprecipitates with Met and this interaction is abolished by increasing doses of HGF. Using proliferation, phosphorylation of Met and Akt as markers of HGF activity, we determined that K5 inhibits HGF-mediated signalling. Taken together, these data support a model by which K5 binds to Met and functions as a competitive antagonist of HGF signalling and presents a novel mechanism of action of K5.

Processing of the matricellular protein hevin in mouse brain is dependent on ADAMTS4

The matricellular SPARC family member hevin (SPARC-like 1/SPARCL-1/SC1/Mast9) contributes to neural development and alters tumor progression in a range of mammalian models. The distribution of hevin in mouse tissues was reexamined with a novel monoclonal antibody that discriminates between hevin and its ortholog SPARC. We now report proteolysis of hevin in many tissues, with the most extensive processing in the brain. We demonstrate a cleavage site within the hevin sequence for the neural tissue proteinase ADAMTS4. Digestion of hevin by ADAMTS4 in vitro produced fragments similar to those present in brain lysates. Monoclonal antibodies revealed a SPARC-like fragment generated from hevin that was co-localized with ADAMTS4 in vivo. We show that proteolysis of hevin by ADAMTS4 in the mouse cerebellum is important for the normal development of this tissue. In conclusion, we have identified the fragmentation of hevin by ADAMTS4 in the mouse brain and propose that this specific proteolysis is integral to cell morphology and extracellular matrix deposition in the developing brain.

Apoptotic death of hematopoietic tumor cells through potentiated and sustained adhesion to fibronectin via VLA-4

It has been postulated that inactivated beta1-integrins are involved in the disordered growth of hematopoietic tumor cells. We recently found that TNIIIA2, a peptide derived from tenascin-C, strongly activates beta1-integrins through binding with syndecan-4. We show here that Ramos Burkitt's lymphoma cells can survive and grow in suspension but undergo apoptosis when kept adhering to fibronectin by stimulation with TNIIIA2. Other integrin activators, Mg(2+) and TS2/16 (an integrin-activating antibody), were also capable of inducing apoptosis. The inactivation of ERK1/2 and Akt and the subsequent activation of Bad were involved in the apoptosis. The results using other hematopoietic tumor cell lines expressing different levels of fibronectin receptors (VLA-4 and VLA-5) showed that potentiated and sustained adhesion to fibronectin via VLA-4 causally induces apoptosis also in various types of hematopoietic tumor cells in addition to Ramos cells. Because TNIIIA2 requires syndecan-4 as a membrane receptor for activation of beta1-integrins, it induced apoptosis preferentially in hematopoietic tumor cells, which expressed both VLA-4 and syndecan-4 as membrane receptors mediating the effects of fibronectin and TNIIIA2, respectively. Therefore, normal peripheral blood cells, such as neutrophils, monocytes, and lymphocytes, which poorly expressed syndecan-4, were almost insusceptible to TNIIIA2-induced apoptosis. The TNIIIA2-related matricryptic site of TN-C could contribute, once exposed, to preventing prolonged survival of hematopoietic malignant progenitors through potentiated and sustained activation of VLA-4.

VLA-5-mediated adhesion to fibronectin accelerates hemin-stimulated erythroid differentiation of K562 cells through induction of VLA-4 expression

Fibronectin plays important roles in erythropoiesis through the fibronectin receptors VLA-4 and VLA-5. However, the substantial role of these fibronectin receptors and their functional assignment in erythroid differentiation are not yet fully understood. Here, we investigated the effects of cell adhesion to fibronectin on erythroid differentiation using K562 human erythroid progenitor cells. Erythroid differentiation could be induced in K562 cells in suspension by stimulating with hemin. This hemin-stimulated erythroid differentiation was highly accelerated when cells were induced to adhere to fibronectin by treatment with TNIIIA2, a peptide derived from tenascin-C, which has recently been found to induce beta1-integrin activation. Another integrin activator, Mn(2+), also accelerated hemin-stimulated erythroid differentiation. Adhesive interaction with fibronectin via VLA-4 as well as VLA-5 was responsible for acceleration of the hemin-stimulated erythroid differentiation in response to TNIIIA2, although K562 cells should have been lacking in VLA-4. Adhesion to fibronectin forced by TNIIIA2 causally induced VLA-4 expression in K562 cells, and this was blocked by the RGD peptide, an antagonist for VLA-5. The resulting adhesive interaction with fibronectin via VLA-4 strongly enhanced the hemin-stimulated activation of p38 mitogen-activated protein kinase, which was shown to serve as a signaling molecule crucial for erythroid differentiation. Suppression of VLA-4 expression by RNA interference abrogated acceleration of hemin-stimulated erythroid differentiation in response to TNIIIA2. Thus, VLA-4 and VLA-5 may contribute to erythropoiesis at different stages of erythroid differentiation.

Novel interactions of perlecan: unraveling perlecan's role in angiogenesis

Perlecan, a highly conserved and ubiquitous basement membrane heparan sulfate proteoglycan, is essential for life, inasmuch as its absence results in embryonic lethality in mice and C. elegans, and neonatal lethality in humans. Perlecan plays an essential role in vasculogenesis and chondrogenesis, as well as in pathological states where these processes are maladapted. Although a large body of evidence supports a pro-angiogenic role for perlecan, recent findings suggests that portions of the perlecan protein core can be antiangiogenic, requiring a further evaluation of the functioning of this complex molecule. This review is focused on the genetics of mammalian and nonmammalian perlecan, the elucidation of its novel interacting partners and its role in angiogenesis. By more fully understanding perlecan's functioning in angiogenesis, we may gain invaluable insight that could lead to therapeutic interventions in cancer and other pathologic states.

A peptide derived from tenascin-C induces beta1 integrin activation through syndecan-4

Tenascin-C (TN-C) is unique for its cell adhesion modulatory function. We have shown that TNIIIA2, a synthetic 22-mer peptide derived from TN-C, stimulated beta1 integrin-mediated cell adhesion of nonadherent and adherent cell types, by inducing activation of beta1 integrin. The active site of TNIIIA2 appeared cryptic in the TN-C molecule but was exposed by MMP-2 processing of TN-C. The following results suggest that cell surface heparan sulfate (HS) proteoglycan (HSPG), including syndecan-4, participated in TNIIIA2-induced beta1 integrin activation: 1) TNIIIA2 bound to cell surface HSPG via its HS chains, as examined by photoaffinity labeling; 2) heparitinase I treatment of cells abrogated beta1 integrin activation induced by TNIIIA2; 3) syndecan-4 was isolated by affinity chromatography using TNIIIA2-immobilized beads; 4) small interfering RNA-based down-regulation of syndecan-4 expression reduced TNIIIA2-induced beta1 integrin activation, and consequent cell adhesion to fibronectin; 5) overexpression of syndecan-4 core protein enhanced TNIIIA2-induced activation of beta1 integrin. However, treatments that targeted the cytoplasmic region of syndecan-4, including ectopic expression of its mutant truncated with the cytoplasmic domains and treatment with protein kinase Calpha inhibitor Gö6976, did not influence the TNIIIA2 activity. These results suggest that a TNIIIA2-related matricryptic site of the TN-C molecule, exposed by MMP-2 processing, may have bound to syndecan-4 via its HS chains and then induced conformational change in beta1 integrin necessary for its functional activation. A lateral interaction of beta1 integrin with the extracellular region of the syndecan-4 molecule may be involved in this conformation change.

Expression of pigment-epithelium-derived factor during kidney development and aging

Inhibitors and stimulators of endothelial cell growth are essential for the coordination of blood vessel formation during organ growth and development. In the adult kidney, one of the major inhibitors of angiogenesis is pigment-epithelium-derived factor (PEDF). We have analyzed the expression and distribution of PEDF during various stages of renal development and aging with particular emphasis on the formation of functional glomeruli. We show that PEDF gene expression and protein levels in the kidney significantly increase with age. We have detected PEDF in the mesenchyme and endothelial cells at all developmental stages studied, in all regions of the nephrogenic zone in which the formation of new blood vessels is associated with the development of nephrons and collecting ducts, and in mature podocytes in the adult kidney. Our results are the first to suggest that PEDF is important in early renal postnatal development, that it could be relevant to the maturation of glomerular function and the filtration barrier formed by these cells, and that it may serve as an anti-angiogenic modulator during kidney development.

The cryptome: a subset of the proteome, comprising cryptic peptides with distinct bioactivities

There is increasing evidence that proteolytic cleavage gives rise to 'hidden' peptides with bioactivities that are often unpredicted and totally distinct to the parent protein. So far, the liberation of these cryptic peptides, or crypteins, has been shown to be prevalent in proteins associated with endocrine signalling, the extracellular matrix, the complement cascade and milk. A broad spectrum of proteases has been implicated in the generation of natural crypteins that appear to play a role in modulating diverse biological processes, such as angiogenesis, immune function and cell growth. The proteolytic liberation of crypteins with novel activities represents an important mechanism for increasing diversity of protein function and potentially offers new opportunities for protein-based therapeutics.

Antiadhesive Sites Present in the Fibronectin Type III-Like Repeats of Human Plasma Fibronectin

We have found that fibronectin (FN) has a functional cryptic site opposing cell adhesion to extracellular matrix (ECM): a synthetic FN peptide derived from the 14th FN type III-like (FN-III) repeat, termed peptide FNIII14, inhibits cell adhesion to the FN without binding to beta1 integrins. This antiadhesive activity of peptide FNIII14 depends on its C-terminal amino acid sequence YTIYVIAL. A 50-kDa membrane protein (p50) has been detected as a specific binding protein of peptide FNIII14. Here we showed that antiadhesive activity of peptide FNIII14 was depedent upon the presence of p50 on cell surfaces. Furthermore, we found that there exists a sequence, analogous to the YTIYVIAL, in the 10th FN-III repeat of the FN molecule and that a FN peptide containing this analogous sequence, termed peptide FNIII10, inhibited cell adhesion to the FN. Peptide FNIII10 appeared to share p50 with peptide FNIII14 in expressing the antiadhesive activity. As a physiological consequence of decreased adhesion, peptides FNIII10 and FNIII14 accelerated the anoikis-like apoptosis of normal fibroblasts by down-regulating Bcl-2 expression through blocking the FAK/PI3K/Akt signaling pathway. Thus, the YTIYVIAL-related sequences of the FN molecule may be involved in cell regulation by modulating negatively cell adhesion to the ECM, in which p50 probably serves as a membrane receptor.

Distribution of SPARC during neovascularisation of degenerative aortic stenosis

OBJECTIVE

To examine the hypothesis that degenerative aortic stenosis (AS) is associated with the development of blood vessels and the expression of the secreted protein, acidic and rich in cysteine/osteonectin (SPARC), a matricellular protein that is involved in ossification, the modulation of angiogenesis and the production of metalloproteinases.

METHODS

30 surgically excised AS valves and 20 normal aortic valves were studied.

RESULTS

Blood vessels were detected in the aortic valves from patients with degenerative AS, whereas normal valves were avascular structures. Blood vessels in AS valves expressed endothelial nitric oxide synthase, CD34 and von Willebrand factor (vWF). Blood vessels were located in three distinct regions: near calcified nodules, under the leaflet border and in rich cellular areas forming cell islands. Blood vessels were predominantly present in early and intermediate grades of calcification. Cell islands were densely populated by CD45-positive cells where endothelial cells (CD34+, vWF+) forming cord-like structures were present. Immunoblotting detected SPARC only in AS valves and immunohistological analysis located SPARC in mature blood vessels. The proportion of blood vessels positive for SPARC was higher in valves with a lower grade of calcification. In cell islands, SPARC was distributed to mature blood vessels and to macrophages, where it co-located with matrix metalloproteinase-9, whereas no expression was detected in endothelial cells forming cord-like structures.

CONCLUSION

The localisation of SPARC to mature blood vessels and its predominant expression in AS valves with a lower calcification grade suggest that the spatial and temporal distribution of this matricellular protein is tightly controlled to participate in the neovascularisation of AS valves.

Endorepellin In Vivo: Targeting the Tumor Vasculature and Retarding Cancer Growth and Metabolism

BACKGROUND

The antiangiogenic approach to controlling cancer requires a better understanding of angiogenesis and the discovery of new compounds that modulate this key biological process. Here we investigated the role of endorepellin, an angiostatic protein fragment that is derived from the C-terminus of perlecan, a heparan sulfate proteoglycan, in controlling tumor angiogenesis in vivo.

METHODS

We administered human recombinant endorepellin systemically to mice bearing orthotopic squamous carcinoma xenografts or syngeneic Lewis lung carcinoma tumors. We monitored tumor growth, angiogenesis, metabolism, hypoxia, and mitotic index by using quantitative immunohistochemistry and positron emission tomography scan imaging. In addition, we determined the localization of injected endorepellin using near-infrared labeling and immunohistochemistry of frozen tumor sections. Finally, we isolated tumor-derived endothelial cells and tested whether endorepellin could interact with these cells and disrupt in vitro capillary morphogenesis. All statistical tests were two-sided.

RESULTS

Endorepellin specifically targeted the tumor vasculature as determined by immunohistochemical analysis and accumulated in the tumor perivascular zones where it persisted for several days as discrete deposits. This led to inhibition of tumor angiogenesis (as measured by decreased CD31-positive cells, mean control = 1902 CD31-positive pixels, mean endorepellin treated = 343.9, difference between means = 1558, 95% confidence interval [CI] = 1296 to 1820, P<.001), enhanced tumor hypoxia, and a statistically significant decrease in tumor metabolism and mitotic index (as measured by decreased Ki67-positive cells, mean control Ki67 pixels = 5970, mean endorepellin-treated Ki67 pixels = 3644, difference between means = 2326, 95% CI = 1904 to 2749, P<.001) compared to untreated controls. Endorepellin was actively internalized by tumor-derived endothelial cells causing a redistribution of alpha2beta1 integrin such that both proteins colocalized to punctate deposits in the perivascular region. Endorepellin treatment inhibited in vitro capillary morphogenesis of both normal and tumor-derived endothelia.

CONCLUSIONS

Our results provide support for the hypothesis that endorepellin is an effective antitumor vasculature agent that could be used as a therapeutic modality to combat cancer.

Integrin Receptor Activation Triggers Converging Regulation of Cav1.2 Calcium Channels by c-Src and Protein Kinase A Pathways

L-type, voltage-gated Ca2+ channels (CaL) play critical roles in brain and muscle cell excitability. Here we show that currents through heterologously expressed neuronal and smooth muscle CaL channel isoforms are acutely potentiated following alpha5beta1 integrin activation. Only the alpha1C pore-forming channel subunit is critical for this process. Truncation and site-directed mutagenesis strategies reveal that regulation of Cav1.2 by alpha5beta1 integrin requires phosphorylation of alpha1C C-terminal residues Ser1901 and Tyr2122. These sites are known to be phosphorylated by protein kinase A (PKA) and c-Src, respectively, and are conserved between rat neuronal (Cav1.2c) and smooth muscle (Cav1.2b) isoforms. Kinase assays are consistent with phosphorylation of these two residues by PKA and c-Src. Following alpha5beta1 integrin activation, native CaL channels in rat arteriolar smooth muscle exhibit potentiation that is completely blocked by combined PKA and Src inhibition. Our results demonstrate that integrin-ECM interactions are a common mechanism for the acute regulation of CaL channels in brain and muscle. These findings are consistent with the growing recognition of the importance of integrin-channel interactions in cellular responses to injury and the acute control of synaptic and blood vessel function.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

TSC-36/FRP inhibits vascular smooth muscle cell proliferation and migration

OBJECTIVE

In-stent restenosis is a vascular proliferation/migration disorder characterized by hyperplasia of vascular smooth muscle cells (VSMCs). Because mounting evidence suggests that the therapeutic potential of anti-proliferation and anti-migration therapy, we investigated possible inhibitory effects of the matricellular protein TGF-beta-stimulated clone 36 (TSC-36) on vascular smooth muscle cell proliferation and migration in vitro and in vivo.

METHODS

Human umbilical artery smooth muscle cells (SMCs) were treated with inducting agents daidzein or estradiol. TSC-36 expression was detected by nested competitive PCR and in situ hybridization. TSC-36 was expressed in Origami (DE3) cells. The recombinant protein was used to immunize rabbits to produce polyclonal antibodies. VSMCs were treated with various concentrations of recombinant TSC-36 (rTSC-36) protein and daidzein. The MTT assay was used to analyze for cell proliferation. A transwell system was used to detect cell migration. Flow cytometry was used to detect cell phase. A rat carotid artery balloon injury model was duplicated. The rats were treated with daidzein or solvent control. Animals were sacrificed 5 weeks later, and injured arteries were taken for pathology and histology.

RESULTS

TSC-36 mRNA and protein expression was induced in SMCs. Cell proliferation and migration were inhibited by rTSC-36. rTSC-36 caused accumulation of SMCs in G2 phase. The inducting agent daidzein decreased neo-intima proliferation. TSC-36 mRNA and protein expression was induced and expressed in the neo-intima.

CONCLUSION

TSC-36 can be induced in VSMCs and inhibits VSMCs proliferation in vitro and in vivo.

Kringle 5 of human plasminogen induces apoptosis of endothelial and tumor cells through surface-expressed glucose-regulated protein 78

Kringle 5 (K5) of human plasminogen has been shown to inhibit angiogenesis by inducing the apoptosis of proliferating endothelial cells. Peptide regions around the lysine-binding pocket of K5 largely mediate these effects, particularly the peptide PRKLYDY, which we show to compete with K5 for the binding to endothelial cells. The cell surface binding site for K5 that mediates these effects has not been defined previously. Here, we report that glucose-regulated protein 78, exposed on cell surfaces of proliferating endothelial cells as well as on stressed tumor cells, plays a key role in the antiangiogenic and antitumor activity of K5. We also report that recombinant K5-induced apoptosis of stressed HT1080 fibrosarcoma cells involves enhanced activity of caspase-7, consistent with the disruption of glucose-regulated protein 78-procaspase-7 complexes. These results establish recombinant K5 as an inhibitor of a stress response pathway, which leads to both endothelial and tumor cell apoptosis.

Expression of collagen XVIII mRNA and protein in human umbilical vein and placenta

Endostatin is a potent angiogenic inhibitor that is derived from collagen XVIII by proteolytic cleavage. Localization of collagen XVIII has been reported in the basement membrane of blood vessels. To examine the involvement of collagen XVIII/endostatin during pregnancy, the distribution of collagen XVIII/endostatin protein in human umbilical vein was evaluated by immunohistochemistry. The expression of collagen XVIII/endostatin in cultured human umbilical vein endothelial cells (HUVEC) was also examined by immunocytochemistry and Northern blot analysis. To examine the release of endostatin in vivo and in vitro, concentrations of endostatin in umbilical venous blood and in HUVEC culture medium were determined using an enzyme-linked immunosorbent assay. Collagen XVIII/endostatin protein was localized to endothelial cells and their basement membrane in the umbilical vein. The expression of collagen XVIII mRNA and protein was detected in HUVEC. However, endostatin was not detected in umbilical venous blood or in HUVEC culture medium. The absence of endostatin release and the presence of its parental protein, collagen XVIII, suggest that the cleavage mechanisms of endostatin might be strongly inhibited under the physiological conditions present during pregnancy. It is therefore considered that vasculature in the feto-placental unit is highly angiogenic, even at the time of parturition.

SPARC and tumor growth: where the seed meets the soil?

Matricellular proteins mediate interactions between cells and their extracellular environment. This functional protein family includes several structurally unrelated members, such as SPARC, thrombospondin 1, tenascin C, and osteopontin, as well as some homologs of these proteins, such as thrombospondin 2 and tensascin X. SPARC, a prototypic matricellular protein, and its homolog hevin, have deadhesive effects on cultured cells and have been characterized as antiproliferative factors in some cellular contexts. Both proteins are produced at high levels in many types of cancers, especially by cells associated with tumor stroma and vasculature. In this Prospect article we summarize evidence for SPARC and hevin in the regulation of tumor cell growth, differentiation, and metastasis, and we propose that matricellular proteins such as these perform critical functions in desmoplastic responses of tumors that culminate in their dissemination and eventual colonization of other sites.

Vasohibin: the feedback on a new inhibitor of angiogenesis

Angiogenesis is regulated in large part by the balance of various proangiogenic stimulators, such as VEGF, and a diverse group of endogenous inhibitors of angiogenesis, most of which are extrinsic to endothelial cells. With respect to the latter, until recently, none have appeared to be induced as a consequence of a specific, self-regulating, feedback inhibition response. A new inhibitor, called vasohibin, has been uncovered. Vasohibin is selectively induced in endothelial cells by proangiogenic stimulatory growth factors such as VEGF; it appears to operate as an intrinsic and highly specific feedback inhibitor of activated endothelial cells engaged in the process of angiogenesis.

Fibroblast growth factor receptor-1 mediates the inhibition of endothelial cell proliferation and the promotion of skeletal myoblast differentiation by SPARC: a role for protein kinase A

The role of the matricellular protein SPARC (secreted protein, acidic and rich in cysteine) in modulation of vascular cell proliferation is believed to be mediated, in part, by its ability to regulate the activity of certain growth factors through direct binding. In this study, we demonstrate that SPARC does not bind to basic fibroblast growth factor (bFGF/FGF-2) or interfere with complex formation between FGF-2 and its high-affinity FGF receptor-1 (FGFR1), yet both native SPARC and a peptide derived from the C-terminal high-affinity Ca(2+)-binding region of protein significantly inhibit ligand-induced autophosphorylation of FGFR1 (>80%), activation of mitogen-activated protein kinases (MAPKs) (>75%), and DNA synthesis in human microvascular endothelial cells (HMVEC) stimulated by FGF-2 (>80%). We also report that in the presence of FGF-2, a factor which otherwise stimulates myoblast proliferation and the repression of terminal differentiation, both native SPARC and the Ca(2+)-binding SPARC peptide significantly promote (>60%) the differentiation of the MM14 murine myoblast cell line that expresses FGFR1 almost exclusively. Moreover, using heparan sulfate proteoglycan (HSPG)-deficient myeloid cells and porcine aortic endothelial cells (PAECs) expressing chimeric FGFR1, we show that antagonism of FGFR1-mediated DNA synthesis and MAPK activation by SPARC does not require the presence of cell-surface, low-affinity FGF-2 receptors, but can be mediated by an intracellular mechanism that is independent of an interaction with the extracellular ligand-binding domain of FGFR1. We also report that the inhibitory effect of SPARC on DNA synthesis and MAPK activation in endothelial cells is mediated in part (>50%) by activation of protein kinase A (PKA), a known regulator of Raf-MAPK pathway. SPARC thus modulates the mitogenic effect of FGF-2 downstream from FGFR1 by selective regulation of the MAPK signaling cascade.

Cleavage of the matricellular protein SPARC by matrix metalloproteinase 3 produces polypeptides that influence angiogenesis

SPARC, a matricellular protein that affects cellular adhesion and proliferation, is produced in remodeling tissue and in pathologies involving fibrosis and angiogenesis. In this study we have asked whether peptides generated from cleavage of SPARC in the extracellular milieu can regulate angiogenesis. Matrix metalloproteinase (MMP)-3, but not MMP-1 or 9, showed significant activity toward SPARC. Limited digestion of recombinant human (rhu)SPARC with purified catalytic domain of rhuMMP-3 produced three major fragments, which were sequenced after purification by HPLC. Three synthetic peptides (Z-1, Z-2, and Z-3) representing motifs from each fragment were tested in distinct assays of angiogenesis. Peptide Z-1 (3.9 kDa, containing a Cu2+-binding sequence KHGK) exhibited a biphasic effect on [3H]thymidine incorporation by cultured endothelial cells and stimulated vascular growth in the chick chorioallantoic membrane (CAM). In contrast, peptides Z-2 (6.1 kDa, containing Ca2+-binding EF hand-1) and Z-3 (2.2 kDa, containing neither Cu2+-binding motifs nor EF hands), inhibited cell proliferation in a concentration-dependent manner and exhibited no effects on vessel growth in the CAM. Reciprocal results were obtained in a migration assay in native collagen gels: peptide Z-1 was ineffective over a range of concentrations, whereas Z-2 or Z-3 stimulated cell migration. Therefore, proteolysis of SPARC by MMP-3 produced peptides that regulate endothelial cell proliferation and/or migration in vitro in a mutually exclusive manner. One of these peptides containing KHGK also demonstrated a concentration-dependent effect on angiogenesis.

Perlecan protein core interacts with extracellular matrix protein 1 (ECM1), a glycoprotein involved in bone formation and angiogenesis

The goal of this study was to discover novel partners for perlecan, a major heparan sulfate proteoglycan of basement membranes, and to examine new interactions through which perlecan may influence cell behavior. We employed the yeast two-hybrid system and used perlecan domain V as bait to screen a human keratinocyte cDNA library. Among the strongest interacting clones, we isolated a approximately 1.6-kb cDNA insert that encoded extracellular matrix protein 1 (ECM1), a secreted glycoprotein involved in bone formation and angiogenesis. The sequencing of the clone revealed the existence of a novel splice variant that we name ECM1c. The interaction was validated by co-immunoprecipitation studies, using both cell-free systems and mammalian cells, and the specific binding site within each molecule was identified employing various deletion mutants. The C terminus of ECM1 interacted specifically with the epidermal growth factor-like modules flanking the LG2 subdomain of perlecan domain V. Perlecan and ECM1 were also co-expressed by a variety of normal and transformed cells, and immunohistochemical studies showed a partial expression overlap, particularly around dermal blood vessels and adnexal epithelia. ECM1 has been shown to regulate endochondral bone formation, stimulate the proliferation of endothelial cells, and induce angiogenesis. Similarly, perlecan plays an important role in chondrogenesis and skeletal development, as well as harboring pro- and anti-angiogenic activities. Thus, a physiological interaction could also occur in vivo during development and in pathological events, including tissue remodeling and tumor progression.

Integrins modulate fast excitatory transmission at hippocampal synapses

The present study provides the first evidence that adhesion receptors belonging to the integrin family modulate excitatory transmission in the adult rat brain. Infusion of an integrin ligand (the peptide GRGDSP) into rat hippocampal slices reversibly increased the slope and amplitude of excitatory postsynaptic potentials. This effect was not accompanied by changes in paired pulse facilitation, a test for perturbations to transmitter release, or affected by suppression of inhibitory responses, suggesting by exclusion that alterations to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptors cause the enhanced responses. A mixture of function-blocking antibodies to integrin subunits alpha(3), alpha(5), and alpha(v) blocked ligand effects on synaptic responses. The ligand-induced increases were (i) blocked by inhibitors of Src tyrosine kinase, antagonists of N-methyl-d-aspartate receptors, and inhibitors of calcium calmodulin-dependent protein kinase II and (ii) accompanied by phosphorylation of both the Thr(286) site on calmodulin-dependent protein kinase II and the Ser(831) site on the GluR1 subunit of the AMPA receptor. N-Methyl-d-aspartate receptor antagonists blocked the latter two phosphorylation events, but Src kinase inhibitors did not. These results point to the conclusion that synaptic integrins regulate glutamatergic transmission and suggest that they do this by activating two signaling pathways directed at AMPA receptors.

Angiogenesis in hematologic malignancies

Angiogenesis is defined as the formation of new capillaries from preexisting blood vessels and plays an important role in the progression of solid tumors. Recently a similar relationship has been described in several hematologic malignancies. Expression of the angiogenic peptides vascular endothelial growth factor (VEGF) and basic fibroblast growth factor correlates with clinical characteristics in leukemia and non-Hodgkin's-lymphoma and the serum/plasma concentrations serve as predictors of poor prognosis. Increased bone marrow microvessels in multiple myeloma (MM) are correlated with decreased overall survival. Thalidomide which has antiangiogenic effects and direct cytotoxic effects was found to be effective in MM, myelodysplastic syndrome and acute myeloid leukemia (AML). Preliminary data indicate activity of VEGF-tyrosine kinase inhibitors in AML. Clinical research is now aimed at testing antiangiogenic treatment strategies in several hematologic neoplasms as well as identifying the best candidate patients for specific approaches.

Endorepellin, a novel inhibitor of angiogenesis derived from the C terminus of perlecan

Perlecan, a ubiquitous basement membrane heparan sulfate proteoglycan, plays key roles in blood vessel growth and structural integrity. We discovered that the C terminus of perlecan potently inhibited four aspects of angiogenesis: endothelial cell migration, collagen-induced endothelial tube morphogenesis, and blood vessel growth in the chorioallantoic membrane and in Matrigel plug assays. The C terminus of perlecan was active at nanomolar concentrations and blocked endothelial cell adhesion to fibronectin and type I collagen, without directly binding to either protein; henceforth we have named it "endorepellin." We also found that endothelial cells possess a significant number of high affinity (K(d) of 11 nm) binding sites for endorepellin and that endorepellin binds endostatin and counteracts its anti-angiogenic effects. Thus, endorepellin represents a novel anti-angiogenic product, which may retard tumor neovascularization and hence tumor growth in vivo.

CRIM1 is involved in endothelial cell capillary formation in vitro and is expressed in blood vessels in vivo

In endothelial cells that form capillary-like structures in vitro a variety of genes is upregulated as we have demonstrated previously. In addition to well known genes, we also identified genes never described in endothelial cells before. Here, we report the further characterization of one selected gene called cysteine-rich motor neuron 1 (CRIM1). CRIM1 is strongly upregulated in endothelial cells during tube formation and is expressed by a variety of adherent growing cell lines whereas cell lines grown in suspension do not express CRIM1. By using antisense technology we were able to inhibit CRIM1 expression and demonstrate impaired formation of capillary-like structures in vitro in transfected endothelial cells. Furthermore, we show that CRIM1 is a glycosylated type I transmembrane protein, that accumulates at sites of close cell-to-cell contact upon stimulation. Finally, we found CRIM1 protein to be expressed by endothelial cells of the inner lining of blood vessels in vivo. Taken together our results imply a possible role of CRIM1 in capillary formation and maintainance during angiogenesis.

Angiogenesis in epithelian ovarian cancer

Angiogenesis, the development of new blood vessels from the existing vasculature, is an essential component of solid tumour growth and metastasis. Several angiogenic factors are expressed by many tumours, suggesting that tumours promote their own vascularisation by activating the host endothelium. This review will discuss various angiogenic stimulators and inhibitors in epithelian ovarian cancer (EOC), including vascular endothelial growth factor and platelet derived endothelial cell growth factor/thymidine phosphorylase. The analysis of tumour vascularisation by microvessel density will also be discussed and the relevance of these markers of angiogenesis in the prognosis of EOC will be assessed.

Molecular basis of endothelial cell morphogenesis in three-dimensional extracellular matrices

Although many studies have focused on blood vessel development and new blood vessel formation associated with disease processes, the question of how endothelial cells (ECs) assemble into tubes in three dimensions (i.e., EC morphogenesis) remains unanswered. EC morphogenesis is particularly dependent on a signaling axis involving the extracellular matrix (ECM), integrins, and the cytoskeleton, which regulates EC shape changes and signals the pathways necessary for tube formation. Recent studies reveal that genes regulating this matrix-integrin-cytoskeletal (MIC) signaling axis are differentially expressed during EC morphogenesis. The Rho GTPases represent an important class of molecules involved in these events. Cdc42 and Rac1 are required for the process of EC intracellular vacuole formation and coalescence that regulates EC lumen formation in three-dimensional (3D) extracellular matrices, while RhoA appears to stabilize capillary tube networks. Once EC tube networks are established, supporting cells, such as pericytes, are recruited to further stabilize these networks, perhaps by regulating EC basement membrane matrix assembly. Furthermore, we consider recent work showing that EC morphogenesis is balanced by a tendency for newly formed tubes to regress. This morphogenesis-regression balance is controlled by differential gene expression of such molecules as VEGF, angiopoietin-2, and PAI-1, as well as a plasmin- and matrix metalloproteinase-dependent mechanism that induces tube regression through degradation of ECM scaffolds that support EC-lined tubes. It is our hope that this review will stimulate increased interest and effort focused on the basic mechanisms regulating capillary tube formation and regression in 3D extracellular matrices.

Matricellular proteins: extracellular modulators of cell function

The term 'matricellular' has been applied to a group of extracellular proteins that do not contribute directly to the formation of structural elements in vertebrates but serve to modulate cell-matrix interactions and cell function. Our understanding of the mode of action of matricellular proteins has been advanced considerably by the recent elucidation of the phenotypes of mice that are deficient in these proteins. In many cases, aspects of these phenotypes have illuminated previously unsuspected consequences of the lack of appropriate interactions of cells with their environment.

The antiangiogenic activity of cleaved high molecular weight kininogen is mediated through binding to endothelial cell tropomyosin

Conformationally altered proteins and protein fragments derived from the extracellular matrix and hemostatic system may function as naturally occurring angiogenesis inhibitors. One example of such a protein is cleaved high molecular weight kininogen (HKa). HKa inhibits angiogenesis by inducing apoptosis of proliferating endothelial cells, effects mediated largely by HKa domain 5. However, the mechanisms underlying the antiangiogenic activity of HKa have not been characterized, and its binding site on proliferating endothelial cells has not been defined. Here, we report that the induction of endothelial cell apoptosis by HKa, as well as the antiangiogenic activity of HKa in the chick chorioallantoic membrane, was inhibited completely by antitropomyosin monoclonal antibody TM-311. TM-311 also blocked the high-affinity Zn2+-dependent binding of HKa to both purified tropomyosin and proliferating endothelial cells. Confocal microscopic analysis of endothelial cells stained with monoclonal antibody TM-311, as well as biotin labeling of cell surface proteins on intact endothelial cells, revealed that tropomyosin exposure was enhanced on the surface of proliferating cells. These studies demonstrate that the antiangiogenic effects of HKa depend on high-affinity binding to endothelial cell tropomyosin.

Decorin suppresses tumor cell-mediated angiogenesis

The progressive growth of most neoplasms is dependent upon the establishment of new blood vessels, a process regulated by tumor-secreted factors and matrix proteins. We examined the in vitro and in vivo angiogenic ability of conditioned media obtained from fibrosarcoma, carcinoma, and osteosarcoma cells and their decorin-transfected counterparts. Human endothelial cells were investigated in vitro by evaluating three essential steps of angiogenesis: migration, attachment, and differentiation. On the whole, wild-type tumor cell-secretions enhanced endothelial cell attachment, migration, and differentiation, whereas their decorin-expressing forms inhibited these processes. Similarly, decorin-containing media suppressed endothelial cell sprouting in an ex vivo aortic ring assay. Since angiogenesis is an important component of tumor expansion, the growth rate of these cells as tumor xenografts was examined by implantation in nude mice. In vivo, the decorin-expressing tumor xenografts grew at markedly lower rates and showed a significant suppression of neovascularization. Immunohistochemical, Northern and Western blot analyses indicated that the decorin-expressing cells produced vascular endothelial growth factor (VEGF) at markedly reduced rates vis-á-vis their wild-type counterparts. Specificity of this process was confirmed by experiments where addition of recombinant decorin to the wild-type tumor cells caused 80-95% suppression of VEGF mRNA and protein. These results provide a novel mechanism of action for decorin, and indicate that decorin could adversely affect in vivo tumor growth by suppressing the endogenous tumor cell production of a powerful angiogenic stimulus.

Aging and survival of cutaneous microvasculature

The growth and turnover of blood vessels in the skin is fundamental in normal development, wound repair, hair follicle cycling, tumor cell metastasis, and in many different states of cutaneous pathology. Whereas many investigations are focused on mechanisms of angiogenesis in the skin, the influence of cellular aging and replicative senescence (i.e., the inability, after a critical number of population doublings, to replicate) on microvascular remodeling events has received relatively less attention. In this article, we review the clinical and pathologic relationships associated with cutaneous vascular aging and update current knowledge of endothelial cell survival characteristics. A hypothesis is presented in which endothelial cell aging and survival are linked to molecular mechanisms controlling cell proliferation, quiescence, apoptosis, and cellular senescence. We review recent results demonstrating how activation of telomerase in human dermal microvascular endothelial cells affects their durability both in vitro and in vivo and conclude by linking these studies with current concepts involving endothelial cell precursors, control of postnatal somatic cell telomerase activity, and murine model systems.

alpha(4)beta(1) Integrin activation of L-type calcium channels in vascular smooth muscle causes arteriole vasoconstriction

A pathway for the regulation of vascular tone appears to involve coupling between integrins and extracellular matrix proteins or their fragments and the subsequent modulation of ion movement across the smooth muscle cell membrane. Here, we report that the activation of L-type voltage-activated Ca(2+) channels occurs through a novel interaction of alpha(4)beta(1) integrin with peptides containing the Leu-Asp-Val (LDV) integrin--binding sequence, which is found in the CS-1 region of an alternately spliced fibronectin variant. Experiments were conducted on arterioles isolated from rat skeletal muscle. Arterioles exhibited sustained concentration-dependent vasoconstriction to LDV peptides but not to Leu-Glu-Val (LEV) control peptides. The constriction was associated with increased smooth muscle cell [Ca(2+)](i), as measured by using fura 2. The response could be inhibited with a function-blocking anti--alpha(4) integrin antibody. Removal of the endothelium did not alter the vasoconstrictor response. Further experiments demonstrated that the vasoconstriction was abolished by the L-type Ca(2+) channel inhibitor nifedipine and the Src family kinase inhibitor PP2. In studies of isolated smooth muscle cells using whole-cell patch-clamp methods, the L-type current was enhanced by the LDV but not LEV peptide and was blocked by PP2 or antibodies to alpha(4) integrin. Collectively, these data indicate that activation of alpha(4)beta(1) integrin leads to enhanced influx of Ca(2+) through L-type channels by activating a tyrosine kinase pathway, leading to vasoconstriction. Involvement of integrins in the modulation of vascular tone may be particularly important in vascular responses to mechanical signals, such as pressure and flow, and to tissue injury after damage to the extracellular matrix.

Anti-angiogenic effects of the thienopyridine SR 25989 in vitro and in vivo in a murine pulmonary metastasis model

Neovascularisation is a key step in tumour growth and establishment of distant metastases. We have recently demonstrated that the thienopyridine SR 25989 an enantiomer of the anti-aggregant clopidogrel (Plavix) lacking anti-aggregant activity, inhibits endothelial cell proliferation in vitro by increasing the expression of endogenous thrombospondin-1, a natural potent inhibitor of angiogenesis. The anti-angiogenic effect of SR 25989 was further assessed in vitro in a quantitative assay of angiogenesis comprising a fragment of rat aorta embedded in a fibrin gel and in vivo in a pulmonary metastatic model using C57BL/6 mice inoculated in the foot pad with the highly metastatic melanoma cell line B16 F10. SR 25989 induced a dose dependent inhibition of spontaneous microvessel development in vitro reaching half maximal inhibition at around less than 50 microM and caused platelet derived growth factor induced angiogenesis to regress as a function of thienopyridine concentration. In vivo, SR 25989 did not alter significantly the growth rate of the primary tumour in the foot pad and did not inhibit development of inguinal nodes which appeared after amputation. However, the number and size of lung metastases were reduced in treated animals when examined at the time of sacrifice. In addition, the few metastases over 1 mm3 did not show any neovascularisation, as confirmed by negative von Willebrand immunostaining and in contrast to intense vascularisation seen in metastases developed by control mice. These results confirm that SR 25989 possesses potent anti-angiogenic properties and is able to inhibit metastatic dissemination and growth. The lack of effect on the primary tumour and inguinal nodes illustrates the complexity of the mechanisms involved in tumoural neo-angiogenesis and points out the possibility for distinct processes leading to neovascularisation in primary tumour as opposed to metastases.

Inhibition of angiogenesis by two-chain high molecular weight kininogen (HKa) and kininogen-derived polypeptides

We recently reported that the two-chain form of human high molecular weight kininogen (HKa) inhibits angiogenesis by inducing endothelial cell apoptosis (Zhang et al. 2000). This property appears to be primarily conferred by HKa domain 5 (HKa D5). In this manuscript, we further characterize the activity of these polypeptides toward proliferating endothelial cells, as well as their in vivo anti-angiogenic activity in the chick chorioallantoic membrane (CAM). We also demonstrate that short peptides derived from endothelial cell binding regions in HKa domains 3 and 5 inhibit endothelial cell proliferation and induce endothelial cell apoptosis. Like HKa and HKa D5, peptides derived from the latter domain induce endothelial cell apoptosis in a Zn(2+)-dependent manner, while those derived from domain 3 function independently of Zn2+. The implications of these findings to the regulation of angiogenesis and development of anti-angiogenic therapeutics are discussed.

Increased fibrovascular invasion of subcutaneous polyvinyl alcohol sponges in SPARC-null mice

The expression of SPARC (secreted protein acidic and rich in cysteine/osteonectin/BM-40) is elevated in endothelial cells participating in angiogenesis in vitro and in vivo. SPARC acts on endothelial cells to elicit changes in cell shape and to inhibit cell cycle progression. In addition, SPARC binds to and diminishes the mitotic activity of vascular endothelial growth factor. To determine the effect(s) of SPARC on angiogenic responses in vivo, we implanted polyvinyl alcohol sponges subcutaneously into wild-type and SPARC-null mice. On days 12 and 20 following implantation, SPARC-null mice showed increased cellular invasion of the sponges in comparison to wild-type mice. Areas of the sponge with the highest cell density exhibited the highest numbers of vascular profiles in both wild-type and SPARC-null animals. The endothelial component of the vessels was substantiated by immunoreactivity with three different markers specific for endothelial cells. Although sponges from SPARC-null relative to wild-type mice were populated by significantly more cells and blood vessels, an increase in the ratio of vascular to nonvascular cells was not apparent. No differences in the percentage of proliferating cells within the sponge were detected between wild-type and SPARC-null sections. However, elevated levels of vascular endothelial growth factor were associated with sponges from SPARC-null versus wild-type mice. An increase in vascular endothelial growth factor production was also observed in SPARC-null primary dermal fibroblasts relative to those of wild-type cells. In conclusion, we have shown that the fibrovascular invasion of polyvinyl alcohol sponges is enhanced in mice lacking SPARC, and we propose that increased levels of vascular endothelial growth factor account, at least in part, for this response.

Role of the matrix metalloproteinase and plasminogen activator-plasmin systems in angiogenesis

Extracellular proteolysis is an absolute requirement for new blood vessel formation (angiogenesis). This review examines the role of the matrix metalloproteinase (MMP) and plasminogen activator (PA)-plasmin systems during angiogenesis. Specifically, a role for gelatinases (MMP-2, MMP-9), membrane-type 1 MMP (MMP-14), the urokinase-type PA receptor, and PA inhibitor 1 has been clearly defined in a number of model systems. The MMP and PA-plasmin systems have also been implicated in experimental vascular tumor formation, and their role during this process will be examined. Antiproteolysis, particularly in the context of angiogenesis, has become a key target in therapeutic strategies aimed at inhibiting tumor growth and other diseases associated with neovascularization.

The short arm of the laminin gamma2 chain plays a pivotal role in the incorporation of laminin 5 into the extracellular matrix and in cell adhesion

Laminin 5 is a basement membrane component that actively promotes adhesion and migration of epithelial cells. Laminin 5 undergoes extracellular proteolysis of the γ2 chain that removes the NH₂-terminal short arm of the polypeptide and reduces the size of laminin 5 from 440 to 400 kD. The functional consequence of this event remains obscure, although lines of evidence indicate that cleavage of the γ2 chain potently stimulated scattering and migration of keratinocytes and cancer cells. To define the biological role of the γ2 chain short arm, we expressed mutated γ2 cDNAs into immortalized γ2-null keratinocytes. By immunofluorescence and immunohistochemical studies, cell detachment, and adhesion assays, we found that the γ2 short arm drives deposition of laminin 5 into the extracellular matrix (ECM) and sustains cell adhesion. Our results demonstrate that the unprocessed 440-kD form of laminin 5 is a biologically active adhesion ligand, and that the γ2 globular domain IV is involved in intermolecular interactions that mediate integration of laminin 5 in the ECM and cell attachment.