Binding of factor VIIa to tissue factor on human fibroblasts leads to activation of phospholipase C and enhanced PDGF-BB–stimulated chemotaxis

High CD142 Level Marks Tumor-Promoting Fibroblasts with Targeting Potential in Colorectal Cancer

Colorectal cancer (CRC) has a high incidence and is one of the leading causes of cancer-related death. The accumulation of cancer-associated fibroblasts (CAF) induces an aggressive, stem-like phenotype in tumor cells, and it indicates a poor prognosis. However, cellular heterogeneity among CAFs and the targeting of both stromal and CRC cells are not yet well resolved. Here, we identified CD142high fibroblasts with a higher stimulating effect on CRC cell proliferation via secreting more hepatocyte growth factor (HGF) compared to CD142low CAFs. We also found that combinations of inhibitors that had either a promising effect in other cancer types or are more active in CRC compared to normal colonic epithelium acted synergistically in CRC cells. Importantly, heat shock protein 90 (HSP90) inhibitor selected against CD142high fibroblasts, and both CRC cells and CAFs were sensitive to a BCL-xL inhibitor. However, targeting mitogen-activated protein kinase kinase (MEK) was ineffective in fibroblasts, and an epigenetic inhibitor selected for a tumor cell population with markers of aggressive behavior. Thus, we suggest BCL-xL and HSP90 inhibitors to eliminate cancer cells and decrease the tumor-promoting CD142high CAF population. This may be the basis of a strategy to target both CRC cells and stromal fibroblasts, resulting in the inhibition of tumor relapse.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Regulation of coagulation by tissue factor pathway inhibitor: Implications for hemophilia therapy

Tissue factor pathway inhibitor (TFPI) is an alternatively spliced anticoagulant protein that primarily dampens the initiation phase of coagulation before thrombin is generated. As such, TFPI's actions are localized to cells expressing TF and to sites of injury, where it is an important regulator of bleeding in hemophilia. The major splice isoforms TFPIα and TFPIβ localize to different sites within and surrounding the vasculature. Both forms directly inhibit factor Xa (FXa) via their Kunitz 2 domain and inhibit TF-FVIIa via their Kunitz 1 domain in a tight complex primarily localized to cells. By forming complexes localized to distinct cellular microenvironments and engaging additional cell surface receptors, TFPI alters cellular trafficking and signaling pathways driven by coagulation proteases of the TF pathway. TFPIα, which circulates in complex with FV and protein S, also serves an inhibitor of FXa independent of the TF initiation complex and prevents the formation of an active prothrombinase. This regulation of thrombin generation in the context of vessel injury is effectively blocked by antibodies to Kunitz 2 domain of TFPI and exploited as a therapy to restore efficient hemostasis in hemophilia.

Platelet-Derived PDGFB Promotes Recruitment of Cancer-Associated Fibroblasts, Deposition of Extracellular Matrix and Tgfβ Signaling in the Tumor Microenvironment

Platelets constitute a major reservoir of platelet-derived growth factor B (PDGFB) and are continuously activated in the tumor microenvironment, exposing tumors to the plethora of growth factors contained in platelet granules. To address the specific role of platelet-derived PDGFB in the tumor microenvironment, we have created a mouse model with conditional knockout of PDGFB in platelets (pl-PDGFB KO). Lack of PDGFB in platelets resulted in 10-fold lower PDGFB concentration in the tumor microenvironment, fewer cancer-associated fibroblasts and reduced deposition of the extracellular matrix (ECM) molecules fibronectin and collagen I in the orthotopic RIP1-Tag2 model for pancreatic neuroendocrine cancer. Myosin light chain phosphorylation, promoting cell contraction and, consequently, the mechano-induced release of active transforming growth factor (TGF) β from extracellular compartments, was reduced in tumors from pl-PDGFB KO mice. In agreement, TGFβ signaling, measured as phosphorylated Smad2, was significantly hampered in tumors from mice lacking PDGFB in their platelets, providing a plausible explanation for the reduced deposition of extracellular matrix. These findings indicate a major contribution of platelet-derived PDGFB to a malignant transformation of the tumor microenvironment and address for the first time the role of PDGFB released specifically from platelets in the remodeling of the ECM in tumors.

Activation of β1 integrins and caveolin-1 by TF/FVIIa promotes IGF-1R signaling and cell survival

The tissue factor/coagulation factor VIIa (TF/FVIIa) complex induces transactivation of the IGF-1 receptor (IGF-1R) in a number of different cell types. The mechanism is largely unknown. The transactivation leads to protection from apoptosis and nuclear translocation of the IGF-1R. The aim of this study was to clarify the signaling pathway between TF and IGF-1R after FVIIa treatment with PC3 and DU145 prostate or MDA-MB-231 breast cancer cells as model systems. Protein interactions, levels, and phosphorylations were assessed by proximity ligation assay or flow cytometry in intact cells and by western blot on cell lysates. The transactivation of the IGF-1R was found dependent on TF/FVIIa-induced activation of β1-integrins. A series of experiments led to the conclusion that the caveolae protein caveolin-1 prevented IGF-1R activation in resting cells via its scaffolding domain. TF/FVIIa/β1-integrins terminated this inhibition by activation of Src family kinases and subsequent phosphorylation of caveolin-1 on tyrosine 14. This phosphorylation was not seen after treatment with PAR1 or PAR2 agonists. Consequently, the protective effect of FVIIa against apoptosis induced by the death receptor agonist TRAIL and the de novo synthesis of cyclin D1 induced by nuclear IGF-1R accumulation were both significantly reduced by down-regulation of β1-integrins or overexpression of the caveolin-1 scaffolding domain. In conclusion, we present a plausible mechanism for the interplay between TF and IGF-1R involving FVIIa, β1-integrins, Src family proteins, and caveolin-1. Our results increase the knowledge of diseases associated with TF and IGF-1R overexpression in general but specifically of TF-mediated signaling with focus on cell survival.

Endosomal NADPH-oxidase is critical for induction of the tissue factor gene in monocytes and endothelial cells

Antiphospholipid antibodies (aPL) have been shown to induce tissue factor (TF) expression in monocytes and endothelial cells. However, the underlying signal transduction has been more or less elusive in the past. We have recently shown that aPL enter the lysosomal route in monocytes and dendritic cells, and subsequently activate endosomal NADPH-oxidase (NOX). The generation of superoxide which is dismutated to hydrogen peroxide upregulates the intracellular toll like receptors (TLR) 7 and 8, and leads to robust production of inflammatory cytokines. Here we show that induction of TF by aPL follows the same signaling pathway. Inhibition of endosomal NOX by the anion channel blocker niflumic acid or capture of superoxide by the radical scavenger N-acetylcysteine blocks TF induction by aPL. Furthermore, monocytes from mice deficient in NOX2 do not increase TF surface expression in response to aPL, while cells from mice deficient in glutathione peroxidase- 1 (GPx-1) show an increased response. Unexpectedly, also induction of TF by tumour necrosis factor (TNF)⍺ and lipopolysaccharide (LPS) was strongly dependent on the activation of endosomal NOX. While TNF⍺ apparently depends almost fully on endosomal NOX, signalling of LPS is only partially dependent on this pathway. These data provide further insight into the well-known role of reactive oxygen species in the induction of TF expression and suggest that endosomal signalling may represent a central coordinating point in this process.

Targeting clotting proteins in cancer therapy - progress and challenges

Cancer-associated thrombosis remains a significant complication in the clinical management of cancer and interactions of the hemostatic system with cancer biology continue to be elucidated. Here, we review recent progress in our understanding of tissue factor (TF) regulation and procoagulant activation, TF signaling in cancer and immune cells, and the expanding roles of the coagulation system in stem cell niches and the tumor microenvironment. The extravascular functions of coagulant and anti-coagulant pathways have significant implications not only for tumor progression, but also for the selection of appropriate target specific anticoagulants in the therapy of cancer patients.

Tissue factor/factor VIIa signalling promotes cytokine-induced beta cell death and impairs glucose-stimulated insulin secretion from human pancreatic islets

AIMS/HYPOTHESIS

Patients diagnosed with type 1 or type 2 diabetes have elevated levels of coagulation factor VIIa (FVIIa) and its receptor tissue factor (TF) in their bloodstream. This may affect the fate of the beta cells. We aimed to study the effects of TF/FVIIa signalling on cytokine-induced beta cell death and islet function in vitro.

METHODS

Human pancreatic islets and MIN-6 beta cells were used to study TF mRNA and protein expression using real-time PCR, immunoblotting and flow cytometry. The effects of TF/FVIIa on cytokine-induced beta cell death were studied in MIN-6 cells and human pancreatic islets using cell-death ELISA and propidium iodide and cleaved caspase-3 staining. Effects of TF/FVIIa on the phosphorylation of p38, extracellular signal-regulated kinase and c-Jun N-terminal kinase (JNK) were investigated by immunoblotting. Glucose-stimulated insulin secretion (GSIS) from human islets was measured with an insulin ELISA.

RESULTS

A combination of the cytokines IL-1β, TNF-α and IFN-γ induced TF expression in human pancreatic islets and in beta cells. TF/FVIIa did not affect basal beta cell death but, independently of downstream coagulation activity, augmented beta cell death in response to cytokines. The effect of TF/FVIIa on cytokine-induced beta cell death was found to be dependent on the stress kinase JNK, since FVIIa addition potentiated cytokine-induced JNK activation and JNK inhibition abolished the effect of TF/FVIIa on cytokine-induced beta cell death. Moreover, TF/FVIIa signalling resulted in inhibition of GSIS from human pancreatic islets.

CONCLUSIONS/INTERPRETATION

These results indicate that TF/FVIIa signalling has a negative effect on beta cell function and promotes beta cell death in response to cytokines.

Role of the protein C receptor in cancer progression

The hemostatic system plays pleiotropic roles in cancer progression by shaping the tumor microenvironment and metastatic niches through thrombin-dependent fibrin deposition and platelet activation. Expanding experimental evidence implicates coagulation protease receptors expressed by tumor cells as additional players that directly influence tumor biology. Pro-angiogenic G protein-coupled signaling of TF through protease activated receptor 2 and regulation of tumor cell and vascular integrins through ligation by alternative spliced TF are established pathways driving tumor progression. Our recent work shows that the endothelial protein C receptor (EPCR), a stem cell marker in hematopoietic, neuronal and epithelial cells, is also crucial for breast cancer growth in the orthotopic microenvironment of the mammary gland. In aggressive triple-negative breast cancer cells, EPCR expression is a characteristic of cancer stem cell-like populations that have tumor initiating properties in vivo. Blocking antibodies to EPCR attenuate in vivo tumor growth and proliferation specifically of EPCR(+) cells on defined integrin matrices in vitro. We also showed that tumor-associated macrophages are a source for upstream coagulation proteases that can activate TF- and EPCR-dependent cellular responses, suggesting that tumor cells utilize the tumor microenvironment for tumor promoting coagulation protease signaling.

Identification of novel downstream molecules of tissue factor activation by comparative proteomic analysis

Tissue factor (TF) is both an initiator of blood coagulation and a signaling receptor. Using a proteomic approach, we investigated the role of TF in cell signaling when stimulated by its ligand, activated factor VII (FVIIa). From a 2-D difference gel electrophoresis (DIGE) study we found forty one spots that were differentially regulated over time in FVIIa stimulated cells or in comparison to nonstimulated cells. Mass spectrometry identifies 23 out of these as 13 different proteins. One of them, elongation factor 2 (EF-2), was investigated in greater detail by Western blot, a protein synthesis assay and cell cycle analysis. When tissue factor was stimulated by FVIIa, the phosphorylation of EF-2 increased which inactivates this protein. Analyzing the effect using site inactivated FVIIa (FVIIai), as well as the protease activated receptor 2 (PAR-2) agonist SLIGKV, indicated that the inactivation was not PAR-2 dependent. A panel of tissue factor mutants was analyzed further to try to pinpoint what part of the cytoplasmic domain that is needed for this effect. Performing a protein synthesis assay in two different cell lines we could confirm that protein synthesis decreased upon stimulation by FVIIa. Cell cycle analysis showed that FVIIa also promotes a higher degree of cell proliferation.

Tissue factor-integrin interactions in cancer and thrombosis: every Jack has his Jill

Tissue factor (TF) is a 47 kDa membrane protein that initiates coagulation by binding to FVII(a) and FX(a) and is a risk factor for thrombosis in many disease states. In addition to its coagulant activity, TF also influences cancer progression by triggering signaling effects via a group of G-protein coupled receptors named protease-activated receptors (PARs). TF localizes to cytoskeletal structures in migrating cells, influences cytoskeleton reorganization and promotes migration. Recently, integrins, important mediators of cell motility, have emerged as important binding partners for TF and influence both TF coagulant and PAR-2-dependent signaling functions. Direct binding of TF to integrins also impacts processes such as cell migration and signaling independent of PAR-2. A recently discovered alternatively spliced, soluble TF isoform also ligates integrins to augment angiogenesis, thus fuelling cancer progression. To date, the literature describes a complex interplay between different integrin subunits and distinct TF isoforms, but our understanding of TF-integrin bidirectional regulation remains clouded. In this review, we aim to summarize the existing knowledge on integrin-TF interaction and speculate on its relevance to physiology and pathology.

Tissue factor non-coagulant signaling - molecular mechanisms and biological consequences with a focus on cell migration and apoptosis

Tissue factor (TF), a transmembrane glycoprotein, is the main initiator of the blood coagulation cascade. TF is also recognized as a true signaling receptor. There is accumulating evidence that the downstream signaling effects of the TF complexes are transduced by several mechanisms, including: activation of protease-activated receptor (PAR)-1 and PAR-2, and the PAR-dependent pathways, via the TF cytoplasmic domain and by transactivation of receptor tyrosine kinases. Triggering of signaling cascades such as the mitogen-activated protein kinase and phosphoinositide 3-kinase/AKT pathways couples TF to a multitude of functions within the cell, such as proliferation, cell migration, and survival. Thus, TF has a Janus face; on the one hand, it has vital life-maintaining functions, and on the other it has harmful effects, exemplified by inflammation, the acute coronary syndromes, and cancer. TF mediates a broad spectrum of signaling mechanisms. Learning more about these different mechanisms/pathways will lead to new treatment strategies, which can ultimately be personalized.

The endothelial protein C receptor supports tissue factor ternary coagulation initiation complex signaling through protease-activated receptors

Protease-activated receptor (PAR) signaling is closely linked to the cellular activation of the pro- and anticoagulant pathways. The endothelial protein C receptor (EPCR) is crucial for signaling by activated protein C through PAR1, but EPCR may have additional roles by interacting with the 4-carboxyglutamic acid domains of procoagulant coagulation factors VII (FVII) and X (FX). Here we show that soluble EPCR regulates the interaction of FX with human or mouse tissue factor (TF)-FVIIa complexes. Mutagenesis of the FVIIa 4-carboxyglutamic acid domain and dose titrations with FX showed that EPCR interacted primarily with FX to attenuate FX activation in lipid-free assay systems. In human cell models of TF signaling, antibody inhibition of EPCR selectively blocked PAR activation by the ternary TF-FVIIa-FXa complex but not by the non-coagulant TF-FVIIa binary complex. Heterologous expression of EPCR promoted PAR1 and PAR2 cleavage by FXa in the ternary complex but did not alter PAR2 cleavage by TF-FVIIa. In murine smooth muscle cells that constitutively express EPCR and TF, thrombin and FVIIa/FX but not FVIIa alone induced PAR1-dependent signaling. Although thrombin signaling was unchanged, cells with genetically reduced levels of EPCR no longer showed a signaling response to the ternary complex. These results demonstrate that EPCR interacts with the ternary TF coagulation initiation complex to enable PAR signaling and suggest that EPCR may play a role in regulating the biology of TF-expressing extravascular and vessel wall cells that are exposed to limited concentrations of FVIIa and FX provided by ectopic synthesis or vascular leakage.

Induction of endothelial cell proliferation by recombinant and microparticle-tissue factor involves beta1-integrin and extracellular signal regulated kinase activation

OBJECTIVE

Increased levels of circulating tissue factor (TF) in the form of microparticles increase the risk of thrombosis. However, any direct influence of microparticle-associated TF on vascular endothelial cell proliferation is not known. In this study, the influence of recombinant and microparticle-associated TF on endothelial cell proliferation and mitogen-activated protein kinase signaling mechanisms was examined.

METHODS AND RESULTS

Incubation of human coronary artery endothelial cells with lipidated recombinant full-length TF, or TF-containing microparticles (50 to 200 pmol/L TF), increased the rate of cell proliferation and induced phosphorylation of extracellular signal regulated kinase 1 in a TF-dependent manner. Inhibition of extracellular signal regulated kinase 1/2 using PD98059 or extracellular signal regulated kinase 1/2 antisense oligonucleotides or inhibition of c-Jun N-terminal kinase reduced recombinant TF-mediated cell proliferation. PD98059 also reduced cell proliferation in response to TF-containing microparticles. Inclusion of FVIIa (5 nmol/L) and FXa (10 nmol/L) or preincubation of cells with an inhibitory anti-FVIIa antibody had no additional influence on TF-mediated cell proliferation. However, preincubation of exogenous TF with a beta1-integrin peptide (amino acids 579 to 799) reduced TF-mediated proliferation.

CONCLUSIONS

High concentrations of recombinant or microparticle-associated TF stimulate endothelial cell proliferation through activation of the extracellular signal regulated kinase 1/2 pathway, mediated through a novel mechanism requiring the interaction of exogenous TF with cell surface beta1-integrin and independent of FVIIa.

Tissue factor in cardiovascular disease pathophysiology and pharmacological intervention

Tissue factor (TF) is the major trigger of the coagulation cascade and thereby crucially involved in the maintenance of vascular hemostasis. By binding factor VIIa, the resulting TF:VIIa complex activates the coagulation factors IX and X ultimately leading to fibrin and clot formation. In the vessel wall, TF expression and activity is detectable in vascular smooth muscle cells and fibroblasts and, at a much lower level, in endothelial cells and can be induced by various stimuli including cytokines. In addition, TF is found in the bloodstream in circulating cells such as monocytes, in TF containing microparticles, and as a soluble splicing isoform. Besides its well-known extracellular role as a trigger of coagulation, TF also functions as a transmembrane receptor, and TF-dependent intracellular signaling events regulate the expression of genes involved in cellular responses such as proliferation and migration. TF indeed appears to be involved in the pathogenesis of neointima formation and tumor growth, and increased levels of TF have been detected in patients with cardiovascular risk factors or coronary artery disease as well as in those with cancer. Therefore, pharmacological or genetic inhibition of TF may be an attractive target for the treatment of cardiovascular disease and cancer. Different strategies for inhibition of TF have been developed such as inhibition of TF synthesis and blockade of TF action. Clinical applications of such strategies need to be tested in appropriate trials, in particular for evaluating the advantages of targeted versus systemic delivery of the inhibitors.

Human peripheral blood endothelial progenitor cells synthesize and express functionally active tissue factor

INTRODUCTION

Endothelial progenitor cells are circulating cells able to home to sites of vascular damage and to contribute to the revascularization of ischemic areas. We evaluated whether endothelial progenitor cells synthesize tissue factor, a procoagulant protein also involved in angiogenesis.

MATERIALS AND METHODS

Endothelial progenitor cells were obtained from the peripheral blood mononuclear fraction of normal donors and cultured in endothelial medium supplemented with specific growth factors. The procoagulant activity expressed by cells disrupted by freeze-thaw cycles was assessed by a one stage clotting assay. Tissue factor mRNA expression was evaluated by RT-PCR.

RESULTS

Endothelial progenitor cells do not express procoagulant activity in baseline conditions. However, lipopolysaccharide induces the expression of procoagulant activity. The effect is dose-dependent and reaches statistical significance at 100 ng/mL lipopolysaccharide. Inhibition with an anti-tissue factor antibody and amplification of cDNA with primers based on the tissue factor sequence confirm the identity of this activity with tissue factor. The kinetics of tissue factor expression by endothelial progenitor cells is identical to that of human umbilical vein endothelial cells showing maximal activity within 4 hours, and then decreasing; in contrast, tissue factor expression by mononuclear cells lasts for longer times. Both 5,6-dichloro-beta D-ribofuranosyl-benzimidazole and cycloheximide prevented the expression of procoagulant activity. Stimulation of endothelial progenitor cells with tumor necrosis factor-alpha did not elicit any detectable procoagulant activity.

CONCLUSIONS

Endothelial progenitor cells can be stimulated by lipopolysaccharide to synthesize tissue factor. This protein might be involved in thrombotic phenomena and might contribute to endothelial progenitor cells related neovascularization.

TF:FVIIa-specific activation of CREB upregulates proapoptotic proteins via protease-activated receptor-2

BACKGROUND

Tissue factor (TF) and factor (F) VIIa are the primary initiators of the coagulation cascade, but also promote non-hemostatic events, such as angiogenesis and tumor growth, via activation of protease activated receptor-2 (PAR2). Our previous findings indicated that the TF:FVIIa complex activates signal transducer and activator of transcription (STAT) signaling, leading to cell survival in TF-transfected baby hamster kidney (BHK) cells.

METHODS

Using BHK TF, keratinocytes (HaCaT) and human umbilical vein endothelial cells (HUVEC), FVIIa-induced phosphorylation and activation of the transcription factor cyclic AMP-responsive binding protein (CREB) were tested and compared to that elicited by thrombin and FXa. In addition, the effect of these factors on cell survival and expression of apoptosis-associated proteins was monitored.

RESULTS

Factor VIIa led to a TF-dependent, but TF cytoplasmic domain-independent phosphorylation and activation of CREB in BHK TF, HaCaT and HUVEC. CREB activation was sensitive to blockade of the extracellular-signal regulated kinase 1/2 pathway and PAR2. Surprisingly, FVIIa decreased cell survival in HaCaT cells but not other cell types and upregulated the pro-apoptotic proteins Bak and Puma in a CREB-dependent manner. Factor Xa, but not FIIa, induced phosphorylation of CREB, but did not have an effect on apoptosis.

CONCLUSION

TF:FVIIa induces CREB phosphorylation and activation in several cell types, but TF:FVIIa induces pro-apoptotic proteins and apoptosis only in selected cell types.

Tissue factor, angiogenesis and tumour progression

Tissue factor, the primary initiator of the coagulation cascade, maintains vascular integrity in response to injury. It is now recognised that, in addition to the role as a procoagulant activator, tissue factor participates in many tumour-related processes that contribute to malignant disease progression. The present review details the recent evidence supporting a role for tissue factor in tumour haemostasis, angiogenesis, metastasis and malignant cell survival. Furthermore, future research directions are discussed that may enhance our understanding of the role and regulation of this protein, which could ultimately lead to the innovative design and development of new anticancer therapies.

TF/FVIIa Transactivate PDGFRβ to Regulate PDGF-BB–Induced Chemotaxis in Different Cell Types

Background— We have previously reported the potentiation of PDGF-BB–induced chemotaxis of fibroblasts, vascular smooth muscle cells, and endothelial cells by FVIIa. Here we studied the role of TF/FVIIa and the induced signaling pathways in regulation of chemotaxis of human monocytes, fibroblasts, and porcine aorta endothelial cells.

Methods and Results— Human monocytes were obtained by using Ficoll-Paque gradient and the MACS system (for highly purified population), fibroblasts and PAE cells have been characterized previously. Inhibitors of selected signaling intermediates were used, and the effect of TF/FVIIa on the migratory response of all cells to chemotactic agents was analyzed. The induced signaling was studied by immunoprecipitation and Western blotting. TF/FVIIa complex selectively enhanced PDGF-BB–induced chemotaxis in a Src-family, PLC, and PAR-2–dependent manner. Using PAE cells we identified c-Src and c-Yes as the Src-family members activated by TF/FVIIa. We report for the first time the PAR-2 and Src family-dependent transactivation of PDGFRβ by TF/FVIIa involving phosphorylation of a subset of PDGFRβ tyrosines.

Conclusions— The described transactivation is a likely mechanism of TF/FVIIa-mediated regulation of PDGF-BB–induced chemotaxis. Similar behavior of 3 principally different cell types in our experimental setup may reflect a general function of TF in regulation of cell migration.

Simvastatin induces apoptosis in human breast cancer cells in a NFkappaB-dependent manner and abolishes the anti-apoptotic signaling of TF/FVIIa and TF/FVIIa/FXa

INTRODUCTION

Statins have benefits independent of the plasma cholesterol properties among cancer patients and tissue factor (TF)/FVIIa induce PI3-kinase/AKT dependent anti-apoptosis during serum starvation. We analyzed how simvastatin induces apoptosis in human breast cancer cells and the influence of FVIIa and/or FXa on the proposed apoptosis.

MATERIALS AND METHODS

MDA-MB-231 cells were serum starved or treated with 5 microM simvastatin and incubated with 10 and 100 nM FVIIa or 5/130 nM FVIIa/FX. RhoA was analyzed by confocal microscopy and caspase-3, nuclear fragmentation, and NFkappaB translocation were measured using the ArrayScan microscope. mRNA for BCL-2, AKT1 and TF were analyzed with RT-PCR or TaqMan. Protein levels and phosphorylation of PKB/AKT were determined by western blotting.

RESULTS AND CONCLUSIONS

Simvastatin-induced apoptosis was recorded at 48 h in the MDA-MB-231 cells. Addition of FVIIa to the cells induced PKB/AKT phosphorylation at 24 h and rescued serum-deprived cells from apoptosis. However, in the presence of simvastatin we were unable to report any phosphorylation of PKB/AKT or anti-apoptotic effect mediated by the TF/FVIIa or TF/FVIIa/FXa complexes. This was due to a RhoA-dependent retention of NFkappaB to the cytosol at 12 h which led to a transcriptional down-regulation of the anti-apoptotic protein BCL-2 as well as reduced AKT1 mRNA production at 24 h and thus diminished levels of PKB/AKT protein. A transcriptional down-regulation of TF at 12 h possibly also contributed to the absent anti-apoptotic signaling. These results thereby support a role for simvastatin in cancer treatment and emphasize the importance of PKB/AKT in TF-signaling.

Differential functions of tissue factor in the trans-activation of cellular signalling pathways

In this study we examined the ability of tissue factor (TF) alone, or in conjunction with factor VIIa, factor Xa and TFPI in activating a number of key signalling pathways associated with cellular growth, stress and differentiation responses in human endothelial cells. We used luciferase reporter systems to demonstrate the activation of p42/44 MAPK by the TF-FVIIa complex, mediated via the PAR1 receptor. TF alone was capable of interacting with the cell surface and was sufficient to activate the JNK-SAPK pathway and subsequently AP-1, but the level of activation was enhanced by the activity of FXa on PAR1 and 2. Furthermore, the phosphorylated form of the transmembrane-cytoplasmic domain of TF was directly responsible for activation of these pathways. CREB activation occurred in response to TF-FVIIa in a non-protease dependent manner but was lowered on addition of FXa. Finally, NFkappaB activation occurred in response to FVIIa or FXa, with the latter exhibiting higher levels of activation. In conclusion, we have shown that TF is capable of activating differing signalling pathways, via more than one mechanism. The differential influence of TF is modified depending on the presence of other coagulation factors and ultimately acts as a deciding factor in the determination of cellular fate.

Role of cardiac myocyte tissue factor in heart hemostasis

BACKGROUND

The tissue-specific pattern of tissue factor (TF) expression suggests that it plays a major role in the hemostatic protection of specific organs, such as the heart and lung. In support of this notion, we found that mice expressing very low levels of TF exhibit hemostatic defects in the heart and lung. Hemosiderosis and fibrosis are observed in the hearts of all low TF mice as early as 3 months of age. In contrast, TF(+/-) mice expressing approximately 50% of wild-type levels of TF had no detectable hemostatic defects.

OBJECTIVE AND METHODS

The objective of this study was to determine the threshold of TF that is required to maintain hemostasis under normal and pathologic conditions, and to investigate the specific role of cardiac myocyte TF in heart hemostasis using mice with altered levels of TF expression in cardiac myocytes.

RESULTS

First, we found that mice with 20% of wild-type levels of TF activity in their hearts had hemosiderosis and fibrosis by 6 months of age. Secondly, mice with a selective deletion of the TF gene in cardiac myocytes had a mild hemostatic defect under normal conditions but exhibited a significant increase in hemosiderosis and fibrosis after challenge with isoproterenol. Finally, we showed that cardiac myocyte-specific overexpression of TF abolished hemosiderin deposition and fibrosis in the hearts of low TF mice.

CONCLUSIONS

Taken together, our results indicate that TF expression by cardiac myocytes is important to maintain heart hemostasis under normal and pathologic conditions.

Transcriptional program induced by factor VIIa-tissue factor, PAR1 and PAR2 in MDA-MB-231 cells

BACKGROUND

Factor VIIa (FVIIa) binding to tissue factor (TF) induces cell signaling via the protease activity of FVIIa and protease-activated receptor 2 (PAR2).

OBJECTIVE

We examined how the gene-expression profile induced by FVIIa corresponds to the profiles induced by protease-activated receptor 1 (PAR1) or PAR2 agonists using MDA-MB-231 breast carcinoma cells that constitutively express TF, PAR1 and PAR2.

RESULTS AND CONCLUSIONS

Out of 8500 genes, FVIIa stimulation induced differential regulation of 39 genes most of which were not previously recognized as FVIIa regulated. All genes regulated by FVIIa were similarly regulated by a PAR2 agonist peptide confirming FVIIa signaling via PAR2. An appreciable fraction of the PAR2-regulated genes was also regulated by a PAR1 agonist peptide suggesting extensive redundancy between FVIIa/PAR2 signaling and thrombin/PAR1 signaling. The FVIIa regulated genes encode cytokines, chemokines and growth factors, and the gene repertoire induced by FVIIa in MDA-MB-231 cells is consistent with a role for TF-FVIIa signaling in regulation of a wound healing type of response. Interestingly, a number of genes regulated exclusively by FVIIa/PAR2-mediated cell signaling in MDA-MB-231 cells were regulated by thrombin and a PAR1 agonist, but not by FVIIa, in the TF-expressing glioblastoma U373 cell line.

Adhesion-related kinase induction of migration requires phosphatidylinositol-3-kinase and ras stimulation of rac activity in immortalized gonadotropin-releasing hormone neuronal cells

GnRH neurons migrate into the hypothalamus during development. Although migratory defects may result in disordered activation of the reproductive axis and lead to delayed or absent sexual maturation, specific factors regulating GnRH neuronal migration remain largely unknown. The receptor tyrosine kinase, adhesion-related kinase (Ark) (also known as Axl, UFO, and Tyro7), has been implicated in the migration of GnRH neuronal cells. Binding of its ligand, growth arrest-specific gene 6 (Gas6), promotes cytoskeletal remodeling and migration of NLT GnRH neuronal cells via Rac and p38 MAPK. Here, we examined the Axl effectors proximal to Rac in the signaling pathway. Gas6/Axl-induced lamellipodia formation and migration were blocked after phosphatidylinositol-3-kinase (PI3K) inhibition in GnRH neuronal cells. The p85 subunit of PI3K coimmunoprecipitated with Axl and was phosphorylated in a Gas6-sensitive manner. In addition, PI3K inhibition in GnRH neuronal cells diminished Gas6-induced Rac activation. Exogenous expression of a dominant-negative form of Ras also decreased GnRH neuronal lamellipodia formation, migration, and Rac activation. PI3K inhibition blocked Ras in addition to Rac activation and migration. In contrast, pharmacological blockade of the phospholipase C gamma effectors, protein kinase C or calcium/calmodulin protein kinase II, had no effect on Gas6/Axl signaling to promote Rac activation or stimulate cytoskeletal reorganization and migration. Together, these data show that the PI3K-Ras pathway is a major mediator of Axl actions upstream of Rac to induce GnRH neuronal cell migration.

Low levels of activated factor VII in systemic sclerosis

INTRODUCTION

Recent investigations show that activated factor VII, the primary enzyme in the extrinsic pathway of blood coagulation, exerts additional extra-coagulant functions, such as apoptosis and angiogenesis. On the basis of these recent acquisitions, the present study was aimed to evaluate activated factor VII in patients with systemic sclerosis and to establish a potential association with pathogenesis and complications of this severe autoimmune disorder.

MATERIALS AND METHODS

Activated factor VII level was measured in twenty-eight consecutive scleroderma patients (2 men and 26 women, mean age 49.7 +/- 14.8 years). The main clinical correlates of disease, such as disease activity, renal function, skin, vascular and lung involvement, were evaluated by clinical and instrumental investigations. Activated factor VII level was also evaluated in 28 sex and age matched controls.

RESULTS

Systemic sclerosis patients exhibited plasma activated factor VII activities significantly lower than those of healthy matched controls (15.2 versus 37.7 U/l, respectively; p < 0.001). No correlation was observed between plasma activated factor VII concentration and age, disease duration, disease subset, disease activity, renal, lung, skin and microvascular involvement.

CONCLUSIONS

Results of our investigation provide first evidence of low activated factor VII activity in patients with systemic sclerosis. Reduced activated factor VII activity might be involved in the pathogenesis of the ischemic complications, by modulating apoptotic and angiogenetic processes.

Verotoxin-1 stimulation of macrophage-like THP-1 cells up-regulates tissue factor expression through activation of c-Yes tyrosine kinase: Possible signal transduction in tissue factor up-regulation

Verotoxin (VT)-producing Escherichia coli (E. coli) O157:H7 infections are frequently complicated by thrombotic angiopathy, hemolytic uremic syndrome (HUS) and neurological symptoms. The present data demonstrate that VT-1 (Shiga toxin) stimulation of macrophage-like THP-1 cells up-regulates the activity, antigen and mRNA levels of tissue factor (TF), a key cofactor of the coagulation-inflammation-thrombosis circuit. This up-regulation is accompanied by phosphorylation of phosphatidylinositol 3-kinase (PI3-kinase), IkappaB kinase beta (IKKbeta) and extracellular signal-regulated kinase 2 (ERK2). Changes in TF mRNA levels were in parallel with the activation of NF-kappaB/Rel and Egr-1 activation, but not with AP-1. Inhibition of PI3-kinase attenuated VT-1-induced phosphorylation of IKKbeta and ERK2, and the up-regulation of TF mRNA levels. VT-1 stimulation rapidly activated c-Yes tyrosine kinase, a member of the Src family. Treatment of the cells with c-Yes antisense oligos attenuated the VT-1-induced phosphorylation of PI3-kinase, IKKbeta and ERK2, activations of NF-kappaB/Rel and Egr-1, and up-regulation of TF mRNA levels. These results suggest that VT-1-induced macrophage stimulation activates c-Yes, which then up-regulates TF expression through activation of the IKKbeta/proteasome/NF-kappaB/Rel and MEK/ERK2/Egr-1 pathways via activation of PI3-kinase. Induction of macrophage TF expression by VT-1 may play an important role in the acceleration of the coagulation-inflammation-thrombosis circuit during infections by VT-producing E. coli.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Genetic Variations in the Tissue Factor Gene Are Associated With Clinical Outcome in Acute Coronary Syndrome and Expression Levels in Human Monocytes

OBJECTIVE

Tissue factor (TF) has, among other factors, a prominent role in acute coronary syndrome (ACS). Our goal was to investigate whether single nucleotide polymorphisms (SNP) in the TF gene (F3) are associated with plasma TF, risk, and outcome in patients with ACS. Moreover, we wanted to investigate the impact of associated TF SNPs on mRNA production in human monocytes.

METHODS AND RESULTS

In 725 patients with ACS [Fragmin and Fast Revascularization during Instability in Coronary Artery Disease II (FRISC-II) study] and 376 controls, 13 SNPs were genotyped and plasma TF measured. Thereafter, the 5466 A>G and the -1812 C>T were genotyped among all of the FRISC-II participants (n=3143) and assessed concerning clinical outcome. Associated SNPs were genotyped in 92 healthy blood donors for comparison of TF activity and TF mRNA expression. None of the SNPs were associated with patient/control status. The 5466 A>G SNP was associated with cardiovascular death (odds ratio, 1.8; P=0.025). The CG haplotype by -1812 C>T and 5466 A>G was associated with a 3-fold increased risk of death (P<0.001). TF mRNA and basal TF activity was significantly lower among 5466 AG carriers, whereas the increase in monocyte TF activity on lipopolysaccharide stimulation was significantly stronger (P=0.04).

CONCLUSIONS

The 5466 AG genotype is a novel predictor of cardiovascular death in ACS and may act through a high TF response.

Vascular Remodeling in Mice Lacking the Cytoplasmic Domain of Tissue Factor

Tissue factor (TF), the cell surface receptor for the serine protease FVIIa supports cell migration by interaction with the cytoskeleton. Intracellular signaling pathways dependent on the cytoplasmic domain of TF modify cell migration and may alter vascular remodeling. Vascular remodeling was analyzed in a femoral artery injury and a blood flow cessation model in mice with a targeted deletion of the 18 carboxy-terminal intracellular amino acids of TF (TF Δct/Δct ) and compared with TF wild-type mice (TF wt/wt ). Morphometric analysis revealed a decrease in the intima/media ratio after vascular injury in arteries from TF Δct/Δct compared with TF wt/wt mice (femoral artery injury: 2.4±0.3 TF wt/wt versus 0.6±0.3 TF Δct/Δct , n=9 to 10, P =0.002; carotis ligation: 0.45+0.11 TF wt/wt versus 0.22+0.03 TF Δct/Δct , n=12 to 14, P =0.09). This was caused by an increase in the media by 54% ( P =0.04) in the femoral artery model and by 32% ( P =0.03) after carotis ligation and was associated with an increased number of proliferating cells. Isolated aortic smooth muscle cells (SMCs) of TF wt/wt mice showed an increased migratory response toward the TF ligand active site-inhibited FVIIa that was abolished in TF Δct/Δct SMC. In contrast, the unstimulated proliferation rate was increased in TF Δct/Δct SMC compared with TF wt/wt SMCs. Thus, retention of SMCs attributable to a migratory defect and increased proliferation results in thickening of the media and in decrease in neointima formation after arterial injury. TF cytoplasmic domain signaling alters vascular remodeling and, thereby, may play a role in the development of restenosis, atherosclerotic disease, and neovascularization.

Signaling of the Tissue Factor Coagulation Pathway in Angiogenesis and Cancer

Activation of coagulation precedes or coincides with angiogenesis in wound healing and postischemic tissue regeneration. Advanced cancer is associated with a hypercoagulable state, and tissue factor expression by cancer cells has received widespread attention because of its significant contribution to the pathogenesis of cancer progression and metastasis. Our recent work demonstrates that tissue factor-mediated cellular signaling is relevant to cancer angiogenesis. Here we review the molecular mechanisms of tissue factor pathways in angiogenesis and tumorigenesis with emphasis on the intriguing role for tissue factor cytoplasmic domain signaling.

Full house: 12 receptors for 27 cytokines

With the sequencing of the human genome nearing completion, it appears that all members of the class II cytokine receptor family (CRF2) have been identified and partially characterized. The entire family is composed of exactly one dozen members. Eleven of them combine as various heterodimers to transduce signals across the cellular membrane for 27 cytokines divided into four structurally related groups: 6 cytokines of the IL-10 family, 17 type I IFNs, 1 type II IFN and 3 IFN-lambdas. The last CRF2 member is the soluble receptor which can neutralize the action of one of the cytokines of the IL-10 family, IL-22. Although the extracellular domains of all CRF2 proteins reveal primary and structural homology, their intracellular domains are very dissimilar. Nevertheless, signaling events induced through various combinations of CRF2 subunits partially overlap, leading to the induction of overlapping but cytokine-specific biological activities.

Sequential 5-Aza 2'-deoxycytidine/depsipeptide FK228 treatment induces tissue factor pathway inhibitor 2 (TFPI-2) expression in cancer cells

cDNA arrays were used to examine gene induction in CALU-6 and H460 lung cancer cells mediated by sequential 5-aza 2'-deoxycytidine (DAC)/depsipeptide FK228 (DP) exposure in order to identify translational end points for clinical trials evaluating these agents. In both cell lines, sequential DAC/DP treatment induced expression of tissue factor pathway inhibitor-2 (TFPI-2), an inhibitor of Factor VII: tissue factor signal transduction known to diminish the malignant phenotype of cancer cells. TFPI-2 expression was diminished or absent in 16 of 32 cell lines established from thoracic malignancies. Sequential DAC/DP treatment induced TFPI-2 in cancer cells deficient for TFPI-2 expression in the basal state. Promoter methylation coincided with loss of TFPI-2 expression in a number of cancer lines. TFPI-2 promoter methylation was observed in one of five pulmonary adenocarcinomas, and seven of seven esophageal adenocarcinomas, but not corresponding normal tissues. DP enhanced acetylation of TFPI-2-associated histones in CALU-6 cells. DP or PDBU, alone, induced TFPI-2 expression in cancer cells deficient for TFPI-2 expression in the absence of promoter methylation. In these cells, DP-mediated TFPI-2 induction was abrogated by calphostin. Induction of TFPI-2 by distinct, yet cooperative mechanisms involving chromatin remodeling and PKC signaling strengthens the preclinical rationale for sequential administration of DNA demethylating agents and HDAC inhibitors in cancer patients. Furthermore, induction of TFPI-2 may be a useful surrogate marker of treatment response in individuals receiving sequential DAC/DP infusions.

Tissue factor-factor VIIa signaling

How does tissue factor (TF), whose principle role is to support clotting factor VIIa (FVIIa) in triggering the coagulation cascade, affect various pathophysiological processes? One of the answers is that TF interaction with FVIIa not only initiates clotting but also induces cell signaling via activation of G-protein-coupled protease activated receptors (PARs). Recent studies using various cell model systems and limited in vivo systems are beginning to define how TF-VIIa-induced signaling regulates cellular behavior. Signaling pathways initiated by both TF-VIIa protease activation of PARs and phosphorylation of the TF-cytoplasmic domain appear to regulate cellular functions. In the present article, we review the emerging data on the mechanism of TF-mediated cell signaling and how it regulates various cellular responses, with particular focus on TF-VIIa protease-dependent signaling.

A quantitative real-time PCR method for tissue factor mRNA

BACKGROUND

Tissue factor (TF) is primarily known for its function to initiate blood coagulation. The range of in vivo expression of TF is wide and requires a dynamic assay for monitoring. A general method for TF mRNA quantitation that is dynamic, sensitive and applicable to a variety of experimental systems or clinical situations is therefore desirable.

OBJECTIVES

To develop a method for sensitive and dynamic quantitation of TF mRNA in human blood cells.

METHODS

TF mRNA expression was analysed and evaluated in monocyte isolations, in whole blood (healthy volunteers and patients scheduled for percutaneous coronary intervention, PCI) and in a panel of human cell lines. RNA was extracted, reverse transcribed and subjected to real-time PCR amplification, according to the TaqMan technology. A TF plasmid was constructed as calibrator of the assay. Two housekeeping genes used as endogenous controls for cDNA quality and integrity were evaluated.

RESULTS

The assay was linear by seven orders of magnitude and detected down to 10(2) copies of the TF plasmid. The coefficient of variation was 4% intra-assay and 28% between the assays when using beta2MG as endogenous control. The beta-actin gene expression was induced by treatment with lipopolysaccharide (LPS) in blood leukocytes and could not be used as an endogenous control. However, beta2MG showed only minor variations upon treatment with LPS. The TF mRNA and antigen expression, measured in a Western blot, correlated well (R(2)=0.903) in a panel of 11 human cell lines.

CONCLUSIONS

We have established a method for sensitive and dynamic quantitation of TF mRNA in experimental systems and for clinical situations.

Emerging roles of tissue factor in viral hemorrhagic fever

Activation of coagulation by tissue factor (TF) is frequently observed in sepsis syndrome and is documented in certain viral hemorrhagic fevers. Coagulation protease complexes signal by activating the G-protein coupled, protease-activated receptors that regulate inflammation. Blockade of TF attenuates lethality in experimental models of Ebola virus infection but - similar to findings in bacterial sepsis - reduction of inflammation, rather than attenuation of coagulation, predicts survival of treated animals. Thus, targeting TF appears to aid the antiviral immune response in hemorrhagic fevers, and further studies are encouraged to define how TF-dependent signaling regulates immunity.

Cross-talk of integrin alpha3beta1 and tissue factor in cell migration

In cancer and angiogenesis, coagulation-independent roles of tissue factor (TF) in cell migration are incompletely understood. Immobilized anti-TF extracellular domain antibodies induce cell spreading, but this phenomenon is epitope specific and is not induced by anti-TF 5G9. Spreading on anti-TF is beta1 integrin-dependent, indicating functional interactions of the TF extracellular domain 5G9 epitope (a presumed integrin-binding site) and integrins. Recombinant TF extracellular domain supports adhesion of cells expressing alphavbeta3 or certain beta1 integrin heterodimers (alpha3beta1, alpha4beta1, alpha5beta1, alpha6beta1, alpha9beta1) and adhesion is blocked by specific anti-integrin antibodies or mutations in the integrin ligand-binding site. Although several studies have linked TF to cell migration, we here demonstrate that TF specifically regulates alpha3beta1-dependent migration on laminin 5. Expression of TF suppresses alpha3beta1-dependent migration, but only when the TF cytoplasmic domain is not phosphorylated. Suppression of migration can be reversed by 5G9, presumably by disrupting integrin interaction, or by the protease ligand VIIa, known to induce PAR-2-dependent phosphorylation of TF. In both cases, release of alpha3beta1 inhibition is prevented by mutation of critical phosphorylation sites in the TF cytoplasmic domain. Thus, TF influences integrin-mediated migration through cooperative intra- and extracellular interactions and phosphorylation regulates TF's function in cell motility.

Regulation of angiogenesis by tissue factor cytoplasmic domain signaling

Hemostasis initiates angiogenesis-dependent wound healing, and thrombosis is frequently associated with advanced cancer. Although activation of coagulation generates potent regulators of angiogenesis, little is known about how this pathway supports angiogenesis in vivo. Here we show that the tissue factor (TF)-VIIa protease complex, independent of triggering coagulation, can promote tumor and developmental angiogenesis through protease-activated receptor-2 (PAR-2) signaling. In this context, the TF cytoplasmic domain negatively regulates PAR-2 signaling. Mice from which the TF cytoplasmic domain has been deleted (TF Delta CT mice) show enhanced PAR-2-dependent angiogenesis, in synergy with platelet-derived growth factor BB (PDGF-BB). Ocular tissue from diabetic patients shows PAR-2 colocalization with phosphorylated TF specifically on neovasculature, suggesting that phosphorylation of the TF cytoplasmic domain releases its negative regulatory control of PAR-2 signaling in angiogenesis. Targeting the TF-VIIa signaling pathway may thus enhance the efficacy of angiostatic treatments for cancer and neovascular eye diseases.

Protease-activated receptor 2-dependent phosphorylation of the tissue factor cytoplasmic domain

Tissue factor (TF) is the physiological activator of the coagulation cascade that plays pathophysiological roles in metastasis, angiogenesis, and inflammation. Downstream in coagulation, thrombin is the central protease that signals through G protein-coupled, protease-activated receptors (PARs). However, the TF-VIIa-Xa complex upstream in coagulation also activates PAR1 and 2. Here, we address the question of whether signaling of the TF initiation complex is a relevant pathway that leads to TF cytoplasmic domain phosphorylation. In heterologous expression systems and primary endothelial cells, we demonstrate that the ternary TF-VIIa-Xa complex induces TF phosphorylation specifically by activating PAR2 but not through PAR1 signaling. In addition, TF cytoplasmic domain phosphorylation is induced only by TF-dependent signaling but not by other coagulation factors in endothelial cells. Phosphorylation of the Pro-directed kinase target site Ser258 is dependent on prior phosphorylation of Ser253 by protein kinase C (PKC) alpha. TF phosphorylation is somewhat delayed and coincides with sustained PKCalpha activation downstream of PAR2 but not PAR1 signaling. Phosphatidylcholine-dependent phospholipase C is the major pathway that leads to prolonged PKCalpha recruitment downstream of PAR2. Thus, PAR2 signaling specifically phosphorylates TF in a receptor cross-talk that distinguishes upstream from downstream coagulation protease signaling.

Inhibition of restenosis by tissue factor pathway inhibitor: in vivo and in vitro evidence for suppressed monocyte chemoattraction and reduced gelatinolytic activity

Activation of inflammatory and procoagulant mechanisms is thought to contribute significantly to the initiation of restenosis, a common complication after balloon angioplasty of obstructed arteries. During this process, expression of tissue factor (TF) represents one of the major physiologic triggers of coagulation that results in thrombus formation and the generation of additional signals leading to vascular smooth muscle cell (VSMC) proliferation and migration. In this study, we have investigated the mechanisms by which inhibition of coagulation at an early stage through overexpression of tissue factor pathway inhibitor (TFPI), an endogenous inhibitor of TF, might reduce restenosis. In a rabbit femoral artery model, percutaneous delivery of TFPI using a recombinant adenoviral vector resulted in a significant reduction of the intimamedia ratio 21 days after injury. Investigating several markers of inflammation and coagulation, we found reduced neointimal expression of monocyte chemoattractant protein-1 (MCP-1), lesional monocyte infiltration, and expression of vascular TF, matrix metalloproteinase-2 (MMP-2), and MMP-9. Moreover, overexpression of TFPI suppressed the autocrine release of platelet-derived growth factor BB (PDGF-BB), MCP-1, and MMP-2 in response to factors VIIa and Xa from VSMCs in vitro and inhibited monocyte TF activity. These results suggest that TFPI exerts its action in vivo through not only thrombotic, but also nonthrombotic mechanisms.

Tissue factor-factor VIIa-specific up-regulation of IL-8 expression in MDA-MB-231 cells is mediated by PAR-2 and results in increased cell migration

Tissue factor (TF), the cellular receptor for factor VIIa (FVIIa), besides initiating blood coagulation, is believed to play an important role in tissue repair, inflammation, angiogenesis, and tumor metastasis. Like TF, the chemokine interleukin-8 (IL-8) is shown to play a critical role in these processes. To elucidate the potential mechanisms by which TF contributes to tumor invasion and metastasis, we investigated the effect of FVIIa on IL-8 expression and cell migration in a breast carcinoma cell line, MDA-MB-231, a cell line that constitutively expresses abundant TF. Expression of IL-8 mRNA in MDA-MB-231 cells was markedly up-regulated by plasma concentrations of FVII or an equivalent concentration of FVIIa (10 nM). Neither thrombin nor other proteases involved in hemostasis were effective in stimulating IL-8 in these cells. Increased transcriptional activation of the IL-8 gene is responsible for increased expression of IL-8 in FVIIa-treated cells. PAR-2-specific antibodies fully attenuated TF-FVIIa-induced IL-8 expression. Additional in vitro experiments showed that TF-FVIIa promoted tumor cell migration and invasion, active site-inactivated FVIIa, and specific antibodies against TF, PAR-2, and IL-8 inhibited TF-FVIIa-induced cell migration. In summary, the studies described herein provide insight into how TF may contribute to tumor invasion.

Formation of tissue factor-factor VIIa-factor Xa complex promotes cellular signaling and migration of human breast cancer cells

Tissue factor (TF) is a transmembrane glycoprotein that initiates blood coagulation when complexed with factor (F)VIIa. Recently, TF has been shown to promote cellular signaling, tumor growth, angiogenesis, and metastasis. In the present study, we examined the pathway by which TF-FVIIa complex induces cellular signaling in human breast cancer cells using the Adr-MCF-7 cell line. This cell line has high endogenous TF expression as measured by flow cytometry and expression of protease-activated receptors 1 and 2 (PAR1 and PAR2) as determined by reverse transcriptase-polymerase chain reaction analysis. Both PAR1 and PAR2 are functionally active as determined by induction of p44/42 mitogen-activated protein kinase (MAPK) phosphorylation using specific agonist peptides. We found that MAPK phosphorylation in this cell line was strongly induced by the combination of FVIIa and factor (F)X, but not by FVIIa alone at a concentration of FVIIa that approaches physiological levels. Induction of MAPK phosphorylation involved the formation of TF-FVIIa-FXa complex and occurred by a pathway that did not require thrombin formation, indicating a critical role for FXa generation. In addition, induction of MAPK phosphorylation was found to be independent of PAR1 activation. We then examined whether TF-FVIIa complex formation could promote tumor cell migration using a modified Boyden chamber chemotaxis assay. The combination of FVIIa and FX, but not FVIIa alone, strongly induced migration of tumor cells by a pathway that probably involves PAR2, but not PAR1 activation. MAPK phosphorylation was found to be required for the induction of cell migration by the combination of FVIIa and FX. These data suggest that TF-FVIIa-mediated signaling in human breast cancer cells occurs most efficiently by formation of the TF-FVIIa-FXa complex. One of the physiological consequences of this signaling pathway is enhanced cell migration that is probably mediated by PAR2, but not PAR1 activation.

Antiapoptotic effect of coagulation factor VIIa

Binding of factor VIIa (FVIIa) to its cellular receptor tissue factor (TF) was previously shown to induce various intracellular signaling events, which were thought to be responsible for TF-mediated biologic effects, including angiogenesis, tumor metastasis, and restenosis. To understand the mechanisms behind these processes, we have examined the effect of FVIIa on apoptosis. Serum deprivation-induced apoptosis of BHK(+TF) cells was characterized by apoptotic blebs, nuclei with chromatin-condensed bodies, DNA degradation, and activation of caspase 3. FVIIa markedly decreased the number of cells with apoptotic morphology and prevented the DNA degradation as measured by means of TdT-mediated dUTP nick end labeling (TUNEL). The antiapoptotic effect of FVIIa was confirmed by the observation that FVIIa attenuated caspase 3 activation. FVIIa-induced antiapoptotic effect was dependent on its proteolytic activity and TF but independent of factor Xa and thrombin. FVIIa-induced cell survival correlated with the activation of Akt and was inhibited markedly by the specific PI3-kinase inhibitor, LY294002. Blocking the activation of p44/42 mitogen-activated protein kinase (MAPK) by the specific mitogen-induced extracellular kinase (MEK) inhibitor, U0126, impaired modestly the ability of FVIIa to promote cell survival. In conclusion, FVIIa binding to TF provided protection against apoptosis induced by growth factor deprivation, primarily through activation of PI3-kinase/Akt pathway, and to a lesser extent, p44/42 MAPK pathway.

Specificity of coagulation factor signaling

Coagulation serine proteases signal through protease-activated receptors (PARs). Thrombin-dependent PAR signaling on platelets is essential for the hemostatic response and vascular thrombosis, but regulation of inflammation by PAR signaling is now recognized as an important aspect of the pro- and anti-coagulant pathways. In tissue factor (TF)-dependent initiation of coagulation, factor (F) Xa is the PAR-1 or PAR-2-activating protease when associated with the transient TF-FVIIa-FXa complex. In the anticoagulant protein C (PC) pathway, the thrombin-thrombomodulin complex activates PC bound to the endothelial cell PC receptor (EPCR), which functions as a required coreceptor for activated PC-mediated signaling through endothelial cell PAR-1. Thus, the pro- and anti-inflammatory receptor cascades are mechanistically coupled to immediate cell signaling, which precedes systemic coagulant or anticoagulant effects. In contrast to the substrate-like recognition of PARs by thrombin, TF- or EPCR-targeted activation of PARs generates cell-type specificity, PAR selectivity and protease receptor cosignaling with the G-protein-coupled PAR response. Protease receptors are thus major determinants of the biological outcome of coagulation factor signaling on vascular cells.

Prothrombotic and antithrombotic pathways in acute coronary syndromes

The acute coronary syndromes arise from procoagulant changes in complex plaques, which trigger both platelet activation and coagulation pathways. These 2 pathways intersect at a number of points that form positive-feedback loops to sustain and accelerate thrombus formation. In normal hemostasis and with a healthy endothelium, intravascular thrombosis is prevented, and vascular patency is protected by the fibrinolytic system and a number of antithrombotic factors, such as antithrombin, thrombomodulin, and tissue factor pathway inhibitor. However, atherosclerosis is characterized by a hypercoagulable state, and the fibrinolytic balance is skewed toward occlusive thrombus formation at critical sites on vulnerable plaques. This review focuses on cellular and humoral mechanisms and the antithrombotic strategies that are important during the acute phase of an ischemic coronary syndrome, both in patients managed conservatively and in patients scheduled for an interventional procedure. These strategies include fibrinolytic therapy, antiplatelet therapies (aspirin, clopidogrel, glycoprotein IIb/IIIa receptor inhibitors), and low-molecular-weight heparin.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Factor VIIa/tissue factor-induced signaling: a link between clotting and disease

Tissue factor is a cellular receptor for plasma clotting factor VII. In health, tissue factor is constitutively expressed in many cells, such as fibroblasts and keratinocytes, but is absent in vascular cells that come in contact with blood. However, tissue factor is induced in vascular cells in certain pathophysiological conditions. Thus, vessel wall injury or a disease condition allows blood to come in contact with tissue factor, resulting in factor VII binding to tissue factor. Once native factor VII complexed with tissue factor is converted to the enzyme factor VIIa, the complex triggers the clotting cascade that ultimately leads to fibrin formation. In addition to its established role in coagulation, molecular links between factor VIIa/tissue factor and various biological processes, such as development, inflammation, and tumor metastasis, are also evident. Recent studies suggest that factor VIIa/tissue factor affects various cellular processes by inducing intracellular signaling. Emerging evidence suggest that factor VIIa/tissue factor participates in cell signaling by two distinct mechanisms: proteolysis-independent signaling via the cytoplasmic domain of tissue factor, and proteolysis-dependent signaling, which is independent of tissue factor's cytoplasmic tail. In proteolysis-independent signaling, filamin 1 is recruited to tissue factor upon its ligation, and this probably provides an essential intracellular link in transmitting signals from tissue factor. In proteolysis-dependent signaling, factor VIIa/tissue factor activates one or more protease-activated receptors, which couple to G proteins, to impact multiple signaling pathways. In this chapter, we review various nonhemostatic functions attributed to factor VIIa and tissue factor, describe signaling mechanisms initiated upon factor VIIa binding to tissue factor, and discuss how factor VIIa/tissue factor-induced signaling could contribute to various pathophysiological processes. The relationship between increased clotting and manifestation of various diseases is well recognized. Although aberrant activation of the coagulation pathway is primarily the consequence of a disease, activation of the coagulation pathway during the disease process, in turn, could contribute to pathogenesis of the disease. Further, recent transgenic studies in mouse suggest that the coagulation system also plays a role in embryogenesis and development. Then the question arises, how do proteins involved in the clotting regulate cellular functions? The coagulant proteases can regulate cell behavior in a number of ways. They can function like hormones, activating multiple signaling pathways, as well as release bioactive fragments and growth factors by proteolysis of cell-surface and extracellular matrix (ECM) components. This chapter reviews our current understanding of the role of factor VIIa/tissue factor (VIIa/TF), an enzyme/cofactor complex that triggers the clotting cascade, in affecting various cellular functions not related to the clotting, and discusses potential mechanisms by which it regulates cellular functions.

Active site blockade of factor VIIa alters its intracellular distribution

Factor VIIa binding to tissue factor on cell surfaces not only triggers the coagulation cascade but also induces various intracellular responses that may contribute to many pathophysiological processes. Active site-inhibited factor VIIa, similar to factor VIIa, binds to tissue factor on cell surfaces and subsequently gets internalized and degraded. At present, it is unknown whether factor VIIa and active site-inhibited factor VIIa undergo a similar intracellular processing. The data presented herein show that although a fraction of both the internalized factor VIIa and active site-inhibited factor VIIa recycle back to the cell surface, the amount of active site-inhibited factor VIIa recycled back to the cell surface was substantially higher than that of factor VIIa. Furthermore, internalized factor VIIa and not active site-inhibited factor VIIa associates with nuclear fractions. Factor VIIa associated with the nuclear fraction was intact and functionally active. In contrast to factor VIIa, tissue factor is not found in the nuclear fraction. Additional studies show that the internalized factor VIIa specifically associates with cytoskeletal proteins, actin, and tubulin. In summary, the present data reveal that despite the common pathway of tissue factor-mediated processing, considerable differences exist in the trafficking of factor VIIa and active site-inhibited factor VIIa in fibroblasts.