SEARCH

SEARCH BY CITATION

Keywords:

  • angiogenesis inducers;
  • beta integrins;
  • blood coagulation factors;
  • cell migration;
  • protease-activated receptor 2

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

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.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

The blood coagulation system is a complex mechanism enabling an organism to control excessive blood loss after vascular damage. The 47 kDa transmembrane protein tissue factor (TF) is the initiator of the coagulation cascade. Loss of the endothelial barrier results in exposure of TF to the circulation, resulting in binding and activation of blood-borne zymogen FVII. The active TF-FVII complex then converts FX into FXa, leading to thrombin formation and a fibrin network, which in turn seals the site of bleeding [1]. Most TF resides at the cell surface in an inactive, cryptic state and it is believed that TF inactivation results from low local exposure of procoagulant phosphatidylserine (PS) [2]. However, increases in cell surface-exposed PS do not completely explain TF activation, as blocking surface PS does not block TF function in all cell models, and protein disulphide isomerase/redox-dependent oxidation of TF has been proposed as an alternative model underlying TF activation/inactivation [3].

Blood coagulation is normally tightly regulated; consequently, deregulation of this system can lead to a variety of pathological events. It has now been established that cancer development leads to an increased risk of thrombosis, and conversely, excessive activation of blood coagulation profoundly influences cancer progression [4, 5]. TF levels are frequently up-regulated in many cancers and are further enhanced in metastatic cells [6-8] through a concerted action of oncogenes and inactivation of tumour suppressors. In colorectal carcinoma, disruption of oncogenic K-ras down-regulates TF levels while loss of the tumour suppressor p53 increases TF levels [9]. In glioblastoma cells down-regulation of the tumour suppressor, PTEN, and constitutive activation of EGFR has a similar effect [10]. Finally, TF is over-expressed in hypoxic tumours [11] and TGFβ up-regulation by breast cancer cells leads to increased levels of TF on stromal fibroblasts [12].

Tissue factor can also trigger signaling events that influence cancer cell behaviour. On the one hand, TF in complex with FVIIa activates a member of the G-protein coupled receptors named protease-activated receptor (PAR)-2 [13], while on the other, TF regulates cell adhesion and migration in PAR-2-dependent and independent manners. Interestingly, both signaling and migration appear to be critically dependent on integrins.

Over-expression of TF on cancer cells and subsequent shedding of TF-positive vesicles called microparticles from cancer cells has also been associated with enhanced risks of venous thrombosis in cancer patients, a phenomenon referred to as Trousseau's syndrome. Emerging evidence suggests that integrins also play a critical role in regulation of TF coagulant and prothrombotic activity. In this review, we will summarize our current insights into the reciprocal interactions between TF and integrins, with a focus on TF-integrin signaling and procoagulant activity.

TF and actin dynamics

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

Cells are highly versatile units that respond to extracellular stimuli by spreading on extracellular matrices or initiating (non-)directional migration. Both processes critically rely on dynamic reorganization of the actin cytoskeleton and formation of focal adhesions. During processes such as migration a cell becomes polarized, with actin polymerization taking place at the leading edge, forming lamellipodia and filopodia, while the rear side of the cell retracts [14]. Of note, the leading edge of a migratory cell is rich in proteins that play a role in protrusion formation and adhesion, [15] and interestingly, in breast cancer cells and invasive bladder carcinoma TF resides at lamellipodia, ruffled membrane areas and invasive edges of the cancer cells [16, 17], suggesting that TF may play a role in actin dynamics and cell migration. Similar localization patterns are observed in non-cancerous cells; in migrating smooth muscle cells TF also translocates to the leading edge [18].

Actin is the main component of cytoskeletal elements. Thus by polymerization and depolymerization it effects cell polarity and morphology. The actin polymerization process is under the control of actin binding proteins [19]. Interestingly, yeast two hybrid screening experiments show that actin binding protein (ABP)-280 is a binding partner for TF [20]. TF has two cytoplasmic serine residues (Ser253, Ser258); stimulated phosphorylation of Ser253 by protein kinase C (e.g. after cell exposure to phorbol myristate acetate) triggers the phosphorylation of Ser258 in a proline-directed kinase-dependent fashion and recently p38α MAP kinase was identified as a proline-directed kinase capable of phosphorylating Ser258 [21, 22]. Binding of ABP-280 to TF is regulated by the phosphorylation status of the TF cytoplasmic tail (TF CT). Mutation of Ser residues into Asp, thus mimicking phosphorylation, increases interaction of TF with ABP-280, while mutating Ser to Ala, thus preventing phosphorylation, has an opposite effect [20]. In addition, TF and ABP-280 co-localize at the leading edge of the cell, indicating a role for TF in adhesion and migration [17], and TF/ABP-280 complex disruption by transfecting cells with TF Ser253Ala/Ser258Ala chimeras reduces the spreading of J82 bladder carcinoma cells [20].

TF may also regulate actin dynamics by influencing activation and expression levels of proteins that are instrumental for actin cytoskeleton remodeling and migration, such as Rac and Cdc42. Binding of FVIIa to TF in fibroblasts induces Src/PI3-kinase dependent activation of Rac and Cdc42, filopodia and lamellipodia formation [23]. In J82 bladder carcinoma cells, treatment with FVIIai leads to a migratory phenotype, dependent on TF CT-induced Rac1 and p38 activation [24]. In addition, silencing of TF leads to down-regulation of Cdc42, RhoA and Rac1 levels, thereby inhibiting actin reorganization and cell migration [18].

TF-integrin complex formation

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

As mentioned above, in migratory cells TF localizes to leading edges, a subcellular domain that is also enriched in integrins, raising the interesting possibility that TF and integrins can functionally interact. Integrins are heterodimeric cell surface receptors composed of an α and β subunit: 18α and 8β monomers can complex with each to form 24 different types of integrin receptors that, in turn, can bind to distinct extracellular matrices (ECMs) such as laminin 5 and fibronectin [25]. Upon binding, focal adhesions are formed and kinases such as FAK and Src family kinases are recruited, while the adaptor proteins talin, paxillin and vinculin connect the integrin cytoplasmic tails to actin filaments [26]. ECM-integrin interactions inform cells on the local milieu (e.g. local ECM deposition), eliciting intracellular pathways that lead to appropriate responses such as migration or apoptosis. Indeed, integrin ligation plays a crucial role in cell survival; cells that do not integrin-dependently adhere to ECM proceed to go into anoikis [27, 28], while it should be noted that the TF:FVIIa complex and the downstream protease FXa inhibit this process [29]. These receptors are also involved in processes that regulate cancer progression, such as proliferation [30], angiogenesis [31, 32] and metastasis [33, 34]. In our review, we will not discuss the various roles of integrins in these processes due to limited space. Instead we refer the reader to reviews available on these subjects [35-37].

As the involvement of both TF and integrins in cancer progression has been described in the literature in detail, the question of whether these proteins interact and reciprocally influence each other's function in the regulation of tumour progression is valid. Co-localization studies using fluorescence microscopy and co-immunoprecipitation experiments (Figs. 1 and 2) [38] demonstrate that TF interacts with integrin α/β dimers. Incubation of MCF-7 lysates with recombinant TF-coated agarose beads results in β1 integrin co-precipitation, suggesting physical interactions between TF and β1 integrins [39]. Yet, transfection of CHO cells with different integrins shows that TF does not physically interact with all integrin complexes; αvβ3, α9β1 and α5β1 but not αvβ5 expression, increases CHO cell binding to immobilized TF [25]. HaCaT keratinocytes bind to immobilized TF-antibodies and binding is sensitive to α3, α5 and β1 integrin blockade [25], while the natural ligand of TF, FVIIa, induces complex formation of TF and β1 integrin [38]. This interaction is seemingly independent of TF:FVIIa's ability to cleave PAR-2, as the use of active site-blocked FVIIa (FVIIai) or a PAR-2-blocking antibody does not prevent TF-β1 integrin complexation [38]. Of note, two different TF-specific monoclonal antibodies, mAb 5G9, which blocks TF-dependent FXa generation, and mAb 10H10, which blocks TF-dependent PAR-2 activation, have opposite effects on TF-integrin complexation: 5G9 potently stimulates while 10H10 down-regulates complex formation. Interestingly, the complex-promoting effects of FVIIa and 5G9 are not observed in malignant breast cancer cells, while 10H10 disruption of TF/integrin binding by 10H10 is maintained. Moreover, in xenograft experiments, growth of the breast cancer cell line MDA-MB-231-mfp is hampered after co-injection of 10H10 with cancer cells orthotopically, but not by 5G9 [38]. Overall, this implies that breast cancer growth in vivo may be a downstream event resulting from TF-integrin complexation (see below).

image

Figure 1. Tissue factor co-localizes and associates with β1 integrin in HaCaT cells. (A) β1 integrin and TF in HaCaT cells were stained using AIIB2 (anti-integrin β1) and 5G9 (anti-TF). Images were captured using confocal microscopy. (B) HaCaT cells were incubated with 10 nm FVIIa for the indicated times. β1 integrin was precipitated from lysates using anti-β1 antibody TS2/16. 1 and co-precipitated TF were assessed on Western Blot.

Download figure to PowerPoint

image

Figure 2. TF-β1 integrin complex formation on cells and functional implications. In this model TF associates with β1 integrin under basal circumstances. Stimulation with FVIIa or the TF mAb 5G9 further stimulates complex formation and may facilitate TF-dependent signaling, while inhibiting coagulation. Exposure to the TF mAb 10H10 disrupts TF-integrin complexes and inhibits TF-dependent signal transduction. Although TF-integrin complexes also contain α integrin subunits (α3 and α6), these are not shown to reduce complexity.

Download figure to PowerPoint

An unsolved question remains regarding how TF associates with integrins, but recent data suggest that TF reduction and divalent cations are involved. Two cysteine residues (Cys186-Cys209) located in the extracellular domain of TF are crucial determinants of TF function. Oxidation of the disulphide bridge between these two residues induces a coagulant, oxidized pool of TF, while reduction results in a coagulant-inactive TF form that facilitates FVIIa-dependent PAR-2 activation [40]. Indeed, both human and murine TF mutants lacking either or both cysteine residues show reduced affinities for FVII(a) and are deficient in FX binding, showing that lack of the allosteric disulphide critically affects TF function [41, 42]. Interestingly, TF/β1 integrin complexation occurs after cellular stimulation with relatively high levels of FVIIa, a feature that is in line with the low affinity of FVIIa for reduced TF. Furthermore, as discussed below, integrin β1 functions as a ‘co-factor’ to reduced signaling TF, supporting the idea that TF should be reduced to bind β1 integrin.

Presence of divalent cations such as Ca2+ and/or Mg2+ appears to be required for complex formation, suggesting a non-covalent association [38, 39]. The membrane proximal region (amino acids 202–210 in mature TF) may be involved as peptides derived from this region inhibit reverse endothelial cell migration of monocytes [43].

In conclusion, the nature of TF-integrin complexation remains unclear. We will now focus on the functional implications of TF-integrin complexes in TF signal transduction, cell behaviour and prothrombotic activity.

Integrin dependent TF signaling

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

Cancer progression, at least in orthotopic breast cancer models, is critically dependent on TF signaling activity via PARs. FVIIa bound to TF forms a proteolytically active complex that can activate PAR-2; cleavage of the PAR-2 N-terminus results in formation of a new N-terminus that can bind to the second solvent-exposed loop of the receptor, in turn activating downstream signaling pathways. Among the four different family members of this receptor (PAR1-4), PAR-2 is the only one that is activated by the binary TF/VIIa complex, but not by thrombin [13].

Extensive crosstalk between PARs and the TF CT is crucial to TF-dependent signaling. In in vivo cancer models, efficient PAR-2-dependent tumour angiogenesis requires presence of the TF CT in cancer cells, while ex vivo aortic sprouting models – mimicking the host compartment – paradoxically show that the TF CT inhibits PAR-2 signaling. Thus, PAR-2 and the TF CT are involved in a complicated bidirectional crosstalk, with the TF CT supporting or inhibiting PAR-2 signaling depending on whether TF and PAR-2 are expressed in tumour cells or in non-malignant stromal and endothelial cells [44, 45].

Recent evidence shows that integrins facilitate TF-dependent PAR-2 activation and signaling. Support for this comes from studies showing that treatment of HaCaT cells with mAb 5G9 results in a subtle increase in β1 integrin binding to TF but does not have an effect on PAR signaling. In contrast, incubation of these cells with the TF/β1 integrin-disrupting mAb 10H10 blocks TF-dependent PAR-2 signaling [38] (Fig. 2). This is in concordance with the fact that incubation with the β1 integrin inhibiting antibody AIIB2 results in diminished TF-dependent PAR-2 signaling [38]. Thus, binding of β1 integrin to TF may have a boosting effect on PAR signaling. It should be noted that 10H10 also inhibits tumour growth in murine xenografts, a feature that is believed to result from inhibition of TF/β1 complexation. Below, we will summarize our knowledge on the involvement of β1 integrin in TF-dependent signaling in migration, angiogenesis and proliferation.

TF integrin signaling in migration

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

Migration is crucial for invasion and metastasis, and recent literature indicates that TF critically regulates cell motility. It is pertinent to note that TF could contribute to cell migration through activation of PARs, but may also potentiate migration in protease-independent manners. TF-dependent migration of SW620 colorectal cancer cells [46], MDA-MB-231 breast cancer cells [47] and glioma cells [48] appears to be dependent on FVIIa proteolytic activity and activation of functional PAR-2. Migration of MCF-7 cells increases after FVIIa exposure but not after FVIIai treatment [17], suggesting involvement of PARs in this setting as well. Also, TF-dependent migration of non-cancerous cells, such as vascular smooth muscle cells [49], often shows requirement for PAR-2. In this context, in porcine cerebral microvascular endothelial cells TF:FVIIa up-regulates RhoA and cortactin, proteins critically involved in migration, in a PAR-2-dependent manner. During PAR-2 activation, cortactin relocates to the cell periphery and assists in lamellipodia formation. Fibroblasts show an increased chemotactic potential towards PDGF-BB upon treatment with FVIIa but not with FVIIai, suggesting that PAR-2 is also crucial to FVIIa-induced chemotaxis [50]. In a physiological setting, TF-PAR-2-dependent migration is likely to be involved in cutaneous wound healing [51].

In contrast to studies identifying a role for PAR-2 in TF-dependent signaling, a number of reports have also indicated that TF induces migration independent of PAR-2 activation. TF antibodies binding to the FVII(a) binding site induce migration of J82 bladder carcinoma cells [20] and this is dependent on α3, α5 and β1 integrins [25]. In the same cell type, migration toward immobilized fibronectin can be induced by FVIIai, which suggests that binding of FVII to TF in J82 cells is sufficient and proteolytic activity is not a prerequisite for migration [24]. In this set-up, migration was dependent on the TF CT, activation of Rac and p38.

Interestingly, binding of 5G9, which promotes TF-integrin complex formation in HaCaT cells, also promotes migration of this cell type on laminin V in a α3β1-dependent manner. Also, in HaCaT cells and A7 cells transfected to express TF, 5G9 induces TF CT phosphorylation while phosphorylation is required for 5G9-dependent migration [25]. The same study also showed that FVIIa – another inducer of TF/β1 complex formation – increased migration of A7 cells. However, FVIIa did not elicit this effect in cells transfected to express TF CT phosphorylation-deficient mutants. Overall, it is reasonable to posit that PAR-2-independent migration is to some extent dependent on interaction of TF binding with integrins, under the control of FVIIa, and TF CT phosphorylation, potentially leading to a higher migratory capacity of cancer cells and metastasis. However, such a role for integrins in TF signaling has primarily been established in vitro and in vivo evidence for such a role is still lacking.

TF-dependent integrin signaling in angiogenesis and proliferation

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

Evidence that TF is critically involved in angiogenic repertoires comes from studies showing that TF null mice do not survive due to irregular formation of yolk sac vasculature, leading to bloodless yolk sacs and wasting of embryos [52, 53]. In ex vivo aortic sprouting experiments, absence of the TF CT augments vessel formation in a PAR-2-dependent manner [44]. In vitro, down-regulation of TF in endothelial cells and vascular smooth muscle cells impedes the formation of tubules on matrigel. Silencing of TF in endothelial cells results in decreased activation of Akt and Raf/ERK and Ets-1 transcription factor, a critical intermediate in TF-dependent angiogenic processes in vitro [54]. Moreover, TF plays a role in vessel maturation by increasing levels of chemokine ligand-2 in endothelial cells, thereby attracting vascular smooth muscle cells around the newly formed vessel [55]. Interestingly, these angiogenic processes were relatively independent of PAR-2 function and it remains unknown whether and when TF signals through PAR-2 to induce angiogenesis, but the experimental setting (in vitro vs. in vivo) and pathological context (physiological angiogenesis vs. tumour angiogenesis) may play a role.

Apart from its clear role in embryogenesis, TF signaling via PARs is also important for vessel formation in a cancer setting. Blockade of TF:FVIIa proteolytic function using a nematode anticoagulant protein (rNAPc2) diminishes tumour weight and vessel formation [56] and treatment of MDA-MB-231 cells with FVIIa or PAR-2 activation peptides increases VEGF expression, which is a key player in integrin signaling [57]. Similarly, TF-PAR-2 signaling in vivo produces VEGF and additional pro-angiogenic molecules such as IL-8 and CXCL-1. Importantly, in these models, the TF-β1 complex-disrupting antibody 10H10 decreases microvascular density in breast cancer xenografts and impairs IL-8 production, demonstrating that functional TF-β1 integrin coupling results in enhanced angiogenesis [38].

A TF isoform that results from alternative splicing and exclusion of exon 5 in the TF transcript yielding a soluble protein (alternatively spliced TF; asTF) [58], has recently also been implicated in angiogenesis. Unlike TF, asTF does not have procoagulant activity [59, 60] and is not involved in PAR activation [61]. Although TF and asTF have functionally different features, they appear to be involved in similar biological processes, albeit through different modes of action. In studies by Hobbs and colleagues, transfection of the pancreatic cancer cell line Mia-Paca-2 with asTF led to bigger and more vascularized tumours [62]. Nevertheless, it remained unclear whether asTF influences tumour growth, resulting in (hypoxia-driven) angiogenesis, or whether asTF is a direct pro-angiogenic molecule. Our own studies revealed that asTF directly induces angiogenesis in matrigel plug assays and ex vivo aortic sprouting models (Fig.3). Interestingly, proteolytically active FVII and PAR-2 were not required for asTF-dependent angiogenesis, but angiogenesis in this setting rather relies on integrin ligation. asTF ligates distinct integrin subsets to induce a repertoire of angiogenesis-related processes. asTF-dependent endothelial (tip) cell migration is dependent on αvβ3 and capillary formation takes place after asTF-α6β1 ligation [61]. Subsequent studies showed that murine asTF (masTF) is a functional homologue to human asTF (hasTF). Similar to what was observed for hasTF, masTF increased ex vivo sprout formation, endothelial cell migration and capillary formation, although masTF-dependent angiogenesis relies solely on β3 ligation, rather than on a combination of β1 and β3 [63].

image

Figure 3. asTF-induced angiogenesis. asTF ligates endothelial αvβ3 integrins to induce (tip) cell migration as determined by transwells assays. In parallel, asTF facilitates capillary formation on a matrigel surface by binding to α6β1 integrin. Both processes are believed to be important to asTF-dependent angiogenesis, as determined in murine matrigel plug assays.

Download figure to PowerPoint

Tissue factor-integrin interaction also influences cell proliferation. Human coronary artery cells treated with either recombinant TF or TF+ microparticles (see below) proliferated faster and TF-dependent proliferation was independent of FVIIa, as addition of recombinant FVIIa and FXa- and FVII-blocking antibodies did not have any effects on proliferation. Rather, proliferation relied on TF binding to β1 integrin as functional blockade of TF-integrin complexation using a β1 integrin peptide diminished the proliferative phenotype [64]. This study again emphasizes that TF-integrin interaction might be a key player in both proliferative events and tumour angiogenesis in the absence of a functional TF-PAR-2 signaling axis. It should, however, be mentioned that an exogenous soluble artificial form of TF (sTF) induces a β1 integrin-dependent decrease, rather than increase, in proliferation rates in MCF-7 breast cancer cells [39]. Nevertheless, the effects of TF-β1 integrin ligation on proliferation may be cell type and integrin subset dependent.

TF-integrin interactions in thrombosis

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

A body of evidence suggests that TF is a major risk factor for thrombotic complications in different disease settings such as sepsis [65], cancer [66] and atherosclerosis [67]. In atherosclerotic plaques, TF is expressed by intraplaque monocytes/macrophages [68], and upon rupture of the vulnerable plaque TF is released into the bloodstream and activates coagulation, thus leading to thrombosis. Similarly, TF may play an important role in cancer-associated thrombosis, as TF is dramatically up-regulated on cancer cells. However, it remains unclear how cell-exposed TF contributes to coagulation activation in disease. While TF is normally tethered to the cell surface, it may localize to the blood on the surface of submicron vesicles that are shed from the surface of intravascular cells, such as platelets, endothelial cells and leukocytes, but also from tumour cells [69]. These vesicles that arise from blebbing of the cell are called microparticles (MPs) and their size ranges from 50 to 1000 nm. Several studies have found that plasma MP-TF concentration or MP-TF procoagulant activity positively correlates with the risk of VTE and even with recurrent VTE. In a cancer setting, TF activity on microparticles is higher in patients with VTE compared with patients without VTE [70-74] and high MP-TF levels in plasma are predictive of VTE in prospective studies [75]. It is not entirely clear how TF+ MPs could contribute to development of a thrombus, but experimental studies suggest that MPs can induce a procoagulant state by fusing with endothelial cells and platelets through binding of MP PSGL-1 to endothelial/platelet P-selectin [76, 77]. Indeed, work by Thomas et al. [78] shows that TF+ MPs decrease bleeding times and lead to arteriole occlusion in a vessel damage model, in a P-selectin-dependent manner. Nevertheless, how TF shedding and TF activity on the surface of MPs are regulated remains somewhat elusive.

In macrophages and smooth muscle cells, ATP-induced P2X7 receptor activation results in prothrombotic MP release in a protein disulphide isomerase-dependent manner. Importantly, these MPs were shown to carry both TF and β1 integrin. Shedding of these proteins on MP surfaces is readily inhibited by the use of free thiol blockers and inhibiting protein disulphide isomerase antibodies, indicating the involvement of thiol-dependent pathways in TF and β1 shedding [79]. At the same time, this demonstrates that also in a prothrombotic setting, TF and β1 localize to similar subcellular domains and it is tempting to speculate that TF and β1 redox-dependently associate on MP surfaces. A recent study shows that not only do TF and β1 co-localize on MPs, disruption of TF/β1 complexes decreases β1 levels on endothelial cell-derived MPs, suggesting that transfer of β1 integrin to MPs is dependent on its binding to TF. Moreover, MP-exposed β1 integrin can act as an adhesion molecule, promoting sustained MP binding to ECMs such as collagen and fibronectin, and thereby promoting coagulant activity of MP-TF [80].

Integrins may also regulate TF coagulant activity in a more direct fashion. Evidence for this comes from our studies employing TF/β1 co-precipitations. FVIIa enhances TF-β1 integrin complexation 2–3-fold, while coagulant activity in these co-precipitates was unchanged. Also, complex formation required high (10 nM) concentrations of FVIIa, a feature that suggests the involvement of (reduced) coagulant-inactive TF. Additionally, cellular exposure to the TF coagulant function-blocking antibody 5G9, thus precluding FX binding to TF:FVIIa, increases TF binding to β1 integrin [38], suggesting that TF complexation with β1 only occurs in the absence of FX binding. It is now appreciated that coagulant-inactive, cryptic TF may not be explained by one model [40, 41, 81-83]. Rather, coagulant-inactive TF may comprise a set of TF molecules that are kept inactive by low local PS exposure, protein disulphide isomerase-dependent mechanisms and β1 integrin-dependent mechanisms. Nevertheless, to support such a theory, further studies on this subject are warranted.

Although asTF itself does not harbour any coagulant activity, asTF-integrin interaction is believed to influence arterial thrombosis. Our recent work showed that asTF is expressed in intraplaque macrophages and asTF can functionally bind to β1 integrins to enhance expression of endothelial cell adhesion molecules, such as VCAM, ICAM and P-selectin [79]. Indeed, exposure of endothelial cells to asTF promotes adhesion of peripheral blood mononuclear cells under orbital shear conditions and under laminar flow. Moreover, asTF potentiates peripheral blood mononuclear cell migration through MVEC monolayers under MCP-1 gradient, showing that asTF-β1 interaction may promote atherosclerosis and plaque instability by facilitating adhesion receptor-dependent monocyte transmigration.

Conclusion

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference

The current understanding of the interaction between TF isoforms and integrins is that they may play a critical role in cancer progression and thrombotic complications, although the mechanistic evidence for this is still slim. They may affect each other's function reciprocally; TF can affect migration and adhesion of cells by binding to integrins, while binding of integrins to TF can influence TF-dependent PAR-2 signaling and coagulant function.

It is still unclear how important these interactions are in (patho)physiology as support for a link between TF/integrin interaction and pathological outcome in, for example, cancer patients is still missing. Furthermore, the emerging picture is complicated by the fact that TF complexation with different integrin subsets and the effect of different extracellular matrices on complex formation have not yet been extensively characterized. Nevertheless, emergence of TF-specific antibodies that differentially modulate TF-integrin complexes and thus TF function may encourage extensive research on the interaction of TF with integrins and its subsequent impact on cancerous and thrombotic disease.

Reference

  1. Top of page
  2. Summary
  3. Introduction
  4. TF and actin dynamics
  5. TF-integrin complex formation
  6. Integrin dependent TF signaling
  7. TF integrin signaling in migration
  8. TF-dependent integrin signaling in angiogenesis and proliferation
  9. TF-integrin interactions in thrombosis
  10. Conclusion
  11. Disclosure of Conflicts of Interest
  12. Reference
  • 1
    Monroe DM, Hoffman M. What does it take to make the perfect clot? Arterioscler Thromb Vasc Biol 2006; 26: 418.
  • 2
    Bach RR. Tissue factor encryption. Arterioscler Thromb Vasc Biol 2006; 26: 45661.
  • 3
    Chen VM, Ahamed J, Versteeg HH, Berndt MC, Ruf W, Hogg PJ. Evidence for activation of tissue factor by an allosteric disulfide bond. Biochemistry 2006; 45: 120208.
  • 4
    Palumbo JS, Talmage KE, Massari JV, La Jeunesse CM, Flick MJ, Kombrinck KW, Jirouskova M, Degen JL. Platelets and fibrin(ogen) increase metastatic potential by impeding natural killer cell-mediated elimination of tumor cells. Blood 2005; 105: 17885.
  • 5
    Palumbo JS, Talmage KE, Massari JV, La Jeunesse CM, Flick MJ, Kombrinck KW, Hu Z, Barney KA, Degen JL. Tumor cell-associated tissue factor and circulating hemostatic factors cooperate to increase metastatic potential through natural killer cell-dependent and-independent mechanisms. Blood 2007; 110: 13341.
  • 6
    Kakkar AK, Lemoine NR, Scully MF, Tebbutt S, Williamson RC. Tissue factor expression correlates with histological grade in human pancreatic cancer. Br J Surg 1995; 82: 11014.
  • 7
    Sawada M, Miyake S, Ohdama S, Matsubara O, Masuda S, Yakumaru K, Yoshizawa Y. Expression of tissue factor in non-small-cell lung cancers and its relationship to metastasis. Br J Cancer 1999; 79: 4727.
  • 8
    Ueno T, Toi M, Koike M, Nakamura S, Tominaga T. Tissue factor expression in breast cancer tissues: its correlation with prognosis and plasma concentration. Br J Cancer 2000; 83: 16470.
  • 9
    Yu JL, May L, Lhotak V, Shahrzad S, Shirasawa S, Weitz JI, Coomber BL, Mackman N, Rak JW. Oncogenic events regulate tissue factor expression in colorectal cancer cells: implications for tumor progression and angiogenesis. Blood 2005; 105: 173441.
  • 10
    Milsom CC, Yu JL, Mackman N, Micallef J, Anderson GM, Guha A, Rak JW. Tissue factor regulation by epidermal growth factor receptor and epithelial-to-mesenchymal transitions: effect on tumor initiation and angiogenesis. Cancer Res 2008; 68: 1006876.
  • 11
    Rong Y, Post DE, Pieper RO, Durden DL, van Meir EG, Brat DJ. PTEN and hypoxia regulate tissue factor expression and plasma coagulation by glioblastoma. Cancer Res 2005; 65: 140613.
  • 12
    Vrana JA, Stang MT, Grande JP, Getz MJ. Expression of tissue factor in tumor stroma correlates with progression to invasive human breast cancer: paracrine regulation by carcinoma cell-derived members of the transforming growth factor beta family. Cancer Res 1996; 56: 506370.
  • 13
    Camerer E, Huang W, Coughlin SR. Tissue factor- and factor X-dependent activation of protease-activated receptor 2 by factor VIIa. Proc Natl Acad Sci USA 2000; 97: 525560.
  • 14
    Huttenlocher A, Horwitz AR. Integrins in cell migration. Cold Spring Harb Perspect Biol 2011; 3: a005074.
  • 15
    Ridley AJ, Schwartz MA, Burridge K, Firtel RA, Ginsberg MH, Borisy G, Parsons JT, Horwitz AR. Cell migration: integrating signals from front to back. Science 2003; 302: 17049.
  • 16
    Fischer EG, Riewald M, Huang HY, Miyagi Y, Kubota Y, Mueller BM, Ruf W. Tumor cell adhesion and migration supported by interaction of a receptor-protease complex with its inhibitor. J Clin Invest 1999; 104: 121321.
  • 17
    Muller M, Albrecht S, Golfert F, Hofer A, Funk RH, Magdolen V, Flossel C, Luther T. Localization of tissue factor in actin-filament-rich membrane areas of epithelial cells. Exp Cell Res 1999; 248: 13647.
  • 18
    Pena E, Arderiu G, Badimon L. Subcellular localization of tissue factor and human coronary artery smooth muscle cell migration. J Thromb Haemost 2012; Sep 1. doi: 10.1111/j.1538-7836.2012.04910.x. [Epub ahead of print].
  • 19
    Winder SJ, Ayscough KR. Actin-binding proteins. J Cell Sci 2005; 118: 6514.
  • 20
    Ott I, Fischer EG, Miyagi Y, Mueller BM, Ruf W. A role for tissue factor in cell adhesion and migration mediated by interaction with actin-binding protein 280. J Cell Biol 1998; 140: 124153.
  • 21
    Ettelaie C, Elkeeb AM, Maraveyas A, Collier ME. p38alpha phosphorylates serine 258 within the cytoplasmic domain of tissue factor and prevents its incorporation into cell-derived microparticles. Biochim Biophys Acta 2013; 1833: 61321.
  • 22
    Zioncheck TF, Roy S, Vehar GA. The cytoplasmic domain of tissue factor is phosphorylated by a protein kinase C-dependent mechanism. J Biol Chem 1992; 267: 35614.
  • 23
    Versteeg HH, Hoedemaeker I, Diks SH, Stam JC, Spaargaren M, van Bergen En Henegouwen PM, van Deventer SJ, Peppelenbosch MP. Factor VIIa/tissue factor-induced signaling via activation of Src-like kinases, phosphatidylinositol 3-kinase, and Rac. J Biol Chem 2000; 275: 287506.
  • 24
    Ott I, Weigand B, Michl R, Seitz I, Sabbari-Erfani N, Neumann FJ, Schomig A. Tissue factor cytoplasmic domain stimulates migration by activation of the GTPase Rac1 and the mitogen-activated protein kinase p38. Circulation 2005; 111: 34955.
  • 25
    Dorfleutner A, Hintermann E, Tarui T, Takada Y, Ruf W. Cross-talk of integrin alpha3beta1 and tissue factor in cell migration. Mol Biol Cell 2004; 15: 441625.
  • 26
    Zamir E, Geiger B. Molecular complexity and dynamics of cell-matrix adhesions. J Cell Sci 2001; 114: 358390.
  • 27
    Frisch SM, Francis H. Disruption of epithelial cell-matrix interactions induces apoptosis. J Cell Biol 1994; 124: 61926.
  • 28
    Meredith JE Jr, Fazeli B, Schwartz MA. The extracellular matrix as a cell survival factor. Mol Biol Cell 1993; 4: 95361.
  • 29
    Versteeg HH, Spek CA, Richel DJ, Peppelenbosch MP. Coagulation factors VIIa and Xa inhibit apoptosis and anoikis. Oncogene 2004; 23: 4107.
  • 30
    Assoian RK, Schwartz MA. Coordinate signaling by integrins and receptor tyrosine kinases in the regulation of G1 phase cell-cycle progression. Curr Opin Genet Dev 2001; 11: 4853.
  • 31
    Brooks PC, Clark RA, Cheresh DA. Requirement of vascular integrin alpha v beta 3 for angiogenesis. Science 1994; 264: 56971.
  • 32
    Kim S, Bell K, Mousa SA, Varner JA. Regulation of angiogenesis in vivo by ligation of integrin alpha5beta1 with the central cell-binding domain of fibronectin. Am J Pathol 2000; 156: 134562.
  • 33
    Roman J, Ritzenthaler JD, Roser-Page S, Sun X, Han S. alpha5beta1-integrin expression is essential for tumor progression in experimental lung cancer. Am J Respir Cell Mol Biol 2010; 43: 68491.
  • 34
    Stroeken PJ, van Rijthoven EA, van der Valk MA, Roos E. Targeted disruption of the beta1 integrin gene in a lymphoma cell line greatly reduces metastatic capacity. Cancer Res 1998; 58: 156977.
  • 35
    Desgrosellier JS, Cheresh DA. Integrins in cancer: biological implications and therapeutic opportunities. Nat Rev Cancer 2010; 10: 922.
  • 36
    Felding-Habermann B. Integrin adhesion receptors in tumor metastasis. Clin Exp Metastasis 2003; 20: 20313.
  • 37
    Schwartz MA, Assoian RK. Integrins and cell proliferation: regulation of cyclin-dependent kinases via cytoplasmic signaling pathways. J Cell Sci 2001; 114: 255360.
  • 38
    Versteeg HH, Schaffner F, Kerver M, Petersen HH, Ahamed J, Felding-Habermann B, Takada Y, Mueller BM, Ruf W. Inhibition of tissue factor signaling suppresses tumor growth. Blood 2008; 111: 1909.
  • 39
    Collier ME, Li C, Ettelaie C. Influence of exogenous tissue factor on estrogen receptor alpha expression in breast cancer cells: involvement of beta1-integrin, PAR-2, and mitogen-activated protein kinase activation. Mol Cancer Res 2008; 6: 180718.
  • 40
    Ahamed J, Versteeg HH, Kerver M, Chen VM, Mueller BM, Hogg PJ, Ruf W. Disulfide isomerization switches tissue factor from coagulation to cell signaling. Proc Natl Acad Sci USA 2006; 103: 139327.
  • 41
    van den Hengel LG, Kocaturk B, Reitsma PH, Ruf W, Versteeg HH. Complete abolishment of coagulant activity in monomeric disulfide-deficient tissue factor. Blood 2011; 118: 34468.
  • 42
    van den Hengel LG, Osanto S, Reitsma PH, Versteeg HH. Murine tissue factor coagulant activity is critically dependent on the presence of an intact allosteric disulfide. Haematologica 2013; 98: 1538.
  • 43
    Randolph GJ, Luther T, Albrecht S, Magdolen V, Muller WA. Role of tissue factor in adhesion of mononuclear phagocytes to and trafficking through endothelium in vitro. Blood 1998; 92: 416777.
  • 44
    Belting M, Dorrell MI, Sandgren S, Aguilar E, Ahamed J, Dorfleutner A, Carmeliet P, Mueller BM, Friedlander M, Ruf W. Regulation of angiogenesis by tissue factor cytoplasmic domain signaling. Nat Med 2004; 10: 5029.
  • 45
    Schaffner F, Versteeg HH, Schillert A, Yokota N, Petersen LC, Mueller BM, Ruf W. Cooperation of tissue factor cytoplasmic domain and PAR-2 signaling in breast cancer development. Blood 2010; 116: 610613.
  • 46
    Zhou H, Hu H, Shi W, Ling S, Wang T, Wang H. The expression and the functional roles of tissue factor and protease-activated receptor-2 on SW620 cells. Oncol Rep 2008; 20: 106976.
  • 47
    Hjortoe GM, Petersen LC, Albrektsen T, Sorensen BB, Norby PL, Mandal SK, Pendurthi UR, Rao LV. 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. Blood 2004; 103: 302937.
  • 48
    Gessler F, Voss V, Dutzmann S, Seifert V, Gerlach R, Kogel D. Inhibition of tissue factor/protease-activated receptor-2 signaling limits proliferation, migration and invasion of malignant glioma cells. Neuroscience 2010; 165: 131222.
  • 49
    Marutsuka K, Hatakeyama K, Sato Y, Yamashita A, Sumiyoshi A, Asada Y. Protease-activated receptor 2 (PAR-2) mediates vascular smooth muscle cell migration induced by tissue factor/factor VIIa complex. Thromb Res 2002; 107: 2716.
  • 50
    Siegbahn A, Johnell M, Rorsman C, Ezban M, Heldin CH, Ronnstrand L. Binding of factor VIIa to tissue factor on human fibroblasts leads to activation of phospholipase C and enhanced PDGF-BB-stimulated chemotaxis. Blood 2000; 96: 34528.
  • 51
    Xu Z, Xu H, Ploplis VA, Castellino FJ. Factor VII deficiency impairs cutaneous wound healing in mice. Mol Med 2010; 16: 16776.
  • 52
    Carmeliet P, Mackman N, Moons L, Luther T, Gressens P, van Vlaenderen I, Demunck H, Kasper M, Breier G, Evrard P, Muller M, Risau W, Edgington T, Collen D. Role of tissue factor in embryonic blood vessel development. Nature 1996; 383: 735.
  • 53
    Toomey JR, Kratzer KE, Lasky NM, Stanton JJ, Broze GJ Jr. Targeted disruption of the murine tissue factor gene results in embryonic lethality. Blood 1996; 88: 15837.
  • 54
    Arderiu G, Pena E, Aledo R, Badimon L. Tissue factor-Akt signaling triggers microvessel formation. J Thromb Haemost 2012; 10: 1895905.
  • 55
    Arderiu G, Pena E, Aledo R, Juan-Babot O, Badimon L. Tissue factor regulates microvessel formation and stabilization by induction of chemokine (C-C motif) ligand 2 expression. Arterioscler Thromb Vasc Biol 2011; 31: 260715.
  • 56
    Hembrough TA, Swartz GM, Papathanassiu A, Vlasuk GP, Rote WE, Green SJ, Pribluda VS. Tissue factor/factor VIIa inhibitors block angiogenesis and tumor growth through a nonhemostatic mechanism. Cancer Res 2003; 63: 29973000.
  • 57
    Illés A, Enyedi B, Tamás P, Balázs A, Bogel G, Melinda  , Lukács  , Buday L. Cortactin is required for integrin-mediated cell spreading. Immunol Lett 2006; 104: 12430.
  • 58
    Bogdanov VY, Balasubramanian V, Hathcock J, Vele O, Lieb M, Nemerson Y. Alternatively spliced human tissue factor: a circulating, soluble, thrombogenic protein. Nat Med 2003; 9: 45862.
  • 59
    Censarek P, Bobbe A, Grandoch M, Schror K, Weber AA. Alternatively spliced human tissue factor (asHTF) is not pro-coagulant. Thromb Haemost 2007; 97: 114.
  • 60
    Szotowski B, Antoniak S, Rauch U. Alternatively spliced tissue factor: a previously unknown piece in the puzzle of hemostasis. Trends Cardiovasc Med 2006; 16: 17782.
  • 61
    van den Berg YW, van den Hengel LG, Myers HR, Ayachi O, Jordanova E, Ruf W, Spek CA, Reitsma PH, Bogdanov VY, Versteeg HH. Alternatively spliced tissue factor induces angiogenesis through integrin ligation. Proc Natl Acad Sci USA 2009; 106: 19497502.
  • 62
    Hobbs JE, Zakarija A, Cundiff DL, Doll JA, Hymen E, Cornwell M, Crawford SE, Liu N, Signaevsky M, Soff GA. Alternatively spliced human tissue factor promotes tumor growth and angiogenesis in a pancreatic cancer tumor model. Thromb Res 2007; 120(Suppl. 2): S1321.
  • 63
    Godby RC, van den Berg YW, Srinivasan R, Sturm R, Hui DY, Konieczny SF, Aronow BJ, Ozhegov E, Ruf W, Versteeg HH, Bogdanov VY. Nonproteolytic properties of murine alternatively spliced tissue factor: implications for integrin-mediated signaling in murine models. Mol Med 2012; 18: 7719.
  • 64
    Collier ME, Ettelaie C. Induction of endothelial cell proliferation by recombinant and microparticle-tissue factor involves beta1-integrin and extracellular signal regulated kinase activation. Arterioscler Thromb Vasc Biol 2010; 30: 18107.
  • 65
    Drake TA, Cheng J, Chang A, Taylor FB Jr. Expression of tissue factor, thrombomodulin, and E-selectin in baboons with lethal Escherichia coli sepsis. Am J Pathol 1993; 142: 145870.
  • 66
    Khorana AA, Francis CW, Menzies KE, Wang JG, Hyrien O, Hathcock J, Mackman N, Taubman MB. Plasma tissue factor may be predictive of venous thromboembolism in pancreatic cancer. J Thromb Haemost 2008; 6: 19835.
  • 67
    Ardissino D, Merlini PA, Ariens R, Coppola R, Bramucci E, Mannucci PM. Tissue-factor antigen and activity in human coronary atherosclerotic plaques. Lancet 1997; 349: 76971.
  • 68
    Wilcox JN, Smith KM, Schwartz SM, Gordon D. Localization of tissue factor in the normal vessel wall and in the atherosclerotic plaque. Proc Natl Acad Sci USA 1989; 86: 283943.
  • 69
    Giesen PL, Rauch U, Bohrmann B, Kling D, Roque M, Fallon JT, Badimon JJ, Himber J, Riederer MA, Nemerson Y. Blood-borne tissue factor: another view of thrombosis. Proc Natl Acad Sci USA 1999; 96: 23115.
  • 70
    Khorana AA, Ahrendt SA, Ryan CK, Francis CW, Hruban RH, Hu YC, Hostetter G, Harvey J, Taubman MB. Tissue factor expression, angiogenesis, and thrombosis in pancreatic cancer. Clin Cancer Res 2007; 13: 28705.
  • 71
    Manly DA, Wang J, Glover SL, Kasthuri R, Liebman HA, Key NS, Mackman N. Increased microparticle tissue factor activity in cancer patients with venous thromboembolism. Thromb Res 2010; 125: 5112.
  • 72
    Tesselaar ME, Romijn FP, van der Linden IK, Bertina RM, Osanto S. Microparticle-associated tissue factor activity in cancer patients with and without thrombosis. J Thromb Haemost 2009; 7: 14213.
  • 73
    Tilley RE, Holscher T, Belani R, Nieva J, Mackman N. Tissue factor activity is increased in a combined platelet and microparticle sample from cancer patients. Thromb Res 2008; 122: 6049.
  • 74
    Zwicker JI, Liebman HA, Neuberg D, Lacroix R, Bauer KA, Furie BC, Furie B. Tumor-derived tissue factor-bearing microparticles are associated with venous thromboembolic events in malignancy. Clin Cancer Res 2009; 15: 683040.
  • 75
    Del Conde I, Bharwani LD, Dietzen DJ, Pendurthi U, Thiagarajan P, Lopez JA. Microvesicle-associated tissue factor and Trousseau's syndrome. J Thromb Haemost 2007; 5: 704.
  • 76
    Furie B, Furie BC. Role of platelet P-selectin and microparticle PSGL-1 in thrombus formation. Trends Mol Med 2004; 10: 1718.
  • 77
    Hrachovinova I, Cambien B, Hafezi-Moghadam A, Kappelmayer J, Camphausen RT, Widom A, Xia L, Kazazian HH Jr, Schaub RG, McEver RP, Wagner DD. Interaction of P-selectin and PSGL-1 generates microparticles that correct hemostasis in a mouse model of hemophilia A. Nat Med 2003; 9: 10205.
  • 78
    Thomas GM, Panicot-Dubois L, Lacroix R, Dignat-George F, Lombardo D, Dubois C. Cancer cell-derived microparticles bearing P-selectin glycoprotein ligand 1 accelerate thrombus formation in vivo. J Exp Med 2009; 206: 191327.
  • 79
    Furlan-Freguia C, Marchese P, Gruber A, Ruggeri ZM, Ruf W. P2X7 receptor signaling contributes to tissue factor-dependent thrombosis in mice. J Clin Invest 2011; 121: 293244.
  • 80
    Ettelaie C, Collier ME, Mei MP, Xiao YP, Maraveyas A. Enhanced binding of tissue factor-microparticles to collagen-IV and fibronectin leads to increased tissue factor activity in vitro. Thromb Haemost 2013; 109: 6171.
  • 81
    Bach RR, Moldow CF. Mechanism of tissue factor activation on HL-60 cells. Blood 1997; 89: 32706.
  • 82
    Sevinsky JR, Rao LV, Ruf W. Ligand-induced protease receptor translocation into caveolae: a mechanism for regulating cell surface proteolysis of the tissue factor-dependent coagulation pathway. J Cell Biol 1996; 133: 293304.
  • 83
    Wolberg AS, Monroe DM, Roberts HR, Hoffman MR. Tissue factor de-encryption: ionophore treatment induces changes in tissue factor activity by phosphatidylserine-dependent and -independent mechanisms. Blood Coagul Fibrinolysis 1999; 10: 20110.