Regulation of tissue factor activity by interaction with the first PDZ domain of MAGI1

BACKGROUND

Tissue factor (TF) activity is stringently regulated through processes termed encryption. Post-translational modification of TF and its interactions with various protein and lipid moieties allows for a multi-step de-encryption of TF and procoagulant activation. Membrane-associated guanylate kinase-with inverted configuration (MAGI) proteins are known to regulate the localisation and activity of a number of proteins including cell-surface receptors.

METHODS

The interaction of TF with MAGI1 protein was examined as a means of regulating TF activity. MDA-MB-231 cell line was used which express TF and MAGI1, and respond well to protease activated receptor (PAR)2 activation. Proximity ligation assay (PLA), co-immunoprecipitation and pull-down experiments were used to examine the interaction of TF with MAGI1-3 proteins and to investigate the influence of PAR2 activation. Furthermore, by cloning and expressing the PDZ domains from MAGI1, the TF-binding domain was identified. The ability of the recombinant PDZ domains to act as competitors for MAGI1, allowing the induction of TF procoagulant and signalling activity was then examined.

RESULTS

PLA and fluorescence microscopic analysis indicated that TF predominantly associates with MAGI1 and less with MAGI2 and MAGI3 proteins. The interaction of TF with MAGI1 was also demonstrated by both co-immunoprecipitation of TF with MAGI1, and co-immunoprecipitation of MAGI1 with TF. Moreover, activation of PAR2 resulted in reduction in the association of these two proteins. Pull-down assays using TF-cytoplasmic domain peptides indicated that the phosphorylation of Ser253 within TF prevents its association with MAGI1. Additionally, the five HA-tagged PDZ domains of MAGI1 were overexpressed separately, and the putative TF-binding domain was identified as PDZ1 domain. Expression of this PDZ domain in cells significantly augmented the TF activity measured both as thrombin-generation and also TF-mediated proliferative signalling.

CONCLUSIONS

Our data indicate a stabilising interaction between TF and the PDZ-1 domain of MAGI1 and demonstrate that the activation of PAR2 disrupts this interaction. The release of TF from MAGI1 appears to be an initial step in TF de-encryption, associated with increased TF-mediated procoagulant and signalling activities. This mechanism is also likely to lead to further interactions and modifications leading to further enhancement of procoagulant activity, or the release of TF.

Abstract 224: Establishing de novo platform for whole genome sequencing of pancreatic cyst fluid for early detection and diagnosis of pancreatic cancer

Background: Pancreatic cancer (PC) is a leading cause of cancer-related deaths globally. Accurate PC detection at early or premalignant stage, when surgery is effective, would increase survival rates and prevent unnecessary surgery or surveillance. About 10% of PC cases arise from pancreatic cystic (PCy) lesions, including intraductal papillary mucinous neoplasms (IPMNs), which constitute up to 30% of resective pancreatic surgery. Current diagnostic methods cannot accurately predict which cysts are malignancy-associated. Molecular diagnostic attempts using PCy fluid (PCyF), as a liquid biopsy, to analyze common mutations associated with PC development are yet to contribute to early diagnosis. Whole genome sequencing (WGS) is utilized in various cancers, PC inclusive, for detecting genetic changes associated with carcinogenesis, but not in PCyF due to technical limitations, including isolated DNA purity.

Aim: To establish a de novo platform for WGS of PCyF.

Methods: Three PC cell lines (PANC1, AsPC1 and MiaPACA2) were cultured in vitro. Five PCyF samples, including one from PC patient (based on histopathology report) were obtained from the University of Hull (UoH)-based ethically approved study (TEM-PAC, NCT03536793, REC 18/LO/0736). Genomic DNA (gDNA) isolation protocol was optimized using magnetic- and column-based kits (MagMAX DNA Multi-sample and PureLink Genomic DNA; ThermoFisher) and varying number of cultured cells (100,000-500,000; to determine detection limits) and used for PCyF samples (35 - 70 μl). gDNA purity (A260/280 ≥ 1.8 and A260/230 ≥ 2) and concentration were determined using NanoDrop2000, and amount per cell was calculated. WGS of PC sample was done using 200ng of gDNA on Illumina NovaSeq6000 platform (Novogene Ltd, Cambridge, UK) at 50x sequencing depth. Sequencing reads were mapped to reference human genome (hg38) with the Burrows-Wheeler Aligner to detect disease-related genomic variants in each chromosome covered - insertion-deletions (InDels), single nucleotide polymorphisms (SNPs), copy number variants (CNVs) and structural variants (SVs) with subsequent analysis using UoH High Performance Computer Viper.

Results: Pure gDNA was isolated from all cell lines (0.03 ± 0.01 ng/cell) and from PCyF samples (217 ng - 13.8 μg; equivalent to 7,000 - 690,000 cells and 8 - 346 ng/µl). WGS of PC patient PCyF revealed several cancer-related changes/variants including 106,776 (12.31%) novel InDels, 181,000 more SNPs, CNVs (337 gains; 149 losses) and 10,024 SVs.

Conclusions: We established a de novo platform for WGS analysis of gDNA isolated from small volumes of PCyF samples, including estimation of previously unknown cellular density in these liquid biopsies. Our proof-of-concept study provides a foundation for a large-scale analysis of PCyF samples from TEM-PAC and other clinical studies using WGS for early detection and diagnosis of PC.

Citation Format: Adenike Adekeye, Farzana Haque, Camille Ettelaie, Leonid Nikitenko, Anthony Maraveyas. Establishing de novo platform for whole genome sequencing of pancreatic cyst fluid for early detection and diagnosis of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 224.

Tissue factor (TF) and factor VII/TF ratio (fVIIa:TF) as potential indicators of malignancy in pancreatic cystic lesions

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Background: Premalignant pancreatic cellular genotype may remain stable for many years, but compounding conditions can produce rapid malignant cellular transformation. This onset is rarely spontaneous and is often associated with the presence of inflammation. One inflammatory modulator is “tissue factor (TF),” which usually acts in complex with “coagulation factor VIIa (fVIIa)” to initiate coagulation. The role of TF in malignancy and its impact beyond thrombosis on cell proliferation, angiogenesis, and metastasis is well established. This suggests that TF may be a diagnostic marker in the inflammatory microenvironment of the precursor lesions of pancreatic cancer. Aim: To examine the potential of TF concentrations and the fVII:TF ratio within pancreatic cyst fluid as indicators of malignant cellular transformation from benign to malignant. Methods: Cyst fluid was prospectively collected from 31 patients with pancreatic cystic lesions (REC 18/LO/0736) and analysed in a blinded fashion. The level of TF and fVIIa proteins were measured by ELISA, and the fVIIa:TF ratios calculated. A cut-off value for TF concentration was determined using a ROC curve and compared to the conventional assessment parameters, including radiological features, carcinoembryonic antigen (CEA) and amylase. Results: Patients were categorised into four groups based on histology. Significant histological stage-dependent increases in TF level were observed, which corresponded to the progression of the normal ductal epithelium to invasive adenocarcinoma. The mean TF concentration was significantly higher ( p= 0.006) in the high-risk group (high-grade dysplasia & malignant; 1.17 ng/ml, 95% CI 0.68, 1.67) vs the low-risk group (benign & low-grade dysplasia; 0.27 ng/ml, 95% CI 0.1, 0.44). A strong positive correlation between TF concentration and the high-risk group was observed (correlation coefficient 0.746, p < 0.001, the cut-off value for TF 0.75 ng/ml, AUC 0.877, p= 0.002). In addition, the fVIIa:TF ratio, was marginally lower ( p= 0.274) in the high-risk group (mean = 84.82 [95% CI 0, 185.04]) vs the low-risk group (mean = 437.46 [95% CI 0, 901.02]). TF concentrations performed consistently better as an indicator of malignant transformation when compared to the conventional parameters and will be presented at the meeting. Conclusions: Cyst-associated TF levels appear to correlate with the cytological progression to the malignant phenotype, while the fVIIa:TF ratio indicates a breakdown in the ability of the body to contain the disease. Such indicators may allow better presurgical discrimination of malignant potential of tumours and offer a more nuanced tool for monitoring indeterminate cystic lesions. Further work is needed with a larger cohort to confirm these findings.

Synthesis and analysis of small molecules to restrain the function of tissue factor within tumour cells

Introduction: The restriction of prolyl-protein cis/trans isomerase 1 (Pin1) activity has been shown to prevent the release of tissue factor (TF) leading to the accumulation of the latter protein within the cell. This study tested the ability of novel small molecules to inhibit Pin1, suppress TF activity and release, and induce cellular apoptosis. Methods: Four compounds were designed and synthesised based on modification of 5-(p-methoxyphenyl)-2-methylfuran-3-carbonyl amide and the outcome on MDA-MB-231 and primary cells examined. These compounds contained 3-(2-naphthyl)-_D-alanine (4a), _D-tryptophan (4b), _D-phenylalanine (4c), and _D-tyrosine (4d) at the amino-termini. Results: Treatment of cells with compound 4b and 4d reduced the cell-surface TF activity after 60 min on MDA-MB-231 cells. Incubation with compound 4d also reduced TF antigen on the cell surface and its incorporation into microvesicles, while compounds 4a and 4b significantly increased TF release. None of the four compounds significantly altered the total amount of TF antigen or TF mRNA expression. Compound 4b and 4d also suppressed the binding of Pin1 to TF-cytoplasmic domain peptide. However, compound 4d reduced while compound 4b increased the Pin1 isomerase activity. Finally, treatment with compound 4b and 4d reduced the cell numbers, increased nuclear localisation of p53, Bax protein and bax mRNA expression and induced cellular apoptosis in MDA-MB-231 but not primary endothelial cells. Conclusions: In conclusion, we have identified small molecules to regulate the function of TF within cells. Two of these compounds may prove to be beneficial in moderating TF function specifically and restrain TF-mediated tumour growth without detrimental outcomes on normal vascular cells.

De-Palmitoylation of Tissue Factor Regulates Its Activity, Phosphorylation and Cellular Functions

In this study, the role of de-palmitoylation of tissue factor (TF) in the decryption of its activity was explored. TF-tGFP constructs were prepared by mutagenesis-substitution at Cys245 to prevent or mimic palmitolyation. Additionally, to reduce TF de-palmitoylation, the expression of palmitoyl-protein thioesterases (PPT) was suppressed. Other TF mutants were prepared with altered flexibility, hydrophobicity or length of the transmembrane domain. The outcome of these alterations on fXa-generation, fVIIa binding, Ser253 phosphorylation and TF-microvesicle release were assessed in endothelial cells, and the influence on endothelial and MCF-7 cell proliferation and apoptosis was analysed. Preventing TF palmitoylation (TF_Ser245-tGFP), increasing the hydrophobicity (TF_Phe241-tGFP) or lengthening (TF_LongTM-tGFP) of the transmembrane domain enhanced fXa-generation in resting cells compared to cells expressing TF_Wt-tGFP, but fXa-generation was not further increased following PAR2 activation. Extending the available length of the transmembrane domain enhanced the TF-tGFP release within microvesicles and Ser253 phosphorylation and increased cell proliferation. Moreover, prevention of PKCα-mediated Ser253 phosphorylation with Gö6976 did not preclude fXa-generation. Conversely, reducing the hydrophobicity (TF_Ser242-tGFP), shortening (TF_ShortTM-tGFP) or reducing the flexibility (TF_Val225-tGFP) of the transmembrane domain suppressed fXa-generation, fVIIa-HRP binding and Ser253 phosphorylation following PAR2 activation. PPT knock-down or mimicking palmitoylation (TF_Phe245-tGFP) reduced fXa-generation without affecting fVIIa binding. This study has for the first time shown that TF procoagulant activity is regulated through de-palmitoylation, which alters the orientation of its transmembrane domain and is independent of TF phosphorylation. However, Ser253 phosphorylation is facilitated by changes in the orientation of the transmembrane domain and can induce TF-cellular signalling that influences cellular proliferation/apoptosis.

Factor VIIa Regulates the Level of Cell-Surface Tissue Factor through Separate but Cooperative Mechanisms

Simple Summary

Under normal conditions, blood coagulation is suppressed to prevent thrombosis. However, during inflammatory conditions such as injury or disease conditions, the protein “tissue factor (TF)” is expressed on the surface of the cells and is also released into the bloodstream within cell-derived vesicles called “microvesicles”. TF appears first at the site of trauma which makes TF suitable for determining the extent of damage and instructing cells to proliferate and repair, or if severely damaged, to die. The relationship between cancer and thrombosis was reported in the early part of the 19th century. Cancer cells and particularly those with aggressive tendencies have the ability to produce, and then optimise the amount of TF on the cell, in order to maximise the pro-survival and proliferative properties of this protein. This study has demonstrated some of the mechanisms by which cells control excessive amounts of TF, to levels ideal for tumour survival and growth.

Abstract

Procoagulant activity of tissue factor (TF) in response to injury or inflammation is accompanied with cellular signals which determine the fate of cells. However, to prevent excessive signalling, TF is rapidly dissipated through release into microvesicles, and/or endocytosis. To elucidate the mechanism by which TF signalling may become moderated on the surface of cells, the associations of TF, fVII/fVIIa, PAR2 and caveolin-1 on MDA-MB-231, BxPC-3 and 786-O cells were examined and compared to that in cells lacking either fVII/fVIIa or TF. Furthermore, the localisation of labelled-recombinant TF with cholesterol-rich lipid rafts was explored on the surface of primary human blood dermal endothelial cells (HDBEC). Finally, by disrupting the caveolae on the surface of HDBEC, the outcome on TF-mediated signalling was examined. The association between TF and PAR2 was found to be dependent on the presence of fVIIa. Interestingly, the presence of TF was not pre-requisite for the association between fVII/fVIIa and PAR2 but was significantly enhanced by TF, which was also essential for the proliferative signal. Supplementation of HDBEC with exogenous TF resulted in early release of fVII/fVIIa from caveolae, followed by re-sequestration of TF-fVIIa. Addition of labelled-TF resulted in the accumulation within caveolin-1-containing cholesterol-rich regions and was also accompanied with the increased assimilation of cell-surface fVIIa. Disruption of the caveolae/rafts in HDBEC using MβCD enhanced the TF-mediated cellular signalling. Our data supports a hypothesis that cells respond to the exposure to TF by moderating the signalling activities as well as the procoagulant activity of TF, through incorporation into the caveolae/lipid rafts.

Accumulation of tissue factor in endothelial cells promotes cellular apoptosis through over-activation of Src1 and involves β1-integrin signalling

Accumulation of tissue factor (TF) within cells leads to cellular apoptosis mediated through p38 and p53 pathways. In this study, the involvement of Src1 in the induction of TF-mediated cell apoptosis, and the mechanisms of Src1 activation were investigated. Human coronary artery endothelial cell (HCAEC) were transfected with plasmids to express the wild-type TF (TF_Wt-tGFP), or a mutant (Ser253 → Ala) which is incapable of being released from cells (TF_Ala253-tGFP). The cells were then activated with PAR2-agonist peptide (SLIGKV-NH) and the phosphorylation of Src and Rac, and also the kinase activity of Src were assessed. Transfected cells were also pre-incubated with pp60c Src inhibitor, FAK inhibitor-14, or a blocking anti-β1-integrin antibody prior to activation and the phosphorylation of p38 as well as cellular apoptosis was examined. Finally, cells were co-transfected with the plasmids, together with a Src1-specific siRNA, activated as above and the cellular apoptosis measured. Activation of PAR2 lead to the phosphorylation of Src1 and Rac1 proteins at 60 min regardless of TF expression. Moreover, Src phosphorylation and kinase activity was prolonged up to 100 min in the presence of TF, with a significantly higher magnitude when the non-releasable TF_Ala253-tGFP was expressed in HCAEC. Inhibition of Src with pp60c, or suppression of Src1 expression in cells, reduced p38 phosphorylation and prevented cellular apoptosis. In contrast, inhibition of FAK had no significant influence on Src kinase activity or cellular apoptosis. Finally, pre-incubation of cells with an inhibitory anti-β1-integrin antibody reduced both Src1 activation and cellular apoptosis. Our data show for the first time that the over-activation of Src1 is a mediator of TF-induced cellular apoptosis in endothelial cells through a mechanism that is dependent on its interaction with β1-integrin.

Apixaban Suppresses the Release of TF-Positive Microvesicles and Restrains Cancer Cell Proliferation through Directly Inhibiting TF-fVIIa Activity

The activation of protease-activated receptor (PAR)-2 by factor Xa (fXa) promotes the release of tissue factor-positive microvesicles (TF⁺MV), and contributes to proliferation in cancer cells. This study examined the ability of direct oral anticoagulants (DOACs), apixaban and rivaroxaban, to inhibit the release of TF⁺MV from two cell lines (MDA-MB-231 and AsPC-1) as well as cell proliferation.Activation of the cells with fXa (10 nM) enhanced the release of TF⁺MV but was suppressed in the presence of either DOAC. These MVs were found to contain fVIIa, but not fXa. Incubation of cell lines with apixaban (1.8 µM) but not rivaroxaban (1.8 µM), in the absence of fXa decreased the release of TF⁺MV below that of resting cells, in a PAR2-dependent manner. Furthermore, incubation with apixaban reduced the proliferation rate in both cells lines. Incubation of purified fVIIa with apixaban but not rivaroxaban resulted in complete inhibition of fVIIa proteolytic activity as measured using two fVIIa chromogenic substrates. Pre-incubation of the cells with an inhibitory anti-fVIIa antibody, with apixaban or the blocking of PAR2 suppressed the release of TF⁺MV to a comparable level, and reduced cell proliferation but the effect was not cumulative.This study has established that the activation of PAR2 by TF-fVIIa complex is the principal mediator in augmenting the release of TF⁺MV as well as cancer cell proliferation. Importantly, for the first time we have shown that apixaban selectively inhibits the proteolytic activity of fVIIa as well as the signalling arising from the TF-fVIIa complex.

The Ratio of Factor VIIa:Tissue Factor Content within Microvesicles Determines the Differential Influence on Endothelial Cells

Tissue factor (TF)-positive microvesicles from various sources can promote cellular proliferation or alternatively induce apoptosis, but the determining factors are unknown. In this study the hypothesis that the ratio of fVIIa:TF within microvesicles determines this outcome was examined. Microvesicles were isolated from HepG2, BxPC-3, 786-O, MDA-MB-231, and MCF-7 cell lines and microvesicle-associated fVIIa and TF antigen and activity levels were measured. Human coronary artery endothelial cells (HCAECs) were incubated with these purified microvesicles, or with combinations of fVIIa-recombinant TF, and cell proliferation/apoptosis was measured. Additionally, by expressing mCherry-PAR2 on HCAEC surface, PAR2 activation was quantified. Finally, the activation of PAR2 on HCAEC or the activities of TF and fVIIa in microvesicles were blocked prior to addition of microvesicles to cells. The purified microvesicles exhibited a range of fVIIa:TF ratios with HepG2 and 786-O cells having the highest (54:1) and lowest (10:1) ratios, respectively. The reversal from proapoptotic to proliferative was estimated to occur at a fVIIa:TF molar ratio of 15:1, but HCAEC could not be rescued at higher TF concentrations. The purified microvesicles induced HCAEC proliferation or apoptosis according to this ruling. Blocking PAR2 activation on HCAEC, or inhibiting fVIIa or TF-procoagulant function on microvesicles prevented the influence on HCAEC. Finally, incubation of HCAEC with recombinant TF resulted in increased surface exposure of fVII. The induction of cell proliferation or apoptosis by TF-positive microvesicles is dependent on the ratio of fVIIa:TF and involves the activation of PAR2. At lower TF concentrations, fVIIa can counteract the proapoptotic stimulus and induce proliferation.

Low molecular weight heparin and direct oral anticoagulants influence tumour formation, growth, invasion and vascularisation by separate mechanisms

The bidirectional association between coagulation and cancer has been established. However, anticoagulant therapies have been reported to have beneficial outcomes by influencing the vascularisation of the tumours. In this study the influence of a set of anticoagulants on tumour formation, invasion and vascularisation was examined. WM-266-4 melanoma and AsPC-1 pancreatic cancer cell lines were treated with LMWH (Tinzaparin and Dalteparin), and DOAC (Apixaban and Rivaroxaban) and the rate of tumour formation, growth and invasion were measured in vitro. In addition, the influence of these anticoagulants on vascularisation was examined using the chorioallantoic membrane assay (CAM) model and compared to the outcome of treatment with Bevacizumab. Using this model the influence of pharmacological concentrations of the anticoagulant on the growth, invasion and vascularisation of tumours derived from WM-266-4 and AsPC-1 cells was also measured in vivo. Tinzaparin and Daltepain reduced tumour formation and invasion by the cell lines in vitro, but with dissimilar potencies. In addition, treatment of CAM with LMWH reduced the local vascular density beyond that achievable with Bevacizumab, particularly suppressing the formation of larger-diameter blood vessels. In contrast, treatment with DOAC was largely ineffective. Treatment of CAM-implanted tumours with LMWH also reduced tumour vascularisation, while treatment of tumours with Apixaban reduced tumour growth in vivo. In conclusion, LMWH and DOAC appear to have anti-cancer properties that are exerted through different mechanisms.

Alteration in endothelial permeability occurs in response to the activation of PAR2 by factor Xa but not directly by the TF-factor VIIa complex

Alterations in the endothelial permeability occur in response to the activation of coagulation mechanisms in order to control clot formation. The activation of the protease activated receptors (PAR) can induce signals that regulate such cellular responses. PAR2 is a target for the coagulation factor Xa (fXa) and tissue factor-factor VIIa (TF-fVIIa) complex. By measuring the permeability of dextran blue across endothelial monolayer, we examined the mechanisms linking coagulation and endothelial permeability. Activation of PAR2 using the agonist peptide (PAR2-AP) resulted in increased permeability across the monolayer and was comparable to that obtained with VEGF at 60 min. Incubation of cells with activated factor Xa (fXa) resulted in an initial decrease in permeability by 30 min, but then significantly increased at 60 min. These responses required fXa activity, and were abrogated by incubation of the cells with a PAR2-blocking antibody (SAM11). Activation of PAR2 alone, or inhibition of PAR1, abrogated the initial reduction in permeability. Additionally, inclusion of Rivaroxaban (0.6 μg/ml) significantly inhibited the response to fXa. Finally, incubation of the endothelial monolayers up to 2 h with TF-containing microvesicles derived from MDA-MB-231 cells, in the presence or absence of fVIIa, did not influence the permeability across the monolayers. In conclusion, fXa but not TF-fVIIa is a noteworthy mediator of endothelial permeability. The rapid initial decrease in permeability requires PAR2 and PAR1 which may act to constrain bleeding. The longer-term response is mediated by PAR2 with increased permeability, presumably to enhance clot formation at the site of damage.

Tissue factor-bearing microparticles and inflammation: a potential mechanism for the development of venous thromboembolism in cancer

Cancer is associated with an increased risk of venous thromboembolism (VTE); the exact mechanisms for the induction of VTE remain to be fully elucidated, but it is widely acknowledged that tissue factor (TF)-bearing microparticles (TF-MPs) may play a significant role. However, TF-MPs have yet to be accepted as a genuine biomarker for cancer-associated VTE, as the presence of elevated TF-MP levels is not always accompanied by thrombosis; interestingly, in certain cases, particularly in pancreatic cancer, VTE seems to be more likely in the context of acute inflammation. Although several potential mechanisms for the development of VTE in cancer have been postulated, this review explores the homeostatic disruption of TF-MPs, as the main reservoir of bloodborne TF, in the context of cancer and inflammation, and considers the abrogated responses of the activated endothelium and mononuclear phagocyte system in mediating this disruption.

Investigation of the Filamin A-Dependent Mechanisms of Tissue Factor Incorporation into Microvesicles

We have previously shown that phosphorylation of tissue factor (TF) at Ser253 increases the incorporation of TF into microvesicles (MVs) following protease-activated receptor 2 (PAR2) activation through a process involving filamin A, whereas phosphorylation of TF at Ser258 suppresses this process. Here, we examined the contribution of the individual phosphorylation of these serine residues to the interaction between filamin A and TF, and further examined how filamin A regulates the incorporation of TF into MVs. In vitro binding assays using recombinant filamin A C-terminal repeats 22-24 with biotinylated phospho-TF cytoplasmic domain peptides as bait showed that filamin A had the highest binding affinities for phospho-Ser253 and double-phosphorylated TF peptides, while the phospho-Ser258 TF peptide had the lowest affinity. Analysis of MDA-MB-231 cells using an in situ proximity ligation assay revealed increased proximity between the C-terminus of filamin A and TF following PAR2 activation, which was concurrent with Ser253 phosphorylation and TF-positive MV release from these cells. Knock-down of filamin A expression suppressed PAR2-mediated increases in cell surface TF procoagulant activity without reducing cell surface TF antigen expression. Disrupting lipid rafts by pre-incubation with methyl-β-cyclodextrin prior to PAR2 activation reduced TF-positive MV release and cell surface TF procoagulant activity to the same extent as filamin A knock-down. In conclusion, this study shows that the interaction between TF and filamin A is dependent on the differential phosphorylation of Ser253 and Ser258. Furthermore, the interaction of TF with filamin A may translocate cell surface TF to cholesterol-rich lipid rafts, increasing cell surface TF activity as well as TF incorporation and release into MVs.

Accumulation of tissue factor in endothelial cells induces cell apoptosis, mediated through p38 and p53 activation

We previously reported that high levels of tissue factor (TF) can induce cellular apoptosis in endothelial cells. In this study, TF-mediated mechanisms of induction of apoptosis were explored. Endothelial cells were transfected to express wild-type TF. Additionally, cells were transfected to express Asp253-substituted, or Ala253-substitued TF to enhance or prevent TF release, respectively. Alternatively, cells were pre-incubated with TF-rich and TF-poor microvesicles. Cell proliferation, apoptosis and the expression of cyclin D1, p53, bax and p21 were measured following activation of cells with PAR2-agonist peptide. Greatest levels of cell proliferation and cyclin D1 expression were observed in cells expressing wild-type or Asp253-substituted TF. In contrast, increased cellular apoptosis was observed in cells expressing Ala253-substituted TF, or cells pre-incubated with TF-rich microvesicles. The level of p53 protein, p53-phosphorylation at ser33, p53 nuclear localisation and transcriptional activity, but not p53 mRNA, were increased in cells expressing wild-type and Ala253-substituted TF, or in cells pre-incubated with TF-rich microvesicles. However, the expression of bax and p21 mRNA, and Bax protein were only increased in cells pre-incubated with TF-rich microvesicle and in cells expressing Ala253-substituted TF. Inhibition of the transcriptional activity of p53 using pifithrin-α suppressed the expression of Bax. Finally, siRNA- mediated suppression of p38α, or inhibition using SB202190 significantly reduced the p53 protein levels, p53 nuclear localisation and transcriptional activity, suppressed Bax expression and prevented cellular apoptosis. In conclusion, accumulation of TF within endothelial cells, or sequestered from the surrounding can induce cellular apoptosis through mechanisms mediated by p38, and involves the stabilisation of p53.

Peptidyl-prolyl isomerase 1 (Pin1) preserves the phosphorylation state of tissue factor and prolongs its release within microvesicles

The exposure and release of TF is regulated by post-translational modifications of its cytoplasmic domain. Here, the potential of Pin1 to interact with the cytoplasmic domain of TF, and the outcome on TF function was examined. MDA-MB-231 and transfected-primary endothelial cells were incubated with either Pin1 deactivator Juglone, or its control Plumbagin, as well as transfected with Pin1-specific or control siRNA. TF release into microvesicles following activation, and also phosphorylation and ubiquitination states of cellular-TF were then assessed. Furthermore, the ability of Pin1 to bind wild-type and mutant forms of overexpressed TF-tGFP was investigated by co-immunoprecipitation. Additionally, the ability of recombinant or cellular Pin1 to bind to peptides of the C-terminus of TF, synthesised in different phosphorylation states was examined by binding assays and spectroscopically. Finally, the influence of recombinant Pin1 on the ubiquitination and dephosphorylation of the TF-peptides was examined. Pre-incubation of Pin1 with Juglone but not Plumbagin, reduced TF release as microvesicles and was also achievable following transfection with Pin1-siRNA. This was concurrent with early ubiquitination and dephosphorylation of cellular TF at Ser253. Pin1 co-immunoprecipitated with overexpressed wild-type TF-tGFP but not Ser258→Ala or Pro259→Ala substituted mutants. Pin1 did interact with Ser258-phosphorylated and double-phosphorylated TF-peptides, with the former having higher affinity. Finally, recombinant Pin1 was capable of interfering with the ubiquitination and dephosphorylation of TF-derived peptides. In conclusion, Pin1 is a fast-acting enzyme which may be utilised by cells to protect the phosphorylation state of TF in activated cells prolonging TF activity and release, and therefore ensuring adequate haemostasis.

Analysis of the potential of cancer cell lines to release tissue factor-containing microvesicles: correlation with tissue factor and PAR2 expression

BACKGROUND

Despite the association of cancer-derived circulating tissue factor (TF)-containing microvesicles and hypercoagulable state, correlations with the incidence of thrombosis remain unclear.

METHODS

In this study the upregulation of TF release upon activation of various cancer cell lines, and the correlation with TF and PAR2 expression and/or activity was examined. Microvesicle release was induced by PAR2 activation in seventeen cell lines and released microvesicle density, microvesicle-associated TF activity, and phoshpatidylserine-mediated activity were measured. The time-course for TF release was monitored over 90 min in each cell line. In addition, TF mRNA expression, cellular TF protein and cell-surface TF activities were quantified. Moreover, the relative expression of PAR2 mRNA and cellular protein were analysed. Any correlations between the above parameters were examined by determining the Pearson's correlation coefficients.

RESULTS

TF release as microvesicles peaked between 30-60 min post-activation in the majority of cell lines tested. The magnitude of the maximal TF release positively correlated with TF mRNA (c = 0.717; p < 0.001) and PAR2 mRNA (c = 0.770; p < 0.001) expressions while the percentage increase correlated with PAR2 mRNA (c = 0.601; p = 0.011) and protein (c = 0.714; p < 0.001). There was only a weak correlation between resting TF release, and microvesicle release. However, TF release in resting cells did not significantly correlate with any of the parameters examined. Furthermore, TF mRNA expression correlated with PAR2 mRNA expression (c = 0.745; p < 0.001).

DISCUSSION AND CONCLUSIONS

In conclusion, our data suggest that TF and PAR2 mRNA, and PAR2 protein are better indicators of the ability of cancer cells to release TF and may constitute more accurate predictors of risk of thrombosis.

Extracellular vesicles, tissue factor, cancer and thrombosis - discussion themes of the ISEV 2014 Educational Day

Although the association between cancer and venous thromboembolism (VTE) has long been known, the mechanisms are poorly understood. Circulating tissue factor–bearing extracellular vesicles have been proposed as a possible explanation for the increased risk of VTE observed in some types of cancer. The International Society for Extracellular Vesicles (ISEV) and International Society on Thrombosis and Haemostasis (ISTH) held a joint Educational Day in April 2014 to discuss the latest developments in this field. This review discusses the themes of that event and the ISEV 2014 meeting that followed.

Characterization of physical properties of tissue factor-containing microvesicles and a comparison of ultracentrifuge-based recovery procedures

Microvesicles were isolated from the conditioned media of 3 cell lines (MDA-MB-231, AsPC-1 and A375) by ultracentrifugation at a range of relative centrifugal forces, and the tissue factor (TF) protein and activity, microvesicle number, size distribution and relative density compared. Also, by expressing TF-tGFP in cells and isolating the microvesicles, the relative density of TF-containing microvesicles was established. Nanoparticle tracking analysis (NTA) indicated that the larger-diameter microvesicles (>200 nm) were primarily sedimented at 100,000g and possessed TF-dependent thrombin and factor Xa generation potential, while in the absence of factor VII, all microvesicles possessed some thrombin generation capacity. Immuno-precipitation of TF-containing microvesicles followed by NTA also indicated the range of these microvesicles to be 200–400 nm. Analysis of the microvesicles by gradient density centrifugation showed that lower-density (<1.1 g/ml) microvesicles were mainly present in the samples recovered at 100,000g and were associated with TF antigen and activity. Analysis of these fractions by NTA confirmed that these fractions were principally composed of the larger-diameter microvesicles. Similar analysis of microvesicles from healthy or patient plasma supported those obtained from conditioned media indicating that TF activity was mainly associated with lower-density microvesicles. Furthermore, centrifugation of healthy plasma, supplemented with TF-tGFP-containing microvesicles, resulted in 67% retrieval of the fluorescent microvesicles at 100,000g, but only 26% could be recovered at 20,000g. Pre-centrifugation of conditioned media or plasma at 10,000g improved the speed and yield of recovered TF-containing microvesicles by subsequent centrifugation at either 20,000g or 100,000g. In conclusion, TF appears to be associated with low-density (1.03–1.08 g/ml), larger-diameter (200–350 nm) microvesicles.

Filamin-A is required for the incorporation of tissue factor into cell-derived microvesicles

We previously reported that the incorporation of tissue factor (TF) into cell-derived microvesicles (MVs) is regulated by the phosphorylation of the cytoplasmic domain of TF. Since the cytoskeletal protein filamin-A is known to bind to the cytoplasmic domain of TF in a phosphorylation-dependent manner, the involvement of filamin-A in the incorporation of TF into MVs was examined. Endothelial cells were transfected to express TF, whereas MDA-MB-231 cells were used to examine endogenously expressed TF. MV release was induced by activating protease-activated receptor-2 (PAR2). Partial suppression of filamin-A expression using two different filamin-A siRNA sequences resulted in significant reductions in the incorporation of TF antigen into MVs as determined by TF-ELISA and western blot analysis, and was reflected in reduced thrombin-generation and FXa-generation capacities of these MVs. Deletion of the cytoplasmic domain of TF also resulted in reduced incorporation of TF into MVs, whereas the suppression of filamin-A expression had no additional effect on the incorporation of truncated TF into MVs. Partial suppression of filamin-A expression had no effect on the number and size distribution of the released MVs. However, >90% suppression of filamin-A expression resulted in increased MV release, possibly as a result of increased instability of the plasma membrane and underlying cytoskeleton. In conclusion, the presence of filamin-A appears to be essential for the incorporation of TF into MVs following PAR2 activation, but is not required for the process of MV formation and release following PAR2 activation.

Microparticle-associated tissue factor is recycled by endothelial cells resulting in enhanced surface tissue factor activity

In this study the uptake of tissue factor (TF)-positive microparticles by endothelial cells and the recycling of the TF component were examined. Human dermal blood endothelial cells (HDBEC) were incubated with microparticles derived from cancer cell lines for up to 6 hours. Measurement of HDBEC cell surface TF antigen revealed two distinct peaks at 30 and 180-240 minutes post-incubation with TF-positive, but not TF-deficient microparticles. However, only the second peak was concurrent with high TF activity as determined by a chromogenic thrombin-generation assay. Annexin V-labelling of HDBEC showed phosphatidylserine exposure following 90 minutes incubation with microparticles, which explains the high TF activity associated with the second antigen peak. Analysis of TF mRNA levels revealed no de novo expression of TF mRNA in response to microparticles, and pre-incubation of cells with cycloheximide did not prevent the appearance of TF. However, blocking endocytosis with a dynamin inhibitor prolonged the disappearance and prevented the reappearance of TF antigen on the cell surface. Incubation of HDBEC with microparticles containing TF-GFP revealed the early co-localisation of TF with Rab4 and Rab5, followed by co-localisation with the late endosomal/trans-Golgi network marker Rab9, and the recycling endosome marker Rab11. siRNA-mediated suppression of Rab11 reduced the reappearance of TF on the cell surface. These data suggest a mechanism by which TF-containing microparticles are internalised by endothelial cells and the TF moiety recycled to the cell surface. Together with the exposure of phosphatidylserine, this is capable of inducing a substantial increase in the procoagulant potential of the surface of endothelial cells.

p38α phosphorylates serine 258 within the cytoplasmic domain of tissue factor and prevents its incorporation into cell-derived microparticles

We previously showed that the phosphorylation of Ser253 within the cytoplasmic domain of human tissue factor (TF) initiates the incorporation and release of this protein into cell-derived microparticles. Furthermore, subsequent phosphorylation of Ser258 terminates this process. However, the identity of the kinase responsible for the phosphorylation of Ser258 and mode of action of this enzyme remain unknown. In this study, p38α was identified as the proline-directed kinase capable of phosphorylating Ser258 specifically, and without any detectable activity towards Ser253. Furthermore, using synthetic peptides, it was shown that the Km for the reaction decreased by approximately 10 fold on substitution of Ser253 with phospho-Ser253. Either inhibition of p38 using SB202190 or knockdown of p38α expression in coronary artery endothelial cells overexpressing wild-type TF, resulted in decreased phosphorylation of Ser258, following activation of cells with PAR2-agonist peptide (PAR2-AP). In agreement with our previous data, inhibition of phosphorylation of this residue maintained the release of TF. Activation of PAR2 in cells transfected to overexpress TF, resulted in two separate peaks of p38 activity at approximately 40 and 120 min post-activation. Furthermore, overexpression of Ala253-substituted TF enhanced the second p38 activation peak. However, the second peak was absent in cells devoid of TF or in cells overexpressing the Asp253-substituted TF. Our data clearly identifies p38α as a kinase capable of phosphorylating Ser258 within the cytoplasmic domain of TF. Moreover, it appears that the presence of TF within the cells regulates the late activation of p38 and consequently the termination of TF release into microparticles.

Enhanced binding of tissue factor-microparticles to collagen-IV and fibronectin leads to increased tissue factor activity in vitro

The role of tissue factor (TF)-containing microparticles in clot propagation has been established, but the ability of circulating microparticles to initiate coagulation has been disputed. However, TF-bearing microparticles, particularly endothelial-microparticles generated during disease, may interact with extracellular matrices which in turn can localise circulating TF to sites of injury. In order to examine this hypothesis in vitro , microparticles were isolated from human coronary artery endothelial cells transfected to overexpress TF, tumour-necrosis factor (TNF) α-treated cells or non-transfected cells lacking TF. The ability of microparticles to bind collagen-IV, fibronectin and fibrin was examined under static conditions and arterial shear rates (650 s⁻¹), and also in the presence of inhibitory antibodies against β1-, β3-, α3- and αv-integrins or an anti-TF antibody. TF-microparticles showed increases of up to 43% and 24% in adherence to collagen-IV and fibronectin, respectively, compared to control microparticles under shear flow. Furthermore, TF-containing microparticles, but not the transfected parent cells had increased levels of β1-integrin compared to TF-deficient microparticles. Pre-incubation of microparticles with a β1-integrin-blocking antibody counteracted the additional adhesion of TF-microparticles compared to control microparticles. Finally, adherence of TF microparticles to collagen-IV or fibronectin resulted in increased TF activity by concentrating TF onto the surface. In conclusion, the presence of TF within microparticles enhances the interactions of endothelial cell-derived microparticles with extracellular matrices in an integrin-dependent manner. Accumulation and localisation of these microparticles in turn results in the enhancement of TF activity. This may be an innate mechanism by which TF-bearing microparticles induce coagulation upon vascular injury.

Gemcitabine versus gemcitabine plus dalteparin thromboprophylaxis in pancreatic cancer

BACKGROUND

Annualised figures show an up to 7-fold higher incidence of vascular thromboembolism (VTE) in patients with advanced pancreatic cancer (APC) compared to other common malignancies. Concurrent VTE has been shown to confer a worse overall prognosis in APC.

METHODS

One hundred and twenty three APC patients were randomised to receive either gemcitabine 1000 mg/m(2) or the same with weight-adjusted dalteparin (WAD) for 12 weeks. Primary end-point was the reduction of all-type VTE during the study period. NCT00462852, ISRCTN: 76464767.

FINDINGS

The incidence of all-type VTE during the WAD treatment period (<100 days from randomisation) was reduced from 23% to 3.4% (p = 0.002), with a risk ratio (RR)of 0.145, 95% confidence interval (CI) (0.035-0.612) and an 85% risk reduction. All-type VTE throughout the whole follow-up period was reduced from 28% to 12% (p = 0.039), RR = 0.419, 95% CI (0.187-0.935) and a 58% risk reduction. Lethal VTE <100 days was seen only in the control arm, 8.3% compared to 0% (p = 0.057), RR = 0.092, 95% CI (0.005-1.635).

INTERPRETATION

Weight adjusted dalteparin used as primary prophylaxis for 12 weeks is safe and produces a highly significant reduction of all-type VTE during the prophylaxis period. The benefit is maintained after dalteparin withdrawal although decreases with time.

Low molecular weight heparin downregulates tissue factor expression and activity by modulating growth factor receptor-mediated induction of nuclear factor-κB

Treatment of cancer patients with low molecular weight heparin (LMWH) appears to have beneficial effects. In this study, the influence of low molecular weight heparin (LMWH) on tissue factor (TF) expression and activity in five cell lines from various tissues was analysed and explored. Incubation of cells with LMWH (0-2000μg/ml) resulted in the downregulation of TF mRNA expression which was both LMWH concentration-dependent and time-dependent. Downregulation of TF was also measured as decreased cellular TF antigen and activity. Consistently, incubation of cells with LMWH suppressed the nuclear localisation and the transcriptional activity of NFκB. Decreased TF mRNA was largely achievable by incubating the cells with an NFκB inhibitor alone whilst incubation with betulinic acid to activate NFκB reversed the inhibitory influence of LMWH. Cells were also incubated with a range of concentrations of EGF (0-10ng/ml), bFGF (0-20ng/ml) or VEGF (0-4ng/ml) in the presence or absence of LMWH (200μg/ml) for 24h and TF antigen measured. Inclusion of LMWH reduced TF expression in response to EGF, bFGF or VEGF but TF expression was partially restored by increasing concentrations of the growth factors. We conclude that LMWH downregulates TF expression in vitro through a mechanism that involves interference with the function of growth factors which in turn is mediated through the downregulation of the transcriptional activity of NFκB. This mechanism may also explain some of the beneficial influences attributed to LMWH therapy in the treatment of cancer patients.

Regulation of the incorporation of tissue factor into microparticles by serine phosphorylation of the cytoplasmic domain of tissue factor

The mechanisms that regulate the incorporation and release of tissue factors (TFs) into cell-derived microparticles are as yet unidentified. In this study, we have explored the regulation of TF release into microparticles by the phosphorylation of serine residues within the cytoplasmic domain of TF. Wild-type and mutant forms of TF, containing alanine and aspartate substitutions at Ser253 and Ser258, were overexpressed in coronary artery and dermal microvascular endothelial cells and microparticle release stimulated with PAR2 agonist peptide (PAR2-AP). The release of TF antigen and activity was then monitored. In addition, the phosphorylation state of the two serine residues within the released microparticles and the cells was monitored for 150 min. The release of wild-type TF as procoagulant microparticles peaked at 90 min and declined thereafter in both cell types. The TF within these microparticles was phosphorylated at Ser253 but not at Ser258. Aspartate substitution of Ser253 resulted in rapid release of TF antigen but not activity, whereas TF release was reduced and delayed by alanine substitution of Ser253 or aspartate substitution of Ser258. Alanine substitution of Ser258 prolonged the release of TF following PAR2-AP activation. The release of TF was concurrent with phosphorylation of Ser253 and was followed by dephosphorylation at 120 min and phosphorylation of Ser258. We propose a sequential mechanism in which the phosphorylation of Ser253 through PAR2 activation results in the incorporation of TF into microparticles, simultaneously inducing Ser258 phosphorylation. Phosphorylation of Ser258 in turn promotes the dephosphorylation of Ser253 and suppresses the release of TF.

Low molecular weight heparin suppresses tissue factor-mediated cancer cell invasion and migration in vitro

Elevated expression of tissue factor (TF) has been associated with an increased risk of thrombosis in the majority of cancers. Moreover, treatment of cancer patients with low molecular weight heparin (LMWH) appears to have beneficial effects that reach beyond controlling the immediate hypercoagulable state. In this study, we investigated the influence of the treatment of cancer cells with LMWH (0-2,000 μg/ml) on cell invasiveness and migration in cancer cell lines from five separate tissues; pancreatic, breast, colocarcinoma, ovarian and melanoma. The rate of cell invasion across collagen IV-coated membranes was suppressed in all cell lines tested on incubation with 2,000 μg/ml LMWH, but BxPC-3 and MDA-MB-231 cells also responded to the lowest concentration of 20 μg/ml LMWH. Furthermore, the rate of cell migration was reduced to varying extents in all of the cell lines tested on incubation with 20 μg/ml or higher concentrations of LMWH. The decrease in the rates of invasion and migration also strongly correlated with the reduction in TF protein expression and TF activity in these cells following incubation with LMWH. Moreover, the LMWH-mediated decreases in cellular invasion in the most affected cell lines (BxPC-3 and MDA-MB-231) were restored by transfection of the cells with the mammalian pCMV-XL5-TF expression vector allowing independent overexpression of TF. In conclusion, LMWH appears to suppress the rate of cancer cell invasion and migration in vitro, through a mechanism that is at least in part dependent on the TF protein expression and activity in cancer cells.

Differential induction of cellular proliferation, hypertrophy and apoptosis in H9c2 cardiomyocytes by exogenous tissue factor

Recent evidence has shown that prolonged exposure to exogenous tissue factor (TF) can alter the cellular functions of cardiomyocytes resulting in cardiac dysfunction. The effect of TF may arise from local inflammation within or in the vicinity of the heart. The aim of this study was to investigate the effect of TF on cardiomyocyte proliferation and growth. H9c2 rat cardiomyocytes were exposed to a range of concentrations of recombinant TF (rTF) (1.3-52 ng/ml) for up to 10 days and the outcome on cell proliferation and induction of apoptosis measured. At lower concentrations examined (1.3 ng/ml), rTF had a proliferative influence on the H9c2 cells. In contrast, elevated concentrations of rTF (52 ng/ml) induced cellular apoptosis as indicated by increased caspase-3 activity and nuclear localisation of p53. Moreover, incubation with intermediate concentrations of rTF (13 ng/ml) resulted in an initial increase in proliferation but subsequently, led to cellular apoptosis by day 7 of the incubation. In order to determine if these effects induced hypertrophic cell growth, expression of mechano-growth factor (MGF) was analysed. Incubation of cells with rTF resulted in enhanced expression of MGF particularly at the intermediate concentrations of rTF (13 ng/ml) as well as mean cellular transverse diameter. In addition, there was a rapid increase in the expression of atrial natriuretic factor (ANF) in the cells, on incubation with rTF but diminished rapidly when exposed to higher concentrations of rTF. These data indicate that exposure to increasing concentrations of rTF can accelerate the rate of cardiomyocyte turnover which may ultimately lead to depletion of viable cells within the heart. Moreover, at lower concentrations of rTF, the induction of cell proliferation together with hypertrophic markers indicates that rTF may contribute to the induction and progression of cardiac hypertrophy.

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.

Influence of exogenous tissue factor on estrogen receptor alpha expression in breast cancer cells: involvement of beta1-integrin, PAR2, and mitogen-activated protein kinase activation

Increased expression of tissue factor (TF) has been associated with invasive forms of breast cancer. Conversely, the loss of estrogen receptor alpha (ERalpha) is associated with increased cell invasiveness. We have examined the influence of exogenous truncated recombinant TF (rTF) on ERalpha expression and cell invasiveness and investigated the mechanism of rTF signaling. The influence of rTF on ERalpha expression in MCF-7 and T47D cell lines was investigated using reverse transcription-PCR and ELISA. Cell invasion was measured using Boyden chamber-based invasion assays. Additionally, the interaction of fluorescein-labeled rTF with the surface of MCF-7 cells and particularly with beta(1)-integrin was examined. Treatment of cells with rTF resulted in the down-regulation of ERalpha mRNA and protein over 24 h, which required beta(1)-integrin and involved the mitogen-activated protein kinase pathway but did not require PAR2 activation. The addition of rTF reduced estradiol-mediated cell proliferation as well as increased cell invasiveness requiring both PAR2 and beta(1)-integrin activation. Fluorescein-labeled rTF was shown to bind to the surface of MCF-7 cells within 5 min and peaked at 15 min. The bound rTF colocalized with cellular beta(1)-integrin and was disrupted in the presence of excess unlabeled rTF and an anti-beta(1) polyclonal antibody. Finally, affinity purification of beta(1)-integrin using rTF-conjugated agarose showed a requirement for the presence of divalent cations but not factor VIIa. The results indicate that rTF is capable of down-regulating ERalpha expression in breast cancer cells, resulting in decreases in estrogen-mediated cell proliferation and increased invasiveness. Furthermore, the mechanisms by which rTF induces these changes involve both PAR2 and beta(1)-integrin.

Investigation of the mechanisms of tissue factor-mediated evasion of tumour cells from cellular cytotoxicity

AIMS

We previously reported that overexpression of tissue factor (TF) protected HT29 tumour cells from cellular cytotoxicity through a mechanism requiring the presence of the cytoplasmic domain of TF. In this investigation the mechanism of TF-mediated immune evasion has been examined.

METHODS

The influence of alanine-substitution at Ser253 and Ser258 of TF (TF(Ala253) and TF( Ala258)) on the induction of cytotoxic evasion, as well as expression of vascular cell adhesion molecule-1 and intra-cellular adhesion molecule-1 (VCAM-1 and ICAM-1) was investigated. Moreover, we examined the effect of transfection of four 20-mer peptides, corresponding to the C-terminal residues of TF, with different phosphorylation states, on promotion of evasion from cell cytotoxicity.

RESULTS

Cells overexpressing TF(Ala258) and to a lesser extent overexpressing TF(Ala253,) exhibited a reduced ability to evade cellular cytotoxicity compared to cells overexpressing the wild-type TF. Furthermore, the increase in protection acquired was greatest on transfection of Ser258-phosphsorylated form of the cytoplasmic peptide, lower in double-phosphorylated and Ser253-phosphorylated peptides respectively, and lowest in the unphosphorylated form. Finally, the expression of VCAM-1 mRNA as well as surface antigen was reduced on overexpression of TF(wt) but was partially reverted in the cells transfected to overexpress TF(Ala253) or TF(Ala258).

CONCLUSIONS

These data show that the phosphorylation of TF at Ser258 and to a lesser extent Ser253, plays an essential role in the protective influence of TF on immune evasion by tumour cells, and that the mechanism could involve the downregulation of key surface antigens, such as adhesion proteins, involved in cell:cell interaction.

Tissue factor-containing microparticles released from mesangial cells in response to high glucose and AGE induce tube formation in microvascular cells

Hyperglycaemia and the associated formation of advanced glycation end-products (AGE) have been implicated in the pathogenesis of diabetic vasculopathy. In addition to its role in coagulation, tissue factor (TF) is known to regulate vascular proliferation and angiogenesis. In this study, the influence of AGE and glucose on the expression of TF in human renal mesangial cells (HRMC) and the subsequent induction of capillary formation by human dermal microvascular endothelial cells (HDMEC) were measured. Furthermore, the activity of TF, incorporated into microparticles was investigated. Both AGE and elevated glucose were capable of upregulating the expression of TF expression in a concentration-dependent manner in HRMC but not in HDMEC. This TF antigen and activity in the conditioned media from HRMC was associated with microparticles. Moreover, the formation of capillaries was readily induced on supplementation of HDMEC with conditioned media, from AGE-treated or high glucose-treated HRMC but not on incubation of HDMEC with either AGE or hyperphysiological concentrations of glucose. Furthermore, the rate of capillary formation was suppressed on incubation of the conditioned media with a polyclonal antibody against TF but not against VEGF. This study indicates that TF-containing microparticles are an important pro-inflammatory mediator acting as a mediator between elevated glucose and the development of diabetic vasculopathy by altering the angiogenic properties of endothelial cells and offers one explanation for the correlation between diabetes and microvascular disease.

The Influence of Exogenous Tissue Factor on the Regulators of Proliferation and Apoptosis in Endothelial Cells

BACKGROUND

The exposure of tissue factor (TF) at the site of injury or trauma is a rapid process that leads to the initiation of blood coagulation as well as homeostatic processes giving rise to vascular repair.

AIMS AND METHODS

By exposing human endothelial cells to combinations of exogenous TF and factor VIIa (FVIIa) in serum-free medium, the influence of TF concentrations on cellular proliferation and apoptosis was investigated.

RESULTS

Lower concentrations of TF resulted in increased cellular proliferation as well as upregulation of cyclin D1, downregulation of p21 and p27 and induction of tube formation in vitro. Conversely, incubation with higher concentrations of TF resulted in the activation of caspase-3, expression of p53 and Bax, translocation of p53 into the nucleus and induction of DNA fragmentation. Incubation of the cells with TF/FVIIa led to a lower proliferation rate with additional upregulation in p27.

CONCLUSIONS

TF seems to have a bifunctional role in determining the fate of endothelial cells, depending on the concentration and the interactions of this protein. The release of TF in the locality of the injured tissue makes this protein an ideal factor for ascertaining the level of injury and determining the fate of the cells.

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.

Plasma tissue factor is a predictor for restenosis after femoropopliteal angioplasty

Background

In vitro studies suggest an association between raised levels of tissue factor and restenosis after coronary percutaneous transluminal angioplasty (PTA). This prospective, controlled study examined the association between plasma tissue factor concentrations and restenosis after femoropopliteal PTA.

Methods

Plasma samples from ten healthy controls and 36 patients with unilateral claudication undergoing femoropopliteal PTA were collected at baseline and, in the patients with claudication, at 24 h and 1, 3 and 6 months after PTA. Clinical assessment and arterial duplex imaging were performed before and at the same time points after PTA to identify restenosis. Plasma tissue factor was measured using a specific enzyme-linked immunosorbent assay.

Results

Baseline plasma tissue factor concentrations were significantly higher in patients with claudication (median 3·4 (interquartile range (i.q.r.) 1·3–7·4) ng/ml) than in controls (median 1·2 (i.q.r. 0·5–1·8) ng/ml) (P &lt; 0·050). Baseline tissue factor concentrations were significantly higher in the ten patients with claudication who developed restenosis after PTA (median 7·0 (i.q.r. 3·4–183·5) ng/ml) than in those who did not (median 1·7 (i.q.r. 1·3–7·2) ng/ml) (P &lt; 0·050). In addition, plasma tissue factor levels increased significantly over time in the patients who developed restenosis after PTA.

Conclusion

High baseline and progressive increases in the plasma tissue factor concentration were useful predictors of restenosis after femoropopliteal angioplasty.

From rabies to transmissible spongiform encephalopathies: An immune-mediated microbial trigger involving molecular mimicry could be the answer

The concept of experimental allergic encephalomyelitis (EAE) being linked to both rabies post-vaccination encephalomyelitis and multiple sclerosis (MS) has raised the intriguing question whether animal studies carried out for the induction and transmission of transmissible spongiform encephalopathies (TSEs) using brain antigens including prions do have a similar immunopathogenetic mechanism. Although an essential link between autoimmunity and MS has been well established, its role in the pathogenesis of TSEs is generally lacking. However, auto-antibodies to myelin proteins and/or other neuronal antigens such as neurofilaments and prion proteins have been reported in animals with bovine spongiform encephalopathy (BSE) and scrapie as well as in patients with Creutzfeld-Jakob disease (CJD) and kuru. Acinetobacter has been suggested as a possible triggering microbial factor in the initiation of the autoimmune responses in these diseases because bacterial molecular sequences resemble brain antigens, especially in animals affected with BSE and patients with MS and CJD. These possibilities need to be evaluated further with longitudinal prospective studies carried out on larger numbers of animals or humans with such diseases. The transplantation of saline suspensions of brain homogenates will evoke immunological responses and therefore, the results in the study of MS and other neurological diseases have to be interpreted with caution.

Tumour-expressed tissue factor inhibits cellular cytotoxicity

AIMS

The association between tissue factor (TF) expression and increased rate of tumour metastasis is well established. In this study, we have examined the hypothesis that the expression of TF by disseminated tumour cells confers protection against immune recognition and cytotoxicity.

MATERIALS AND METHODS

A hybrid EGFP-TF protein was expressed in HT29 colon carcinoma and K562 lymphoblast cell lines. To assess the cytotoxic activity against tumour cells over-expressing TF, a novel method was used, based on the direct measurement of fluorescently labelled HT29 or K562 target cells.

RESULTS

Upon challenge with peripheral blood mononuclear cells (PBMC), tumour cells expressing TF partially evaded cellular cytotoxicity (Delta=15-40% reduction in cytotoxicity). Moreover, the influence of TF was not primarily dependent on its procoagulant function, although the inclusion of 20% (v/v) plasma did lower the rate of cytotoxicity against untransfected cells. However, expression of a truncated form of TF, devoid of the cytoplasmic domain, did not mediate any degree of inhibition of cytotoxicity, suggesting that the protective function of TF is principally due to this domain.

CONCLUSIONS

We conclude that TF can promote immune evasion in tumour cells expressing this protein leading to increased survival and therefore metastatic rate in such cells.

Induction of tissue factor expression and release as microparticles in ECV304 cell line by Chlamydia pneumoniae infection

The association between Chlamydia pneumoniae (C. pneumoniae) infection and the onset and progression of atherosclerosis has become apparent recently. Moreover, increased expression of tissue factor (TF) as a result of C. pneumoniae infection has been previously demonstrated. We have examined the expression of TF on the surface of endothelial cells and the release of TF-containing cell-derived microparticles, over seven days. Additionally, using cells expressing a procoagulantly active EGFP-TF hybrid protein, we examined the kinetics of TF trafficking on the cells and incorporation into shed microparticles. Finally, in an attempt to associate this with the activation of NFkappaB, we used a luciferase reporter to measure the duration of the activation of this transcription factor. TF-containing microparticles were released within 24h of infection and continued for up to 7 days. Moreover, the initial release of TF containing microparticles was associated with NFkappaB activation and was suppressed on inclusion of an NFkappaB inhibitor, pyrrolidinedithiocarbamate ammonium. Moreover, persistent dissemination of TF-containing microparticles at later stages of infection was associated with the release of the infective C. pneumoniae elementary bodies. The released procoagulant, cellular microparticles are known to be strongly atherogenic and therefore we suggest a mechanism for the involvement of C. pneumoniae in the onset and progression of vascular disease.

Heat Shock Proteins in Vascular Disease—A Review

INTRODUCTION

There is growing evidence that heat shock proteins (HSPs), a family of stress-inducible proteins may be involved in the pathogenesis of atherosclerotic vascular diseases. Here, we systematically review the evidence behind this notion.

METHODS

A detailed literature search and extensive bibliographic review of literature relating to HSPs and atherosclerotic vascular disease.

RESULTS

Atherosclerotic vascular disease is classified into four main areas of presentation: carotid, coronary, aortic and peripheral vascular disease, for consideration in this review. In each of these vascular diseases, the evidence linking HSPs and atherosclerosis is outlined in a systematic manner. Current evidence suggests that components of the immune system may be involved in the pathogenesis of atherosclerosis, with HSPs acting as auto-antigens in the immune response. HSPs are detected in atherosclerotic lesions and antibodies to HSPs are increased in patients with vascular disease; the rise often correlating with the severity of atherosclerosis. The levels of anti-HSP antibodies have been shown to be independent predictors of risk and have prognostic value.

CONCLUSION

There is a strong link between heat shock protein expression and the principal manifestations of atherosclerotic vascular diseases. A better understanding of this involvement could lead to the development of new and improved treatment strategies.

Antibodies to prion and Acinetobacter peptide sequences in bovine spongiform encephalopathy

An amino acid sequence homology has been identified between the bovine prion sequence (RPVDQ) and the Acinetobacter calcoaceticus enzyme, uridine-diphosphate-N-acetyl glucosamine-1-carboxy-vinyl-transferase which also contains (RPVDQ). Class-specific IgA, IgG and IgM antibodies against synthetic peptides containing the structurally related sequences present in bovine prion and A. calcoaceticus were measured in 189 bovine spongiform encephalopathy (BSE) positive cattle, 127 BSE negative cattle and 87 healthy control animals using an ELISA technique. Class-specific IgA, IgG and IgM antibodies against the structurally related synthetic peptides were significantly elevated in BSE positive cattle when compared to BSE negative cattle (P < 0.001) and healthy control animals (P < 0.001). These autoantibodies may have a role in the pathogenesis of BSE.

Inhibition of tissue factor activity reduces the density of cellular network formation in an in vitro model of angiogenesis

Tissue factor (TF) is a transmembrane glycoprotein that was originally recognized for its ability to initiate the extrinsic pathway of coagulation. More recently, additional functions of TF in cellular signalling have emerged, notably the role of TF in vasculogenesis and angiogenesis. We have described previously the ability of a peptide derived from the apolipoprotein B100 (apoB100) moiety of low-density lipoproteins (KRAD14) to inhibit the procoagulant function of TF. In this study, we demonstrate the ability of the KRAD14 peptide to attenuate the density of cellular network structures of T24 cells grown on specialized matrix (Matrigel). In addition, an alternative inhibitor of TF activity, the TF8 5G9 antibody, also reduces the density of cellular network formation. Targeted use of a stable structural equivalent of the KRAD14 peptide may thus prove useful in the prophylactic treatment of diseases whose pathologies feature the formation of neovascular tissue, e.g. tumour growth and metastasis, rupture of atherosclerotic plaques and retinopathy secondary to diabetes.

Characterisation of red and white muscle myosin heavy chain gene coding sequences from antarctic and tropical fish

To understand molecular adaptation for locomotion at different environmental temperatures, we have studied the myosin heavy chain genes as these encode the molecular motors involved. For this purpose, cDNA libraries from white (fast) and red (slow) myotomal muscle of an Antarctic and a tropical fish were constructed and from these different myosin heavy chain cDNAs were isolated. Northern and in situ hybridisation confirmed in which type of muscle these isoform genes are expressed. The cDNAs were sequenced and the structure of the ATPase sites compared. There was a marked similarity between the tropical fast myosin and the Antarctic slow myosin in the loop 1 region, which has similar amino acid side chains, charge distribution and conformation. These findings help to explain why the myofibrils isolated from white muscle of tropical fish show a lower specific ATPase activity than the white muscle of Antarctic fish but a similar activity to the Antarctic red (slow) muscle. It also provides insight into the way molecular motors in Antarctic fish have evolved to produce more power and thus ensure effective swimming at near zero temperatures by the substitution or addition of a few residues in strategic regions, which include the ATPase site.

The role of the C-terminal domain in the inhibitory functions of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) inhibits the activity of coagulation factors VIIa and Xa through Kunitz domains, thereby inhibiting the activity of tissue factor. However, it has been shown that the C-terminal of this inhibitor is essential for the maximal anticoagulant activity of TFPI. We have investigated the endogenous ability of the C-terminal of TFPI to influence coagulation. A synthetic peptide corresponding to residues 254-265 within the C-terminal of TFPI was prepared and shown to be capable of inhibiting tissue factor pathway by preventing the activation of factor VII. Mutational analysis of the peptide revealed the identity of the key lysine residues.

Comparison of the inhibitory effects of ApoB100 and tissue factor pathway inhibitor on tissue factor and the influence of lipoprotein oxidation

The procoagulant activity of tissue factor is regulated by circulating inhibitors such as tissue factor pathway inhibitor (TFPI) and LDL. These 2 inhibitors also readily associate making the distinction between their activities difficult. We have examined the relative contributions of intact and C-terminal truncated TFPI and ApoB100. By following the inhibitory potential of the preparations, over a period of 120 minutes, it was demonstrated that TFPI and LDL-resembling particles inhibited tissue factor at different rates. TFPI was found to be a short, fast-acting inhibitor, whereas the action of LDL-resembling particles was more prolonged but slower. The oxidation of LDL has been closely associated with the development of cardiovascular disease, including atherosclerosis and thrombosis. Positively charged amino acids, particularly lysine residues, are prone to alterations via the formation of adducts by lipid peroxidation products. These residues are important in the inhibition of tissue factor activity by ApoB100. They also play an important role in the inhibitory Kunitz domains of TFPI. We have shown that the decline in the ability of LDL to inhibit tissue factor was as a result of modifications in LDL arising from oxidation. By examining the effects of oxidation on full-length and C-terminal truncated TFPI bound to LDL-resembling particles, we found that TFPI is only affected when in close association with ApoB100. C-terminal truncated TFPI was not affected significantly by oxidation. Finally, chemical modification of lysine and arginine residues reduced the overall inhibition of tissue factor by TFPI. We propose that TFPI and LDL act separately to inhibit tissue factor in vivo. However, the oxidation of LDL can alter both the endogenous activity of ApoB100 and reduce that of closely associated TFPI, compromising normal hemostasis.

Identification of a domain in apolipoprotein B-100 that inhibits the procoagulant activity of tissue factor

The ability of low-density lipoprotein (LDL) to inhibit the procoagulant activity of tissue factor is mediated by a direct protein-protein interaction involving apolipoprotein (apo) B-100. A lysine-rich sequence within apo B-100 (residues 3121-3217), which we have termed lysine-rich apo B-100-derived (KRAD)-98 peptide, may be responsible for its activity. Within this region, residues 3147-3160 (KRAD-14) contain an exceptionally high proportion of positive amino acids. Both recombinant KRAD-98 and KRAD-14 peptides inhibited the procoagulant activity of tissue factor by preventing the activation of factor VII. KRAD-14 also inhibited the prothrombinase components, factors Xa and V. In comparison with the parent protein (apo B-100), KRAD-14 peptide displayed a 20-fold enhancement in the rate of inhibition, whereas KRAD-98 peptide exhibited a rate closer to that of apo B-100. Mutational analysis of KRAD-14 peptide revealed three adjacent amino acids, alteration of which greatly reduced the inhibitory potential of this peptide. A peptide derived from tissue factor (residues 58-66) was found to act co-operatively with tissue factor itself, but also augmented the inhibition of tissue-factor activity by apo B-100. In conclusion, LDL may be a physiological regulator of haemostatic mechanisms through the interactions of lysine-rich domains of apo B-100 with tissue factor.

Modification of tissue factor by peroxynitrite influences its procoagulant activity

Peroxynitrite, a reactive oxidising species resulting from a reaction between nitric oxide and the superoxide anion, modifies proteins by nitration of certain amino acids such as tyrosine. Tissue factor (TF), a transmembrane protein, is expressed on cells under inflammatory conditions and initiates the coagulation cascade. The extracellular domain of TF is rich in tyrosine. Exposure of recombinant TF and cellular TF to peroxynitrite was associated with a reduction in procoagulant activity. This was accompanied by an elevated level of nitrotyrosine residues. Peroxynitrite may have a protective role by attenuation of the thrombotic properties of TF.