Conservation of tissue factor primary sequence among three mammalian species

Evaluation of different commercial antibodies for their ability to detect human and mouse tissue factor by western blotting

BACKGROUND

Western blotting is used to measure protein expression in cells and tissues. Appropriate interpretation of resulting data is contingent upon antibody validation.

OBJECTIVES

We assessed several commercial anti-human and anti-mouse tissue factor (TF) antibodies for their ability to detect TF by western blotting.

MATERIAL AND METHODS

We used human pancreatic cancer cell lines expressing different levels of TF and a mouse pancreatic cancer cell line expressing TF with a matched knockout derivative.

RESULTS

Human and mouse TF protein detected by western blotting correlated with levels of TF mRNA in these cell lines. The apparent molecular weight of TF is increased by N-linked glycosylation and, as expected, deglycosylation decreased the size of TF based on western blotting. We found that four commercial anti-human TF antibodies detected TF in a TF-positive cell line HPAF-II whereas no signal was observed in a TF-negative cell line MIA PaCa-2. More variability was observed in detecting mouse TF. Two anti-mouse TF antibodies detected mouse TF in a TF-positive cell line and no signal was observed in a TF knockout cell line. However, a third anti-mouse TF antibody detected a nonspecific protein in both the mouse TF-positive and TF-negative cell lines. Two anti-human TF antibodies that are claimed to cross react with mouse TF either recognized a nonspecific band or did not detect mouse TF.

DISCUSSION

Our results indicate that there is a range in quality of commercial anti-TF antibodies.

CONCLUSION

We recommend that all commercial antibodies should be validated to ensure that they detect TF.

Establishment of reference values for various coagulation tests in healthy Florida manatees (Trichechus manatus latirostris) and evaluation of coagulation in debilitated manatees during rehabilitation

OBJECTIVE

To establish reference ranges for coagulation parameters in healthy Florida manatees (Trichechus manatus latirostris) and compare results with those for debilitated manatees undergoing treatment at a rehabilitation facility.

DESIGN

Prospective study.

ANIMALS

29 healthy manatees and 45 debilitated manatees with various diseases.

PROCEDURES

Manatees considered healthy on the basis of results of physical examination, CBC, and serum biochemical analysis underwent coagulation testing including measurement of prothrombin time, partial thromboplastin time, D-dimer concentration, platelet count, and fibrinogen concentration to establish reference ranges. For comparison, a group of manatees undergoing rehabilitation was also tested, and the results were compared. Thromboelastography was also performed on some animals.

RESULTS

Values for D-dimer concentration were significantly higher in debilitated versus healthy animals. There was no significant difference for prothrombin time, partial thromboplastin time, platelet count, or fibrinogen concentration between groups. Thromboelastography was performed on 8 healthy animals.

CONCLUSIONS AND CLINICAL RELEVANCE

Reference ranges were established for various tests of coagulation that may assist clinicians during the initial evaluation and rehabilitation of Florida manatees. Future research to evaluate the effect of specific disease processes on the coagulation cascade is recommended.

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

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

Role of tissue factor in thrombosis in antiphospholipid antibody syndrome

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder defined by the presence of an antiphospholipid antibody (aPL) and the occurrence of at least one associated clinical condition that includes venous thrombosis, arterial thrombosis or pregnancy morbidity. The aPL detected in APS have long been thought to have a direct prothrombotic effect in vivo. However, the pathophysiology underlying their coagulopathic effect has not been defined. Emerging data suggest a role for the procoagulant protein tissue factor (TF). In this review we provide an overview of TF, describe mouse models used in the evaluation of the role of TF in thrombosis, as well as summarize recent work on TF and APS.

Efficient suppression of tissue factor synthesis using antisense oligonucleotides selected by an enhanced strategy for evaluation of structural characteristics

Selection of optimal antisense constructs is still a problem. Among a huge number of antisense oligonucleotides (AS-ONs) only a small piece show inhibitory efficacy. We want to develop an enhanced strategy for specific selection of effective AS-ONs based on prediction of secondary structure of the target messenger RNA (mRNA) and analysis of thermodynamic properties of the mRNA/AS-ON hybrid. Numerous AS-ONs targeted on human tissue factor (TF) mRNA were investigated to evaluate the relevance of different thermodynamic and structural properties on inhibitory efficacy. Cell viability, TF protein and TF mRNA were determined after transfection of bladder cancer cell line J82. Inhibitory efficacy was related to GC content, target region within the TF mRNA and stability of the mRNA/AS-ON hybrid or affinity of the AS-ON to the target mRNA. We found effective AS-ONs targeted on translated region or 3'-untranslated region of TF RNA. We also detected a great correlation between inhibitory efficacy and GC content as well as stability of the mRNA/AS-ON hybrid.

NF-kappaB transcription factor p50 critically regulates tissue factor in deep vein thrombosis

NF-kappaB transcription factors regulate the expression of tissue factor (TF), a principal initiator of the coagulation cascade. Dominant among them is the p50/p65 heterodimer. Here we report that Andrographolide (Andro; a p50 inhibitor) and genetic deletion of p50 attenuated TF activity in stimulated endothelial cells and monocytes/macrophages. Results of the electrophoretic mobility "supershift" assay and chromatin immunoprecipitation demonstrated the direct interaction of the p50/p65 heterodimer with the NF-kappaB site of the human TF promoter. Andro-treated and p50 null mice both exhibited blunted TF expression and reduced venous thrombosis, which were recapitulated by an anti-murine TF antibody in vivo. Our findings thus indicate that regulation of TF by NF-kappaB transcription factor p50 is essential for the pathogenesis of deep vein thrombosis and suggest that specific inhibitors of p50, such as Andro, may be therapeutically valuable for preventing and perhaps treating venous thrombosis.

Suppression of HUVEC tissue factor synthesis by antisense oligodeoxynucleotide

Tissue factor (TF) is an important regulator and effector molecule of coagulation. It is primary known as a cofactor for factor VIIa-mediated triggering of blood coagulation, which proceeds in a cascade of extracellular reactions, ultimately resulting in thrombin formation. In sepsis, expression of TF by activated monocytes, macrophages and endothelial cells may lead to disseminated intravascular coagulation. Further studies have suggested that TF also plays non-haemostatic roles in blood vessel development, tumor angiogenesis, metastasis and inflammation. In the present study we examined the feasibility of inhibiting lipopolysaccharide (LPS)-induced TF expression in cultured human umbilical vein endothelial cells (HUVECs) using a modified phosphorothioate antisense oligodeoxynucleotide targeted to the TF mRNA. CD31 receptor-mediated endocytosis was used as a means of delivering TF antisense oligomer to HUVECs. This DNA carrier system consists of anti-CD31 antibody conjugated to the antisense. Co-exposure of HUVECs with TF antisense and LPS resulted in 54.6+/-3.2% suppression of TF activity when compared with control LPS stimulated cells. The antisense also reduced the LPS-induced TF mRNA level. Control experiments with TF sense and mismatched antisense oligomers were performed to exclude non-specific inhibitory effects. The cytotoxicity of the antisense oligomer conjugate was also evaluated. Results demonstrate that this TF antisense oligomer specifically suppressed the synthesis of biologically active endothelial TF and that antisense oligomers might represent a useful tool in the investigation of endothelial TF function/biology.

Studies on rabbit natural and recombinant tissue factors: intracellular retention and regulation of surface expression in cultured cells

Tissue factor (TF) is the most important trigger of blood coagulation in vascular pathology. Rabbit TF, with or without (ΔC) its COOH-terminal intracellular tail, has been conjugated to green fluorescent protein (GFP) to study subcellular localization and other functions of TF. TF-GFP and TFΔC-GFP are associated with Na2CO3-resistant buoyant fractions in HEK-293 cells (lipid rafts); there is no morphological difference in the surface distribution of these or other GFP-labeled membrane proteins present in or excluded from rafts (confocal microscopy, HEK-293 cells). Endogenous TF expressed by rabbit aortic smooth muscle cells (SMCs) is also raft associated. Membranes from HEK-293 cells expressing recombinant TF-GFP or wild-type TF were equipotent to clot human plasma; however, TFΔC-GFP was ∼20-fold more active (per membrane weight). Immunoblot confirmed that the deletion mutant is more abundantly expressed, and confocal microscopy showed that it has preferential membrane localization, whereas TF-GFP is mainly intracellular (nuclear lining and multiple granules). With a similar half-life (<4 h), the two constructions differ by their intracellular retention, lower for TFΔC-GFP. In serum-starved SMCs, the expression of endogenous TF was upregulated by interleukin-1β and/or FBS treatment (immunoblot, immunofluorescence, clotting assay). However, TF secretion or surface expression was not regulated by stimuli of physiological intensity (such as stimulation of the coexpressed kinin B1receptors), although a calcium ionophore was highly active in this respect. TF is a raft-associated molecule whose surface expression (secretion) is apparently retarded or impaired by structural determinant(s) located in its COOH-terminal tail.

Characterization of recombinant murine factor VIIa and recombinant murine tissue factor: a human-murine species compatibility study

Tissue factor (TF) is believed to play an important role in coagulation, inflammation, angiogenesis and wound healing as well as in tumor growth and metastasis. To facilitate in vivo studies in experimental murine models, we have produced recombinant murine factor VII (FVII) and the ectodomain of murine TF, TF(1-223). Murine FVII was activated to FVIIa with human factor Xa and upon reaction with FFR-chloromethyl ketone converted into an active site-blocked TF antagonist, FFR-FVIIa. The activity of murine FVIIa was characterized in factor X activation assays as well as in clot assays with murine and human thromboplastin in murine and human plasma. In these assays murine FVIIa exhibited a specific activity equivalent to or higher than human FVIIa. Further analysis showed that murine FVIIa binds with high affinity to both murine and human TF, whereas the association of human FVIIa to murine TF is about three orders of magnitude weaker than the association to human TF. This difference was further emphasized by the effect of murine-and human FFR-FVIIa on bleeding in an in vivo mouse model. Intra-peritoneal administration of 1 mg/kg murine FFR-FVIIa significantly prolonged the tail-bleeding time, whereas no effect on bleeding was observed with a 25-times higher dose of the human FFR-FVIIa. Together, these data confirms the notion of poor species compatibility between human FVII and murine TF and emphasizes the requirement for autologous FVIIa in studies on the role of the TF in experimental in vivo pharmacology.

Expression of recombinant rabbit tissue factor in Pichia pastoris, and its application in a prothrombin time reagent

Tissue factor (TF), or thromboplastin, is a cell membrane-associated glycoprotein composed, in full length, of cytoplasmic, transmembrane, and extracellular domains. It functions as a cofactor in a complex with factor VII (FVII), generating activated factor VII (FVIIa) and initiating blood coagulation. The prothrombin time (PT) assay uses TF as the in vitro activator of coagulation under defined conditions, and it is primarily used to diagnose and manage the extrinsic-pathway factor defficiencies. To overcome the limitations of natural-source TF, we have expressed the mature full-length recombinant rabbit TF (rRTF) protein in Pichia pastoris. Isolation, by purification by immobilized metal-affinity chromatography, of full-length rRTF was facilitated by engineering a (His)(6) tail on its C-terminus, which maximizes the selection of rRTF with intact transmembrane and cytoplasmic domains, critical for proper activity. A PT reagent that incorporates this purified rRTF has performance characteristics similar to those of PT reagents made with natural TF as indicated in method comparison studies, and shows lot-to-lot consistency and reproducibility.

Inhibition of the tissue factor-thrombin pathway limits infarct size after myocardial ischemia-reperfusion injury by reducing inflammation

Functional inhibition of tissue factor (TF) has been shown to improve coronary blood flow after myocardial ischemia/reperfusion (I/R) injury. TF initiates the coagulation protease cascade, resulting in the generation of the serine protease thrombin and fibrin deposition. Thrombin can also contribute to an inflammatory response by activating various cell types, including vascular endothelial cells. We used a rabbit coronary ligation model to investigate the role of TF in acute myocardial I/R injury. At-risk areas of myocardium showed increased TF expression in the sarcolemma of cardiomyocytes, which was associated with a low level of extravascular fibrin deposition. Functional inhibition of TF activity with an anti-rabbit TF monoclonal antibody administered either 15 minutes before or 30 minutes after coronary ligation reduced infarct size by 61% (P = 0.004) and 44% (P = 0.014), respectively. Similarly, we found that inhibition of thrombin with hirudin reduced infarct size by 59% (P = 0.014). In contrast, defibrinogenating the rabbits with ancrod had no effect on infarct size, suggesting that fibrin deposition does not significantly contribute to infarct size. Functional inhibition of thrombin reduced chemokine expression and inhibition of either TF or thrombin reduced leukocyte infiltration. We propose that cardiomyocyte TF initiates extravascular thrombin generation, which enhances inflammation and injury during myocardial I/R.

Functional implications of tissue factor localization to cell-cell contacts in myocardium

Recently published studies suggest that the procoagulant receptor protein tissue factor (TF) is involved in vitro in cell adhesion and migration, via an interaction of its cytoplasmic domain with cytoskeletal proteins. Interestingly, TF is abundantly expressed in myocardium, but not in skeletal muscle. To elucidate the possible roles of TF in the myocardium, this study examined the cellular distribution of TF in relation to cytoskeletal proteins, as well as its relative amounts in different segments of premature, mature, and pathologically altered cardiac muscle. In juvenile and adult hearts, TF was predominantly detectable in the transverse part of the intercalated discs, where it co-localized with cytoskeletal proteins such as desmin and vinculin. The lowest amount of TF was observed in right atrial and the highest in left ventricular myocardium, which correlated with the number of contact sites of cardiomyocytes in these segments of the cardiac muscle. Lower levels of TF were present in structurally altered myocardium from patients with hypertension or ventricular hypertrophy. In addition, TF expression was decreased in human heart during sepsis and transiently decreased in rabbit heart in an endotoxaemia model, which indicates that a reduction in TF may contribute to cardiac failure in sepsis. The microtopography of TF at cardiomyocyte contact sites indicates that TF may play a structural role in the maintenance of cardiac muscle.

Lipopolysaccharide induction of tissue factor expression in rabbits

Tissue factor (TF) is the major activator of the coagulation protease cascade and contributes to lethality in sepsis. Despite several studies analyzing TF expression in animal models of endotoxemia, there remains debate about the cell types that are induced to express TF in different tissues. In this study, we performed a detailed analysis of the induction of TF mRNA and protein expression in two rabbit models of endotoxemia to better understand the cell types that may contribute to local fibrin deposition and disseminated intravascular coagulation. Northern blot analysis demonstrated that lipopolysaccharide (LPS) increased TF expression in the brain, lung, and kidney. In situ hybridization showed that TF mRNA expression was increased in cells identified morphologically as epithelial cells in the lung and as astrocytes in the brain. In the kidney, in situ hybridization experiments and immunohistochemical analysis showed that TF mRNA and protein expression was increased in renal glomeruli and induced in tubular epithelium. Dual staining for TF and vWF failed to demonstrate TF expression in endothelial cells in LPS-treated animals. These results demonstrate that TF expression is induced in many different cell types in LPS-treated rabbits, which may contribute to local fibrin deposition and tissue injury during endotoxemia.

A peptide sequence from mouse tissue factor inhibits human tissue factor dependent factor X activation

Synthetic peptides based on the putative factor X recognition site of human (Thr-Leu-Tyr-Tyr-Trp-Lys-Ser-Ser-Ser-Ser), rabbit (Thr-Leu-Tyr-Tyr-Trp-Arg-Ala-Ser-Ser-Thr), and murine tissue factor (Ile-Ile-Thr-Tyr-Arg-Lys-Gly-Ser-Ser-Thr) were dose-dependent inhibitors of human tissue factor/factor VIIa catalyzed factor X activation with IC50 values of 220, 17, and 33 microM, respectively. The mouse results were highly surprising given the low homology between the human and mouse sequence (40%) and that mouse tissue factor, in contrast with rabbit tissue factor, does not support the procoagulant activity of human factor VIIa on factor X. The inhibitory mechanism of the murine peptide was noncompetitive with respect to factor X but competitive with respect to tissue factor, indicating the peptide competes with tissue factor (or the tissue factor/factor VIIa complex) for binding to factor X. The peptide could be N-terminally truncated by two Ile without loss of inhibitory activity or changed inhibitory mechanism. Substitution of two Gly for the two Ile, which increased solubility, decreased IC50 to 17 microM whereas scrambling the peptide made it inactive.

Expression of tissue factor in the rabbit aorta after balloon injury

Tissue factor (TF) is a primary initiator of the extrinsic pathway of blood coagulation. Recently TF has been shown to be overexpressed in atherosclerotic lesions and it is thought to contribute to the thrombogenicity of the plaques. We studied TF expression in the media and the neointima of rabbit aortas at various intervals after balloon injury. TF protein was immunohistochemically detected in smooth muscle cells (SMCs) of the inner layer of the media at 2 h after injury and was subsequently detected in SMCs in the neointima, whereas no TF expression was detected in the uninjured aortas except for the adventitia. Immunohistochemical and immunoelectron microscopic studies revealed that TF-positive SMCs were of an immature or synthetic phenotype and TF protein was detected in the rough endoplasmic reticulum in SMCs. TF mRNA in the intima and media increased at 2 h after injury and returned to near baseline levels at 12-24 h, whereas TF activity also increased at 2 h and continued at similar levels over the next 72 h. TF mRNA and activity increased markedly at 2-8 weeks after injury. These data suggest that TF is rapidly induced in the medial SMCs and hereafter is constitutively expressed in the neointima. TF expressed in the neointima may contribute to hypercoagulable properties of injured arteries.

A Soluble Tissue Factor Mutant Is a Selective Anticoagulant and Antithrombotic Agent

One approach to developing safer and more efficacious agents for the treatment of thrombotic disease involves the design and testing of inhibitors that block specific steps in the coagulation cascade. We describe here the development of a mutant of human tissue factor (TF ) as a specific antagonist of the extrinsic pathway of blood coagulation and the testing of this mutant in a rabbit model of arterial thrombosis. Alanine substitutions of Lys residues 165 and 166 in human TF have been shown previously to diminish the cofactor function of TF in support of factor X (FX) activation catalyzed by factor VIIa (FVIIa). The K165A:K166A mutations have been incorporated into soluble TF (sTF; residues 1-219) to generate the molecule “hTFAA.” hTFAA binds FVIIa with kinetics and affinity equivalent to wild-type sTF, but the hTFAA⋅FVIIa complex shows a 34-fold reduction in catalytic efficiency for FX activation relative to the activity measured for sTF⋅FVIIa. hTFAA inhibits the activation of FX catalyzed by the complex formed between FVIIa and relipidated TF(1-243). hTFAA prolongs prothrombin time (PT) determined with human plasma and relipidated TF(1-243) or membrane bound TF, and has no effect on activated partial thromboplastin time, but is 70-fold less potent as an inhibitor of PT with rabbit plasma. The rabbit homologue of this mutant (“rTFAA”) was produced and shown to have greater potency with rabbit plasma. Both hTFAA and rTFAA display an antithrombotic effect in a rabbit model of arterial thrombosis with rTFAA giving full efficacy at a lower dose than hTFAA. Compared to heparin doses of equal antithrombotic potential, hTFAA and rTFAA cause less bleeding as judged by measurements of the cuticle bleeding time. These results indicate that TF⋅FVIIa is a good target for the development of new anticoagulant drugs for the treatment of thrombotic disease.

Monocytes and tissue factor promote thrombosis in a murine model of oxygen deprivation

Clinical conditions associated with local or systemic hypoxemia can lead to prothrombotic diatheses. This study was undertaken to establish a model of whole-animal hypoxia wherein oxygen deprivation by itself would be sufficient to trigger tissue thrombosis. Furthermore, this model was used to test the hypothesis that hypoxia-induced mononuclear phagocyte (MP) recruitment and tissue factor (TF) expression may trigger the local deposition of fibrin which occurs in response to oxygen deprivation. Using an environmental chamber in which inhaled oxygen tension was lowered to 6%, hypoxic induction of thrombosis was demonstrated in murine pulmonary vasculature by 8 h based upon: (a) immunohistologic evidence of fibrin formation in hypoxic lung tissue using an antifibrin antibody, confirmed by 22.5-nm strand periodicity by electron microscopy; (b) immunoblots revealing fibrin gamma-gamma chain dimers in lungs from hypoxic but not normoxic mice or hypoxic mice treated with hirudin; (c) accelerated deposition of 125I-fibrin/fibrinogen and 111In-labeled platelets in the lung tissue of hypoxic compared with normoxic animals; (d) reduction of tissue 125I-fibrin/fibrinogen accumulation in animals which had either been treated with hirudin or depleted of platelets before hypoxic exposure. Because immunohistochemical analysis of hypoxic pulmonary tissue revealed strong MP staining for TF, confirmed by increased TF RNA in hypoxic lungs, and because 111In-labeled murine MPs accumulated in hypoxic pulmonary tissue, we evaluated whether recruited MPs might be responsible for initiation of hypoxia-induced thrombosis. This hypothesis was supported by several lines of evidence: (a) MP depletion before hypoxia reduced thrombosis, as measured by reduced 125I-fibrin/fibrinogen deposition and reduced accumulation of cross-linked fibrin by immunoblot; (b) isolated murine MPs demonstrated increased TF immunostaining when exposed to hypoxia; and (c) administration of an anti-rabbit TF antibody that cross-reacts with murine TF decreased 125I-fibrin/fibrinogen accumulation and cross-linked fibrin accumulation in response to hypoxia in vivo. In summary, these studies using a novel in vivo model suggest that MP accumulation and TF expression may promote hypoxia-induced thrombosis.

Suppression of human monocyte tissue factor synthesis by antisense oligodeoxynucleotide

Tissue factor (TF) is a cellular receptor and cofactor for factor V11/V11a which initiates the blood coagulation cascade. An understanding of TF cell biology is therefore of critical importance to the pathophysiology of many disorders. We have utilized an antisense oligodeoxynucleotide (aODN), directed against human blood monocyte TF mRNA, to investigate the feasibility of inhibiting the synthesis of TF. CD14 receptor-mediated endocytosis was used as a means of delivering TF aODN to monocytes. This DNA carrier system consists of the fab portion of anti-CD14 antibody covalently linked to poly (L-lysine). Co-treatment of monocytes with TF aODN and endotoxin resulted in 80.4 +/- 2.2% suppression of TF activity when compared with control endotoxin stimulated cells. Control experiments with TF sense ODN, mismatched aODN, and an irrelevant aODN were performed to exclude nonspecific inhibitory effects. The cytotoxicity of the DNA carrier complex was also evaluated. These results demonstrate that this TF mRNA antisense ODN specifically suppressed the synthesis of biologically active monocyte TF and that antisense ODNs might therefore represent a useful tool in the investigation of monocyte/macrophage TF function.

Co-localization of tissue factor protein and its mRNA in human blood monocytes

Triggering of both the extrinsic and intrinsic coagulation pathways is mediated by the cell surface receptor Tissue Factor (TF). The ability to observe the cell surface TF protein and its mRNA at the single cell level would facilitate our understanding of the cellular biology of TF in health and diseased states. Employing the methods of immuno-gold silver staining and in situ hybridization using non-isotopically labelled oligoprobes, tissue factor antigen and mRNA were detected simultaneously in endotoxin stimulated human peripheral blood monocytes.

Tissue factor mediates prolonged procoagulant activity on the luminal surface of balloon-injured aortas in rabbits

BACKGROUND

Activation of coagulation has been implicated in both acute thrombotic occlusion and restenosis after balloon angioplasty. However, concomitant administration of antithrombotic agents has thus far failed to prevent these complications. Importantly, the factors contributing to procoagulant activity of balloon-injured arteries over time have not been defined. This study was designed to determine the duration of procoagulant activity on the luminal surface of balloon-injured arteries and the relative roles of tissue factor and thrombin in this response.

METHODS AND RESULTS

Abdominal aortas in rabbits were subjected to repetitive balloon hyperinflations sufficient to disrupt the internal elastic lamina. Aortas were excised at < 1, 2, 4, 8, 16, 24, 48, and 72 hours and 1, 2, and 4 weeks after injury; divided into segments; and perfused with recalcified human pooled plasma (n = 58) or plasma depleted of vitamin K-dependent coagulation factors (n = 27) or first incubated with a monoclonal antibody to rabbit tissue factor (n = 33) followed by perfusion with human plasma. Samples of the effluent and plasma perfusate were collected over 10 minutes and assayed for fibrinopeptide A (FPA) as an index of the rate of thrombin-induced fibrin formation. FPA in the effluent from segments perfused with recalcified plasma, expressed as a percentage of FPA in the perfusate, was elevated for 16 hours after balloon-induced injury and exhibited two distinct increases occurring < 1 hour (1297 +/- 473%, mean +/- SD, n = 5) and 8 hours (1052 +/- 330%, n = 6) after injury (P < or = .000001 versus uninjured vessels). Preincubation of segments at these intervals with an antibody to tissue factor markedly attenuated the increases in FPA, as did perfusion of segments with plasma depleted of vitamin K-dependent coagulation factors, indicating that the observed increases in FPA in whole plasma did not result from performed thrombin bound to the injured vessel wall.

CONCLUSIONS

Tissue factor-mediated coagulation appears to be primarily responsible for prolonged procoagulant activity of balloon-injured arteries.

The regulation of uterine tissue factor by estrogen

Tissue factor (TF) is a transmembrane protein that initiates coagulation and indirectly catalyzes the conversion of prothrombin to thrombin. We previously showed that treatment of immature rats with estradiol (E(2)) stimulated a rapid increase in TF mRNA and protein in the uterus. Our current experiments usingin situ hybridization show that the increase in TF mRNA occurred primarily in the stromal cell layer. The effect of E(2) to increase TF mRNA occurred in uterine organ cultures but not in separated epithelial and stromal cellsin vitro. Thrombin and the phorbol ester, TPA, compounds which regulate TF expression in other cell types by activation of protein kinase C (PKC), increased TF mRNA in both uterine organ cultures and in separated uteriné cells. The 5' regulatory region of the TF gene was examined for the presence of an estrogen response element (ERE) using a plasmid, pTFCAT, containing -740 to + 15 bp of the mouse TF promoter upstream of the chloramphenicol acetyltransferase (CAT) reporter gene. There was no response to E(2) in HeLa cells cotransfected with pTFCAT and a human ER construct, pHEO. In contrast, E(2) increased CAT activity in cells cotransfected with a positive-control plasmid, containing the consensus ERE cloned upstream of the thymidine kinase promoter-driven CAT gene, and pHEO. CAT activity was also increased by TPA in cells transfected with pTFCAT. In summary, E(2) induces TF mRNA in uterine organ culture indicating that systemic factors are not absolutely required for the effect. However, E(2) injection induces transudation of plasma prothrombin into the uterus where it may be converted to thrombin. Thus thrombin may contribute to E(2)-induction of TF mRNAin vivo. An ERE was not identified in the 750 bp immediately 5' to the transcription start site of the TF gene although a TPA-responsive element was present. It is postulated that E(2) may induce TF mRNA by multiple indirect pathways including stimulation of PKC and Jun and Fos transcription factors, and by generation of thrombin in the uterus.

Production of tissue factor by monocyte progenitor cells

Tissue factor (TF) is known to be produced by monocytes from human peripheral blood. However the production of this factor by haematopoietic progenitor cells is not yet known. We thus studied human monocyte progenitor cells isolated from bone marrow of normal and diseased individuals. These cells were non-adherent, monocytic and able to phagocytose particles ranging from 0.3-1 microns. Unactivated partial thromboplastin time clotting assay demonstrated procoagulant activity consistent with TF function, which was blocked by a neutralizing anti-TF monoclonal antibody, G12. The production of TF messenger RNA was demonstrated on dot blot and northern blot analysis utilizing an oligonucleotide probe.

Increased expression of tissue factor mRNA and procoagulant activity in ovine lentivirus-infected alveolar macrophages

To link ovine lentivirus infection to lung tissue damage, we studied the procoagulant response in alveolar macrophages from experimentally infected lambs and in in vitro infected alveolar macrophages. We cloned ovine tissue factor cDNA and analysed its in vitro expression by Northern blotting. Visna-maedi virus induced tissue factor mRNA. In order to correlate this mRNA induction with its cellular function, we analysed macrophage procoagulant activity after in vitro and in vivo infection. The procoagulant activity was increased by interaction with the virus in both cases. Thus, visna-maedi virus-induced expression of tissue factor mRNA was associated with enhanced macrophage procoagulant activity. These findings indicate an active role of alveolar macrophages in the pathogenesis of these inflammatory lung lesions.

Sequence characterization of a sheep cDNA for antithrombin III

We determined the cDNA sequence of the mRNA for antithrombin III (AT III) from sheep liver. It encodes a protein of 465 amino acids, including a signal peptide of 32 amino acids. The amino acid sequence of the mature protein shows a sequence identity of 89.1%, 95.6% and 85.0% to the human, bovine and rabbit equivalents, respectively. Cysteine residues involved in disulfide bonds as well as potential glycosylation sites are conserved between the four species. In contrast, the amino acid sequence of the signal peptide shows a smaller identity, i.e., 68.7% and 56.3% compared to the human and rabbit preprotein, respectively.

Structure of the murine tissue factor gene. Chromosome location and conservation of regulatory elements in the promoter

Tissue factor (TF) is a transmembrane glycoprotein that mediates cellular initiation of the coagulation serine protease cascades. Moreover, expression of TF in human atherosclerotic plaques is likely to play a significant role in the thrombotic complications associated with plaque rupture. In this study the complete murine TF gene, Cf-3, was isolated from mouse NIH 3T3 cells and was found to consist of six exons spanning about 11 kilobase pairs (kbp) of DNA. A major transcriptional start site was located 24 bp downstream of a TATA box. Cf-3 was mapped to chromosome 3 by analysis of an intersubspecies test cross. Conserved transcription factor-binding sites were identified by comparison of 5' flanking regions of the murine and human TF genes. A region of the TF promoter required for constitutive expression exhibited 85% identity in DNA sequence and included two conserved binding sites for Sp1. Furthermore, two AP-1 sites and an NF-kappa B site were conserved in a 56-bp region necessary for transcriptional activation in response to bacterial lipopolysaccharide. These highly conserved regions of the TF promoter, which contain several binding sites for well-characterized transcription factors, are likely to be functionally important in the complex pattern of TF gene expression observed in a variety of cell types.

The third Trp-Lys-Ser (WKS) tripeptide motif in tissue factor is associated with a function site

The tripeptide sequence Trp-Lys-Ser (WKS) is repeated three times in the extracellular ligand binding domain of human Tissue Factor (TF). Using site-directed mutagenesis, we replaced each of the WKS motifs in human TF by Arg-Lys-Gly (RKG), the least conserved replacement for the motif found in murine TF. This substitution in the first repeat W14KS, as well as a Trp14----Arg substitution, resulted in a structurally altered protein, whereas a conservative hydrophobic Trp14----Phe substitution resulted in a functionally normal protein. This suggests that Trp14 may contribute to a hydrophobic core rather than involvement of this motif in function. Replacement of the W45KS and W158KS motifs was associated with no detectable structural alterations; however, function was diminished with the RKG replacement of the third repeat. Mutant proteins with Lys159----Ala and Tyr157----Ala substitutions exhibited loss of function, whereas Tyr156----Ala and Ser160----Ala substitutions flanking the YWK sequence resulted in functional proteins. These data demonstrate that the W158KS motif in human TF is associated with a functional site and identify Lys159 in this motif as a functionally important residue.

cDNA and amino acid sequences of bovine tissue factor

A cDNA encoding bovine tissue factor has been isolated from a lambda gt11 bovine adrenal cDNA library. The cDNA insert was 1877 base pairs with an open reading frame of 876 base pairs that encoded a presequence of 35 amino acids and a mature tissue factor of 257 amino acids. Bovine tissue factor had three potential N-glycosylation sites, four extracellular cysteine residues, a cytoplasmic cysteine residue, and one tripeptide tryptophan-lysine-serine motif. Identities of the amino acid sequences of the mature forms between the bovine tissue factor and each of human, mouse, and rabbit tissue factors were 70.4%, 57.2%, and 74.1%, respectively.

Tissue factor mRNA in THP-1 monocytic cells is regulated at both transcriptional and posttranscriptional levels in response to lipopolysaccharide

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.

Tissue factor mRNA in THP-1 monocytic cells is regulated at both transcriptional and posttranscriptional levels in response to lipopolysaccharide

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.