Regulation of tissue factor gene expression in epithelial cells. Induction by serum and phorbol 12-myristate 13-acetate

The garlic-derived organosulfur compound diallyl trisulphide suppresses tissue factor function

Tissue factor (TF) is a critical initiator of extrinsic coagulation that sometimes causes thromboembolism. Diallyl trisulphide (DATS) is a secondary metabolite of allicin generated in crushed garlic, with various pharmacological effects. This study aimed to clarify the effect of DATS on the extrinsic coagulation elicited by TF and arteriosclerosis. TF activity was measured using a clotting assay in TF-expressing HL60 cells. DATS inhibited TF activity in a dose-dependent manner. TF expression in TNF-α-stimulated human umbilical vein endothelial cells was examined using real-time PCR and western blotting. DATS inhibited TF mRNA and protein expression induced by TNF-α via inhibition of JNK signalling. The effect of DATS on arteriosclerosis was also examined in apolipoprotein E-deficient mice. DATS administration in these mice tended to decrease atherosclerotic lesion size. These results strongly suggest that DATS prevents thromboembolism triggered by atherosclerosis via the inhibition of plaque formation and TF function.

A unique protein kinase C-dependent pathway for tissue factor downregulation in pericytes

Essentials Many mediators increase tissue factor (TF) expression in a wide variety of cell types. The only known example of TF downregulation is by pericytes during wound healing angiogenesis. Downregulation of TF mRNA and protein in cultured pericytes is Protein Kinase C (PKC) dependent. Pericyte TF regulation is unique, since PKC mediates increased TF in all other cell types tested. SUMMARY: Background Embryonic and tumor-associated angiogenesis are linked to elevated expression of the procoagulant transmembrane receptor tissue factor (TF). In contrast, we have reported that high baseline TF expression by perivascular cells (pericytes) is dramatically reduced during angiogenesis at sites of wound healing. This is the only setting in which active TF downregulation has been reported, thus revealing a novel mechanism of TF regulation. Objectives To define the mechanisms underlying the unique pattern of TF expression in pericytes. Methods TF expression in primary cultures of human pericytes is not altered by angiogenic cytokines or growth factors, but is actively downregulated by phorbol 12-myristate 13-acetate (PMA). We characterized TF transcription, protein stability and trafficking in response to PMA. Results Exposure to PMA reduced TF mRNA synthesis and shortened the half-life of TF protein from 11 h to 4.5 h. Addition of PMA rapidly triggered endocytosis of cell surface TF, followed by degradation in lysosomes. Cell surface TF coagulant activity was maintained until internal stores were depleted. Reduction of TF transcription, TF endocytosis and enhanced degradation of TF protein were all blocked by broad-spectrum inhibitors of protein kinase C (PKC). This was a surprising finding, because PKC activation increases TF expression in other cell types that have been tested. Conclusions The unique PKC-dependent pathway of TF downregulation in pericytes suggests that TF downregulation may play a functional role in angiogenesis. Distinct pathways regulating pathological and physiological TF expression could be utilized to modulate TF expression for therapeutic purposes.

p21-activated kinase-1 signaling regulates transcription of tissue factor and tissue factor pathway inhibitor

Tissue factor (TF) is a cell-surface glycoprotein responsible for initiating the coagulation cascade. Besides its role in homeostasis, studies have shown the implication of TF in embryonic development, cancer-related events, and inflammation via coagulation-dependent and -independent (signaling) mechanisms. Tissue factor pathway inhibitor (TFPI) plays an important role in regulating TF-initiated blood coagulation. Therefore, transcriptional regulation of TF expression and its physiological inhibitor TFPI would allow us to understand the critical step that controls many different processes. From a gene profiling study aimed at identifying differentially regulated genes between wild-type (WT) and p21-activated kinase 1-null (PAK1-KO) mouse embryonic fibroblasts (MEFs), we found TF and TFPI are differentially expressed in the PAK1-KO MEFs in comparison with wild-type MEFs. Based on these findings, we further investigated in this study the transcriptional regulation of TF and TFPI by PAK1, a serine/threonine kinase. We found that the PAK1·c-Jun complex stimulates the transcription of TF and consequently its procoagulant activity. Moreover, PAK1 negatively regulates the expression of TFPI and additionally contributes to increased TF activity. For the first time, this study implicates PAK1 in coagulation processes, through its dual transcriptional regulation of TF and its inhibitor.

Zinc finger transcription factor Egr-1 is involved in stimulation of NHE2 gene expression by phorbol 12-myristate 13-acetate

The apical membrane Na(+)/H(+) exchanger isoforms NHE2 and NHE3 are involved in transepithelial Na(+) absorption in the intestine. However, they exhibit differences in their pattern of tissue expression and regulation of their activity by various molecular signals. To study the mechanisms involved in the transcriptional regulation of these genes, we characterized cis-acting elements within the human NHE2 promoter that regulate NHE2 promoter expression in C2BBe1 cells. A small DNA region (-85/+249) was involved in the regulation of basal transcriptional activity of the NHE2 promoter as determined by transient transfection assays. RT-PCR analysis showed that NHE2 mRNA was upregulated in response to phorbol 12-myristate 13-acetate (PMA). Results from actinomycin D-treated cells indicated that the regulation of the NHE2 gene by PMA occurs in part at the transcriptional level. Furthermore, PMA treatment led to a 100% increase in promoter activity through elements located on the -415/+249 DNA fragment. A PMA-induced nuclear factor that bound to the NHE2 promoter was identified as the transcription factor Egr-1. We identified two PMA response elements in the -415/+1 promoter region that bind to Sp1 and Sp3 in untreated nuclear extracts and to Egr-1 in PMA-treated nuclear extracts. In cotransfection experiments, Egr-1 was able to transactivate the NHE2 promoter. Our data indicate that Egr-1 may play a key role in regulated expression of the human NHE2 gene.

Adenoviral-mediated delivery of early growth response factor-1 gene increases tissue perfusion in a murine model of hindlimb ischemia

To test the hypothesis that overexpression of early growth response factor-1 (Egr-1) contributes to the revascularization of ischemic limbs, a constitutively active form of Egr-1 (Egr-1*) was made and evaluated in vitro and in vivo. Analyses of the transduced myocytes revealed significant upregulation of bFGF, PDGF-A, PDGF-B, IGF-II, and TGF-beta1. A coculture assay of the paracrine effects indicated that Ad-Egr-1* promoted proliferation and migration of endothelial cells. When Ad-Egr-1* was injected into the tibialis anterior muscle of mice, followed by explant culture in growth factor-reduced Matrigel, many capillary-like structures were observed in the Egr-1* group compared with minimal sprouting from the LacZ group, suggesting an angiogenic potential of Egr-1*. Next we evaluated Ad-Egr-1* in a murine model of hindlimb ischemia. Compared with slow revascularization in the control PBS or LacZ group, a rapid increase in tissue perfusion was observed in the Egr-1* group and the difference in flux ratio was statistically significant at day 7. In the injected muscle, expression of Egr-1*, upregulation of its target genes, and increased number of vessels staining positive for smooth muscle alpha-actin were observed. These results suggest that Egr-1 plays an important role in vascular recovery after occlusion and could be a potential target for therapeutic angiogenesis.

Tissue factor: (patho)physiology and cellular biology

The transmembrane glycoprotein tissue factor (TF) is the initiator of the coagulation cascade in vivo. When TF is exposed to blood, it forms a high-affinity complex with the coagulation factors factor VII/activated factor VIIa (FVII/VIIa), activating factor IX and factor X, and ultimately leading to the formation of an insoluble fibrin clot. TF plays an essential role in hemostasis by restraining hemorrhage after vessel wall injury. An overview of biological and physiological aspects of TF, covering aspects consequential for thrombosis and hemostasis such as TF cell biology and biochemistry, blood-borne (circulating) TF, TF associated with microparticles, TF encryption-decryption, and regulation of TF activity and expression is presented. However, the emerging role of TF in the pathogenesis of diseases such as sepsis, atherosclerosis, certain cancers and diseases characterized by pathological fibrin deposition such as disseminated intravascular coagulation and thrombosis, has directed attention to the development of novel inhibitors of tissue factor for use as antithrombotic drugs. The main advantage of inhibitors of the TF*FVIIa pathway is that such inhibitors have the potential of inhibiting the coagulation cascade at its earliest stage. Thus, such therapeutics exert minimal disturbance of systemic hemostasis since they act locally at the site of vascular injury.

Induction of tissue factor expression in human endothelial cells by CD40 ligand is mediated via activator protein 1, nuclear factor kappa B, and Egr-1

Induction of tissue factor expression in endothelial cells via ligation of CD40 probably figures prominently in the pathogenesis of prevalent inflammatory diseases, including atherosclerosis. However, the molecular mechanisms of tissue factor gene expression triggered by CD40 ligand (CD40L) in this cell type remain unknown. We demonstrate here that the tissue factor promoter region -278 bp to +121 bp contains the CD40L-responsive elements, consisting of activator protein 1 (AP-1)+/-, nuclear factor (NF) kappaB-, and Egr-1-binding sites. Mutations of either the AP-1- or NF-kappaB-binding sites markedly reduced the CD40L-dependent promoter activation. The AP-1 and NF-kappaB sites displayed constitutive and CD40L-enhanceable DNA binding activity, respectively. Of note, mutation of the Egr-1-binding sites, previously not associated with CD40 signaling, impaired activation of the tissue factor promoter. Accordingly, CD40L strongly induced Egr-1 protein expression and DNA binding activity to all three bindings sites. In contrast to CD40L, other established inducers of tissue factor in endothelial cells, interleukin-1beta or tumor necrosis factor alpha, did not increase the expression of Egr-1. In conclusion, induction of tissue factor gene expression in human endothelial cells by CD40L involves AP-1 and NF-kappaB as well as Egr-1, a pathway previously not implicated in CD40 signaling and distinct from that employed by certain other proinflammatory cytokines.

Cyclic strain stimulates early growth response gene product 1-mediated expression of membrane type 1 matrix metalloproteinase in endothelium

SUMMARY

Matrix metalloproteinases (MMPs) are hypothesized to be involved in the processes of endothelial cell (EC) migration and matrix remodeling during angiogenesis. Although hemodynamic forces (such as blood pressure, wall tension, and shear stress) are considered to be strong stimuli for angiogenesis, the role of hemodynamic forces on the regulation of MMPs including membrane type 1 matrix metalloproteinase (MT1-MMP) has not been fully elucidated. To study this, rat microvascular EC were exposed to 60 cycles/minute of 24% maximum strain for up to 24 hours. MT1-MMP mRNA and protein increased in a time-dependent manner through 24 hours of exposure to cyclic strain. Cyclic strain induced early growth response gene product (Egr-1) mRNA and protein within 1 hour. A specific nucleoprotein complex was formed when an oligonucleotide containing binding sites for Sp1 and Egr-1 was incubated with nuclear extracts from EC exposed to 1 hour of cyclic strain. Antibodies to Egr-1 completely supershifted this complex. Increased binding of Egr-1 by cyclic strain to the MT1-MMP promoter correlated with enhanced transcriptional activity. These results suggest that cyclic strain up-regulates the Egr-1-mediated expression of MT1-MMP in rat microvascular EC, emphasizing the importance of hemodynamic forces in the regulation of MT1-MMP in vivo.

Angiotensin II (AT(1)) receptor blockade reduces vascular tissue factor in angiotensin II-induced cardiac vasculopathy

Tissue factor (TF), a main initiator of clotting, is up-regulated in vasculopathy. We tested the hypothesis that chronic in vivo angiotensin (ANG) II receptor AT(1) receptor blockade inhibits TF expression in a model of ANG II-induced cardiac vasculopathy. Furthermore, we explored the mechanisms by examining transcription factor activation and analyzing the TF promoter. Untreated transgenic rats overexpressing the human renin and angiotensinogen genes (dTGR) feature hypertension and severe left ventricular hypertrophy with focal areas of necrosis, and die at age 7 weeks. Plasma and cardiac ANG II was three- to fivefold increased compared to Sprague-Dawley rats. Chronic treatment with valsartan normalized blood pressure and coronary resistance completely, and ameliorated cardiac hypertrophy (P < 0.001). Valsartan prevented monocyte/macrophage infiltration, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) activation, and c-fos expression in dTGR hearts. NF-kappaB subunit p65 and TF expression was increased in the endothelium and media of cardiac vessels and markedly reduced by valsartan treatment. To analyze the mechanism of TF transcription, we then transfected human coronary artery smooth muscle cells and Chinese hamster ovary cells overexpressing the AT(1) receptor with plasmids containing the human TF promoter and the luciferase reporter gene. ANG II induced the full-length TF promoter in both transfected cell lines. TF transcription was abolished by AT(1) receptor blockade. Deletion of both AP-1 and NF-kappaB sites reduced ANG II-induced TF gene transcription completely, whereas the deletion of AP-1 sites reduced transcription. Thus, the present study clearly shows an aberrant TF expression in the endothelium and media in rats with ANG II-induced vasculopathy. The beneficial effects of AT(1) receptor blockade in this model are mediated via the inhibition of NF-kappaB and AP-1 activation, thereby preventing TF expression, cardiac vasculopathy, and microinfarctions.

Detection of mononuclear cells as the source of the increased tissue factor mRNA in the liver from lipopolysaccharide-treated rats

Tissue factor (TF) triggers the coagulation cascade reaction in vivo. Overexpression of TF mRNA is one leading cause of disseminated intravascular coagulation and thrombosis-related organ failure. In response to lipopolysaccharide (LPS) stimulation, various cell types can produce TF mRNA in vitro. However, there is currently no agreement on what types of cells in the liver overexpress TF mRNA after LPS treatment. For the first report, we found the increased TF mRNA with reverse transcription-polymerase chain reaction (RT-PCR), and confirmed a fourfold increase (p<0.001 vs. control, t-test) of the TF mRNA level with RT-competitive PCR in the liver of LPS-treated (2.0 mg/kg i.v. injection) rats. There was no significant difference in the glyceraldehyde-3-phosphate dehydrogenase mRNA level between LPS-treated rats and control rats. To clarify the localization and cellular source of LPS-induced TF mRNA, we performed in situ hybridization analysis with [35S]-labeled oligonucleotides probes, which we originally designed. We detected intense signals of TF mRNA in mononuclear cells but not in endothelial cells around the hepatic vein of LPS-treated rats. In this study, we showed that the TF mRNA level induced by LPS treatment, which may indicate mononuclear cells associated, significantly increased in the liver of rats. These results will provide circumstantial support for the therapeutic strategy that mononuclear cell should be one of the target cells to be treated in the early phase of disseminated intravascular coagulation in the liver, and that the need to suppress its overexpression of TF mRNA is essential for preventing hypercoagulable condition.

Native and oxidized low density lipoprotein induction of tissue factor gene expression in smooth muscle cells is mediated by both Egr-1 and Sp1

Tissue factor, in association with factor VIIa, initiates the coagulation cascade. We studied the influences of two pathophysiological stimuli, native (unmodified) and oxidized low density lipoprotein, on tissue factor gene expression in a cell important in vascular remodeling and vascular diseases, the smooth muscle cell. Our results demonstrated that both lipoproteins significantly induced tissue factor gene expression in rat aortic smooth muscle cells; oxidized low density lipoprotein was slightly more potent. Both lipoproteins increased tissue factor mRNA in a concentration- and time-dependent manner. Results from nuclear run-on assays and mRNA stability experiments indicated that increased tissue factor mRNA accumulation in response to the lipoproteins was principally controlled at the transcriptional level. By using lipid extracts of low density lipoprotein or methylation of the intact lipoprotein to block receptor recognition, we showed that this lipoprotein induced tissue factor mRNA via both receptor-independent and receptor-augmented pathways. Transfection studies using a series of deleted tissue factor promoters revealed that a -143- to +106-base pair region of the rat tissue factor promoter contained regulatory elements required for lipoprotein-mediated induction. Electrophoretic mobility shift assays showed that the binding activities of the transcription factor Egr-1, but not Sp1, were markedly elevated in response to these lipoproteins. Transfection of site-directed mutants of the tissue factor (TF) promoter demonstrated that not only Egr-1 but also Sp1 cis-acting elements in the TF (-143) promoter construct were necessary for optimal TF gene induction. Our data show for the first time that both low density lipoprotein and oxidized low density lipoprotein induce tissue factor gene expression in smooth muscle cells and that this tissue factor gene expression is mediated by both Egr-1 and Sp1 transcription factors.

Tissue factor is induced by monocyte chemoattractant protein-1 in human aortic smooth muscle and THP-1 cells

Monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine thought to play a major role in recruiting monocytes to the atherosclerotic plaque. Tissue factor (TF), the initiator of coagulation, is found in the atherosclerotic plaque, macrophages, and human aortic smooth muscle cells (SMC). The exposure of TF during plaque rupture likely induces acute thrombosis, leading to myocardial infarction and stroke. This report demonstrates that MCP-1 induces the accumulation of TF mRNA and protein in SMC and in THP-1 myelomonocytic leukemia cells. MCP-1 also induces TF activity on the surface of human SMC. The induction of TF by MCP-1 in SMC is inhibited by pertussis toxin, suggesting that the SMC MCP-1 receptor is coupled to a Gi-protein. Chelation of intracellular calcium and inhibition of protein kinase C block the induction of TF by MCP-1, suggesting that in SMC it is mediated by activation of phospholipase C. SMC bind MCP-1 with a Kd similar to that previously reported for macrophages. However, mRNA encoding the macrophage MCP-1 receptors, CCR2A and B, is not present in SMC, indicating that they possess a distinct MCP-1 receptor. These data suggest that in addition to being a chemoattractant, MCP-1 may have a procoagulant function and raise the possibility of an autocrine pathway in which MCP-1, secreted by SMC and macrophages, induces TF activity in these same cells.

Tissue factor expression in human monocytic cell lines

Tissue factor (TF) is a main initiator of the coagulation protease cascade. Control of the expression of this protein in monocytes is essential, since these cells are the only circulating blood cells responsible for TF expression. In this report we have used two human cell lines, arrested at different stages of monocytic differentiation, to study TF expression. The monoblastic cell line U-937 had a constitutive expression of TF surface protein and low TF mRNA levels detected by immunofluorescence or quantitative reverse transcriptase polymerase chain reaction respectively. The phorbol-12-myristate-13-acetate (PMA) was a potent enhancer of TF expression in U-937. Lipopolysaccharide (LPS) and tumor necrosis factor (TNF) had no effect on TF expression in U-937. The Mono Mac 6 cell line, with phenotypic features similar to that of mature monocytes, expressed lower basal levels of TF mRNA and surface TF antigen. However, in Mono Mac 6 cells TF expression was induced in response to LPS and TNF. These results indicate differences in basal and induced TF expression between U-937 and Mono Mac 6 cell lines.

Characterization of tissue factor expression on the human endothelial cell line ECV304

The endothelial cell line ECV304 is a spontaneously transformed cell line established from human umbilical vein. The characterization of tissue factor (TF) expression by ECV304 cells has been accomplished in this study. ECV304 cells expressed both TF mRNA and antigen (TFag) constitutively. In ECV304 cell lysates, the levels of TFag (1.4+/-0.3 ng of TFag/10[6] cells) were considerably higher than in THP-1 monocytoid cells (0.07+/-0.03 ng of TFag/10[6] cells). TFag was also detected on the ECV304 cell surface by flow cytometric studies. In binding analyses, 3.5+/-0.7 x 10(4) molecules of TF per cell were estimated, similar to the amounts found in ECV304 cell lysates (2.9+/-0.6 x 10(4) molecules/cell), suggesting that all TFag was translocated to the cell surface. Phorbol myristate acetate (PMA) stimulation of ECV304 cells resulted in an increase of TF mRNA levels, which was abrogated when gene transcription was impaired, suggesting a transcriptional regulation of the TF gene by PMA. In contrast, TFag was not elevated by PMA-stimulation, indicating the existence of additional posttranscriptional mechanisms. Thus, ECV304 cells constitute a singular endothelial cell model for exploring the regulation of TF expression.

Shear stress induction of the tissue factor gene

Using flow channel, we report that the application of a laminar shear stress induced a transient increase of tissue factor (TF) procoagulant activity in human umbilical vein endothelial cells (HUVEC), which was accompanied by a rapid and transient induction of the TF mRNA in the HUVEC. Functional analysis of the 2.2 kb TF 5' promoter indicated that a GC-rich region containing three copies each of the EGR-1 and Sp1 sites was required for induction. Mutation of the Sp1 sites, but not the EGR-1 sites, attenuated the response of TF promoter to shear stress. Thus, Sp1 is a newly defined shear stress responsive element. Electrophoretic mobility shift assays showed there was no increase in binding of nuclear extracts from sheared cells to an Sp1 consensus site. In contrast, immunoblotting of these nuclear extracts with antibody against transcription factor Sp1 demonstrated that shear stress increased the phosphorylation of Sp1. We also showed that shear stress, like the phosphatase inhibitor okadaic acid, increased the transcriptional activity of Sp1. These findings suggest that the shear stress induction of TF gene expression is mediated through an increased Sp1 transcriptional activity with a concomitant hyperphosphorylation of Sp1.

Lipopolysaccharide induction of THP-1 cells activates binding of c-Jun, Ets, and Egr-1 to the tissue factor promoter

These studies examine the molecular basis for increased transcription of tissue factor (TF) in THP-1 cells stimulated with lipopolysaccharide (LPS). DNase I footprinting identified six sites of protein-DNA interaction between -383 and the cap site that varied between control and induced extracts. Four footprints show qualitative differences in nuclease sensitivity. Footprints I (-85 to -52) and V (-197 to -175) are induction-specific and localize to regions of the promoter that mediate serum, phorbol ester, partial LPS response (-111 to +14), and the major LPS-inducible element (-231 to -172). Electrophoretic mobility shift assays with the -231 to -172 probe demonstrate JunD and Fos binding in both control and induced nuclear extracts; however, binding of c-Jun is only detected following LPS stimulation. Antibody inhibition studies implicate binding of Ets-1 or Ets-2 to the consensus site between -192 and -177, a region that contains an induction-specific footprint. The proximal region (-85 to -52), containing the second inducible footprint, binds Egr-1 following induction. These data suggest that LPS stimulation of THP-1 cells activates binding of c-Jun, Ets, and Egr-1 to the TF promoter and implicates these factors in the transcriptional activation of TF mRNA synthesis.

Egr-1-induced endothelial gene expression: a common theme in vascular injury

A number of pathophysiologically relevant genes, including platelet-derived growth factor B-chain (PDGF-B), are induced in the vasculature after acute mechanical injury. In rat aorta, the activated expression of these genes was preceded by a marked increase in the amount of the early-growth-response gene product Egr-1 at the endothelial wound edge. Egr-1 interacts with a novel element in the proximal PDGF-B promoter, as well as with consensus elements in the promoters of other genes induced by endothelial injury. This interaction is crucial for injury-induced PDGF-B promoter-dependent expression. Sp1, whose binding site in the PDGF-B promoter overlaps that of Egr-1, occupies this element in unstimulated cells and is displaced by increasing amounts of Egr-1. These findings implicate Egr-1 in the up-regulated expression of PDGF-B and other potent mediators in mechanically injured arterial endothelial cells.

Transcriptional regulation of the tissue factor gene in human epithelial cells is mediated by Sp1 and EGR-1

Tissue factor (TF) gene expression is rapidly induced in epithelial cells by phorbol 12-myristate 13-acetate and serum. We have shown that this induction is mediated by a novel serum response region (SRR) (-111 to +14 bp) within the human TF promoter. In this study, we characterized cis-acting genetic elements within the SRR that regulated basal and inducible expression of the TF gene in HeLa cells. Gel mobility shift assays using oligonucleotides spanning the entire SRR identified three 12-base pair (bp) motifs within subregions 1, 2, and 3 that bound constitutively expressed Sp1 and inducibly expressed EGR-1. Analysis of protein binding to these 12-bp motifs by competition with Sp1 and EGR-1 sites, mutation, and antibody supershift experiments indicated that they each contained distinct EGR-1 and Sp1 sites that overlapped by 6 bp. Functional studies using HeLa cells transfected with plasmids containing the wild-type TF promoter (-111 to +14 bp) or derivatives containing mutations in the three Sp1 and/or EGR-1 sites examined basal and inducible expression. The Sp1 sites mediated basal promoter activity, and both Sp1 and EGR-1 sites were required for maximal induction of the TF promoter by phorbol 12-myristate 13-acetate or serum. These data indicated that TF gene expression in HeLa cells was regulated by both Sp1 and EGR-1.

Basal tissue factor expression in endothelial cell cultures is caused by contaminating smooth muscle cells. Reduction by using chymotrypsin instead of collagenase

A discrepancy exists between basal tissue factor (TF) expression found in endothelial cell cultures and the failure to detect TF in unpertubated endothelial cells in vivo. We demonstrated that basal TF expression in endothelial cell cultures originated from contaminating cells. These cells were ultrastructurally and flowcytometrically identified as smooth muscle cells. The cell cultures had been obtained from collagenase-treated human umbilical cord vessels. Histologic studies revealed that after collagenase treatment the basement membrane was digested and underlying structures were disrupted at some areas of the vein. We selected chymotrypsin as an alternative for the isolation of endothelial cells. Using chymotrypsin, the endothelial lining was selectively lost leaving the basement membrane undisturbed. Furthermore, use of chymotrypsin instead of collagenase minimized the level of basal TF activity. Taken together, we demonstrated that basal TF expression in endothelial cell cultures is caused by contaminating smooth muscle cells. This contamination can strongly be reduced using chymotrypsin instead of collagenase for isolation of endothelial cells.

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.