Inhibitory properties of human recombinant Arg24-->Gln type-2 tissue factor pathway inhibitor (R24Q TFPI-2)

Amblyomin-X having a Kunitz-type homologous domain, is a noncompetitive inhibitor of FXa and induces anticoagulation in vitro and in vivo

BACKGROUND

Cancer has long been associated with thrombosis and many of the standard chemotherapeutics used to treat cancer are pro-thrombotic. Thus, the identification of novel selective anticancer drugs that also have antithrombotic properties is of enormous significance. Amblyomin-X is an anticancer protein derived from the salivary glands of the Amblyomma cajennense tick.

METHODS

In this work, we determined the inhibition profile of Amblyomin-X and its effect on activated partial thromboplastin time (aPTT) and prothrombin time (PT), using various approaches such as, kinetic analyses, amidolytic assays, SDS-PAGE, and mass spectrometry.

RESULTS

Amblyomin-X inhibited factor Xa, prothrombinase and tenase activities. It was hydrolyzed by trypsin and plasmin. MS/MS data of tryptic hydrolysate of Amblyomin-X suggested the presence of Cys(8)-Cys(59) and Cys(19)-Cys(42) but not Cys(34)-Cys(55) disulfide bond. Instead of Cys(34)-Cys(55), two noncanonical Cys(34)-Cys(74) and Cys(55)-Cys(74) disulfide bonds were identified. Furthermore, when Amblyomin-X (1mg/kg) injected in rabbits, it prolonged aPTT and PT.

CONCLUSION

Amblyomin-X is a noncompetitive inhibitor (Ki=3.9μM) of factor Xa. It is a substrate for plasmin and trypsin, but not for factor Xa and thrombin. The disulfide Cys(34)-Cys(55) bond probably scrambles with interchain seventh free cysteine residues (Cys(74)) of Amblyomin-X. The prolongation of PT and aPTT is reversible.

GENERAL SIGNIFICANCE

In term of anticoagulant property, this is structural and functional characterization of Amblyomin-X. All together, these results and previous findings suggest that Amblyomin-X has a potential to become an anticancer drug with antithrombotic property.

Tissue factor pathway inhibitor-2: a novel gene involved in zebrafish central nervous system development

Tissue factor pathway inhibitor-2 (Tfpi-2) is an important serine protease inhibitor in the extracellular matrix (ECM), but its precise physiological significance remains unknown. This work is part of a series of studies intended to investigate functional roles of Tfpi-2 and explore the underlying molecular mechanisms. First, we cloned and identified zebrafish Tfpi-2 (zTfpi-2) as an evolutionarily conserved protein essential for zebrafish development. We also demonstrated that ztfpi-2 is mainly expressed in the central nervous system (CNS) of zebrafish, and embryonic depletion of ztfpi-2 caused severe CNS defects. In addition, changes of neural markers, including pax2a, egr2b, huC, ngn1, gfap and olig2, confirmed the presence of developmental abnormalities in the relevant regions of ztfpi-2 morphants. Using microarray analysis, we found that members of the Notch pathway, especially her4 and mib, which mediate lateral inhibition in CNS development, were also downregulated. Intriguingly, both her4 and mib were able to partially rescue the ztfpi-2 morphant phenotype. Furthermore, Morpholino knockdown of ztfpi-2 resulted in upregulation of neuronal markers while downregulation of glial markers, providing evidence that the Notch pathway is probably involved in ztfpi-2-mediated CNS development.

Expression and characterization of Kunitz domain 3 and C-terminal of human tissue factor pathway inhibitor-2

Human tissue factor pathway inhibitor-2 (hTFPI-2) is a serine protease inhibitor and its inhibitory activity is enhanced by heparin. The Kunitz domain 3 and Cterminal of hTFPI-2 (hTFPI-2/KD3C), which has the activity toward heparin calcium, have been successfully expressed in Pichia pastoris and purified by SPSepharose and heparin-Sepharose chromatography. The Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, and circular dichroism (CD) experiment results implied that hTFPI-2/KD3C contained small contents of alpha-helix and beta-strand, but large amounts of random coil and two kinds of disulfide bonds, gauche-gauche-gauche (ggg) and trans-gauchetrans (tgt). The interaction of hTFPI-2/KD3C with heparin calcium was investigated by CD. It was found that heparin calcium induced b-strands in hTFPI-2/ KD3C to different extents depending on the ratio of hTFPI-2/KD3C and heparin calcium.

A family of diverse Kunitz inhibitors from Echinococcus granulosus potentially involved in host-parasite cross-talk

The cestode Echinococcus granulosus, the agent of hydatidosis/echinococcosis, is remarkably well adapted to its definitive host. However, the molecular mechanisms underlying the successful establishment of larval worms (protoscoleces) in the dog duodenum are unknown. With the aim of identifying molecules participating in the E. granulosus-dog cross-talk, we surveyed the transcriptomes of protoscoleces and protoscoleces treated with pepsin at pH 2. This analysis identified a multigene family of secreted monodomain Kunitz proteins associated mostly with pepsin/H(+)-treated worms, suggesting that they play a role at the onset of infection. We present the relevant molecular features of eight members of the E. granulosus Kunitz family (EgKU-1 - EgKU-8). Although diverse, the family includes three pairs of close paralogs (EgKU-1/EgKU-4; EgKU-3/EgKU-8; EgKU-6/EgKU-7), which would be the products of recent gene duplications. In addition, we describe the purification of EgKU-1 and EgKU-8 from larval worms, and provide data indicating that some members of the family (notably, EgKU-3 and EgKU-8) are secreted by protoscoleces. Detailed kinetic studies with native EgKU-1 and EgKU-8 highlighted their functional diversity. Like most monodomain Kunitz proteins, EgKU-8 behaved as a slow, tight-binding inhibitor of serine proteases, with global inhibition constants (K(I) (*)) versus trypsins in the picomolar range. In sharp contrast, EgKU-1 did not inhibit any of the assayed peptidases. Interestingly, molecular modeling revealed structural elements associated with activity in Kunitz cation-channel blockers. We propose that this family of inhibitors has the potential to act at the E. granulosus-dog interface and interfere with host physiological processes at the initial stages of infection.

Tissue factor pathway inhibitor-2 gene methylation is associated with low expression in carotid atherosclerotic plaques

BACKGROUND

The tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine-protease inhibitor which is expressed in atherosclerotic plaques. Epigenetic regulation of the TFPI-2 gene, through methylation of CpG islands, has been advocated in cancer. We hypothesized that TFPI-2 gene methylation could regulate TFPI-2 expression in atherosclerosis.

METHODS

We used Methylation Specific PCR (MSP) and pyrosequencing in order to identify 18 CpG of the TFPI-2 promoter, in 59 carotid atherosclerotic plaques and 26 control mammary arteries.

RESULTS

MSP showed methylation of the TFPI-2 gene (MSP+) in 16 plaques (27%), while no methylation (MSP-) was found in control arteries. Pyrosequencing confirmed that MSP+ plaques presented higher methylation levels than MSP- ones and arteries (p=0.03 and 0.01). Moreover, the TFPI-2 mRNA levels were lower in methylated plaques than in unmethylated ones and than in arteries (p=0.04 and <0.0001). The methylated plaques contained less lipids and macrophage infiltration than unmethylated ones. Their TFPI-2 immunoreactivity was mainly detected in the macrophages located in the media on the adventitial side, rather than in the lipid-rich core.

CONCLUSION

Methylation of the TFPI-2 gene takes place in atherosclerotic plaques and is associated with decreased TFPI-2 expression. The place of this process in atherosclerosis progression remains to be investigated.

Spectroscopic analysis on the effect of temperature on Kunitz domain 1 of human tissue factor pathway inhibitor-2

The conformation of Kunitz domain 1 of human tissue factor pathway inhibitor-2 (hTFPI-2/KD1) has been studied by fourier transform infrared spectroscopy, circular dichroism, and Raman spectroscopy. It was found that hTFPI-2/KD1 contained approximately 17% alpha-helices, 24% beta-strands, 46% random coils, 13% beta-turns, and two kinds of disulfide bonds(ggg and tgt) at 25 degrees C. The detailed conformational changes of the heated protein observed by fourier transform infrared spectroscopy, circular dichroism and Raman spectroscopy revealed that hTFPI-2/KD1 was thermally stable. However, KD1 could form an intermediate form at high temperature, then return to its normal conformation when the temperature was lowered. Activity assays also showed that hTFPI-2/KD1 was able to keep its inhibitory activity on plasmin after being heated to 80 degrees C for 5 min.

Tissue Factor Pathway Inhibitor-2 Is Upregulated by Vascular Endothelial Growth Factor and Suppresses Growth Factor-Induced Proliferation of Endothelial Cells

Objective— The purpose of this study is to investigate the expression and regulation of type-2 tissue factor pathway inhibitor (TFPI-2) in endothelial cells, as well as the regulation of human endothelial cell (EC) function by TFPI-2.

Methods and Results— Real-time polymerase chain reaction (PCR) and Western blot analysis revealed that vascular endothelial growth factor (VEGF) induced both time- and dose-dependent increase in TFPI-2 mRNA and protein expression in endothelial cells. TFPI-2 mRNA expression was also significantly upregulated by IL-1β, and modestly increased by both tumor necrosis factor (TNF)-α and fibroblast growth factor (FGF)-2, but not placental growth factor (PlGF). VEGF upregulation of TFPI-2 was dramatically reduced by inhibition of the MEK pathway. Administration of TFPI-2 protein suppressed both VEGF and FGF-2 stimulation of EC proliferation in a dose-dependent manner. A recombinant preparation of the first Kunitz-type domain of TFPI-2 (KD1) did not suppress growth factor stimulation of EC proliferation, suggesting a mechanism distinct from the proteinase inhibitory activity of TFPI-2. Exogenously added TFPI-2 protein suppressed VEGF-induced EC migration in 2 different assays. Recombinant wt-KD1 or the R24K mutant of KD1, but not the R24Q mutant, dramatically suppressed VEGF-induced EC migration. TFPI-2 protein, but not recombinant KD1, blocked VEGF-induced activation of both Akt and ERK1/2 in ECs. At higher doses, TFPI-2 protein blocked VEGFR2 activation.

Conclusion— Our data suggest that VEGF-upregulation of TFPI-2 expression in endothelial cells may represent a mechanism for negative feedback regulation and modulation of its pro-angiogenic action on endothelial cells. TFPI-2, or derivatives of TFPI-2, may be novel therapeutics for treatment of angiogenic disease processes.

Crystal structure of Kunitz domain 1 (KD1) of tissue factor pathway inhibitor-2 in complex with trypsin. Implications for KD1 specificity of inhibition

Kunitz domain 1 (KD1) of tissue factor pathway inhibitor-2 inhibits trypsin, plasmin, and factor VIIa (FVIIa)/tissue factor with Ki values of 13, 3, and 1640 nM, respectively. To investigate the molecular specificity of KD1, crystals of the complex of KD1 with bovine beta-trypsin were obtained that diffracted to 1.8 A. The P1 residue Arg-15 (bovine pancreatic trypsin inhibitor numbering) in KD1 interacts with Asp-189 (chymotrypsin numbering) and with the carbonyl oxygens of Gly-219 and Ogamma of Ser-190. Leu-17, Leu-18, Leu-19, and Leu-34 in KD1 make van der Waals contacts with Tyr-39, Phe-41, and Tyr-151 in trypsin, forming a hydrophobic interface. Molecular modeling indicates that this complementary hydrophobic patch is composed of Phe-37, Met-39, and Phe-41 in plasmin, whereas in FVIIa/tissue factor, it is essentially absent. Arg-20, Tyr-46, and Glu-39 in KD1 interact with trypsin through ordered water molecules. In contrast, insertions in the 60-loop in plasmin and FVIIa allow Arg-20 of KD1 to directly interact with Glu-60 in plasmin and Asp-60 in FVIIa. Moreover, Tyr-46 in KD1 electrostatically interacts with Lys-60A and Arg-60D in plasmin and Lys-60A in FVIIa. Glu-39 in KD1 interacts directly with Arg-175 of the basic patch in plasmin, whereas in FVIIa, such interactions are not possible. Thus, the specificity of KD1 for plasmin is attributable to hydrophobic and direct electrostatic interactions. For trypsin, hydrophobic interactions are intact, and electrostatic interactions are weak, whereas for FVIIa, hydrophobic interactions are missing, and electrostatic interactions are partially intact. These findings provide insight into the protease selectivity of KD1.

Expression and characterization of the first kunitz domain of human tissue factor pathway inhibitor-2

Human tissue factor pathway inhibitor-2 (hTFPI-2) has three kunitz domains whose structure and function are unclear. We expressed the first kunitz domain of hTFPI-2 (hTFPI-2/KD1) as functional form using Pichia pastoris and investigated its characterization. In the experiment, hTFPI-2/KD1 can inhibit the plasmin and trypsin activity and the Ki of hTFPI-2/KD1 towards plasmin (30nM) and trypsin (50nM) was determined as 10 and 7nM by chromogenic assay, respectively. hTFPI-2/KD1 can also inhibit MMP-2 and MMP-9 in zymography assay. Furthermore, the inhibition of hTFPI-2/KD1 to the Matrigel invasion by HT-1080 is also described. This study provides a method to produce hTFPI-2/KD1 efficiently and some insights into the structure and function of hTFPI-2/KD1.

Structure-Function Analysis of the Reactive Site in the First Kunitz-type Domain of Human Tissue Factor Pathway Inhibitor-2

Human tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type proteinase inhibitor that regulates a variety of serine proteinases involved in coagulation and fibrinolysis through their non-productive interaction with a P(1) residue (Arg-24) in its first Kunitz-type domain (KD1). Previous kinetic studies revealed that TFPI-2 was a more effective inhibitor of plasmin than several other serine proteinases, but the molecular basis for this specificity was unclear. In this study, we employed molecular modeling and mutagenesis strategies to produce several variants of human TFPI-2 KD1 in an effort to identify interactive site residues other than the P(1) Arg that contribute significantly to its inhibitory activity and specificity. Molecular modeling of KD1 based on the crystal structure of bovine pancreatic trypsin inhibitor revealed that KD1 formed a more energetically favorable complex with plasmin versus trypsin and/or the factor VIIa-tissue factor complex primarily due to strong ionic interactions between Asp-19 (P(6)) and Arg residues in plasmin (Arg-644, Arg-719, and Arg-767), Arg-24 (P(1)) with Asp-735 in plasmin, and Arg-29 (P(5)') with Glu-606 in plasmin. In addition, Leu-26 through Leu-28 (P(2)'-P(4)') in KD1 formed strong van der Waals contact with a hydrophobic cluster in plasmin (Phe-583, Met-585, and Phe-587). Mutagenesis of Asp-19, Tyr-20, Arg-24, Arg-29, and Leu-26 in KD1 resulted in substantial reductions in plasmin inhibitory activity relative to wild-type KD1, but the Asp-19 and Tyr-20 mutations revealed the importance of these residues in the specific inhibition of plasmin. In addition to the reactive site residues in the P(6)-P(5)' region of KD1, mutation of a highly conserved Phe at the P(18)' position revealed the importance of this residue in the inhibition of serine proteinases by KD1. Thus, together with the P(1) residue, the nature of other residues flanking the P(1) residue, particularly at P(6) and P(5)', strongly influences the inhibitory activity and specificity of human TFPI-2.

The effect of human tissue factor pathway inhibitor-2 on the growth and metastasis of fibrosarcoma tumors in athymic mice

Human tissue factor pathway inhibitor-2 (TFPI-2) is a matrix-associated Kunitz inhibitor that inhibits the plasmin- and trypsin-mediated activation of zymogen matrix metalloproteinases involved in tumor progression, invasion, and metastasis. To directly assess its role in tumor growth and metastasis in vivo, we stably transfected HT-1080 fibrosarcoma cells expressing either fully active wild-type human TFPI-2 (WT) or inactive R24Q TFPI-2 (QT) and examined their ability to form tumors and metastasize in athymic mice in comparison to mock-transfected cells (MT). MT and QT fibrosarcoma tumors grew 2 to 3 times larger than WT tumors. Tumor metastasis was confined to the lung and was observed in 75% of mice treated with either MT or QT cells, whereas only 42% of mice treated with WT cells developed lung metastases. Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analyses of each tumor group revealed 3- to 6-fold lower levels of murine vascular endothelial growth factor gene expression in WT tumors in relation to either MT or QT tumors. Comparative tumor gene expression analysis revealed that several human genes implicated in oncogenesis, invasion, metastasis, apoptosis, and angiogenesis had significantly altered levels of expression in WT tumors. Our collective data demonstrate that secretion of inhibitory TFPI-2 by a highly metastatic tumor cell markedly inhibits its growth and metastasis in vivo by regulating pericellular extracellular matrix (ECM) remodeling and angiogenesis. (Blood. 2004;103:1069-1077)

Molecular cloning, expression, and characterization of bovine tissue factor pathway inhibitor-2

Human tissue factor pathway inhibitor-2 (TFPI-2) is a matrix-associated Kunitz-type serine proteinase inhibitor that is secreted by all cells of the vasculature, and presumably plays a role in the regulation of plasmin-mediated matrix remodeling. In this report, we describe the cloning and expression of a full-length cDNA for bovine TFPI-2 that exhibits 72% sequence identity with that of human TFPI-2. Following a 22 residue signal peptide, the mature protein contains 212 amino acids with 18 cysteines, three putative N-glycosylation sites, and one putative O-glycosylation site. The deduced sequence of mature bovine TFPI-2 revealed a short acidic amino-terminal region, three tandem Kunitz-type domains, and a carboxy-terminal tail highly enriched in basic amino acids. Recombinant bovine TFPI-2 was expressed in HEK 293 cells and resolved into two isoforms, designated as alpha-TFPI-2 (M(r) 33 kDa) and beta-TFPI-2 (M(r) 31 kDa), which presumably represent differentially glycosylated forms of the inhibitor. Similar to human TFPI-2, both bovine TFPI-2 isoforms exhibited strong inhibitory activity towards trypsin and plasmin, and weak inhibitory activity towards the factor VIIa-tissue factor complex.

Regulation of functions of vascular wall cells by tissue factor pathway inhibitor: basic and clinical aspects

Tissue factor pathway inhibitor (TFPI) is a Kunitz-type protease inhibitor that inhibits the initial reactions of blood coagulation. A major pool of TFPI is the form associated with the surface of endothelial cells, which is speculated to play an important role in regulating the functions of vascular wall cells. TFPI consists of 3 tandem Kunitz inhibitor domains, the first and second of which inhibit the tissue factor-factor VIIa complex and factor Xa, respectively. Recent findings indicate that TFPI has another function, ie, the modulation of cell proliferation. This function is based on the interaction of the C-terminal region of TFPI with these cells. In addition to endothelial cells, it has been shown that many other vascular wall cells can synthesize TFPI, eg, mesangial cells, smooth muscle cells, monocytes, fibroblasts, and cardiomyocytes. TFPI is associated with these cells mainly through heparan sulfate proteoglycans on their surface. However, recent findings suggest that there are several other candidates for TFPI-binding proteins on these cells. On the other hand, studies on plasma levels of TFPI in patients with various diseases suggest that TFPI may be a marker of endothelial cell dysfunction. An increasing number of reports suggest that recombinant TFPI may attenuate thrombosis and prevent restenosis. Clinical trials are needed to explore these possibilities. Recent reports also indicate that the application of recombinant TFPI or TFPI gene transfer prevents restenosis in addition to thrombosis after arterial injury in the animal model; corroboration of these reports awaits clinical investigation.