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SummaryTissue factor pathway inhibitor (TFPI) plays an important role in regulating tissue factor (TF)-initiated blood coagulation. Since serum stimulation of fibroblasts, vascular smooth muscle cells and cardiac myocytes in culture increases the expression of TF mRNA and antigen (Ag) in these cells, we hypothesized that serum may also induce increased synthesis of TFPI in these cells to regulate the TF-induced extravascular clotting at an injury site. To test this concept, we used primary isolates of the following human cell types – fetal and adult lung fibroblasts, pulmonary and aortic smooth muscle cells, and cardiac myocytes. Serum-stimulation of these cells resulted in an increased expression of TF mRNA and Ag (8 to10-fold). Upon serum stimulation, expression of TFPI mRNA and Ag was also increased in these cells. However, the increase in TFPI-Ag (6 to 8-fold) was significantly greater than the TFPI mRNA (2 to 3-fold). Notably, increased expression of TFPI persisted after the TF expression had declined. Further, increased synthesis of TFPI initially led to the saturation of heparin-releasable binding sites. TFPI-Ag was detected by Western blotting, 35S-metabolic labeling and activity assays on the conditioned media, heparin-released material from cells, and in cell lysates. TFPI-Ag was also detected by immunofluorescence staining of cells. Actinomycin D partially whereas cycloheximide completely prevented the serum-induced increased expression of TFPI synthesis by these cells, suggesting control primarily at the translational but some at the transcriptional level as well. The Mr of undegraded TFPI in all cases was ~45 kDa and was of full length. TFPI synthesized locally by fibroblasts, vascular smooth muscle cells and cardiac myocytes could play a significant role in regulating TF-initiated extravascular clotting especially since plasma TFPI that may be available at the injury site lacks a portion of the carboxyl segment and is a less efficient inhibitor.

SummaryUnder normal physiologic conditions, tissue factor pathway inhibitor (TFPI) is synthesized primarily by the microvascular endothelium. Using Northern blotting, we studied its transcriptional expression in different organs and compared it with the expression of two other endothelial specific proteins, namely thrombomodulin (TM) and von Willebrand factor (vWF). The order of mRNA expression for each protein was: TFPI–placenta>lung>liver>kidney>heart>skeletal muscle≥pancreas>brain; TM–heart>pancreas>lung>skeletal muscle>kidney≥liver>placenta>brain; and vWF–heart>skeletal muscle>pancreas>lung≥kidney>placenta>brain>liver. Notably, heart expressed TM and vWF mRNA in large amounts and only small amounts of TFPI whereas lung expressed all three mRNAs in significant amounts. Placenta, on the contrary, expressed large amounts of TFPI but only small amounts of TM and vWF mRNAs. Brain by this technique was found to express undetectable amounts of TFPI and TM mRNAs but small amounts of vWF mRNA. The expression of TFPI mRNA in the brain was however detected by RT/PCR and the antigen was localized to the endothelium of microvessels as well as to the astrocytes and oligodendrocytes. Since ultimate expression of proteins is linked to the expression of their mRNAs, our data support a concept that vascular endothelium is made up of phenotypically diverse groups of cells and that endothelial cells of different vascular beds express specific sets of genes that enable them to carry out tissue-specific functions. Importantly, since astrocytes are known to express tissue factor, the TFPI expression by these cells may control coagulation in their microenvironment and their response to injury and inflammation.

We recently proposed that endothelium may represent the primary physiologic site of synthesis of the tissue factor pathway inhibitor (TFPI). In support of this conclusion, we have now found that the poly(A)+ RNAs obtained from rabbit and bovine lung tissues contain abundant amounts of TFPI messenger RNAs (mRNAs), whereas the poly(A)+ RNAs obtained from the liver of these animals contain less than 5% of that found in the lung tissues. Because inflammatory mediators are known to upregulate tissue factor (TF) expression by the endothelium, we have examined the effect of these agents on the TFPI expression by the cultured endothelial cells. When cultured human umbilical vein endothelial cells were stimulated (in 10% fetal bovine serum) with phorbol myristate acetate (PMA), endotoxin, interleukin-1, or tumor necrosis factor-alpha, the TF mRNA increased approximately 7- to 10- fold within 2 to 4 hours. Unstimulated cells constitutively expressed TFPI mRNA and its levels either did not change or increased slightly (up to 1.5-fold) upon stimulation with these inflammatory agents. TF mRNA abruptly declined to a negligible level and the TFPI mRNA returned essentially to the basal level at approximately 24 hours. The membrane- bound TF clotting activity of induced cells peaked between 4 and 8 hours, and finally declined. The cumulative TFPI activity secreted into the media was either unchanged or slightly higher in the induced cell cultures as compared with that present in the noninduced cultures. Endothelial cells were also cultured in 10% heat-inactivated human serum derived from plasma or whole blood. TFPI secreted into the media containing whole blood serum was consistently higher (approximately 1.5- fold at 8 hours) than that secreted into the media supplemented with serum obtained from plasma lacking the formed elements; these cells also expressed similarly increased levels of TFPI mRNA. Moreover, PMA- stimulated cells cultured in whole blood serum expressed modestly increased levels of TFPI mRNA (approximately 1.5-fold); supernatants from these cells also contained similarly increased TFPI activity. Cumulatively, our data indicate that, unlike thrombomodulin and fibrinolytic enzymes synthesized by the endothelial cells, TFPI synthesis is not downregulated and may be slightly upregulated during an inflammatory response. Inspection of the 5′ flanking region of the TFPI gene showed a conserved GATA-binding motif located approximately 400 bp upstream of the proposed transcription initiation site(s). This motif by binding to the GATA-2 transcriptional factor may keep the endothelium in an ‘on’ state for constitutive expression of TFPI.(ABSTRACT TRUNCATED AT 400 WORDS)

Factor IX is a multidomain protein essential for hemostasis. We describe a mutation in a patient affecting the first epidermal growth factor (EGF)-like domain of the protein. All exons and the promoter region of the gene were amplified by the polymerase chain reaction method, and sequenced. Only a single mutation (C----G), that predicts the substitution of Pro55 by Ala in the first EGF domain was found in the patient's gene. This mutation leads to new restriction sites for four enzymes. One new site (Nsi) was tested in the amplified exon IV fragment and was shown to provide a rapid and reliable marker for carrier detection and prenatal diagnosis in the affected family. The factor IX protein, termed factor IXHollywood (IXHW), was isolated to homogeneity from the patient's plasma. As compared with normal factor IX (IXN), IXHW contained the same amount of gamma-carboxy glutamic acid but twice the amount of beta-OH aspartic acid. Both IXHW and IXN contained no detectable free -SH groups. Further, IXHW could be readily cleaved to yield a factor IXa-like molecule by factor Xla/Ca2+. However, IXaHW (compared with IXaN) activated factor X approximately twofold slower in the presence of Ca2+ and phospholipid (PL), and 8- to 12-fold slower in the presence of Ca2+, PL, and factor VIIIa. Additionally, IXaHW had only approximately 10% of the activity of IXaN in an aPTT assay. In agreement with the nuclear magnetic resonance- derived structure of EGF, the Chou-Fasman algorithm strongly predicted a beta turn involving residues Asn-Pro55-Cys-Leu in IXN. Replacement of Pro55 by Ala gave a fourfold decrease in the beta turn probability for this peptide, suggesting a change(s) in the secondary structure in the EGF domain of IXHW. Since this domain of IXN is thought to have one high-affinity Ca2+ binding site and may be involved in PL and/or factor VIIIa binding, the localized secondary structural changes in IXHW could lead to distortion of the binding site(s) for the cofactor(s) and, thus, a dysfunctional molecule.