Identification of vitamin K-dependent carboxylase activity in lung type II cells but not in lung macrophages

Fibrinogen inhibits fibroblast-mediated contraction of collagen

Extracellular matrix changes in composition and organization as it transitions from the provisional matrix of the fibrin/platelet plug to collagen scar in healed wounds. The manner in which individual matrix proteins affect these activities is not well established. In this article we describe the interactions of two important extracellular matrix components, fibrin and collagen, using an in vitro model of wound contraction, the fibroblast-populated collagen lattice. We utilized different fibrinogen sources and measured tissue reorganization in floating and tensioned collagen lattices. Our results showed that both fibrin and fibrinogen decreased the contraction of fibroblast populated collagen lattices in a dose-dependent manner. Polymerization of fibrinogen to fibrin using thrombin had no effect on this inhibition. Further, there was no effect due to changes in protein concentration, alternate components of the fibrin sealant, or the enzymatic action of thrombin. These results suggest that the initial stability of the fibrin provisional matrix is due to the fibrin, because this protein appears to inhibit contraction of the matrix. This may be important in the early phases of wound healing when clot stability is vital for hemostasis. Later, as fibrin is replaced by collagen, wound contraction can occur.

Tissue factor procoagulant expression by rat alveolar epithelial cells

Fibrin deposition in the alveolar space is characteristic of inflammatory lung injury. The formation of fibrin in the alveolus results from the coagulation of extravasated plasma. The cellular elements that promote intra-alveolar clotting have not been completely defined. We have investigated the capacity of alveolar epithelial cells (AEC) to promote coagulation through the expression of procoagulant activity (PCA) in tissue culture. Using a single-stage coagulation assay, rat AEC monolayers were found to contain 20,750 +/- 4,035 procoagulant units (PCU)/10(6) cells; 10- to 20-fold greater activity than that found in concomitantly isolated alveolar macrophages. The epithelial-derived procoagulant was shown to be tissue factor by a series of assays using clotting factor-deficient human plasmas. Freshly isolated AEC also possessed PCA (2,500 +/- 1,000 PCU/10(6) cells) and expressed a 2.1-kb mRNA that hybridized with a cDNA for murine tissue factor. Using a kinetic turbidometric assay of clot acceleration, PCA was found on the surface of unstimulated epithelial monolayers and could be increased to 170% of control by incubation with phorbol myristate acetate (PMA). This response to PMA was accompanied by a parallel increase in the relative abundance of tissue factor mRNA. AEC shed particulate PCA into the culture media that displayed a specific activity similar to that recovered from alveolar lining fluid. Therefore, by expressing both cell surface and particulate PCA, the alveolar epithelium likely contributes significantly to the modulation of intra-alveolar coagulation.

A549 lung epithelial cells synthesize anticoagulant molecules on the cell surface and matrix and in conditioned media

To investigate mechanisms regulating intra-alveolar coagulation, we studied monolayers of the A549 human lung epithelial cell line. The surface of A549 cells delayed the onset of prothrombin-to-thrombin conversion and prevented total prothrombin consumption in normal plasma compared to plastic cell-free wells. Similar results were achieved with bovine pulmonary endothelial (CPAE) and rat intestinal epithelial (IEC-6) cell lines, whereas Madin-Darby canine kidney renal epithelial cell line accelerated thrombin formation. The A549 surface catalyzed antithrombin III-thrombin complex formation with no significant increase in thrombin inactivation from heparin cofactor II. The A549 cell surface effects were largely, but not completely, reversed to values obtained for plastic when protein C-deficient plasma was used. Pretreatment of the cell surface with chondroitinase ABC plus heparitinase prior to thrombin generation experiments had no effect on the total prothrombin consumed but decreased the initial delay. Heparan sulfate as well as dermatan sulfate and other chondroitin sulfates were detected on the A549 surface using alcian blue staining. Conditioned media from A549, CPAE, and IEC-6 cells delayed the clot time of recalcified plasma. Use of chondroitinase ABC and heparitinase were both required to obliterate the A549 conditioned media activity. After growing A549 cells in 35SO(2-)4-containing medium, the resultant conditioned medium was found to contain 2,000 kD and 300- to 1,000-kD proteoglycans that yielded chains of less than or equal to 100 kD on reductive elimination with base.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin K-dependent carboxylation in articular chondrocytes

A nonhepatic vitamin K-dependent protein, matrix Gla protein, has recently been identified in cartilage where it may play an important role in the control of mineralization or matrix development. We have investigated the vitamin K cycle in chondrocytes isolated from bovine and rabbit articular cartilage and examined these cells for their ability to synthesize vitamin K-dependent proteins. Chondrocytes were found to have an active vitamin K-dependent carboxylation system. Preincubation of the cells with warfarin resulted in a significant increase in the measured carboxylase activity. Both vitamin K epoxide reductase and DT-diaphorase (EC 1.6.99.2) activity were present indicating that chondrocytes are capable of producing reduced vitamin K1H2, the cofactor for the vitamin K-dependent carboxylase. Specific 14C-labeling of microsomal vitamin K-dependent protein precursors demonstrated synthesis of several vitamin K-dependent proteins by chondrocytes. 35S-labeling of chondrocyte proteins provided evidence that matrix Gla protein is synthesized by these cells.

The vitamin K-dependent carboxylation system in human osteosarcoma U2-OS cells. Antidotal effect of vitamin K1 and a novel mechanism for the action of warfarin

An osteoblast-like human osteosarcoma cell line (U2-OS) has been shown to possess a vitamin K-dependent carboxylation system which is similar to the system in human HepG2 cells and in liver and lung from the rat. In an 'in vitro' system prepared from these cells, vitamin K1 was shown to overcome warfarin inhibition of gamma-carboxylation carried out by the vitamin K-dependent carboxylase. The data suggest that osteoblasts, the cells involved in synthesis of vitamin K-dependent proteins in bone, can use vitamin K1 as an antidote to warfarin poisoning if enough vitamin K1 can accumulate in the tissue. Five precursors of vitamin K-dependent proteins were identified in osteosarcoma and HepG2 cells respectively. In microsomes (microsomal fractions) from the osteosarcoma cells these precursors revealed apparent molecular masses of 85, 78, 56, 35 and 31 kDa. When osteosarcoma cells were cultured in the presence of warfarin, vitamin K-dependent 14C-labelling of the 78 kDa precursor was enhanced. Selective 14C-labelling of one precursor was also demonstrated in microsomes from HepG2 cells and from rat lung after warfarin treatment. In HepG2 cells this precursor was identified as the precursor of (clotting) Factor X. This unique 14C-labelling pattern of precursors of vitamin K-dependent proteins in microsomes from different cells and tissues reflects a new mechanism underlying the action of warfarin.

Allogenic induction of thromboplastin synthesis in monocytes and endothelial cells. Biphasic effect of cyclosporin A

Monocytes and endothelial cells were stimulated in co-culture with allogeneic lymphocytes to produce thromboplastin (TPL). The induction was biphasic, an early response (8-24 h) was greatly augmented by cyclosporin A (CS) (0.5-5 micrograms/ml) whereas the late response (day 3-4) was inhibited. Prednisolone inhibited both responses. Both drugs inhibited lymphocyte proliferation. Interferon-gamma decreased MLC TPL activity but increased thymidine incorporation. CD4+ cells were instrumental in inducing the early TPL peak in monocytes, whereas CD8+ cells decreased the TPL effect. With endothelial cells both T cell classes were equally effective. Conditioned medium from MLC as well as from co-cultures of endothelial cells and lymphocytes induced early TPL synthesis in endothelial cells. Upon allogeneic stimulation monocytes, but not endothelial cells, produced a significant amount of F-VII, most of which was apparently undercarboxylated.

No evidence for vitamin K-dependent carboxylation of canine surfactant apoproteins, 28-36 kDa

Recent research has shown that rat surfactant apoproteins (26-38 kDa) are vitamin K-dependent [Rannels, Gallaher, Wallin & Rannels (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 5952-5956]. We have investigated the effect of the vitamin K antagonist warfarin on this family of apoproteins in surfactant from dog lung. Our data suggest that warfarin does not interfere with synthesis and secretion of these proteins into dog lung surfactant. Abnormal surfactant apoproteins, produced in response to warfarin treatment of the dog, were also not found in lung surfactant. 4-Carboxyglutamic acid analysis of purified dog apoproteins also failed to detect the vitamin K-modification. When vitamin K-dependent 14C labelling of precursors of vitamin K-dependent proteins was carried out, fluorography of these precursors, when electrophoresed into SDS/polyacrylamide gels, revealed 14C-labelled proteins of apparent molecular mass 74, 46, 42, 34, 31 and 23 kDa. Antibodies produced against purified dog surfactant apoproteins recognized precursors of the surfactant apoproteins in lung microsomes but did not recognize any 14C-labelled carboxylase substrates. These precursors appeared on immunoblots with apparent molecular mass 29, 32, 33 and 50 kDa. Our data suggest that there are significant differences between this class of surfactant apoproteins in the rat and the dog.