The binding sites on fibrin(ogen) for guinea pig liver transglutaminase are similar to those of blood coagulation factor XIII. Characterization of the binding of liver transglutaminase to fibrin

The interaction between fibrinogen and zymogen FXIII-A2B2 is mediated by fibrinogen residues γ390-396 and the FXIII-B subunits

Coagulation transglutaminase factor XIII (FXIII) exists in circulation as heterotetrameric proenzyme FXIII-A₂B₂ Effectively all FXIII-A₂B₂ circulates bound to fibrinogen, and excess FXIII-B₂ circulates in plasma. The motifs that mediate interaction of FXIII-A₂B₂ with fibrinogen have been elusive. We recently detected reduced binding of FXIII-A₂B₂ to murine fibrinogen that has γ-chain residues 390-396 mutated to alanines (Fibγ^390-396A). Here, we evaluated binding features using human components, including recombinant fibrinogen variants, FXIII-A₂B₂, and isolated FXIII-A₂ and -B₂ homodimers. FXIII-A₂B₂ coprecipitated with wild-type (γA/γA), alternatively-spliced (γ'/γ'), and αC-truncated (Aα251) fibrinogens, whereas coprecipitation with human Fibγ^390-396A was reduced by 75% (P <0001). Surface plasmon resonance showed γA/γA, γ'/γ', and Aα251 fibrinogens bound FXIII-A₂B₂ with high affinity (nanomolar); however, Fibγ^390-396A did not bind FXIII-A₂B₂ These data indicate fibrinogen residues γ390-396 comprise the major binding motif for FXIII-A₂B₂ Compared with γA/γA clots, FXIII-A₂B₂ activation peptide release was 2.7-fold slower in Fibγ^390-396A clots (P < .02). Conversely, activation of recombinant FXIII-A₂ (lacking FXIII-B₂) was similar in γA/γA and Fibγ^390-396A clots, suggesting fibrinogen residues γ390-396 accelerate FXIII-A₂B₂ activation in a FXIII-B₂-dependent mechanism. Recombinant FXIII-B₂ bound γA/γA, γ'/γ', and Aα251 with similar affinities as FXIII-A₂B₂, but did not bind or coprecipitate with Fibγ^390-396A FXIII-B₂ also coprecipitated with fibrinogen from FXIII-A-deficient mouse and human plasmas. Collectively, these data indicate that FXIII-A₂B₂ binds fibrinogen residues γ390-396 via the B subunits, and that excess plasma FXIII-B₂ is not free, but rather circulates bound to fibrinogen. These findings provide insight into assembly of the fibrinogen/FXIII-A₂B₂ complex in both physiologic and therapeutic situations.

Factor XIII: a coagulation factor with multiple plasmatic and cellular functions

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

Expression of keratinocyte transglutaminase in cornea of vitamin A-deficient rats

PURPOSE

To determine the role played by keratinocyte transglutaminase (TG1, TG(K)) in the abnormal keratinization of the cornea.

METHODS

Vitamin A-deficient rats were produced as a model of severe dry eyes, and the expression of the mRNA and the enzyme activity of TG1 were examined in the corneas. The envelope proteins and keratins of cornified cells were also examined immunohistochemically.

RESULTS

The expression and enzyme activity of TG1 mRNA on the ocular surface were significantly upregulated as the vitamin A deficiency developed. As the TG1 expression was upregulated, involucrin, loricrin, and keratin 10 began to be expressed on the epithelial cells of the cornea.

CONCLUSIONS

Upregulation of TG1 expression followed by the appearance of the envelope proteins and keratin10 in cornified cells indicated that TG1 is involved in the abnormal keratinization of the cornea.

Cell surface tissue transglutaminase is involved in adhesion and migration of monocytic cells on fibronectin

Expression of tissue transglutaminase (transglutaminase II, tTG) was shown to increase drastically during monocyte differentiation into macrophages; however, its role in monocytic cells remains largely unknown. This study describes a novel function of cell surface tTG as an adhesion and migration receptor for fibronectin (Fn). Two structurally related transglutaminases, tTG and the A subunit of factor XIII (FXIIIA), are expressed on the surface of monocytic cells, whereas only surface tTG is associated with multiple integrins of the beta1 and beta3 subfamilies. Both surface levels of tTG and the amounts of integrin-bound tTG are sharply up-regulated during the conversion of monocytes into macrophages. In contrast, a reduction in biosynthesis and surface expression of FXIIIA accompanies monocyte differentiation. Cell surface tTG is colocalized with beta1- and beta3-integrins in podosomelike adhesive structures of macrophages adherent on Fn. Down-regulation of surface tTG by expression of antisense tTG construct or its inhibition by function-blocking antibodies significantly decreases adhesion and spreading of monocytic cells on Fn and, in particular, on the gelatin-binding fragment of Fn consisting of modules I6II1,2I7-9. Likewise, interfering with the adhesive function of surface tTG markedly reduces migration of myeloid cells on Fn and its gelatin-binding fragment. These data demonstrate that cell surface tTG serves as an integrin-associated adhesion receptor that might be involved in extravasation and migration of monocytic cells into tissues containing Fn matrices during inflammation.

Tissue transglutaminase is an integrin-binding adhesion coreceptor for fibronectin

The protein cross-linking enzyme tissue transglutaminase binds in vitro with high affinity to fibronectin via its 42-kD gelatin-binding domain. Here we report that cell surface transglutaminase mediates adhesion and spreading of cells on the 42-kD fibronectin fragment, which lacks integrin-binding motifs. Overexpression of tissue transglutaminase increases its amount on the cell surface, enhances adhesion and spreading on fibronectin and its 42-kD fragment, enlarges focal adhesions, and amplifies adhesion-dependent phosphorylation of focal adhesion kinase. These effects are specific for tissue transglutaminase and are not shared by its functional homologue, a catalytic subunit of factor XIII. Adhesive function of tissue transglutaminase does not require its cross-linking activity but depends on its stable noncovalent association with integrins. Transglutaminase interacts directly with multiple integrins of beta1 and beta3 subfamilies, but not with beta2 integrins. Complexes of transglutaminase with integrins are formed inside the cell during biosynthesis and accumulate on the surface and in focal adhesions. Together our results demonstrate that tissue transglutaminase mediates the interaction of integrins with fibronectin, thereby acting as an integrin-associated coreceptor to promote cell adhesion and spreading.

Cardiac specific overexpression of transglutaminase II (G(h)) results in a unique hypertrophy phenotype independent of phospholipase C activation

Tissue type transglutaminase (TGII, also known as G(h)) has been considered a multifunctional protein, with both transglutaminase and GTPase activity. The role of the latter function, which is proposed as a coupling mechanism between alpha(1)-adrenergic receptors and phospholipase C (PLC), is not well defined. TGII was overexpressed in transgenic mice in a cardiac specific manner to delineated relevant signaling pathways and their consequences in the heart. Cardiac transglutaminase activity in the highest expressing line was approximately 37-fold greater than in nontransgenic lines. However, in vivo signaling to PLC, as assessed by inositol phosphate turnover in [(3)H]myoinositol organ bath atrial preparations, was not increased in the TGII mice at base line or in response to alpha(1)-adrenergic receptor stimulation; nor was protein kinase Calpha (PKCalpha) or PKCepsilon activity enhanced in the TGII transgenic mice. This is in contrast to mice moderately (approximately 5-fold) overexpressing G(alphaq), where inositol phosphate turnover and PKC activity were found to be clearly enhanced. TGII overexpression resulted in a remodeling of the heart with mild hypertrophy, elevated expression of beta-myosin heavy chain and alpha-skeletal actin genes, and diffuse interstitial fibrosis. Resting ventricular function was depressed, but responsiveness to beta-agonist was not impaired. This set of pathophysiologic findings is distinct from that evoked by overexpression of G(alphaq). We conclude that TGII acts in the heart primarily as a transglutaminase, and modulation of this function results in unique pathologic sequelae. Evidence for TGII acting as a G-protein-like transducer of receptor signaling to PLC in the heart is not supported by these studies.

Significance of diminished factor XIII in Crohn's disease

OBJECTIVE

Coagulation factor XIII is a plasma transglutaminase involved in crosslinking of fibrin, the last step of the coagulation system and a connective tissue factor contributing to the wound healing process. It circulates as a heterotetrameric molecule consisting of two identical proenzyme subunits (factor XIIIA) and two carrier protein subunits (factor XIIIS). The aim of this study was to determine the disease features associated with the diminution of factor XIII in Crohn's disease.

METHODS

Factor XIIIA and factor XIIIS levels were assessed in patients presenting with Crohn's disease, ulcerative colitis, infectious colitis, or diverticulitis, in patients with rheumatoid arthritis, and in control subjects. Prothrombin fragment 1 + 2 assay, as a marker of the generation of thrombin and measurement of C-terminal telopeptide of type I collagen as an estimate of degradation of collagen type I, were performed.

RESULTS

Factor XIIIA was significantly decreased in Crohn's disease, in ulcerative colitis, and in infectious colitis by comparison with subjects presenting with diverticulitis, normal, and rheumatoid subjects p = 0.0001). Factor XIIIS was unmodified in patients with Crohn's disease by comparison with controls but was reduced in those presenting with intestinal bleeding (p = 0.0002). In Crohn's disease, the lowest level of factor XIIIA was observed in patients with intestinal bleeding (p = 0.0003). Factor XIIIA was correlated with the Van Hees index (r = -0.5661; p = 0.0001) and with the C-terminal telopeptide of type I collagen (r = -0.4110; p = 0.0011) but not with prothrombin fragment 1 + 2. The multiple regression analysis showed that only Van Hees index and intestinal bleeding were independent variables for explaining the diminution of Factor XIIIA in Crohn's disease.

CONCLUSIONS

Factor XIIIA subunit is an indicator of Crohn's disease activity. Our study suggests that a low factor XIIIA level is related to the presence of intestinal lesions and might be linked to intestinal repair mechanisms; loss in intestinal lumen could be also involved, especially in patients with intestinal bleeding.

Protein cross-linking mediated by tissue transglutaminase correlates with the maturation of extracellular matrices during lung development

At birth, the mammalian lung is still immature. The alveoli are not yet formed and the interairspace walls contain two capillary layers which are separated by an interstitial core. After alveolarization (first 2 postnatal weeks in rats) the alveolar septa mature: their capillary layers merge, the amount of connective tissue decreases, and the mature lung parenchyma is formed (second and third week). During the first 3 wk of life the role of tissue transglutaminase (tTG) was studied in rat lung by immunostaining of cryostat and paraffin sections, by Northern and Western blotting, and by a quantitative determination of gamma-glutamyl-epsilon-lysine. While enzyme activity and intracellular tTG were already present before term, the enzyme product (gamma-glutamyl-epsilon-lysine-crosslink) and extracellular tTG appeared between postnatal days 10 and 19 in the lung parenchyma. In large blood vessels and large airways, which mature earlier than the parenchyma, both the enzyme product and extracellular tTG had already appeared at the end of the first postnatal week. We conclude that tTG is expressed and externalized into the extracellular matrix of lung shortly before maturation of an organ area. Because tTG covalently and irreversibly crosslinks extracellular matrix proteins, we hypothesize that it may prevent or delay further remodeling of basement membranes and may stabilize other extracellular components, such as microfibrils.

Alpha 1-adrenergic receptor coupling with Gh in the failing human heart

BACKGROUND

We recently demonstrated that Gh, which transfers the signal from the alpha 1-adrenergic receptor to the 69-kD phospholipase C, is the previously identified tissue-type transglutaminase (TGase II). The alpha 1-adrenergic receptor mediates actions of the sympathetic nervous system, including cardiac, arteriolar, and smooth muscle contractions. In human cardiac tissue, the expression of the alpha 1-adrenergic receptor is increased under pathophysiological conditions, but changes in the physiological response are small. Therefore, it has been suggested that the other components involved in the alpha 1-adrenergic receptor-mediated signaling pathway are probably altered.

METHODS AND RESULTS

Immunological and biochemical studies with nonfailling and failing human heart tissues revealed that the GTP-binding and TGase activities of human heart TGase II (hhG alpha n) are downregulated in both ischemic and dilated cardiomyopathic human heart. In ischemic cardiomyopathy, the alpha 1-adrenergic receptor number increased twofold (27.0 fmol/mg) compared with the nonfailing (12.8 fmol/mg) and the dilated cardiomyopathic (15.6 fmol/mg) heart tissues, but the coupling of hhG alpha h with the alpha 1-adrenergic receptor did not increase. The intrinsic activity of hhG alpha h, was greatly decreased in membrane fractions, whereas the cytosolic TGase activity was not changed. In the dilated cardiomyopathic human heart, these intrinsic enzyme activities of hhG alpha h were also downregulated in the membrane fraction, whereas the amount of hhG alpha h protein was greatly increased (2.8-fold) compared with the nonfailing heart.

CONCLUSIONS

The results of the present study clearly demonstrate that the alpha 1-adrenergic receptor in human heart couples with Gh (TGase II) and indicate that downregulation of hhG alpha h activity is associated with human cardiac failure but that the mechanism differs between ischemic and dilated cardiomyopathies.

Transglutaminases in Crohn's disease

Transglutaminases are a family of Ca-dependent enzymes involved in various biological events. Circulating transglutaminase (factor XIIIa) is decreased in blood of patients with inflammatory bowel diseases. There is evidence that factor XIIIa and tissue type transglutaminase, present in cell cytosol, bind to various proteins of the extracellular matrix. This study examined the value of serum transglutaminase assay in the treatment and follow up of Crohn's disease and then investigated the intestinal location of both forms of transglutaminases by immunohistochemistry in normal and abnormal tissues. Serum transglutaminase activity was assayed in 36 patients with active Crohn's disease (CDAI > 150). Eighteen patients were studied prospectively from relapse into remission. A significant inverse correlation (p < 0.001) was found between circulating transglutaminase and Crohn's disease activity index; a correlation was also found between serum transglutaminase and serum orosomucoid (p < 0.01) and C reactive protein (p < 0.01). Patients were prospectively studied until clinical remission showed improvement in both their CDAI score mean (SD) (230 (46) to 72 (34), p < 0.01) and transglutaminase activity mean (SD) (0.61 (0.12) to 0.93 (0.13) mU/ml, p < 0.01). The immunohistochemistry assessment showed a colocalisation of factor XIIIa and tissue transglutaminase to the extracellular matrix of damaged tissues. In conclusion, these data confirm the value of serum transglutaminase assay as marker of Crohn's disease activity, extend the utility of serum transglutaminase assay to follow up of the disease, and emphasised the role of different types of transglutaminases in extracellular matrix assembly in the damaged tissues.

Immunochemical analyses of human plasma fibronectin-cytosolic transglutaminase interactions

Fibronectin is a glycoprotein involved in cell adhesion, tissue organization and wound healing. Transglutaminase binding and covalent cross-linking of fibronectin are physiologically important reactions. We describe microtiter plate-based immunochemical methods to analyze cytosolic transglutaminase-human plasma fibronectin interactions. The method was sensitive, specific, species-independent and capable of simultaneously analyzing 96 samples for binding. Binding was time-, temperature- and concentration-dependent and demonstrable with either protein immobilized to the plastic. The assay detected 1-5 ng transglutaminase or 50 pg fibronectin and was comparable in sensitivity to enzyme-linked immunosorbent assays. CaCl2 (8 mM) enhanced transglutaminase binding by two-fold. Molar concentrations of NaCl or millimolar concentrations of chloride salts of barium, copper or zinc inhibited binding by 50-60%. The binding was also competitively blocked by soluble fibronectin (IC50 = 2.3 nM) or by anti-fibronectin IgG (IC50 = 0.5 microM). Inclusion of dithiothreitol or 2-mercaptoethanol during binding resulted in a concentration-dependent inhibition of transglutaminase-fibronectin interactions (IC50 = 1.5 mM and 20 mM, respectively). A complex of [anti-transglutaminase IgG-transglutaminase-fibronectin-anti- fibronectin IgG] suggested that the binding sites and antibody epitopes could overlap, but are distinct and surface-exposed in the two proteins. Liver transglutaminase bound fibronectin 30-50% less compared to erythrocyte transglutaminase. Fibronectin-transglutaminase affinity was adequate for quantitating either antigen in lysates of lung fibroblasts, breast carcinomas or Escherichia coli. These immunochemical analyses will be useful for determining the affinity and mapping the domains involved in antibody recognition or protein-protein interactions using recombinant molecules of transglutaminase and fibronectin.

Transglutaminase in azoxymethane-induced colon cancer in the rat

A widespread from of transglutaminase, tissue transglutaminase, has been identified in a number of mammalian cell types, both normal and transformed cells; its biological role is not well understood. We investigated the effect of experimentally induced colon cancer on transglutaminase activity in the rat. Azoxymethane (15 mg/kg for six weeks), given by a course of weekly intraperitoneal injections, produces tumors almost exclusively confined to the intestinal tract. Transglutaminase activity was assayed on tissue homogenates both during the period of treatment and, when the cancer had developed, on tumor tissue and on microscopically uninjured adjacent tissue. A transient proliferative phase was present in the intestine during azoxymethane treatment: in this phase we found a coincidentally increased transglutaminase levels. Transglutaminase activity in tumors of both small and large intestine was significantly higher than in adjacent tissue. Immunohistochemistry revealed higher levels of transglutaminase in tumors, mainly localized in the extracellular matrix, than in adjacent tissues, where it was widely distributed. The present study shows that transglutaminase, besides its potential role in intracellular process during early proliferative phase of carcinogenesis, may also play an important role in matrix processing during tumor growth and differentiation.

Cross-linking of galectin 3, a galactose-binding protein of mammalian cells, by tissue-type transglutaminase

The 30 kDa beta-galactoside-binding protein of baby hamster kidney (BHK) cells [Mehul et al. (1994), J. Biol. Chem. 269, 18250-18258] homologous to galectin 3, a widely distributed mammalian lectin, has been found to be a substrate for tissue type transglutaminase, as shown by the incorporation in a calcium- and time-dependent manner of 5-(biotinamido) pentylamine in the presence of guinea pig liver transglutaminase. The amino-terminal domain of hamster galectin 3, which is a repetitive sequence rich in glutamine, tyrosine, glycine and proline, is also an excellent substrate. A single lysine residue in the N-terminal domain is an essential requirement for transglutaminase-mediated oligomerization, and two equivalent glutamine residues present in identical sequence repeats within this domain appear to be involved as amine acceptors in cross-linking reactions. Transglutaminase-mediated cross-linking of galectin 3 to itself or to matrix components may be one mechanism for stabilisation of a multivalent binding form of the lectin in cell secretions or in extracellular matrices.

Butyrate, mesalamine, and factor XIII in experimental colitis in the rat: effects on transglutaminase activity

BACKGROUND/AIMS

Butyrate and factor XIII may improve ulcerative colitis; they also affect tissue and serum transglutaminase levels. We investigated the therapeutic potential of sodium butyrate and factor XIII and the role of transglutaminase during mucosal repair in experimental colitis.

METHODS

Rats with induced colitis were treated with sodium butyrate, mesalamine, sodium butyrate plus mesalamine, or saline enemas. Thromboxane B2 was monitored as index of inflammation. In a fifth group, the effectiveness of intravenous Factor XIII was assessed.

RESULTS

Sodium butyrate, alone or plus mesalamine, reduced histological activity from 13.7 +/- 1.7 (saline) to 2.5 +/- 1.3 and 2.3 +/- 1.1 (P < 0.01), respectively. Transglutaminase, reduced in the colons of the saline group (783 +/- 157 vs. normal 1800 +/- 192 mU/g; P < 0.01), returned toward normal values in the sodium butyrate or sodium butyrate plus mesalamine groups (1390 +/- 228 and 1226 +/- 172 mU/g, respectively; P < 0.01 vs. saline). Furthermore, sodium butyrate plus mesalamine reduced thromboxane B2 levels by day 5 (0.92 +/- 0.16 vs. saline 1.85 +/- 0.34 ng/mL; P < 0.05). Factor XIII therapy improved the histological picture (2.7 +/- 2.1 vs. saline 13.8 +/- 1.7; P < 0.01) and increased transglutaminase levels both in serum (2.81 +/- 0.11 vs. saline 1.45 +/- 0.09 mU/mL; P < 0.01) and in colon (1503 +/- 127 vs. saline 747 +/- 103).

CONCLUSIONS

Sodium butyrate and factor XIII improve colitis, sodium butyrate plus mesalamine reduce early thromboxane B2 synthesis, and transglutaminase(s) plays a role in ulcer healing.

Packaging zinc, fibrinogen, and factor XIII in platelet alpha-granules

Zinc(II) accumulated by platelets has profound effects on platelet activity. This study is focused on the distribution of Zn(II) between human platelet subcellular compartments. After incubation with 86Rb+ and platelet lysis, the organelles were separated by sucrose density gradient centrifugation. Fibrinogen served as a marker for alpha-granules. 86Rb+ and factor XIII served as markers for the cytoplasmic fractions. Zn(II) was found to be distributed between the cytoplasm and the alpha-granules, with variations between different individual units. The total platelet Zn concentration and its relative subcellular distribution were dependent on its extracellular level. Incubation of platelets with 100 microM Zn(II) resulted in a twofold increase of its level in the cytoplasm and by one order of magnitude in the alpha-granules. In addition to the anticipated factor XIII activity in the cytoplasmic pool fraction, we found thrombin-inducible factor XIII activity within the alpha-granules. Immunoblotting confirmed the presence of both the a and b subunits of plasma factor XIII (a2b2 form) in the alpha-granules. As fibrinogen is not synthesized in the platelet, we propose that by virtue of their mutual binding, fibrinogen, Zn(II) and plasma factor XIII-a2b2 are simultaneously taken up into the alpha-granules by endocytosis, presumably through the vehicle of the GPIIb/IIIa fibrinogen receptor. A rationale for co-packaging these components within the alpha-granules is that Zn(II) inhibits factor XIII activity and thereby prevents the premature cross-linking of the concentrated fibrinogen prior to platelet activation and secretion. By contrast, cytoplasmic Zn(II) may increase platelet responsiveness to agonists due to its interaction with cytoplasmic modulators of platelet activity.

Activity and distribution of tissue transglutaminase in association with nerve-muscle synapses

We have measured, characterized, and localized calcium-dependent protein cross-linking activity in rat skeletal muscle, and in myotubes cultured independently or in coculture with spinal neurones, catalyzed by the enzyme tissue transglutaminase (tTG). The enzyme activity was present in both motor endplate and endplate-free zones of rat diaphragm muscle. tTG in the endplate zone was more tightly associated with the tissue. This form of association was absent in extracts of peripheral nerve. Cross-linking of endogenous proteins, as measured by the content of epsilon-(gamma-glutamyl)lysine isopeptide, was higher in the endplate than in the nonendplate zone. Cytosolic (C) and particulate (B) forms of tTG were separated by ion-exchange chromatography from both regions of the muscle. In the motor endplate zone, a higher proportion of tightly bound tTG was recovered as a separate (B1) particulate form. Km values for calcium activation of the three forms of tTG were in the range of 5-15 microM. Immunocytochemistry with polyclonal and monoclonal antibodies revealed the enzyme at motor endplates and at contacts between neurites of rat embryo spinal neurones and myotubes in primary cocultures. Appearance of the B1 transglutaminase could be induced by coculturing myotubes of the mouse C2C12 cell line with neurones. The results suggest that tTG is most concentrated and active at the motor endplate.

Localization of cellular transglutaminase on the extracellular matrix after wounding: characteristics of the matrix bound enzyme

Extending our previous observation that tissue transglutaminase (TGase) binds to extracellular matrix (ECM) fibronectin, we report here that endogenous tissue TGase is localized on the adjacent ECM after puncture wounding embryonic human lung fibroblasts (WI-38). The bound TGase persisted at the wound site for many hours, demonstrated by immunofluorescence and by catalytic activity using an overlay assay. The binding characteristics of TGase with ECM were studied further by the addition of exogenous TGase to cell monolayers and monitoring by immunofluorescence or overlay catalytic activity assays. Binding occurred equally well at 4 degrees C or 37 degrees C. Prior incubation of exogenous TGase with guanosine 5'-triphosphate (GTP), guanosine 5'-diphosphate (GDP), or adenosine triphosphate (ATP) had little effect on the amount bound to matrix, but prior treatment with calcium, magnesium, strontium, or manganese ions enhanced binding 2- to 3-fold. The Ca(++)-dependent change was a concentration-dependent effect on soluble exogenous TGase, rather than an effect on ECM. Immunofluorescent techniques showed that binding of exogenous TGase to ECM was prevented by prior mixing with fibronectin or collagen, but not with several other ECM components, including laminin, elastin, chondroitin sulfate, heparan sulfate, and hyaluronic acid. ECM-bound TGase was released by 2 M potassium thiocyanate (KSCN) treatment but was not released by treatment with a variety of amino acids, salts, reducing agents, glycerol, or other chaotropic agents.

Human mononuclear phagocyte transglutaminase activity cross-links fibrin

The physiologic function of the monocyte transglutaminases is not known. In this study, we detected Factor XIII A-subunit antigen and "tissue" transglutaminase antigen in human monocytes by polyacrylamide gel electrophoresis and immunoblotting techniques. Flow cytometric analysis demonstrated that 27% and 49% of the total Factor XIII antigen in monocytes and human peritoneal macrophages, respectively, are expressed on the surface of the cells. Monocytes maintained in culture for 8 days had a 4-fold increase in Factor XIIIa activity and a 3.2-fold increase in the amount of Factor XIII antigen/mg cell protein. However, there was no increase in the "tissue" transglutaminase activity or antigen levels in cultured monocytes. In addition, we identified a Factor XIII deficient individual who does not express Factor XIII activity or antigen in plasma, platelets, monocytes, lymphocytes or erythrocytes. Intact monocytes from normal donors were able to cross-link fibrin formed in the plasma from the Factor XIII deficient individual. This suggests that transglutaminase activity expressed by peripheral blood monocytes may play a physiologic role in cross-linking fibrin during blood clotting or inflammation.