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Biomedical subjects

L A Miles

Publications and source records attributed to L A Miles.

54 records · Page 3Linked to original sources
PubMed1990

Regulation of plasminogen receptor expression on human monocytes and monocytoid cell lines.

The capacity of human monocytoid cell lines and peripheral blood monocytes to modulate their expression of plasminogen receptors has been assessed. After PMA stimulation, THP-1 or U937 monocytoid cells were separated into adherent and nonadherent populations. Plasminogen bound to adherent cells with similar capacity and affinity as to nonstimulated cells. In contrast, the nonadherent cells bound plasminogen with 5-17-fold higher capacity (without a change in affinity). This increase was selective as urokinase bound with similar affinity and capacity to the adherent and nonadherent populations. Upregulation of plasminogen receptors on the nonadherent monocytoid cells was rapid, detectable within 30 min, and reversible, adhesion of the nonadherent cells resulted in a sixfold decrease in plasminogen binding within 90 min. The increase in plasminogen binding to the nonadherent cells was associated with a marked increase in their capacity to generate plasmin activity from cell-bound plasminogen. PMA stimulation of human peripheral blood monocytes increased their expression of plasminogen receptors by two- to fourfold. This increase was observed in both adherent and nonadherent monocytes. Freshly isolated monocytes maximally bound 5.0 x 10(5) plasminogen molecules per cell, whereas monocytes cultured for 18 h or more maximally bound 1.7 x 10(7) molecules per cell, a 30-fold difference in receptor number. These results indicate that both monocytes and monocytoid cell lines can rapidly and markedly regulate their expression of plasminogen binding sites. As enhanced plasminogen binding is correlated with an increased capacity to generate plasmin, an enzyme with broad substrate recognition, modulation of plasminogen receptors may have profound functional consequences.

Cell Line↗
PubMed1989

Gangliosides interact directly with plasminogen and urokinase and may mediate binding of these fibrinolytic components to cells.

Receptors for the fibrinolytic molecules plasminogen and urokinase are expressed at high capacity on a wide variety of peripheral blood cells and transformed cell lines. We have considered whether gangliosides, components of the outer leaflets of cell membranes, may modulate the interactions of these fibrinolytic ligands with cells. Radiolabeled plasminogen and urokinase bound directly to insolubilized gangliosides. The interactions were saturable and were 50% inhibited by 2.2 microM unlabeled plasminogen or 12 nM unlabeled urokinase, respectively. A panel of gangliosides inhibited binding of both ligands to U937 monocytoid cells, and the order of decreasing inhibitory effectiveness was GD1a greater than GM1 greater than GT1b greater than GM2, while GM3 was minimally effective. The individual components of gangliosides, hexoses, hexosamines, sialic acid, GM1 pentasaccharide, ceramides, and glucocerebrosides were ineffective in in inhibiting the binding of plasminogen and urokinase either to cells or to insolubilized gangliosides. Binding of both ligands to endothelial cells and granulocytes and binding of plasminogen to platelets were also inhibited by gangliosides. U937 cells were cultured with gangliosides to allow incorporation of these glycolipids into the cell membranes. After 3 days of culture, both urokinase binding and plasminogen binding to the cells became enhanced. These results suggest that gangliosides can directly bind to these fibrinolytic components and may mediate or modulate the interactions of plasminogen and urokinase with a variety of cell types.

Carbohydrates↗
PubMed1989

A linear amino acid sequence involved in the interaction of t-PA with its endothelial cell receptor.

Endothelial cell receptors for tissue plasminogen activator (t-PA) have been demonstrated recently, and we have sought to identify a region of the t-PA molecule involved in its interaction with these receptors on human umbilical vein endothelial cells. Of three monoclonal antibodies against various regions of t-PA, one directed against the finger region inhibited 125I-t-PA binding to the cells. Synthetic peptides corresponding in amino acid sequences to segments from within the finger region were constructed, and one of these inhibited t-PA binding. This peptide corresponded to residues 7 through 17 of t-PA. The inhibition by this peptide was specific as other peptides from the finger region were inactive. The inhibitory peptide also did not affect the binding of another fibrinolytic ligand, urokinase, to the cells. Although a role for other regions of t-PA in binding to endothelial cells cannot be excluded, the results implicate a short span of linear amino acid sequence within the finger region in the interaction of t-PA with endothelial cells.

Amino Acid Sequence↗
PubMed1989

A potential basis for the thrombotic risks associated with lipoprotein(a).

Lipoprotein(a) (Lp(a)) has been strongly linked with atherosclerosis and is an independent risk factor for myocardial infarction. Distinguishing Lp(a) from other low-density lipoprotein particles is its content of a unique apoprotein, apo(a). The recently described sequence of apo(a) indicates a remarkable homology with plasminogen, the zymogen of the primary thrombolytic enzyme, plasmin. Lp(a) may contain 37 or more disulphide-looped kringle structures, which are 75-85% identical to the fourth kringle of plasminogen. Plasminogen receptors are widely distributed on blood cells and are present at extremely high density on endothelial cells. These receptors promote thrombolysis by accelerating plasminogen activation and protecting plasmin from inhibition. If, by molecular mimicry, Lp(a) competes with plasminogen for receptors, then thrombolysis would be inhibited and thrombosis promoted. Here we provide support for such a mechanism being responsible for the thrombotic risks associated with elevated Lp(a) by demonstrating that Lp(a) inhibits plasminogen binding to cells.

Binding, Competitive↗
PubMed1988

The cell-binding domains of plasminogen and their function in plasma.

Plasminogen binding sites are expressed by a wide variety of cell types and serve to promote fibrinolysis and local proteolysis. In this study, the recognition specificity of cells for plasminogen has been examined, primarily using platelets as models. Analyses with plasminogen fragments implicated residues 79-337 (or 353), comprising the first three kringles of plasminogen, as a primary recognition site for plasminogen binding to both thrombin-stimulated and nonstimulated platelets. Other regions of plasminogen, namely residues 354-439 and 442-790, can also participate in the interaction, and these other regions contribute differentially to the binding of the ligand to stimulated and nonstimulated platelets. Binding to nucleated cells, with U937 cells serving as the prototype, is dependent upon a recognition specificity similar to that of unstimulated platelets. Binding of Glu-plasminogen, the native form of the molecule, to thrombin-stimulated platelets has been shown previously to require platelet fibrin. By comparing the interaction of Glu-plasminogen and its degradation product, Lys-plasminogen, with thrombin-stimulated platelets, it is concluded that the cell surface uniquely enhances the affinity of Glu-, but not Lys-plasminogen, for fibrin. Finally, we have demonstrated that cellular receptors and interactive sites within plasminogen are available in the plasma environment. Thus, the functions ascribed to cellular plasminogen receptors can occur within a physiologic setting.

Binding Sites↗
PubMed1988

Plasminogen receptors, urokinase receptors, and their modulation on human endothelial cells.

Endothelial cells are centrally involved in regulation of fibrinolysis, and receptors for plasminogen and urokinase provide a mechanism by which cells can regulate their fibrinolytic function. Therefore, the existence and characteristics of receptors for these fibrinolytic components on cultured human umbilical vein endothelial cells were examined. We verified the presence of plasminogen receptors on these cells (Kd = 2.1 +/- 1.3 mumol/L, and 1.8 +/- 1.3 x 10(7) binding sites/cell). These binding parameters and other characteristics indicate that these receptors are closely related to the plasminogen receptors on many circulating and adherent cells. Specific binding sites that interact with two-chain urokinase of mol wt 55,000 with a dissociation constant of 2.1 +/- 1.7 nmol/L, with 2.9 +/- 2.9 x 10(5) sites/cell were also identified. Single-chain urokinase of mol wt 55,000, but not the two-chain degradation product of mol wt 33,000 bound to the cells, implicating the amino-terminal aspects of the ligand in receptor recognition. When endothelial cells were stimulated with thrombin, an agent that modulates their fibrinolytic potential, both receptor types were modestly affected; urokinase binding increased 17%, whereas plasminogen binding decreased 19%. The presence and modulation of plasminogen and urokinase receptors provide a potentially important additional mechanism by which endothelial cells may regulate fibrinolysis.

Aminocaproic Acid↗
PubMed1987

Receptor mediated binding of the fibrinolytic components, plasminogen and urokinase, to peripheral blood cells.

Glu-plasminogen binds to platelets; the monocytoid line, U937, and the human fetal fibroblast line, GM1380 bind both plasminogen and its activator, urokinase. This study assesses the interaction of these fibrinolytic proteins with circulating human blood cells. Plasminogen bound minimally to red cells but bound saturably and reversibly to monocytes, granulocytes and lymphocytes with apparent Kd values of 0.9-1.4 microM. The interactions were of high capacity with 1.6 to 49 X 10(5) sites/cell and involved the lysine binding sites of plasminogen. Both T cells and non-rosetting lymphocytes and two B cell lines saturably bound plasminogen. Urokinase bound saturably to granulocytes, monocytes, non-rosetting lymphocytes and a B cell line, but minimally to T cells, platelets and red cells. Therefore, plasminogen binding sites of high capacity, of similar affinities, and with common recognition specificities are expressed by many peripheral blood cells. Urokinase receptors are also widely distributed, but less so than plasminogen binding sites. The binding of plasminogen and/or urokinase to these cells may lead to generation of cell-associated proteolytic activity which contributes to a variety of cellular functions.

Blood Cells↗
PubMed1986

Topography of the high-affinity lysine binding site of plasminogen as defined with a specific antibody probe.

An antibody population that reacted with the high-affinity lysine binding site of human plasminogen was elicited by immunizing rabbits with an elastase degradation product containing kringles 1-3 (EDP I). This antibody was immunopurified by affinity chromatography on plasminogen-Sepharose and elution with 0.2 M 6-aminohexanoic acid. The eluted antibodies bound [125I]EDP I, [125I]Glu-plasminogen, and [125I]Lys-plasminogen in radioimmunoassays, and binding of each ligand was at least 99% inhibited by 0.2 M 6-aminohexanoic acid. The concentrations for 50% inhibition of [125I]EDP I binding by tranexamic acid, 6-aminohexanoic acid, and lysine were 2.6, 46, and 1730 microM, respectively. Similar values were obtained with plasminogen and suggested that an unoccupied high-affinity lysine binding site was required for antibody recognition. The antiserum reacted exclusively with plasminogen derivatives containing the EDP I region (EDP I, Glu-plasminogen, Lys-plasminogen, and the plasmin heavy chain) and did not react with those lacking an EDP I region [miniplasminogen, the plasmin light chain or EDP II (kringle 4)] or with tissue plasminogen activator or prothrombin, which also contain kringles. By immunoblotting analyses, a chymotryptic degradation product of Mr 20,000 was derived from EDP I that retained reactivity with the antibody. The high-affinity lysine binding site was equally available to the antibody probe in Glu- and Lys-plasminogen and also appeared to be unoccupied in the plasmin-alpha 2-antiplasmin complex. alpha 2-Antiplasmin inhibited the binding of radiolabeled EDP I, Glu-plasminogen, or Lys-plasminogen by the antiserum, suggesting that the recognized site is involved in the noncovalent interaction of the inhibitor with plasminogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies↗
PubMed1986

The plasminogen system and cell surfaces: evidence for plasminogen and urokinase receptors on the same cell type.

The capacity of cells to interact with the plasminogen activator, urokinase, and the zymogen, plasminogen, was assessed using the promyeloid leukemic U937 cell line and the diploid fetal lung GM1380 fibroblast cell line. Urokinase bound to both cell lines in a time-dependent, specific, and saturable manner (Kd = 0.8-2.0 nM). An active catalytic site was not required for urokinase binding to the cells, and 55,000-mol-wt urokinase was selectively recognized. Plasminogen also bound to the two cell lines in a specific and saturable manner. This interaction occurred with a Kd of 0.8-0.9 microM and was of very high capacity (1.6-3.1 X 10(7) molecules bound/cell). The interaction of plasminogen with both cell types was partially sensitive to trypsinization of the cells and required an unoccupied high affinity lysine-binding site in the ligand. When plasminogen was added to the GM1380 cells, a line with high intrinsic plasminogen activator activity, the bound ligand was comprised of both plasminogen and plasmin. Urokinase, in catalytically active or inactive form, enhanced plasminogen binding to the two cell lines by 1.4-3.3-fold. Plasmin was the predominant form of the bound ligand when active urokinase was added, and preformed plasmin can also bind directly to the cells. Plasmin on the cell surface was also protected from its primary inhibitor, alpha 2-antiplasmin. These results indicate that the two cell lines possess specific binding sites for plasminogen and urokinase, and a family of widely distributed cellular receptors for these components may be considered. Endogenous or exogenous plasminogen activators can generate plasmin on cell surfaces, and such activation may provide a mechanism for arming cell surfaces with the broad proteolytic activity of this enzyme.

Cell Line↗
PubMed1986

Plasminogen interacts with human platelets through two distinct mechanisms.

Glu-plasminogen, the native form of plasminogen, interacts in a specific and saturable manner with unstimulated human platelets, and the binding is enhanced fivefold by thrombin stimulation (Miles and Plow, 1985. J. Biol. Chem. 260:4303). This study characterizes the nature of the Glu-plasminogen binding sites by analyzing platelets deficient in selected proteins and functions. Platelets from patients with afibrinogenemia, Gray platelet syndrome, and the Cam Variant of thrombasthenia, a form of thrombasthenia with near normal levels of glycoprotein IIb/IIIa (GPIIb/IIIa), showed minimal augmentation of plasminogen binding to thrombin-stimulated platelets but normal binding to unstimulated platelets. This selective deficiency indicates that two distinct mechanisms are involved in the interaction of plasminogen with platelets. These abnormal platelets share a deficiency in fibrinogen. Surface expression of platelet fibrinogen, however, was not sufficient for enhanced plasminogen binding to stimulated platelets, and experiments with alpha-thrombin and gamma-thrombin indicated that fibrin formation on the platelet surface is necessary for the augmented plasminogen binding. Unstimulated and stimulated thrombasthenic platelets deficient in GPIIb/IIIa bound markedly reduced levels of plasminogen, which suggests a role for GPIIb/IIIa in plasminogen binding to unstimulated platelets. Treatment of platelets to dissociate the heterodimeric complex of GPIIb/IIIa did not significantly perturb plasminogen binding to unstimulated platelets, but the complex may be necessary for thrombin-stimulated plasminogen binding via its interaction with platelet fibrin.

Blood Platelets↗
PubMed1985

Binding and activation of plasminogen on the platelet surface.

A mechanism by which platelets might participate in fibrinolysis by binding plasminogen and influencing its activation has been examined. Binding of radioiodinated human Glu-plasminogen to washed human platelets was time-dependent and was enhanced 3-9-fold by stimulation of platelets with thrombin but not with ADP. The interaction with both stimulated and unstimulated cells was specific, saturable, divalent ion-independent, and reversible. The platelet-bound ligand had the molecular weight of plasminogen, and no conversion to plasmin was detected. Scatchard analyses provided evidence for a single class of plasminogen-binding sites on both stimulated and unstimulated cells. The Kd for thrombin-stimulated platelets was 2.6 +/- 1.3 microM, and 190,000 +/- 45,000 molecules were bound per cell, whereas unstimulated platelets bound 37,000 +/- 10,500 molecules/cell with a Kd of 1.9 +/- 0.15 microM. Plasminogen binding was inhibited in a dose-dependent manner by omega-aminocarboxylic acids at concentrations consistent with a requirement for an unoccupied high affinity lysine-binding site for plasminogen binding to the cells. When platelet-bound plasminogen was incubated with tissue plasminogen activator, urokinase, or streptokinase, gel analysis established that plasmin was preferentially associated with the platelet relative to the supernatant. Plasminogen and plasmin interacted with thrombin-stimulated platelets with similar binding characteristics, and there was no evidence for a binding site for plasmin which did not also bind plasminogen. Therefore, the results suggest that plasminogen activation is enhanced on the cell surface. In sum, these results indicate that platelets bind plasminogen at physiologic zymogen concentrations and this interaction may serve to localize and promote plasminogen activation.

Adenosine Diphosphate↗
PubMed1983

A comparison of the abilities of plasma kallikrein, beta-Factor XIIa, Factor XIa and urokinase to activate plasminogen.

In order to compare the relative potencies of plasma kallikrein, beta-Factor XIIa, Factor XIa and urokinase as plasminogen activators, plasminogen activation by these proteins was studied using a radiolabeled fibrin plate assay. Urokinase was approximately 20,000 times more active than kallikrein or Factor XIa and 300,000 times more active than beta-Factor XIIa. Kallikrein and Factor XIa were approximately equal in plasminogen activator activity and were 20 times more potent than beta-Factor XIIa.

Endopeptidases↗
PubMed1983

Dextran sulfate-dependent fibrinolysis in whole human plasma.

This study shows that Flu-beta-Ala can reduce the ability of human plasma to inhibit plasmin. This observation was utilized to develop a method for generating detectable fibrinolytic activity in whole human plasma as assessed on a radiolabeled fibrin plate. Plasma was pretreated with Flu-beta-Ala to remove inhibitors of fibrinolysis: then dextran sulfate was added and the mixture was further incubated at 4 degrees C. When normal plasma was treated in this manner, the rate of generation of fibrinolytic activity after 0.75 hr incubation with radiolabeled fibrin was equivalent to that of 35 ng/ml plasmin. The plasminogen dependence of this activity was tested by pretreating plasma with antibodies against plasminogen. The generation of fibrinolytic activity was totally blocked by this treatment, indicating that the observed fibrinolytic activity was plasminogen-dependent. When plasmas deficient in prekallikrein, factor XII, or high-molecular-weight kininogen were treated with Flu-beta-Ala and dextran sulfate, the initial rate of fibrinolytic activity was less than normal. But after 3 hr incubation with radiolabeled fibrin, the rate of fibrinolytic activity in these deficient plasmas approached that of normal plasma. Thus this dextran sulfate-dependent fibrinolytic activity is dependent on factor XII, prekallikrein, and high-molecular-weight kininogen, but the requirement is not absolute.

Dextran Sulfate↗
PubMed1982

A bleeding disorder due to deficiency of alpha 2-antiplasmin.

A deficiency of alpha 2-antiplasmin has been identified in a female patient with severe and frequent bleeding episodes. Routine coagulation and platelet assays of the patient's plasma were within normal limits. However, abnormally rapid whole blood or dilute plasma clot lysis times and an abnormal FXIII test in which clots were lysed in the presence of urea or saline suggested an abnormal fibrinolytic system. Analysis of alpha 2-antiplasmin levels by radioimmunoassay revealed less than 1.0 microgram/ml alpha 2-antiplasmin. Functional assays indicated an alpha 2-antiplasmin level less than or equal to 10% of normal. Addition of purified alpha 2-antiplasmin to the patient's plasma restored its ability to inhibit plasmin in in vitro assays, and mixtures of patient plasma with normal plasma did not interfere with the antiplasmin activity of the normal plasma. Whereas normal platelets contain 68 ng alpha 2-antiplasmin/10(9) platelets, platelets from the patient contained 30% of the normal level of antigen. Analysis of alpha 2-antiplasmin functional and antigenic levels in the plasma of both parents and four siblings of the propositus provided evidence consistent with an autosomal mechanism of inheritance of alpha 2-antiplasmin deficiency. One sibling appeared to be homozygous and three siblings and the parents were heterozygous for the deficiency. Two heterozygotes had positive bleeding histories. The association of a bleeding disorder with a deficiency of alpha 2-antiplasmin emphasizes that lack of regulation of the fibrinolytic system can result in a hemostatic dysfunction.

Adolescent↗
PubMed1981

Inactivation of purified human alpha 2-antiplasmin and purified human C1 inhibitor by synthetic fibrinolytic agents.

3-Hydroxypropyl flufenamide (Flu-HPA) is one of a series of flufenamic acid derivatives that enhances blood clot lysis in vitro. Studies of possible mechanisms of action of Flu-HPA were undertaken. The profibrinolytic activity of Flu-HPA in clot lysis assays was found to be dependent on plasminogen. The influence of Flu-HPA on the ability of purified alpha 2-antiplasmin to inhibit purified plasmin was studied. Plasmin activity was determined using 125I-fibrin plates or the spectrophotometric tripeptide substrate, Val-Leu-Lys-paranitroanilide. At Flu-HPA concentrations greater than 1 mM, the inhibitory activity of alpha 2-antiplasmin was abolished in a time-dependent and concentration-dependent manner. The influence of Flu-HPA on the ability of purified Cl inhibitor to inhibit purified plasma kallikrein and beta-Factor XIIa was also studied. Cl inhibitor activity was abolished by Flu-HPA at concentrations greater than 2 mM. Notably, Flu-HPA up to 60 mM did not affect the amidolytic activities of plasmin, kallikrein, or beta-Factor XIIa. Flu-HPA did not release enzyme activity from preformed complexes of either alpha 2-antiplasmin and plasmin of Cl inhibitor and kallikrein. A water-soluble derivative of flufenamic acid, N-flufenamyl-glutamic acid, also inactivated alpha 2-antiplasm and Cl inhibitor. This inactivation was shown to be reversible. These results indicate that synthetic fibrinolytic compounds such as flufenamic acid derivatives may promote fibrinolysis by directly inactivating alpha 2-antiplasmin and Cl inhibitor.

Blood Coagulation↗
PubMed1980

Human plasma prekallikrein. Studies of its activation by activated factor XII and of its inactivation by diisopropyl phosphofluoridate.

Human plasma prekallikrein was purified from normal plasma. The purified prekallikrein appeared homogeneous on polyacrylamide gels in the presence of sodium dodecyl sulfate and mercaptoethanol and gave two protein bands with approximate Mr 85 000. Proteolytic activation of prekallikrein by purified human beta-factor XIIa (Mr 28 000 form) resulted in the formation of kallikrein. The apparent molecular weight of kallikrein determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence of mercaptoethanol was identical with that of prekallikrein; reduction of kallikrein yielded a heavy chain of Mr 52 000 and two light chains of Mr 42 000 and 37 000. The appearance of kallikrein activity was directly correlated with the limited proteolysis due to beta-factor XIIa. Kinetic and immunologic studies demonstrated that plasma prekallikrein is a factor XII dependent plasminogen proactivator. The rate constant for the inactivation of prekallikrein by diisopropyl phosphofluoridate was similar to that previously reported for trypsinogen. This observation raises the possibility that low intrinsinc catalytic activity of prekallikrein may play a role in the initiation of the intrinsic blood coagulation pathway.

Amino Acids↗