Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin-activatable fibrinolysis inhibitor (TAFI) circulates as an inactive proenzyme of a carboxypeptidase B-like enzyme (TAFIa). It functions by removing C-terminal lysine residues from partially degraded fibrin that are important in tissue-type plasminogen activator mediated plasmin formation. TAFI was classified as a metallocarboxypeptidase, which contains a Zn(2+), since its amino acid sequence shows approximately 40% identity with pancreatic carboxypeptidases, the Zn(2+) pocket is conserved, and the Zn(2+) chelator o-phenanthroline inhibited TAFIa activity. In this study we showed that TAFI contained Zn(2+) in a 1:1 molar ratio. o-Phenanthroline inhibited TAFIa activity and increased the susceptibility of TAFI to trypsin digestion. TAFIa is spontaneously inactivated (TAFIai) by a temperature-dependent intrinsic mechanism. The lysine analogue epsilon-ACA, which stabilizes TAFIa, delayed the o-phenanthroline mediated inhibition of TAFIa. We investigated if inactivation of TAFIa involves the release of Zn(2+). However, the zinc ion was still incorporated in TAFIai, indicating that inactivation is not caused by Zn(2+) release. After TAFIa was converted to TAFIai, it was more susceptible to proteolytic degradation by thrombin, which cleaved TAFIai at Arg(302). Proteolysis may make the process of inactivation by a conformational change irreversible. Although epsilon-ACA stabilizes TAFIa, it was unable to reverse inactivation of TAFIa or R302Q-rTAFIa, in which Arg(302) was changed into a glutamine residue and could therefore not be inactivated by proteolysis, suggesting that conversion to TAFIai is irreversible.
 ...
PMID:Role of zinc ions in activation and inactivation of thrombin-activatable fibrinolysis inhibitor. 1180 20

Fischer rat thyroid (FRT) cells organize a matrix of extracellular fibronectin (FN) fibrils, which undergoes extensive remodeling according to cell culture confluence. In non-confluent cells FN forms a fibrillar array associated with the ventral cell surface. However, basal FN is progressively removed in confluent cultures and substituted by non-fibrillar FN deposits at lateral cell domains in regions of cell-cell contacts. FRT cells secrete and expose on the plasma membrane the tissue-type plasminogen activator and, in serum-free cultures, plasminogen induces a rapid loss of FN fibrils. Incubation with plasmin inhibitors greatly reduces this effect. FRT cells also express annexin II, a plasminogen receptor, suggesting that plasmin activity is associated with the pericellular enviroment. This is in agreement with the observation that a great reduction in FN degradation is observed if the cells are pre-incubated with carboxypeptidase B, which prevents plasminogen binding to the cells. A gelatinolytic activity with a molecular weigth equivalent to MMP-2 has been demonstrated by zymography of culture media, and the presence of MMP-2 and MT1-MMP on the cell plasma membrane has been detected by immunofluorescence. These results indicate that in the FN remodeling process, occurring during FRT epithelium maturation, both plasmin-dependent (tPA activated) and plasmin-independent proteolytic activities are involved.
 ...
PMID:The role of proteases in fibronectin matrix remodeling in thyroid epithelial cell monolayer cultures. 1192 11

In order to further investigate the effect of annexin II (Ann-II) on tissue plasminogen activator (t-PA)-dependent plasminogen (PLG) activation and its interactive mechanism, recombinant native Ann-II bound t-PA, PLG and plasmin with high affinity was examined. The flow cytometric assay showed that the ann-II expression rate was higher in the human umbilical vein endothelial cell (HUVEC) (87.65%) than in the HL-60 cells as controls (35.79%). Two irrelevant proteins, bovine serum albumin (BSA) and equine IgG (EIG) had no effect on the production of plasmin. Ann-II-mediated enhancement of t-PA-dependent PLG activation was inhibited by epsilon-aminocaproic acid or by pretreatment of Ann-II with carboxypeptidase B with the inhibitive rate being 77.8% and 77.0%, respectively. It was revealed that the effect of Ann-II on PLG activation was specific for t-PA. Urokinase didn't bind to Ann-II, demonstrating the role of receptor-related lysine residues on activation of PLG, showing that the Ann-II-PLG interaction was dependent upon carboxyl-terminal lysine residues. These findings suggest that annexin II-mediated co-assembly of t-PA and PLG may promote plasmin generation and play a key role in modulating fibrinolysis on the endothelial surface.
 ...
PMID:Study on the mechanism of the annexin II-mediated co-assembly of t-PA and plasminogen. 1265 74

Activated thrombin-activable fibrinolysis inhibitor (TAFIa) is a carboxypeptidase B-like plasma enzyme that can slow clot lysis by removing lysine residues exposed on fibrin as it is cleaved by plasmin. Previously, it was shown that fibrin treated with TAFIa is less able to promote plasminogen activation by tissue-type plasminogen activator. In this study, the effect of TAFIa modification of a fibrin surface on the rate of plasmin inhibition by antiplasmin was studied using high molecular weight fibrin degradation products (HMw-FDPs) as a soluble model for intact plasmin-modified fibrin. To quantify the inhibition, a novel end point assay was employed where plasmin, antiplasmin, and cofactors were mixed in the presence of a chromogenic substrate and the end point in the substrate hydrolysis reaction was used to measure the second order rate constant of inhibition. When HMw-FDPs were titrated in the presence of plasmin and antiplasmin, the rate constant for inhibition decreased by 16-fold at saturation (9.6 x 10(6) m(-1) s(-1) to 0.59 x 10(6) m(-1) s(-1)). When HMw-FDPs were pretreated with TAFIa, nearly two-thirds of the protective effect was lost. When 730 nm HMw-FDPs were treated for 20 min with TAFIa, the rate constant for plasmin inhibition was increased 3-fold from 1.9 x 10(6) m(-1) s(-1) to 6.2 x 10(6) m(-1) s(-1). Therefore, a novel mechanism was identified whereby TAFIa can modulate plasmin levels by increasing the susceptibility of plasmin to inhibition by antiplasmin.
 ...
PMID:Activated thrombin-activatable fibrinolysis inhibitor reduces the ability of high molecular weight fibrin degradation products to protect plasmin from antiplasmin. 1471 54

Plasma procarboxypeptidase B, also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is converted by thrombin into the active enzyme, carboxypeptidase B (CPB)/activated TAFI. Plasma CPB down-regulates fibrinolysis by removing carboxy-terminal lysines, the ligands for plasminogen and tissue-type plasminogen activator (tPA), from partially degraded fibrin. To target thrombosis in a new way, we have identified and optimized a phosphinic acid-containing inhibitor of CPB, EF6265 [(S)-7-amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino) propyl]hydroxyphosphinoyl]methyl]heptanoic acid] and determined both the pharmacological profile and pathophysiological role of CPB in rat thrombolysis. EF6265 specifically inhibited plasma CPB activity with an IC(50) (50% inhibitory concentration) of 8.3 nM and enhanced tPA-mediated clot lysis in a concentration-dependent manner. EF6265 decreased detectable thrombi (percentage of glomerular fibrin deposition; control, 98 +/- 1.1; EF6265, 0.1 mg/kg, 27 +/- 9.1) that had been generated by tissue factor in a rat microthrombosis model with concomitant increases in plasma D-dimer concentration (control, <0.5 microg/ml; EF6265, 0.1 mg/kg, 15 +/- 3.5 microg/ml). EF6265 reduced plasma alpha2-antiplasmin activity to a lesser extent than tPA. In an arteriovenous shunt model, EF6265 (1 mg/kg) enhanced exogenous tPA-mediated thrombolysis under the same conditions that neither EF6265 nor tPA (600 kIU/kg) alone reduced thrombi. EF6265 (1 and 30 mg/kg) did not affect the bleeding time in rats. Moreover, it did not prolong the bleeding time evoked by tPA (600 kIU/kg). These results confirm that circulating procarboxypeptidase B functions as a fibrinolysis inhibitor's zymogen and validates the use of CPB inhibitors as both an enhancer of physiological fibrinolysis in microcirculation and as a novel adjunctive agent to tPA for thromboembolic diseases while maintaining a small effect on primary hemostasis.
 ...
PMID:Enhancement of fibrinolysis by EF6265 [(S)-7-amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic acid], a specific inhibitor of plasma carboxypeptidase B. 1476 98

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.
 ...
PMID:Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice. 1509 84

Activated thrombin-activable fibrinolysis inhibitor (TAFIa) is intrinsically unstable, a property that complicates the study of its role in regulating fibrinolysis. To investigate the effect of basic carboxypeptidases on fibrinolysis under conditions of constant carboxypeptidase activity, we employed pancreatic carboxypeptidase B (CPB), a homologous, stable basic carboxypeptidase, as a surrogate for TAFIa. Clots formed from TAFI-depleted plasma or from purified components were supplemented with tissue-type plasminogen activator and either CPB or TAFIa. The clot lysis data indicate that the down-regulation of fibrinolysis mediated by basic carboxypeptidases involves a threshold mechanism. At carboxypeptidase concentrations above the threshold, plasminogen activation is maintained in a fully down-regulated state; experiments in plasma showed that fibrinolysis is essentially halted by saturating concentrations of TAFIa and that fibrinolysis can be prolonged more than 45-fold by a stable carboxypeptidase. The threshold carboxypeptidase concentration was dependent on tissue-type plasminogen activator and antiplasmin concentrations, indicating that the threshold is determined by the steady-state plasmin concentration. Although obvious with CPB, the threshold was masked by the intrinsic instability of TAFIa and became apparent only when the effect of TAFIa was investigated over the picomolar concentration range. Because of the threshold effect and the instability of TAFIa, exponential increases in TAFIa concentration generate linear increases in lysis time. A model relating lysis time to TAFIa concentration, TAFIa half-life, and the threshold concentration of TAFIa is provided. The threshold effect has potentially important implications regarding the role of TAFIa and the regulation of clot lysis in vivo.
 ...
PMID:The intrinsic threshold of the fibrinolytic system is modulated by basic carboxypeptidases, but the magnitude of the antifibrinolytic effect of activated thrombin-activable fibrinolysis inhibitor is masked by its instability. 1512 44

A major component of neuritic plaques in brain tissue of Alzheimer's disease patients is the beta-amyloid peptide (Abeta). Accumulation of Abeta has been associated with increased neuronal cell death and cognitive decline. We have previously shown that amyloid peptides like Abeta bind tissue-type plasminogen activator (tPA) and stimulate plasmin production. Here we investigated how Abeta regulates plasmin formation by N1E-115 neuroblastoma cells and the effects of Abeta-mediated plasmin formation on cell attachment and cell survival. We find that Abeta induces excessive cell-associated plasmin generation that causes cell detachment. Cell detachment is inhibited by carboxypeptidase B (CPB), an enzyme that blocks plasmin formation by cleaving off C-terminal lysine residues. Plasmin and CPB control Abeta-induced cell detachment independently of direct effects on cell viability. Abeta40 as well as oligomeric and fibrillar forms of Abeta42 stimulated tPA-mediated plasminogen activation and cell detachment. Our results suggest that plasmin-mediated cell detachment could contribute to the pathological effects of Abeta in diseased brain.
 ...
PMID:Beta-amyloid (Abeta) causes detachment of N1E-115 neuroblastoma cells by acting as a scaffold for cell-associated plasminogen activation. 1573 40

Bleeding, the most serious complication of thrombolytic therapy with tissue-type plasminogen activator (t-PA), is thought to result from lysis of fibrin in hemostatic plugs and from the systemic lytic state caused by unopposed plasmin. One mechanism by which systemic plasmin can impair hemostasis is by partially degrading fibrinogen to fragment X, a product that retains clottability but forms clots with reduced tensile strength that stimulate plasminogen activation by t-PA more than fibrin clots. The purpose of this study was to elucidate potential mechanisms by which fragment X accelerates t-PA-mediated fibrinolysis. In the presence of t-PA, clots containing fragment X were degraded faster than fibrin clots and exhibited higher rates of plasminogen activation. Although treatment with carboxypeptidase B, an enzyme that reduces plasminogen binding to fibrin, prolonged the lysis times of fragment X and fibrin clots, clots containing fragment X still were degraded more rapidly. Furthermore, plasmin or trypsin also degraded clots containing fragment X more rapidly than fibrin clots, suggesting that this effect is largely independent of plasminogen activation. Fragment X-derived degradation products were not preferentially released by plasmin from clots composed of equal concentrations of fibrinogen and fragment X, indicating that fragment X does not constitute a preferential site for proteolysis. These data suggest that structural changes resulting from incorporation of fragment X into clots promote their lysis. Thus, attenuation of thrombolytic therapy-induced fragment X formation may reduce the risk of bleeding.
 ...
PMID:Incorporation of fragment X into fibrin clots renders them more susceptible to lysis by plasmin. 1656

Cryptococcus neoformans can invade the central nervous system through diverse mechanisms. We examined a possible role for host plasma proteases in the neurotropic behaviour of this blood-borne fungal pathogen. Plasminogen is a plasma-enriched zymogen that can passively coat the surface of blood-borne pathogens and, upon conversion to the serine protease plasmin, facilitate pathogen dissemination by degrading vascular barriers. In this study, plasminogen-to-plasmin conversion on killed and viable hypoencapsulated strains of C. neoformans required the addition of plasminogen activator (PA), but this conversion occurred in the absence of supplemented PA when viable strains were cultured with brain microvascular endothelial cells (BMEC). Plasmin-coated C. neoformans showed an enhanced invasive ability in Matrigel invasion assays that was significantly augmented in the presence of BMEC. The invasive effect of plasmin required viable pathogen and correlated with rapid declines in BMEC barrier function. Plasmin-enhanced invasion was inhibited by aprotinin, carboxypeptidase B, the lysine analogue epsilon-aminocaproic acid, and by capsule development. C. neoformans caused plasminogen-independent declines in BMEC barrier function that were associated with pathogen-induced host damage; however, such declines were significantly delayed and less extensive than those observed with plasmin-coated pathogen. BMEC adhesion and damage by hypoencapsulated C. neoformans were diminished by capsule induction but unaltered by plasminogen and/or PA. We conclude that hypoencapsulated C. neoformans can invade BMEC by a plasmin-dependent mechanism, in vitro, and that small, or minimal, surface capsule expression during the blood-borne phase of cryptococcosis may promote virulence by means of plasmin(ogen) acquisition.
 ...
PMID:Blood-brain barrier invasion by Cryptococcus neoformans is enhanced by functional interactions with plasmin. 2199 62


<< Previous 1 2 3 Next >>