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)

Thioglycolate-stimulated mouse peritoneal macrophages secrete a Proteinase which degrades insoluble elastin. There is little elastase activity in cell lysates but the bulk of the enzyme accumulates extracellularly during culture in serum-free medium. The secretion of elastase is sustained for over 12 days in culture and continued secretion of elastase requires protein synthesis. Unstimulated macrophages secrete very little elastase activity but can be triggered to secrete higher levels of this enzyme by phagocytosis and intracellular storage of latex particles. The macrophages elastase is a distinctive proteinase differing from the elastases of pancreas and granulocytes and is distinct from the other secreted proteinases of macrophages, namely, collagenase and plasminogen activator. The macrophages elastase is a serine proteinase and is inhibited by di-isopropyl phosphoro-fluoridate, ovoinhibitor, EDTA, dithiothretiol, and serum. Its activity is little affected by soybean trypsin inhibitor, turkey ovomucoid and chloromethyl ketones derived from tosyl lysine, tosyl phenylalanine, and acetyltetra alanine. Hydrolysis by macrophage elastase of chromogenic ester substrates for pancreatic elastase could not be detected. Elastase secretion by stimulated macrophages exceeds that by primary and established fibroblast cell strains. It is likely that elastase secretion by macrophages plays a major role in the pathogenesis of chronic destructive pulmonary diseases such as emphysema.
 ...
PMID:Elastase secretion by stimulated macrophages. Characterization and regulation. 16 96

Glucocorticoids affect the composition and function of the plasma membrane in a variety of cell types. Cultured rat hepatoma (HTC) cells in tissue culture provide an excellent model system for analysis of such effects. In these cells, dexamethasone rapidly and dramatically inhibits the influx of amino acids sharing the A or alanine-preferring transport system. Inhibition is half-maximal within 2 h, and maximal after 6 h incubation with the hormone. The inhibition is rapidly reversed by insulin, and more slowly by removing the steroid. Microtubules and microfilaments are not apparently involved in this hormonal effect, but continuous protein synthesis is required for the glucocorticoid inhibition of transport. Dexamethasone also decreases the number of microvilli on the surface of HTC cells, increases their adhesiveness to a substratum, and dramatically decreases the production of plasminogen activator, but it does not affect the growth rate or plating efficiency of the cells. Variant cell lines stably resistant to dexamethasone inhibition of plasminogen activator production have been isolated using an agar-fibrin overlay technique to detect protease production by individual colonies of HTC cells. The hormonal resistance to inhibition of protease production is associated witha maintenance of inducibility of other glucocorticoid-regulated functions and therefore is not apparently secondary to abnormal or absent glucocorticoid receptor, but due to a lesion in a later step in hormone action specific for plasminogen activator. Combined genetic and biochemical analysis of such dexamethasone-resistant variants should facilitate study of the hormonal regulation of specific membrane phenotypes and of the role of proteases in this regulation.
 ...
PMID:Glucocorticoids and the plasma membrane. 38 92

Recombinant variants of tissue-type plasminogen activator (t-PA) were constructed by site-directed mutagenesis and expressed in Chinese hamster ovary cells. Five variants were designed to improve the function of t-PA by mutagenesis in the kringle 1 (K1) domain. The amino acids were replaced with the corresponding residues present in the kringle 2 (K2) domain of native t-PA. The t-PA mutants expressed were as follows: variant E94V.D95G with point mutations in Glu94----Val and Asp95----Gly; variant N115P.S119M, Asn115----Pro and Ser119----Met; variant P125A.R129Q.R13OS, Pro125----Ala, Arg129----Gln and Arg130----Ser; variant G161R.K162R.-S165W, Gly161----Arg, Lys162----Arg and Ser165----Trp; and variant N115P, Asn115----Pro, respectively. The half-life following intravenous bolus injection in rabbits was prolonged in all variants except P125A.R130S. This was particularly true for N115P.S119M. The kinetic parameters for plasminogen activation were improved in t-PA G161R.K162R.S165W which showed a 0.6-fold decrease in Km, and a 1.8-fold increase in Vmax, thus promoting a 2.7-fold increase in kcat/Km compared to native t-PA. For a similar degree of thrombolysis in the rabbit jugular vein thrombosis model, the thrombolytic activity of G161R.K162R.S165W, at the dose tested, was four-fold greater than that of native t-PA. Thus, the substitution of the amino acids in the K1 domain with those corresponding in the K2 domain significantly enhanced the enzymatic activity of t-PA and improved the plasma survival.
 ...
PMID:Characterization of human tissue-type plasminogen activator variants with amino acid mutations in the kringle 1 domain. 133 23

The tetra-alanine substitution variant KHRR 296-299 AAAA of tissue-type plasminogen activator (t-PA) was previously shown to have enhanced fibrin specificity and enhanced activity in the presence of fibrin compared with the wild-type form of the molecule. The structural requirements for these alterations in enzymatic activity were investigated by constructing several amino acid substitution variants at each of the positions from 296 to 299 and evaluating their activities under a variety of conditions. Effects on plasminogen activator activity were common among the point mutants at positions 296-299; nearly all had a phenotype similar to the KHRR 296-299 AAAA variant. The greatest effects on enzymatic function were found with multiple substitution variants, but some single charge reversals and proline substitutions had substantial effects. The enhanced fibrin specificity of KHRR 296-299 AAAA t-PA results in less fibrinogenolysis than seen with wild-type t-PA. Approximately four times greater concentration of KHRR 296-299 AAAA compared with wild-type t-PA was required to consume 50% of the fibrinogen in human plasma.
 ...
PMID:Involvement of residues 296-299 in the enzymatic activity of tissue-type plasminogen activator. 140 47

Tissue-type plasminogen activator (t-PA) is less active in vivo and in vitro against clots that are enriched in platelets, even at therapeutic concentrations. The release of radioactivity from 125I-fibrin-labeled clots was decreased by 47% 6 hours after the addition of t-PA 400 U/mL when formed in platelet-rich versus platelet-poor plasma. This difference was not due to the release of plasminogen activator inhibitor-1 (PAI-1) by platelets. Thus, the fibrinolytic activity of t-PA in the supernatant was similar in the two preparations and fibrin autography demonstrated only a minor degree of t-PA-PAI-1 complex formation. Furthermore, a similar platelet-dependent reduction in clot lysis was seen with a t-PA mutant resistant to inhibition by PAI-1. The reduction in t-PA activity correlated with a decrease in t-PA binding to platelet-enriched clot (60% +/- 3% v platelet-poor clot, n = 5). This reduction in binding was also shown using t-PA treated with the chloromethylketone, D-Phe-Pro-Arg-CH2Cl (PPACK) (36% +/- 13%, n = 3), and with S478A, a mutant t-PA in which the active site serine at position 478 has been substituted by alanine (43% +/- 6%, n = 3). In contrast, fixed platelets and platelet supernatants had no effect on the binding or lytic activity of t-PA. Pretreatment with cytochalasin D 1 mumol/L, which inhibits clot retraction, also abolished the platelet-induced inhibition of lysis and t-PA binding by platelets. These data suggest that platelets inhibit clot lysis at therapeutic concentrations of t-PA as a consequence of clot retraction and decreased access of fibrinolytic proteins.
 ...
PMID:Inhibition of clot lysis and decreased binding of tissue-type plasminogen activator as a consequence of clot retraction. 154 40

Plasminogen activator inhibitor-1 (PAI-1) is a specific inhibitor of the serine proteases tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). To systematically investigate the roles of the reactive center P1 and P1' residues in PAI-1 function, saturation mutagenesis was utilized to construct a library of PAI-1 variants. Examination of 177 unique recombinant proteins indicated that a basic residue was required at P1 for significant inhibitory activity toward uPA, whereas all substitutions except proline were tolerated at P1'. P1Lys variants exhibited lower inhibition rate constants and greater sensitivity to P1' substitutions than P1Arg variants. Alterations at either P1 or P1' generally had a larger effect on the inhibition of tPA. A number of variants that were relatively specific for either uPA or tPA were identified. P1Lys-P1'Ala reacted 40-fold more rapidly with uPA than tPA, whereas P1Lys-P1'Trp showed a 6.5-fold preference for tPA. P1-P1' variants containing additional mutations near the reactive center demonstrated only minor changes in activity, suggesting that specific amino acids in this region do not contribute significantly to PAI-1 function. These findings have important implications for the role of reactive center residues in determining serine protease inhibitor (serpin) function and target specificity.
 ...
PMID:Saturation mutagenesis of the plasminogen activator inhibitor-1 reactive center. 155 96

The goal of the present study was to assess the relative importance of receptor-bound and secreted plasminogen activator urokinase (u-PA) in generating cell-surface plasmin and fostering destruction of normal tissue by tumor cells. We first showed that active site-inhibited u-PA could displace endogenous u-PA from the surface of the human colon adenocarcinoma cell line HCT 116. We then prepared expression vectors for u-PA and for a mutant molecule in which the codon for the active site serine residue was changed to encode alanine. Expression of non-functional mutant u-PA decreased the level of cell-bound active u-PA by more than 95% via a mechanism that involved competition for receptor sites. Decreased cell-surface u-PA activity was associated with a decrease in cell-bound plasmin activity to undetectable levels, suggesting that receptor-bound u-PA plays an important role in the generation of plasmin on the cell surface. Transfectants that secreted eightfold to 20-fold elevated levels of active wild-type u-PA showed approximately 50% increases in cell-associated u-PA and only twofold to fourfold increases in cell-associated plasmin, suggesting that the role of secreted u-PA in generating cell-surface plasmin activity was relatively minor. In parent cells and both types of transfectants there was a good correlation between the amount of plasmin bound to the tumor cell surface and the extent to which a basement membrane substrate was degraded. These studies show that receptor-bound u-PA provides an efficient mechanism for plasmin generation on the surface of tumor cells, which, in turn, contributes significantly to their degradative potential.
 ...
PMID:Effects of urokinase receptor occupancy on plasmin generation and proteolysis of basement membrane by human tumor cells. 164 83

Thrombolytic effects of tissue-type plasminogen activator (t-PA) are limited by in vivo platelet activation and dynamic coronary vasoconstriction. To examine if the concurrent administration of a fibrin(ogen)-degradation product, pentapeptide 6A (Ala-Arg-Pro-Ala-Lys) with t-PA would improve the thrombolytic effects of t-PA, dogs with electrically induced coronary thrombus were given t-PA alone or with peptide 6A. In dogs given t-PA alone (0.75 mg/kg over 20 min), coronary blood flow was restored in 69% of animals (9 of 13 dogs), with a mean time to reflow of 21 +/- 10 min and duration of reflow of 35 +/- 18 min. Reocclusion occurred in 77% of dogs (7 of 9 dogs). With concurrent administration of peptide 6A (200 mumol), coronary venous 6-keto-PGF1 alpha concentrations increased from 221 +/- 71 to 422 +/- 161 pg/ml (p less than 0.05), but not with t-PA given alone. Coronary blood flow was restored in 7 of 11 dogs (reperfusion rate 64%), with mean time to reflow of 17 +/- 7 min and duration of reflow of 35 +/- 15 min. The coronary reocclusion rate was 86%. All these indices of thrombolysis were similar to those in dogs given t-PA alone. In ex vivo experiments, we also demonstrated release of endothelium-derived relaxing factor from canine coronary artery rings in response to peptide 6A. To further examine the role of prostacyclin (PGI2) in thrombolytic response to t-PA, eight other dogs were given t-PA with a PGI2 analog iloprost (100 ng/kg/min for 40 min).(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Combined thrombolytic effects of tissue-plasminogen activator and a fibrinogen-degradation product peptide 6A or iloprost. 171 84

The dissolution of blood clots by plasmin is normally initiated in vivo by the activation of plasminogen to plasmin through the activity of tissue plasminogen activator (t-PA). The rate of plasminogen activation can be stimulated several orders of magnitude by the presence of fibrin-related proteins. Here we describe the kinetic analysis of both recombinant human t-PA (wild-type) and a t-PA variant produced by site-directed mutagenesis in which the original sequence from amino acids 296 to 299, KHRR, has been altered to AAAA. This tetra-alanine variant form of t-PA, K296A/H297A/R298A/R299A t-PA, we refer to as "KHRR" t-PA here. The plasminogen activating kinetics of wild-type t-PA (Activase alteplase) showed a catalytic efficiency which changed over 100-fold dependent on the stimulator in the assay. The lowest rate was in the absence of a stimulator. The following stimulators showed increasing ability to accelerate the catalytic efficiency of the reaction: fibrinogen, fragments of fibrinogen obtained by digestion with plasmin, fibrin, and slightly degraded fibrin. This increase in efficiency was driven primarily by decreases in the Michaelis constant (KM) of the reaction, whereas the catalytic rate constant (kcat) of the reaction did not change significantly. The "KHRR" variant of t-PA displayed novel kinetics with all stimulators tested. In the absence of a stimulator or with the poorer stimulators (fibrinogen and fibrinogen fragments), the KM values of the reaction with Activase alteplase and "KHRR" t-PA were similar. The kcat however, was lower with "KHRR" t-PA than with wild-type t-PA.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:A region of tissue plasminogen activator that affects plasminogen activation differentially with various fibrin(ogen)-related stimulators. 173 99

We present evidence that over-expression of human plasminogen, the precursor to the serine protease plasmin, can be cytotoxic to mammalian cells. When an expression vector containing plasminogen cDNA is transfected into baby hamster kidney cells, the number of drug-resistant colonies as well as the levels of plasminogen secreted by those colonies is lower than observed in similar transfections of other protease precursor genes. The recombinant plasminogen accumulates intracellularly as degraded NH2-terminal fragments. In contrast, a mutant of plasminogen that produces inactive plasmin (active site Ser740 changed to Ala) is synthesized by these cells as a full-length plasminogen molecule, and the colony numbers and expression levels are normal. Thus, the generation of plasmin activity is responsible for the cytotoxic phenomena and the degradation associated with plasminogen expression. In addition, experiments using a plasminogen mutant that cannot be activated to plasmin (activation cleavage site Arg560 to Gly) or using coexpression of antisense urokinase RNA indicate that an endogenous plasminogen activator is responsible for converting newly synthesized plasminogen to plasmin. Finally, coexpression of plasminogen with alpha 2-plasmin inhibitor, a serpin which is the physiologic inhibitor of plasmin, prevents the toxic effects of intracellular plasmin activity and allows the synthesis and secretion of native human plasminogen.
 ...
PMID:Expression of recombinant human plasminogen in mammalian cells is augmented by suppression of plasmin activity. 183 Dec 1


1 2 3 4 5 6 7 8 9 10 Next >>