Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.7 (plasmin)
 9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Effects of urokinase receptor occupancy on plasmin generation and proteolysis of basement membrane by human tumor cells. 164 83

The giant Amazon leech Haementeria ghilianii manufactures blood anticoagulant which is present in the posterior and anterior salivary glands. The mechanism of blood anticoagulation by Haementeria ghilianii is completely different from that used by Hirudo medicinalis. The anticoagulant is mostly associated with a fibrinogen-degrading proteinase, hementin. However, other inhibitors of blood coagulation are also present in the salivary glands. The salivary gland extract inhibits platelet aggregation that is mostly attributable to the degradation of fibrinogen. Hementin purified by various methods has a molecular weight in the range of 80,000-120,000 and appears to be a metalloproteinase that is regulated by calcium ions. The enzyme degrades both fibrinogen and fibrin. The Michaelis constant for human fibrinogen is 1 microM. The cleavage of the isolated chains of fibrinogen is inefficient implying that the native conformation of the substrate may play a role in the recognition mechanism. The pattern of fibrinogen degradation by hementin resembles that caused by plasmin since products analogous to fragments Y, D and E are generated. However, the unique action of hementin on fibrinogen is in the initial proteolytic attack in the coiled-coil connector region while proteolysis of the alpha-chain is very slow. In consequence, unique fibrinogen fragments are formed that contain the entire COOH-terminus of the alpha-chain. The mechanism of blood anticoagulation by hementin is very efficient since the cleavage of only three peptide bonds in the fibrinogen molecule disassembles its bivalent structure and renders it non-functional.
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PMID:Interaction of hementin with fibrinogen and fibrin. 177 82

Normal levels of factor XII and of high and low molecular weight kininogens (HMWK and LMWK) were registered in plasma specimens from 5 individuals who had developed anaphylactoid reactions upon injection of dextran during surgery (dextran reactors, DR). Factor XII was assayed as prekallikrein activator (PKA) activated with kaolin at 0 degrees, and kininogen fractions were estimated through the release of kinin caused by plasma kallikrein or hog pancreas kallikrein (HPK). Subnormal levels of factor XII apparently present in plasma from one DR, and after affinity chromatography on a lysine-Sepharose column also in plasma from another DR, were normalized by addition of plasma deficient in factor XII or by addition of purified HMWK. Treatment of plasma from DR with acetone (25% v/v) induced a conversion of HMWK into a state which was non-functional as a cofactor in the surface-dependent activation of factor XII, and the passage of plasma from DR through a lysine-Sepharose column altered the HMWK present to a substance that released kinin only very slowly by incubation with HPK. It is concluded that the treatments mentioned will favour the activation in plasma from DR of a factor that will cause the conversion of HMWK. Previous experiments with rat plasma demonstrated that plasmin and also a plasmin-like factor without affinity for lysine-Sepharose were able to destroy the capacity of HMWK to function as a cofactor in the surface-dependent activation of factor XII, without a corresponding release of kinin.
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PMID:Dextran-induced anaphylactoid reaction in man: altered reactivity of high molecular weight kininogen. 615 74

A number of RGD-type integrins rely on a synergistic site in addition to the canonical RGD site for ligand binding and signaling, although it is still unclear whether these two recognition sites function independently, synergistically, or competitively. Experimental evidence has suggested that fibrinogen binding to the RGD-type integrin alphaIIbbeta3 occurs exclusively through the synergistic gamma(400-411) sequence, thus questioning the functional role of the RGD recognition site. Here we have investigated the respective role of the fibrinogen gamma(400-411) sequence and the RGD motif in the molecular events leading to ligand-induced alphaIIbbeta3-dependent Chinese hamster ovary (CHO) cell or platelet spreading, by using intact fibrinogen and well characterized plasmin-generated fibrinogen fragments containing either the RGD motif (fragment C) or the gamma(400-411) sequence (fragment D), and CHO cells expressing resting wild type (alphaIIbbeta3wt), constitutively active (alphaIIbbeta3T562N), or non-functional (alphaIIbbeta3D119Y) receptors. Our data provide evidence that the gamma(400-411) site by itself is able to initiate alphaIIbbeta3 clustering and recruitment of intracellular proteins to early focal complexes, mediating cell attachment, FAK phosphorylation, and Rac1 activation, while the RGD motif subsequently acts as a molecular switch on the beta3 subunit to trigger cell spreading. More importantly, we show that the premier functional role of the RGD site is not to reinforce cell attachment but, rather, to imprint a conformational change on the beta3 subunit leading to maximal RhoA activation and actin cytoskeleton organization in CHO cells as well as in platelets. Finally, alphaIIbbeta3-dependent RhoA stimulation and cell spreading, but not cell attachment, are Src-dependent and phosphoinositide 3-kinase-independent and are inhibited by the Src antagonist PP2.
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PMID:A new functional role of the fibrinogen RGD motif as the molecular switch that selectively triggers integrin alphaIIbbeta3-dependent RhoA activation during cell spreading. 1595 23

Synthetic hydrogels with tunable properties are appealing for regenerative medicine. A critical limitation in hydrogel design at low solids concentration is the formation of defects, which increase gelation times and swelling, and reduce elasticity. Here, we report that trifunctional cross-linking peptides applied to 4-arm poly-(ethylene glycol) (PEG) hydrogels decreased swelling and gelation time relative to bi-functional crosslinkers. In contrast to bi-functional peptides, the third cross-linking site on the peptide created a branch point if an intramolecular cross-link formed, which prevented non-functional "dangling-ends" in the hydrogel network and enhanced the number of elastically active cross-links. The improved network formation enabled mouse ovarian follicle encapsulation and maturation in vitro. Hydrogels with bi-functional crosslinkers resulted in cellular dehydration, likely due to osmosis during the prolonged gelation. For trifunctional crosslinkers, the hydrogels supported a 17-fold volumetric expansion of the tissue during culture, with expansion dependent on the ability of the follicle to rearrange its microenvironment, which is controlled through the sensitivity of the cross-linking peptide to the proteolytic activity of plasmin. The improved network design enabled ovarian follicle culture in a completely synthetic system, and can advance fertility preservation technology for women facing premature infertility from anticancer therapies.
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PMID:Hydrogel network design using multifunctional macromers to coordinate tissue maturation in ovarian follicle culture. 2124 29