Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have prepared a conjugate of the plasminogen activator urokinase (UK) and ferritin, which maintains fibrinolytic activity. Monolayers of BALB/c-3T3 cells and of Rous sarcoma virus-transformed highly malignant line AA12-3T3, subcultured in plasminogen-free serum, were incubated with UK-ferritin at 0 degree and processed for transmission electron microscopy. Under these conditions, both of the lines showed specific receptors on the cell surface that were distributed in singlets, in small or large clusters. In the presence of excess native UK, the binding of ferritin was reduced by 99%, indicating the interaction of UK:ferritin with a specific receptor. The ligand-receptor interaction involves the catalytic site of UK, since the binding was completely impaired by preincubation of UK:ferritin with p-aminobenzamidine, a competitive inhibitor of the catalytic site of UK. The number and density of receptors decreased about one order of magnitude on the membrane of AA12 cells when compared with normal 3T3 cells. Saturation kinetics, using 125I-labeled UK, indicate the presence of 4 X 10(4) and 2.5 X 10(3) receptors on the membrane of 3T3 and AA12 cells, respectively. At 37 degrees, UK:ferritin redistributed on the plane of the membrane, in a process which was faster in malignant than in normal cells. Ferritin particles clustered in large groups on coated areas of the surface and were internalized by adsorptive pinocytosis. After 10 min at 37 degrees, the vesicles showed a progressively deeper internalization and a fusion with lysosomes, and some were observed in the Golgi complex area. Since the experiments were planned in order to exclude the presence of protease-nexin in the incubation medium, these data suggest the existence of a plasminogen-independent novel receptor for the catalytic site of plasminogen activators, the number on the cell surface of which decreases in Rous sarcoma virus-transformed mouse fibroblasts.
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PMID:Receptors for plasminogen activator, urokinase, in normal and Rous sarcoma virus-transformed mouse fibroblasts. 298 11

Using a direct conjugate of urokinase and ferritin, the binding has been followed at the plasma membrane and the internalization of urokinase into BALB/C-3T3 fibroblasts, cultured in plasminogen-free conditions. At 0 degree C, the conjugate was observed bound on both coated and uncoated cell surface regions as singlets, and small and large clusters. No binding was observed in the presence of excess native urokinase. The binding was impaired by preincubation of the conjugate with a competitive inhibitor of the catalytic site, suggesting an interaction between the receptor and the catalytic site of the enzyme. Within 1 min at 37 degrees C, urokinase clustered on coated regions of the plasma membrane. At 5 min after warming, ferritin was found on deeply indented coated pits and in both coated and uncoated vesicles close to the cell surface. By 10 min at 37 degrees C, ferritin particles were present in uncoated endosomes and in multivesicular bodies in the Golgi area. Within 10 min, the receptors on the surface strongly decreased. New receptors were observed on the membrane after 20 min at 37 degrees C. At this time, ferritin was observed both in endosomes or multivesicular bodies and in vesicles close to the plasma membrane.
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PMID:Plasminogen activator: morphological evidence of binding, internalization and delivery to lysosomes in 3T3 mouse fibroblasts. 299 2

We have found the existence of specific receptors for the plasminogen activator, urokinase, in A431 human epidermoid carcinoma cells, cultures in plasminogen-free conditions. Two subsets of receptors have been recognized on the basis of 125I-labelled urokinase binding analysis: about 1 X 10(3) high-affinity (Kd = 5.0 X 10(-11) M) and 1 X 10(5) low-affinity (Kd = 9 X 10(-9) M) receptors per cell. The electron microscopic observation of a urokinase: ferritin conjugate has shown single and clustered receptors at the cell surface. Down-regulation of the receptors (T1/2 = 3.77 h) follows the binding of urokinase. The binding does not involve an intact catalytic site and is inhibited by a monoclonal antibody against the Mr 17500 proteolytic fragment of the A chain of urokinase.
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PMID:The Mr 17500 region of the A chain of urokinase is required for interaction with a specific receptor in A431 cells. 300 4

We have recently shown that urokinase-type plasminogen activator (u-PA) and plasminogen activator inhibitor type 1 are both found extracellularly beneath cultured human skin fibroblasts and HT-1080 sarcoma cells, but in distinct localizations. Here, the ultrastructural distribution of u-PA was studied using immunoferritin electron microscopy. In HT-1080 cells, u-PA on the extracellular aspect of the plasma membrane was detected at sites of direct contact of the cell with the growth substratum beneath all parts of the ventral cell surface. The ferritin-labeled adhesion plaques, which were enriched in submembraneous microfilaments, were frequently seen at the leading lamellae of the cells as well as in lamellipodia and microspikes. Besides the cell-substratum adhesion plaques, ferritin label was detected at cell-cell contact sites. Double-label immunofluorescence showed a striking colocalization of u-PA and vinculin in both HT-1080 cells and WI-38 lung fibroblasts, which is consistent with u-PA being a focal contact component. The u-PA-containing focal contacts of WI-38 cells had no direct codistribution with fibronectin fibrils. In WI-38 cells made stationary by cultivation in a medium containing 0.5% FCS, vinculin plaques became highly elongated and more centrally located, whereas u-PA immunolabel disappeared from such focal adhesions. These findings show that plasma membrane-associated u-PA is an intrinsic component of focal contacts, where, we propose, it enables directional proteolysis for cell migration and invasion.
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PMID:Ultrastructural localization of plasma membrane-associated urokinase-type plasminogen activator at focal contacts. 312 96

Activation of covalently intact plasminogen by tissue-type plasminogen activator (tPA) is facilitated by a majority of proteins subjected to denaturing conditions. Except for heat-denatured apoferritin, the denatured proteins examined require partial proteolysis by plasmin for cofactor activity. The same proteins in their native state are resistant to proteolysis with plasmin and develop no activity. Denatured preparations of apoferritin, antithrombin, alpha1-protease inhibitor, alpha2-macroglobulin, and albumin also accelerate des(1-77)-plasminogen activation by tPA. The rate enhancements are comparable with that of the fibrin(ogen) fragments on a w/w basis. The cofactor activities are inhibited by 6-aminohexanoate and inactivated by pepsin. Analysis of heat-denatured apoferritin and albumin preparations by ultracentrifugation and gel chromatography indicates that cofactor is associated predominately with aggregates, which have binding capacity for both tPA and zymogen. Heat-denatured albumin pretreated with plasmin decreases K(M) and increases k(cat) for both intact plasminogen and des(1-77)-plasminogen activation by tPA, yielding catalytic efficiencies in excess of 8 x 10(3) M(-1) s(-1) and 2 x 10(4) M(-1) s(-1), respectively. Because of enhanced plasmin-catalyzed proteolysis of plasminogen to des(1-77)-plasminogen, activation by urokinase-type plasminogen activator is also facilitated by denatured proteins; activation of des(1-77)-plasminogen is not affected. It is concluded that denatured proteins serve as both cofactors and substrates in the fibrinolytic system, and that enhancement of plasminogen activation by denatured proteins is mechanistically indistinguishable from that observed with fibrin.
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PMID:Denatured proteins as cofactors for plasminogen activation. 926 48

Urokinase-type plasminogen activator (uPA) on prostate cancer cell surfaces mediates pericellular proteolysis and destruction of extracellular matrix barriers to tumor invasion and metastasis. Increased expression of tumor-associated uPA leads to enhanced tumor dissemination and poor cancer outcomes in men with prostate cancer. Expression of uPA is regulated in part by the oxidant-sensitive transcription factor, NF-kappa B (NF-kappaB), which is activated by intracellular reactive oxygen intermediates (ROI). This study examined the effect of iron on the production of ROI, activation of NF-kappaB and expression of uPA in the human prostate cancer cell line, PC-3. Treatment of PC-3 cells with iron in the form of ferric nitrilotriacetate (FeNTA) in the absence of added transferrin resulted in a dose-dependent increase in cellular ferritin content in both the presence and absence of neutralizing antibody to the transferrin receptor. Cellular uptake of iron resulted in stimulation of intracellular ROI production, and increases in uPA mRNA, antigen, and activity. Concurrent treatment with the iron chelator, desferrioxamine (DFO) abrogated these effects, and treatment with DFO alone inhibited constitutive uPA production. Finally, we observed nuclear translocation, and therefore activation of NF-kappaB in response to iron exposure. We conclude that iron enters PC-3 cells via a non-transferrin dependent pathway and increases uPA expression. Our data indicate that one mechanism by which iron may stimulate uPA production is through the generation of intracellular ROI and activation of NF-kappaB-mediated signaling pathways.
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PMID:Iron stimulates urokinase plasminogen activator expression and activates NF-kappa B in human prostate cancer cells. 1757 74