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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

Proteodermatan sulfate was isolated from the skin of human, female breast in 6-M urea and proteolytic inhibitors at 70 degrees C and purified on Sephacryl S-200. It was composed of 55% protein and 45% dermatan sulfate, displayed one protein and carbohydrate-stainable band on agarose-polyacrylamide gels, yielded dermatan sulfate after digestion by papain, and its calculated E0.1% 1 cm, 280 nm was 16.2. Its mucopolysaccharide portion was digested by chondroitinase ABC but not by chondroitinase AC. This proteoglycan was used to immunize rabbits. Double diffusion of antiserum against the antigen or its core protein resulted in one precipitation band. Antiserum did not cross-react with bovine collagen type I, human fibronectin, dermatan sulfate, hyaluronic acid, heparin, heparan sulfate or the chondroitin sulfates by double diffusion. The antiserum titer determined by radioimmunoassay was 1:16,000. This assay was not affected by a 40-fold excess of dermatan sulfate. Purified IgG molecules were apparently associated with collagen in human breast mid-dermis as demonstrated by indirect immunoelectron microscopy with ferritin-labeled goat antirabbit IgG. The results indicate that rabbit anti-human, anti-proteodermatan sulfate IgG is highly specific for the core protein of dermatan sulfate and confirm the hypothesis that in vivo proteodermatan sulfate is closely associated with collagen.
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PMID:Immunoelectron microscopy of proteodermatan sulfate in human mid-dermis. 315 40

When human blood platelets spread on a substratum they increase their surface area as much as 4-fold. We investigated the mechanism of spreading by light microscopy and by scanning and transmission electron microscopy. Contact of a platelet with a glass surface induces formation of thin extensions which spread out over the substratum. These extensions resemble the actin-containing microspikes and lammelipodia of tissue cells in culture and appear to be drawn from the peripheral cortical layer associated with the plasma membrane. If platelets are initially labeled on their external surface with cationic ferritin or lentil-conjugated gold particles and then allowed to spread, the labels are retained in the central region, or granulomere. Proteins released by the spreading platelet--fibronectin and fibrinogen--also remain in this central unspread region. Peripheral regions of spread platelet surface (hyalomere) were unlabeled following the above procedures but could be labeled with cationic ferritin or lentil-conjugated gold provided these were applied after spreading was completed. These markers are cleared with time from the periphery, moving centripetally to accumulate at the granulomere. We suggest, on the basis of these observations, that platelets spread onto a substratum by a closely similar mechanism to that used by cells such as fibroblasts. In both cases the spreading involves the peripheral actin cortex and is accompanied by a continual centripetal movement of surface components--a "membrane flow"--which continues even after spreading is completed.
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PMID:Surface movements during the spreading of blood platelets. 316 30

Fibronectin was immunolocated in embryonic chick bone marrow by the use of both a direct peroxidase conjugated antiserum and an indirect Streptavidin bridge technique. Fibronectin is located in the extravascular granulopoietic compartment and, to a lesser extent, in the vascular, erythropoietic compartment. There is no evidence of fibronectin being associated with blood-stromal cell interactions involving either erythropoiesis or thrombopoiesis. However, mature thrombocytes display a substantial surface coat containing fibronectin. Much of the fibronectin appears to be situated on surfaces of those fibroblastic stromal cells which support granulopoiesis. Fibronectin containing extracellular material connects surfaces of developing granulocytes with surfaces of stromal cells. Fibronectin is a surface component of granulocytes as well as nearby stromal cells. However, there appear to be fewer ferritin particles per unit of surface on granulocytic cells. Many of the ferritin particles are not clearly associated with amorphous matrix material at cell surfaces. Immunocytochemical attempts to identify laminin were unsuccessful. These studies indicate that fibronectin is situated at sites where it could mediate adhesive interaction between granulopoietic cells and their stromal cells. Furthermore, cell surface-matrix interaction involving fibronectin could mediate migration of blood cells within the extravascular spaces.
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PMID:Ultrastructural localization of fibronectin in bone marrow of the embryonic chick and its relationship to granulopoiesis. 329 94

A trophoblast-like cell line, TL, was established from a normal-term human placenta. The TL cells were epithelial in morphology with relatively large vesicular nuclei, prominent nucleoli, and numerous microvilli on the cell surface. Cytoplasmic organelles were generally sparse but mitochondria and polysomes were abundant. The cells grew as compact sheets with close membrane approximation interconnected occasionally by desmosome-like junctions. TL cells contained placental alkaline phosphatase, a placenta-associated antigen, cytokeratin, and prekeratin, but not keratin. In parallel, they were negative for factor VIII, vimentin, and fibronectin. Population doubling time was estimated to be about 34 h. TL cells were tumorigenic in nude mice and an increase in tumorigenicity was observed after a certain number of passages in vitro. Chromosome analysis revealed that TL cells were highly heterogenous and had a female aneuploid karyotype with a hypotriploid mode. Unlike trophoblastic cell lines established from neoplastic tissues, TL cells did not synthesize human chorionic gonadotropin or other gonadal hormones, and only a small amount of ferritin (40.3 ng/10(6) cells) could be detected in the cell supernatant and cell extract. Based on various morphological and histochemical criteria, we suggest that the TL cells are derived from the Langhans cells (villous cytotrophoblast), and due to their special features, the cells may be valuable for the study of the differentiation and tumorigenesis of trophoblastic cells.
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PMID:Establishment and characterization of a tumorigenic trophoblast-like cell line from a human placenta. 358 Oct 66

The distribution of sialic acid moieties in the trabecular wall of Schlemm's canal in normal human and monkey eyes, as well as in limited tissue samples from patients with primary open-angle glaucoma (POAG), was investigated by using polycationic ferritin (PCF) at varying pH and colloidal iron at pH 1.8. At pH 1.8-1.9, both PCF and colloidal iron labeled the luminal surface of the endothelial cells of Schlemm's canal in normotensive monkey and human eyes, whereas binding was sparse and random on the basal surface. At a pH of 3.3 and higher, PCF showed increased binding that was confirmed exclusively to the luminal surface of the cells. In trabeculectomy tissue samples from eyes with POAG, PCF at pH 1.9 showed a greater density of labeling on both the basal and luminal cell surfaces, as well as in the subendothelial region, than was observed in normotensive eyes. Given the fact that sialic acid is a moiety which stabilizes cell membranes, we suggest that in normal eyes the absence of sialated molecules on the basal cell surface leaves 'receptor' sites for the initiation of the macrovacuolation process which allows the bulk outflow of aqueous humor across the endothelial barrier of Schlemm's canal. Our preliminary observations in glaucomatous eyes indicate a loss of such receptor sites, which may account for the depletion of macrovacuolar configurations in cases of advanced POAG. Our discussion relates these findings to the pathogenesis of POAG and to the possible role for a defective transmembrane interaction of the surface glycoproteins (fibronectin and laminin) with the cytoskeleton of the endothelial cells lining Schlemm's canal and the cells in the pericanalicular tissue.
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PMID:Localization of sialic acid moieties in the endothelial lining of Schlemm's canal in normal and glaucomatous eyes. 358 14

Fibronectin is an anionic asialoglycoprotein that is found on a variety of cell types. This study was undertaken in an attempt to localize fibronectin to the rat retinal pigment epithelium with ultrastructural immunocytochemistry. Using Fab-HRP conjugates specific for fibronectin, reaction product was localized on the surface of the apical processes and within the cell to GERL. After treatment of tissue by the biotin-avidin method employing ferritin-avidin, ferritin particles marked the apical processes in a quasi-regular distribution. Tufts of particles were separated by a linear distance of 65-85 nm. Fibronectin was not localized to rod outer segments.
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PMID:Immunocytochemical localization of fibronectin to the retinal pigment epithelium of the rat. 370 34

Ricinus communis agglutinin I (RCA-I), a lectin that binds to D-galactosyl residues, intensely stained capillaries in cryostat sections of canine cerebral cortex when evaluated by the avidin-biotin-peroxidase complex method. Of seven lectins tested, only RCA-I gave strong staining of vessels and capillaries with little staining of other cortical cells. Ultrastructural studies using ferritin-, biotin-, and peroxidase-labeled RCA-I indicated that this lectin was bound to the luminal membrane of the cerebral capillary endothelial cell and that lectin receptors were distributed continuously along this membrane. Plasmalemma invaginations that bound RCA-I were also present in endothelial cells. Primary cultures of cerebral capillary endothelial cells grown on plastic or gelatin-coated glass substrates demonstrated staining of the cell membrane and perinuclear structures which appeared to be the Golgi complex and secondary lysosomes. These staining characteristics were retained when the cells were subcultured and were confirmed by ultrastructural studies. In contrast, light microscopy showed that fibronectin was more widely distributed in the cytoplasm, a finding consistent with its occurrence in the endoplasmic reticulum. This work provides support for the concept that lectins may be useful endothelial cell markers in both intact tissue and cell culture.
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PMID:Light and electron microscopic localization of D-galactosyl residues in capillary endothelial cells of the canine cerebral cortex. 370 Oct 30

Previous studies suggest that the baby hamster kidney (BHK) cell fibronectin receptor is also a wheat germ agglutinin receptor (WGA-R). To analyze this possibility further, IgG and Fab fragments of antibodies produced against a BHK cell WGA-R preparation were tested to determine their effects on cell adhesion mediated by fibronectin, wheat germ agglutinin, concanavalin A, and polycationic ferritin. The WGA-R preparation was isolated by octylglucoside extraction of BHK cells followed by chromatography of the extract on WGA-agarose. The antibodies against the WGA-R preparation reacted primarily with polypeptides of molecular weights 48, 61, 83, 105, 120, 165, 210, and 230 kilodaltons (kdaltons). It was concluded that the antibodies interfered with BHK cell fibronectin receptors on the basis of the ability of anti-WGA-R IgG or Fab fragments to (a) inhibit cell spreading on fibronectin-coated substrata; (b) cause rounding and detachment of cells previously spread on fibronectin-coated substrata; and (c) inhibit binding of fibronectin-coated latex beads to the cells. Antibody activity was blocked by treatment of anti-WGA-R with the WGA-R preparation or by absorption of anti-WGA-R with intact BHK cells. The antibodies also appeared to prevent coupling of ligand-receptor complexes (involving concanavalin A or polycationic ferritin) with the cytoskeleton. Finally, cell rounding and detachment caused by the antibodies were found to require metabolic energy since it did not occur in the presence of azide or at 4 degrees C.
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PMID:Inhibition of fibronectin receptor function by antibodies against baby hamster kidney cell wheat germ agglutinin receptors. 629 59

Successful invasion of mammalian cells by pathogenic parasites is generally considered, from circumstantial evidence, to be a consequence of specific mechanisms of recognition of cell surface components--this has stimulated investigations of the biochemical characterization of such molecules. Several studied of trypanosomiasis have examined the ability of parasites to interact with mammalian cells. However, knowledge of the mammalian cell surface 'receptors' which interact with the parasite is limited. We now report that fibronectin, which is a high molecular weight glycoprotein present in blood, connective tissue and at cell surfaces, binds specifically to Trypanosoma cruzi trypomastigotes. The reaction is specific, reversible (in the presence of a 100-fold molar excess of unlabelled ligand) and of moderate affinity (Kd = 11.36 nM). Various other proteins (for example, thyroglobulin, ferritin, catalase, aldolase, human IgG and bovine serum albumin) had no significant effect on the binding of labelled ligand to the parasite surface. Addition of anti-fibronectin antibodies to the culture medium significantly inhibited the infection of rat fibroblasts (3T3 FR) by T. cruzi trypomastigotes, suggesting that cell surface fibronectin may act as a recognition site for attachment of the parasites.
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PMID:Fibronectin receptors on Trypanosoma cruzi trypomastigotes and their biological function. 632 89


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