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

In the present study ultrastructural localization of binding sites for 5 lectins was studied in rat liver cell surface membrane fractions. For this purpose ferritin-coupled Concanavalin A, wheat germ agglutinin, soybean agglutinin, Ricinus communis agglutinin 120 and Lotus tetragonolobus agglutinin I were used as probes for mannose, N-acetyl glucosamine, N-acetyl galactosamine, galactose and fucose moieties in glycoproteins and glycolipids. Although recent reports suggest presence of glycogroups on the cytoplasmic surface of cellular membranes ultrastructural identification of membrane surfaces in the present study indicated an asymmetric localization of lectin-binding sites exclusively on the extracellular side of the membranes.
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PMID:Lectin-binding sites are found in rat liver cell plasma membrane only on its extracellular surface. 62 8

Iron absorption by intestinal epithelial cells, passage onto plasmatic apotransferrin, and regulation of the process remain largely misunderstood. To investigate this problem, we have set up an in vitro model, consisting in CaCo2 cells (a human colon adenocarcinoma line, which upon cultivation displays numerous differentiation criteria of small intestine epithelial cells). Cells are cultivated in a serum-free medium, containing 1 microgram/ml insulin, 1 ng/ml epidermal growth factor, 10 micrograms/ml albumin-linoleic acid, 100 nM hydrocortisone, and 2 nM T3 on new, transparent, Cyclopore polyethyleneterephthalate microporous membranes coated with type I collagen. Cells rapidly adhere, grow, and form confluent monolayers; after 15 days, scanning electron microscopy reveals numerous uniform microvilli. Domes, which develop on nonporous substrata, are absent on high porosity membranes. Culture medium from upper and lower compartments of microplate inserts and cell lysates were immunoprecipitated after labeling with [3H]glucosamine and leucine; analysis was done by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by autoradiography. [3H]transferrin is found mainly in the lower compartment and in cells; [3H]apolipoprotein B is released in both compartments, and fibronectin almost entirely recovered in the lower compartment; [3H]transferrin receptors and ferritin are only present in cell lysates. Binding experiments also show that transferrin receptors are accessible from the lower compartment. These results suggest that CaCo2 cells, cultivated in synthetic medium on membranes of appropriate porosity, could provide an in vitro model of the intestinal barrier, with the upper compartment of the culture insert corresponding to the apical pole facing the intestinal lumen and the lower one to the basal pole in contact with blood.
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PMID:Iron absorption by intestinal epithelial cells: 1. CaCo2 cells cultivated in serum-free medium, on polyethyleneterephthalate microporous membranes, as an in vitro model. 183 Mar 3

The binding of Phaseolus vulgaris (PHA) isolectins L4 and E4 to the brush border membrane of differentiated Caco-2 cells was studied and the impact on cellular metabolism and microvilli was assessed. Computer analysis of the data based on binding experiments with peroxidase conjugated isolectins gave mean (SD) values for maximal binding of 2540 (151).10(-9) M for PHA-L4 and 2104 (140).10(-9) M for PHA-E4 per mg of brush border membrane protein. The dissociation constants for L4 and E4 binding were 4.3 (1.4).10(-6) M and 1.1 (0.8).10(-6) M, respectively. Incubation of differentiated Caco-2 cells for 30 minutes with ferritin conjugated PHA isolectins showed that, as indicated by the number of ferritin particles, PHA-E4 bound to the microvilli to a greater extent than PHA-L4. Ferritin particles were also localised intracellularly over endocytotic invaginations and vesicles. After incubation for 48 hours with PHA-L4 or PHA-E4, the relative incorporation of precursors for DNA, RNA, and (glyco)protein synthesis into the trichloroacetic acid insoluble fraction of the Caco-2 cells was determined. Both isolectins stimulated the incorporation of thymidine and glucosamine, but neither PHA-L4 nor PHA-E4 were able to influence the incorporation of uridine. With respect to fucose, methionine, and N-acetyl mannosamine, the stimulatory effect remained confined to PHA-E4. Since PHA-L4 and PHA-E4 were tested at the same concentrations, PHA-E4 is more effective than PHA-L4. The changes in the uptake of radioactive precursors were lost after heat inactivation of PHA-E4. Compared with control and PHA-L4 incubated Caco-2 cells, the microvilli of PHA-E4 incubated cells were shortened significantly (p less than 0.01).
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PMID:Binding of kidney bean (Phaseolus vulgaris) isolectins to differentiated human colon carcinoma Caco-2 cells and their effect on cellular metabolism. 186 41

Administration of estrogen to gilts on Days 9 and 10 of pregnancy results in total embryonic loss by Day 18. The present study examined changes in the uterine endometrial surface and secretion during conceptus attachment in control and estrogen-treated (Days 9 and 10) pregnant gilts. Gilts were unilaterally hysterectomized on either Days 12 and 14 or Days 16 and 18 of gestation. Uterine horns were flushed with saline and conceptuses were evaluated. Intact conceptuses were recovered from all control gilts, whereas estrogen-treated gilts contained normal intact conceptuses only on Day 12 of gestation. Antiviral activity, which reflects conceptus viability, was reduced (p less than 0.01) in uterine flushings after Day 14 in estrogen-treated gilts. Culture of endometrial explants with [3H]glucosamine revealed several glycoproteins that are synthesized during the period of conceptus attachment; however, no difference in glycoprotein synthesis between treatment groups was detected by analysis with two-dimensional PAGE and fluorography. Analyses of the uterine epithelium by scanning and transmission electron microscopy demonstrated that estrogen administration caused an alteration in the uterine surface, a thinning of the uterine epithelial glycocalyx, and a reduction of cationic ferritin binding to the microvilli of the uterine epithelium. Results indicate that conceptus mortality after early administration of estrogen is associated with alterations in the uterine endometrial surface during the period of conceptus attachment in the pig.
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PMID:Endometrial surface and secretory alterations associated with embryonic mortality in gilts administered estradiol valerate on days 9 and 10 of gestation. 187 82

We previously reported, in the spontaneously diabetic Bio-Breeding (BB) rat, an increase in horseradish peroxidase (HRP) uptake that was associated with reduction and patching of cationized ferritin (CF) binding to anionic sites on the luminal plasma membrane of the retinal capillary endothelium. To see whether alterations in the negatively charged terminal sugar residues, N-acetyl-glucosamine (NAG) and sialic acid (SA), might contribute to these changes in the diabetic rat retina, we used lectin-ferritin (Fe) conjugates to study the distribution of these sugars on the retinal endothelial luminal membranes. Wheat germ agglutin (WGA, binds to NAG and SA) and Limax flavius (LFA, binds only SA) were used. Plasma membrane WGA-Fe binding was dense and uniform in control animals. Binding sites were also found in coated luminal vesicles, within some uncoated luminal vesicles and on their diaphragms. Unlabeled uncoated luminal vesicles were also seen, suggesting two populations of uncoated vesicles. In diabetic animals, the binding sites were present within the same membrane associated microdomains as in the controls. However, in the majority of outer plexiform layer (OPL) vessels in diabetic animals, WGA-Fe binding was reduced to a single, discontinuous layer of particles (p less than 0.02). In both diabetic and control vessels, WGA-Fe binding was greatly reduced by the addition of competitive sugars. A few particles remained on the plasma membrane, on the diaphragms of some vesicles, and at the edge of vesicles. LFA-Fe binding was similar to that seen with WGA-Fe in the presence of competitive sugars. These results suggest that luminal membranes of retinal capillaries are rich in NAG and contain little SA. The sparse WGA-Fe binding pattern in the diabetic OPL may reflect decreases in number or accessibility of NAG residues, since similar binding patterns are seen in both the control and diabetic animals under conditions specific for SA. Thus, alteration of terminal NAG residues may contribute to decreased luminal surface anionic sites and increased pinocytotic transport in the retinal microvasculature of spontaneously diabetic BB rats.
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PMID:Lectin-ferritin binding on spontaneously diabetic and control rat retinal microvasculature. 270 43

Chrysotile asbestos interacts with mucin-secreting cells of tracheal organ cultures, causing an increase in secretion of mucin into the culture medium. This response occurs in the absence of obvious morphologic damage to tracheal epithelial cells. We speculated that asbestos-induced hypersecretion was regulated by the interaction of fibers with specific carbohydrate residues on the cell surface. To test this hypothesis, lectins, i.e., proteins with a high affinity for mono- and oligosaccharides on the plasma membrane, were added to tissues 30 min before addition of chrysotile. Secretion of mucin into the medium was then determined over a 2-hr period by using incorporation of 3H-glucosamine. Blocking of alpha-D-mannose and alpha-D-glucose residues inhibited chrysotile-induced hypersecretion (p less than 0.05), whereas lectins blocking residues of alpha-D-N-acetylgalactosamine, beta-D-N-acetylglucosamine, alpha-L-fucose and sialic acids were ineffective. Preincubation of cultures with carboxypeptidase A or phospholipase A2, but not with neuraminidase, diminished mucin secretion caused by chrysotile. To determine if the positive surface charge of chrysotile was important in interaction with mucin cells, we examined comparatively the effects of various polycations (cationic ferritin, polylysine, DEAE-dextran) and chrysotile after leaching of fibers to remove Mg2+. Although use of polycations enhanced secretion of mucin, effects were not as striking as those observed with chrysotile. In contrast, leached chrysotile failed to elicit a hypersecretory response. These results suggest the interaction of a positively charged component (presumably Mg2+) of chrysotile with glycolipids and glycoproteins containing terminal residues of alpha-D-mannose or alpha-D-glucose.
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PMID:Studies using lectins to determine mineral interactions with cellular membranes. 631 63

The subcellular location of the major malarial glycoprotein in erythrocytes infected with schizonts of Plasmodium falciparum has been studied by two methods. In the first, glycoproteins were labelled with [3H]glucosamine or [3H]isoleucine during in vitro culture. Trypsin treatment of intact infected erythrocytes caused no major qualitative or quantitative changes in [3H]glucosamine labelled glycoproteins or [3H]isoleucine labelled proteins separated by sodium dodecylsulfate polyacrylamide gel electrophoresis. However, in the presence of Triton X-100 the labelled glycoproteins and proteins were completely cleaved by trypsin. In the second method, two monoclonal antibodies which specifically immunoprecipitate the major 195 kDa glycoprotein failed to react on indirect immunofluorescence with intact non-fixed schizont-infected erythrocytes, but reacted strongly with saponin released schizonts indicating specificity for the surface of mature intracellular parasites. Immunoelectronmicroscopy using ferritin-conjugated secondary antibody confirmed the location of the epitope(s) recognized by these monoclonals on the surface of intracellular parasites. Ferritin particles were not associated with knob-bearing erythrocyte membranes. The results indicate that only a small proportion or none of the 195 kDa glycoprotein is on the surface of the infected erythrocyte and that the largest proportion is expressed on the surface of mature intraerythrocytic parasites.
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PMID:Localization of the major Plasmodium falciparum glycoprotein on the surface of mature intraerythrocytic trophozoites and schizonts. 637 50

A 1-J/cm2 dose of single laser-irradiation applied on primary human embryo fibroblast culture was not followed either by functional or micromorphological alterations of cell surfaces. This dose, however, applied four times with 24-hour intervals changed the functional conditions as well as surface charges of cell membranes. As detection methods, radioactive glucosamine uptake, lectin, and cationized ferritin-binding techniques were applied. At the same time, the scanning and transmission electron microscopy of laser-irradiated cells did not reveal any micromorphological or ultrastructural alterations. The effect of a 5-J/cm2 dose did not differ from that of 1 J/cm2. It is suggested that laser radiation-induced circumstances on cell surfaces can contribute to the strength of cell-to-cell contacts, i.e., to the stimulation of epithelization experienced in the clinical gynecologic practice.
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PMID:Biological effect of He-Ne laser: investigations on functional and micromorphological alterations of cell membranes, in vitro. 652

Corneas with central epithelial wounds, 3 mm in diameter, were organ cultured in the presence of tunicamycin (TM) (1 microgram/ml), an antibiotic that inhibits glycosylation of asparagine-linked glycoproteins. Compared with control corneas, which healed in 22 hr, corneas cultured in the presence of TM for the entire culture time or for only the first 6 hr displayed a progressively slower epithelial healing rate that essentially dropped to zero by 24 hr of culture time. At 24 hr, approximately 75% of the wound was covered. After repeated washings with TM-free culture media (6X, 10 min each), this effect could consistently be reversed in corneas exposed to TM for 6 hr. Incorporation of [3H]glucosamine into trichloroacetic acid-precipitable proteins of migrating epithelial sheets was reduced to 14% that of controls after 12 hr of culture with TM, whereas [14C]leucine incorporation was not significantly affected. The decreased glycosylation was reflected on the cell surface after 12 and 20 hr culture in the presence of TM: apical cell membranes of the first six cells of the leading edge of the migrating sheet bound significantly fewer ferritin-concanavalin A particles per micrometer of membrane than did controls. These results indicate that synthesis of asparagine-linked glycoproteins is required for continued migration of corneal epithelial sheets. The asparagine-linked glycoproteins that are required for migration probably include cell-surface glycoproteins.
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PMID:Epithelial sheet movement: effects of tunicamycin on migration and glycoprotein synthesis. 669 74

The cell surface of Tritrichomonas foetus was characterized by using 18 highly purified lectins with specificities for N-acetyl glucosamine, N-acetyl galactosamine, galactose, mannose, and sialic acid. The specificity of the lectin-induced cell agglutination was verified by inhibition of the agglutination with the specific sugars. By using cytochemical techniques associated with electron microscopy, carbohydrates were detected on the cell surface of T. foetus. The following techniques were used: periodic acid--thiosemicarbazide--silver proteinate, concanavalin A--horseradish peroxidase, and ruthenium red. Anionic sites were detected on the cell surface of the protozoan at pH's 1.8 and 7.2 with the use of colloidal iron hydroxide and cationized ferritin particles, respectively. The binding of colloidal iron particles, as well as the agglutination induced by the lectin from Limulus polyphemus, indicated the presence of sialic acid on the cell surface of T. foetus.
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PMID:Cell surface carbohydrates in Tritrichomonas foetus. 731 Jul 44


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