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PubMed2003

Glycodelin and amniotic fluid transferrin as inhibitors of E-selectin-mediated cell adhesion.

Human amniotic fluid contains a variety of glycoproteins. Several of these substances have been shown to exert immunomodulatory effects. Glycodelin, previously known as placental protein 14, is one of these glycoproteins. It has a unique carbohydrate configuration, consistent with fucosylated LacdiNAc structures that are very unusual for mammals. Oligosaccharides with fucosylated LacdiNAc antennae have previously been shown to block selectin-mediated cell adhesion. Another glycoprotein, human transferrin, is also present in amniotic fluid in relatively high concentrations. This transferrin shows a different glycosylation compared with serum transferrin. Amniotic fluid transferrin carries sialylated Lewis X antigens. Glycodelin and transferrin were isolated from amniotic fluid and for comparison from serum of pregnant women by chromatographic methods. The purified proteins were used as ligands to block E-selectin-mediated HepG2 cell adhesion. Two types of binding assays with distinct receptor accommodations (immobilised E-selectin and activated HUVECs) were used to quantify inhibition efficiencies of the different proteins. We found that glycodelin is a strong inhibitor with a 10(3)-fold potency compared to the monovalent tetrasaccharide sialyl Lewis X whereas the potency of transferrin is rather low.

Adult↗
PubMed2005

Transferrin recycling and dextran transport to lysosomes is differentially affected by bafilomycin, nocodazole, and low temperature.

The effects of bafilomycin, nocodazole, and reduced temperature on recycling and the lysosomal pathway have been investigated in various cultured cell lines and have been shown to vary dependent on the cell type examined. However, the way in which these treatments affect recycling and transport to lysosomes within the same cell line has not been analyzed. In the current study, we used fluorophore-labeled transferrin and dextran as typical markers for the recycling and the lysosomal pathways, respectively, to explore the morphology and the intravesicular pH of endocytic compartments in HeLa cells. The V-ATPase inhibitor bafilomycin selectively inhibited the transport of marker destined for lysosomal degradation in early endosomes, whereas the transport of transferrin to the perinuclear recycling compartment (PNRC) still occurred. The kinetics of transferrin acidification was found to be biphasic, indicative of fast and slow recycling pathways via early endosomes (pH 6.0) and PNRC (pH 5.6), respectively. Furthermore, the disruption of microtubules by nocodazole blocked the transport of transferrin to the PNRC in early endosomes and of lysosome-directed marker into endosomal carrier vesicles. In contrast, incubation at 20 degrees C affected the lysosomal pathway by causing retention of internalized dextran in late endosomes and a delay in transferrin recycling. Taken together, these data clearly demonstrate, for the first time, that the transferrin recycling pathway and transport of endocytosed material to lysosomes are differentially affected by bafilomycin, nocodazole, and low temperature in HeLa cells. Consequently, these treatments can be applied to investigate whether internalized macromolecules such as viruses follow a recycling or degradative pathway.

Cold Temperature↗
PubMed1989

Stimulatory effect of transferrin on the proliferation of embryonic mouse molar pre-odontoblasts and pre-ameloblasts in organ culture.

The effects of transferrin on the proliferation kinetics of these cells from day-14 lower first molars, cultured for 2-6 days in a chemically defined medium supplemented with 5 and 50 micrograms/ml of human diferric transferrin, were studied. Transferrin stimulated the mitotic and [3H]-thymidine labelling indices. These data were correlated with immunolocalization of the transferrin receptor using indirect immunofluorescence and specific monoclonal antibodies. The presence of specific transferrin receptors in pre-odontoblasts and pre-ameloblasts, and in ameloblasts of older teeth (day-18 to day-21), was also assessed by indirect immunofluorescence and binding experiments using iodinated transferrin.

Ameloblasts↗
PubMed1988

A study on the intracellular transport of prothrombin, albumin and transferrin in rat.

The intracellular transport of prothrombin in rat has been studied and compared with the transport of albumin and transferrin. The proteins were immunoisolated from plasma samples after pulse labelling with [3H]leucine and the secretion kinetics were determined. The half-times for secretion (t1/2) were approx. 30, 53 and 75 min for albumin, prothrombin and transferrin, respectively, whereas the minimal transit time for prothrombin was approx. 30 min, and those for albumin and transferrin 15-20 min. After injection of vitamin K-1 into warfarin-treated rats, the accumulated prothrombin precursor was gamma-carboxylated and secreted with a t1/2 of 37 min. This indicates that the gamma-carboxylation of prothrombin in rough endoplasmic reticulum cannot account for the delay in the transport of prothrombin as compared to albumin. Comparison of the incorporation of [3H]leucine and [3H]glucosamine into plasma prothrombin and transferrin suggested that transferrin is secreted randomly from an intracellular pool, whereas prothrombin is transported in a more orderly sequence. Moreover, treatment of rough microsomes with 0.05% sodium deoxycholate indicated that prothrombin is more tightly associated with the membranes of rough endoplasmic reticulum than albumin and transferrin.

Animals↗
PubMed1976

Competitive binding of iron by transferrins from different vertebrates.

1. A competitive dialysis technique has been used to study the relative affinities of the two iron-binding sites on transferrin molecules and the relative binding strengths of transferrins isolated from plasma of different species. 2. The comparisons were extended to include desialylated human transferrin, ovotransferrin, and a cyanogen bromide fragment of the latter. 3. Although the results of bilateral experiments could generally be accounted for in terms of the theory of independent sites, there were some exceptions, and cyclic comparisons were inconsistent. 4. All the comparisons made were compatible with a model in which site-interaction occurred, but it was not possible to decide whether the sites were intrinsically identical or not. For most species this corresponded to positive cooperativity, but for rabbit it was negative. 5. The average affinity of transferrin for iron depended on species, but the variation was never more than about one order of magnitude. 6. No effect on the binding constants for human transferrin could be detected when the sialic acid residues were removed. 7. The fragment of ovotransferrin competed fairly effectively with the native molecule for iron, although the average relative affinity was only about 1:15. 8. The relative binding of iron by ovotranferrin and human transferrin was affected little when bicarbonate anion was replaced by oxalate, although the ratio of the two binding constants for ovotranferrin increased.

Animals↗
PubMed1976

Effect of iron on sedimentation-velocity and gel filtration behaviour of transferrins from several vertebrates.

1. The effect of iron binding on the conformation of transferrins has been studied using analytical gel filtration and differential velocity sedimentation. 2. In all cases where bicarbonate is the anion the transferrin molecules undergo changes in Stokes' radius and sedimentation coefficient of the same order of magnitude, but of opposite sign. 3. Replacement of the bicarbonate ion with oxalate results in smaller changes in these two parameters. 4. In all cases except ovotranferrin, sheep serum transferrin, and human transferrin with oxalate as the anion, changes in Stokes' radius for the addition of the first and second iron atoms are similar. 5. For ovotransferrin and sheep transferrin it is necessary to postulate interaction between the iron-binding sites to account for the change in Stokes' radius caused by the second iron atom binding being greater than for the first. 6. Human transferrin with oxalate as the anion shows a greater change for the first atom bound than for the second which is consistent with the increased size of the oxalate ion compared with bicarbonate.

Animals↗
PubMed1980

The effect of trypsin digestion on the structure and iron-donating properties of transferrins from several species.

The effect of trypsin digestion on iron-saturated and iron-free (apo) human, rabbit, bovine, pig and horse tranferrins has been studied. Iron-binding fragments were produced only from iron-saturated pig and bovine transferrins although some cleavage of the polypeptide chain occurred in all cases. The apo-transferrins were generally degraded to a greater extent than the corresponding iron-saturated proteins. The ability of the different transferrins to donate iron to rabbit reticulocytes varied in the order rabbit approximately pig greater than human approximately horse greater than bovine. Trypsin digestion considerably reduced the ability of pig and bovine transferrins to donate iron to rabbit reticulocytes, slightly reduced the iron-donating ability of rabbit transferrin, and had almost no effect on that of human or horse transferrins.

Animals↗
PubMed1990

The chicken oviduct and embryonic red blood cell transferrin receptors are distinct molecules.

We recently described an estrogen-inducible transferrin receptor from the chicken oviduct. We now report on the comparison of the oviduct transferrin receptor with the transferrin receptor obtained from chick embryo red blood cells. Western blot analysis reveals that rabbit polyclonal antibodies raised against one receptor do not cross react with the heterologous receptor. Furthermore, peptide map analyses of either affinity purified, native [125I]-labelled transferrin receptors (dimers) or dissociated, and repurified monomers obtained from oviducts and embryonic red blood cells yield distinct patterns. Therefore, the estrogen-modulated oviduct transferrin receptor appears to be structurally distinct from the iron-modulated red cell transferrin receptor.

Animals↗
PubMed1990

Transferrin expression in myelinated and non-myelinated peripheral nerves.

Transferrin and its receptor are involved in the delivery of iron to most cells. Previous studies have demonstrated that transferrin is associated with oligodendrocytes, the myelin-producing cells in the central nervous system. In the peripheral nervous system, the Schwann cell produces myelin. This study used immunohistochemistry and immunoblot analysis to determine whether expression of transferrin is unique to myelinated peripheral nerves. Immunohistochemical examination demonstrated cytoplasmic accumulation of transferrin in Schwann cells of the myelinated sciatic nerve, but not in the unmyelinated cervical sympathetic trunk. Immunoblot analysis revealed there is 10 X the amount of transferrin in the sciatic nerve compared to the cervical sympathetic trunk. These results are consistent with the hypothesis that transferrin may play a role in myelination.

Animals↗
PubMed1991

Transferrin can alter physiological properties of retinal neurons.

The role of transferrin as a possible neurotransmitter was examined in cultured chick retinal cells. Brief exposure to transferrin caused a dramatic and transient increase in intracellular calcium levels in approximately 20% of the total population of cultured retinal neurons. The increase in intracellular calcium was observed in cell bodies and neuronal processes. Electrophysiological analysis of a subset of the population, bipolar-like neurons, demonstrated that more than half of these cells responded to the application of transferrin with a transient membrane depolarization. Under voltage clamp conditions, the currents evoked by transferrin were similar to glutamate in that they both displayed non-linear voltage dependence. Furthermore, acute transferrin exposure resulted in a 200% increase in the amount of Na+ independent [3H]glutamate binding observed in these cultures. These results suggest that transferrin may function as a neurotransmitter or neuromodulator in the developing vertebrate nervous system.

Animals↗
PubMed1992

Adaptation of transferrin protein and glycan synthesis.

We report the patterns of variability in transferrin structure in pregnancy, iron deficiency anemia, women using oral contraceptives, nonanaemic rheumatoid arthritis, iron deficient rheumatoid arthritis and anemia of the chronic diseases. Changes in microheterogeneity were assessed by crossed immuno isoelectric focusing of serum transferrin. Intra-individual variation in the control group was minimal. Equally, inter-individual variation in controls and groups with established stable disease was very limited. In pregnancy an increase in transferrin concentration was accompanied by redirection of glycan synthesis to the highly sialylated and highly branched glycans, an effect also shown in women using oral contraceptives. Iron deficiency anemia was accompanied by increased protein core synthesis without the large shifts in the microheterogeneity pattern as seen in pregnancy at similar transferrin concentration. In contrast to this, rheumatoid arthritis was accompanied by decreased protein synthesis while the microheterogeneity pattern shifted significantly towards the highly branched glycans. Interpreted in the respective pathophysiological contexts results show that: (1) N-linked glycosylation of transferrin is a strictly controlled process, both in the physiological states and in disease. (2) Microheterogeneity is determined independently from transferrin protein synthetic rate. (3) Provisionally observed changes in the glycosylation can modulate the biological activity of the glycoprotein and as a result redirect internal iron fluxes. This proposition can be applied to altered iron metabolism in both pregnancy, oral contraceptives and rheumatoid arthritis. Changes are not operative in iron deficiency because qualitatively iron metabolism is not altered in this state.

Adult↗
PubMed1986

Transferrin and the trophic effect of neural tissue on amphibian limb regeneration blastemas.

Nerves promote regeneration of amputated urodele limbs, but the chemical basis of the effect is not known. We have examined the possible involvement of the iron-transport factor transferrin, which is important for cell proliferation and is present in vertebrate nervous tissue. Newt brain extract stimulated incorporation of [3H]thymidine in cultured blastemas from regenerating newt forelimbs, showing a biphasic dose-response similar to that of heterologous transferrin. As shown previously for transferrin, the inhibitory effect of brain extract at high concentrations was relieved by the addition of iron. Activity of brain extract was reduced by treatment with an iron-chelating agent and fully restored by the readdition of iron. Double immunodiffusion of newt tissue extracts and antibodies against newt plasma transferrin demonstrated the presence of transferrin-like factors in brain, spinal cord, and peripheral nerve. These results indicate that activity of transferrin may be part of the trophic effect of brain extract on cultured blastemas.

Animals↗
PubMed1984

Effect of corynetoxin isolated from parasitized annual ryegrass on albumin and transferrin synthesis and secretion by cultured fetal rat hepatocytes.

A group of glycolipid toxins, corynetoxin (CT), isolated from parasitized annual ryegrass, was shown to suppress the synthesis of both albumin and transferrin by cultured fetal rat hepatocytes. Based on [3H]leucine incorporation, inhibition of transferrin synthesis was greater than that of both albumin and total protein synthesis. As a result, the secretion of albumin and transferrin was decreased. The incorporation of [3H]N-AcGlc into cellular glycoproteins was only marginally affected by CT, although a dramatic reduction was observed with respect to the secreted proteins. Transferrin secreted into the culture medium was substantially non-glycosylated, judging by the absence of [3H]N-AcGlc. These studies suggested that the toxin preferentially affects the synthesis, and hence the secretion of glycoproteins, although it did not block the secretion of the proteins albumin and transferrin, as these did not accumulate intercellularly. Since transferrin labelled with [3H]leucine but not [3H]N-AcGlc is detected in the culture medium of hepatocytes exposed to CT, it was concluded that glycosylation of the protein is not required for secretion. This study shows that the effects of CT on protein synthesis and secretion in cultured hepatocytes are similar to those reported for tunicamycin (TM).

Albumins↗
PubMed1990

Proteoglycan synthesis by cultured liver endothelium: the role of membrane-associated heparan sulfate in transferrin binding.

Liver endothelium has been reported to possess membrane receptors for the iron-binding protein transferrin (Tf). Similarly, the core protein of proteoglycans (PG) associated with cell membrane in many cell systems can bind Tf. To find out if membrane-associated proteoglycans can explain Tf-binding ability of liver endothelium, we investigated the synthesis and distribution of proteoglycans by isolated, cultured liver capillary endothelium. Cells were isolated and cultured for 48 h in sulfate-free medium and pulse-labeled with 35SO4. The relative distribution of 35SO4-labeled macromolecules, determined in the extracellular (EC), membrane-associated (MA), and intracellular (IC) pools, was respectively 74, 15, and 10%. Membrane-associated proteoglycan (MA-PG) was further purified by ion exchange and gel chromatography. Glycosaminoglycan (GAG) chain characterization indicated about 78% chondroitin sulfate, 7% dermatan sulfate, and about 14% heparan sulfate (HS). Similar GAG chain characterization was made for PG in the EC and IC pools. Transferrin-binding ability of MA-PG was studied by affinity column chromatography, using CNBr-activated sepharose bound to transferrin. About 15% of the labeled MA-PG was specifically bound to Tf-affinity column and could be eluted by excess soluble Tf. This proportion was similar to the proportion of HS in the total membrane-associated pool. Moreover, the eluted labeled material was susceptible to pretreatment with heparitinase, confirming its HS nature. We conclude that the transport capillary endothelium of the liver can synthesize HS proteoglycans which are membrane-associated and this MA-HS pool can bind transferrin. The finding may provide a molecular basis for transferrin binding to liver endothelium and may explain the subsequent transendothelial transport of iron-transferrin complexes into the liver.

Animals↗
PubMed1990

Lactating mouse mammary cell uptake of 59Fe-transferrin. The effect of KCN, 2,4-dinitrophenol, ethanol and ATP.

1. Amounts of KCN of 0.2, 1.0 and 2.0 X 10(-11) mol in a probe do not prevent the uptake of transferrin iron from lactating mouse mammary gland cells. 2. The effect of 5, 10 and 100 X 10(-11) mol in a probe 2,4-dinitrophenol dissolved in 20% ethanol is also negative on the iron-transferrin uptake from the cell. 3. There is a statistically significant decrease of uptake of transferrin-iron under the influence of 20% ethanol in the incubation mixture (25, 50 and 100 microliters). The effect of ethanol is diminished by 2,4-dinitrophenol in the solution. 4. The uptake of 59Fe-transferrin from cells of lactating gland was blocked by ATP (in amounts 0.5, 1.0 and 10.0 X 10(-11) mol per probe) while other concentrations have no effect. It seems that ATP does not release 59Fe from transferrin, nor help the iron uptake from the cells. 5. All evidence indicates that the uptake of transferrin-iron from lactating mammary gland cells is not an energy dependent process.

2,4-Dinitrophenol↗
PubMed1981

Ultrastructural localization of transferrin synthesis in rat hepatocytes during prenatal and postnatal development.

The synthesis of transferrin has been investigated in rat hepatocytes during pre- and postnatal development of the liver by ultrastructural immunoperoxidase cytochemistry. Transferrin was detected in fetal and postnatal hepatocytes on the rough endoplasmic reticulum and in the Golgi apparatus, but the amount and distribution of the protein varied according to the stage of the hepatocyte maturation. Between days 13 and 19 of gestation, nearly all hepatocytes exhibited transferrin. After day 20 of pregnancy more and more unstained hepatocytes were detected. Two periods (19th day of gestation and one day after birth) were characterized by an intense labeling of the Golgi apparatus; in contrast, only a small amount of transferrin was located in this organelle at other stages of the rat liver development. The accumulation of transferrin in the Golgi apparatus is interpreted as a transitory storage of the protein. Transferrin could be produced by immature as well as mature hepatocytes.

Animals↗
PubMed1985

Specificity of chicken and mammalian transferrins in myogenesis.

Chicken transferrins isolated from eggs, embryo extract, serum or ischiatic-peroneal nerves are able to stimulate incorporation of [3H]thymidine, and promote myogenesis by primary chicken muscle cells in vitro. Mammalian transferrins (bovine, rat, mouse, horse, rabbit, and human) do not promote [3H]thymidine incorporation or myotube development. Comparison of the peptide fragments obtained after chemical or limited proteolytic cleavage demonstrates that the four chicken transferrins are all indistinguishable, but they differ considerably from the mammalian transferrins. The structural differences between chicken and mammalian transferrins probably account for the inability of mammalian transferrins to act as mitogens for, and to support myogenesis of, primary chicken muscle cells.

Animals↗
PubMed1989

Seminal plasma transferrin concentration in idiopathic oligozoospermia.

To investigate whether or not transferrin production is decreased in the testis of idiopathic oligozoospermia, the seminal plasma transferrin concentration was measured and the values were compared in two groups (15 men of pregnancy-proved normozoospermia and 22 patients with idiopathic oligozoospermia). Seminal plasma transferrin concentration in the pregnancy-proved normozoospermic group was 78.5 +/- 37.9 micrograms/mL, and the concentration in the patients with idiopathic oligozoospermia was 44.4 +/- 37.6 micrograms/mL. There was a significant difference between them (P less than 0.01). The patients with idiopathic oligozoospermia could be divided into two subgroups according to seminal plasma transferrin concentration and serum gonadotropin levels. One group had high transferrin levels with elevated serum gonadotropin levels. The results indicate that the determination of seminal plasma transferrin concentration is one of the useful parameters for evaluation of testicular function and also suggest that additional studies may allow for the subdivision of the patients with so-called idiopathic oligozoospermia.

Adolescent↗