Journal articles: 'Transferrin – Receptors'

1

Kawabata, Hiroshi. "Transferrin and transferrin receptors update." Free Radical Biology and Medicine 133 (March 2019): 46–54. http://dx.doi.org/10.1016/j.freeradbiomed.2018.06.037.

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Richard, Cyrielle, and Frédérique Verdier. "Transferrin Receptors in Erythropoiesis." International Journal of Molecular Sciences 21, no. 24 (December 19, 2020): 9713. http://dx.doi.org/10.3390/ijms21249713.

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Erythropoiesis is a highly dynamic process giving rise to red blood cells from hematopoietic stem cells present in the bone marrow. Red blood cells transport oxygen to tissues thanks to the hemoglobin comprised of α- and β-globin chains and of iron-containing hemes. Erythropoiesis is the most iron-consuming process to support hemoglobin production. Iron delivery is mediated via transferrin internalization by the endocytosis of transferrin receptor type 1 (TFR1), one of the most abundant membrane proteins of erythroblasts. A second transferrin receptor—TFR2—associates with the erythropoietin receptor and has been implicated in the regulation of erythropoiesis. In erythroblasts, both transferrin receptors adopt peculiarities such as an erythroid-specific regulation of TFR1 and a trafficking pathway reliant on TFR2 for iron. This review reports both trafficking and signaling functions of these receptors and reassesses the debated role of TFR2 in erythropoiesis in the light of recent findings. Potential therapeutic uses targeting the transferrin-TFR1 axis or TFR2 in hematological disorders are also discussed.

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Huebers, H. A., and C. A. Finch. "The physiology of transferrin and transferrin receptors." Physiological Reviews 67, no. 2 (April 1987): 520–82. http://dx.doi.org/10.1152/physrev.1987.67.2.520.

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FAST, Beate, Katrin KREMP, Michael BOSHART, and Dietmar STEVERDING. "Iron-dependent regulation of transferrin receptor expression in Trypanosoma brucei." Biochemical Journal 342, no. 3 (September 5, 1999): 691–96. http://dx.doi.org/10.1042/bj3420691.

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Transferrin is an essential growth factor for African trypanosomes. Here we show that expression of the trypanosomal transferrin receptor, which bears no structural similarity with mammalian transferrin receptors, is regulated by iron availability. Iron depletion of bloodstream forms of Trypanosoma brucei with the iron chelator deferoxamine resulted in a 3-fold up-regulation of the transferrin receptor and a 3-fold increase of the transferrin uptake rate. The abundance of expression site associated gene product 6 (ESAG6) mRNA, which encodes one of the two subunits of the trypanosome transferrin receptor, is regulated 5-fold by a post-transcriptional mechanism. In mammalian cells the stability of transferrin receptor mRNA is controlled by iron regulatory proteins (IRPs) binding to iron-responsive elements (IREs) in the 3′-untranslated region (UTR). Therefore, the role of a T. brucei cytoplasmic aconitase (TbACO) that is highly related to mammalian IRP-1 was investigated. Iron regulation of the transferrin receptor was found to be unaffected in δaco::NEO/δaco::HYG null mutants generated by targeted disruption of the TbACO gene. Thus, the mechanism of post-transcriptional transferrin receptor regulation in trypanosomes appears to be distinct from the IRE/IRP paradigm. The transferrin uptake rate was also increased when trypanosomes were transferred from medium supplemented with foetal bovine serum to medium supplemented with sera from other vertebrates. Due to varying binding affinities of the trypanosomal transferrin receptor for transferrins of different species, serum change can result in iron starvation. Thus, regulation of transferrin receptor expression may be a fast compensatory mechanism upon transmission of the parasite to a new host species.

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Moura, Ivan C., Olivier Hermine, Catherine Lacombe, and Patrick Mayeux. "Erythropoiesis and transferrin receptors." Current Opinion in Hematology 22, no. 3 (May 2015): 193–98. http://dx.doi.org/10.1097/moh.0000000000000133.

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6

Anderson, Gregory J., June W. Halliday, and Lawrie W. Powell. "Transferrin receptors in hemochromatosis." Hepatology 7, no. 5 (September 1987): 967–69. http://dx.doi.org/10.1002/hep.1840070529.

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7

Kuiper-Kramer, Ellen P. A., Jules L. L. M. Coenen, Carla M. S. Huisman, André Abbes, Jan van Raan, and Henk G. van Elsacker. "Relationship between Soluble Transferrin Receptors in Serum and Membrane-Bound Transferrin Receptors." Acta Haematologica 99, no. 1 (January 29, 1998): 8–11. http://dx.doi.org/10.1159/000040707.

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8

Hirata, T., P. B. Bitterman, J. F. Mornex, and R. G. Crystal. "Expression of the transferrin receptor gene during the process of mononuclear phagocyte maturation." Journal of Immunology 136, no. 4 (February 15, 1986): 1339–45. http://dx.doi.org/10.4049/jimmunol.136.4.1339.

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Abstract The expression of transferrin receptors by blood monocytes, human alveolar macrophages, and in vitro matured macrophages was evaluated by immunofluorescence, radioligand binding, and Northern analysis, using the monoclonal anti-human transferrin receptor antibody OKT9, [125I]-labeled human transferrin and a [32P]-labeled human transferrin receptor cDNA probe, respectively. By immunofluorescence, the majority of alveolar macrophages expressed transferrin receptors (86 +/- 3%). The radioligand binding assay demonstrated the affinity constant (Ka) of the alveolar macrophage transferrin receptor was 4.4 +/- 0.7 X 10(8) M-1, and the number of receptors per cell was 4.4 +/- 1.2 X 10(4). In marked contrast, transferrin receptors were not present on the surface or in the cytoplasm of blood monocytes, the precursors of the alveolar macrophages. However, when monocytes were cultured in vitro and allowed to mature, greater than 80% expressed transferrin receptors by day 6, and the receptors could be detected by day 3. Consistent with these observations, a transferrin receptor mRNA with a molecular size of 4.9 kb was demonstrated in alveolar macrophages and in vitro matured macrophages but not in blood monocytes. Thus, although blood monocytes do not express the transferrin receptor gene, it is expressed by mature macrophages, an event that probably occurs relatively early in the process of monocyte differentiation to macrophages.

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9

Cerneus, DP, GJ Strous, and A. van der Ende. "Bidirectional transcytosis determines the steady state distribution of the transferrin receptor at opposite plasma membrane domains of BeWo cells." Journal of Cell Biology 122, no. 6 (September 15, 1993): 1223–30. http://dx.doi.org/10.1083/jcb.122.6.1223.

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Trophoblast-like BeWo cells form well-polarized epithelial monolayers, when cultured on permeable supports. Contrary to other polarized cell systems, in which the transferrin receptor is found predominantly on the basolateral cell surface, BeWo cells express the transferrin receptor at both apical and basolateral cell surfaces (Cerneus, D.P., and A. van der Ende. 1991. J. Cell Biol. 114: 1149-1158). In the present study we have addressed the question whether BeWo cells use a different sorting mechanism to target transferrin receptors to the cell surface, by examining the biosynthetic and transcytotic pathways of the transferrin receptor in BeWo cells. Using trypsin and antibodies to detect transferrin receptors at the cell surface of filter-grown BeWo cells, we show that at least 80% of newly synthesized transferrin receptor follows a direct pathway to the basolateral surface, demonstrating that the transferrin receptor is efficiently intracellularly sorted. After surface arrival, pulse-labeled transferrin receptor equilibrates between apical and basolateral cell surfaces, due to ongoing transcytotic transport in both directions. The subsequent redistribution takes over 120 min and results in a steady state distribution with 1.5-2.0 times more transferrin receptors at the basolateral surface than at the apical surface. By monitoring the fate of surface-bound 125I-transferrin, internalized either from the apical or basolateral surface transcytosis of the transferrin receptor was studied. About 15% of 125I-transferrin is transcytosed in the basolateral to apical direction, whereas 25% is transcytosed in the opposite direction, indicated that the fraction of receptors involved in transcytosis is roughly twofold higher for the apical receptor pool, as compared to the basolateral pool. Upon internalization, both apical and basolateral receptor pools become redistributed on both surfaces, resulting in a twofold higher number of transferrin receptors at the basolateral surface. Our results indicate that in BeWo cells bidirectional transcytosis is the main factor in surface distribution of transferrin receptors on apical and basolateral surfaces, which may represent a cell type-specific, post-endocytic, sorting mechanism.

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10

Steinle, Alexander. "Transferrin‘ activation: Bonding with transferrin receptors tunes KLRG1 function." European Journal of Immunology 44, no. 6 (May 7, 2014): 1600–1603. http://dx.doi.org/10.1002/eji.201444670.

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11

Bretscher, M. S. "Expression and changing distribution of the human transferrin receptor in developing Drosophila oocytes and embryos." Journal of Cell Science 109, no. 13 (December 15, 1996): 3113–19. http://dx.doi.org/10.1242/jcs.109.13.3113.

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In order to understand better the membrane systems in a developing Drosophila oocyte, the human transferrin receptor has been expressed there. This was achieved using the armadillo promoter combined with K10 or oskar trailer sequences; these enable the messenger RNA to be transcribed in nurse cells and then transported to, and translated in, oocytes. This is the first exogenous protein to be expressed in oocytes. At stage 8, the transferrin receptors are mainly concentrated towards the posterior pole of the oocyte and are associated with large cytoplasmic vesicles; when combined with the shibire mutation the transferrin receptors are transferred to the oolemma, demonstrating that they participate in an endocytic cycle. At stage 10, the transferrin receptors are localised either to the anterior margin of the oocyte or to the posterior pole, depending on where the mRNA is located. In newly laid eggs, all the transferrin receptors are found in large cytoplasmic vesicles. The results reveal remarkable sorting processes which occur as oocytes mature and show that ring canals, which separate the oolemma from nurse cell plasma membranes, act as barriers to prevent components in these two compartments from intermixing.

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12

Gray-Owen, Scott D., and Anthony B. Schyvers. "Bacterial transferrin and lactoferrin receptors." Trends in Microbiology 4, no. 5 (May 1996): 185–91. http://dx.doi.org/10.1016/0966-842x(96)10025-1.

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13

Beguin, Y., H. A. Huebers, B. Josephson, and C. A. Finch. "Transferrin receptors in rat plasma." Proceedings of the National Academy of Sciences 85, no. 2 (January 1, 1988): 637–40. http://dx.doi.org/10.1073/pnas.85.2.637.

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14

Orita, T., T. Akimura, T. Nishizaki, T. Kamiryo, Y. Ikeyama, H. Aoki, and H. Ito. "Transferrin receptors in injured brain." Acta Neuropathologica 79, no. 6 (April 1990): 686–88. http://dx.doi.org/10.1007/bf00294248.

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15

Intragumtornchai, T., H. A. Huebers, M. Eng, and C. A. Finch. "In vivo transferrin-iron receptor relationships in erythron of rats." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 255, no. 2 (August 1, 1988): R326—R331. http://dx.doi.org/10.1152/ajpregu.1988.255.2.r326.

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Quantitative measurements of transferrin receptors, tissue transferrin, tissue iron uptake, and erythroid cellularity have been carried out in rats with altered erythropoiesis and altered iron balance. Erythroid receptors increased with erythroid hyperplasia, with the increase in proportion to the increased number of red cell precursors in phenylhydrazine-treated rats. Receptors increased disproportionately in iron deficiency due to both erythroid hyperplasia and an increase in receptors in the individual cell. There was a ratio of 1:1 between cell-related transferrin and receptors in circulating reticulocytes but a disproportionate amount of cell-related transferrin in fixed erythroid tissues (marrow and spleen), suggesting that there was some other reason for the concentration of transferrin in these tissues. Erythron iron uptake was increased in proportion to the increased receptor number in phenylhydrazine-treated animals but was reduced in iron deficiency because of the limited amount of iron-bearing transferrin. These studies demonstrate the dominant role of erythron cellularity and iron status in vivo in determining total receptor number and the importance of receptor number and iron supply in tissue iron uptake.

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16

Vogt, Todd M., Aaron D. Blackwell, Anthony M. Giannetti, Pamela J. Bjorkman, and Caroline A. Enns. "Heterotypic interactions between transferrin receptor and transferrin receptor 2." Blood 101, no. 5 (March 1, 2003): 2008–14. http://dx.doi.org/10.1182/blood-2002-09-2742.

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Cellular iron uptake in most tissues occurs via endocytosis of diferric transferrin (Tf) bound to the transferrin receptor (TfR). Recently, a second transferrin receptor, transferrin receptor 2 (TfR2), has been identified and shown to play a critical role in iron metabolism. TfR2 is capable of Tf-mediated iron uptake and mutations in this gene result in a rare form of hereditary hemochromatosis unrelated to the hereditary hemochromatosis protein, HFE. Unlike TfR, TfR2 expression is not controlled by cellular iron concentrations and little information is currently available regarding the role of TfR2 in cellular iron homeostasis. To investigate the relationship between TfR and TfR2, we performed a series of in vivo and in vitro experiments using antibodies generated to each receptor. Western blots demonstrate that TfR2 protein is expressed strongest in erythroid/myeloid cell lines. Metabolic labeling studies indicate that TfR2 protein levels are approximately 20-fold lower than TfR in these cells. TfR and TfR2 have similar cellular localizations in K562 cells and coimmunoprecipitate to only a very limited extent. Western analysis of the receptors under nonreducing conditions reveals that they can form heterodimers.

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17

McGregor, S. J., M. L. Naves, R. Oria, J. K. Vass, and J. H. Brock. "Effect of aluminium on iron uptake and transferrin-receptor expression by human erythroleukaemia K562 cells." Biochemical Journal 272, no. 2 (December 1, 1990): 377–82. http://dx.doi.org/10.1042/bj2720377.

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Incubation of human erythroleukaemia K562 cells with Al-transferrin inhibited iron uptake from 59Fe-transferrin by about 80%. The inhibition was greater than that produced by a similar quantity of Fe-transferrin. Preincubation of cells for 6 h with either Al-transferrin or Fe-transferrin diminished the number of surface transferrin receptors by about 40% compared with cells preincubated with apo-transferrin. Al-transferrin did not compete significantly with Fe-transferrin for transferrin receptors and, when cells were preincubated for 15 min instead of 6 h, the inhibitory effect of Al-transferrin on receptor expression was lost. Both forms of transferrin also decreased the level of transferrin receptor mRNA by about 50%, suggesting a common regulatory mechanism. Aluminium citrate had no effect on iron uptake or transferrin-receptor expression. AlCl3 also had no effect on transferrin-receptor expression, but at high concentration it caused an increase in iron uptake by an unknown, possibly non-specific, mechanism. Neither Al-transferrin nor AlCl3 caused a significant change in cell proliferation. It is proposed that aluminium, when bound to transferrin, inhibits iron uptake partly by down-regulating transferrin-receptor expression and partly by interfering with intracellular release of iron from transferrin.

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18

Watts, C. "Rapid endocytosis of the transferrin receptor in the absence of bound transferrin." Journal of Cell Biology 100, no. 2 (February 1, 1985): 633–37. http://dx.doi.org/10.1083/jcb.100.2.633.

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The rate of endocytosis of transferrin receptors, occupied or unoccupied with transferrin, was measured on the cell line K562. At 37 degrees C, receptors, radioiodinated on the cell surface at 4 degrees C, were internalized equally rapidly in the presence or absence of transferrin. In both cases, 50% of the labeled receptors became resistant to externally added trypsin in 5 min. An antitransferrin antibody was used to show directly that the receptors had entered the cells without bound transferrin. The distribution of the receptors on the cell surface was revealed by antibody and protein A-gold staining after prolonged incubation in the presence or absence of transferrin. The receptors were concentrated in coated pits under both conditions. The data suggest that endocytosis of transferrin receptors is not "triggered" by ligand binding and raise the possibility that ligand-induced down-regulation of surface receptors may not occur by this mechanism. Instead receptors may be recognized as being ligand-occupied, not at the cell surface, but at some other site in the recycling pathway such as the endosome.

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Kleven, Mark D., Shall Jue, and Caroline A. Enns. "Transferrin Receptors TfR1 and TfR2 Bind Transferrin through Differing Mechanisms." Biochemistry 57, no. 9 (February 2018): 1552–59. http://dx.doi.org/10.1021/acs.biochem.8b00006.

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20

Ruthner, Monika, Alajos Berczi, and Hans Goldenberg. "Interaction of a doxorubicin-transferrin conjugate with isolated transferrin receptors." Life Sciences 54, no. 1 (January 1994): 35–40. http://dx.doi.org/10.1016/0024-3205(94)00575-3.

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21

Takahashi, S., L. Esserman, and R. Levy. "An epitope on the transferrin receptor preferentially exposed during tumor progression in human lymphoma is close to the ligand binding site." Blood 77, no. 4 (February 15, 1991): 826–32. http://dx.doi.org/10.1182/blood.v77.4.826.826.

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Abstract We have previously reported an anti-transferrin receptor antibody, Trump, which was originally selected for its ability to discriminate low- and high-grade lymphomas. This feature was distinct from the other anti-transferrin receptor antibodies such as OKT9. In the present study, further immunochemical analysis was performed to define the nature of the antigenic site recognized by the Trump antibody. Trump was found to block the binding of transferrin both to solubilized and to surface transferrin receptors; conversely, transferrin could block the binding of Trump only to surface transferrin receptors. Therefore, the epitope recognized by Trump is near but not identical to the transferrin binding site. Stimulation of peripheral blood lymphocytes with phytohemagglutinin induced both the OKT9 epitope and the Trump epitope, but 12-phorbol 13 myristate acetate induced only the OKT9 epitope. Growth of some cell lines was inhibited by Trump but not by OKT9. No structural difference was found between transferrin receptor molecules reactive with Trump and those reactive with OKT9. In support of these results, Trump was able to immunoprecipitate transferrin receptor molecules solubilized from low-grade follicular lymphoma cells even though it did not bind to the receptors exposed on the surface of these cells. These findings imply that low-grade lymphoma cells differ from high-grade lymphoma cells not in the structures of their transferrin receptors but in their exposure of the molecule on the cell surface.

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Takahashi, S., L. Esserman, and R. Levy. "An epitope on the transferrin receptor preferentially exposed during tumor progression in human lymphoma is close to the ligand binding site." Blood 77, no. 4 (February 15, 1991): 826–32. http://dx.doi.org/10.1182/blood.v77.4.826.bloodjournal774826.

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We have previously reported an anti-transferrin receptor antibody, Trump, which was originally selected for its ability to discriminate low- and high-grade lymphomas. This feature was distinct from the other anti-transferrin receptor antibodies such as OKT9. In the present study, further immunochemical analysis was performed to define the nature of the antigenic site recognized by the Trump antibody. Trump was found to block the binding of transferrin both to solubilized and to surface transferrin receptors; conversely, transferrin could block the binding of Trump only to surface transferrin receptors. Therefore, the epitope recognized by Trump is near but not identical to the transferrin binding site. Stimulation of peripheral blood lymphocytes with phytohemagglutinin induced both the OKT9 epitope and the Trump epitope, but 12-phorbol 13 myristate acetate induced only the OKT9 epitope. Growth of some cell lines was inhibited by Trump but not by OKT9. No structural difference was found between transferrin receptor molecules reactive with Trump and those reactive with OKT9. In support of these results, Trump was able to immunoprecipitate transferrin receptor molecules solubilized from low-grade follicular lymphoma cells even though it did not bind to the receptors exposed on the surface of these cells. These findings imply that low-grade lymphoma cells differ from high-grade lymphoma cells not in the structures of their transferrin receptors but in their exposure of the molecule on the cell surface.

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McGraw, T. E., L. Greenfield, and F. R. Maxfield. "Functional expression of the human transferrin receptor cDNA in Chinese hamster ovary cells deficient in endogenous transferrin receptor." Journal of Cell Biology 105, no. 1 (July 1, 1987): 207–14. http://dx.doi.org/10.1083/jcb.105.1.207.

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Transferrin (Tf) receptor-variant Chinese hamster ovary cells have been isolated by selection for resistance to two Tf-toxin conjugates. The hybrid toxins contain Tf covalently linked to ricin A chain or a genetically engineered diphtheria toxin fragment. The Tf-receptor-variant (TRV) cells do not have detectable cell-surface Tf receptor; they do not bind fluorescein-Tf or 125I-Tf. TRV cells are at least 100-fold more resistant to the Tf-diphtheria toxin conjugate than are the parent cells. The TRV cells have retained sensitivity to native diphtheria toxin, indicating that the increased resistance to the conjugate is correlated with the loss of Tf binding. The endocytosis of fluorescein-labeled alpha 2-macroglobulin is normal in TRV cells, demonstrating that the defect does not pleiotropically affect endocytosis. Since these cells lack endogenous Tf receptor activity, they are ideally suited for studies of the functional expression of normal or altered Tf receptors introduced into the cells by cDNA transfection. One advantage of this system is that Tf binding and uptake can be used to monitor the behavior of the transfected receptor. A cDNA clone of the human Tf receptor has been transfected into TRV cells. In the stably expressing transfectants, the behavior of the human receptor is very similar to that of the endogenous Chinese hamster ovary cell Tf receptor. Tf binds to cell surface receptors, and is internalized into the para-Golgi region of the cell. Iron is released from Tf, and the apo-Tf and its receptor are recycled back to the cell surface. Thus, the TRV cells can be used to study the behavior of genetically altered Tf receptors in the absence of interfering effects from endogenous receptors.

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Khumalo, Hlosukwazi, Zvenyika A. R. Gomo, Victor M. Moyo, Victor R. Gordeuk, Thokozile Saungweme, Tracey A. Rouault, and Innocent T. Gangaidzo. "Serum transferrin receptors are decreased in the presence of iron overload." Clinical Chemistry 44, no. 1 (January 1, 1998): 40–44. http://dx.doi.org/10.1093/clinchem/44.1.40.

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Abstract To test the hypothesis that the quantities of circulating transferrin receptors are reduced in iron overload, we studied serum transferrin receptors and indirect measures of iron status in 150 subjects from rural Zimbabwe. We found significant inverse correlations between serum concentrations of transferrin receptors and ferritin, the ratio of ferritin to aspartate aminotransferase, and transferrin saturation (r ≥0.44; P <0.001). The mean ± SD concentration of serum transferrin receptors in 23 subjects classified as having iron overload (ferritin >300 μg/L and transferrin saturation >60%) was 1.55 ± 0.61 mg/L, significantly lower than the 2.50 ± 0.62 mg/L in 75 subjects with normal iron stores (ferritin 20–300 μg/L and transferrin saturation 15–55%; P <0.0005) and the 2.83 ± 1.14 mg/L in 8 subjects with iron deficiency (ferritin <20 μg/L; P = 0.001). In keeping with the regulation of transferrin receptor expression at the cellular level, our findings suggest that serum transferrin receptors are decreased in the presence of iron overload.

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Moura, Ivan C., Miguel N. Centelles, Michelle Arcos-Fajardo, Denise M. Malheiros, James F. Collawn, Max D. Cooper, and Renato C. Monteiro. "Identification of the Transferrin Receptor as a Novel Immunoglobulin (Ig)a1 Receptor and Its Enhanced Expression on Mesangial Cells in Iga Nephropathy." Journal of Experimental Medicine 194, no. 4 (August 13, 2001): 417–26. http://dx.doi.org/10.1084/jem.194.4.417.

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The biological functions of immunoglobulin (Ig)A antibodies depend primarily on their interaction with cell surface receptors. Four IgA receptors are presently characterized. The FcαRI (CD89) expressed by myeloid cells selectively binds IgA1 and IgA2 antibodies, whereas the poly-IgR, Fcα/μR, and asialoglycoprotein receptors bind other ligands in addition to IgA. IgA binding by mesangial cells, epithelial cells, and proliferating lymphocytes is also well documented, but the nature of the IgA receptors on these cells remains elusive. A monoclonal antibody (A24) is described here that specifically blocks IgA binding to epithelial and B lymphocyte cell lines. Both the A24 antibody and IgA1 myelomas bind a cell surface protein that is identified as the transferrin receptor (CD71). The transferrin receptor selectively binds IgA1 antibodies, monomeric better than polymeric forms, and the IgA1 binding is inhibitable by transferrin. Transferrin receptor expression is upregulated on cultured mesangial cells as well as on glomerular mesangial cells in patients with IgA nephropathy. The characterization of transferrin receptor as a novel IgA1 receptor on renal mesangial cells suggests its potential involvement in the pathogenesis of IgA nephropathy.

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Jing, S. Q., T. Spencer, K. Miller, C. Hopkins, and I. S. Trowbridge. "Role of the human transferrin receptor cytoplasmic domain in endocytosis: localization of a specific signal sequence for internalization." Journal of Cell Biology 110, no. 2 (February 1, 1990): 283–94. http://dx.doi.org/10.1083/jcb.110.2.283.

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Wild-type and mutant human transferrin receptors have been expressed in chicken embryo fibroblasts using a helper-independent retroviral vector. The internalization of mutant human transferrin receptors, in which all but four of the 61 amino acids of the cytoplasmic domain had been deleted, was greatly impaired. However, when expressed at high levels, such "tailless" mutant receptors could provide chicken embryo fibroblasts with sufficient iron from diferric human transferrin to support a normal rate of growth. As the rate of recycling of the mutant receptors was not significantly different from wild-type receptors, an estimate of relative internalization rates could be obtained from the distribution of receptors inside the cell and on the cell surface under steady-state conditions. This analysis and the results of iron uptake studies both indicate that the efficiency of internalization of tailless mutant receptors is approximately 10% that of wild-type receptors. Further studies of a series of mutant receptors with different regions of the cytoplasmic domain deleted suggested that residues within a 10-amino acid region (amino acids 19-28) of the human transferrin receptor cytoplasmic domain are required for efficient endocytosis. Insertion of this region into the cytoplasmic domain of the tailless mutant receptors restored high efficiency endocytosis. The only tyrosine residue (Tyr 20) in the cytoplasmic domain of the human transferrin receptor is found within this 10-amino acid region. A mutant receptor containing glycine instead of tyrosine at position 20 was estimated to be approximately 20% as active as the wild-type receptor. We conclude that the cytoplasmic domain of the transferrin receptor contains a specific signal sequence located within amino acid residues 19-28 that determines high efficiency endocytosis. Further, Tyr 20 is an important element of that sequence.

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Grasso, J. A., M. Bruno, A. A. Yates, L. Wei, and P. M. Epstein. "Calmodulin dependence of transferrin receptor recycling in rat reticulocytes." Biochemical Journal 266, no. 1 (February 15, 1990): 261–72. http://dx.doi.org/10.1042/bj2660261.

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Kinetic analysis of transferrin receptor properties in 6-8 day rat reticulocytes showed the existence of a single class of high-affinity receptors (Kd 3-10 nM), of which 20-25% were located at the cell surface and the remainder within an intracellular pool. Total transferrin receptor cycling time was 3.9 min. These studies examined the effects of various inhibitors on receptor-mediated transferrin iron delivery in order to define critical steps and events necessary to maintain the functional integrity of the pathway. Dansylcadaverine inhibited iron uptake by blocking exocytic release of transferrin and return of receptors to the cell surface, but did not affect transferrin endocytosis; this action served to deplete the surface pool of transferrin receptors, leading to shutdown of iron uptake. Calmidazolium and other putative calmodulin antagonists exerted an identical action on iron uptake and receptor recycling. The inhibitory effects of these agents on receptor recycling were overcome by the timely addition of Ca2+/ionomycin. From correlative analyses of the effects of these and other inhibitors, it was concluded that: (1) dansylcadaverine and calmodulin antagonists inhibit iron uptake by suppression of receptor recycling and exocytic transferrin release, (2) protein kinase C, transglutaminase, protein synthesis and release of transferrin-bound iron are not necessary for the functional integrity of the iron delivery pathway, (3) exocytic transferrin release and concomitant receptor recycling in rat reticulocytes is dependent upon Ca2+/calmodulin, (4) dansylcadaverine, dimethyldansylcadaverine and calmidazolium act on iron uptake by interfering with calmodulin function, and (5) the endocytotic and exocytotic arms of the iron delivery pathway are under separate regulatory control.

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28

Tijanić, Ivan, Miodrag Vučić, and Lana Mačukanović Golubović. "The significance of soluble transferrin receptors in diagnosing iron deficiency anemia." Revista Romana de Medicina de Laborator 23, no. 3 (August 1, 2015): 275–83. http://dx.doi.org/10.1515/rrlm-2015-0030.

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AbstractIntroduction. In recent years, determination of soluble transferrin receptor levels has been emerging as a test that can reliably indicate iron deficiency in various states, and that is non-invasive and easy to use. The aim of this study was: to determine reference values of soluble transferrin receptor concentrations in serums in our population, to examine the reliability of this method in the diagnosis of anemia due to iron deficiency and associated iron deficiency in anemia accompanying malignant hemopathies, and to identify possible limitations of the test in certain conditions.Material and Methods. The prospective research included 86 patients with anemia: 46 patients with iron deficiency anemia, and 40 patients with malignant hemopathies. The control group consisted of 40 healthy persons aging over 18.Results. Ferritin values were reduced in 76.1% of patients, while higher levels of soluble transferrin receptors appeared in 100% of patients with iron deficiency anemia. In patients with reduced serum ferritin levels, the soluble transferrin receptor/log ferritin index was statistically significantly higher than in patients in whom ferritin concentration was in the normal range (p <0.001). ROC analysis of patients with iron deficiency anemia showed that the soluble transferrin receptor/log ferritin index (AUC 0.977) and levels of soluble transferrin receptors (AUC 0.931) occupied the largest area under the curve. The best diagnostic parameter for detecting iron deficiency in patients with malignant hemopathies by ROC analysis is the soluble transferrin receptor/log ferritin index (AUC 0.770).Conclusion. Soluble transferrin receptors are useful in the diagnosis of iron deficiency anemia, especially when ferritin values are not reduced. The calculation of soluble transferrin receptor/log ferritin index is even more reliable. In patients with malignant hemopathies, the associated iron deficiency could be best indicated by soluble transferrin receptor/log ferritin index.

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Alvarez, E., N. Gironès, and R. J. Davis. "A point mutation in the cytoplasmic domain of the transferrin receptor inhibits endocytosis." Biochemical Journal 267, no. 1 (April 1, 1990): 31–35. http://dx.doi.org/10.1042/bj2670031.

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The rate of receptor-mediated endocytosis of diferric 125I-transferrin by Chinese-hamster ovary cells expressing human transferrin receptors was compared with the rate measured for cells expressing hamster transferrin receptors. It was observed that the rate of endocytosis of the human transferrin receptor was significantly higher than that for the hamster receptor. In order to examine the molecular basis for the difference between the observed rates of endocytosis, a cDNA clone corresponding to the cytoplasmic domain of the hamster receptor was isolated. The predicted primary sequence of the cytoplasmic domain of the hamster transferrin receptor is identical with that of the human receptor, except at position 20, where a tyrosine residue in the human sequence is replaced with a cysteine residue. To test the hypothesis that this structural change in the receptor is related to the difference in the rate of internalization, we used site-directed mutagenesis to examine the effect of the replacement of tyrosine-20 with a cysteine residue in the human transferrin receptor. It was observed that the substitution of tyrosine-20 with cysteine caused a 60% inhibition of the rate of iron accumulation by cells incubated with [59Fe]diferric transferrin. No significant difference between the rate of internalization of the mutant (cysteine-20) human receptor and the hamster receptor was observed. Thus the substitution of tyrosine-20 with a cysteine residue can account for the difference between the rate of endocytosis of the human and hamster transferrin receptors.

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Hunt, R. C., A. Dewey, and A. A. Davis. "Transferrin receptors on the surfaces of retinal pigment epithelial cells are associated with the cytoskeleton." Journal of Cell Science 92, no. 4 (April 1, 1989): 655–66. http://dx.doi.org/10.1242/jcs.92.4.655.

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Retinal pigment epithelial cells, derived from human donor eyes, have been grown in culture as monolayers on membrane filters or plastic surfaces and shown to possess transferrin receptors with a monomeric molecular mass of 93,000. These receptors internalize 125I-labelled transferrin and recycle it to the surrounding medium in a similar manner to other cell types. Scatchard analyses show that there are about 100,000 high-affinity receptors on the surface of each cell and most of these receptors are associated with the cytoskeleton. In total cell extracts, there are additional low-affinity binding sites that do not appear to be strongly associated with the cytoskeleton. The apparent interaction of transferrin receptors with the cytoskeleton was confirmed in two ways: first, using 200 kV electron microscopy for stereo analyses, skeleton-associated transferrin receptors were detected by a monoclonal anti-receptor antibody and a colloidal gold-conjugated second antibody after Triton X-100 extraction of pigment epithelial cells grown directly on laminin-coated gold grids; and, second, when cell surface receptors were labelled with radioiodinated transferrin and then incubated for various periods of time, the labelled transferrin was observed to move from a Triton X-100-insoluble fraction (a putative cytoskeletal compartment) to a Triton-soluble compartment that was not associated with the cytoskeleton. Using either horseradish peroxidase or colloidal gold-labelled transferrin, it has been shown that basolateral and apical surface-located receptors participate in receptor-mediated endocytosis via clathrin-coated pits, endosomes and tubular structures. Initially, transferrin internalized from the apical surface is observed in small endosomes that often appear to be embedded in an apical layer of microfilaments. From these peripheral regions of the cells, the labelled receptors move to larger endosomes and multivesicular bodies deeper in the cytoplasm. These structures have no apparent association with cytoskeletal elements.

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NIITSU, YOSHIRO, YUTAKA KOHGO, TAKUJI NISHISATO, HITOSHI KONDO, JUNJI KATO, YOICHI URUSHIZAKI, and ICHIRO URUSHIZAKI. "Transferrin receptors in human cancerous tissues." Tohoku Journal of Experimental Medicine 153, no. 3 (1987): 239–43. http://dx.doi.org/10.1620/tjem.153.239.

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Morris, C. M., J. M. Candy, S. Omar, C. A. Bloxham, and J. A. Edwardson. "Transferrin receptors in the Parkinsonian midbrain." Neuropathology and Applied Neurobiology 20, no. 5 (October 1994): 468–72. http://dx.doi.org/10.1111/j.1365-2990.1994.tb00997.x.

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Zoli, A., L. Altomonte, L. Mirone, M. Magaro, B. M. Ricerca, S. Storti, A. Candido, and M. Bizzi. "Serum transferrin receptors in rheumatoid arthritis." Annals of the Rheumatic Diseases 53, no. 10 (October 1, 1994): 699–701. http://dx.doi.org/10.1136/ard.53.10.699.

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34

Maneva, A., and B. Taleva. "Receptors for Transferrin on Human Neutrophils." Biotechnology & Biotechnological Equipment 23, sup1 (January 2009): 477–79. http://dx.doi.org/10.1080/13102818.2009.10818467.

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35

Lombard, M., W. Vogel, A. Bomford, R. Williams, R. Sciot, J. J. Van Den Ord, V. J. Desmet, et al. "Hepatic Transferrin Receptors in Hereditary Hemochromatosis." Hepatology 8, no. 3 (May 1988): 704–7. http://dx.doi.org/10.1002/hep.1840080355.

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36

Schryvers, Anthony B., and Guido C. Gonzalez. "Receptors for transferrin in pathogenic bacteria are specific for the host's protein." Canadian Journal of Microbiology 36, no. 2 (February 1, 1990): 145–47. http://dx.doi.org/10.1139/m90-026.

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Transferrin receptors detected by a solid-phase binding assay were shown to be specific for the host's transferrin in the representative bacterial pathogens Neisseria meningitidis (human), Pasteurella haemolytica (bovine), and Actinobacillus pleuropneumoniae (porcine). Consistent with the receptor specificity, iron-deficient bacteria were only capable of utilizing transferrin from the host as a source of iron for growth. Key words: iron, transferrin, receptor.

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37

Alford, C. E., T. E. King, and P. A. Campbell. "Role of transferrin, transferrin receptors, and iron in macrophage listericidal activity." Journal of Experimental Medicine 174, no. 2 (August 1, 1991): 459–66. http://dx.doi.org/10.1084/jem.174.2.459.

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It is not yet known what properties distinguish macrophages which can kill facultative intracellular bacteria, such as Listeria monocytogenes, from those which cannot. Listeria is an organism which requires iron for growth, yet macrophage listericidal mechanisms are also likely to be iron dependent. We show here that resident peritoneal macrophages and thioglycollate-elicited macrophages cannot kill listeria, but proteose peptone-elicited and FCS-elicited macrophages can. All these cell populations phagocytose listeria. Transferrin receptor expression is low on resident cells, intermediate on peptone- and FCS-elicited cells, and high on thioglycollate-elicited cells. Transferrin transports iron into cells via the transferrin receptor: thus, iron content of resident cells is low, of peptone- and FCS-elicited cells is intermediate, and of thioglycollate-elicited cells is high. Moreover, antibody to transferrin, which prevents it binding its receptor, inhibits listericidal macrophages from killing this bacterium. Finally, nonlistericidal cells with high transferrin receptor expression and high intracellular iron become listericidal if they are incubated with apotransferrin, an iron-free ligand which prevents iron uptake by cells. These data suggest that macrophages must have enough available intracellular iron to support listericidal mechanisms, but too much iron favors growth of the bacterium, which no longer can be killed by the macrophage.

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MORRIS, CHRISTOPHER M., JENNIFER A. COURT, ALI A. MOSHTAGHIE, ANDREW SKILLEN, JOHN M. CANDY, ROBERT H. PERRY, JAMES A. EDWARDSON, and ANDREW FAIRBAIRN. "Transferrin and transferrin receptors in normal brain and in Alzheimer's disease." Biochemical Society Transactions 15, no. 5 (October 1, 1987): 891–92. http://dx.doi.org/10.1042/bst0150891.

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Stamatos, C., and R. E. Fine. "Chick embryo myotubes contain transferrin receptors and internalize and recycle transferrin." Journal of Neuroscience Research 15, no. 4 (1986): 529–42. http://dx.doi.org/10.1002/jnr.490150410.

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40

Subtil, A., and A. Dautry-Varsat. "Microtubule depolymerization inhibits clathrin coated-pit internalization in non-adherent cell lines while interleukin 2 endocytosis is not affected." Journal of Cell Science 110, no. 19 (October 1, 1997): 2441–47. http://dx.doi.org/10.1242/jcs.110.19.2441.

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The microtubule cytoskeleton is generally not considered to be essential for the first steps of clathrin-mediated endocytosis of membrane receptors. Its role in clathrin-independent endocytosis has not been investigated. We have previously shown that the cytokine interleukin 2 (IL2) is internalized in lymphoid cells expressing its receptors when clathrin-dependent endocytosis is inhibited. Here we compare the internalization of IL2 and of transferrin, a marker of clathrin-dependent endocytosis, after microtubule disruption. In hemopoietic cell lines, which express IL2 receptors, transferrin receptor entry was inhibited by about 40%. However, in adherent cell lines, transferrin entry was unaffected by microtubule disruption, as previously reported. Unlike the case for transferrin, internalization of IL2 receptors was not affected by depolymerization of the microtubule cytoskeleton in hemopoietic cell lines. These results show that IL2 and transferrin receptors do not have the same endocytic properties and support our previous conclusion that these receptors follow different pathways of endocytosis.

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Tanner, L. I., and G. E. Lienhard. "Localization of transferrin receptors and insulin-like growth factor II receptors in vesicles from 3T3-L1 adipocytes that contain intracellular glucose transporters." Journal of Cell Biology 108, no. 4 (April 1, 1989): 1537–45. http://dx.doi.org/10.1083/jcb.108.4.1537.

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Transferrin receptors in detergent extracts of subcellular membrane fractions prepared from 3T3-L1 adipocytes were measured by a binding assay. There was a small but significant increase (1.2-fold) in the amount of receptor in a crude plasma membrane fraction and a 40% decrease in the number of transferrin receptors in microsomal membranes prepared from insulin-treated cells, when compared with corresponding fractions from control cells. Intracellular vesicles containing insulin-responsive glucose transporters (GT) have been isolated by immunoadsorption from the microsomal fraction (Biber, J. W., and G. E. Lienhard. 1986. J. Biol. Chem. 261:16180-16184). All of the transferrin receptors in this fraction were localized in these vesicles; however, because the GT vesicles contain approximately 30-fold fewer transferrin receptors than GT, on the average only one vesicle in three contains a transferrin receptor. The binding of 125I-pentamannose 6-phosphate BSA to 3T3-L1 adipocytes at 4 degrees C was used to monitor surface insulin-like growth factor II (IGF-II)/mannose 6-phosphate receptors. Exposure of cells to insulin at 37 degrees C for 5 min resulted in a 2.5-4.5-fold increase in surface receptors. There was a corresponding 20% decrease in the amount of IGF-II receptors in the microsomal membranes prepared from insulin-treated cells, as assayed by immunoblotting. Moreover, the IGF-II receptors and GT were located in the same intracellular vesicles, since antibodies to the carboxyterminal peptide of either protein immunoadsorbed vesicles containing 70-95% of both proteins initially present in the microsomal fraction. In conjunction with other studies, these results indicate that in 3T3-L1 adipocytes, three membrane proteins (the GT, the transferrin receptor, and the IGF-II receptor) respond similarly to insulin, by redistributing to the surface from intracellular compartment(s) in which they are colocalized.

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Nezu, M., H. Iwagaki, H. Aoki, N. Tanaka, and K. Orita. "Tumour Necrosis Factor-α Upregulates Transferrin Receptors in K 562 Cells." Journal of International Medical Research 22, no. 3 (May 1994): 145–52. http://dx.doi.org/10.1177/030006059402200302.

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The effects of tumour necrosis factor-α on transferrin receptor expression in a human chronic myelocytic leukaemia cell line, K 562 cells, were studied. Cytofluorometry studies showed that the numbers of transferrin receptors in exponentially growing K 562 cells were increased when the cells were incubated with tumour necrosis factor-α for 24 h. The induction of transferrin receptors by tumour necrosis factor-α may be mediated by a mechanism that is independent of growth since cell growth in treated cultures did not differ from that in the controls. The DNA contents of K 562 cells treated with tumour necrosis factor-α showed that after 24 h there were less cells in the G1 and S phases and more cells in the G2/M phase than in the control group. The phase of upregulation of transferrin receptors induced by tumour necrosis factor-α may be dependent on the cell cycle. This new evidence that tumour necrosis factor-α upregulates transferrin receptors suggests a cancer-anaemia cascade in which the cancer burden state activates macrophage release of tumour necrosis factor-α as a result of transferrin receptor expression.

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Weiel, J. E., D. O. Adams, and T. A. Hamilton. "Biochemical models of gamma-interferon action: altered expression of transferrin receptors on murine peritoneal macrophages after treatment in vitro with PMA or A23187." Journal of Immunology 134, no. 1 (January 1, 1985): 293–98. http://dx.doi.org/10.4049/jimmunol.134.1.293.

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Abstract The number of transferrin receptors in thioglycollate-elicited murine peritoneal macrophages is markedly depressed after exposure to murine gamma-interferon (IFN gamma) in vitro. This change has been used as a model system to study the molecular and cellular mechanisms of IFN gamma signal transduction. We observed that the downshift of the transferrin receptor could be mimicked by exposure to the calcium ionophore (A23187) or the potent tumor promoter, phorbol 12-myristate 13-acetate (PMA). Saturation binding studies on thioglycollate (TG)-elicited peritoneal macrophages after exposure to A23187 or PMA showed the reduced expression of transferrin binding activity attributable to a decrease in the total number of cellular transferrin receptors and not an alteration in receptor-ligand affinity, in agreement with previous results obtained after exposure to IFN gamma. The loss of transferrin receptors in response to A23187 or PMA was dose dependent, and the kinetics of the change were identical to those observed with IFN gamma treatment. Phorbol 12,13-dibutyrate or 4-beta-phorbol 12,13-didecanoate, both biologically active phorbol esters, also induced reduced expression of transferrin receptors, whereas nonesterified phorbol or 4-alpha-phorbol 12,13-didecanoate, an inactive phorbol ester, had no effect on transferrin receptor expression. Finally, PMA and A23187, when used together, acted cooperatively to modulate transferrin receptor expression when both agents were present at subthreshold concentrations. These results, taken together, suggest that elevation of intracellular Ca++ levels and/or stimulation of protein kinase C are involved in the response of macrophages to IFN gamma.

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Yu, Ronghua, and Anthony B. Schryvers. "Transferrin receptors on ruminant pathogens vary in their interaction with the C-lobe and N-lobe of ruminant transferrins." Canadian Journal of Microbiology 40, no. 7 (July 1, 1994): 532–40. http://dx.doi.org/10.1139/m94-086.

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The interaction between ruminant transferrins and receptor proteins on the surface of the ruminant pathogens Pasteuerella haemolytica, Haemophilus somnus, Pasteurella multocida, Haemophilus agnii, and Moraxella bovis was evaluated by a combination of binding assays and affinity isolation procedures. Membranes isolated from P. haemolytica, P. multocida, and H. agnii were capable of binding sheep, goat, and cattle transferrins whereas binding by membranes from H. somnus and M. bovis was specific for bovine transferrin. Proteolytically derived bovine transferrin C-lobe was capable of inhibiting the interaction between bovine transferrin and both Tbpl and Tbp2 from P. haemolytica and M. bovis but only Tbpl from H. somnus and P. multocida. Proteolytically derived N-lobe inhibited the binding of P. multocida and H. somnus Tbp2 to bovine transferrin and the binding of bovine transferrin to the single receptor protein identified in H. agnii. The implications of these results regarding the nature of the ligand–receptor interaction and similarities of this interaction with ligand–receptor interactions in different species are discussed.Key words: iron acquisition, transferrin receptor, binding specificity, Pasteurella, ruminants.

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45

Rao, K., J. B. Harford, T. Rouault, A. McClelland, F. H. Ruddle, and R. D. Klausner. "Transcriptional regulation by iron of the gene for the transferrin receptor." Molecular and Cellular Biology 6, no. 1 (January 1986): 236–40. http://dx.doi.org/10.1128/mcb.6.1.236-240.1986.

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Treatment of K562 cells with desferrioxamine, a permeable iron chelator, led to an increase in the number of transferrin receptors. Increasing intracellular iron levels by treatment of cells with either human diferric transferrin or hemin lowered the level of the transferrin receptors. By using a cDNA clone of the human transferrin receptor, we showed that the changes in the levels of the receptor by iron were accompanied by alterations in the levels of the mRNA for the receptor. The rapidity of these changes indicated that the mRNA had a very short half-life. By using an in vitro transcriptional assay with isolated nuclei, we obtained evidence that this regulation occurred at the transcriptional level.

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46

Rao, K., J. B. Harford, T. Rouault, A. McClelland, F. H. Ruddle, and R. D. Klausner. "Transcriptional regulation by iron of the gene for the transferrin receptor." Molecular and Cellular Biology 6, no. 1 (January 1986): 236–40. http://dx.doi.org/10.1128/mcb.6.1.236.

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Treatment of K562 cells with desferrioxamine, a permeable iron chelator, led to an increase in the number of transferrin receptors. Increasing intracellular iron levels by treatment of cells with either human diferric transferrin or hemin lowered the level of the transferrin receptors. By using a cDNA clone of the human transferrin receptor, we showed that the changes in the levels of the receptor by iron were accompanied by alterations in the levels of the mRNA for the receptor. The rapidity of these changes indicated that the mRNA had a very short half-life. By using an in vitro transcriptional assay with isolated nuclei, we obtained evidence that this regulation occurred at the transcriptional level.

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47

Damke, H., K. von Figura, and T. Braulke. "Simultaneous redistribution of mannose 6-phosphate and transferrin receptors by insulin-like growth factors and phorbol ester." Biochemical Journal 281, no. 1 (January 1, 1992): 225–29. http://dx.doi.org/10.1042/bj2810225.

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Insulin-like growth factors I and II (IGF-I and IGF-II) and phorbol ester are known to induce in fibroblasts a rapid redistribution of mannose 6-phosphate (M6P)/IGF II-receptors to the cell surface. We compared the redistribution of the M6P/IGF-II receptor with that of the 46 kDa M6P receptor (MPR46) and of receptors for transferrin, low-density lipoprotein (LDL) and epidermal growth factor (EGF) in human fibroblasts under the influence of these effectors. None of the effectors altered the surface expression of receptors for LDL or EGF, which are predominantly located at the cell surface. IGF-I, IGF-II and phorbol ester increased the surface expression of the M6P/IGF-II receptor and of MPR46. The concentration of the transferrin receptor at the cell surface was increased only by IGF-I and IGF-II, with similar kinetics as for the M6P/IGF-II receptor, suggesting that the same mechanism causes redistribution. The increased surface expression of M6P receptors was accompanied by an increased uptake of receptor ligands. The number of transferrin receptors did not correlate with iron uptake, although neither the rate nor the extent of transferrin internalization was changed. These results indicate that the redistribution of several endocytic receptors induced by IGF-I, IGF-II and phorbol ester shows selectivity, and that the uptake of receptor ligand may become uncoupled from the surface expression of the receptors via distinct mechanisms.

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Weissman, A. M., R. D. Klausner, K. Rao, and J. B. Harford. "Exposure of K562 cells to anti-receptor monoclonal antibody OKT9 results in rapid redistribution and enhanced degradation of the transferrin receptor." Journal of Cell Biology 102, no. 3 (March 1, 1986): 951–58. http://dx.doi.org/10.1083/jcb.102.3.951.

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When the human erythroleukemia cell line K562 is treated with OKT9, a monoclonal antibody against the transferrin receptor, effects on receptor dynamics and degradation ensue. The apparent half-life of the receptor is decreased by greater than 50% as a result of OKT9 treatment. The transferrin receptor is also rapidly redistributed in response to OKT9 such that a lower percentage of the cellular receptors are displayed on the cell surface. OKT9 treatment also leads to a decrease in the total number of receptors participating in the transferrin cycle for cellular iron uptake. The reduction in iron uptake that results from the loss of receptors from the cycle leads to enhanced biosynthesis of the receptor. Receptors with bound OKT9 continue to participate in multiple cycles of iron uptake. However, OKT9 treatment appears to result in a relatively small increase per cycle in the departure of receptors from participation in iron uptake to a pathway leading to receptor degradation. Radiolabeled OKT9 is itself degraded by K562 cells and this degradation is inhibitable by leupeptin or chloroquine. In the presence of leupeptin, OKT9 treatment results in the enhanced intracellular accumulation of transferrin. Because the time involved in the transferrin cycle is shorter (12.5 min) than the normal half-life of the receptor (8 h), a small change in recycling efficiency caused by OKT9 treatment could account for the marked decrease in receptor half-life. In this paper the implications of these findings are discussed as they relate to systems in which receptor number is regulated by ligand.

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Shannon, KM, JW Larrick, SA Fulcher, KB Burck, J. Pacely, JC Davis, and DB Ring. "Selective inhibition of the growth of human erythroid bursts by monoclonal antibodies against transferrin or the transferrin receptor." Blood 67, no. 6 (June 1, 1986): 1631–38. http://dx.doi.org/10.1182/blood.v67.6.1631.1631.

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Abstract The relative requirements of colonies derived from erythroid (BFU-E) and myeloid (CFU-c) progenitors for transferrin were examined using monoclonal antibodies directed against the transferrin molecule (TF-6) or its cell surface receptor (TFR-A12, TFR1–2B). Growth of erythroid bursts was profoundly reduced at concentrations of all three antibodies that had no effect on CFU-c-derived colonies. When TFR1–2B was layered over cultures established one to seven days previously, further burst development was inhibited, and degeneration of early erythroid colonies was observed. Addition of erythropoietin augmented transferrin receptor expression on cells harvested after 1 to 2 weeks in culture and analyzed by flow cytometry. Recombinant human erythropoietin gave results comparable to those obtained in experiments using human urinary erythropoietin. Analysis of erythroblasts plucked directly from culture plates confirmed the presence of transferrin receptors on BFU-E-derived colonies. Thymidine incorporation was maximal early in the second week of culture and coincided with high transferrin receptor expression. These data demonstrate that transferrin must be available into the second week of culture to support the growth and differentiation of BFU- E-derived erythroid bursts, that the generation of erythroid colonies from BFU-E is more dependent on transferrin than myeloid colony formation from CFU-c, and that erythropoietin modulates the expression of transferrin receptors on growing bursts.

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50

Shannon, KM, JW Larrick, SA Fulcher, KB Burck, J. Pacely, JC Davis, and DB Ring. "Selective inhibition of the growth of human erythroid bursts by monoclonal antibodies against transferrin or the transferrin receptor." Blood 67, no. 6 (June 1, 1986): 1631–38. http://dx.doi.org/10.1182/blood.v67.6.1631.bloodjournal6761631.

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The relative requirements of colonies derived from erythroid (BFU-E) and myeloid (CFU-c) progenitors for transferrin were examined using monoclonal antibodies directed against the transferrin molecule (TF-6) or its cell surface receptor (TFR-A12, TFR1–2B). Growth of erythroid bursts was profoundly reduced at concentrations of all three antibodies that had no effect on CFU-c-derived colonies. When TFR1–2B was layered over cultures established one to seven days previously, further burst development was inhibited, and degeneration of early erythroid colonies was observed. Addition of erythropoietin augmented transferrin receptor expression on cells harvested after 1 to 2 weeks in culture and analyzed by flow cytometry. Recombinant human erythropoietin gave results comparable to those obtained in experiments using human urinary erythropoietin. Analysis of erythroblasts plucked directly from culture plates confirmed the presence of transferrin receptors on BFU-E-derived colonies. Thymidine incorporation was maximal early in the second week of culture and coincided with high transferrin receptor expression. These data demonstrate that transferrin must be available into the second week of culture to support the growth and differentiation of BFU- E-derived erythroid bursts, that the generation of erythroid colonies from BFU-E is more dependent on transferrin than myeloid colony formation from CFU-c, and that erythropoietin modulates the expression of transferrin receptors on growing bursts.

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Journal articles on the topic 'Transferrin – Receptors'

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