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Human Transferrin Receptor (human + transferrin_receptor)
Selected AbstractsThe human brain endothelial cell line hCMEC/D3 as a human blood-brain barrier model for drug transport studiesJOURNAL OF NEUROCHEMISTRY, Issue 5 2008Birk Poller Abstract The human brain endothelial capillary cell line hCMEC/D3 has been developed recently as a model for the human blood-brain barrier. In this study a further characterization of this model was performed with special emphasis on permeability properties and active drug transport. Para- or transcellular permeabilities (Pe) of inulin (0.74 × 10,3 cm/min), sucrose (1.60 × 10,3 cm/min), lucifer yellow (1.33 × 10,3 cm/min), morphine (5.36 × 10,3 cm/min), propranolol (4.49 × 10,3 cm/min) and midazolam (5.13 × 10,3 cm/min) were measured. By addition of human serum the passive permeability of sucrose could be reduced significantly by up to 39%. Furthermore, the expression of a variety of drug transporters (ABCB1, ABCG2, ABCC1,5) as well as the human transferrin receptor was demonstrated on the mRNA level. ABCB1, ABCG2 and transferrin receptor proteins were detected and functional activity of ABCB1, ABCG2 and the ABCC family was quantified in efflux experiments. Furthermore, ABCB1-mediated bidirectional transport of rhodamine 123 was studied. The transport rate from the apical to the basolateral compartment was significantly lower than that in the inverse direction, indicating directed p-glycoprotein transport. The results of this study demonstrate the usefulness of the hCMEC/D3 cell line as an in vitro model to study drug transport at the level of the human blood-brain barrier. [source] Trafficking of the human transferrin receptor in plant cells: effects of tyrphostin A23 and brefeldin ATHE PLANT JOURNAL, Issue 5 2006Elena Ortiz-Zapater Summary Plant cells possess much of the molecular machinery necessary for receptor-mediated endocytosis (RME), but this process still awaits detailed characterization. In order to identify a reliable and well-characterized marker to investigate RME in plant cells, we have expressed the human transferrin receptor (hTfR) in Arabidopsis protoplasts. We have found that hTfR is mainly found in endosomal (Ara7- and FM4-64-positive) compartments, but also at the plasma membrane, where it mediates binding and internalization of its natural ligand transferrin (Tfn). Cell surface expression of hTfR increases upon treatment with tyrphostin A23, which inhibits the interaction between the YTRF endocytosis signal in the hTfR cytosolic tail and the ,2-subunit of the AP2 complex. Indeed, tyrphostin A23 inhibits Tfn internalization and redistributes most of hTfR to the plasma membrane, suggesting that the endocytosis signal of hTfR is functional in Arabidopsis protoplasts. Co-immunoprecipitation experiments show that hTfR is able to interact with a , -adaptin subunit from Arabidopsis cytosol, a process that is blocked by tyrphostin A23. In contrast, treatment with brefeldin A, which inhibits recycling from endosomes back to the plasma membrane in plant cells, leads to the accumulation of Tfn and hTfR in larger patches inside the cell, reminiscent of BFA compartments. Therefore, hTfR has the same trafficking properties in Arabidopsis protoplasts as in animal cells, and cycles between the plasma membrane and endosomal compartments. The specific inhibition of Tfn/hTfR internalization and recycling by tyrphostin A23 and BFA, respectively, thus provide valuable molecular tools to characterize RME and the recycling pathway in plant cells. [source] Analyses for binding of the transferrin family of proteins to the transferrin receptor 2BRITISH JOURNAL OF HAEMATOLOGY, Issue 4 2004Hiroshi Kawabata Summary Transferrin receptor 2, (TfR2,), the major product of the TfR2 gene, is the second receptor for transferrin (Tf), which can mediate cellular iron uptake in vitro. Homozygous mutations of TfR2 cause haemochromatosis, suggesting that TfR2, may not be a simple iron transporter, but a regulator of iron by identifying iron-Tf. In this study, we analysed the ligand specificity of TfR2, using human transferrin receptor 1 (TfR1) and TfR2, -stably transfected and expressing cells and flow-cytometric techniques. We showed that human TfR2, interacted with both human and bovine Tf, whereas human TfR1 interacted only with human Tf. Neither human TfR1 nor TfR2, interacted with either lactoferrin or melanotransferrin. In addition, by creating point mutations in human TfR2,, the RGD sequence in the extracellular domain of TfR2, was shown to be crucial for Tf-binding. Furthermore, we demonstrated that mutated TfR2, (Y250X), which has been reported in patients with hereditary haemochromatosis, also lost its ability to interact with both human and bovine Tf. Although human TfR1 and TfR2, share an essential structure (RGD) for ligand-binding, they have clearly different ligand specificities, which may be related to the differences in their roles in iron metabolism. [source] | ||||||||||