Human transferrin receptors

The equivalent of the tryptic fragment of human transferrin receptor has been expressed in Chinese hamster ovary cells and its structure determined at a resolution of 0.32 nm (Lawrence et ah, 1999). The asymmetric unit of the crystals contains four transferrin receptor dimers. Interpretable electron density is found for the entire tryptic fragment except for Arg-121 at the amino terminus, and density is also seen for the first N-acetylglucosamine residue at each of the N-glycosylation sites. The transferrin receptor monomer is made up of three distinct domains, organized such that the dimer is butterfly shaped (Figure 5.10, Plate 7). The likely orientation of the dimer with respect to the plasma membrane has been assigned on the basis of the... 

U)SPIO (ultrasmall) superparamagnetic iron oxide (h)TfR (human) transferrin receptor... 

Weissleder et al. [84] first showed that the human transferrin receptor (hTfR) can be used to internalize MRI contrast agents. The hTfR regulates cellular uptake of iron from transferrin, a plasmatic iron transport protein [85], via a receptor mediated endocytosis mechanism. Thus, MION particles (dextran coated iron oxide) were oxidized with sodium periodate. Holotransferrin was added and the resulting Schiff base adduct was reduced with sodium cyanoborohydride to give transferrin labeled MIONs, Tf-MION (Scheme 3). 

Cheng Y, Zak O, Aisen P, Harrison SC, Walz T. Structure of the human transferrin receptor-transferrin complex. Cell 2004 116 565-576. 

Transferrin Receptor. Transferrin receptor is a cell membrane glycoprotein that binds to transferrin to transport iron ion into cells by receptor-mediated endocytosis. Human transferrin receptors are overexpressed... 

Taketani, S., Kohno, H., Sawamura, T, and Tokunaga, R. (1990). Hemopexin-dependent downregulation of expression of the human transferrin receptor. /. Biol. Chem. 265, 13981-13985. 

Schneider C, Owen MJ, Banville D, Williams JG. 1984. Primary structure of human transferrin receptor deduced from the mRNA sequence. Nature 311 675-78... 

Jing S, Trowbridge IS. 1987. Identification of the intermolecular disulfide bonds of the human transferrin receptor and its lipid-attachment site. EMBO J. 6 327-31... 

The attributes of the 7D3 MAb directed against the human transferrin receptor have been reported (33). Hybridoma clones are injected into pristane-primed BALB/c mice or Swiss nu/nu athymic mice (Taconic, Germantown, NY), ascites fluid is collected and the 150 kDa anti-DT MAb is isolated by (NH4)2S04 precipitation and size fractionation on a high resolution Sephacryl S-300 column. The antibodies were -90% pure as judged by PAGE. 

Human transferrin receptor-positive target cells are cultured at 37°C with 5% C02 in tissue culture flasks containing RPMI-1640 medium with 10% fetal calf serum, L-glutamine, and penicillin-streptomycin (GIBCO, Grand Island, NY). Adherent cells are released from the culture flask using 0.05% trypsin, and 0.02% EDTA for 10 min at 37°C, and then medium plus serum is added to inactivate the trypsin. 

Another peptide derivative of MTX was prepared [362] with the aim of covalently attaching it to antibodies. Condensation of oxidized glutathione tetraethyl ester with 4-amino-4-deoxy-A °-methylpteroic acid with the aid of diethyl phosphorocyanidate afforded the tetraethyl ester (VIII.262) (47% yield). Hydrolysis of the ester groups with Ba(OH)2 followed by ion-exchange chromatography in the presence of 2-mercaptoethanol gave a crude product which was assumed to be the reduced tripeptide. On further purification by gel filtration without 2-mercaptoethanol, this compound underwent spontaneous oxidation to disulphide (VIII.263). In a model experiment, an IgG, monoclonal antibody directed against human transferrin receptor was activated by reaction with A-succinimidyl-3-(2-pyridyldithio)propionate, and con-... 

Binding studies of I-labeled human transferrin to membrane preparations revealed the presence of a high affinity saturable binding site K = 2.2 x 10 m), similar to that of human transferrin receptor. Purified amastigotes of L. infantum and L. mexicana amazonensis also bind I-labeled transferrin similarly to promastigote membrane preparations. It is thus likely that transferrin mediates iron transport in both life stages of Leishmania parasites. 

Immunotoxins composed of ricin A chain coupled to a cell-specific monoclonal antibody have continued to show promise as a new class of antitumor agents. Gnt tin and Raso investigated the use of the carboxylic ionophor monensin formulated in an O/W emulsion for the in vitro and in vivo potentiation of immu-notoxin.s. Monensin in this pharmacologically available form significantly improved the in vivo efficacy of both anti-human transferrin receptor immunotoxin and anticarcinoembryonic antigen immunotoxin when used as regional therapy. 

Antibodies Rabbit anti-LRP light chain was obtained from Dr. J. Herz (University of Texas Southwestern Medical Center, Dallas, TX), rabbit anti-SR-BI antibody from Dr. M. Krieger (Massachusetts Institute of Technology, Cambridge, MA), mouse monoclonal anti-human transferrin receptor (TfnR) antibody (H ) from Dr. I. S. Trowbridge (Salk Institute, La Jolla, CA), and mouse monoclonal anti-asialoglycoprotein receptor (ASGPR) antibody from Daiichi Pure Chemicals Co., Ltd (Ibaraki, Japan). 

Schuler, J., J. Frank, W. Saenger, and Y. Georgahs. 1999. Thermally induced aggregation of human transferrin receptor studied by light-scattering techniques. Biophysical Journal 77 (2) 1117-1125. 

Xia H, Anderson B, Mao Q, Davidson BL. Recombinant human adenovirus targeting to the human transferrin receptor improves gene transfer to brain microcapillary endothelium. J Virol 2000 74 11359-11366. 

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