Presence Of Transferrin Receptors Research Articles

Real-Time Specific Light-Up Sensing of Transferrin Receptor: Image-Guided Photodynamic Ablation of Cancer Cells through Controlled Cytomembrane Disintegration.

Transferrin receptor (TfR) represents a unique target for specific imaging of cancer cells and targeted delivery of therapeutic reagents. Detection and qualification of TfR is thus of great importance for cancer diagnosis and therapy. In this contribution, a light-up probe TPETH-2T7 was developed by conjugating a red-emissive photosensitizer with aggregation-induced emission (AIE) characteristics to a TfR-targeting peptide T7. The probe is almost nonemissive by itself, but it gives turn-on fluorescence in the presence of TfR with a detection limit of 0.45 μg/mL. Cellular experiments show that the probe specifically binds to TfR-overexpressed cancer cells. Real-time imaging results reveal that the probe stains the MDA-MB-231 cell membrane in 30 min, which is followed by probe internalization. Experiments on image-guided photodynamic cancer ablation show that the therapeutic performance is better when TPETH-2T7 is localized on the cell membrane as compared to that being internalized into cells. Confocal laser scanning microscopy (CLSM) study reveals that cytomembrane disintegration allows quick ablation of MDA-MB-231 cells.

Fabrication of Transferrin Functionalized Gold Nanoclusters/Graphene Oxide Nanocomposite for Turn-On Near-Infrared Fluorescent Bioimaging of Cancer Cells and Small Animals

Transferrin (Tf)-functionalized gold nanoclusters (Tf-AuNCs)/graphene oxide (GO) nanocomposite (Tf-AuNCs/GO) was fabricated as a turn-on near-infrared (NIR) fluorescent probe for bioimaging cancer cells and small animals. A one-step approach was developed to prepare Tf-AuNCs via a biomineralization process with Tf as the template. Tf acted not only as a stabilizer and a reducer but also as a functional ligand for targeting the transferrin receptor (TfR). The prepared Tf-AuNCs gave intense NIR fluorescence that can avoid interference from biological media such as tissue autofluorescence and scattering light. The assembly of Tf-AuNCs and GO gave the Tf-AuNCs/GO nanocomposite, a turn-on NIR fluorescent probe with negligible background fluorescence due to the super fluorescence quenching property of GO. The NIR fluorescence of the Tf-AuNCs/GO nanocomposite was effectively restored in the presence of TfR, due to the specific interaction between Tf and TfR and the competition of TfR with the GO for the Tf in Tf-AuNCs/GO composite. The developed turn-on NIR fluorescence probe offered excellent water solubility, stability, and biocompatibility, and exhibited high specificity to TfR with negligible cytotoxicity. The probe was successfully applied for turn-on fluorescent bioimaging of cancer cells and small animals.

Transferrin receptor 2 mediates uptake of transferrin-bound and non-transferrin-bound iron

Transferrin receptor 2 appears to have dual roles in iron metabolism; one is signalling, the other is iron transport. It is sensitive to high levels of diferric transferrin, which is associated with disorders of iron overload. Also present in these disorders are increased levels of plasma non-transferrin-bound iron. This study sought to clarify the role of transferrin receptor 2 in the uptake of transferrin-bound and non-transferrin-bound iron. Variant Chinese Hamster Ovary (CHO) cells, transfected with transferrin receptor 2, were incubated with radio-labelled transferrin-bound or non-transferrin-bound iron. Competition studies were performed in the presence of unlabelled dimetallic transferrin; knockdown was performed using specific siRNA. Cells expressing transferrin receptor 2 bound and internalised transferrin and transferrin-bound iron. Transferrin recycling occurred with an average cycling time of 11-15 min. Interestingly, the presence of transferrin receptor 2 was also associated with uptake of non-transferrin-bound iron which was inhibited by unlabelled transferrin-bound metals. Knockdown reduced transferrin-bound and non-transferrin-bound iron uptake by approximately 60%. Transferrin receptor 2 mediates transferrin-bound iron uptake by receptor-mediated endocytosis. It is also involved in the uptake of non-transferrin-bound iron and the inhibition of non-transferrin-bound iron uptake by diferric transferrin in CHO cells.

Transcytosis of 6.6-nm gold-labeled transferrin: an ultrastructural study in cultured porcine blood–brain barrier endothelial cells

The mechanism and regulation of iron transport to the brain are largely unknown. The large surface area of the blood–brain barrier capillaries and the presence of transferrin receptors on the luminal plasma membranes of the blood–brain barrier endothelial cells (BBB-ECs) suggest that these cells actively participate in the transport of iron into the brain. In this paper, we describe the ultrastructural morphology of primary and first-passage cultures of BBB-ECs grown on different types of porous membranes. To investigate the mechanism of iron transport into and across the BBB-ECs, porous membrane grown first-passage cells were incubated with 6.6-nm gold-labeled transferrin and studied with electron microscopy. Results are suggestive for a transcytosis of transferrin through the BBB-ECs.

The expression of transferrin receptors on erythroblasts in anaemia of chronic disease, myelodysplastic syndromes and iron deficiency.

The presence of transferrin receptors on erythroblasts in patients with iron deficiency, anaemia of chronic disease (ACD) and myelodysplastic syndrome (MDS) was studied by two-colour analysis on a flow cytometer. CD 71 was used to quantify the number of transferrin receptors and GLY-A to identify erythroblasts. In cases of iron deficiency, the number of transferrin receptors was increased on part of the erythroblasts thus facilitating iron uptake by the cells. In patients with ACD or MDS, a decrease of the number of transferrin receptors on erythroblasts was found. This leads to the conclusion that the ineffective response to iron therapy in cases of ACD and MSD can be explained by a decline of transferrin receptors on the red cells.

Age-dependent uptake and retrograde axonal transport of exogenous albumin and transferrin in rat motor neurons

This study presents evidence for retrograde axonal transport of exogenous albumin and transferrin in adult brainstem motor neurons, whereas plasma proteins are not transported in neonatal motor neurons. The plasma protein uptake in motor neurons was dose-dependent, suggesting a nonspecific (fluid-phase) uptake mechanism. Further evidence for nonspecific uptake of exogenous transferrin in the motor neuron was found in the presence of transferrin receptor only on the soma and not on the axon terminal. The immunoreaction product of the exogenous plasma proteins was localized as perinuclear granules in association with the lysosomal system, as verified by staining for the lysosomal marker cathepsin D and by ultrastructural examinations. The results suggest that albumin and transferrin derived from hepatic synthesis gain access to motor neurons nonspecifically by retrograde axonal transport, whereas transferrin derived from intracerebral synthesis specifically gains access to motor neurons due to receptor-mediated uptake at the soma of the neuron. The lack of plasma proteins in developing motor neurons suggests that retrograde axonal transport of plasma proteins has no significance for developing axons. Plasma proteins have a potential for transporting toxic metals to motor neurons. Intraneuronal uptake of aluminum-transferrin either by nonspecific uptake in axon terminals or by receptor-mediated uptake at the soma may have a role in the pathogenesis of the motor neuron disease amyotrophic lateral sclerosis.

In vitro efficacy of transferrin-toxin conjugates against glioblastoma multiforme.

The cytotoxic activity of immunotoxins constructed with human diferric transferrin (Tfn) as the carrier ligand and an abrin variant Pseudomonas exotoxin A (PE) and the diphtheria toxin mutant cross-reacting material (CRM) 107 as the toxin moieties were studied in vitro. Three malignant human cell lines, the glioblastomas multiforme SNB19 and SF295 and the LOX melanoma, and a nonhuman control murine melanoma cell line B16 were assessed. The presence of transferrin receptors on the cell lines was confirmed by direct 125I-Tfn binding assays. The 50% protein synthesis inhibitory concentration (IC50) values for all cell lines demonstrated that Tfn-abrin variant and Tfn-PE had comparable potency and were both more effective than Tfn-CRM 107. Monensin, a carboxylic ionophore, potentiated the effect of Tfn-abrin variant against glioma cells approximately 35-fold with IC50 values of 4.0 x 10(-13) M and 4.7 x 10(-12) M for SNB19 and SF295, respectively. Cytotoxic activity of Tfn-abrin variant (with or without monensin) and Tfn-PE was correlated with the degree of Tfn receptor expression measured on the cell lines. The exquisite in vitro cytotoxicity of Tfn-abrin variant and Tfn-PE immunotoxins against glioma and melanoma cells warrants further in vivo evaluation and future consideration of these agents for potential clinical application against glioblastoma multiforme and leptomeningeal neoplasia.

Characterization of transferrin receptors on plasma membranes of lactating rat mammary tissue

Little is known about the transport of iron into the mammary secretory cell and the process of milk iron secretion. The concentration of iron in milk is remarkably unaffected by maternal iron status, suggesting that the uptake of iron into the mammary gland is regulated. It is known that iron enters other cells via transferrin receptor-mediated endocytosis. This study was designed to isolate and characterize the mammary gland transferrin receptor in lactating rat mammary tissue using immunochemical techniques. The existence of functional mammary gland transferrin receptors in lactating rodents was demonstrated using radiolabel-binding techniques. Isolation of mammary transferrin receptors by affinity chromatography was confirmed using immunoelectrophoresis and slot blot analysis. The intact transferrin receptor was found to have a molecular weight of 176 kd as determined by Western blotting followed by scanning densitometry. Reduction of the receptor with β-mercaptoethanol gave a molecular weight of 98 kd. An additional immunoreactive band of 135 kd was observed. The presence of transferrin receptors in normal lactating rat mammary tissue is likely to explain iron transport into mammary tissue for both cellular metabolism and milk iron secretion.

Iron uptake from transferrin and lactoferrin by rat intestinal brush-border membrane vesicles

Interaction of 59Fe-labeled rat transferrin, human lactoferrin, and bovine lactoferrin with rat small intestinal brush-border membrane vesicles was investigated with the use of a rapid filtration technique. Specific binding of 59Fe-labeled rat transferrin and bovine lactoferrin to brush-border membrane vesicles from suckling and adult rats was identified. In contrast, no binding of human lactoferrin occurred. The presence of transferrin receptors on the brush-border membrane of suckling rats was confirmed by immunoblotting, and the molecular mass of the receptor was 96 kDa under nonreducing conditions. Scatchard plot analysis indicated 2.4 x 10(14) binding sites/mg of membrane protein with an affinity constant (Ka) of 4.9 x 10(6) M-1 for rat milk transferrin and 2.2 x 10(14) binding sites/mg of membrane protein with a Ka of 3.2 x 10(6) M-1 for bovine lactoferrin. Bovine lactoferrin competitively inhibited the binding of rat transferrin to the brush-border membrane vesicles. Deglycosylation of rat transferrin and bovine lactoferrin had no influence on the binding of these proteins. The results suggested that bovine lactoferrin bound to the receptor for rat transferrin on the brush-border membrane and that the polypeptide chain rather than the glycan moiety is responsible for the interaction of these proteins with the rat brush-border membrane.

Localization of transferrin receptor in the chorionic villi of complete molar pregnancy

Transferrin receptors have been identified on the villous trophoblast of normal chorionic villi by immunohistochemical techniques. The current study investigated the expression of transferrin receptors on molar chorionic villi by using a monoclonal antibody in immunofluorescence assays. The villous trophoblast of molar chorionic villi was brightly positive for transferrin receptor in the immunofluorescence assay. The presence of transferrin receptors on molar villous trophoblast may influence the immunologic relationship between molar and host tissues.

Trophoblast transferrin and transferrin receptors in the host--parasite relationship of human pregnancy.

Transferrin and specific transferrin receptors are demonstrated on the microvillous surface of syncytiotrophoblast in human immature and term placentae by immuno histological techniques with the use of light and electron microscopy. That the distribution of transferrin is limited to the materno-foetal interface supports the hypothesis that binding of maternal transferrin to trophoblast receptors is involved in the process of iron transport to the foetus. Parallel studies with baboon placentae demonstrate the presence of trophoblast receptors which bind both baboon and human transferrin, thereby putting forward an experimental model which might be used to test the biological significance of placental transferrin receptors in primates. In addition, investigation of a large number of human cell lines shows that many transformed cells, but no normal cells (such as blood lymphocytes) or cells from primary culture (such as neonatal foreskin fibroblasts), possess the ability to bind transferrin to their membranes. These findings suggest that transferrin receptors may play important biological roles in addition to that of iron transport from mother to foetus. One such role could be the limitation of iron in intervillous spaces, thus depriving iron-requiring microorganisms of iron, hence serving as a non-specific factor of resistance for placentae. Another role for foetal transferrin receptors on trophoblasts could be to bind maternal transferrin at the materno-foetal interface, thus frustrating maternal immunosurveillance. This is similar to a mechahism used by schistosomes in the host-parasite relation where host proteins are bound by the parasite to escape immunological recognition. The presence of transferrin receptors on transformed cells suggests that this mechanism might also be employed by tumour cells. Finally, in view of previous studies which show that transferrin is required by stimulated lymphocytes to pass from the G1 to the S phase of cellular replication, it is proposed that trophoblast transferrin receptors could limit the amount of transferrin in intervillous spaces and thus impede the proliferation and possible cytotoxicity of maternal activated lymphocytes at the materno-foetal interface.