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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Monolayers of normal human fibroblasts were observed to bind ferritin-labeled low density lipoprotein (LDL-ferritin) at specific receptor sites on the cell surface membrane. When fibroblasts were incubated with LDL-ferritin at 4 degrees, more than 70% of the surface-bound ferritin cores were localized by electron microscopy to short segments of the plasma membrane where the membrane appeared indented and coated on both of its sides by a fuzzy material. These membrane segments corresponded to "coated regions" previously described in other cell types. Unver the conditions of these experiments, an average of 55 LDL-ferritin particles were bound to each millimeter of plasma membrane in normal cells. In the presence of a 15-fold excess of native LDL, the number of bound ferritin cores was reduced by 75%, suggesting that the LDL-ferritin was binding to specific LDL receptor sites. Although fibroblasts from a patient with the homozygous form of familial hypercholesterolemia contained the same number of indented, coated membrane regions per millimeter of cell surface as did normal cells, no LDL-ferritin was observed to bind to the cell membrane in these mutant cells. The present ultrastructural data are consistent with previous biochemical and genetic evidence indicating that LDL exerts its regulatory action on cellular cholesterol metabolism in fibroblasts through an interaction with a specific cell surface receptor and that this receptor is defective in homozygous familial hypercholesterolemia fibroblasts. Moreover, the data suggest that the LDL receptor is localized to indented, coated regions of the plasma membrane that appear to participate in the adsorptive endocytosis of proteins.
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PMID:Localization of low density lipoprotein receptors on plasma membrane of normal human fibroblasts and their absence in cells from a familial hypercholesterolemia homozygote. 18 51

Cationized ferritin (CF) was used as an ultrastructural marker to study differences in the distribution and density of surface anionic charges between normal and neoplastic cells. In anchorage-independent cell systems, CF induces a redistribution of cell surface receptor-ligand complexes into clusters, patches, and caps on the surfaces of transformed cells, but not on the surfaces of normal cells. In the present report, the authors have, for the first time, extended the CF labeling studies to a system of anchorage-dependent, rat bladder epithelial cell lines: normal RBTC cells and RBTCC-8 carcinoma cells. Cells were grown to confluency and labeled with 500 micrograms/ml CF for 3 minutes. After completion of CF labeling, cells were incubated for 0, 15, 60, 120 minutes, or overnight and were fixed then with buffered glutaraldehyde for electron microscopy. The results show that (a) CF induces grouping of surface anionic charge sites into patches and clusters on RBTCC-8 carcinoma cells (CF covers 53.86 +/- 2.15% of the plasma membrane), but not on normal RBTC cells (CF covers the entire plasma membrane); (b) CF densities are well correlated to the cell surface sialic acid contents of RBTC (2.42 +/- 0.30 microM/10(9) cells) and RBTCC-8 cells (1.26 +/- 0.25 microM/10(9) cells); and (c) CF-labeled membrane is internalized at equal rates by RBTC and RBTCC-8 cells (30% in 15 minutes; 60% in 60 minutes; 70% in 120 minutes; 100% overnight). These data indicate that CF-induced patching of anionic sites is a surface characteristic that is common to anchorage-dependent and independent tumor cells. Mechanisms of CF patching in neoplastic cells are discussed.
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PMID:Surface charge distribution in normal and transformed rat bladder epithelial cells in vitro. 299 43

We have previously demonstrated that lentil phytohemagglutinin (lentil-PHA) binds to human platelet membranes without causing either aggregation or the release reaction. When platelets are treated with thrombin, there is an increase in lentil-PHA binding suggesting the appearance of new receptor sites on the cell surface. We prepared a lentil-PHA-ferritin conjugate using affinity chromatography which was used to saturate cell surface receptor sites. Studies using this conjugate suggest that thrombin causes a complex change in the platelet surface involving a decrease in the number of lentil-PHA receptor sites on the external platelet surface with a marked increase in sites within the center of the canalicular system. These increased sites may result from fusion of granule membranes with the canalicular membranes during the secretion process. There is no obvious relationship between lentil-PHA receptor sites and intramembranous particles.
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PMID:The effects of thrombin on phytohemagglutinin receptor sites in human platelets. 420 95

Human diferric transferrin binds to the surface of K562 cells, a human leukemic cell line. There are about 1.6 X 10(5) binding sites per cell surface, exhibiting a KD of about 10(-9) M. Upon warming cells to 37 degrees C there is a rapid increase in uptake to a steady state level of twice that obtained at 0 degree C. This is accounted for by internalization of the ligand as shown by the development of resistance to either acid wash or protease treatment of the ligand-cell association. After a minimum residency time of 4-5 min, undegraded transferrin is released from the cell. Internalization is rapid but is dependent upon cell surface occupancy; at occupancies of 20% or greater the rate coefficient is maximal at about 0.1-0.2 min-1. In the absence of externally added ligand only 50% of the internalized transferrin completes the cycle and is released to the medium with a rate coefficient of 0.05 min-1. The remaining transferrin can be released from the cell only by the addition of ligand, suggesting a tight coupling between cell surface binding, internalization, and release of internalized ligand. There is a loss of cell surface-binding capacity that accompanies transferrin internalization. At low (less than 50%) occupancy this loss is monotonic with the extent of internalization. Even at saturating levels of transferrin, the loss of surface receptors upon internalization never exceeds 60-70% of the initial binding capacity. This suggests that receptors enter the cell with ligand but are replaced so as to maintain a constant, albeit reduced, receptor number on the cell surface. In the absence of ligand, the cell surface receptor number returns at 37 degrees C. Neither sodium azide nor NH4Cl blocks internalization of ligand. However, they both prevent the release of transferrin from the cell thus halting the transferrin cycle. Excess ligand can overcome the block due to NH4Cl but not azide although the cycle is markedly slower. Iron is delivered to these cells by transferrin at 37 degrees C with a rate coefficient of 0.15 to 0.2 min-1. The iron is released from the transferrin and the majority is found in intracellular ferritin. There is a large internal receptor pool comprising 70 to 80% of the total cell receptors and this may be involved in maintaining the steady state iron uptake.
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PMID:Receptor-mediated endocytosis of transferrin in K562 cells. 630 98

For electron microscopic demonstration of carbohydrate moieties on cell surfaces of HeLa-cells the lectins from Viscum albumin, Canavalia ensiformis and Dolichos biflorus have been used. The staining experiments were performed by reaction of the cell surface receptor localized lectin with purified antiferritin-antibody followed by ferritin. The three-step reaction cell surface receptors leads to lectin leads to antiferritin antibody leads to ferritin is proposed as general method for electron microscopic localization of lectin receptors without covalent coupling.
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PMID:Electron microscopic visualization by the unlabelled lectin/antiferritin-antibody/ferritin method of lectin receptors on cell surfaces. 678 78

The clinical criteria according to the Polycythemia Vera Study Group (PVSG) do not distinguish between essential thrombocythemia (ET), thrombocythemia associated with early-stage polycythemia vera (PV) and prefibrotic chronic idiopathic myelofibrosis (CIMF). The criteria only classify the advanced stage of PV with increased red cell mass. The classification of myeloproliferative disorders (MPDs), proposed by the World Health Organization (WHO) in 2001, is a compromise of the clinical PVSG and WHO bone marrow criteria, and excludes early stages of ET and PV. The updated European clinical and pathological criteria combine the WHO bone marrow criteria with established and new clinical, laboratory, biological, and molecular MPD markers. This allows clinicians and pathologists to diagnose early-stage MPD and to differentiate ET, PV, and prefibrotic chronic idiopathic myelofibrosis (CIMF). Depending on laboratory tests and diagnostic criteria used, the population of the MPD patients defined as ET, PV, and CIMF are heterogeneous at the clinical, laboratory, and biological and pathological levels. The recent discovery of the JAK2 V617F mutation, which is the cause of a distinct trilinear MPD in its manifold clinical manifestations during long-term follow-up, increases the specificity of a positive JAK2 V617F polymerase chain reaction (PCR) test for the diagnosis of MPD (near 100%), but only half of the ET and CIMF patients according to the PVSG (sensitivity 50%) and the majority of PV patients (sensitivity 95%) are JAK2 V617F positive. A comparison of the laboratory features of JAK2 V617-positive and JAK2 wild-type ET patients clearly showed that JAK2 V617-positive ET is characterized by higher values for hemoglobin, hematocrit, and neutrophil counts; lower values for serum erythropoietin (EPO) levels, serum ferritin, and mean corpuscular volume; and by increased cellularity of the bone marrow in biopsy material. This indicates that JAK2 V617-positive ET patients, diagnosed according to the PVSG criteria, represent a "forme fruste of PV" consistent with early PV mimicking ET (JAK2 V617F trilinear MPD). In contrast, the JAK2 wild-type ET patients had significantly higher platelet counts and usually had a clinical picture of ET with normal serum EPO levels, PRV-1 expression, and leukocyte alkaline phosphatase score, and a typical WHO ET bone marrow picture. The clinical and pathological data on JAK2 V617F-positive MPD patients suggest that the JAK2 V617F mutation defines one disease entity with several sequential steps of ET, PV, and secondary myelofibrosis during long-term follow-up, and that the wild-type JAK2 MPDs may represent another distinct entity with a related but different molecular etiology. MPD-specific markers such as serum EPO, endogenous erythroid colony formation (EEC), and JAK2 V617F have high specificities, but the sensitivities are not high enough to detect the early stages of the MPDs, ET, PV, and prefibrotic CIMF. Bone marrow histopathology in addition to clinical, laboratory, biological, and molecular markers, including the JAK2 V617 PCR test, serum EPO, PRV-1, EEC, LAP score, peripheral blood parameters, and spleen size on echogram will detect the early stages of MPD and allows diagnostic differentiation of the three primary MPDs (ET, PV, and CIMF) in both JAK2 V617F-positive and JAK2 wild-type MPD patients.
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PMID:The 2001 World Health Organization and updated European clinical and pathological criteria for the diagnosis, classification, and staging of the Philadelphia chromosome-negative chronic myeloproliferative disorders. 1681 Jun 9

The aim of this study was to determine whether the burden of JAK2(V617F) allele correlated with major clinical outcomes in patients with polycythemia vera (PV). To this end, we determined JAK2 mutant allele levels in granulocytes of 173 PV patients at diagnosis. The mean (+/-s.d.) mutant allele burden was 52% (+/-29); 32 patients (18%) had greater than 75% mutant allele. The burden of JAK2(V617F) allele correlated with measurements of stimulated erythropoiesis (higher hematocrit, lower mean cell volume, serum ferritin and erythropoietin levels) and myelopoiesis (higher white cell count, neutrophil count and serum lactate dehydrogenase) and with markers of neutrophil activation (elevated leukocyte alkaline phosphatase and PRV-1 expression). As compared to those with less than 25% mutant allele, patients harboring greater than 75% JAK2(V617F) allele were at higher relative risk (RR) of presenting larger spleen (RR 4.7; P<0.001) or suffering from pruritus (RR 3.1; P<0.001). In these patients, the risk of requiring chemotherapy (RR 1.8; P=0.001) or developing major cardiovascular events (RR 7.1; P=0.003) during follow up were significantly increased. We conclude that a burden of JAK2(V617F) allele greater than 75% at diagnosis points to PV patients with high-risk disease.
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PMID:Prospective identification of high-risk polycythemia vera patients based on JAK2(V617F) allele burden. 1762 6