Transferrin receptors of human fibroblasts. Analysis of receptor properties and regulation

Abstract

Normal human skin fibroblasts cultured in vitro exhibit specific binding sites for 125I-labelled transferrin. Kinetic studies revealed a rate constant for association (Kon) at 37 degrees C of 1.03 X 10(7) M-1 X min-1. The rate constant for dissociation (Koff) at 37 degrees C was 7.9 X 10(-2) X min-1. The dissociation constant (KD) was 5.1 X 10(-9) M as determined by Scatchard analysis of binding and analysis of rate constants. Fibroblasts were capable of binding 3.9 X 10(5) molecules of transferrin per cell. Binding of 125I-labelled diferric transferrin to cells was inhibited equally by either apo-transferrin or diferric transferrin, but no inhibition was evident with apo-lactoferrin, iron-saturated lactoferrin, or albumin. Preincubation of cells with saturating levels of diferric transferrin or apo-transferrin produced no significant change in receptor number or affinity. Preincubation of cells with ferric ammonium citrate caused a time- and dose-dependent decrease in transferrin binding. After preincubation with ferric ammonium citrate for 72 h, diferric transferrin binding was 37.7% of control, but no change in receptor affinity was apparent by Scatchard analysis. These results suggest that fibroblast transferrin receptor number is modulated by intracellular iron content and not by ligand-receptor binding.

Vitamin C modulation of H2O2-induced damage and iron homeostasis in human cells

“…Conversely, iron chelation with 300 µM DFO for 12 hours doubled the steady-state levels of TfR mRNA (p < 0.001). This agrees with the current understanding of the regulation of the TfR expression by the IRE/IRP system in HDFs [46,47]. Notably, incubation of HDFs with 100 µM AA or AA2P for 12 hours caused a 2-fold down-regulation of the TfR (p < 0.001; Fig.…”

“…6C). As expected [46] The levels of cellular ferritin were measured using a commercial ELISA. HDFs responded to iron overload (FAC for 16 hours) with a dramatic increase in ferritin levels, whereas the chelation of intracellular iron pools with DFO reduced the levels of ferritin by half (Fig.…”

Limited Transferrin Receptor Clustering Allows Rapid Diffusion of Canine Parvovirus into Clathrin Endocytic Structures

“…shorter than that of holotransferrin-TfR complexes (ϳ8 min) on other mammalian cells (17,49). The short half-life of CPV-TfR complexes indicates that CPV has a much lower affinity for TfR than holotransferrin (K d , ϳ5 nM) (24,49). We speculate that this low receptor affinity, combined with steric limitations imposed by the capsid architecture, restricts the number of receptors that simultaneously engage a capsid.…”

“…Right, plot of the CPV and TfR fluorescence intensity for the images at left. shorter than that of holotransferrin-TfR complexes (ϳ8 min) on other mammalian cells (17,49). The short half-life of CPV-TfR complexes indicates that CPV has a much lower affinity for TfR than holotransferrin (K d , ϳ5 nM) (24,49).…”

Doxorubicin-transferrin conjugate selectively overcomes multidrug resistance in leukaemia cells

“…Furthermore, the potential benefits of DOX may be blocked by the development of drug-resistant cancer cells. Neoplastic cells have increased numbers of receptors for transferrin (150,000-1,000,000 per cell) compared to normal cells like fibroblasts [24]. Therefore, transferrin can deliver drugs directly to neoplastic cells with a reduced injury to normal tissue cells [6,25].…”