Transferrin receptors of human fibroblasts. Analysis of receptor properties and regulation.
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.
D001059:Apoproteins; D002478:Cells, Cultured; D005290:Ferric Compounds / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011990:Receptors, Transferrin; D012867:Skin / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism*
D001059:Apoproteins; D005290:Ferric Compounds; D000644:Quaternary Ammonium Compounds; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin; C028284:apotransferrin; C028283:diferric transferrin; C013531:ferric ammonium citrate