title: Demonstration of the specific binding of bovine transferrin to the human transferrin receptor in K562 cells: evidence for interspecies transferrin internalization.
abstract: Specific binding of ferric bovine transferrin to the human transferrin receptor was investigated using K562 cells propagated in serum-free medium without transferrin supplemented with 10(-5) elemental iron. Affinity chromatography of solubilized extracts of K562 cells surface-labeled with 125I was performed using bovine transferrin- and human transferrin-Sepharose 4B resins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of resin eluates reveal that bovine transferrin specifically binds a Mr = 188,000 protein which dissociates into a Mr = 94,000 protein under reducing conditions, a finding identical to what is seen with human transferrin. The Mr = 94,000 reduced protein isolated by bovine transferrin resin shows an identical one-dimensional partial proteolytic digestion map with that of the human transferrin receptor. Unlabeled bovine transferrin was shown to specifically compete 125I-labeled human transferrin from the human transferrin receptor on the surface of K562 cells at 4 degrees C in a similar manner as unlabeled human transferrin; however, approximately a 2,000-fold higher concentration of bovine ligand was required to achieve comparable competition (50% inhibition of binding). Indirect immunofluorescence cytolocalization of bovine transferrin in K562 cells grown in serum-free medium supplemented with ferric bovine transferrin reveal patterns similar to those seen for human transferrin (both focal perinuclear and diffuse cytoplasmic fluorescence). Monensin treatment results in a dramatic accumulation of bovine ligand in perinuclear aggregates, suggesting that it is recycled through the Golgi, as is human transferrin. K562 cells grown in serum-free medium supplemented with either 300 micrograms/ml of ferric human or ferric bovine transferrin were found to demonstrate superimposable growth curves.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002846:Chromatography, Affinity; D003470:Culture Media; D005455:Fluorescent Antibody Technique; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000032:analysis / Q000378:metabolism* / Q000473:pathology; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000302:isolation & purification; D011990:Receptors, Transferrin; D013045:Species Specificity; D014168:Transferrin / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D003470:Culture Media; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin