title: Internalization of radioiodinated erythropoietin and the ligand-induced modulation of its receptor in murine erythroleukemia cells.
abstract: We have studied the internalization of 125I-erythropoietin (Epo) and regulation of Epo receptors by the ligand in a murine erythroleukemia cell clone, TSA8. To determine internalization, a high-salt acid wash was performed. Internalization of 125I-Epo was found in TSA8 cells as well as in fetal mouse liver cells (FMLC), although the percentage of internalized radioactivity reached 40% after incubation at 37 degrees C for 150 min and was lower than that in FMLC. Exposure of TSA8 cells to unlabeled Epo resulted in a rapid, time-dependent reduction in 125I-Epo binding activity. The net loss of the activity was related to the ambient Epo concentration and 5 X 10(-8)M Epo induced approximately 80% loss of total binding capacity. Scatchard analysis of the binding data revealed that the high-affinity receptor number was decreased but the affinity was increased in the Epo-treated cells. In low-affinity receptors, however, the receptor affinity was decreased and the receptor number was not changed much by preincubation with Epo. These results suggest that the decrease in 125I-Epo binding activity after preincubation with unlabeled Epo is mainly accounted for by a decrease in the number of high-affinity receptors, and the high-affinity receptors play an important role in the biological response to Epo.
mesh_terms: D000818:Animals; D001681:Biological Assay; D002460:Cell Line; D004705:Endocytosis; D004921:Erythropoietin / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism*; D008024:Ligands; D051379:Mice
chemical_list: D008024:Ligands; D004921:Erythropoietin