title: Down-modulation of high-affinity receptors for erythropoietin on murine erythroblasts by interleukin 3.
abstract: Erythropoiesis is regulated by the glycoprotein hormone erythropoietin (Epo) and by several other factors including interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor. The possibility that IL-3 and GM-CSF may act by modulating Epo receptor expression was investigated using erythroblasts purified from the spleens of phenylhydrazine-treated mice. AT 37 degrees C, in the presence of sodium azide to inhibit receptor internalization. 125I-labeled human recombinant Epo bound to a single class of high-affinity receptors on splenic erythroblasts (450 sites/cell, Kd = 700 pM). Autoradiographic studies indicated that 94% of specifically bound Epo was associated with erythroblasts, decreased Epo binding being observed with increasing erythroid cell maturation. Whereas recombinant mouse IL-3 and GM-CSF did not compete with 125I-Epo for binding to the Epo receptor, preincubation of cells with IL-3 resulted in a concentration-dependent loss of 125I-Epo binding without altering the affinity of residual receptors for Epo. Complete loss of Epo receptors was effected within 2 h at IL-3 concentrations above 2500 U/ml. Preincubation with recombinant mouse GM-CSF had no effect on binding, even at 100,000 U/ml. In comparison, preincubation of cells with Epo (50 U/ml) caused complete loss of 125I-Epo binding within 30-60 min, an effect not explained by receptor saturation with unlabeled Epo. Thus, in addition to trans-down-modulating growth factor receptors of the granulocyte-macrophage series, IL-3 also trans-down-modulates a growth factor receptor of the erythroid lineage.
authors.affiliation: Malaghan Institute of Medical Research, Wellington School of Medicine, New Zealand.
authors.forename: J K
authors.initials: JK
authors.lastname: Fraser
authors.forename: J
authors.initials: J
authors.lastname: Nicholls
authors.forename: C
authors.initials: C
authors.lastname: Coffey
authors.forename: F K
authors.initials: FK
authors.lastname: Lin
authors.forename: M V
authors.initials: MV
authors.lastname: Berridge
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D003115:Colony-Stimulating Factors / Q000494:pharmacology; D004900:Erythroblasts / Q000187:drug effects / Q000378:metabolism*; D004921:Erythropoietin / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006133:Growth Substances / Q000494:pharmacology; D007377:Interleukin-3 / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D010659:Phenylhydrazines; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D017467:Receptors, Erythropoietin; D013154:Spleen / Q000166:cytology
chemical_list: D003115:Colony-Stimulating Factors; D006133:Growth Substances; D007377:Interleukin-3; D010659:Phenylhydrazines; D011956:Receptors, Cell Surface; D017467:Receptors, Erythropoietin; C030299:phenylhydrazine; D004921:Erythropoietin; D016178:Granulocyte-Macrophage Colony-Stimulating Factor