title: Specific binding, internalization, and degradation of human recombinant interleukin-3 by cells of the acute myelogenous, leukemia line, KG-1.
abstract: We have studied the interaction of 35S-labeled recombinant IL-3 with the acute myelogenous leukemia cell line, KG-1. 35S-IL-3 bound to these cells in a time dependent, saturable, and specific manner at 4 degrees C. Scatchard transformation of binding isotherms demonstrated the existence of a small number (200) of binding sites, with an apparent dissociation constant of 70-105 pM. After a temperature shift from 4 degrees C to 37 degrees C, surface-bound 35S-IL-3 was rapidly internalized and processed into a trichloroacetic acid soluble form that was released into the medium. Experiments to address the specificity of the IL-3 binding site revealed that neither human IL-2, M-CSF, erythropoietin, transferrin, bovine insulin, nor murine nerve growth factor compete with IL-3 for binding to KG-1 cells. Both human and gibbon recombinant IL-3 and, surprisingly, human recombinant GM-CSF effectively competed the binding of the labeled IL-3 to these cells at 4 degrees C. The competition by GM-CSF was found to be concentration dependent, but much higher concentrations were required to achieve the levels obtained with IL-3. These results suggest that GM-CSF may also interact with the high-affinity IL-3 binding site on KG-1 cells or, alternatively, that GM-CSF binding to its own receptor may decrease the affinity of the IL-3 receptor for its ligand.
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D003115:Colony-Stimulating Factors / Q000378:metabolism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D007377:Interleukin-3 / Q000493:pharmacokinetics*; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism; D016185:Receptors, Interleukin-3; D011994:Recombinant Proteins / Q000493:pharmacokinetics
chemical_list: D003115:Colony-Stimulating Factors; D006133:Growth Substances; D007377:Interleukin-3; D011971:Receptors, Immunologic; D016185:Receptors, Interleukin-3; D011994:Recombinant Proteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor