IL-3 inhibits the binding of GM-CSF to AML blasts, but the two cytokines act synergistically in supporting blast proliferation.
Equilibrium binding of 125I-labeled recombinant granulocyte macrophage colony-stimulating factor (GM-CSF) to the blast cells of acute myeloblastic leukemia (AML) revealed the presence of two classes of binding components of high and low affinity, with dissociation constants (Kd) in the range of 5-10 pM and 1-10 nM, respectively. Specificity studies revealed that interleukin-3 (IL-3) could partially inhibit the binding of GM-CSF to AML blasts and to the cells of the leukemic lines M07-E, KG-1, and HL-60. The inhibition of GM-CSF binding by IL-3 was directly dependent on the presence of IL-3 receptors. Analysis of competition curves indicated that the Kd and the number of binding sites per cell of unlabeled and iodinated GM-CSF were identical. In contrast, the inhibition of GM-CSF binding by IL-3 was mediated by IL-3 occupancy of a high affinity receptor only, with the same number of sites as the high affinity GM-CSF receptor but a slightly higher Kd. Despite this competitive binding, IL-3 augmented AML blast proliferation in the presence of GM-CSF, indicating that the two growth factors have converging pathways in supporting blast proliferation. In striking contrast to AML blasts, GM-CSF binding to neutrophils was compatible with the presence of only one class of binding site of intermediate affinity (Kd approximately 100-160 pM). Furthermore, IL-3 does not compete for the binding of GM-CSF to neutrophils.
Onetto-Pothier
N
N
Clinical Research Institute of Montreal, Quebec, Canada.
Aumont
N
N
Haman
A
A
Park
L
L
Clark
S C
SC
De Léan
A
A
Hoang
T
T
D001665:Binding Sites; D001667:Binding, Competitive; D002455:Cell Division; D003115:Colony-Stimulating Factors / Q000378:metabolism* / Q000494:pharmacology; D004357:Drug Synergism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006133:Growth Substances / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007377:Interleukin-3 / Q000378:metabolism / Q000494:pharmacology*; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism* / Q000473:pathology; D009504:Neutrophils / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism; D016185:Receptors, Interleukin-3; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000473:pathology
D003115:Colony-Stimulating Factors; D006133:Growth Substances; D007377:Interleukin-3; D011971:Receptors, Immunologic; D016185:Receptors, Interleukin-3; D016178:Granulocyte-Macrophage Colony-Stimulating Factor