Granulocyte-macrophage colony-stimulating factor receptors alter their binding characteristics during myeloid maturation through up-regulation of the affinity converting beta subunit (KH97)

Acute myeloid leukemia blasts express dual affinity (high and low) granulocyte-macrophage colony-stimulating factor (GM-CSF) binding, and the high affinity GM-CSF binding is counteracted by excess interleukin-3 (IL-3). Neutrophils express a single class of GM-CSF-R with intermediate affinity that lack IL-3 cross-reactivity. Here we demonstrate the differentiation associated changes of GM-CSF binding characteristics in three models representative of different stages of myeloid maturation. We find that high affinity GM-CSF binding is converted into intermediate affinity binding, which still cross-reacts with IL-3, beyond the stage of promyelocytes. During terminal maturation towards neutrophils, IL-3 cross-reactivity is gradually lost. We sought to determine the mechanism underlying the affinity conversion of the GM-CSF-R. Northern and reverse transcriptase-polymerase chain reaction analysis of GM-CSF-R alpha and -beta c (KH97) transcripts did not provide indications for the involvement of GM-CSF-R splice variants in the formation of the intermediate affinity GM-CSFR complex. In COS-cell transfectants with increasing amounts of beta c in the presence of a fixed number of GM-CSF-R alpha chains, the high affinity GM-CSF binding converted into intermediate affinity GM-CSF binding. These results are discussed in view of the concept that increasing expression of beta c subunits may cause alternative oligomerization of the GM-CSF-R alpha and -beta c subunits resulting in the formation of intermediate rather than high affinity GM-CSFR alpha.beta c complexes.