Cytoplasmic domains of the human granulocyte-macrophage colony- stimulating factor (GM-CSF) receptor β chain (hβc) responsible for human GM-CSF-induced myeloid cell differentiation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates differentiation, survival, and proliferation of myeloid progenitor cells. The biologic actions of GM-CSF are mediated by its binding to the α and β subunits of the GM-CSF receptor (GM-CSFRα and βc, respectively). To determine whether identical regions of the βc protein mediate both cell growth and differentiation, we expressed cDNA constructs encoding the human wild-type (897 amino acids) and truncated βc (hβc) subunits along with the wild-type human GM-CSFRα subunit in the murine WT19 cell line, an FDC-P1- derived cell line that differentiates toward the monocytic lineage in response to murine GM-CSF. Whereas the WT19 cell line carrying the C-terminal deleted hβc subunit of 627 amino acids was still able to grow in human GM- CSF (hGM-CSF), 681 amino acids of the hβc were necessary for cell differentiation. The addition of hGM-CSF to WT19 cell lines containing the hβc627 subunit stimulated the phosphorylation of ERK (extracellular signal- regulated kinase) and induced the tyrosine-phosphorylation of SHP-2 and STAT5, suggesting that the activation of these molecules is insufficient to mediate the induction of differentiation. A point mutation of tyrosine 628 to phenylalanine (Y628F) within hβc681 abolished the ability of hGM-CSF to induce differentiation. Our results indicate that the signals required for hGM-CSF-induced differentiation and cell growth are mediated by different regions of the hβc subunit.