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 alpha and beta subunits of the GM-CSF receptor (GM-CSFR alpha and beta c, respectively). To determine whether identical regions of the beta c protein mediate both cell growth and differentiation, we expressed cDNA constructs encoding the human wild-type (897 amino acids) and truncated beta c (h beta c) subunits along with the wild-type human GM-CSFR alpha 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 h beta c subunit of 627 amino acids was still able to grow in human GM-CSF (hGM-CSF), 681 amino acids of the hpc were necessary for cell differentiation. The addition of hGM-CSF to WT19 cell lines containing the h beta c627 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 h beta c681 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 h beta c subunit.