The Cytoplasmic Domain of Granulocyte-Macrophage Colony-stimulating Factor (GM-CSF) Receptor α Subunit Is Essential for Both GM-CSF-mediated Growth and Differentiation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates differentiation, survival, and proliferation of colony-forming unit-granulocyte-macrophage progenitor cells. The biologic actions of GM-CSF are mediated by binding to a specific receptor consisting of two chains designated as alpha and beta subunits. We have demonstrated that the murine FDC-P1-derived cell line WT-19 transfected with the human GM-CSF receptor alpha and beta subunits (GM-CSFRalpha and beta) can be induced to differentiate by the addition of human GM-CSF (hGM-CSF). By expressing a series of GM-CSFRalpha mutants in WT19 cells, we have determined the amino acid domains of the GM-CSFRalpha cytoplasmic domain that regulate cell differentiation, proliferation, and survival. We found that the membrane proximal proline-rich domain and adjacent 16 residues are essential for both hGM-CSF-dependent cell proliferation and differentiation. In contrast, the C-terminal region of the GM-CSFRalpha cytoplasmic domain was not necessary for cell differentiation mediated by hGM-CSF, but the removal of this region severely impaired the ability of hGM-CSF to support cell survival. While the activation of JAK2, Shc, Erk, and STAT5 proteins correlated with hGM-CSF-mediated cell growth, cellular differentiation occurred in the absence of activation of these signal transduction pathways.