Mapping the intracytoplasmic regions of the alpha granulocyte-macrophage colony-stimulating factor receptor necessary for cell growth regulation.

The granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor is composed of an a subunit which binds GM-CSF and a p subunit, which together form the high affinity receptor.By transfecting the human a subunit into murine Ba/F3 cells, we have been able to investigate the role of the short 54-amino acid intracytoplasmic portion (amino acid 346-400) of this subunit in mediating cell growth.We have shown that the intracytoplasmic amino acids 346-382 are necessary for GM-CSF-mediated cell growth.In contrast, amino acids 3 8 U O O can be removed without effect.The stable transfection of the human /3 subunit into the cell lines containing the mutant a subunits did not affect the growth characteristics of these cells.The ability of GM-CSF to stimulate cell growth of the B&3 cells a subunit transfectants was correlated with the ability of this hormone to translocate protein kinase C to the particulate fraction.In contrast, the ability of GM-CSF addition to increase phosphorylation of the human p subunit did not correlate with cell growth and required the entire intracytoplasmic domain of the a subunit.These results demonstrate an important role for the intracytoplasmic portion of the a subunit in mediating both signal transduction and cell cycle commitment stimulated by GM-CSF.Granulocyte-macrophage colony-stimulating factor (GM-CSF)' stimulates the growth and differentiation of hematopoietic cells by binding to a receptor composed of a and p subunits (1-3).The a portion of the receptor binds GM-CSF with low affinity (4) while the p protein complexes with the a subunit reconstituting the high affinity receptor (5).The p subunit is shared by both the IL-3 and IL-5 receptors (6, 7), suggesting a basis for overlapping biologic effects of these hormones.Murine cells have been shown to contain two /3 subunits, one of which (AIC2B) is capable of interacting with the human a GM-CSF subunit (8).The a GM-CSF subunit is largely extracellular but contains a 54-amino acid intracytoplasmic tail.Removal of this intracytoplasmic tail appears t o inhibit the ability of the human GM-CSF receptor subunit to stimulate growth of murine DK44741 (to A. S. K.) and CA45672 (to M. B. L.)