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 alpha subunit which binds GM-CSF and a beta subunit , which together form the high affinity receptor. By transfecting the human alpha subunit into murine Ba/F3 cells, we have been able to inve stigate 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 382-400 can be r emoved without effect. The stable transfection of the human beta subun it into the cell lines containing the mutant alpha subunits did not af fect the growth characteristics of these cells. The ability of GMCSF t o stimulate cell growth of the Ba/F3 cells alpha subunit transfectants was correlated with the ability of this hormone to translocate protei n kinase C to the particulate fraction. In contrast, the ability of GM -CSF addition to increase phosphorylation of the human beta subunit di d not correlate with cell growth and required the entire intracytoplas mic domain of the alpha subunit. These results demonstrate an importan t role for the intracytoplasmic portion of the alpha subunit in mediat ing both signal transduction and cell cycle commitment stimulated by G M-CSF.