Human granulocyte-macrophage colony-stimulating factor receptor signal transduction requires the proximal cytoplasmic domains of the alpha and beta subunits.
Human granulocyte-macrophage colony-stimulating factor (GM-CSF) controls the production, maturation, and function of cells in multiple hematopoietic lineages. These effects are mediated by a cell-surface receptor (GM-R) composed of alpha and beta subunits, each containing 378 and 881 amino acids, respectively. Whereas the alpha subunit exists as several isoforms that bind GM-CSF with low affinity, the beta common subunit (beta c) does not bind GM-CSF itself, but acts as a high-affinity converter for GM-CSF, interleukin-3 (IL-3), and IL-5 receptor alpha subunits. The cytoplasmic region of GM-R alpha consists of a membrane-proximal conserved region shared by the alpha 1 and alpha 2 isoforms and a C-terminal variable region that is divergent between alpha 1 and alpha 2. The cytoplasmic region of beta c contains membrane proximal serine and acidic domains. To investigate the amino acid sequences that influence signal transduction by this receptor complex, we constructed a series of cytoplasmic truncation mutants of the alpha 2 and beta subunits. To study these truncations, we stably transfected the IL-3-dependent murine cell line Ba/F3 with wild-type or mutant cDNAs. We found that the wild-type and mutant alpha subunits conferred similar low-affinity binding sites for human GM-CSF to Ba/F3, and the wild-type or mutant beta subunit converted some of these sites to high-affinity; the cytoplasmic domain of beta was unnecessary for this high-affinity conversion. Proliferation assays showed that the membrane-proximal conserved region of GM-R alpha and the serine-acidic domain of beta c are required for both cell proliferation and ligand-dependent phosphorylation of a 93-kD cytoplasmic protein. We suggest that these regions may represent an important signal transduction motif present in several cytokine receptors.
Weiss
M
M
Division of Pediatric Hematology and Oncology, Dana-Farber Cancer Institute, Boston, MA 02115.
Yokoyama
C
C
Shikama
Y
Y
Naugle
C
C
Druker
B
B
Sieff
C A
CA
D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D003593:Cytoplasm; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
D007377:Interleukin-3; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D014443:Tyrosine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor