title: Molecular assembly of the ternary granulocyte-macrophage colony-stimulating factor receptor complex.
abstract: Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine that stimulates the production and functional activity of granulocytes and macrophages, properties that have encouraged its clinical use in bone marrow transplantation and in certain infectious diseases. Despite the importance of GM-CSF in regulating myeloid cell numbers and function, little is known about the exact composition and mechanism of assembly of the GM-CSF receptor complex. We have now produced soluble forms of the GM-CSF receptor alpha chain (sGMRalpha) and beta chain (sbetac) and utilized GM-CSF, the GM-CSF antagonist E21R (Glu21Arg), and the betac-blocking monoclonal antibody BION-1 to define the molecular assembly of the GM-CSF receptor complex. We found that GM-CSF and E21R were able to form low-affinity, binary complexes with sGMRalpha, each having a stoichiometry of 1:1. Importantly, GM-CSF but not E21R formed a ternary complex with sGMRalpha and sbetac, and this complex could be disrupted by E21R. Significantly, size-exclusion chromatography, analytical ultracentrifugation, and radioactive tracer experiments indicated that the ternary complex is composed of one sbetac dimer with a single molecule each of sGMRalpha and of GM-CSF. In addition, a hitherto unrecognized direct interaction between betac and GM-CSF was detected that was absent with E21R and was abolished by BION-1. These results demonstrate a novel mechanism of cytokine receptor assembly likely to apply also to interleukin-3 (IL-3) and IL-5 and have implications for our molecular understanding and potential manipulation of GM-CSF activation of its receptor.
authors.affiliation: Cytokine Receptor Laboratory and Protein Laboratory, Division of Human Immunology, Institute of Medical and Veterinary Science (IMVS), Adelaide, South Australia.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: McClure
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Hercus
authors.forename: Bronwyn A
authors.initials: BA
authors.lastname: Cambareri
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Woodcock
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Bagley
authors.forename: Geoff J
authors.initials: GJ
authors.lastname: Howlett
authors.forename: Angel F
authors.initials: AF
authors.lastname: Lopez
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D001665:Binding Sites; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007553:Isotope Labeling; D015394:Molecular Structure; D010761:Phosphorus Radioisotopes; D016133:Polymerase Chain Reaction; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D012995:Solubility; D021241:Spectrometry, Mass, Electrospray Ionization; D018411:Spodoptera / Q000378:metabolism; D014162:Transfection; D014461:Ultracentrifugation
chemical_list: D018076:DNA, Complementary; D010761:Phosphorus Radioisotopes; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D011994:Recombinant Proteins; C101659:granulocyte-macrophage colony-stimulating factor, Arg(21)-; D016178:Granulocyte-Macrophage Colony-Stimulating Factor