title: Human interleukin-3 (IL-3) induces disulfide-linked IL-3 receptor alpha- and beta-chain heterodimerization, which is required for receptor activation but not high-affinity binding.
abstract: The human interleukin-3 receptor (IL-3R) is a heterodimer that comprises an IL-3 specific alpha chain (IL-3R alpha) and a common beta chain (beta C) that is shared with the receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5. These receptors belong to the cytokine receptor superfamily, but they are structurally and functionally more related to each other and thus make up a distinct subfamily. Although activation of the normal receptor occurs only in the presence of ligand, the underlying mechanisms are not known. We show here that human IL-3 induces heterodimerization of IL-3R alpha and beta c and that disulfide linkage of these chains is involved in receptor activation but not high-affinity binding. Monoclonal antibodies (MAb) to IL-3R alpha and beta c were developed which immunoprecipitated, in the absence of IL-3, the respective chains from cells labelled with 125I on the cell surface. However, in the presence of IL-3, each MAb immunoprecipitated both IL-3R alpha and beta c. IL-3-induced receptor dimers were disulfide and nondisulfide linked and were dependent on IL-3 interacting with both IL-3R alpha and beta c. In the presence of IL-3 and under nonreducing conditions, MAb to either IL-3R alpha or beta c immunoprecipitated complexes with apparent molecular weights of 215,000 and 245,000 and IL-3R alpha and beta c monomers. Preincubation with iodoacetamide prevented the formation of the two high-molecular-weight complexes without affecting noncovalent dimer formation or high-affinity IL-3 binding. Two-dimensional gel electrophoresis and Western blotting (immunoblotting) demonstrated the presence of both IL-3R alpha and beta c in the disulfide-linked complexes. IL-3 could also be coimmunoprecipitated with anti-IL-3R alpha or anti-beta c MAB, but it was not covalently attached to the receptor. Following IL-3 stimulation, only the disulfide-linked heterodimers exhibited reactivity with antiphosphotyrosine antibodies, with beta c but not IL-3R alpha being the phosphorylated species. A model of IL-3R activation is proposed which may be also applicable to the related GM-CSF and IL-5 receptors.
authors.affiliation: Hanson Centre for Cancer Research, Institute of Medical and Veterinary Science, Adelaide, South Australia.
authors.forename: F C
authors.initials: FC
authors.lastname: Stomski
authors.forename: Q
authors.initials: Q
authors.lastname: Sun
authors.forename: C J
authors.initials: CJ
authors.lastname: Bagley
authors.forename: J
authors.initials: J
authors.lastname: Woodcock
authors.forename: G
authors.initials: G
authors.lastname: Goodall
authors.forename: R K
authors.initials: RK
authors.lastname: Andrews
authors.forename: M C
authors.initials: MC
authors.lastname: Berndt
authors.forename: A F
authors.initials: AF
authors.lastname: Lopez
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D002460:Cell Line; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology*; D007700:Kinetics; D008954:Models, Biological; D008970:Molecular Weight; D011487:Protein Conformation / Q000187:drug effects; D016185:Receptors, Interleukin-3 / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D004220:Disulfides; D007377:Interleukin-3; D016185:Receptors, Interleukin-3