Two modes of beta-receptor recognition are mediated by distinct epitopes on mouse and human interleukin-3.
The cytokine interleukin-3 (IL-3) is a critical regulator of inflammation and immune responses in mammals. IL-3 exerts its effects on target cells via receptors comprising an IL-3-specific alpha-subunit and common beta-subunit (beta c; shared with IL-5 and granulocyte-macrophage colony-stimulating factor) or a beta-subunit that specifically binds IL-3 (beta(IL-3); present in mice but not humans). We recently identified two splice variants of the alpha-subunit of the IL-3 receptor (IL-3R alpha) that are relevant to hematopoietic progenitor cell differentiation or proliferation: the full length ("SP1" isoform) and a novel isoform (denoted "SP2") lacking the N-terminal Ig-like domain. Although our studies demonstrated that each mouse IL-3 (mIL-3) R alpha isoform can direct mIL-3 binding to two distinct sites on the beta(IL-3) subunit, it has remained unclear which residues in mIL-3 itself are critical to the two modes of beta(IL-3) recognition and whether the human IL-3R alpha SP1 and SP2 orthologs similarly instruct human IL-3 binding to two distinct sites on the human beta c subunit. Herein, we describe the identification of residues clustering around the highly conserved A-helix residue, Glu(23), in the mIL-3 A- and C-helices as critical for receptor binding and growth stimulation via the beta(IL-3) and mIL-3R alpha SP2 subunits, whereas an overlapping cluster was required for binding and activation of beta(IL-3) in the presence of mIL-3R alpha SP1. Similarly, our studies of human IL-3 indicate that two different modes of beta c binding are utilized in the presence of the hIL-3R alpha SP1 or SP2 isoforms, suggesting a possible conserved mechanism by which the relative orientations of receptor subunits are modulated to achieve distinct signaling outcomes.
Mirza
Shamaruh
S
Department of Structural Biology, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
Chen
Jinglong
J
Wen
Bin
B
Ewens
Cameron L
CL
Dai
Jin
J
Murphy
James M
JM
Young
Ian G
IG
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D049109:Cell Proliferation; D053648:Cytokine Receptor Common beta Subunit / Q000737:chemistry / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004789:Enzyme Activation; D000939:Epitopes / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D007377:Interleukin-3 / Q000737:chemistry / Q000378:metabolism*; D053650:Interleukin-3 Receptor alpha Subunit / Q000378:metabolism; D053614:Janus Kinase 2 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism
D053648:Cytokine Receptor Common beta Subunit; D000939:Epitopes; C508596:IL3 protein, human; D007377:Interleukin-3; D053650:Interleukin-3 Receptor alpha Subunit; D050505:Mutant Proteins; D020033:Protein Isoforms; D018698:Glutamic Acid; D053614:Janus Kinase 2
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