In vitro characterization of the human recombinant soluble granulocyte- macrophage colony-stimulating factor receptor

Abstract

We have cloned, expressed, and partially purified a naturally occurring, truncated, soluble form of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor alpha subunit to investigate its biochemical and biologic properties. The soluble receptor species lacks the transmembrane and cytoplasmic domains that are presumably removed from the intact receptor cDNA by a mechanism of alternative splicing. The resulting soluble 55- to 60-kD glycosylated receptor species binds GM-CSF with a dissociation constant (kd) of 3.8 nmol/L. The soluble GM-CSF receptor successfully competes for GM-CSF binding not only with the transmembrane-anchored GM-CSF receptor alpha subunit but also with the native oligomeric high-affinity receptor complex. In addition, in human bone marrow colony-forming assays, the soluble GM-CSF receptor species can antagonize the activity of GM-CSF. Our data suggest that the soluble GM-CSF receptor may be capable of acting in vivo as a modulator of the biologic activity of GM-CSF.

Lungs of patients with idiopathic pulmonary alveolar proteinosis express a factor which neutralizes granulocyte‐macrophage colony stimulating factor

“…Previously, soluble GM‐CSF receptor α chain has been reported to be a specific ligand that bind to GM‐CSF [20–22]. It is possible that soluble GM‐CSF receptor may be overexpressed in the lungs of IPAP patients and inhibits the binding of GM‐CSF to the receptor.…”

GM-CSF as a therapeutic target in autoimmune diseases

“…There also exists a soluble GM-CSF receptor alpha subunit [ 42 ]. The function of this soluble GM-CSF receptor is unclear, but it may be required to inhibit ligand binding to cells which express membrane-bound GM-CSF receptors [ 43 ].…”

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“…The soluble granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor, for example, consists of the low-affinity ␣ subunit and has a K i that is 100-fold higher than the K d of the high-affinity complex consisting of ␣ and ␤ subunits [113]. Thus a substantial excess of soluble GM-CSF receptor is required to inhibit ligand binding to cells that express high-affinity receptors [27]. Soluble receptors can also act as binding proteins to protect the ligand from degradation (Fig.…”

“…1D). In this model, the soluble receptor binds ligand in the [10][11][12] splicing I Nerve growth factor R [13,14] cleavage CD27 [15] CD30 [16][17][18] I Growth hormone R [19][20][21] cleavage, splicing, combined BP GM-CSF R [22][23][24][25][26][27] splicing I Erythropoietin-R [28][29][30] splicing Thrombopoietin R [31][32][33] splicing I, Ag G-CSF R [34] splicing I IL-IRI [35] I IL-IRII [35][36][37] cleavage, ?splicing I IL-2R␣ (Tac, CD25) [38][39][40][41] cleavage I IL-4R [42][43][44][45] cleavage, splicing BP, I IL-5R␣ [46][47][48][49] splicing I IL-7R [50] splicing IL-6R␣ [51][52][53][54][55][56] splicing, cleavage Ag...…”