The cell surface expression level of the human interleukin-5 receptor alpha subunit determines the agonistic/antagonistic balance of the human interleukin-5 E13Q mutein.
The human interleukin-5 (IL-5) receptor consists of an alpha-chain that specifically binds the ligand with intermediate affinity, and a beta c-chain, that associates with the IL-5/IL-5R alpha complex, leading to a high-affinity, signal transducing receptor complex. Structure-function studies showed that modification of the putative beta c-chain binding site in IL-5 (E13Q mutein) converted the molecule into an antagonist. However, analysis of the effect of this mutant IL-5 on COS-1 cells transfected with both receptor subunits, did not show reduced interaction with the beta c subunit [Tavernier, J., Tuypens, T., Verhee, A., Plaetinck, G., Devos, R., Van der Heyden, J., Guisez, Y. & Oefner, C. (1995) Proc. Natl Acad. Sci. USA 89, 7041-7045]. To gain more insight into the mechanism of IL-5 antagonism by E13Q, we tested its biological activity on two FDC-P1 subclones that express clearly different numbers of alpha-subunits yet an almost constant number of murine beta c-subunits. Here we show that E13Q has a biological activity comparable to wild-type IL-5 only when a high number of alpha-chains is present on the cells. Confirming the critical role of the IL5R alpha cell-surface expression level, treatment with suboptimal doses of a neutralising anti-IL-5R alpha antibody results in reduced activity of the mutant but not of wild-type IL-5.
Van Ostade
X
X
Flanders' Interuniversity Institute for Biotechnology, Department of Medical Protein Research, Faculty of Medicine, University of Ghent, Belgium.
Van der Heyden
J
J
Verhee
A
A
Vandekerckhove
J
J
Tavernier
J
J
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D019556:COS Cells; D002455:Cell Division / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D011485:Protein Binding / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D018123:Receptors, Interleukin / Q000037:antagonists & inhibitors / Q000235:genetics*; D053649:Receptors, Interleukin-5; D015398:Signal Transduction / Q000235:genetics; D014162:Transfection / Q000235:genetics
D000911:Antibodies, Monoclonal; D011956:Receptors, Cell Surface; D018123:Receptors, Interleukin; D053649:Receptors, Interleukin-5