Direct binding to integrins and loss of disulfide linkage in IL-1β are involved in the agonistic action of IL-1β

There is a strong link between integrins and IL-1β, but the specifics of the role of integrins in IL-1β signaling are unclear. We describe that IL-1β specifically bound to integrins αvβ3 and α5β1. The E128K mutation in the IL1R-binding site enhanced integrin binding. We studied if direct integrin binding is involved in IL-1β signaling. We compared sequences of IL-1β and IL-1 receptor antagonist (IL1RN), which is an IL-1β homologue but has no agonistic activity. Several surface-exposed Lys residues are present in IL-1β, but not in IL1RN. A disulfide-linkage is present in IL1RN, but is not in IL-1β due to natural C117F mutation. Substitution of the Lys residues to Glu markedly reduced integrin binding of E128K IL-1β, suggesting that the Lys residues mediate integrin binding. The Lys mutations reduced, but not completely abrogated, agonistic action of IL-1β. We studied if the disulfide linkage plays a role in agonistic action of IL-1β. Re-introduction of the disulfide linkage by the F117C mutation did not affect agonistic activity of WT IL-1β, but effectively reduced the remaining agonistic activity of the Lys mutants. Also, deletion of the disulfide linkage in IL1RN by the C116F mutation did not make it agonistic. We propose that the direct binding to IL-1β to integrins is primarily important for agonistic IL-1β signaling, and that the disulfide linkage indirectly affect signaling by blocking conformational changes induced by weak integrin binding to the Lys mutants. The integrin-IL-1β interaction is a potential target for drug discovery.