Interleukin-36 (IL-36) Ligands Require Processing for Full Agonist (IL-36α, IL-36β, and IL-36γ) or Antagonist (IL-36Ra) Activity

• Published in: The Journal of biological chemistry Vol. 286; no. 49; pp. 42594 - 42602
• Main Authors: Towne, Jennifer E., Renshaw, Blair R., Douangpanya, Jason, Lipsky, Brian P., Shen, Min, Gabel, Christopher A., Sims, John E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09.12.2011; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Animals; Cell Membrane - metabolism; COS Cells; Cytokine; Cytokine Action; Humans; IL-1; IL-1F; IL-36; IL-36Ra; Immunology; Interleukin; Interleukin-1 - agonists; Interleukin-1 - antagonists & inhibitors; Interleukin-1 - metabolism; Interleukins - chemistry; Interleukins - metabolism; Jurkat Cells; Ligands; Mice; Molecular Sequence Data; Receptors, Interleukin-1 - metabolism; Sequence Homology, Amino Acid; Skin; Immunology; IL-1; IL-36Ra; Interleukin; Cytokine; Cytokine Action; IL-1F; Skin; IL-36
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.267922

IL-36α, IL-36β, and IL-36γ (formerly IL-1F6, IL-1F8, and IL-1F9) are IL-1 family members that signal through the IL-1 receptor family members IL-1Rrp2 (IL-1RL2) and IL-1RAcP. IL-36Ra (formerly IL-1F5) has been reported to antagonize IL-36γ. However, our previous attempts to demonstrate IL-36Ra antagonism were unsuccessful. Here, we demonstrate that IL-36Ra antagonist activity is dependent upon removal of its N-terminal methionine. IL-36Ra starting at Val-2 is fully active and capable of inhibiting not only IL-36γ but also IL-36α and IL-36β. Val-2 of IL-36Ra lies 9 amino acids N-terminal to an A-X-Asp motif conserved in all IL-1 family members. In further experiments, we show that truncation of IL-36α, IL-36β, and IL-36γ to this same point increased their specific activity by ∼103–104-fold (from EC50 1 μg/ml to EC50 1 ng/ml). Inhibition of truncated IL-36β activity required ∼102–103-fold excess IL-36Ra, similar to the ratio required for IL-1Ra to inhibit IL-1β. Chimeric receptor experiments demonstrated that the extracellular (but not cytoplasmic) domain of IL-1Rrp2 or IL-1R1 is required for inhibition by their respective natural antagonists. IL-36Ra bound to IL-1Rrp2, and pretreatment of IL-1Rrp2-expressing cells with IL-36Ra prevented IL-36β-mediated co-immunoprecipitation of IL-1Rrp2 with IL-1RAcP. Taken together, these results suggest that the mechanism of IL-36Ra antagonism is analogous to that of IL-1Ra, such that IL-36Ra binds to IL-1Rrp2 and prevents IL-1RAcP recruitment and the formation of a functional signaling complex. In addition, truncation of IL-36α, IL-36β, and IL-36γ dramatically enhances their activity, suggesting that post-translational processing is required for full activity. Background: IL-36 proteins are IL-1 family members with a key role in the skin. Results: Truncation of IL-36 ligands and IL-36Ra is required for full activity. IL-36Ra binds IL-1Rrp2 and prevents signaling. Conclusion: The mechanism of action of IL-36Ra is directly analogous to that of IL-1Ra. Significance: Protease(s) that activate IL-36 cytokines could be excellent drug targets for psoriasis.