HOIL‐1‐catalysed, ester‐linked ubiquitylation restricts IL‐18 signaling in cytotoxic T cells but promotes TLR signalling in macrophages

• Published in: The FEBS journal 2021-10, Vol.288 (20), p.5909-5924
• Main Authors: Petrova, Tsvetana, Zhang, Jiazhen, Nanda, Sambit K., Figueras‐Vadillo, Clara, Cohen, Philip
• Format: Article
• Language: English
• Subjects: Bone marrow; Cytokines; Cytotoxicity; HOIL‐1; Immune system; Interferon; IRAK protein; Leukocytes (granulocytic); Ligands; Lymphocytes; Lymphocytes T; macrophage; Macrophages; mRNA; myddosome; Signal transduction; Signaling; T cell; Threonine; TRAF6 protein; Ubiquitin; Ubiquitin-protein ligase; ubiquitylation; γ-Interferon
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.15896

The atypical E3 ligase HOIL‐1 forms ester bonds between ubiquitin and serine/threonine residues in proteins, but the physiological roles of this unusual modification are unknown. We now report that IL‐18 signalling leading to the production of interferon γ (IFNγ) and granulocyte–macrophage colony‐stimulating factor (GM‐CSF) is enhanced in cytotoxic T cells from knock‐in mice expressing the E3 ligase‐inactive HOIL‐1[C458S] mutant, demonstrating that the formation of HOIL‐1‐catalysed ester‐linked ubiquitin bonds restricts the activation of this pathway. We show that the interaction of IRAK2 with TRAF6 is required for IL‐18‐stimulated IFN‐γ and GM‐CSF production, and that the increased production of these cytokines in cytotoxic T cells from HOIL‐1[C458S] mice correlates with an increase in both the number and size of the Lys63/Met1‐linked hybrid ubiquitin chains attached to IRAK2 in these cells. In contrast, the secretion of IL‐12 and IL‐6 and the formation of il‐12 and il‐6 mRNA induced in bone marrow‐derived macrophages (BMDMs) by prolonged stimulation with TLR‐activating ligands that signal via myddosomes, which also requires the interaction of IRAK2 with TRAF6, were not increased but modestly reduced in HOIL‐1[C458S] BMDM. The decreased production of these cytokines correlated with reduced ubiquitylation of IRAK2. Our results establish that changes in HOIL‐1‐catalysed ester‐linked ubiquitylation can promote or reduce cytokine production depending on the ligand, receptor and immune cell and may be explained by differences in the ubiquitylation of IRAK2. HOIL‐1 is an atypical E3 ligase that catalyses the attachment of ubiquitin to the hydroxyl side chains of serine and threonine residues in proteins, forming ester bonds. The physiological roles of ester‐linked ubiquitination remain unclear, but recent work indicates that the modification may affect the production of inflammatory mediators. Here, Philip Cohen and co‐authors exploited cytotoxic T cells and bone marrow‐derived macrophages from E3 ligase‐inactive HOIL‐1[C458S] mutant mice to identify specific roles of the enzyme in regulating ‘myddosome’‐dependent signalling pathways. They show that changes in HOIL‐1‐catalysed ester‐linked ubiquitylation can promote or reduce cytokine production depending on the ligand, receptor and immune cell.