Deubiquitination of RIPK2 by OTUB2 augments NOD2 signalling and protective effects in intestinal inflammation

Background: Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract, but the molecular mechanisms underlying IBD are incompletely understood. In this study, we explored the role and regulating mechanism of otubain 2 (OTUB2), a deubiquitinating Enzyme, in IBD.

Methods: To study the function of OTUB2 in IBD, we generated OTUB2^-/- mice and treated them with dextran sulfate sodium (DSS) to induce experimental colitis. Bone marrow transplantation was performed to identify the cell populations that were affected by OTUB2 in colitis. The molecular mechanism of OTUB2 in signal transduction was studied by various biochemical methods.

Results: OTUB2 was highly expressed in colon-infiltrating macrophages in both humans with IBD and mice with DSS-induced experimental colitis. Colitis was significantly aggravated in OTUB2^-/- mice and bone marrow chimeric mice receiving OTUB2^-/- bone marrow. OTUB2-deficiency impaired the production of cytokines and chemokines in macrophages in response to the NOD2 Agonist muramyl dipeptide (MDP). Upon MDP stimulation, OTUB2 promoted NOD2 signaling by stabilizing RIPK2. Mechanistically, OTUB2 inhibited the proteasomal degradation of RIPK2 by removing K48-linked polyubiquitination on RIPK2, which was mediated by the active C51 residue in OTUB2. In mice, OTUB2 ablation abolished the protective effects of MDP administration in colitis.

Conclusion: This study identified OTUB2 as a novel regulator of intestinal inflammation.

OTUB2; RIPK2; inflammatory bowel disease; signal transduction; ubiquitination.