Roles of Deubiquitinases OTUD3 and OTUD5 in Inflammatory Bowel Diseases.

Excessive production of type I interferons (IFNs) underlies the immunopathogenesis of autoimmune disorders, including systemic lupus erythematosus and autoimmune pancreatitis. Whether type I IFNs play pathogenic or protective roles in the development of inflammatory bowel diseases (IBD) has been a matter of debate. The production of type I IFNs is tightly regulated by the conjugation and removal of polyubiquitin chains on or from intracellular signaling molecules. OTU deubiquitinases 3 (OTUD3) and 5 (OTUD5) are enzymes that cleave various polyubiquitin chains from target proteins. OTUD3 and OTUD5 deubiquitinate key critical intracellular molecules of the type I IFN signaling pathways, stimulator of interferon genes (STING), and TNF receptor-associated factor 3 (TRAF3), respectively, and thus regulate the production of type I IFNs by innate immune cells. Recent studies provided evidence that the impaired function of OTUD3 and OTUD5 increases susceptibility to human and experimental IBD owing to the excessive production of type I IFNs caused by the activation of STING and TRAF3, respectively. Collectively, OTUD3 and OTUD5 play protective rather than pathogenic roles in the development of IBD through the negative regulation of type I IFN-mediated signaling pathways. In this review article, we discuss the association between the development of IBD and impaired function of OTUD3 or OTUD5 by focusing on their deubiquitinase activity and type I IFN responses.