The dynamic regulations of ubiquitination and deubiquitination play important roles in TGF-b-activated kinase 1 (TAK1)-mediated NF-kB activation, which regulates various physiological and pathological events. We identified ubiquitin-specific protease (USP)19 as a negative regulator of TNF-a-and IL-1b-triggered NF-kB activation by deubiquitinating TAK1. Overexpression of USP19 but not its enzymatic inactive mutant inhibited TNF-a-and IL-1b-triggered NF-kB activation and transcription of downstream genes, whereas USP19 deficiency had the opposite effects. Usp19 2/2 mice produced higher levels of inflammatory cytokines and were more susceptible to TNF-a-and IL-1b-triggered septicemia death compared with their wild-type littermates. Mechanistically, USP19 interacted with TAK1 in a TNF-a-or IL-1b-dependent manner and specifically deconjugated K63-and K27-linked polyubiquitin chains from TAK1, leading to the impairment of TAK1 activity and the disruption of the TAK1-TAB2/3 complex. Our findings provide new insights to the complicated molecular mechanisms of the attenuation of the inflammatory response.

TIR domain-containing adaptor inducing interferon-β (TRIF) is an essential adaptor protein required for innate immune responses mediated by Toll-like receptor (TLR) 3- and TLR4. Here we identify USP19 as a negative regulator of TLR3/4-mediated signaling. USP19 deficiency increases the production of type I interferons (IFN) and proinflammatory cytokines induced by poly(I:C) or LPS in vitro and in vivo. Usp19-/- mice have more serious inflammation after poly(I:C) or LPS treatment, and are more susceptible to inflammatory damages and death following Salmonella typhimurium infection. Mechanistically, USP19 interacts with TRIF and catalyzes the removal of TRIF K27-linked polyubiquitin moieties, thereby impairing the recruitment of TRIF to TLR3/4. In addition, the RING E3 ubiquitin ligase complex Cullin-3-Rbx1-KCTD10 catalyzes K27-linked polyubiquitination of TRIF at K523, and deficiency of this complex inhibits TLR3/4-mediated innate immune signaling. Our findings thus reveal TRIF K27-linked polyubiquitination and deubiquitination as a critical regulatory mechanism of TLR3/4-mediated innate immune responses.

The proinflammatory cytokine IL-1β plays critical roles in inflammatory and autoimmune diseases. IL-1β signaling is tightly regulated to avoid excessive inflammatory response. In this study, we identified the E3 ubiquitin ligase membrane-associated RING-CH-type finger 3 (MARCH3) as a critical negative regulator of IL-1β–triggered signaling. Overexpression of MARCH3 inhibited IL-1β–triggered activation of NF-κB as well as expression of inflammatory genes, whereas MARCH3 deficiency had the opposite effects. MARCH3-deficient mice produced higher levels of serum inflammatory cytokines and were more sensitive to inflammatory death upon IL-1β injection or Listeria monocytogenes infection. Mechanistically, MARCH3 was associated with IL-1 receptor I (IL-1RI) and mediated its K48-linked polyubiquitination at K409 and lysosomal-dependent degradation. Furthermore, IL-1β stimulation triggered dephosphorylation of MARCH3 by CDC25A and activation of its E3 ligase activity. Our findings suggest that MARCH3-mediated IL-1RI degradation is an important mechanism for attenuating IL-1β–triggered inflammatory response.