Ubiquitin-specific protease 4 mitigates Toll-like/interleukin-1 receptor signaling and regulates innate immune activation

The Toll-like receptor (TLR)/interleukin 1 receptor (IL-1R) signaling pathway is essential for innate immune responses and immune homeostasis. Lysine 63 polyubiquitinated Tumor necrosis factor receptor-associated factor (TRAF)6 mediates its downstream signaling activation. In a gain of expression screen of 66 different deubiquitinating enzymes (DUBs), we identified ubiquitin-specific protease (USP)4 as a potent negative regulator of TLR/IL-1R signaling and TRAF6 interacting protein. USP4 deubiquitinates TRAF6 and thereby prevents the activation of NF-κB and AP-1 transcriptional factors and subsequent pro-inflammatory responses. LPS-treated usp4-depleted zebrafish larvaes expressed higher levels of pro-inflammatory cytokines and were more susceptible to endotoxic challenge. Taken together, our results demonstrate that USP4 plays an essential role in negative regulation of the TLR-IL-1R signaling-mediated innate immune response.