USP18 negatively regulates NF-κB signaling by targeting TAK1 and NEMO for deubiquitination through distinct mechanisms

Abstract

Nuclear factor κB (NF-κB) is a key transcription factor in inflammatory immune responses and cell survival. Multiple types of ubiquitination play critical roles in the activation of NF-κB signaling, yet the molecular mechanisms responsible for their reversible deubiquitination are still poorly understood. In this study, we identified a member of the deubiquitinases family, ubiquitin-specific protease 18 (USP18), as a novel negative regulator in Toll-like receptor (TLR)-mediated NF-κB activation in human macrophages. USP18 is an interferon inducible gene, which is also upregulated by various TLR ligands in human monocytes and macrophages. Knockdown of USP18 enhanced the phosphorylation of IKK, the degradation of IκB, and augmented the expression of pro-inflammatory cytokines. Furthermore, USP18 interacted with TAK1-TAB1 complex and IKKα/β-NEMO complex, respectively. USP18 cleaved the K63-linked polyubiquitin chains attached to TAK1 in a protease-dependent manner. Moreover, USP18 targeted the IKK complex through the regulatory subunit NEMO of IKK, and specifically inhibited K63-linked ubiquitination of NEMO. Mutation analysis revealed direct binding of USP18 to the UBAN motif of NEMO. Our study has identified a previously unrecognized role for USP18 in the negative regulation of NF-κB activation by inhibiting K63-linked ubiquitination of TAK1 and NEMO through distinct mechanisms.

USP18 protects against hepatic steatosis and insulin resistance through its deubiquitinating activity

“…The data collected in our study validated that the 255‐372 amino acids of USP18 can associate with the 1‐300 amino acids of TAK1 and that the USP domain of USP18 enables its deubiquitinating effect on TAK1. Therefore, the up‐regulated activation of TAK1 by HFD or PA stimulation was constrained by USP18 through its DUB enzymatic activity in hepatocytes, which is consistent with the results discovered in immune cells . Here, we also provided evidence that treating HFD‐fed mice with enzymatic active‐site mutant USP18 failed to inhibit TAK1 activation.…”

Tissue and time specific expression pattern of interferon regulated genes in the chicken

“…The same seems to be applicable to chickens as a significant upregulation of SOCS1 and SOCS3 in spleen and lung, with a strong 3 h peak in the spleen and a plateau in the spleen was obseved. USP18 does maintain long-term desensitization by either removing ISG15 conjugated proteins or intracellular binding to IFNAR2 [69, 70]. Strong upregulation of USP18 in spleen and lung after 3 h demonstrates the conservation of negative control mechanisms of the type I IFN response in chickens.…”

Deubiquitinases: Novel Therapeutic Targets in Immune Surveillance?

“…However, we now know that USP18 also mediates and regulates TLR-induced NF- κ B activation by cleavage of K63-polyubiquitin chains, but not K48 chains, of TAK1 and NEMO [28]. …”