Posttranslational Modification of HOIP Blocks Toll-Like Receptor 4-Mediated Linear-Ubiquitin-Chain Formation

Abstract

Linear ubiquitination is an atypical posttranslational modification catalyzed by the linear-ubiquitin-chain assembly complex (LUBAC), containing HOIP, HOIL-1L, and Sharpin. LUBAC facilitates NF-κB activation and inflammation upon receptor stimulation by ligating linear ubiquitin chains to critical signaling molecules. Indeed, linear-ubiquitination-dependent signaling is essential to prevent pyogenic bacterial infections that can lead to death. While linear ubiquitination is essential for intracellular receptor signaling upon microbial infection, this response must be measured and stopped to avoid tissue damage and autoimmunity. While LUBAC is activated upon bacterial stimulation, the mechanisms regulating LUBAC activity in response to bacterial stimuli have remained elusive. We demonstrate that LUBAC activity itself is downregulated through ubiquitination, specifically, ubiquitination of the catalytic subunit HOIP at the carboxyl-terminal lysine 1056. Ubiquitination of Lys1056 dynamically altered HOIP conformation, resulting in the suppression of its catalytic activity. Consequently, HOIP Lys1056-to-Arg mutation led not only to persistent LUBAC activity but also to prolonged NF-κB activation induced by bacterial lipopolysaccharide-mediated Toll-like receptor 4 (TLR4) stimulation, whereas it showed no effect on NF-κB activation induced by CD40 stimulation. This study describes a novel posttranslational regulation of LUBAC-mediated linear ubiquitination that is critical for specifically directing TLR4-mediated NF-κB activation.

Transcriptional analyses provide new insight into the late-stage immune response of a diseased Caribbean coral

“…This protein has previously been shown to be an important part of the coral immune response in multiple studies and has been linked to host production of antimicrobial compounds [ 47 , 48 ]. Other TLR-related contigs we observed to be differentially expressed included tumour necrosis factor receptor-associated factor 6 [ 49 , 50 ], and contigs involved in the negative regulation of TLR signalling, E3 ubiquitin-protein ligase RNF31 [ 51 ] and 4 copies of ubiquitin carboxyl-terminal hydrolase CYLD [ 52 ]. Additionally, we observed upregulation of the protein argonaute 2, an antiviral protein that has previously been described as part of the response of acroporid corals to white diseases [ 53 ].…”

Ubiquitin-conjugating enzyme UBE2J1 negatively modulates interferon pathway and promotes RNA virus infection

“…For example, E3 RNF125 induces degradation of RIG-I, MDA5, and MAVS [ 30 , 31 ]. E3 enzymes HOIL-1 L and HOIP mediate linear ubiquitination, in which the C-terminal carboxyl groups of ubiquitin is conjugated to the α-amino group of N-terminus of another ubiquitin, inhibit RIG-I signaling [ 32 , 33 ].…”

Role of Linear Ubiquitination in Health and Disease

“…Bowman and colleagues showed that, when nondegradative ubiquitin chains are attached to Lys1056, a conformational change is triggered that inhibits the ligase activity of HOIP. Conversely, a single amino acid substitution at this location (K1056R) prevents ubiquitination and results in a constitutively active LUBAC and corresponds to increased abundance of linear chains in resting and LPS-stimulated B cells (63). Together, these studies highlight the diverse pathways engaged in maintaining tight control over NF-kB activation downstream of LUBAC.…”