STING induces HOIP-mediated synthesis of M1 ubiquitin chains to stimulate NF-kB signaling
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ABSTRACT:
SUBMITTER: Dr. Tara, D Fischer
PROVIDER: S-SCDT-10_1038-S44318-024-00291-2 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:STING activation by cyclic dinucleotides in mammals induces interferon- and NFκB -related gene expression, and the lipidation of LC3B at Golgi membranes. While mechanisms of the interferon response are well understood, the mechanisms of NFκB activation mediated by STING remain unclear. We report that STING activation induces K63- and M1-linked/linear ubiquitin chain formation at LC3B-associated Golgi membranes. Loss of the LUBAC E3 ubiquitin ligase prevents formation of linear, but not K63-linked ubiquitin chains or STING activation and inhibits STING-induced NFκB and IRF3-mediated signaling in monocytic THP1 cells. The proton channel activity of STING is also important for both K63 and linear ubiquitin chain formation, and NFκB- and interferon-related gene expression. Thus, LUBAC synthesis of linear ubiquitin chains regulates STING-mediated innate immune signaling.
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Project description:STING activation by cyclic dinucleotides in mammals induces Type I Interferon- and NFkB-related gene expression, and the lipidation of LC3B at Golgi membranes. While the mechanisms of the Interferon-related responses are well understood, the mechanism of NFkB activation mediated by STING activation, and how the multi-functional responses downstream of STING signaling are related remain unknown. We report that STING activation induces K63 and linear ubiquitin chain formation, and ubiquitin co-localizes with STING and LC3B at Golgi-derived vesicles. Loss of the LUBAC E3 ubiquitin ligase subunit, HOIP, prevents formation of the linear, but not K63-linked, ubiquitin chains. The ubiquitin and LC3B binding proteins, Optineurin and TNIP1, are co-localized with STING activation-induced, perinuclear LC3B foci via their UBAN domains, however loss of HOIP does not influence this localization, indicating they may bind the K63-linked ubiquitin chains. HOIP-mediated linear ubiquitin chains are well established to mediate NFkB downstream of TNFa and IL1beta receptor stimulation. Loss of HOIP in monocytic THP-1 cells inhibits STING-induced NFkB activation and NFkB-related gene transcription, as well as Interferon-related transcription. Further, the recently reported proton channel activity of STING that blocks LC3B lipidation at Golgi membranes is also important for both K63 and Linear ubiquitin chain formation, and NFkB signaling. Thus, STING induces HOIP and linear ubiquitin chain formation to activate NFkB.
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Project description:Ubiquitination is a post-translational modification that regulates cellular processes by altering the interactions of proteins to which ubiquitin, a small protein adduct, is conjugated. Ubiquitination yields various products, including mono- and poly-ubiquitinated substrates, as well as unanchored poly-ubiquitin chains whose accumulation is considered toxic. We previously showed that transgenic, unanchored poly-ubiquitin is not problematic in Drosophila melanogaster. In the fruit fly, free chains exist in various lengths and topologies and are degraded by the proteasome; they are also conjugated onto other proteins as one unit, eliminating them from the free ubiquitin chain pool. Here, to further explore the notion of unanchored chain toxicity, we examined when free poly-ubiquitin might become problematic. We found that unanchored chains can be highly toxic if they resemble linear poly-ubiquitin that cannot be modified into other topologies. These species upregulate NF-κB signaling, and modulation of the levels of NF-κB components reduces toxicity. In additional studies, we show that toxicity from untethered, linear chains is regulated by isoleucine 44, which anchors a key interaction site for ubiquitin. We conclude that free ubiquitin chains can be toxic, but only in uncommon circumstances, such as when the ability of cells to modify and regulate them is markedly restricted.
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