Abstract
BackgroundLinear ubiquitination is a novel type of ubiquitination that plays important physiological roles in signalling pathways such as tumour necrosis factor (TNF) signalling. However, little is known about the regulatory mechanisms of linear ubiquitination, except the well-described enzymatic regulators E3 ligase linear ubiquitin chain assembly complex (LUBAC) and deubiquitinase OTULIN.ResultsPreviously, we identified SNX27, a member of the sorting nexin family protein, as a selective linear ubiquitin chain interactor in mass spectrometry-based ubiquitin interaction screening. Here, we demonstrated that the interaction between the linear ubiquitin chain and SNX27 is mediated by the OTULIN. Furthermore, we found that SNX27 inhibits LUBAC-mediated linear ubiquitin chain formation and TNFα-induced signalling activation. Mechanistic studies showed that, upon TNFα stimulation, OTULIN-SNX27 is localised to membrane-associated TNF receptor complex, where OTULIN deubiquitinates the linear polyubiquitin chain that formed by the LUBAC complex. Significantly, chemical inhibition of SNX27-retromer translocation by cholera toxin inhibits OTULIN membrane localization.ConclusionsIn conclusion, our study demonstrated that SNX27 inhibits TNFα induced NF-κB signalling activation via facilitating OTULIN to localize to TNF receptor complex.
Highlights
Linear ubiquitination is a novel type of ubiquitination that plays important physiological roles in signalling pathways such as tumour necrosis factor (TNF) signalling
In line with our hypothesis, we found that biotin tagged Met1 was precipitated only when OTULIN was added into the interaction system together with SNX27 (Fig. 1E, lane 4 vs. lane 3)
We showed that the phosphorylation of IκBα, IKKα/β and p65 were upregulated in SNX27 knockout mouse embryonic fibroblast (MEF) cells compared to control cells (Additional file 3: Figure S3D)
Summary
Linear ubiquitination is a novel type of ubiquitination that plays important physiological roles in signalling pathways such as tumour necrosis factor (TNF) signalling. Little is known about the regulatory mechanisms of linear ubiquitination, except the well-described enzymatic regulators E3 ligase linear ubiquitin chain assembly complex (LUBAC) and deubiquitinase OTULIN. Multiple studies have demonstrated that linear ubiquitination modifies key receptors and adaptor proteins and participates in inflammatory signalling activation, such as TNFα signalling [4]. SNXs have common functions in recycling, they regulate different receptors. This cargo specificity is mainly mediated by SNXs-specific protein interacting domains. Previous studies have showed that SNX27 involves in the recycling of multiple receptors, such as NMDAR, AMPAR, GRP17 and plays important roles in neuronal functions [13, 14]
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