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    LUBAC is essential for embryogenesis by preventing cell death and enabling haematopoiesis
    Peltzer, N ; Darding, M ; Montinaro, A ; Draber, P ; Draberova, H ; Kupka, S ; Rieser, E ; Fisher, A ; Hutchinson, C ; Taraborrelli, L ; Hartwig, T ; Lafont, E ; Haas, TL ; Shimizu, Y ; Boiers, C ; Sarr, A ; Rickard, J ; Alvarez-Diaz, S ; Ashworth, MT ; Beal, A ; Enver, T ; Bertin, J ; Kaiser, W ; Strasser, A ; Silke, J ; Bouillet, P ; Walczak, H (NATURE PUBLISHING GROUP, 2018-05-03)
    The linear ubiquitin chain assembly complex (LUBAC) is required for optimal gene activation and prevention of cell death upon activation of immune receptors, including TNFR1 1 . Deficiency in the LUBAC components SHARPIN or HOIP in mice results in severe inflammation in adulthood or embryonic lethality, respectively, owing to deregulation of TNFR1-mediated cell death2-8. In humans, deficiency in the third LUBAC component HOIL-1 causes autoimmunity and inflammatory disease, similar to HOIP deficiency, whereas HOIL-1 deficiency in mice was reported to cause no overt phenotype9-11. Here we show, by creating HOIL-1-deficient mice, that HOIL-1 is as essential for LUBAC function as HOIP, albeit for different reasons: whereas HOIP is the catalytically active component of LUBAC, HOIL-1 is required for LUBAC assembly, stability and optimal retention in the TNFR1 signalling complex, thereby preventing aberrant cell death. Both HOIL-1 and HOIP prevent embryonic lethality at mid-gestation by interfering with aberrant TNFR1-mediated endothelial cell death, which only partially depends on RIPK1 kinase activity. Co-deletion of caspase-8 with RIPK3 or MLKL prevents cell death in Hoil-1-/- (also known as Rbck1-/-) embryos, yet only the combined loss of caspase-8 with MLKL results in viable HOIL-1-deficient mice. Notably, triple-knockout Ripk3-/-Casp8-/-Hoil-1-/- embryos die at late gestation owing to haematopoietic defects that are rescued by co-deletion of RIPK1 but not MLKL. Collectively, these results demonstrate that both HOIP and HOIL-1 are essential LUBAC components and are required for embryogenesis by preventing aberrant cell death. Furthermore, they reveal that when LUBAC and caspase-8 are absent, RIPK3 prevents RIPK1 from inducing embryonic lethality by causing defects in fetal haematopoiesis.
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    Linear ubiquitin chain assembly complex coordinates late thymic T-cell differentiation and regulatory T-cell homeostasis
    Teh, CE ; Lalaoui, N ; Jain, R ; Policheni, AN ; Heinlein, M ; Alvarez-Diaz, S ; Sheridan, JM ; Rieser, E ; Deuser, S ; Darding, M ; Koay, H-F ; Hu, Y ; Kupresanin, F ; O'Reilly, LA ; Godfrey, DI ; Smyth, GK ; Bouillet, P ; Strasser, A ; Walczak, H ; Silke, J ; Gray, DHD (NATURE PUBLISHING GROUP, 2016-11-18)
    The linear ubiquitin chain assembly complex (LUBAC) is essential for innate immunity in mice and humans, yet its role in adaptive immunity is unclear. Here we show that the LUBAC components HOIP, HOIL-1 and SHARPIN have essential roles in late thymocyte differentiation, FOXP3+ regulatory T (Treg)-cell development and Treg cell homeostasis. LUBAC activity is not required to prevent TNF-induced apoptosis or necroptosis but is necessary for the transcriptional programme of the penultimate stage of thymocyte differentiation. Treg cell-specific ablation of HOIP causes severe Treg cell deficiency and lethal immune pathology, revealing an ongoing requirement of LUBAC activity for Treg cell homeostasis. These data reveal stage-specific requirements for LUBAC in coordinating the signals required for T-cell differentiation.