Linear ubiquitination prevents inflammation and regulates immune signalling

Abstract

Members of the tumour necrosis factor (TNF) receptor superfamily have important functions in immunity and inflammation. Recently linear ubiquitin chains assembled by a complex containing HOIL-1 and HOIP (also known as RBCK1 and RNF31, respectively) were implicated in TNF signalling, yet their relevance in vivo remained uncertain. Here we identify SHARPIN as a third component of the linear ubiquitin chain assembly complex, recruited to the CD40 and TNF receptor signalling complexes together with its other constituents, HOIL-1 and HOIP. Mass spectrometry of TNF signalling complexes revealed RIP1 (also known as RIPK1) and NEMO (also known as IKKγ or IKBKG) to be linearly ubiquitinated. Mutation of the Sharpin gene (Sharpin(cpdm/cpdm)) causes chronic proliferative dermatitis (cpdm) characterized by inflammatory skin lesions and defective lymphoid organogenesis. Gene induction by TNF, CD40 ligand and interleukin-1β was attenuated in cpdm-derived cells which were rendered sensitive to TNF-induced death. Importantly, Tnf gene deficiency prevented skin lesions in cpdm mice. We conclude that by enabling linear ubiquitination in the TNF receptor signalling complex, SHARPIN interferes with TNF-induced cell death and, thereby, prevents inflammation. Our results provide evidence for the relevance of linear ubiquitination in vivo in preventing inflammation and regulating immune signalling.

TAK1 control of cell death

“…Upon TNFa stimulation, adaptor molecules including TNFa receptor type-1-associated death domain protein (TRADD), TNFa receptorassociated factor 2 and 5 (TRAF2 and TRAF5), cellular inhibitor of apoptosis 1 and 2 (cIAP1/2) and RIPK1 are recruited to the receptor complex (TNF receptor 1 (TNFR1) Complex I) (Figure 1), in which RIPK1 acquires a K63-linked or linear polyubiquitin chain by E3 ligases, TRAF2/5 cIAP1/2 or linear ubiquitin chain assembly complex containing two E3 ligases HOIL-1 and HOIP. [18][19][20][21][22] TAK1 is recruited and activated through TAK1-binding protein 2 (TAB2) binding to the RIPK1 polyubiquitin chain. 23,24 Upon binding the polyubiquitin chain, TAK1 phosphorylates and activates the IKK complex composed of IKKa, IKKb and NEMO (also called IKKg), which leads to phosphorylation and degradation of IkB resulting in activation of NF-kB ( Figure 1).…”

NIK promotes tissue destruction independently of the alternative NF-κB pathway through TNFR1/RIP1-induced apoptosis

“…3,4 The formation of this complex is initiated by the interaction of ligand-bound TNFR1 with TNF receptor-associated death domain (TRADD) and by the recruitment of the kinase receptor interacting protein kinase 1 (RIP1), the adaptor proteins TNF receptor-associated factor 2/5 and the ubiquitin ligase cellular inhibitor of apoptosis 1/2 (c-IAP1/2) and linear ubiquitin chain assembly complex (LUBAC). [5][6][7][8][9] c-IAP1/2 and LUBAC target RIP1 for K11, K63 and linear polyubiquitination priming RIP1 for the recruitment of two kinase-containing complexes, namely, TAK1/TAK1-binding protein 1 (TAB1)/TAB2 and NEMO/ inhibitor of NF-κB kinase α (IKKα)/IKKβ. 5,[10][11][12][13] Ultimately, activation of IKKβ leads to the phosphorylation and proteasomal degradation of IκBα and the nuclear translocation of NF-κB, a pathway defined as the classical, or the canonical, NF-κB pathway.…”

“…[5][6][7][8][9] c-IAP1/2 and LUBAC target RIP1 for K11, K63 and linear polyubiquitination priming RIP1 for the recruitment of two kinase-containing complexes, namely, TAK1/TAK1-binding protein 1 (TAB1)/TAB2 and NEMO/ inhibitor of NF-κB kinase α (IKKα)/IKKβ. 5,[10][11][12][13] Ultimately, activation of IKKβ leads to the phosphorylation and proteasomal degradation of IκBα and the nuclear translocation of NF-κB, a pathway defined as the classical, or the canonical, NF-κB pathway. [14][15][16] Besides its role in the activation of NF-κB, the dissociation of complex I from TNFR1 triggers the recruitment of Fas-associated protein with death domain (FADD) and caspase-8 to form a cytosolic death complex, initially defined as complex II.…”

The role of K63‐linked polyubiquitination in cardiac hypertrophy

“…The removal of Lys63‐ubiquitylation chains from adaptor protein receptor‐interacting protein 1 (RIP1) by CYLD negatively regulates NF‐κB signalling, and this deubiquitinating event blocks the aberrant expression of survival genes in germ cells 53. A mass spectrometric study showed that TNFR1 complex can conjugate with Ub system by multiple polyubiquitin linkages including K48, K63, K11 and linear chains 54. Each linkage exhibits different responses.…”