cIAPs control RIPK1 kinase activity‐dependent and ‐independent cell death and tissue inflammation.

Cellular inhibitor of apoptosis proteins (cIAPs) are RING‐containing E3 ubiquitin ligases that ubiquitylate receptor‐interacting protein kinase 1 (RIPK1) to regulate TNF signalling. Here, we established mice simultaneously expressing enzymatically inactive cIAP1/2 variants, bearing mutations in the RING domains of cIAP1/2 (cIAP1/2 mutant RING, cIAP1/2MutR). cIap1/2MutR/MutR mice died during embryonic development due to RIPK1‐mediated apoptosis. While expression of kinase‐inactive RIPK1D138N rescued embryonic development, Ripk1D138N/D138N/cIap1/2MutR/MutR mice developed systemic inflammation and died postweaning. Cells expressing cIAP1/2MutR and RIPK1D138N were still susceptible to TNF‐induced apoptosis and necroptosis, implying additional kinase‐independent RIPK1 activities in regulating TNF signalling. Although further ablation of Ripk3 did not lead to any phenotypic improvement, Tnfr1 gene knock‐out prevented early onset of systemic inflammation and premature mortality, indicating that cIAPs control TNFR1‐mediated toxicity independent of RIPK1 and RIPK3. Beyond providing novel molecular insights into TNF‐signalling, the mouse model established in this study can serve as a useful tool to further evaluate ongoing therapeutic protocols using inhibitors of TNF, cIAPs and RIPK1. Synopsis: cIAPs control RIPK1‐dependent and ‐independent TNF toxicity in mouse. This study finds ubiquitylation and inhibition of RIPK1 by cIAPs to be required for mouse embryonic development, while RIPK1‐independent cIAP inhibition of TNF‐induced cell death regulates tissue inflammation in adult mice. cIAP1/2 E3 ubiquitin ligase activity is required for mouse embryonic development.Catalytic activity of cIAPs regulates RIPK1 kinase activity to promote embryonic survival.TNF induces apoptosis and necroptosis in cells lacking the cIAPs‐RIPK1 regulatory axis.cIAPs control non‐overlapping signalling processes downstream of RIPK1 and TNFR1. [ABSTRACT FROM AUTHOR]