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, cIAP1/2(MutR)). cIap1/2 ( MutR/MutR ) mice died during embryonic development due to RIPK1‐mediated apoptosis. While expression of kinase‐inactive RIPK1(D138N) rescued embryonic development, Ripk1 ( D138N/D138N ) /cIap1/2 ( MutR/MutR ) mice developed systemic inflammation and died postweaning. Cells expressing cIAP1/2(MutR) and RIPK1(D138N) 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.