RIP3 mediates the embryonic lethality of caspase-8-deficient mice

Abstract

Apoptosis and necroptosis are complementary pathways controlled by common signaling adaptors, kinases and proteases; among these, caspase-8 (Casp8) is critical for death receptor (DR)-induced apoptosis. This caspase has also been implicated in nonapoptotic pathways that regulate Fas-associated via death domain (FADD)-dependent signaling and other less defined biological processes as diverse as innate immune signaling and myeloid or lymphoid differentiation patterns 1. Casp8 suppresses RIP3/RIP1 kinase complex-dependent 2–4 necroptosis 5 that follows DR-activation as well as a RIP3-dependent, RIP1-independent necrotic pathway that has emerged as a host defense mechanism against murine cytomegalovirus (MCMV) 6. Disruption of Casp8 expression leads to embryonic lethality in mice between E10.5 and E11.5 7. Thus, Casp8 may naturally hold alternative RIP3-dependent death pathways in check in addition to its role promoting apoptosis. We find that RIP3 is responsible for the midgestational death of Casp8-deficient embryos. Remarkably, Casp8−/−Rip3−/− double mutant mice are viable and mature into fertile adults with a full immune complement of myeloid and lymphoid cell types. These mice appear immunocompetent but develop lymphadenopathy by four months of age marked by accumulation of abnormal T cells in the periphery, a phenotype reminiscent of mice with Fas-deficiency (lpr/lpr). Casp8 contributes to homeostatic control in the adult immune system; however, RIP3 and Casp8 are together completely dispensable for mammalian development.

Distinct roles of RIP1–RIP3 hetero- and RIP3–RIP3 homo-interaction in mediating necroptosis

“…From the cells co-expressing FKBP-RIP1 RHIM mut , FRB*-RIP3 WT , and HA-RIP3, we found that HA-RIP3 only interacted with AP21976-induced RIP1 RHIM mut -RIP3 WT complex, but not RIP1 RHIM mut -RIP3 RHIM mut complex (Figure 2g), thereby suggesting that inducible RIP1-RIP3 heterodimer could recruit another RIP3 protein and this recruitment may be required for necroptosis. Caspase-8 is known to inhibit necroptosis 19,20,31 and zVAD indeed tended to increase the cell death induced by RIP1-RIP3 complex, although the enhancement is not always statistically significant (Figures 2c, d and f). The participation of caspase-8 in RIP1-RIP3 dimer-induced cell death was supported by the data that caspase-8 can be detected in AP21967-induced RIP1-RIP3 complex (Supplementary Figure S2d).…”

“…[5][6][7] Physiological function of necroptosis has been illustrated in host defense, [8][9][10][11] inflammation, [12][13][14][15][16] tissue injury, 10,17,18 and development. [19][20][21] Necroptosis can be induced by a number of different extracellular stimuli such as tumor necrosis factor (TNF). TNF stimulation leads to formation of TNF receptor 1 (TNFR1) signaling complex (named complex I), and complex II containing RIP1, TRADD, FAS-associated protein with a death domain (FADD), and caspase-8, of which the activation initiates apoptosis.…”

RIP kinases: key decision makers in cell death and innate immunity

“…61 Interestingly, RIP3 and its catalytic activity facilitate a switch between TNF-induced apoptosis and necrosis, 60 with embryonic fibroblasts from RIP3-deficient mice being resistant to TNF-induced necrosis 61 and RIP3 kinase dead knock-in mice displaying developmental lethality due to RIP1-and caspase 8-driven apoptosis. 63 RIP3 deficiency also rescues the prenatal lethality of caspase 8 knockout mice with double knockouts lacking both caspase 8 and RIP3 surviving and reaching maturity, 64,65 indicating that RIP3 mediates lethality in the absence of caspase 8. This is consistent with the ability of caspase 8 to cleave RIP3 resulting in loss of the kinase domain of RIP3 and abrogation of its ability to trigger caspaseindependent cell death.…”

TAK1 control of cell death

“…Tak1 deletion is associated with the activation of downstream caspase-3, 55,82 whereas deletion of caspase-8 induces necroptosis in vivo, which is rescued by deletion of Ripk3. 54,95,96 Why are the timing and features of tissue injury so similar in mice having deletion of Tak1 or …”