Project description:Human mutations in the death receptor Fas or its ligand FasL cause autoimmune lymphoproliferative syndrome (ALPS), whereas mutations in caspase-8 or its adaptor FADD â which mediate cell death downstream of Fas/FasL â cause severe immunodeficiency in addition to ALPS. Mouse models have corroborated a role for FADD-caspase-8 in promoting inflammatory responses, but the mechanisms underlying immunodeficiency remain undefined. Here, we identify NEDD4-binding protein 1 (N4BP1) as a suppressor of cytokine production that is cleaved and inactivated by caspase-8. N4BP1 deletion in mice significantly increased production of select cytokines upon Toll-like receptor (TLR) 1/2, TLR7, or TLR9 stimulation, but not upon TLR3 or TLR4 engagement. N4BP1 did not suppress TLR3 or TLR4 responses in wild-type macrophages owing to TRIF- and caspase-8-dependent cleavage of N4BP1. Notably, impaired TLR3 and TLR4 cytokine responses of caspase-8-deficient macrophages were largely rescued by co-deletion of N4BP1. Thus, persistence of intact N4BP1 in caspase-8-deficient macrophages impairs their ability to mount robust cytokine responses. Tumor necrosis factor (TNF), like TLR3 or TLR4 agonists, also induced caspase-8-dependent cleavage of N4BP1, thereby licensing TRIF-independent TLRs to produce higher levels of inflammatory cytokines. Illustrating the importance of this function of TNF in vivo, TNF blockade increased the mortality of mice infected with Streptococcus Pneumoniae, but did not do so when infected mice lacked N4BP1. Collectively, our results identify N4BP1 as a potent suppressor of cytokine responses; reveal N4BP1 cleavage by Caspase-8 as a point of signal integration during inflammation; and offer an explanation for immunodeficiency caused by FADD-caspase-8 mutations.
Project description:Human mutations in the death receptor Fas or its ligand FasL cause autoimmune lymphoproliferative syndrome (ALPS), whereas mutations in caspase-8 or its adaptor FADD â which mediate cell death downstream of Fas/FasL â cause severe immunodeficiency in addition to ALPS. Mouse models have corroborated a role for FADD-caspase-8 in promoting inflammatory responses, but the mechanisms underlying immunodeficiency remain undefined. Here, we identify NEDD4-binding protein 1 (N4BP1) as a suppressor of cytokine production that is cleaved and inactivated by caspase-8. N4BP1 deletion in mice significantly increased production of select cytokines upon Toll-like receptor (TLR) 1/2, TLR7, or TLR9 stimulation, but not upon TLR3 or TLR4 engagement. N4BP1 did not suppress TLR3 or TLR4 responses in wild-type macrophages owing to TRIF- and caspase-8-dependent cleavage of N4BP1. Notably, impaired TLR3 and TLR4 cytokine responses of caspase-8-deficient macrophages were largely rescued by co-deletion of N4BP1. Thus, persistence of intact N4BP1 in caspase-8-deficient macrophages impairs their ability to mount robust cytokine responses. Tumor necrosis factor (TNF), like TLR3 or TLR4 agonists, also induced caspase-8-dependent cleavage of N4BP1, thereby licensing TRIF-independent TLRs to produce higher levels of inflammatory cytokines. Illustrating the importance of this function of TNF in vivo, TNF blockade increased the mortality of mice infected with Streptococcus Pneumoniae, but did not do so when infected mice lacked N4BP1. Collectively, our results identify N4BP1 as a potent suppressor of cytokine responses; reveal N4BP1 cleavage by Caspase-8 as a point of signal integration during inflammation; and offer an explanation for immunodeficiency caused by FADD-caspase-8 mutations.
Project description:Innate immune activation coupled with metabolic disruptions play critical roles in many diseases, often leading to mitochondrial dysfunction and oxidative stress that drive pathogenesis. However, mechanistic regulation under these conditions remains poorly defined. Here, we report a distinct lytic cell death mechanism induced by innate immune signaling and metabolic disruption, independent of caspase activity and previously described pyroptosis, PANoptosis, necroptosis, ferroptosis, and oxeiptosis. Instead, mitochondria undergoing BAX/BAK1/BID-dependent oxidative stress maintained prolonged plasma membrane contact, leading to local oxidative damage, a process we termed mitoxyperiosis. This process then caused membrane lysis and cell death, mitoxyperilysis. mTORC2 regulated the cell death, and mTOR inhibition restored cytoskeletal activity for lamellipodia retractions to mobilize mitochondria away from the membrane, preserving integrity. Activating this pathway in vivo regressed tumors in an mTORC2-dependent manner. Overall, our results identify a lytic cell death modality in response to the synergism of innate immune signaling and metabolic disruption.