SCIMP is a spatiotemporal transmembrane scaffold for Erk1/2 to direct pro-inflammatory signaling in TLR-activated macrophages

Immune cells are armed with Toll-like receptors (TLRs) for sensing and responding to pathogens and other danger cues. The role of extracellular-signal-regulated kinases 1/2 (Erk1/2) in TLR signaling remains enigmatic, with both pro- and anti-inflammatory functions described. We reveal here that the immune-specific transmembrane adaptor SCIMP is a direct scaffold for Erk1/2 in TLR pathways, with high-resolution, live-cell imaging revealing that SCIMP guides the spatial and temporal recruitment of Erk2 to membrane ruffles and macropinosomes for pro-inflammatory TLR4 signaling. SCIMP-deficient mice display defects in Erk1/2 recruitment to TLR4, c-Fos activation, and pro-inflammatory cytokine production, with these effects being phenocopied by Erk1/2 signaling inhibition. Our findings thus delineate a selective role for SCIMP as a key scaffold for the membrane recruitment of Erk1/2 kinase to initiate TLR-mediated pro-inflammatory responses in macrophages

Noncanonical inflammasome signaling elicits gasdermin D-dependent neutrophil extracellular traps.

Neutrophil extrusion of neutrophil extracellular traps (NETs) and concomitant cell death (NETosis) provides host defense against extracellular pathogens, whereas macrophage death by pyroptosis enables defense against intracellular pathogens. We report the unexpected discovery that gasdermin D (GSDMD) connects these cell death modalities. We show that neutrophil exposure to cytosolic lipopolysaccharide or cytosolic Gram-negative bacteria (Salmonella ΔsifA and Citrobacter rodentium) activates noncanonical (caspase-4/11) inflammasome signaling and triggers GSDMD-dependent neutrophil death. GSDMD-dependent death induces neutrophils to extrude antimicrobial NETs. Caspase-11 and GSDMD are required for neutrophil plasma membrane rupture during the final stage of NET extrusion. Unexpectedly, caspase-11 and GSDMD are also required for early features of NETosis, including nuclear delobulation and DNA expansion; this is mediated by the coordinate actions of caspase-11 and GSDMD in mediating nuclear membrane permeabilization and histone degradation. In vivo application of deoxyribonuclease I to dissolve NETs during murine Salmonella ΔsifA challenge increases bacterial burden in wild-type but not in Casp11 <sup>-/-</sup> and Gsdmd <sup>-/-</sup> mice. Our studies reveal that neutrophils use an inflammasome- and GSDMD-dependent mechanism to activate NETosis as a defense response against cytosolic bacteria