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

Abstract

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.

The transmembrane adapter SCIMP recruits tyrosine kinase Syk to phosphorylate Toll-like receptors to mediate selective inflammatory outputs

“…Lastly, we examined LPS-induced cytokine responses in SCIMP-deficient BMMs and Syk-inhibitor treated BMMs. Consistent with our previous results ( 25 ), we found that the expression of proinflammatory cytokines TNF, IL-6, and IL-12p40 was significantly decreased in SCIMP-deficient BMMs in response to LPS compared with control BMMs ( Fig. 6 A ).…”

“…3 C ). In addition, the recruitment of the SCIMP effector Erk1/2 ( 25 ) was not affected by Syk inhibition, suggesting the phosphorylation of SCIMP is not required for Erk1/2 binding ( Fig. S5 ).…”

“…Cytokines are crucial mediators in the orchestration of inflammatory and innate immune responses, and homeostasis is highly dependent on the balance of various cytokines ( 45 , 46 ). Previously, we have shown that SCIMP strongly promotes secretion of proinflammatory cytokines ( 11 , 25 ). The selective role of SCIMP in regulating the secretion of proinflammatory cytokines including TNF, IL-12p40, and IL-6, but not anti-inflammatory cytokine IL-10 or chemokine CCL2, is confirmed in this study.…”

“…GFP-Syk and V5-SCIMP constructs were subcloned to pEF6/V5-His TOPO vector (Invitrogen). For the design of Halo-tagged expressible SCIMP construct, details were published previously by our lab ( 25 ).…”

“…Consideration must be given also to other nonconventional interactions for Syk recruitment. We recently showed that the signaling kinase ERK1/2 bypasses the need for ITAM-mediated recruitment by using the transmembrane adapter, SCIMP, as a scaffold for spatiotemporal recruitment to activated TLR4 ( 25 ). SCIMP is a TLR adapter belonging to the palmitoylated transmembrane adapter protein (pTRAP) family.…”