Autocrine prostaglandin feedback determines the kinetics of bacterial type I interferon induction by restricting endosomal TLR4/TRIF complex assembly

Abstract TLR4 is unique in its capacity to initiate two qualitatively distinct transcriptional programs from two cellular locations. Cell surface TLR4/MyD88 complexes drive pro-inflammatory cytokine transcription through NF-κB, while endosomal TLR4/TRIF complexes activate IRF3 and a type I interferon response. Feedback circuits to limit signals from both locations are necessary to balance the inflammatory response to Gram negative bacteria, yet how endosomal TLR4/TRIF signals are terminated has remained an open question. We find that activation of TLR4 triggers rapid prostaglandin PGE2 production, necessary to limit the kinetics of endosomal TRIF, but not MyD88, signaling. Mechanistically, autocrine PGE2 activates the specific EP4 receptor to inhibit small GTPase mediated TLR4 trafficking to endosomes and to accelerate autophagic degradation of active TLR4/TRIF complexes. Inhibition of EP4 receptor function does not impair cell surface MyD88 signals, but leads to hyper TRIF dependent type I interferon production in response to bacterial LPS or to macrophage infection by live Gram negative pathogens.