Novel signaling interactions between proteinase‐activated receptor 2 and Toll‐like receptors in vitro and in vivo

Abstract

Toll‐like receptors (TLRs) and proteinase‐activated receptors (PARs) function as innate immune biosensors in mucosal epithelial cells (ECs). We previously reported the functional and physical interactions between TLR4 and PAR2, and more recently, between PAR2 and the TLR adapter, TRIF, and established a novel model of “receptor cooperativity” between PAR2 and TLR4. We hypothesized that intracellular signaling pathways utilized by TLRs and PAR2 would converge either cooperatively or non‐cooperatively when co‐engaged. We demonstrate herein the cooperation between PAR2 and TLR2, TLR3, or TLR4 for activation of NF‐κB‐dependent signaling in mucosal EC lines. In contrast, activation of PAR2 negatively regulated TLR3‐dependent antiviral pathway, blunting the expression of TLR3/IRF‐3‐driven genes, as well as activation of IRF‐3 and STAT1. Similarly, TLR4‐TRIF‐activated, IRF‐3‐driven genes were also attenuated by PAR2 co‐activation. Consistent with these in vitro observations, PAR2−/− and TLR4−/− mice, which were refractory to footpad edema induced by PAR2 agonist peptide, were protected from mouse‐adapted H1N1 influenza A virus‐induced lethality when compared to wild‐type mice. These data support and extend our recently described, novel model of PAR2‐TLR4 “receptor cooperativity” and highlight the complexity of signaling integration between heterologous innate immune biosensors. (Supported by NIH Grants T32‐AI‐07540 (QN), R37 AI‐18797 (SV), R01 DK048373 (AF), R01 HL084387, R01 DK081376, R01 CA098369 (TA), R01 AI50632S1 (JT), and R01 AI050632 (DF))