Cutting edge: Differential inhibition of TLR signaling pathways by cell-permeable peptides representing BB loops of TLRs

We designed cell-penetrating peptides comprised of the translocating segment of Drosophila antennapedia homeodomain fused with BB loop sequences of TLR2, TLR4, and TLR1/6 TLR2- and TLR4-BB peptides (BBPs) inhibited NF-kappa B translocation and early IL-1 beta mRNA expression induced by LPS, and the lipopeptides S-[2,3-bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-Cys-Ser-Lys(4)-OH (P3C) and S-[2,3-bis(palmitoyloxy)-(2-RS)-propyl]-CysSer-Lys(4)-OH (P2C). TLR4- and TLR2-BBPs also strongly inhibited LPS-induced-activation of ERK. Only TLR2-BBP significantly inhibited ERK activation induced by P3C, which acts via TLR2/1 heterodimers. BBPs did not inhibit activation of ERK induced by P2C, a M2/6agonist. The TLR2-BBP induced weak activation of p38, but not ERK or cytokine mRNA. The TLR1/6-BBP failed to inhibit NF-kappa B or MAPK activation induced by any agonist. Our results suggest that the receptor BBPs selectively affect different TLR sionaling pathways, and that the BB loops of TLR1/6 and TLR2 play distinct roles in formation of receptor heterodimers and recruitment ofadaptor proteins.