The human antimicrobial peptide LL-37, but not the mouse ortholog, mCRAMP, can stimulate signaling by poly(I:C) through a FPRL1-dependent pathway

J Biol Chem. 2013 Mar 22;288(12):8258-8268. doi: 10.1074/jbc.M112.440883. Epub 2013 Feb 5.

Abstract

LL-37 is an antimicrobial peptide produced by human cells that can down-regulate the lipopolysaccharide-induced innate immune responses and up-regulate double-stranded (ds) RNA-induced innate responses through Toll-like receptor 3 (TLR3). The murine LL-37 ortholog, mCRAMP, also inhibited lipopolysaccharide-induced responses, but unlike LL-37, it inhibited viral-induced responses in mouse cells. A fluorescence polarization assay showed that LL-37 was able to bind dsRNA better than mCRAMP. In the human lung epithelial cell line BEAS-2B, LL-37, but not mCRAMP, colocalized with TLR3, and the colocalization was increased in the presence of dsRNA. The presence of poly(I:C) increased the accumulation of LL-37 in Rab5 endosomes. Signaling by cells induced with both LL-37 and poly(I:C) was sensitive to inhibitors that affect clathrin-independent trafficking, whereas signaling by poly(I:C) alone was not, suggesting that the LL-37-poly(I:C) complex trafficked to signaling endosomes by a different mechanism than poly(I:C) alone. siRNA knockdown of known LL-37 receptors identified that FPRL1 was responsible for TLR3 signaling induced by LL-37-poly(I:C). These results show that LL-37 and mCRAMP have different activities in TLR3 signaling and that LL-37 can redirect trafficking of poly(I:C) to effect signaling by TLR3 in early endosomes in a mechanism that involves FPRL1.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antimicrobial Cationic Peptides / physiology*
  • Cathelicidins / physiology*
  • Cell Line
  • Endocytosis / drug effects
  • Endosomes / metabolism
  • Humans
  • Interleukin-6 / genetics
  • Interleukin-6 / metabolism
  • Lipopolysaccharides / pharmacology
  • Mice
  • Molecular Sequence Data
  • Poly I-C / pharmacology*
  • Protein Binding
  • Protein Transport
  • Receptors, Formyl Peptide / metabolism*
  • Receptors, Formyl Peptide / physiology
  • Receptors, Lipoxin / metabolism*
  • Receptors, Lipoxin / physiology
  • Signal Transduction
  • Toll-Like Receptor 3 / metabolism
  • beta-Cyclodextrins / pharmacology

Substances

  • Antimicrobial Cationic Peptides
  • Cathelicidins
  • FPR2 protein, human
  • IL6 protein, human
  • Interleukin-6
  • Lipopolysaccharides
  • Receptors, Formyl Peptide
  • Receptors, Lipoxin
  • TLR3 protein, human
  • Toll-Like Receptor 3
  • beta-Cyclodextrins
  • methyl-beta-cyclodextrin
  • Poly I-C