title: LL-37 peptide enhancement of signal transduction by Toll-like receptor 3 is regulated by pH: identification of a peptide antagonist of LL-37.
abstract: LL-37 is a peptide secreted by human epithelial cells that can lyse bacteria, suppress signaling by Toll-like receptor 4 (TLR4), and enhance signaling to double-stranded RNA (dsRNA) by TLR3. How LL-37 interacts with dsRNA to affect signal transduction by TLR3 is not completely understood. We determined that LL-37 binds dsRNA and traffics to endosomes and releases the dsRNA in a pH-dependent manner. Using dynamic light scattering spectroscopy and cell-based FRET experiments, LL-37 was found to form higher order complexes independent of dsRNA binding. Upon acidification LL-37 will dissociate from a larger complex. In cells, LL-37 has a half-live of ∼ 1 h. LL-37 half-life was increased by inhibiting endosome acidification or inhibiting cathepsins, which include proteases whose activity are activated by endosome acidification. Residues in LL-37 that contact poly(I:C) and facilitate oligomerization in vitro were mapped. Peptide LL-29, which contains the oligomerization region of LL-37, inhibited LL-37 enhancement of TLR3 signal transduction. LL-29 prevented LL-37 · poly(I:C) co-localization to endosomes containing TLR3. These results shed light on the requirements for LL-37 enhancement of TLR3 signaling.
authors.affiliation: From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405.
authors.forename: Divyendu
authors.initials: D
authors.lastname: Singh
authors.affiliation: From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405.
authors.forename: Robert
authors.initials: R
authors.lastname: Vaughan
authors.affiliation: From the Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405 ckao@indiana.edu.
authors.forename: C Cheng
authors.initials: CC
authors.lastname: Kao
mesh_terms: D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000378:metabolism; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D054804:Cathelicidins
chemical_list: D023181:Antimicrobial Cationic Peptides; D010455:Peptides; D012330:RNA, Double-Stranded; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; D054804:Cathelicidins
keywords: Endosome; Innate Immunity; RNA-binding Protein; Toll-like Receptor (TLR); pH; pH Regulation
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