Human Integrin α3β1 Regulates TLR2 Recognition of Lipopeptides from Endosomal Compartments

• Published in: PloS one 2010-09, Vol.5 (9), p.e12871
• Main Authors: Marre, Meghan L, Petnicki-Ocwieja, Tanja, DeFrancesco, Alicia S, Darcy, Courtney T, Hu, Linden T
• Format: Article
• Language: English
• Subjects: Acidification; Adapters; Adaptor proteins; Antibodies; Arthritis; Avian flu; Bacteria; Blocking antibodies; Borrelia burgdorferi; Cell adhesion & migration; Compartments; Cytokines; Endocytosis; Extracellular matrix; Fluorescence; Gene expression; Immune system; Immunology; Infectious diseases; Inflammation; Ligands; Lipopeptides; Localization; Lyme disease; Macrophages; Medicine; Microscopy; Polymerase chain reaction; Proteins; Receptor mechanisms; Receptors; Recognition; Signaling; Tethering; TLR1 protein; TLR2 protein; Toll-like receptors; Viruses
• ISSN: 1932-6203
• DOI: 10.1371/journal.pone.0012871

Background Toll-like receptor (TLR)-2/TLR1 heterodimers recognize bacterial lipopeptides and initiate the production of inflammatory mediators. Adaptors and co-receptors that mediate this process, as well as the mechanisms by which these adaptors and co-receptors function, are still being discovered. Methodology/Principal Findings Using shRNA, blocking antibodies, and fluorescent microscopy, we show that U937 macrophage responses to the TLR2/1 ligand, Pam3CSK4, are dependent upon an integrin, α3β1. The mechanism for integrin α3β1 involvement in TLR2/1 signaling is through its role in endocytosis of lipopeptides. Using inhibitors of endosomal acidification/maturation and physical tethering of the ligand, we show that the endocytosis of Pam3CSK4 is necessary for the complete TLR2/1-mediated pro-inflammatory cytokine response. We also show that TLR2/1 signaling from the endosome results in the induction of different inflammatory mediators than TLR2/1 signaling from the plasma membrane. Conclusion/Significance Here we identify integrin α3β1 as a novel regulator for the recognition of bacterial lipopeptides. We demonstrate that induction of a specific subset of cytokines is dependent upon integrin α3β1-mediated endocytosis of the ligand. In addition, we address an ongoing controversy regarding endosomal recognition of bacterial lipopeptides by demonstrating that TLR2/1 signals from within endosomal compartments as well as the plasma membrane, and that downstream responses may differ depending upon receptor localization. We propose that the regulation of endosomal TLR2/1 signaling by integrin α3β1 serves as a mechanism for modulating inflammatory responses.