TLR2 and TLR4 agonists synergistically up-regulate SR-A in RAW264.7 through p38

Mol Immunol. 2007 Mar;44(9):2315-23. doi: 10.1016/j.molimm.2006.11.013. Epub 2006 Dec 14.

Abstract

It is known that macrophage scavenger receptor A (SR-A) can protect mice from endotoxemia. In addition, Escherichia coli O111:B4 LPS from Sigma (sLPS), which contains both TLR4 and TLR2 agonists, was previously reported to be able to induce SR-A expression on murine macrophage cell line RAW264.7. However, the relative role of both TLR4 and TLR2 agonists from Sigma (sLPS) in the up-regulation of SR-A on RAW264.7 is still undefined. Here, we found that sLPS could only slightly up-regulate SR-A on RAW264.7 following removing its TLR4 and TLR2 agonists, respectively. In contrast, the combination of TLR4 agonist uLPS (re-extracted sLPS) and TLR2 agonist Pam3CSK4 dramatically induced SR-A expression, and synergistically promoted RAW264.7 to bind and internalize FITC-LPS specifically through SR-A. The combination had no such effect either on TLR2 or TLR4 expression, and incubation with IL-6, IL-10, IL-12 or TNF-alpha alone could not induce SR-A expression on RAW264.7. In addition, treatment with a NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) could only weakly suppress the up-regulation of SR-A by the combination. However, the combination synergistically promoted MAPK p38 phosphorylation, and p38 specific inhibitor SB203580 completely suppressed its inducible effect on SR-A expression. Hence, we demonstrated that up-regulation of SR-A by sLPS was resulted from the cooperation of its TLR4 and TLR2 agonists through p38, and we also presented a novel synergy effect of TLR2 and TLR4 agonists.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cytokines / metabolism
  • Drug Synergism
  • Endocytosis / drug effects
  • Fluorescein-5-isothiocyanate
  • Humans
  • Lipopeptides
  • Lipopolysaccharides / pharmacology*
  • Macrophages / drug effects*
  • Macrophages / enzymology
  • Mice
  • NF-kappa B / metabolism
  • Peptides / pharmacology
  • Polymyxin B / pharmacology
  • Scavenger Receptors, Class A / genetics
  • Scavenger Receptors, Class A / metabolism*
  • Toll-Like Receptor 2 / agonists*
  • Toll-Like Receptor 4 / agonists*
  • Up-Regulation / genetics*
  • p38 Mitogen-Activated Protein Kinases / metabolism*

Substances

  • Cytokines
  • Lipopeptides
  • Lipopolysaccharides
  • NF-kappa B
  • Pam(3)CSK(4) peptide
  • Peptides
  • Scavenger Receptors, Class A
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • p38 Mitogen-Activated Protein Kinases
  • Fluorescein-5-isothiocyanate
  • Polymyxin B