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

• Published in: Molecular immunology 2007-03, Vol.44 (9), p.2315-2323
• Main Authors: Xu, Wen-Yue, Wang, Li, Wang, Hui-Ming, Wang, Yi-Qin, Liang, Yun-Fei, Zhao, Ting-Ting, Wu, Yu-Zhang
• Format: Article
• Language: English
• Subjects: Animals; Class A scavenger receptor; Cytokines - metabolism; Drug Synergism; Endocytosis - drug effects; Escherichia coli; Fluorescein-5-isothiocyanate; Humans; Lipopeptides; Lipopolysaccharide; Lipopolysaccharides - pharmacology; Macrophages; Macrophages - drug effects; Macrophages - enzymology; Mice; NF-kappa B - metabolism; p38 Mitogen-Activated Protein Kinases - metabolism; Peptides - pharmacology; Polymyxin B - pharmacology; Rodent; Scavenger Receptors, Class A - genetics; Scavenger Receptors, Class A - metabolism; Toll-like receptor; Toll-Like Receptor 2 - agonists; Toll-Like Receptor 4 - agonists; Up-Regulation - genetics
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2006.11.013

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-α alone could not induce SR-A expression on RAW264.7. In addition, treatment with a NF-κB 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.