Rac1 regulates peptidoglycan-induced nuclear factor-kappaB activation and cyclooxygenase-2 expression in RAW 264.7 macrophages by activating the phosphatidylinositol 3-kinase/Akt pathway

Mol Immunol. 2009 Mar;46(6):1179-88. doi: 10.1016/j.molimm.2008.11.006. Epub 2008 Dec 31.


Previously, we found that peptidoglycan (PGN), a cell wall component of the gram-positive bacterium Staphylococcus aureus, may activate the Ras/Raf-1/extracellular signal-regulated kinase (ERK) pathway, which in turn initiates IkappaB kinases alpha/beta (IKKalpha/beta) and nuclear factor-kappaB (NF-kappaB) activation, and ultimately induces cyclooxygenase-2 (COX-2) expression in RAW 264.7 macrophages. In this study, we further investigated the roles of Rac1, phosphatidylinositol 3-kinase (PI3K), and Akt in PGN-induced NF-kappaB activation and COX-2 expression in RAW 264.7 macrophages. PGN-induced COX-2 expression was attenuated by a Rac1 dominant negative mutant (RacN17), PI3K inhibitors (wortmannin and LY 294002), and an Akt inhibitor (1L-6-hydroxymethyl-chiro-inositol2-[(R)-2-O-methyl-3-O-octadecylcarbonate]). PGN-induced PGE(2) release was also inhibited by RacN17. Treatment of RAW 264.7 macrophages with PGN caused the activation of Rac and Akt. PGN-induced Akt activation was inhibited by RacN17, LY 294002, and the Akt inhibitor. Stimulation of RAW 264.7 macrophages with PGN resulted in an increase in IKKalpha/beta phosphorylation and p65 Ser536 phosphorylation; these effects were inhibited by RacN17, LY 294002, an Akt inhibitor, and an Akt dominant negative mutant (AktDN). The PGN-induced increases in kappaB-luciferase activity were also inhibited by RacN17, wortmannin, LY 294002, an Akt inhibitor, and AktDN. Treatment of macrophages with PGN induced the recruitment of p85alpha and Rac1 to Toll-like receptor 2 (TLR2) in a time-dependent manner. These results indicate that PGN may activate the Rac1/PI3K/Akt pathway through the recruitment of p85alpha and Rac1 to TLR2 to mediate IKKalpha/beta activation and p65 phosphorylation, which in turn induces NF-kappaB transactivation, and ultimately causes COX-2 expression in RAW 264.7 macrophages.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Androstadienes / pharmacology
  • Animals
  • Cell Line
  • Chromones / pharmacology
  • Cyclooxygenase 2 / biosynthesis*
  • Dinoprostone / biosynthesis
  • Humans
  • I-kappa B Kinase / metabolism
  • Inositol / analogs & derivatives
  • Inositol / pharmacology
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Mice
  • Morpholines / pharmacology
  • Mutation
  • NF-kappa B / antagonists & inhibitors
  • NF-kappa B / metabolism*
  • Peptidoglycan / metabolism*
  • Peptidoglycan / pharmacology
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Toll-Like Receptor 2 / metabolism
  • Wortmannin
  • rac1 GTP-Binding Protein / genetics
  • rac1 GTP-Binding Protein / physiology*


  • 1L-6-hydroxymethyl-chiro-inositol 2(R)-2-O-methyl-3-O-octadecylcarbonate
  • Androstadienes
  • Chromones
  • Morpholines
  • NF-kappa B
  • Peptidoglycan
  • Phosphoinositide-3 Kinase Inhibitors
  • Tlr2 protein, mouse
  • Toll-Like Receptor 2
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Inositol
  • Cyclooxygenase 2
  • Akt1 protein, mouse
  • Proto-Oncogene Proteins c-akt
  • I-kappa B Kinase
  • rac1 GTP-Binding Protein
  • Dinoprostone
  • Wortmannin