Toll-like receptor 2-mediated NF-kappa B activation requires a Rac1-dependent pathway

Nat Immunol. 2000 Dec;1(6):533-40. doi: 10.1038/82797.


Mammalian Toll-like receptors (TLRs) are expressed on innate immune cells and respond to the membrane components of Gram-positive or Gram-negative bacteria. When activated, they convey signals to transcription factors that orchestrate the inflammatory response. However, the intracellular signaling events following TLR activation are largely unknown. Here we show that TLR2 stimulation by Staphylococcus aureus induces a fast and transient activation of the Rho GTPases Rac1 and Cdc42 in the human monocytic cell line THP-1 and in 293 cells expressing TLR2. Dominant-negative Rac1N17, but not dominant-negative Cdc42N17, block nuclear factor-kappa B (NF-kappa B) transactivation. S. aureus stimulation causes the recruitment of active Rac1 and phosphatidylinositol-3 kinase (PI3K) to the TLR2 cytosolic domain. Tyrosine phosphorylation of TLR2 is required for assembly of a multiprotein complex that is necessary for subsequent NF-kappa B transcriptional activity. A signaling cascade composed of Rac1, PI3K and Akt targets nuclear p65 transactivation independently of I kappa B alpha degradation. Thus Rac1 controls a second, I kappa B-independent, pathway to NF-kappa B activation and is essential in innate immune cell signaling via TLR2.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cell Line
  • Drosophila Proteins*
  • Gene Expression
  • Humans
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Models, Biological
  • NF-kappa B / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphotyrosine / metabolism
  • Protein Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Signal Transduction
  • Staphylococcus aureus / immunology
  • Toll-Like Receptor 2
  • Toll-Like Receptors
  • Transfection
  • cdc42 GTP-Binding Protein / metabolism
  • rac1 GTP-Binding Protein / metabolism*


  • Drosophila Proteins
  • Membrane Glycoproteins
  • NF-kappa B
  • Proto-Oncogene Proteins
  • Receptors, Cell Surface
  • TLR2 protein, human
  • Toll-Like Receptor 2
  • Toll-Like Receptors
  • Phosphotyrosine
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • cdc42 GTP-Binding Protein
  • rac1 GTP-Binding Protein