NF-kappaB- and C/EBPbeta-driven interleukin-1beta gene expression and PAK1-mediated caspase-1 activation play essential roles in interleukin-1beta release from Helicobacter pylori lipopolysaccharide-stimulated macrophages

J Biol Chem. 2005 Feb 11;280(6):4279-88. doi: 10.1074/jbc.M412820200. Epub 2004 Nov 23.


Helicobacter pylori is a Gram-negative microaerophilic bacterium that causes chronic gastritis, peptic ulcer, and gastric carcinoma. Interleukin-1beta (IL-1beta) is one of the potent proinflammatory cytokines elicited by H. pylori infection. We have evaluated the role of H. pylori lipopolysaccharide (LPS) as one of the mediators of IL-1beta release and dissected the signaling pathways leading to LPS-induced IL-1beta secretion. We demonstrate that both the NF-kappaB and the C/EBPbeta-binding elements of the IL-1beta promoter drive LPS-induced IL-1beta gene expression. NF-kappaB activation requires the classical TLR4-initiated signaling cascade leading to IkappaB phosphorylation as well as PI-3K/Rac1/p21-activated kinase (PAK) 1 signaling, whereas C/EBPbeta activation requires PI-3K/Akt/p38 mitogen-activated protein (MAP) kinase signaling. We observed a direct interaction between activated p38 MAP kinase and C/EBPbeta, suggesting that p38 MAPK is the immediate upstream kinase responsible for activating C/EBPbeta. Most important, we observed a role of Rac1/PAK1 signaling in activation of caspase-1, which is necessary for maturation of pro-IL-1beta. H. pylori LPS induced direct interaction between PAK1 and caspase-1, which was inhibited in cells transfected with dominant-negative Rac1. PAK1 immunoprecipitated from lysates of H. pylori LPS-challenged cells was able to phosphorylate recombinant caspase-1, but not its S376A mutant. LPS-induced caspase-1 activation was abrogated in cells transfected with caspase-1(S376A). Taken together, these results suggested a role of PAK1-induced phosphorylation of caspase-1 at Ser376 in activation of caspase-1. To the best of our knowledge our studies show for the first time that LPS-induced Rac1/PAK1 signaling leading to caspase-1 phosphorylation is crucial for caspase-1 activation. These studies also provide detailed insight into the regulation of IL-1beta gene expression by H. pylori LPS and are particularly important in the light of the observations that IL-1beta gene polymorphisms are associated with increased risk of H. pylori-associated gastric cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • CCAAT-Enhancer-Binding Protein-beta / metabolism*
  • Caspase 1 / metabolism
  • Caspase 1 / physiology*
  • Cell Line
  • Cell Line, Tumor
  • Dose-Response Relationship, Drug
  • Enzyme Activation
  • Gene Expression Regulation*
  • Genes, Dominant
  • Genes, Reporter
  • Helicobacter pylori / metabolism*
  • Humans
  • Immunoprecipitation
  • Interleukin-1 / genetics
  • Interleukin-1 / metabolism*
  • Lipopolysaccharides / chemistry
  • Lipopolysaccharides / metabolism
  • Luciferases / metabolism
  • MAP Kinase Signaling System
  • Macrophages / metabolism*
  • Macrophages / microbiology
  • NF-kappa B / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Plasmids / metabolism
  • Polymorphism, Genetic
  • Promoter Regions, Genetic
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • RNA / metabolism
  • Recombinant Proteins / chemistry
  • Reverse Transcriptase Polymerase Chain Reaction
  • Serine / chemistry
  • Signal Transduction
  • Time Factors
  • Transcription, Genetic
  • Transfection
  • p21-Activated Kinases
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • CCAAT-Enhancer-Binding Protein-beta
  • Interleukin-1
  • Lipopolysaccharides
  • NF-kappa B
  • Proto-Oncogene Proteins
  • Recombinant Proteins
  • Serine
  • RNA
  • Luciferases
  • AKT1 protein, human
  • PAK1 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • p21-Activated Kinases
  • p38 Mitogen-Activated Protein Kinases
  • Caspase 1