Roles of intracellular calcium and NF-kappa B in the Clostridium difficile toxin A-induced up-regulation and secretion of IL-8 from human monocytes.
Clostridium difficile causes an intense inflammatory colitis through the actions of two large exotoxins, toxin A and toxin B. IL-8 is believed to play an important role in the pathophysiology of C. difficile-mediated colitis, although the mechanism whereby the toxins up-regulate the release of IL-8 from target cells is not well understood. In this study, we investigated the mechanisms through which toxin A induces IL-8 secretion in human monocytes. We found that cellular uptake of toxin A is required for the up-regulation of IL-8, an effect that is not duplicated by a recombinant toxin fragment comprising the cell-binding domain alone. Toxin A induced IL-8 expression at the level of gene transcription and this effect occurred through a mechanism requiring intracellular calcium and calmodulin activation. Additionally, the effects of toxin A were inhibited by the protein tyrosine kinase inhibitor genistein, but were unaffected by inhibitors of protein kinase C and phosphatidylinositol-3 kinase. We determined that toxin A activates nuclear translocation of the transcription factors NF-kappa B and AP-1, but not NF-IL-6. NF-kappa B inhibitors blocked the ability of toxin A to induce IL-8 secretion, and supershift analysis indicated that the major isoform of NF-kappa B activated by the toxin is a p50-p65 heterodimer. This study is the first to identify intracellular signaling pathways and transcription factors involved in the C. difficile toxin-mediated up-regulation of IL-8 synthesis and release by target cells. This information should increase our understanding of the pathogenesis of C. difficile colitis and the nature of IL-8 gene regulation as well.
Jefferson
K K
KK
Department of Medicine, Health Sciences Center, University of Virginia, Charlottesville 22908, USA.
Smith
M F
MF
Bobak
D A
DA
D001427:Bacterial Toxins; D001692:Biological Transport / Q000235:genetics; D022762:CCAAT-Enhancer-Binding Proteins; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000276:immunology; D002147:Calmodulin / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D016360:Clostridioides difficile / Q000276:immunology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004768:Enterotoxins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D052002:NF-kappa B p50 Subunit; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D051996:Transcription Factor RelA; D014158:Transcription, Genetic / Q000276:immunology; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology*
D001427:Bacterial Toxins; D022762:CCAAT-Enhancer-Binding Proteins; D002147:Calmodulin; D004268:DNA-Binding Proteins; D004768:Enterotoxins; D004791:Enzyme Inhibitors; D016209:Interleukin-8; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D009687:Nuclear Proteins; D010446:Peptide Fragments; D018808:Transcription Factor AP-1; D051996:Transcription Factor RelA; C041348:tcdA protein, Clostridium difficile; D017346:Protein Serine-Threonine Kinases; D002118:Calcium