Aggregatibacter actinomycetemcomitans cytolethal distending toxin activates the NLRP3 inflammasome in human macrophages, leading to the release of proinflammatory cytokines

Infect Immun. 2015 Apr;83(4):1487-96. doi: 10.1128/IAI.03132-14. Epub 2015 Feb 2.

Abstract

The cytolethal distending toxin (Cdt) is produced from a number of bacteria capable of causing infection and inflammatory disease. Our previous studies with Actinobacillus actinomycetemcomitans Cdt demonstrate not only that the active toxin subunit functions as a phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase but also that macrophages exposed to the toxin were stimulated to produce proinflammatory cytokines. We now demonstrate that the Cdt-induced proinflammatory response involves the activation of the NLRP3 inflammasome. Specific inhibitors and short hairpin RNA (shRNA) were employed to demonstrate requirements for NLRP3 and ASC as well as caspase-1. Furthermore, Cdt-mediated inflammasome activation is dependent upon upstream signals, including reactive oxygen species (ROS) generation and Cdt-induced increases in extracellular ATP levels. Increases in extracellular ATP levels contribute to the activation of the P2X7 purinergic receptor, leading to K+ efflux. The relationship between the abilities of the active toxin subunit CdtB to function as a lipid phosphatase, activate the NLRP3 inflammasome, and induce a proinflammatory cytokine response is discussed. These studies provide new insight into the virulence potential of Cdt in mediating the pathogenesis of disease caused by Cdt-producing organisms such as Aggregatibacter actinomycetemcomitans.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Bacterial Toxins / genetics
  • Bacterial Toxins / immunology*
  • Bacterial Toxins / metabolism
  • Carrier Proteins / immunology*
  • Caspase 1 / immunology
  • Cell Line, Tumor
  • Cytokines / metabolism*
  • Enzyme Activation / immunology
  • Humans
  • Inflammasomes / immunology*
  • Inflammation / immunology
  • Inflammation / microbiology
  • Interleukin-18 / immunology
  • Interleukin-18 / metabolism
  • Interleukin-1beta / immunology
  • Interleukin-1beta / metabolism
  • Interleukin-6 / immunology
  • Interleukin-6 / metabolism
  • Macrophages / immunology*
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • Phosphoric Monoester Hydrolases / metabolism
  • Potassium / metabolism
  • RNA Interference
  • RNA, Small Interfering / genetics
  • Reactive Oxygen Species / metabolism
  • Receptors, Purinergic P2X7 / metabolism
  • Tumor Necrosis Factor-alpha / immunology
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Bacterial Toxins
  • Carrier Proteins
  • Cytokines
  • IL1B protein, human
  • IL6 protein, human
  • Inflammasomes
  • Interleukin-18
  • Interleukin-1beta
  • Interleukin-6
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • NLRP3 protein, human
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Receptors, Purinergic P2X7
  • Tumor Necrosis Factor-alpha
  • cytolethal distending toxin, Actinobacillus actinomycetemcomitans
  • Adenosine Triphosphate
  • phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase
  • Phosphoric Monoester Hydrolases
  • Caspase 1
  • Potassium