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      Pannexin-1-mediated recognition of bacterial molecules activates the cryopyrin inflammasome independent of Toll-like receptor signaling.

      Immunity
      Animals, Apoptosis Regulatory Proteins, metabolism, Bacteria, immunology, Calcium-Binding Proteins, Carrier Proteins, genetics, Caspase 1, Connexins, Cytosol, microbiology, Enzyme Activation, Inflammation, Interleukin-1beta, Lipopolysaccharides, pharmacology, Mice, Mice, Mutant Strains, Nerve Tissue Proteins, physiology, Receptors, Purinergic P2, Receptors, Purinergic P2X7, Toll-Like Receptors

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          Abstract

          Cryopyrin is essential for caspase-1 activation triggered by Toll-like receptor (TLR) ligands in the presence of adenosine triphosphate (ATP). However, the events linking bacterial products and ATP to cryopyrin remain unclear. Here we demonstrate that cryopyrin-mediated caspase-1 activation proceeds independently of TLR signaling, thus dissociating caspase-1 activation and IL-1beta secretion. Instead, caspase-1 activation required pannexin-1, a hemichannel protein that interacts with the P2X(7) receptor. Direct cytosolic delivery of multiple bacterial products including lipopolysaccharide, but not flagellin, induced caspase-1 activation via cryopyrin in the absence of pannexin-1 activity or ATP stimulation. However, unlike Ipaf-dependent caspase-1 activation, stimulation of the pannexin-1-cryopyrin pathway by several intracellular bacteria was independent of a functional bacterial type III secretion system. These results provide evidence for cytosolic delivery and sensing of bacterial molecules as a unifying model for caspase-1 activation and position pannexin-1 as a mechanistic link between bacterial stimuli and the cryopyrin inflammasome.

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