Article

Potentiation of caspase-1 activation by the P2X7 receptor is dependent on TLR signals and requires NF-kappaB-driven protein synthesis.

Department of Pathology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.
The Journal of Immunology (Impact Factor: 5.36). 01/2006; 175(11):7611-22. DOI: 10.4049/jimmunol.175.11.7611
Source: PubMed

ABSTRACT The proinflammatory cytokines IL-1beta and IL-18 are inactive until cleaved by the enzyme caspase-1. Stimulation of the P2X7 receptor (P2X7R), an ATP-gated ion channel, triggers rapid activation of caspase-1. In this study we demonstrate that pretreatment of primary and Bac1 murine macrophages with TLR agonists is required for caspase-1 activation by P2X7R but it is not required for activation of the receptor itself. Caspase-1 activation by nigericin, a K+/H+ ionophore, similarly requires LPS priming. This priming by LPS is dependent on protein synthesis, given that cyclohexamide blocks the ability of LPS to prime macrophages for activation of caspase-1 by the P2X7R. This protein synthesis is likely mediated by NF-kappaB, as pretreatment of cells with the proteasome inhibitor MG132, or the IkappaB kinase inhibitor Bay 11-7085 before LPS stimulation blocks the ability of LPS to potentiate the activation of caspase-1 by the P2X7R. Thus, caspase-1 regulation in macrophages requires inflammatory stimuli that signal through the TLRs to up-regulate gene products required for activation of the caspase-1 processing machinery in response to K+-releasing stimuli such as ATP.

Download full-text

Full-text

Available from: George R Dubyak, Nov 02, 2014
0 Followers
 · 
112 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inflammatory diseases are often multiorganic diseases with manifestations not related directly to the primary affected organ. They are often complicated by a generalized bone loss that subsequently leads to osteoporosis and bone fractures. The exact mechanism for the accompanying bone loss is not understood in full detail, but factors such as glucocorticoid treatment, immobilization, malnutrition, and insufficient intake of vitamin D play a role. However, it has become evident that the inflammatory process itself is involved and the resulting bone loss is termed immune-mediated bone loss. It stems from an increase in bone resorption and the pro-inflammatory cytokines tumor necrosis factor alpha and interleukin 1 beta and has been shown to not only mediate the inflammatory response but also to strongly stimulate bone degradation. The purinergic P2X7 receptor is central in the processing of these two cytokines and in the initiation of the inflammatory response, and it is a key molecule in the regulation of both bone formation and bone resorption. The aim of this review is therefore to provide evidence-based novel hypotheses of the role of ATP-mediated purinergic signalling via the P2X7 receptor in immune-mediated bone loss and -osteoporosis.
    The Scientific World Journal 01/2014; 2014:954530. DOI:10.1155/2014/954530 · 1.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The ability of the immune system to give rise to an effective response against pathogens while maintaining tolerance towards self-tissues has always been an object of keen interest for immunologist. Over the years, different theories have been proposed to explain if and how the immune system is able to discriminate between self and non-self, including the Infectious Non-self theory from Charles Janeway and Polly Matzinger's Danger theory. Nowadays we know Janeway's theory is largely true, however the immune system does respond to injured, stressed and necrotic cells releasing danger signals (DAMPs) with a potent inflammatory response. To avoid unwanted prolonged autoimmune reactions, though, danger-induced inflammation should be tightly regulated. In the present review we discuss how prototypic DAMPs are able to induce inflammation and the peculiarity of danger-induced inflammation, as opposed to a complete immune response to fight pathogen invasions.
    Molecular Immunology 01/2014; 63(2). DOI:10.1016/j.molimm.2014.06.037 · 3.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: P2X7 receptors (P2X7R) are extracellular ATP-gated ion channels expressed in the immune effector cells that carry out critical protective responses during the early phases of microbial infection or acute tissue trauma. P2X7R-positive cells include monocytes, macrophages, dendritic cells and T cells. Given its presence in all host and pathogen cell types, ATP can be readily released into extracellular compartments at local sites of tissue damage and microbial invasion. Thus, extracellular ATP and its target receptors on host effector cells can be considered as additional elements of the innate immune system. In this regard, stimulation of P2X7R rapidly triggers a key step of the inflammatory response: induction of NLRP3/caspase-1 inflammasome signalling complexes that drive the proteolytic maturation and secretion of the proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18). IL-1β (and IL-18) lacks a signal sequence for compartmentation within the Golgi and classical secretory vesicles and the proIL-1β precursor accumulates within the cytosol following translation on free ribosomes. Thus, ATP-induced accumulation of the mature IL-1β cytokine within extracellular compartments requires non-classical mechanisms of export from the cytosolic compartment. Five proposed mechanisms include: (i) exocytosis of secretory lysosomes that accumulate cytosolic IL-1β via undefined protein transporters; (ii) release of membrane-delimited microvesicles derived from plasma membrane blebs formed by evaginationsof the surface membrane that entrap cytosolic IL-β; (iii) release of membrane-delimited exosomes secondary to the exocytosis of multivesicular bodies formed by invaginations of recycling endosomes that entrap cytosolic IL-β; (iv) exocytosis of autophagosomes or autophagolysosomes that accumulate cytosolic IL-1β via entrapment during formation of the initial autophagic isolation membrane or omegasome and (v) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. These mechanisms are not mutually exclusive and may represent engagement of parallel or intersecting membrane trafficking responses to P2X7R activation.
    Cellular Microbiology 08/2012; 14(11):1697-706. DOI:10.1111/cmi.12001 · 4.82 Impact Factor