Anthrax Toxin Induces Macrophage Death by p38 MAPK Inhibition but Leads to Inflammasome Activation via ATP Leakage

Laboratory of Signal Transduction, Department of Pharmacology, University of California, San Diego, La Jolla, California, USA.
Immunity (Impact Factor: 21.56). 06/2011; 35(1):34-44. DOI: 10.1016/j.immuni.2011.04.015
Source: PubMed


Detection of microbial constituents by membrane associated and cytoplasmic pattern recognition receptors is the essence of innate immunity, leading to activation of protective host responses. However, it is still unclear how immune cells specifically respond to pathogenic bacteria. Using virulent and nonvirulent strains of Bacillus anthracis, we have shown that secretion of ATP by infected macrophages and the sequential activation of the P2X7 purinergic receptor and nucleotide binding oligomerization domain (NOD)-like receptors are critical for IL-1-dependent host protection from virulent B. anthracis. Importantly, lethal toxin produced by virulent B. anthracis blocked activation of protein kinases, p38 MAPK and AKT, resulting in opening of a connexin ATP release channel and induction of macrophage death. Prevention of cell death or ATP release through constitutive p38 or AKT activation interfered with inflammasome activation and IL-1β production, thereby compromising antimicrobial immunity.

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    • "Activation of NOD-like receptors (NLRs), Aim2, and RIG-I all trigger inflammasome activation upon sensing of bacterial flagellin, DNA, and RNA, respectively (Fig 2). Cytosolic presence of cathepsin B or ATP leakage, that indicates vesicle damage induced by phagocytosed bacteria, activates NLRP3 and NRLP1 inflammasomes (Duncan et al, 2009; Meixenberger et al, 2010; Ali et al, 2011). "
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    ABSTRACT: Macrophages detect bacterial infection through pattern recognition receptors (PRRs) localized at the cell surface, in intracellular vesicles or in the cytosol. Discrimination of viable and virulent bacteria from non-virulent bacteria (dead or viable) is necessary to appropriately scale the anti-bacterial immune response. Such scaling of anti-bacterial immunity is necessary to control the infection, but also to avoid immunopathology or bacterial persistence. PRR-mediated detection of bacterial constituents in the cytosol rather than at the cell surface along with cytosolic recognition of secreted bacterial nucleic acids indicates viability and virulence of infecting bacteria. The effector responses triggered by activation of cytosolic PRRs, in particular the RIG-I-induced simultaneous rapid type I IFN induction and inflammasome activation, are crucial for timely control of bacterial infection by innate and adaptive immunity. The knowledge on the PRRs and the effector responses relevant for control of infection with intracellular bacteria will help to develop strategies to overcome chronic infection.
    The EMBO Journal 09/2014; 33(20). DOI:10.15252/embj.201489055 · 10.43 Impact Factor
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    • "Cleavage by the anthrax toxin directly activates CARD, leading to activation of caspase-1 [13]. An alternative mechanism of NLRP1 activation is by the toxin inhibiting p38 mitogen-activated protein kinase and Akt kinase, leading to opening of the connexion channel for ATP release, resulting in P2X7R signaling [14]. There are similarities with the mechanism of activation of the NLRP3 inflammasome. "
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    ABSTRACT: The inflammasome is a large, multiprotein complex that drives proinflammatory cytokine production in response to infection and tissue injury. Pattern recognition receptors that are either membrane bound or cytoplasmic trigger inflammasome assembly. These receptors sense danger signals including damage-associated molecular patterns and pathogen-associated molecular patterns (DAMPS and PAMPS respectively). The best-characterized inflammasome is the NLRP3 inflammasome. On assembly of the NLRP3 inflammasome, post-translational processing and secretion of pro-inflammatory cytokines IL-1beta and IL-18 occurs; in addition, cell death may be mediated via caspase-1. Intrinsic renal cells express components of the inflammasome pathway. This is most prominent in tubular epithelial cells and, to a lesser degree, in glomeruli. Several primary renal diseases and systemic diseases affecting the kidney are associated with NLRP3 inflammasome/IL-1beta/IL-18 axis activation. Most of the disorders studied have been acute inflammatory diseases. The disease spectrum includes ureteric obstruction, ischaemia reperfusion injury, glomerulonephritis, sepsis, hypoxia, glycerol-induced renal failure, and crystal nephropathy. In addition to mediating renal disease, the IL-1/ IL-18 axis may also be responsible for development of CKD itself and its related complications, including vascular calcification and sepsis. Experimental models using genetic deletions and/or receptor antagonists/antiserum against the NLRP3 inflammasome pathway have shown decreased severity of disease. As such, the inflammasome is an attractive potential therapeutic target in a variety of renal diseases.
    BMC Nephrology 01/2014; 15(1):21. DOI:10.1186/1471-2369-15-21 · 1.69 Impact Factor
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    • "In addition to its direct cardiovascular effects, LT may contribute to shock by promoting B. anthracis infection [44]. LT inactivates MAPKK pathways central to innate and adaptive immune responses and, therefore, may impair host defense and microbial clearance [22,25,45-47]. In one murine model, pretreatment with sublethal LT doses before intravenous E. coli challenge, increased blood bacterial counts and worsened survival [48]. "
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    ABSTRACT: The development of cardiovascular dysfunction and shock in patients with invasive Bacillus anthracis infection has a particularly poor prognosis. Growing evidence indicates that several bacterial components likely play important pathogenic roles in this injury. As with other pathogenic Gram-positive bacteria, the B. anthracis cell wall and its peptidoglycan constituent produce a robust inflammatory response with its attendant tissue injury, disseminated intravascular coagulation and shock. However, B. anthracis also produces lethal and edema toxins that both contribute to shock. Growing evidence suggests that lethal toxin, a metalloprotease, can interfere with endothelial barrier function as well as produce myocardial dysfunction. Edema toxin has potent adenyl cyclase activity and may alter endothelial function, as well as produce direct arterial and venous relaxation. Furthermore, both toxins can weaken host defense and promote infection. Finally, B. anthracis produces non-toxin metalloproteases which new studies show can contribute to tissue injury, coagulopathy and shock. In the future, an understanding of the individual pathogenic effects of these different components and their interactions will be important for improving the management of B. anthracis infection and shock.
    BMC Medicine 10/2013; 11(1):217. DOI:10.1186/1741-7015-11-217 · 7.25 Impact Factor
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