Anthrax Lethal Toxin Induced Lysosomal Membrane Permeabilization and Cytosolic Cathepsin Release Is Nlrp1b/Nalp1b-Dependent

Department of Microbiology, Immunology & Molecular Genetics, University of California Los Angeles, Los Angeles, California, USA.
PLoS ONE (Impact Factor: 3.23). 11/2009; 4(11):e7913. DOI: 10.1371/journal.pone.0007913
Source: PubMed

ABSTRACT NOD-like receptors (NLRs) are a group of cytoplasmic molecules that recognize microbial invasion or 'danger signals'. Activation of NLRs can induce rapid caspase-1 dependent cell death termed pyroptosis, or a caspase-1 independent cell death termed pyronecrosis. Bacillus anthracis lethal toxin (LT), is recognized by a subset of alleles of the NLR protein Nlrp1b, resulting in pyroptotic cell death of macrophages and dendritic cells. Here we show that LT induces lysosomal membrane permeabilization (LMP). The presentation of LMP requires expression of an LT-responsive allele of Nlrp1b, and is blocked by proteasome inhibitors and heat shock, both of which prevent LT-mediated pyroptosis. Further the lysosomal protease cathepsin B is released into the cell cytosol and cathepsin inhibitors block LT-mediated cell death. These data reveal a role for lysosomal membrane permeabilization in the cellular response to bacterial pathogens and demonstrate a shared requirement for cytosolic relocalization of cathepsins in pyroptosis and pyronecrosis.

Download full-text


Available from: Matthew R Pratt, Sep 26, 2015
22 Reads
  • Source
    • "Many of the activating substrates for the other three inflammasomes are also known. The NLRP1 inflammasome is recruited by Bacillus anthracis lethal toxin and muramyl dipeptide of bacteria (Averette et al., 2009). The AIM2 inflammasome is stimulated by double stranded DNA in the cytosol and is responsible for the development of inflammatory response to viruses, bacterial DNA, and in some cases one's own DNA (Choubey, 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Gardnerella vaginalis is a Gram-positive bacterium associated with bacterial vaginosis (BV), pelvic inflammatory disease, and preterm birth. BV is the most prevalent vaginal infection in women, characterized by the absence of normal Lactobacilli and overgrowth of G. vaginalis and other bacterial species. This study tested the hypothesis that G. vaginalis induces an inflammatory response in the human cell line, THP-1. The objectives of the study were to 1) determine whether different strains of G. vaginalis cause proinflammatory cytokinesproduction in THP-1 cells, 2) characterize intracellular pathways by which these cytokines are produced, and 3) determine molecular mechanisms involved in death of cells treated with strains of G. vaginalis. In these studies, G. vaginalis strain 14018 induced statisticaliy significant increases in the inflammasome-dependent cytokines IL-1β, IL-18, as well as TNF-α in THP-1 monocytes. This same strain of G. vaginalis also caused statistically significant cell death in THP-1 monocytes and cleavage of caspase-1 by 24 h following treatment. Knockdown of the inflammasome component, NLRP3, in THP-1 cells reduced secretion of IL-1β. Additionally, THP-1 cells stably expressing ASC with a fluorescent tag exhibited colocalization of NLRP3 with ASC in G. vaginalis-treated THP-1 cells. These studies confirmed the role of the NLRP3 inflammasome in G. vaginalis inflammation. In a strain-specific study, a statistically significant increase in THP-1 monocyte differentiation and IL-1β secretion were detected in response to G. vaginalis strains 14018 and 49145 but not strain 14019. Cytokine and inflammasome responses were similar for strains 14018 and 49145, but strain 14019 did not induce an inflammatory response in THP-1 cells. The strain-specific ability of G. vaginalis to induce inflammation could con- tribute to the variability observed clinically between women colonized with G. vaginalis. The deleterious effects of G. vaginalis observed in THP-1 monocytes were not observed for the human trophoblast cell line HTR8 when treated with any of the G. vaginalis strains. The results of these studies increase the understanding of how G. vaginal- is activates the innate immune system and suggests that a strain-dependent activation of inflammation may be involved in bacterial vaginosis and preterm birth.
    12/2014, Degree: Ph.D., Supervisor: Anthony Farone
  • Source
    • "There is evidence supporting a function in bacterial recognition for several NLRs. These include NOD1/2 (recognizing peptidoglycan fragments) (Martinon et al., 2009), NLRP1 (sensing anthrax lethal toxin) (Averette et al., 2009), NLRP3 (activated by exposure to many pathogens, bacterial RNA, toxins, and crystal structures) (Davis et al., 2011; Duewell et al., 2010; Halle et al., 2008; Hornung et al., 2008; Kanneganti et al., 2006; Sander et al., 2011), NLRC4 (sensing of Salmonella, intracellular flagellin and bacterial type III secretion rod proteins) (Franchi et al., 2006; Miao et al., 2010), and Naip5 (promoting resistance to Legionella) (Kofoed and Vance, 2011; Molofsky et al., 2006; Ren et al., 2006). Recent results also suggested a role for NLRP6 in maintenance of bacterial homeostasis in the colon and for NLRP7 in the recognition of lipoproteins (Khare et al., 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Yersinia pestis, the causative agent of plague, is able to suppress production of inflammatory cytokines IL-18 and IL-1β, which are generated through caspase-1-activating nucleotide-binding domain and leucine-rich repeat (NLR)-containing inflammasomes. Here, we sought to elucidate the role of NLRs and IL-18 during plague. Lack of IL-18 signaling led to increased susceptibility to Y. pestis, producing tetra-acylated lipid A, and an attenuated strain producing a Y. pseudotuberculosis-like hexa-acylated lipid A. We found that the NLRP12 inflammasome was an important regulator controlling IL-18 and IL-1β production after Y. pestis infection, and NLRP12-deficient mice were more susceptible to bacterial challenge. NLRP12 also directed interferon-γ production via induction of IL-18, but had minimal effect on signaling to the transcription factor NF-κB. These studies reveal a role for NLRP12 in host resistance against pathogens. Minimizing NLRP12 inflammasome activation may have been a central factor in evolution of the high virulence of Y. pestis.
    Immunity 07/2012; 37(1):96-107. DOI:10.1016/j.immuni.2012.07.006 · 21.56 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gram-positive bacterial infections have risen over recent years and current antibiotic treatments are not always sufficient to control these infections. Specifically, antibiotics target bacteria themselves, but not the bacterially secreted proteins that contribute to bacterial pathogenesis and host tissue damage (i.e. virulence factors). These virulence factors may linger after bacteria are eradicated, making their interaction with the host important to understand for the development of novel therapeutics to supplement antibiotics. One class of virulence factors studied in our laboratory is a large pore-forming toxin family known as the cholesterol-dependent cytolysins (CDC). These exotoxins are secreted by over twenty species of gram-positive bacteria and have been shown to contribute to the virulence of the bacteria that secrete them. We are interested in exploring the pathways initiated by CDC in host innate immune cells such as macrophages and dendritic cells. These cells would be expected to first encounter CDC after bacterial infection and therefore, pathways initiated in these cells by CDC could be targeted for the benefit of the host.We have characterized the mechanism of mature IL-1beta secretion induced by CDC tetanolysin O (TLO) from LPS-primed murine bone marrow-derived macrophages (BMDM). This process is dependent on TLO dose and relies on the caspase-1-containing NLRP3 inflammasome as well as associated signaling pathways, which include ion fluxes and iPLA2 and cathepsin B activities. Furthermore, TLO induces different cell death programs in BMDM that are dependent on TLO dose. High TLO doses induce conventional necrotic cell death while low TLO doses cause NLRP3 inflammasome-dependent and cathepsin B-dependent necrotic cell death that is characterized by lactate dehydrogenase (LDH) and high mobility group box 1 (HMGB1) release. Both IL-1beta and HMGB1 are pro-inflammatory cytokines that contribute to inflammation and may be useful therapeutic targets, in addition to the inflammasome. Finally, susceptibility to CDC-induced cell killing varies based on cell type. In order to determine pathways that might explain these differences, we created a variant murine dendritic cell line resistant to pore formation. Though this cell line has been characterized to some degree, future studies will be needed to pinpoint the pathways responsible for the phenotype observed.
Show more