Differential requirement for Caspase-1 autoproteolysis in pathogen-induced cell death and cytokine processing.

Department of Microbiology and Immunology, Stanford School of Medicine, Stanford University, Stanford, CA 94305, USA.
Cell host & microbe (Impact Factor: 13.02). 12/2010; 8(6):471-83. DOI: 10.1016/j.chom.2010.11.007
Source: PubMed

ABSTRACT Activation of the cysteine protease Caspase-1 is a key event in the innate immune response to infections. Synthesized as a proprotein, Caspase-1 undergoes autoproteolysis within multiprotein complexes called inflammasomes. Activated Caspase-1 is required for proteolytic processing and for release of the cytokines interleukin-1β and interleukin-18, and it can also cause rapid macrophage cell death. We show that macrophage cell death and cytokine maturation in response to infection with diverse bacterial pathogens can be separated genetically and that two distinct inflammasome complexes mediate these events. Inflammasomes containing the signaling adaptor Asc form a single large "focus" in which Caspase-1 undergoes autoproteolysis and processes IL-1β/IL-18. In contrast, Asc-independent inflammasomes activate Caspase-1 without autoproteolysis and do not form any large structures in the cytosol. Caspase-1 mutants unable to undergo autoproteolysis promoted rapid cell death, but processed IL-1β/18 inefficiently. Our results suggest the formation of spatially and functionally distinct inflammasomes complexes in response to bacterial pathogens.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Nucleotide binding oligomerization domain (NOD)-like receptors are cytoplasmic pattern-recognition receptors that together with RIG-I-like receptor (retinoic acid-inducible gene 1), Toll-like receptor (TLR), and C-type lectin families make up the innate pathogen pattern recognition system. There are 22 members of NLRs in humans, 34 in mice, and even a larger number in some invertebrates like sea urchins, which contain more than 200 receptors. Although initially described to respond to intracellular pathogens, NLRs have been shown to play important roles in distinct biological processes ranging from regulation of antigen presentation, sensing metabolic changes in the cell, modulation of inflammation, embryo development, cell death, and differentiation of the adaptive immune response. The diversity among NLR receptors is derived from ligand specificity conferred by the leucine-rich repeats and an NH2-terminal effector domain that triggers the activation of different biological pathways. Here, we describe NLR genes associated with different biological processes and the molecular mechanisms underlying their function. Furthermore, we discuss mutations in NLR genes that have been associated with human diseases. Copyright © 2015 the American Physiological Society.
    Physiological Reviews 01/2015; 95(1):149-178. · 29.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Type III secretion systems (T3SS) translocate effector proteins into target cells in order to disrupt or modulate host cell signaling pathways and establish replicative niches. However, recognition of T3SS activity by cytosolic pattern recognition receptors (PRRs) of the nucleotide-binding domain leucine rich repeat (NLR) family, either through detection of translocated products or membrane disruption, induces assembly of multiprotein complexes known as inflammasomes. Macrophages infected with Yersinia pseudotuberculosis strains lacking all known effectors or lacking the translocation regulator YopK induce rapid activation of both the canonical NLRP3 and noncanonical caspase-11 inflammasomes. While this inflammasome activation requires a functional T3SS, the precise signal that triggers inflammasome activation in response to Yersinia T3SS activity remains unclear. Effectorless strains of Yersinia as well as ΔyopK strains translocate elevated levels of T3SS substrates into infected cells. To dissect the contribution of pore formation and translocation to inflammasome activation, we took advantage of variants of YopD and LcrH that separate these functions of the T3SS. Notably, YopD variants that abrogated translocation but not pore-forming activity failed to induce inflammasome activation. Furthermore, analysis of individual infected cells revealed that inflammasome activation at the single-cell level correlated with translocated levels of YopB and YopD themselves. Intriguingly, LcrH mutants that are fully competent for effector translocation but produce and translocate lower levels of YopB and YopD also fail to trigger inflammasome activation. Our findings therefore suggest that hypertranslocation of YopD and YopB is linked to inflammasome activation in response to the Yersinia T3SS. The innate immune response is critical to effective clearance of pathogens. Recognition of conserved virulence structures and activities by innate immune receptors such as NLRs constitute one of the first steps in mounting the innate immune response. However, pathogens such as Yersinia actively evade or subvert components of host defense, such as inflammasomes. The T3SS-secreted protein YopK is an essential virulence factor that limits translocation of other Yops, thereby limiting T3SS-induced inflammasome activation. However, what triggers inflammasome activation in cells infected by YopK-deficient Yersinia is not clear. Our findings indicate that hypertranslocation of pore complex proteins promotes inflammasome activation and that YopK prevents inflammasome activation by the T3SS by limiting translocation of YopD and YopB themselves. Copyright © 2015 Zwack et al.
    mBio 01/2015; 6(1):e02095-14. · 6.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inflammasome 2015; 2: 1–6 an important innate immune mechanism for combating intracellular pathogens [3]. The existence of this unusual cell death modality was first implied in 1992, when the Sansonetti laboratory observed that murine macrophages infected with the Gram-negative bacterium, Shigella flexneri, undergo a form of cell death similar to apoptosis [4]. The Falkow laboratory made similar observations in cells infected with a closely related pathogen, Salmonella Typhimurium, reporting the presence of DNA degradation, changes in nuclear morphology and vacuole formation [5]. In addition to these apoptosis-like features, Cookson and co-workers reported that cell death by such infected cells also presented features similar to necrosis [6]. These cells formed membrane pores of 1-2.5 nm and displayed swelling and Ca 2+ influx, leading to membrane rupture and the extracellular release of cellular contents. This unusual form of pathogen-induced cell death, containing hallmarks of both apoptosis and necrosis [6], was found to be dependent on the activity of a proinflammatory protease, caspase-1 [5]. The term 'pyroptosis' was coined by Cookson and Brennan in 2001 to distinguish this form of cell death from apoptosis and necrosis [7]. 2 Pyroptosis initiation by canonical Caspase-1 inflammasomes Caspase-1 is a protease that drives potent inflammatory responses. Caspase-1 consists of a N-terminal CARD domain, followed by a bipartite catalytic domain, composed of large and small subunits [8]. The protease is synthesized within the cell as an inactive monomeric zymogen (pro-caspase-1) and is activated upon formation of the inflammasome, a large molecular signalling complex that assembles upon sensing of microbial or endogenous-derived danger molecules [9-12]. So-called canonical inflammasomes are composed of a sensor molecule and caspase-1, and often include the common adaptor protein, ASC. Sensing of endogenous or pathogen-derived danger molecules occurs through one or more nucleotide-binding domain and leucine-rich repeat containing receptor (NLR) Abstract: Many programmed cell death pathways are essential for organogenesis, development, immunity and the maintenance of homeostasis in multicellular organisms. Pyroptosis, a highly proinflammatory form of cell death, is a critical innate immune response to prevent intracellular infection. Pyroptosis is induced upon the activation of proinflammatory caspases within macromolecular signalling platforms called inflammasomes. This article reviews our understanding of pyroptosis induction, the function of inflammatory caspases in pyroptosis execution, and the importance of pyroptosis for pathogen clearance. It also highlights the situations in which extensive pyroptosis may in fact be detrimental to the host, leading to immune cell depletion or cytokine storm. Current efforts to understand the beneficial and pathological roles of pyroptosis bring the promise of new approaches to fight infectious diseases.
    Inflammasome. 01/2015; 2(1):1-6.

Full-text (2 Sources)

Available from
Jun 3, 2014