Differential Requirement for Caspase-1 Autoproteolysis in Pathogen-Induced Cell Death and Cytokine Processing

Article (PDF Available)inCell host & microbe 8(6):471-83 · December 2010with127 Reads
DOI: 10.1016/j.chom.2010.11.007 · Source: PubMed
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.

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Available from: Petr Broz
    • "This suggests a similar mechanism of signalling between the ASC-dependent and ASCinflammasomes . The CARDs of the NLRC4/NAIP inflammasome then recruit and activate caspase-1, without the need for the adaptor ASC [138] . Unravelling the mechanisms of signalling amongst the inflammasomes, and determining if it is universal or diverse, is an important area of continued research. "
    [Show abstract] [Hide abstract] ABSTRACT: Intracellular NLR (Nucleotide- binding domain and Leucine-rich Repeat-containing) receptors are sensitive monitors that detect pathogen invasion of both plant and animal cells. NLRs confer recognition of diverse molecules associated with pathogen invasion. NLRs must exhibit strict intramolecular controls to avoid harmful ectopic activation in the absence of pathogens. Recent discoveries have elucidated the assembly and structure of oligomeric NLR signalling complexes in animals, and provided insights into how these complexes act as scaffolds for signal transduction. In plants, recent advances have provided novel insights into signalling-competent NLRs, and into the myriad strategies that diverse plant NLRs use to recognise pathogens. Here, we review recent insights into the NLR biology of both animals and plants. By assessing commonalities and differences between kingdoms, we are able to develop a more complete understanding of NLR function.
    Full-text · Article · Jun 2016
    • "Inflammasomes are vital signaling platforms that detect pathogenic microorganisms and sterile stressors [21]. The NLRP3 inflammasome, which functions as a molecular platform, includes the NLRP3 scaffold, the ASC adaptor, caspase-1, and the effector molecule IL-1b [4]. We observed a marked increment of the NLRP3/caspase-1/IL- 1b axis levels in the patients with Modic changes. "
    [Show abstract] [Hide abstract] ABSTRACT: Background Modic changes are the MRI signal changes of degenerative lumbar vertebral endplate and which lead to or accelerate intervertebral disc degeneration. NLRP3, caspase-1, and interleukin-1β (IL-1β) play a pivotal role in the pathogenesis of many inflammatory diseases, such as osteoarthritis. However, the roles of IL-1β and its activators caspase-1 and NLRP3 are unclear in the degenerative endplate. Questions/purposes We asked: (1) What are the degenerative changes of the histologic features and chondrogenic markers’ gene expressions between the cartilaginous endplates of patients with Modic changes and trauma (control)? (2) How does the NLRP3/caspase-1/IL-1β axis in the cartilaginous endplates of patients with Modic changes compare with control (trauma) specimens? Methods Surgical specimens of cartilaginous endplates were divided into Modic changes (n = 56) and the trauma control (n = 16) groups. Hematoxylin and eosin and safranin O staining of cartilaginous endplate tissues were done to evaluate the extracellular matrix. Reverse transcription-polymerase chain reaction was performed on these tissues to investigate mRNA expression of type II collagen (Col II), SOX-9, matrix metalloproteinase-3, and a disintegrin like and metalloproteinase thrombospondin type I motifs-5. NLRP3, caspase-1, and IL-1β were evaluated by reverse transcription-polymerase chain reaction and immunohistochemistry. Results Hematoxylin and eosin and safranin O staining showed the extracellular matrix degraded in the cartilaginous endplates of patients with Modic changes but not in the control cartilaginous endplates. Chondrogenic Col II (p = 0.024) and SOX9 (p = 0.053) were downregulated in the Modic changes group compared with the control group. In contrast to the control group, the transcriptional levels of NLRP3 (p < 0.001), caspase-1 (p = 0.054), and IL-1β (p = 0.001) were all upregulated in the Modic changes group. Conclusions The expression of NLRP3, caspase-1, and IL-1β was upregulated in the patients with low back pain and Modic changes on MRI compared with patients with vertebral burst fracture without degenerative changes on MRI. The data suggest the NLRP3/caspase-1/IL-1β axis may be implicated in lumbar cartilaginous endplate degeneration. Clinical Relevance The NLRP3/caspase-1/IL-1β axis is active in cartilaginous endplates of patients with Modic changes and inflammatory cascades can exacerbate the cartilaginous endplate degeneration which may act as a trigger for intervertebral disc degeneration and low back pain. If these findings can be confirmed by others, we hope that new and effective therapy could be developed directed against this target.
    Full-text · Article · May 2016
    • "ASC is dispensable for NAIP/NLRC4-dependent pyroptosis in human cells, because VHH ASC does not impair LDH release in response to MxiH treatment. Similarly , Salmonella-induced pyroptosis of mouse macrophages does not require ASC, whereas it is necessary for efficient cytokine release (Broz et al., 2010b). Direct recruitment of pro–caspase-1 by NLRC4 may be sufficient to trigger caspase-1–dependent cell death. "
    [Show abstract] [Hide abstract] ABSTRACT: Myeloid cells assemble inflammasomes in response to infection or cell damage; cytosolic sensors activate pro–caspase-1, indirectly for the most part, via the adaptors ASC and NLRC4. This leads to secretion of proinflammatory cytokines and pyroptosis. To explore complex formation under physiological conditions, we generated an alpaca single domain antibody, VHH ASC , which specifically recognizes the CARD of human ASC via its type II interface. VHH ASC not only impairs ASC CARD interactions in vitro , but also inhibits inflammasome activation in response to NLRP3, AIM2, and NAIP triggers when expressed in living cells, highlighting a role of ASC in all three types of inflammasomes. VHH ASC leaves the Pyrin domain of ASC functional and stabilizes a filamentous intermediate of inflammasome activation. Incorporation of VHH ASC -EGFP into these structures allowed the visualization of endogenous ASC PYD filaments for the first time. These data revealed that cross-linking of ASC PYD filaments via ASC CARD mediates the assembly of ASC foci.
    Full-text · Article · Apr 2016
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