CARD4/Nod1 mediates NF-|[kappa]|B and JNK activation by invasive Shigella flexneri

Unité des Virus Oncogènes, and Unité INSERM 389, Institut Pasteur, 28 rue du Dr Roux, Paris, Cédex 15, 75724 France.
EMBO Reports (Impact Factor: 9.06). 07/2001; 2(8):736-742. DOI: 10.1093/embo-reports/kve155
Source: PubMed


Epithelial cells are refractory to extracellular lipopolysaccharide (LPS), yet when presented inside the cell, it is capable of initiating an inflammatory response. Using invasive Shigella flexneri to deliver LPS into the cytosol, we examined how this factor, once intracellular, activates both NF-kappaB and c-Jun N-terminal kinase (JNK). Surprisingly, the mode of activation is distinct from that induced by toll-like receptors (TLRs), which mediate LPS responsiveness from the outside-in. Instead, our findings demonstrate that this response is mediated by a cytosolic, plant disease resistance-like protein called CARD4/Nod1. Biochemical studies reveal enhanced oligomerization of CARD4 upon S. flexneri infection, an event necessary for NF-kappaB induction. Dominant-negative versions of CARD4 block activation of NF-kappaB and JNK by S. flexneri as well as microinjected LPS. Finally, we showed that invasive S. flexneri triggers the formation of a transient complex involving CARD4, RICK and the IKK complex. This study demonstrates that in addition to the extracellular LPS sensing system mediated by TLRs, mammalian cells also possess a cytoplasmic means of LPS detection via a molecule that is related to plant disease-resistance proteins.

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Available from: Moshe Yaniv, Oct 05, 2015
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    • "We employed Shigella flexneri, an invasive Gram-negative enteropathogenic bacterium, as an infection model to study the complex host–pathogen interactions that shape the immune response of intestinal epithelial cells in response to bacterial infection . The host response to intracellular Shigella involves NOD1 signaling followed by activation of RIPK2, leading to the activation of NF-jB and the production and secretion of pro-inflammatory cytokines such as IL-8 (Girardin et al, 2001). However, Shigella has evolved a number of strategies to actively down-regulate the host cell immune response to ensure bacterial survival and propagation within the human intestinal epithelium. "
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    ABSTRACT: The X-linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor, best known for its anti-apoptotic function in cancer. During apoptosis, XIAP is antagonized by SMAC, which is released from the mitochondria upon caspase-mediated activation of BID. Recent studies suggest that XIAP is involved in immune signaling. Here, we explore XIAP as an important mediator of an immune response against the enteroinvasive bacterium Shigella flexneri, both in vitro and in vivo. Our data demonstrate for the first time that Shigella evades the XIAP-mediated immune response by inducing the BID-dependent release of SMAC from the mitochondria. Unlike apoptotic stimuli, Shigella activates the calpain-dependent cleavage of BID to trigger the release of SMAC, which antagonizes the inflammatory action of XIAP without inducing apoptosis. Our results demonstrate how the cellular death machinery can be subverted by an invasive pathogen to ensure bacterial colonization.
    The EMBO Journal 07/2014; 33(19). DOI:10.15252/embj.201387244 · 10.43 Impact Factor
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    • "Intestinal pathogens such as Salmonella and Shigella have been shown to activate NFκB in intestinal epithelial cells in a TLR independent manner. For example, Shigella flexneri invades and activates NOD1, which senses bacterial peptidoglycan, leading to IL-8 production [35]. In Salmonella, the T3SS effector SopE activates NFκB [36] by engaging small Rho GTPases CDC42 and Rac1, which in turn trigger NOD1 and RIP2 activation of NFκB [25]. "
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    ABSTRACT: Background Burkholderia pseudomallei is the causative agent of melioidosis, a potentially fatal disease endemic in Southeast Asia and Northern Australia. This Gram-negative pathogen possesses numerous virulence factors including three “injection type” type three secretion systems (T3SSs). B. pseudomallei has been shown to activate NFκB in HEK293T cells in a Toll-like receptor and MyD88 independent manner that requires T3SS gene cluster 3 (T3SS3 or T3SSBsa). However, the mechanism of how T3SS3 contributes to NFκB activation is unknown. Results Known T3SS3 effectors are not responsible for NFκB activation. Furthermore, T3SS3-null mutants are able to activate NFκB almost to the same extent as wildtype bacteria at late time points of infection, corresponding to delayed escape into the cytosol. NFκB activation also occurs when bacteria are delivered directly into the cytosol by photothermal nanoblade injection. Conclusions T3SS3 does not directly activate NFκB but facilitates bacterial escape into the cytosol where the host is able to sense the presence of the pathogen through cytosolic sensors leading to NFκB activation.
    BMC Microbiology 05/2014; 14(1):115. DOI:10.1186/1471-2180-14-115 · 2.73 Impact Factor
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    • "Upon ligand recognition, the NBD domain of NOD1 or NOD2 oligomerizes and initiates the interaction of the CARD domain with RIPK2 (also called RIP2/RICK), which is a member of the CARD protein family [49,55]. RIPK2 is activated subsequently by proximity and promotes the formation of a signaling complex that contains the regulatory subunit of the IKK complex, NEMO [64], leading to NF-κB activation (see Figure  2, left panel). "
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    ABSTRACT: The calcineurin/nuclear factor of activated T cells (NFATs) signaling pathway plays a central role in T cell mediated adaptive immune responses, but a number of recent studies demonstrated that calcineurin/NFAT signaling also plays a key role in the control of the innate immune response by myeloid cells. Calcineurin inhibitors, such as cyclosporine A (CsA) and tacrolimus (FK506), are commonly used in organ transplantation to prevent graft rejection and in a variety of immune diseases. These immunosuppressive drugs have adverse effects and significantly increase host's susceptibility towards bacterial or fungal infections. Recent studies highlighted the role of NFAT signaling in fungal infection and in the control of the pattern recognition receptor nucleotide-binding oligomerization domain-containing protein 1 (NOD1), which predominantly senses invasive Gram-negative bacteria and mediates neutrophil phagocytic functions. This review summarises some of the current knowledge concerning the role of NFAT signaling in the innate immune response and the recent advances on NFAT-dependent inhibition of NOD1-mediated innate immune response caused by CsA, which may contribute to sensitizing transplant recipients to bacterial infection.
    Cell Communication and Signaling 01/2014; 12(1):8. DOI:10.1186/1478-811X-12-8 · 3.38 Impact Factor
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