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The Yersinia virulence effector YopM binds caspase-1 to arrest inflammasome assembly and processing.

ABSTRACT: Inflammasome assembly activates caspase-1 and initiates the inflammatory cell death program pyroptosis, which is protective against numerous pathogens. Consequently, several pathogens, including the plague causing bacterium Yersinia pestis, avoid activating this pathway to enhance their virulence. However, bacterial molecules that directly modulate the inflammasome have yet to be identified. Examining the contribution of Yersinia type III secretion effectors to caspase-1 activation, we identified the leucine-rich repeat effector YopM as a potent antagonist of both caspase-1 activity and activation. YopM directly binds caspase-1, which both inhibits caspase-1 activity and sequesters it to block formation of the mature inflammasome. Caspase-1 activation antagonizes Yersinia survival in vivo, and consequently YopM inhibition of caspase-1 is required for Yersinia pathogenesis. Thus, a bacterium obstructs pyroptosis utilizing a direct mechanism of caspase-1 inhibition that is distinct from known viral or host inhibitors.

SUBMITTER: LaRock CN

PROVIDER: S-EPMC3703949 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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The Yersinia virulence effector YopM binds caspase-1 to arrest inflammasome assembly and processing.

LaRock Christopher N CN Cookson Brad T BT

Cell host & microbe 20121201 6

Inflammasome assembly activates caspase-1 and initiates the inflammatory cell death program pyroptosis, which is protective against numerous pathogens. Consequently, several pathogens, including the plague causing bacterium Yersinia pestis, avoid activating this pathway to enhance their virulence. However, bacterial molecules that directly modulate the inflammasome have yet to be identified. Examining the contribution of Yersinia type III secretion effectors to caspase-1 activation, we identifie ...[more]

PMID: 23245324

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Project description:Type III secretion systems (T3SS) are central virulence factors for many pathogenic Gram-negative bacteria, and secreted T3SS effectors can block key aspects of host cell signaling. To counter this, innate immune responses can also sense some T3SS components to initiate anti-bacterial mechanisms. The Yersinia pestis T3SS is particularly effective and sophisticated in manipulating the production of pro-inflammatory cytokines IL-1β and IL-18, which are typically processed into their mature forms by active caspase-1 following inflammasome formation. Some effectors, like Y. pestis YopM, may block inflammasome activation. Here we show that YopM prevents Y. pestis induced activation of the Pyrin inflammasome induced by the RhoA-inhibiting effector YopE, which is a GTPase activating protein. YopM blocks YopE-induced Pyrin-mediated caspase-1 dependent IL-1β/IL-18 production and cell death. We also detected YopM in a complex with Pyrin and kinases RSK1 and PKN1, putative negative regulators of Pyrin. In contrast to wild-type mice, Pyrin deficient mice were also highly susceptible to an attenuated Y. pestis strain lacking YopM, emphasizing the importance of inhibition of Pyrin in vivo. A complex interplay between the Y. pestis T3SS and IL-1β/IL-18 production is evident, involving at least four inflammasome pathways. The secreted effector YopJ triggers caspase-8- dependent IL-1β activation, even when YopM is present. Additionally, the presence of the T3SS needle/translocon activates NLRP3 and NLRC4-dependent IL-1β generation, which is blocked by YopK, but not by YopM. Taken together, the data suggest YopM specificity for obstructing the Pyrin pathway, as the effector does not appear to block Y. pestis-induced NLRP3, NLRC4 or caspase-8 dependent caspase-1 processing. Thus, we identify Y. pestis YopM as a microbial inhibitor of the Pyrin inflammasome. The fact that so many of the Y. pestis T3SS components are participating in regulation of IL-1β/IL-18 release suggests that these effects are essential for maximal control of innate immunity during plague.

Project description:YopM is a leucine-rich repeat (LRR)-containing effector in several Yersinia species, including Yersinia pestis and Y. pseudotuberculosis. Different Yersinia strains encode distinct YopM isoforms with variable numbers of LRRs but conserved C-terminal tails. A 15-LRR isoform in Y. pseudotuberculosis YPIII was recently shown to bind and inhibit caspase-1 via a YLTD motif in LRR 10, and attenuation of YopM(-) YPIII was reversed in mice lacking caspase-1, indicating that caspase-1 inhibition is a major virulence function of YopM(YPIII). To determine if other YopM proteins inhibit caspase-1, we utilized Y. pseudotuberculosis strains natively expressing a 21-LRR isoform lacking the YLTD motif (YopM(32777)) or ectopically expressing a Y. pestis 15-LRR version with a functional (YopM(KIM)) or inactivated (YopM(KIM) D271A) YLTD motif. Results of mouse and macrophage infections with these strains showed that YopM(32777), YopM(KIM), and YopM(KIM) D271A inhibit caspase-1 activation, indicating that the YLTD motif is dispensable for this activity. Analysis of YopM(KIM) deletion variants revealed that LRRs 6 to 15 and the C-terminal tail are required to inhibit caspase-1 activation. YopM(32777), YopM(KIM), and YopM(KIM) deletion variants were purified, and binding partners in macrophage lysates were identified. Caspase-1 bound to YopM(KIM) but not YopM(32777). Additionally, YopM(KIM) bound IQGAP1 and the use of Iqgap1(-/-) macrophages revealed that this scaffolding protein is important for caspase-1 activation upon infection with YopM(-) Y. pseudotuberculosis. Thus, while multiple YopM isoforms inhibit caspase-1 activation, their variable LRR domains bind different host proteins to perform this function and the LRRs of YopM(KIM) target IQGAP1, a novel regulator of caspase-1, in macrophages. Importance: Activation of caspase-1, mediated by macromolecular complexes termed inflammasomes, is important for innate immune defense against pathogens. Pathogens can, in turn, subvert caspase-1-dependent responses through the action of effector proteins. For example, the Yersinia effector YopM inhibits caspase-1 activation by arresting inflammasome formation. This caspase-1 inhibitory activity has been studied in a specific YopM isoform, and in this case, the protein was shown to act as a pseudosubstrate to bind and inhibit caspase-1. Different Yersinia strains encode distinct YopM isoforms, many of which lack the pseudosubstrate motif. We studied additional isoforms and found that these YopM proteins inhibit caspase-1 activation independently of a pseudosubstrate motif. We also identified IQGAP1 as a novel binding partner of the Yersinia pestis YopM(KIM) isoform and demonstrated that IQGAP1 is important for caspase-1 activation in macrophages infected with Yersinia. Thus, this study reveals new insights into inflammasome regulation during Yersinia infection.

Project description:A type III secretion system (T3SS) in pathogenic Yersinia species functions to translocate Yop effectors, which modulate cytokine production and regulate cell death in macrophages. Distinct pathways of T3SS-dependent cell death and caspase-1 activation occur in Yersinia-infected macrophages. One pathway of cell death and caspase-1 activation in macrophages requires the effector YopJ. YopJ is an acetyltransferase that inactivates MAPK kinases and IKK? to cause TLR4-dependent apoptosis in naïve macrophages. A YopJ isoform in Y. pestis KIM (YopJ(KIM)) has two amino acid substitutions, F177L and K206E, not present in YopJ proteins of Y. pseudotuberculosis and Y. pestis CO92. As compared to other YopJ isoforms, YopJ(KIM) causes increased apoptosis, caspase-1 activation, and secretion of IL-1? in Yersinia-infected macrophages. The molecular basis for increased apoptosis and activation of caspase-1 by YopJ(KIM) in Yersinia-infected macrophages was studied. Site directed mutagenesis showed that the F177L and K206E substitutions in YopJ(KIM) were important for enhanced apoptosis, caspase-1 activation, and IL-1? secretion. As compared to YopJ(CO92), YopJ(KIM) displayed an enhanced capacity to inhibit phosphorylation of I?B-? in macrophages and to bind IKK? in vitro. YopJ(KIM) also showed a moderately increased ability to inhibit phosphorylation of MAPKs. Increased caspase-1 cleavage and IL-1? secretion occurred in IKK?-deficient macrophages infected with Y. pestis expressing YopJ(CO92), confirming that the NF-?B pathway can negatively regulate inflammasome activation. K+ efflux, NLRP3 and ASC were important for secretion of IL-1? in response to Y. pestis KIM infection as shown using macrophages lacking inflammasome components or by the addition of exogenous KCl. These data show that caspase-1 is activated in naïve macrophages in response to infection with a pathogen that inhibits IKK? and MAPK kinases and induces TLR4-dependent apoptosis. This pro-inflammatory form of apoptosis may represent an early innate immune response to highly virulent pathogens such as Y. pestis KIM that have evolved an enhanced ability to inhibit host signaling pathways.

Dataset Information

The Yersinia virulence effector YopM binds caspase-1 to arrest inflammasome assembly and processing.

Publications

The Yersinia virulence effector YopM binds caspase-1 to arrest inflammasome assembly and processing.

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