| First Author | Suzuki S | Year | 2014 |
| Journal | PLoS Pathog | Volume | 10 |
| Issue | 2 | Pages | e1003926 |
| PubMed ID | 24516390 | Mgi Jnum | J:246374 |
| Mgi Id | MGI:5914889 | Doi | 10.1371/journal.ppat.1003926 |
| Citation | Suzuki S, et al. (2014) Shigella type III secretion protein MxiI is recognized by Naip2 to induce Nlrc4 inflammasome activation independently of Pkcdelta. PLoS Pathog 10(2):e1003926 |
| abstractText | Recognition of intracellular pathogenic bacteria by members of the nucleotide-binding domain and leucine-rich repeat containing (NLR) family triggers immune responses against bacterial infection. A major response induced by several Gram-negative bacteria is the activation of caspase-1 via the Nlrc4 inflammasome. Upon activation, caspase-1 regulates the processing of proIL-1beta and proIL-18 leading to the release of mature IL-1beta and IL-18, and induction of pyroptosis. The activation of the Nlrc4 inflammasome requires the presence of an intact type III or IV secretion system that mediates the translocation of small amounts of flagellin or PrgJ-like rod proteins into the host cytosol to induce Nlrc4 activation. Using the Salmonella system, it was shown that Naip2 and Naip5 link flagellin and the rod protein PrgJ, respectively, to Nlrc4. Furthermore, phosphorylation of Nlrc4 at Ser533 by Pkcdelta was found to be critical for the activation of the Nlrc4 inflammasome. Here, we show that Naip2 recognizes the Shigella T3SS inner rod protein MxiI and induces Nlrc4 inflammasome activation. The expression of MxiI in primary macrophages was sufficient to induce pyroptosis and IL-1beta release, which were prevented in macrophages deficient in Nlrc4. In the presence of MxiI or Shigella infection, MxiI associated with Naip2, and Naip2 interacted with Nlrc4. siRNA-mediated knockdown of Naip2, but not Naip5, inhibited Shigella-induced caspase-1 activation, IL-1beta maturation and Asc pyroptosome formation. Notably, the Pkcdelta kinase was dispensable for caspase-1 activation and secretion of IL-1beta induced by Shigella or Salmonella infection. These results indicate that activation of caspase-1 by Shigella is triggered by the rod protein MxiI that interacts with Naip2 to induce activation of the Nlrc4 inflammasome independently of the Pkcdelta kinase. |
